Chapt14 lecture (4)

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Chapter 14*Lecture PowerPoint

The Brain and Cranial Nerves

Introduction• The human brain is complex• Brain function is associated with life• This chapter is a study of brain and cranial nerves

directly connected to it• Will provide insight into brain circuitry and function

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Introduction• Aristotle thought brain was “radiator” to cool blood

• Hippocrates was more accurate: “from the brain only, arises our pleasures, joys, laughter, and jests, as well as our sorrows, pains, griefs, and tears”

• Cessation of brain activity—clinical criterion of death

• Evolution of the central nervous system shows spinal cord has changed very little while brain has changed a great deal– Greatest growth in areas of vision, memory, and motor

control of the prehensile hand

Overview of the Brain

• Expected Learning Outcomes– Describe the major subdivisions and anatomical

landmarks of the brain.– Describe the locations of its gray and white matter.– Describe the embryonic development of the CNS and

relate this to adult brain anatomy.

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Major Landmarks

• Rostral—toward the forehead

• Caudal—toward the spinal cord

• Brain weighs about 1,600 g (3.5 lb) in men, and 1,450 g in women

Figure 14.1b

Brainstem

Cerebellum

Cerebrum

Spinal cord

Rostral Caudal

Central sulcus

Lateral sulcus

Gyri

(b) Lateral view

Temporal lobe


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Major Landmarks

• Three major portions of the brain– Cerebrum is 83% of brain

volume; cerebral hemispheres, gyri and sulci, longitudinal fissure, corpus callosum

– Cerebellum contains 50% of the neurons; second largest brain region, located in posterior cranial fossa

– Brainstem is the portion of the brain that remains if the cerebrum and cerebellum are removed; diencephalon, midbrain, pons, and medulla oblongata

Figure 14.1b

Brainstem

Cerebellum

Cerebrum

Spinal cord

Rostral Caudal

Central sulcus

Lateral sulcus

Gyri

(b) Lateral view

Temporal lobe


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Major Landmarks

• Longitudinal fissure—deep groove that separates cerebral hemispheres

• Gyri—thick folds

• Sulci—shallow grooves

• Corpus callosum—thick nerve bundle at bottom of longitudinal fissure that connects hemispheres

Figure 14.1a

Frontal lobe

Occipital lobe

Central sulcus

Longitudinal fissure

Parietal lobe

(a) Superior view

Cerebralhemispheres


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Major Landmarks

• Occupies posterior cranial fossa

• Marked by gyri, sulci, and fissures

• About 10% of brain volume

• Contains over 50% of brain neurons

Figure 14.1b

Brainstem

Cerebellum

Cerebrum

Spinal cord

Rostral Caudal

Central sulcus

Lateral sulcus

Gyri

(b) Lateral view

Temporal lobe


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Major Landmarks

• Brainstem—what remains of the brain if the cerebrum and cerebellum are removed

• Major components– Diencephalon– Midbrain– Pons– Medulla oblongata

Figure 14.1b

Brainstem

Cerebellum

Cerebrum

Spinal cord

Rostral Caudal

Central sulcus

Lateral sulcus

Gyri

(b) Lateral view

Temporal lobe


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Major Landmarks

Figure 14.2a


Thalamus

Hypothalamus

Frontal lobe

Corpus callosum

Cingulate gyrus

Optic chiasm

Pituitary gland

Mammillary body

Midbrain

Pons

Central sulcus

Parietal lobe

Parieto–occipital sulcus

Occipital lobe

Pineal glandHabenula

Posterior commissure

Cerebral aqueduct

Fourth ventricle

Cerebellum

(a)

EpithalamusAnteriorcommissure

Temporal lobe

Medullaoblongata

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Major Landmarks

Figure 14.2b


b: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer

Corpus callosum

Cingulate gyrus

Lateral ventricle

Thalamus

Hypothalamus

Midbrain

Cerebellum

Fourth ventriclePons

(b)

Choroid plexusPineal gland

Occipital lobe

Medullaoblongata

Parieto–occipitalsulcus

Posteriorcommissure

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Gray and White Matter• Gray matter—the seat of neuron cell bodies,

dendrites, and synapses– Dull white color when fresh, due to little myelin– Forms surface layer (cortex) over cerebrum and

cerebellum– Forms nuclei deep within brain

• White matter—bundles of axons– Lies deep to cortical gray matter, opposite relationship

in the spinal cord– Pearly white color from myelin around nerve fibers– Composed of tracts, or bundles of axons, that connect

one part of the brain to another, and to the spinal cord

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Embryonic Development• Nervous system develops from ectoderm

– Outermost tissue layer of the embryo

• Early in third week of development– Neuroectoderm: dorsal streak appears along the length of

embryo– Thickens to form neural plate

• Destined to give rise to most neurons and all glial cells except microglia, which come from mesoderm

• As thickening progresses– Neural plate sinks and its edges thicken

• Forming a neural groove with a raised neural fold on each side

• Neural folds fuse along the midline– Beginning in the cervical region and progressing rostrally

and caudally

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Embryonic Development• By fourth week, creates a hollow channel—neural

tube– Neural tube separates from overlying ectoderm – Sinks deeper– Grows lateral processes that later will form motor nerve

fibers– Lumen of neural tube becomes fluid-filled space

• Central canal in spinal cord• Ventricles of the brain

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Embryonic DevelopmentCont.• Neural crest—formed from ectodermal cells that lay

along the margins of the groove and separate from the rest forming a longitudinal column on each side– Gives rise to the two inner meninges, most of the

peripheral nervous system, and other structures of the skeletal, integumentary, and endocrine systems

• By fourth week, the neural tube exhibits three anterior dilations (primary vesicles)– Forebrain (prosencephalon)– Midbrain (mesencephalon)– Hindbrain (rhombencephalon)

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Embryonic Development

• By fifth week, it subdivides into five secondary vesicles– Forebrain divides into two of them

• Telencephalon—becomes cerebral hemispheres• Diencephalon—has optic vesicles that become retina of the

eye

– Midbrain remains undivided • Mesencephalon

– Hindbrain divides into two vesicles• Metencephalon• Myelencephalon


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Figure 14.3


(a) 19 days

(c) 22 days

Ectoderm

Notochord

Neural groove

Neural fold

Neural plate

(b) 20 days

(d) 26 days

Somites

Neural crestNeural crest

Neuralcrest

Neuraltube

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• Fourth week– Forebrain– Midbrain– Hindbrain

• Fifth week– Telencephalon– Diencephalon– Mesencephalon– Metencephalon– Myelencephalon

Figure 14.4


Diencephalon

Mesencephalon

Forebrain

Pons

CerebellumMetencephalon

Spinal cord

Hindbrain

Optic vesicle

Diencephalon

Metencephalon

Myelencephalon

Spinal cord

Rhombencephalon

Mesencephalon

Prosencephalon

(a) 4 weeks (b) 5 weeks

(c) Fully developed

Midbrain

Telencephalon

Myelencephalon(medulla oblongata)

Telencephalon

Meninges, Ventricles, Cerebrospinal Fluid, and Blood Supply

• Expected Learning Outcomes– Describe the meninges of the brain.– Describe the fluid-filled chambers within the brain.– Discuss the production, circulation, and function of

the cerebrospinal fluid that fills these chambers.– Explain the significance of the brain barrier system.

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Meninges

• Meninges—three connective tissue membranes that envelop the brain– Lies between the nervous tissue and bone– As in spinal cord, they are the dura mater,

arachnoid mater, and the pia mater– Protect the brain and provide structural framework

for its arteries and veins

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Meninges

• Dura mater– In cranial cavity; has two layers

• Outer periosteal—equivalent to periosteum of cranial bones• Inner meningeal—continues into vertebral canal and forms

dural sac around spinal cord

– Cranial dura mater is pressed closely against cranial bones

• No epidural space• Not attached to bone except: around foramen magnum, sella

turcica, the crista galli, and sutures of the skull• Layers separated by dural sinuses—collect blood circulating

through brain

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Meninges

Cont.– Folds inward to extend between parts of the brain

• Falx cerebri separates the two cerebral hemispheres• Tentorium cerebelli separates cerebrum from cerebellum• Falx cerebelli separates the right and left halves of

cerebellum

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Meninges• Arachnoid mater and pia mater are similar to those in the

spinal cord

• Arachnoid mater – Transparent membrane over brain surface– Subarachnoid space separates it from pia mater below– Subdural space separates it from dura mater above in some

places

• Pia mater – Very thin membrane that follows contours of brain, even dipping

into sulci– Not usually visible without a microscope

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Meninges

Figure 14.5


Subdural space

Skull

Pia mater

Blood vessel

Dura mater: Periosteal layer Meningeal layer

Arachnoid mater

Brain:

Gray matter

White matter

Arachnoid granulationSubarachnoidspace

Superior sagittalsinus

Falx cerebri(in longitudinalfissure only)

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Meningitis• Meningitis—inflammation of the meninges

– Serious disease of infancy and childhood– Especially between 3 months and 2 years of age

• Caused by bacterial and virus invasion of the CNS by way of the nose and throat

• Pia mater and arachnoid are most often affected

• Bacterial meningitis can cause swelling of the brain, enlargment of the ventricles, and hemorrhage

• Signs include high fever, stiff neck, drowsiness, and intense headache; may progress to coma then death within hours of onset

• Diagnosed by examining the CSF for bacteria– Lumbar puncture (spinal tap) draws fluid from subarachnoid

space between two lumbar vertebrae

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Ventricles and Cerebrospinal Fluid

Figure 14.6a,b


Lateral ventricles

Central canal

Lateral apertureFourth ventricle

Third ventricle

Median aperture

Lateral ventricle

Third ventricle

Cerebrum

Lateral aperture

Fourth ventricle

Median aperture

(a) Lateral view

Caudal Rostral

Interventricularforamen

Cerebralaqueduct

Interventricularforamen

Cerebralaqueduct

(b) Anterior view

Choroid plexus

Thalamus

GyrusSulcus

Caudate nucleus

Frontal lobe

White matter

Lateral ventricle

Temporal lobeThird ventricleLateral sulcus

Insula

Lateral ventricle

Occipital lobe

(c)

Rostral (anterior)

Caudal (posterior)

Corpus callosum(anterior part)

Septumpellucidum

Corpus callosum(posterior part)Longitudinalfissure

Gray matter(cortex)

Longitudinalfissure

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Figure 14.6c


c: © The McGraw-Hill Companies, Inc./Rebecca Gray,photographer/Don Kincaid, dissections

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• Ventricles—four internal chambers within the brain– Two lateral ventricles: one in each cerebral hemisphere

• Interventricular foramen—a tiny pore that connects to third ventricle

– Third ventricle: single narrow medial space beneath corpus callosum

• Cerebral aqueduct runs through midbrain and connects third to fourth ventricle

– Fourth ventricle: small triangular chamber between pons and cerebellum

• Connects to central canal, runs down through spinal cord

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Ventricles and Cerebrospinal FluidCont.

• Choroid plexus—spongy mass of blood capillaries on the floor of each ventricle

• Ependyma—neuroglia that lines the ventricles and covers choroid plexus– Produces cerebrospinal fluid

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Ventricles and Cerebrospinal Fluid• Cerebrospinal fluid (CSF)—clear, colorless liquid that fills

the ventricles and canals of CNS– Bathes its external surface

• Brain produces and absorbs 500 mL/day– 100 to 160 mL normally present at one time– 40% formed in subarachnoid space external to brain– 30% by the general ependymal lining of the brain ventricles– 30% by the choroid plexuses

• Production begins with the filtration of blood plasma through the capillaries of the brain– Ependymal cells modify the filtrate, so CSF has more sodium and

chloride than plasma, but less potassium, calcium, glucose, and very little protein

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• CSF continually flows through and around the CNS– Driven by its own pressure, beating of ependymal cilia,

and pulsations of the brain produced by each heartbeat

• CSF secreted in lateral ventricles flows through intervertebral foramina into third ventricle

• Then down the cerebral aqueduct into the fourth ventricle

• Third and fourth ventricles add more CSF along the way

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Ventricles and Cerebrospinal Fluid• Small amount of CSF fills the central canal of the spinal

cord– All escapes through three pores

• Median aperture and two lateral apertures• Leads into subarachnoid space of brain and spinal

cord surface

• CSF is reabsorbed by arachnoid villi– Cauliflower-shaped extension of the arachnoid meninx– Protrudes through dura mater– Into superior sagittal sinus– CSF penetrates the walls of the villi and mixes with the

blood in the sinus

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Ventricles and Cerebrospinal Fluid• Functions of CSF

– Buoyancy• Allows brain to attain considerable size without being impaired by

its own weight• If it rested heavily on floor of cranium, the pressure would kill the

nervous tissue

– Protection• Protects the brain from striking the cranium when the head is jolted• Shaken child syndrome and concussions do occur from severe

jolting

– Chemical stability• Flow of CSF rinses away metabolic wastes from nervous tissue

and homeostatically regulates its chemical environment

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Figure 14.7


Arachnoid villus

Choroid plexus

Third ventricle

Lateral aperture

Fourth ventricle

Median aperture

Dura mater

Arachnoid mater

1

2

3

4

56

7

7

8

1

2

3

4

5

6

7

8

Superiorsagittalsinus

Subarachnoidspace

Cerebralaqueduct

Central canalof spinal cord

Subarachnoidspace ofspinal cord

CSF is secreted bychoroid plexus ineach lateral ventricle.

CSF flows throughinterventricular foraminainto third ventricle.

Choroid plexus in thirdventricle adds more CSF.

CSF flows down cerebralaqueduct to fourth ventricle.

Choroid plexus in fourthventricle adds more CSF.

CSF fills subarachnoid space andbathes external surfaces of brainand spinal cord.

At arachnoid villi, CSF is reabsorbedinto venous blood of duralvenous sinuses.

CSF flows out two lateral aperturesand one median aperture.

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Blood Supply and the Brain Barrier System

• Brain is only 2% of the adult body weight, and receives 15% of the blood– 750 mL/min.

• Neurons have a high demand for ATP, and therefore, oxygen and glucose, so a constant supply of blood is critical to the nervous system

– A 10-second interruption of blood flow may cause loss of consciousness

– A 1- to 2-minute interruption can cause significant impairment of neural function

– Going 4 minutes without blood causes irreversible brain damage

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• Blood is also a source of antibodies, macrophages, bacterial toxins, and other harmful agents

• Brain barrier system—strictly regulates what substances can get from the bloodstream into the tissue fluid of the brain

• Two points of entry must be guarded– Blood capillaries throughout the brain tissue– Capillaries of the choroid plexus

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• Blood–brain barrier—protects blood capillaries throughout brain tissue– Consists of tight junctions between endothelial cells that

form the capillary walls– Astrocytes reach out and contact capillaries with their

perivascular feet– Induce the endothelial cells to form tight junctions that

completely seal off gaps between them– Anything leaving the blood must pass through the cells,

and not between them– Endothelial cells can exclude harmful substances from

passing to the brain tissue while allowing necessary ones to pass

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• Blood–CSF barrier—protects the brain at the choroid plexus– Forms tight junctions between the ependymal cells– Tight junctions are absent from ependymal cells

elsewhere• Important to allow exchange between brain tissue and CSF

• Blood barrier system is highly permeable to water, glucose, and lipid-soluble substances such as oxygen, carbon dioxide, alcohol, caffeine, nicotine, and anesthetics

• Slightly permeable to sodium, potassium, chloride, and the waste products urea and creatinine

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• Obstacle for delivering medications such as antibiotics and cancer drugs

• Trauma and inflammation can damage BBS and allow pathogens to enter brain tissue– Circumventricular organs (CVOs)—places in the third

and fourth ventricles where the barrier is absent• Blood has direct access to the brain• Enables the brain to monitor and respond to fluctuations in

blood glucose, pH, osmolarity, and other variables• CVOs afford a route for invasion by the human

immunodeficiency virus (HIV)

The Hindbrain and Midbrain

• Expected Learning Outcomes– List the components of the hindbrain and midbrain and

their functions.– Describe the location and functions of the reticular

formation.

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The Medulla Oblongata• Embryonic myelencephalon

becomes medulla oblongata

• Begins at foramen magnum of the skull

• Extends for about 3 cm rostrally and ends at a groove between the medulla and pons

• Slightly wider than spinal cord

• Pyramids—pair of external ridges on anterior surface– Resembles side-by-side

baseball bats

Figure 14.2a


Thalamus

Hypothalamus

Frontal lobe

Corpus callosum

Cingulate gyrus

Optic chiasm

Pituitary gland

Mammillary body

Midbrain

Pons

Central sulcus

Parietal lobe


Occipital lobe



Cerebral aqueduct

Fourth ventricle

Cerebellum

(a)


Temporal lobe

Medullaoblongata

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The Medulla Oblongata

• Olive—a prominent bulge lateral to each pyramid

• Posteriorly, gracile and cuneate fasciculi of the spinal cord continue as two pair of ridges on the medulla

• All nerve fibers connecting the brain to the spinal cord pass through the medulla

• Four pairs of cranial nerves begin or end in medulla—IX, X, XI, XII

Figure 14.2a


Thalamus

Hypothalamus

Frontal lobe

Corpus callosum

Cingulate gyrus

Optic chiasm

Pituitary glandMammillary body

Midbrain

Pons

Central sulcus

Parietal lobe

Parieto–occipital sulcusOccipital lobe



Cerebral aqueduct

Fourth ventricle

Cerebellum

(a)


Temporal lobe

Medullaoblongata

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• Cardiac center – Adjusts rate and force of heart

• Vasomotor center – Adjusts blood vessel diameter

• Respiratory centers – Control rate and depth of breathing

• Reflex centers – For coughing, sneezing, gagging, swallowing, vomiting,

salivation, sweating, movements of tongue and head

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• Pyramids contain descending fibers called corticospinal tracts– Carry motor signals to skeletal muscles

• Inferior olivary nucleus—relay center for signals to cerebellum• Reticular formation—loose network of nuclei extending throughout

the medulla, pons, and midbrain– Contains cardiac, vasomotor, and respiratory centers

Figure 14.9c


Hypoglossal nerve

Medial lemniscusTectospinal tract

Nucleus Tract

Gracile nucleus

Cuneate nucleus

Olive

Pyramids of medullaCorticospinal tract

Trigeminal nerve:

Fourth ventricle

Reticular formation

(a) Midbrain

(c) Medulla oblongata

(c) Medulla

(b) Pons

Nucleus ofhypoglossal nerve

Dorsal spinocerebellartract

Nucleus ofvagus nerve

Inferior olivarynucleus


Diencephalon:

Midbrain:

Thalamus

Optic tract

Cranial nerves:

Oculomotor nerve (III)

Optic nerve (II)

Trochlear nerve (IV)

Trigeminal nerve (V)

Abducens nerve (VI)

Facial nerve (VII)

Vestibulocochlear nerve (VIII)

Glossopharyngeal nerve (IX)

Vagus nerve (X)

Accessory nerve (XI)

Hypoglossal nerve (XII)

Spinal nerves

InfundibulumMammillary body

Cerebral peduncle

PyramidAnterior median fissure

Pyramidal decussation

Spinal cord

(a) Ventral view

Pons

Medulla oblongata: Regions of the brainstem

Midbrain

Diencephalon

Pons

Medulla oblongata

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Figure 14.8a

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The Pons

Figure 14.8b


Diencephalon:

Midbrain:

Thalamus

Pineal gland

Superior colliculusInferior colliculus

Spinal cord

Pons

Olive

Cerebral peduncle

Medial geniculate body

Lateral geniculate body

Optic tract

Fourth ventricle

Cuneate fasciculus

Gracile fasciculus

(b) Dorsolateral view

Regions of the brainstem

Midbrain

Diencephalon

Pons

Medulla oblongata

Medullaoblongata

Superior cerebellarpeduncle

Middle cerebellarpeduncle

Inferior cerebellarpeduncle

Thalamus

Hypothalamus

Frontal lobe

Corpus callosum

Cingulate gyrus

Optic chiasm


Midbrain

Pons

Central sulcus

Parietal lobe




Cerebral aqueduct

Fourth ventricle

Cerebellum

(a)


Temporal lobe

Medullaoblongata

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The Pons

Figure 14.2a

• Metencephalon—develops into the pons and cerebellum• Pons—anterior bulge in brainstem, rostral to medulla• Cerebral peduncles—connect cerebellum to pons and midbrain


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The Pons• Ascending sensory tracts

• Descending motor tracts

• Pathways in and out of cerebellum

• Cranial nerves V, VI, VII, and VIII– Sensory roles: hearing, equilibrium, taste, facial

sensations– Motor roles: eye movement, facial expressions,

chewing, swallowing, urination, and secretion of saliva and tears

• Reticular formation in pons contains additional nuclei concerned with sleep, respiration, posture


Reticular formation

Trigeminal nerve

Trigeminal nerve nuclei

Vermis of cerebellum

Medial lemniscus

Tectospinal tract

Anterolateral system

Transverse fascicles

Longitudinal fascicles

Fourth ventricle

(a) Midbrain

(c) Medulla

(b) Pons

(b) Pons

Superior cerebellarpeduncle

Sensory root oftrigeminal nerve

Ventralspinocerebellar tract

Middle cerebellarpeduncle

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The Pons

Figure 14.9b

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The Midbrain

• Mesencephalon becomes one mature brain structure, the midbrain– Short segment of brainstem that connects the hindbrain

to the forebrain– Contains cerebral aqueduct– Contains continuations of the medial lemniscus and

reticular formation– Contains the motor nuclei of two cranial nerves that

control eye movements: CN III (oculomotor) and CN IV (trochlear)

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The Midbrain• Mesencephalon (cont.)

– Tectum: rooflike part of the midbrain posterior to cerebral aqueduct

• Exhibits four bulges, the corpora quadrigemina• Upper pair, the superior colliculi, function in visual

attention, tracking moving objects, and some reflexes• Lower pair, the inferior colliculi, receives signals from

the inner ear– Relays them to other parts of the brain, especially the

thalamus

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The MidbrainCont.

– Cerebral peduncles: two stalks that anchor the cerebrum to the brainstem anterior to the cerebral aqueduct

• Cerebral peduncles—three main components– Tegmentum

• Dominated by the red nucleus• Pink color due to high density of blood vessels

• Connections go to and from cerebellum• Collaborates with cerebellum for fine motor control

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The Midbrain

– Substantia nigra • Dark gray to black nucleus pigmented with melanin• Motor center that relays inhibitory signals to thalamus and

basal nuclei preventing unwanted body movement• Degeneration of neurons leads to tremors of Parkinson

disease

– Cerebral crus• Bundle of nerve fibers that connect the cerebrum to the

pons• Carries corticospinal tracts

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The Midbrain

Figure 14.9a


TegmentumCerebral peduncle:

Cerebral crus

TectumSuperior colliculus

Cerebral aqueduct

Medial geniculate nucleusReticular formation Central gray matter

Oculomotor nucleusMedial lemniscus

Red nucleus

Substantia nigra


Posterior

Anterior

(a) Midbrain

(a) Midbrain

(c) Medulla

(b) Pons

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The Reticular Formation• Loosely organized web of

gray matter that runs vertically through all levels of the brainstem

• Clusters of gray matter scattered throughout pons, midbrain, and medulla

• Occupies space between white fiber tracts and brainstem nuclei

• Has connections with many areas of cerebrum– More than 100 small neural

networks without distinct boundaries

Figure 14.10


Reticular formation

Auditory input

Thalamus

Visual input

Ascending generalsensory fibersDescending motorfibers to spinal cord

Radiations tocerebral cortex

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The Reticular Formation• Networks

– Somatic motor control• Adjust muscle tension to maintain tone, balance, and

posture• Especially during body movements• Relays signals from eyes and ears to the cerebellum• Integrates visual, auditory, and balance and motion

stimuli into motor coordination• Gaze center—allows eyes to track and fixate on

objects• Central pattern generators—neural pools that

produce rhythmic signals to the muscles of breathing and swallowing

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The Reticular FormationCont.

– Cardiovascular control• Includes cardiac and vasomotor centers of medulla

oblongata

– Pain modulation• One route by which pain signals from the lower body

reach the cerebral cortex• Origin of descending analgesic pathways—fibers act

in the spinal cord to block transmission of pain signals to the brain

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The Reticular Formation– Sleep and consciousness

• Plays central role in states of consciousness, such as alertness and sleep

• Injury to reticular formation can result in irreversible coma

– Habituation• Process in which the brain learns to ignore repetitive,

inconsequential stimuli while remaining sensitive to others

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The Cerebellum

• The largest part of the hindbrain and the second largest part of the brain as a whole

• Consists of right and left cerebellar hemispheres connected by vermis• Cortex of gray matter with folds (folia) and four deep nuclei in each

hemisphere

• Contains more than half of all brain neurons—about 100 billion– Granule cells and Purkinje cells synapse on deep nuclei

• White matter branching pattern is called arbor vitae

Figure 14.11b(b) Superior view

Folia

Anterior

Posterior

Anterior lobe

Vermis

Posterior lobe

Cerebellarhemisphere



Superior colliculus


Pineal glandInferior colliculus

Mammillary bodyMidbrain

Cerebral aqueduct

Oculomotor nerve

Pons

Fourth ventricle

Medulla oblongata

Gray matter

(a) Median section

White matter(arbor vitae)

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The Cerebellum

• Cerebellar peduncles—three pairs of stalks that connect the cerebellum to the brainstem– Inferior peduncles: connected to medulla oblongata

• Most spinal input enters the cerebellum through inferior peduncle– Middle peduncles: connected to the pons

• Most input from the rest of the brain enters by way of middle peduncle– Superior peduncles: connected to the midbrain

• Carries cerebellar output• Consist of thick bundles of nerve fibers that carry signals to and from

the cerebellum

Figure 14.11a

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The Cerebellum

• Monitors muscle contractions and aids in motor coordination

• Evaluation of sensory input– Comparing textures without looking at them– Spatial perception and comprehension of different views of three-

dimensional objects belonging to the same object

• Timekeeping center– Predicting movement of objects– Helps predict how much the eyes must move in order to compensate

for head movements and remain fixed on an object

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The CerebellumCont.• Hearing

– Distinguish pitch and similar-sounding words

• Planning and scheduling tasks

• Lesions may result in emotional overreactions and trouble with impulse control

The Forebrain• Expected Learning Outcomes

– Name the three major components of the diencephalon and describe their locations and functions.

– Identify the five lobes of the cerebrum and their functions.– Identify the three types of tracts in the cerebral white

matter.– Describe the distinctive cell types and histological

arrangement of the cerebral cortex.– Describe the location and functions of the basal nuclei

and limbic system.

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Diencephalon

Mesencephalon

Forebrain

Pons

CerebellumMetencephalon

Spinal cord

Hindbrain

(c) Fully developed

Midbrain

Myelencephalon(medulla oblongata)

Telencephalon

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The Forebrain• Forebrain consists of two

parts– Diencephalon

• Encloses the third ventricle

• Most rostral part of the brainstem

• Has three major embryonic derivatives

– Thalamus– Hypothalamus– Epithalamus

– Telencephalon• Develops chiefly into the

cerebrum

Figure 14.4c

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The Diencephalon: Thalamus

• Thalamus—ovoid mass on each side of the brain perched at the superior end of the brainstem beneath the cerebral hemispheres– Constitutes about four-fifths of the diencephalon– Two thalami are joined medially by a narrow intermediate mass– Composed of at least 23 nuclei; to consider five major functional groups

Figure 14.12a


Part of limbic system;memory and emotion

Emotional output to prefrontalcortex; awareness of emotions

Somesthetic output topostcentral gyrus; signalsfrom cerebellum and basalnuclei to motor areas of cortex

Somesthetic output toassociation areas of cortex;contributes to emotional functionof limbic system

Relay of visual signals tooccipital lobe (via lateralgeniculate nucleus) and auditorysignals to temporal lobe (viamedial geniculate nucleus)

(a) Thalamus

Medial geniculate nucleus

Lateral geniculate nucleus

Thalamic Nuclei

Anterior group

Medial group

Ventral group

Lateral group

Posterior group

The Diencephalon: ThalamusCont.

– “Gateway to the cerebral cortex”: nearly all input to the cerebrum passes by way of synapses in the thalamic nuclei, filters information on its way to cerebral cortex

– Plays key role in motor control by relaying signals from cerebellum to cerebrum and providing feedback loops between the cerebral cortex and the basal nuclei

– Involved in the memory and emotional functions of the limbic system: a complex of structures that include some cerebral cortex of the temporal and frontal lobes and some of the anterior thalamic nuclei

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14-67

• Hypothalamus—forms part of the walls and floor of the third ventricle

• Extends anteriorly to optic chiasm and posteriorly to the paired mammillary bodies

• Each mammillary body contains three or four mammillary nuclei– Relay signals from the

limbic system to the thalamus

The Diencephalon: Hypothalamus

Figure 14.2a


Thalamus

Hypothalamus

Frontal lobe

Corpus callosum

Cingulate gyrus

Optic chiasm


Midbrain

Pons

Central sulcus

Parietal lobe




Cerebral aqueduct

Fourth ventricle

Cerebellum

(a)


Temporal lobe

Medullaoblongata

The Diencephalon: Hypothalamus• Infundibulum—a stalk that attaches the pituitary gland to the

hypothalamus

• Major control center of autonomic nervous system and endocrine system– Plays essential role in homeostatic regulation of all body systems

• Functions of hypothalamic nuclei– Hormone secretion

• Controls anterior pituitary• Regulates growth, metabolism, reproduction, and stress responses

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The Diencephalon: HypothalamusCont.

– Hormone secretion• Controls anterior pituitary• Regulates growth, metabolism, reproduction, and stress responses

– Autonomic effects• Major integrating center for autonomic nervous system• Influences heart rate, blood pressure, gastrointestinal secretions,

motility, etc.

– Thermoregulation• Hypothalamic thermostat monitors body temperature• Activates heat-loss center when temp is too high• Activates heat-promoting center when temp is too low

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The Diencephalon: HypothalamusCont.

– Food and water intake • Hunger and satiety centers monitor blood glucose and amino

acid levels– Produce sensations of hunger and satiety

• Thirst center monitors osmolarity of the blood– Rhythm of sleep and waking

• Controls 24-hour (circadian) rhythm of activity– Memory

• Mammillary nuclei receive signals from hippocampus– Emotional behavior

• Anger, aggression, fear, pleasure, and contentment

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The Diencephalon: Epithalamus

• Epithalamus—very small mass of tissue composed of:– Pineal gland: endocrine gland– Habenula: relay from the limbic system to the midbrain– Thin roof over the third ventricle

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Figure 14.2a

Thalamus

Hypothalamus

Frontal lobe

Corpus callosum

Cingulate gyrus

Optic chiasm


Midbrain

Pons

Central sulcus

Parietal lobe


Occipital lobe



Cerebral aqueduct

Fourth ventricle

Cerebellum

(a)


Temporal lobe

Medullaoblongata


The Telencephalon: Cerebrum

• Cerebrum—largest and most conspicuous part of the human brain– Seat of sensory perception, memory, thought, judgment, and

voluntary motor actions14-72

Figure 14.2a

Thalamus

Hypothalamus

Frontal lobe

Corpus callosum

Cingulate gyrus

Optic chiasm


Midbrain

Pons

Central sulcus

Parietal lobe




Cerebral aqueduct

Fourth ventricle

Cerebellum

(a)


Temporal lobe

Medullaoblongata


Brainstem

Cerebellum

Cerebrum

Spinal cord

Rostral Caudal

Central sulcus

Lateral sulcus

Gyri

(b) Lateral view

Temporal lobe


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The Cerebrum

• Two cerebral hemispheres divided by longitudinal fissure– Connected by white fibrous tract, the corpus callosum– Gyri and sulci: increase amount of cortex in the cranial cavity– Gyri increases surface area for information-processing capability– Some sulci divide each hemisphere into five lobes named for the

cranial bones overlying them

Figure 14.1a,b

Frontal lobe

Occipital lobe

Central sulcus


Parietal lobe

(a) Superior view

Cerebralhemispheres

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• Frontal lobe– Voluntary motor functions – Motivation, foresight,

planning, memory, mood, emotion, social judgment, and aggression

• Parietal lobe– Receives and integrates

general sensory information, taste, and some visual processing

• Occipital lobe– Primary visual center of

brain• Temporal lobe

– Areas for hearing, smell, learning, memory, and some aspects of vision and emotion

• Insula (hidden by other regions)– Understanding spoken

language, taste and sensory information from visceral receptors

The Cerebrum


Postcentral gyrus

Occipital lobe

Temporal lobe

Lateral sulcus

Frontal lobe Parietal lobe

Insula

Rostral Caudal

Precentralgyrus

Centralsulcus

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Tracts of Cerebral White Matter

Figure 14.14


Projection tracts

Parietal lobe

Occipital lobe

Commissural tracts

Lateral ventricle

Third ventricle

Mammillary body

Pons

Pyramid

Medulla oblongata

Thalamus

Association tracts

Frontal lobe

Temporal lobe

Corpus callosum


Corpus callosum

Basal nuclei

Cerebral peduncle

Projection tracts

Decussation in pyramids

(b) Frontal section

(a) Sagittal section

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The Cerebral White Matter

• Most of the volume of cerebrum is white matter– Glia and myelinated nerve fibers transmitting

signals from one region of the cerebrum to another and between cerebrum and lower brain centers

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• Three types of tracts– Projection tracts

• Extends vertically between higher and lower brain and spinal cord centers

• Carries information between cerebrum and rest of the body

– Commissural tracts• Cross from one cerebral hemisphere through bridges called

commissures– Most pass through corpus callosum– Anterior and posterior commissures– Enables the two sides of the cerebrum to communicate with

each other

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Cont.– Association tracts

• Connect different regions within the same cerebral hemisphere

• Long association fibers—connect different lobes of a hemisphere to each other

• Short association fibers—connect different gyri within a single lobe


I

II

III

IV

V

VI

Cortical surface

Stellate cells

Small pyramidalcells

Large pyramidalcells

Whitematter

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The Cerebral Cortex

• Neural integration is carried out in the gray matter of the cerebrum

• Cerebral gray matter found in three places– Cerebral cortex– Basal nuclei– Limbic system

Figure 14.15


I

II

III

IV

V

VI

Cortical surface

Stellate cells

Small pyramidalcells

Large pyramidalcells

Whitematter

14-80

The Cerebral Cortex

• Cerebral cortex—layer covering the surface of the hemispheres– Only 2 to 3 mm thick– Cortex constitutes about

40% of brain mass– Contains 14 to 16 billion

neurons

Figure 14.15

The Cerebral Cortex• Contains two principal types of neurons

– Stellate cells• Have spheroid somas with dendrites projecting in all directions• Receive sensory input and process information on a local level

– Pyramidal cells• Tall, and conical, with apex toward the brain surface• A thick dendrite with many branches with small, knobby

dendritic spines• Include the output neurons of the cerebrum• Only neurons that leave the cortex and connect with other

parts of the CNS.

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The Cerebral Cortex• Neocortex—six-layered tissue that constitutes about

90% of the human cerebral cortex– Relatively recent in evolutionary origin

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The Basal Nuclei

• Basal nuclei—masses of cerebral gray matter buried deep in the white matter, lateral to the thalamus– Receives input from the substantia nigra of the midbrain and the

motor areas of the cortex– Send signals back to both these locations– Involved in motor control

Figure 14.16


Cerebrum

Corpus callosum

Lateral ventricle

Thalamus

Insula

Optic tractHypothalamusThird ventricle

Pituitary gland

Internal capsuleCaudate nucleus

Putamen

Subthalamic nucleus

Globus pallidus

CorpusstriatumLentiform

nucleus

The Basal Nuclei • At least three brain centers form basal nuclei

– Caudate nucleus– Putamen– Globus pallidus

• Lentiform nucleus—putamen and globus pallidus collectively

• Corpus striatum—putamen and caudate nucleus collectively

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The Limbic System• Limbic system—important

center of emotion and learning

• Most anatomically prominent components are:– Cingulate gyrus: arches

over the top of the corpus callosum in the frontal and parietal lobes

– Hippocampus: in the medial temporal lobe; memory

– Amygdala: immediately rostral to the hippocampus; emotion

Figure 14.17


Basal nuclei

Amygdala

Fornix

Hippocampus

Medialprefrontalcortex

CorpuscallosumCingulategyrus

Orbitofrontalcortex

Temporal lobe

ThalamicnucleiMammillarybody

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The Limbic System

• Limbic system components are connected through a complex loop of fiber tracts allowing for somewhat circular patterns of feedback

• Limbic system structures have centers for both gratification and aversion– Gratification: sensations

of pleasure or reward– Aversion: sensations of

fear or sorrow

Figure 14.17


Basal nuclei

Amygdala

Fornix

Hippocampus

Medialprefrontalcortex

CorpuscallosumCingulategyrus

Orbitofrontalcortex

Temporal lobe

ThalamicnucleiMammillarybody

Integrative Functions of the Brain

• Expected Learning Outcomes– List the types of brain waves and discuss their relationship

to mental states.– Describe the stages of sleep, their relationship to the

brain waves, and the neural mechanisms of sleep.– Identify the brain regions concerned with consciousness

and thought, memory, emotion, sensation, motor control, and language.

– Discuss the functional differences between the right and left cerebral hemispheres.

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Integrative Functions of the Brain• Higher brain functions—sleep, memory, cognition,

emotion, sensation, motor control, and language

• Involve interactions between cerebral cortex and basal nuclei, brainstem, and cerebellum

• Functions of the brain do not have easily defined anatomical boundaries

• Integrative functions of the brain focus mainly on the cerebrum, but involve combined action of multiple brain levels

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The Electroencephalogram• Alpha waves 8 to 13 Hz

– Awake and resting with eyes closed and mind wandering– Suppressed when eyes open or performing a mental task

• Beta waves 14 to 30 Hz– Eyes open and performing mental tasks– Accentuated during mental activity and sensory stimulation

• Theta waves 4 to 7 Hz– Drowsy or sleeping adults – If awake and under emotional stress

• Delta waves (high amplitude) <3.5 Hz– Deep sleep in adults

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The Electroencephalogram

• Electroencephalogram (EEG)—monitors surface electrical activity of the brain waves– Useful for studying normal brain functions as sleep and

consciousness– In diagnosis of degenerative brain diseases, metabolic

abnormalities, brain tumors, etc.

Figure 14.18a

Figure 14.18b

Delta (δ)

(b) 1 second

Alpha ()

Theta ()

Beta ()


The ElectroencephalogramCont. • Brain waves—rhythmic voltage changes resulting from

synchronized postsynaptic potentials at the superficial layer of the cerebral cortex– Four types distinguished by amplitude (mV) and

frequency (Hz)

• Persistent absence of brain waves is common clinical and legal criterion of brain death

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Sleep• Sleep occurs in cycles called circadian rhythms

– Events that reoccur at intervals of about 24 hours

• Sleep—temporary state of unconsciousness from which one can awaken when stimulated– Characterized by stereotyped posture

• Lying down with eyes closed– Sleep paralysis: inhibition of muscular activity– Resembles unconsciousness but can be aroused by sensory

stimulation– Coma or hibernation: states of prolonged unconsciousness where

individuals cannot be aroused by sensory stimulation

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SleepCont. • Restorative effect

– Brain glycogen and ATP levels increase in non-REM sleep– Memories strengthened in REM sleep

• Synaptic connections reinforced

• Four stages of sleep– Stage 1

• Feel drowsy, close eyes, begin to relax• Often feel drifting sensation, easily awakened if stimulated• Alpha waves dominate EEG

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SleepCont.– Stage 2

• Pass into light sleep• EEG declines in frequency but increases in amplitude• Exhibits sleep spindles—high spikes resulting from

interactions between neurons of the thalamus and cerebral cortex

– Stage 3• Moderate to deep sleep• About 20 minutes after stage 1• Theta and delta waves appear• Muscles relax and vital signs fall (body temperature, blood

pressure, heart and respiratory rates)

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SleepCont.– Stage 4

• Called slow-wave sleep (SWS)—EEG dominated by low-frequency, high-amplitude delta waves

• Muscles now very relaxed, vital signs at their lowest, and more difficult to awaken

• About five times a night, a sleeper backtracks from stage 3 or 4 to stage 2– Exhibits bouts of rapid eye movement (REM) sleep, eyes

oscillate back and forth– Also called paradoxical sleep, because EEG resembles the

waking state, but sleeper is harder to arouse than any other stage

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Sleep

Cont.– Vital signs increase, brain uses more oxygen than when

awake– Sleep paralysis stronger to prevent sleeper from acting out

dreams

• Dreams occur in both REM and non-REM sleep– REM tends to be longer and more vivid

• Parasympathetic nervous system active during REM sleep– Causing constriction of the pupils– Erection of the penis and clitoris

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Sleep

• Rhythm of sleep is controlled by a complex interaction between the cerebral cortex, thalamus, hypothalamus, and reticular formation– Arousal induced in the upper reticular formation, near

junction of pons and midbrain– Sleep induced by nuclei below pons, and in ventrolateral

preoptic nucleus in the hypothalamus

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Sleep

• Suprachiasmatic nucleus (SCN)—another important control center for sleep– Above optic chiasma in anterior hypothalamus

– Input from eye allows SCN to synchronize multiple body rhythms with external rhythms of night and day

• Sleep, body temperature, urine production, secretion, and other functions

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Sleep

• Sleep has a restorative effect, and sleep deprivation can be fatal to experimental animals– Bed rest alone does not have the restorative effect of sleep—

why must we lose consciousness?

– Sleep may be the time to replenish such energy sources as glycogen and ATP

– REM sleep may consolidate and strengthen memories by reinforcing some synapses, and eliminating others

14-100

Sleep Stages and Brain Activity

Figure 14.19


0

0 1 2 3 4 5 6 7 8

10

Awake

Stage 1

Stage 2

Stage 3

Stage 4

EEG

sta

ges

20 30 40

(a) One sleep cycle

Stag

e

50 60 70

REM REM REMREMREM

Sleep spindles

Stage 1Drowsy

Stage 2Light sleep

Stage 3Moderate todeep sleep

Stage 4Deepest sleep

REMsleep

Time (min.)

Awake

(b) Typical 8-hour sleep period Time (hours)

14-101

Cognition

• Cognition—the range of mental processes by which we acquire and use knowledge– Such as sensory perception, thought, reasoning,

judgment, memory, imagination, and intuition

• Association areas of cerebral cortex have above functions – Constitute about 75% of all brain tissue

14-102

Cognition

• Studies of patients with brain lesions, cancer, stroke, and trauma yield information on cognition– Parietal lobe association area: perceiving stimuli

• Contralateral neglect syndrome—unaware of objects on opposite side of the body

– Temporal lobe association area: identifying stimuli• Agnosia—inability to recognize, identify, and name

familiar objects• Prosopagnosia—person cannot remember familiar faces

– Frontal lobe association area: planning our responses and personality; inability to execute appropriate behavior

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Memory• Information management entails:

– Learning: acquiring new information– Memory: information storage and retrieval– Forgetting: eliminating trivial information; as important

as remembering

• Amnesia—defects in declarative memory: inability to describe past events

• Procedural memory—ability to tie one’s shoes– Anterograde amnesia: unable to store new information– Retrograde amnesia: person cannot recall things

known before the injury

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Memory

• Hippocampus—important memory-forming center– Does not store memories

– Organizes sensory and cognitive information into a unified long-term memory

– Memory consolidation: the process of “teaching the cerebral cortex” until a long-term memory is established

– Long-term memories are stored in various areas of the cerebral cortex

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MemoryCont.

– Vocabulary and memory of familiar faces stored in superior temporal lobe

– Memories of one’s plans and social roles stored in the prefrontal cortex

• Cerebellum—helps learn motor skills

• Amygdala—emotional memory

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Accidental Lobotomy

• Phineas Gage—railroad construction worker; severe injury with metal rod

• Injury to the ventromedial region of both frontal lobes

• Extreme personality change – Fitful, irreverent, grossly profane– Opposite of previous personality

• Prefrontal cortex functions – Planning, moral judgment, and

emotional control

Figure 14.20

14-107

Emotion

• Emotional feelings and memories are interactions between prefrontal cortex and diencephalon

• Prefrontal cortex—seat of judgment, intent, and control over expression of emotions

• Feelings come from hypothalamus and amygdala– Nuclei generate feelings of fear or love

14-108

Emotion• Amygdala receives input from sensory systems

– Role in food intake, sexual behavior, and drawing attention to novel stimuli

– One output goes to hypothalamus influencing somatic and visceral motor systems

• Heart races, raises blood pressure, makes hair stand on end, induces vomiting

– Other output to prefrontal cortex important in controlling expression of emotions

• Ability to express love, control anger, or overcome fear

• Behavior shaped by learned associations between stimuli, our responses to them, and the reward or punishment that results

14-109

Sensation• Primary sensory cortex—sites

where sensory input is first received and one becomes conscious of the stimulus

• Association areas nearby to sensory areas that process and interpret that sensory information– Primary visual cortex is

bordered by visual association area: interprets and makes cognitive sense of visual stimuli

– Multimodal association areas: receive input from multiple senses and integrate this into an overall perception of our surroundings

Figure 14.22a

Anterior

Posterior

(a)

Precentralgyrus

Centralsulcus

Postcentralgyrus Occipital

lobe

Parietallobe

Frontallobe


14-110

The Special Senses• Special senses—limited to the head and employ relatively

complex sense organs• Primary cortices and association areas listed below• Vision

– Visual primary cortex in far posterior region of occipital lobe

– Visual association area: anterior, and occupies all the remaining occipital lobe

• Much of inferior temporal lobe deals with facial recognition and other familiar objects

• Hearing– Primary auditory cortex in the superior region of the temporal

lobe and insula– Auditory association area: temporal lobe deep and inferior to

primary auditory cortex• Recognizes spoken words, a familiar piece of music, or a

voice on the phone

14-111

The Special Senses• Equilibrium

– Signals for balance and sense of motion project mainly to the cerebellum and several brainstem nuclei concerned with head and eye movements and visceral functions

– Association cortex in the roof of the lateral sulcus near the lower end of the central sulcus

• Seat of consciousness of our body movements and orientation in space

• Taste and smell– Gustatory (taste) signals received by primary gustatory

cortex in inferior end of the postcentral gyrus of the parietal lobe and anterior region of insula

– Olfactory (smell) signals received by the primary olfactory cortex in the medial surface of the temporal lobe and inferior surface of the frontal lobe

14-112

The General Senses• General (somesthetic, somatosensory, or somatic)

senses—distributed over the entire body and employ relatively simple receptors– Senses of touch, pressure, stretch, movement, heat, cold, and

pain• Several cranial nerves carry general sensations from head• Ascending tracts bring general sensory information from the

rest of the body– Thalamus processes the input– Selectively relays signals to the postcentral gyrus

• Fold of the cerebrum that lies immediately caudal to the central sulcus and forms the rostral border of the parietal lobe

– Primary somesthetic cortex is the cortex of the postcentral gyrus

– Somesthetic association area: caudal to the gyrus and in the roof of the lateral sulcus

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The General Senses• Awareness of stimulation occurs in primary somesthetic

cortex

• Making cognitive sense of the stimulation occurs in the somesthetic association area

• Because of decussation, the right postcentral gyrus receives input from the left side of the body and vice versa

• Sensory homunculus—upside-down sensory map of the contralateral side of the body

• Somatotopy—point-for-point correspondence between an area of the body and an area of the CNS

ThighShoulder

Arm

V

(b)

Insula

Lateral sulcus

Genitalia

Leg

HipTrunk

EyeNoseFaceUpper lip

Lower lip

Thumb (I)Hand

Forearm

NeckElbow

II IIIIV

FingersI

II III IVV

Lateral Medial

Tongue

Teeth, gums

Wrist

Toes

Viscerosensory areaAbdominal

viscera


The General SensesFigure 14.22b

• Sensory homunculus—diagram of the primary somesthetic cortex which resembles an upside-down sensory map of the contralateral side of the body

• Shows receptors in the lower limbs projecting to the superior and medial parts of the gyrus

• Shows receptors from the face projecting to the inferior and lateral parts

• Somatotopy—point-to-point correspondence between an area of the body and an area of the CNS

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Functional Regions of the Cerebral Cortex

Figure 14.21

Wernicke area

Broca area

Primary motorcortex

Motor associationarea

Prefrontalcortex

Olfactoryassociationarea

Primary somatosensorycortex

Somatosensoryassociation area

Primary gustatorycortex

Visual associationareaPrimaryvisual cortex

Primaryauditory cortexAuditoryassociation area


14-116

Motor Control

• The intention to contract a muscle begins in motor association (premotor) area of frontal lobes– Where we plan our behavior– Where neurons compile a program for degree and

sequence of muscle contraction required for an action– Program transmitted to neurons of the precentral gyrus

(primary motor area)• Most posterior gyrus of the frontal lobe

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Motor Control• Premotor area (cont.)

– Neurons send signals to the brainstem and spinal cord– Ultimately resulting in muscle contraction– Precentral gyrus also exhibits somatotopy

• Neurons for toe movement are deep in the longitudinal fissure of the medial side of the gyrus

• The summit of the gyrus controls the trunk, shoulder, and arm

• The inferolateral region controls the facial muscles– Motor homunculus has a distorted look because the

amount of cortex devoted to a given body region is proportional to the number of muscles and motor units in that body region

14-118

Motor Control• Pyramidal cells of the precentral gyrus are called upper

motor neurons– Their fibers project caudally– About 19 million fibers ending in nuclei of the brainstem– About 1 million forming the corticospinal tracts– Most fibers decussate in lower medulla oblongata– Form lateral corticospinal tracts on each side of the spinal

cord

• In the brainstem or spinal cord, the fibers from upper motor neurons synapse with lower motor neurons whose axons innervate the skeletal muscles

• Basal nuclei and cerebellum are also important in muscle control

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Motor Control• Basal nuclei

– Determines the onset and cessation of intentional movements• Repetitive hip and shoulder movements in walking

– Highly practiced, learned behaviors that one carries out with little thought

• Writing, typing, driving a car– Lies in a feedback circuit from the cerebrum, to the basal

nuclei, to the thalamus, and back to the cerebrum– Dyskinesias: movement disorders caused by lesions in the

basal nuclei

• Cerebellum– Highly important in motor coordination– Aids in learning motor skills– Maintains muscle tone and posture– Smoothes muscle contraction – Coordinates eye and body movements– Coordinates the motions of different joints with each other– Ataxia: clumsy, awkward gait

Fingers

Eye and eyelid

Tongue

Ankle

Lips

Face

JawPh

aryn

x

SalivationMasticationSwallowing

NeckBrow

VHand

Wrist

Elbow

Shoulder

Trunk

Knee

Hip

IVIIIII

Thumb (I)

I

IIIII

IVV

(b)

Lateral Medial

Vocalization

Toes

14-120

Motor Homunculus

Figure 14.23b


14-121

Motor Pathways Involving the Cerebellum

Figure 14.24

Cerebrum

Cerebrum

Motor cortex

Cerebellum

Cerebellum

Brainstem

Brainstem

Inner ear

Eye

Reticular formation

Muscle and joint proprioceptors

(a) Input to cerebellum (b) Output from cerebellum

Spinocerebellartracts of spinal cord

Reticulospinaland vestibulospinaltracts of spinal cord

Limb and posturalmuscles


14-122

Language• Language include several abilities: reading, writing, speaking,

and understanding words assigned to different regions of the cerebral cortex

• Wernicke area– Permits recognition of spoken and written language and creates plan

of speech– When we intend to speak, Wernicke area formulates phrases

according to learned rules of grammar– Transmits plan of speech to Broca area

• Broca area – Generates motor program for the muscles of the larynx, tongue,

cheeks, and lips – Transmits program to primary motor cortex for commands to the lower

motor neurons that supply relevant muscles• Affective language area lesions produce aprosody—flat

emotionless speech


Precentral gyrus

Anterior Posterior

Speech center ofprimary motor cortex

Primary auditory cortex(in lateral sulcus)

Brocaarea

Postcentralgyrus

Angulargyrus

Primaryvisual cortex

Wernickearea

14-123

Language Centers of the Left Hemisphere

Figure 14.25

14-124

Aphasia• Aphasia—any language deficit from lesions in same

hemisphere (usually left) containing the Wernicke and Broca areas

• Nonfluent (Broca) aphasia– Lesion in Broca area– Slow speech, difficulty in choosing words, using words that only

approximate the correct word

• Fluent (Wernicke) aphasia– Lesion in Wernicke area– Speech normal and excessive, but uses senseless jargon– Cannot comprehend written and spoken words

• Anomic aphasia – Can speak normally and understand speech, but cannot identify

written words or pictures

14-125

Cerebral Lateralization

Figure 14.26


Olfaction, left nasal cavity

Memory for shapes

Left hand motor control

Musical ability

Intuitive, nonverbal thought

Speech

Olfaction, right nasal cavity

Left hemisphere Right hemisphere

Posterior

Anterior

Verbal memory

Right handmotor control

Feeling shapeswith right hand

Hearing vocal sounds(right ear advantage)

Rational, symbolicthought

Superior languagecomprehension

Vision, right field

(Limited languagecomprehension, mute)

Feeling shapes withleft hand

Hearing nonvocal sounds(left ear advantage)

Superior recognition offaces and spatialrelationships

Vision, left field

14-126

Cerebral Lateralization• Cerebral lateralization—the difference in the structure and

function of the cerebral hemispheres• Left hemisphere—categorical hemisphere

– Specialized for spoken and written language– Sequential and analytical reasoning (math and science)– Breaks information into fragments and analyzes it in a linear

way• Right hemisphere—representational hemisphere

– Perceives information in a more integrated holistic way – Seat of imagination and insight– Musical and artistic skill– Perception of patterns and spatial relationships– Comparison of sights, sounds, smells, and taste

14-127

Cerebral Lateralization

• Highly correlated with handedness – Left hemisphere is the categorical one in 96% of right-handed

people• Right hemisphere in 4%

– Left-handed people: right hemisphere is categorical in 15% and left in 70%

• Lateralization develops with age– Males exhibit more lateralization than females and suffer more

functional loss when one hemisphere is damaged

The Cranial Nerves

• Expected Learning Outcomes– List the 12 cranial nerves by name and number.– Identify where each cranial nerve originates and

terminates.– State the functions of each cranial nerve.

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The Cranial Nerves

• Brain must communicate with rest of body

– Most of the input and output travels by way of the spinal cord

– 12 pairs of cranial nerves arise from the base of the brain

– Exit the cranium through foramina

– Lead to muscles and sense organs located mainly in the head and neck

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Cranial Nerve Pathways

• Most motor fibers of the cranial nerves begin in nuclei of brainstem and lead to glands and muscles

• Sensory fibers begin in receptors located mainly in head and neck and lead mainly to the brainstem– Sensory fibers for proprioception may travel to

brain in a different nerve from motor nerve

14-131

Cranial Nerve Pathways

• Most cranial nerves carry fibers between brainstem and ipsilateral receptors and effectors– Lesion in left brainstem causes sensory or motor

deficit on same side• Exceptions: optic nerve where half the fibers

decussate, and trochlear nerve where all efferent fibers lead to a muscle of the contralateral eye

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Cranial Nerve Classification

• Some cranial nerves are classified as motor, some sensory, others mixed

– Sensory (I, II, and VIII)

– Motor (III, IV, VI, XI, and XII) • Stimulate muscle but also contain fibers of proprioception

– Mixed (V, VII, IX, X)• Sensory functions may be quite unrelated to their motor

function– Facial nerve (VII) has sensory role in taste and motor role in

facial expression

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The Cranial NervesFigure 14.27a,b Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

b: © The McGraw-Hill Companies, Inc./Rebecca Gray, photographer/DonKincaid, dissections

Cranial nerves:

Optic nerve (II)


Trigeminal nerve (V)

Abducens nerve (VI)

Facial nerve (VII)

Vestibulocochlear nerve (VIII)





Frontal lobeFrontal lobe

Cerebellum

Cerebellum

Olfactory tract

Temporal lobe

Infundibulum

Pons

Medulla

Optic chiasm

Optic chiasm

Olfactory tract

Pons

Spinal cordSpinal cord

(a) (b)

Longitudinalfissure

Medullaoblongata

Olfactory bulb(from olfactory nerve, I)

Vagus nerve (X)

Temporal lobe

14-134

The Olfactory Nerve (I)

• Sense of smell• Damage causes impaired sense of smell

Figure 14.28


Olfactory bulbOlfactory tract

Nasal mucosa

Cribriform plate ofethmoid boneFascicles ofolfactory nerve (I)

14-135

The Optic Nerve (II)

• Provides vision

• Damage causes blindness in part or all of visual field

Figure 14.29


Eyeball

Optic nerve (II)

Optic chiasmOptic tract

Pituitary gland

14-136

The Oculomotor Nerve (III)

• Controls muscles that turn the eyeball up, down, and medially, as well as controlling the iris, lens, and upper eyelid

• Damage causes drooping eyelid, dilated pupil, double vision, difficulty focusing, and inability to move eye in certain directions

Figure 14.30

Oculomotor nerve (III):

Superior orbital fissure

Superior branchInferior branch

Ciliary ganglion


14-137

The Trochlear Nerve (IV)

• Eye movement (superior oblique muscle)• Damage causes double vision and inability to rotate eye

inferolaterally

Figure 14.31


Superior oblique muscle



14-138

The Trigeminal Nerve (V)

• Largest of the cranial nerves

• Most important sensory nerve of the face

• Forks into three divisions

– Ophthalmic division (V1): sensory

– Maxillary division (V2): sensory

– Mandibular division (V3): mixed Figure 14.32


Lingual nerve

V1

V3

V2


Foramen ovale

Foramen rotundum

Temporalis muscle

Medial pterygoid muscle

Masseter muscle

Lateral pterygoid muscle

InfraorbitalnerveSuperioralveolar nerves

Inferioralveolar nerve

Ophthalmic division (V1)Trigeminal ganglionTrigeminal nerve (V)Maxillary division (V2)

Mandibular division (V3)

Anterior trunk of V3 tochewing muscles

Anterior belly ofdigastric muscle

Motor branches of themandibular division (V3)

Distribution of sensoryfibers of each division

14-139

The Abducens Nerve (VI)

• Provides eye movement (lateral rectus m.)• Damage results in inability to rotate eye laterally and at rest eye

rotates medially

Figure 14.33


Abducens nerve (VI)


Lateral rectus muscle

14-140

The Facial Nerve (VII)

• Motor—major motor nerve of facial muscles: facial expressions; salivary glands and tear, nasal, and palatine glands

• Sensory—taste on anterior two-thirds of tongue• Damage produces sagging facial muscles and disturbed sense

of taste (no sweet and salty)

Figure 14.34a


Geniculate ganglion

Pterygopalatine ganglion

Lacrimal (tear) gland

Submandibular gland

Stylomastoid foramen

Sublingual gland

Internal acoustic meatus

Facial nerve (VII)

(a)

Parasympathetic fibers

Submandibular ganglion

Chorda tympanibranch (taste andsalivation)

Motor branchto muscles offacial expression

14-141

Five Branches of Facial Nerve

Clinical test: test anterior two-thirds of tongue with substances such as sugar, salt, vinegar, and quinine; test response of tear glands to ammonia fumes; test motor functions by asking subject to close eyes, smile, whistle, frown, raise eyebrows, etc.

Figure 14.34b,c


TemporalZygomatic

Buccal

Mandibular

Cervical

(c)c: © The McGraw-Hill Companies, Inc./Joe DeGrandis, photographer

Zygomatic

Buccal

Mandibular

Cervical

(b)

Temporal

Cochlear nerve

Cochlea

Semicircularducts

Vestibular gangliaVestibular nerve

Vestibulocochlearnerve (VIII)

Internalacoustic meatus

Vestibule


14-142

The Vestibulocochlear Nerve (VIII)

• Nerve of hearing and equilibrium• Damage produces deafness, dizziness, nausea, loss of balance,

and nystagmus (involuntary rhythmic oscillation of the eyes from side to side)

Figure 14.35

14-143

The Glossopharyngeal Nerve (IX)

• Swallowing, salivation, gagging, control of BP and respiration

• Sensations from posterior one-third of tongue

• Damage results in loss of bitter and sour taste and impaired swallowing

Figure 14.36


Parotid salivary gland

Jugular foramenSuperior ganglionInferior ganglionOtic ganglion

Carotid sinusPharyngeal muscles


14-144

The Vagus Nerve (X)• Most extensive distribution of

any cranial nerve

• Major role in the control of cardiac, pulmonary, digestive, and urinary function

• Swallowing, speech, regulation of viscera

• Damage causes hoarseness or loss of voice, impaired swallowing, and fatal if both are cut

Figure 14.37


Heart

Lung

Liver

Spleen

Small intestine

Stomach

Kidney

Carotid sinus

Laryngeal nerve

Pharyngeal nerve

Jugular foramen

Vagus nerve (X)

Colon

(proximal portion)

14-145

The Accessory Nerve (XI)

• Swallowing; head, neck, and shoulder movement– Damage causes impaired head, neck, shoulder movement;

head turns toward injured side

Figure 14.38



Posterior view

Jugularforamen

Foramenmagnum

Spinal nervesC3 and C4

Sternocleidomastoidmuscle

Vagus nerve

Trapezius muscle

14-146

The Hypoglossal Nerve (XII)

• Tongue movements for speech, food manipulation, and swallowing– If both are damaged: cannot protrude tongue – If one side is damaged: tongue deviates toward injured

side; see ipsilateral atrophy

Figure 14.39


Hypoglossal canal


Intrinsic musclesof the tongueExtrinsic musclesof the tongue

14-147

Cranial Nerve Disorders

• Trigeminal neuralgia (tic douloureux)– Recurring episodes of intense stabbing pain in trigeminal

nerve area (near mouth or nose)– Pain triggered by touch, drinking, washing face– Treatment may require cutting nerve

• Bell palsy– Degenerative disorder of facial nerve causes paralysis of

facial muscles on one side– May appear abruptly with full recovery within 3 to 5 weeks

14-148

Images of the Mind

• Positron emission tomography (PET) and MRI visualize increases in blood flow when brain areas are active– Injection of radioactively labeled glucose

• Busy areas of brain “light up”

• Functional magnetic resonance imaging (fMRI) looks at increase in blood flow to an area (additional glucose is needed in active area)—magnetic properties of hemoglobin depend on how much oxygen is bound to it (additional oxygen is there due to additional blood flow)– Quick, safe, and accurate method to see brain function

14-149

Images of the Mind

Figure 14.40


Broca area

Primary motor cortexPremotor areaPrimary auditory cortex

1 2 3 4

Rostral Caudal

Wernicke area conceivesof the verb drive to go with it.

Broca area compiles amotor program to speakthe word drive.

The primary motor cortexexecutes the program andthe word is spoken.

Wernicke areaVisual cortex

The word car is seen in the visual cortex.

Date post:	21-Apr-2017
Category:	Environment
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Chapt14 lecture (4)

Environment