An Introduction to the Brain and Cranial Nerves

The Adult Human Brain

Contains almost 97% of the body’s neural

tissue

Average weight about 1.4 kg (3 lb)

About 400 g at birth

Adult range = 1100-1700 g

Reached by about 18 yoa

Decline in weight starts at about age 50

The Brain

Eight Major Regions of the Brain Cortex (Cerebrum)

Limbic System

Thalamus

Hypothalamus

Cerebellum

Midbrain (Mesencephalon)

Pons

Medulla oblongata

Diencephalon

Brainstem

The Brain

Fig 14-1

Brain Protection and Support

Physical protection

Bones of the cranium

Cranial meninges

Cerebrospinal fluid

Biochemical isolation

Blood–brain barrier

Brain Protection and Support

The Cranial Meninges

Have three layers:

Dura mater (“tough mother” – attached to inner surface of skull)

Arachnoid mater (web-like matrix)

– Space between arachnoid and pia is filled with CSF

Pia mater (“tender mother” – attached to the brain)

Are continuous with spinal meninges

Protect the brain from cranial trauma

Brain Protection and Support

The Cranial Meninges Dura mater

Inner fibrous layer (meningeal layer)

Outer fibrous layer (endosteal layer) fused to periosteum

Venous sinuses form between the two layers (dural sinuses)

Arachnoid mater Covers brain

Contacts epithelial layer of dura mater

Subarachnoid space: between arachnoid mater and pia mater

Pia mater Covered by many blood vessels and attached to brain

surface by astrocytes

Brain Protection and Support

Fig 14-3

Brain Protection and Support

Dural Folds

Folded inner layer of dura mater

Extend into cranial cavity

Stabilize and support brain

Contain collecting veins (dural sinuses), where

cerebral veins will empty

Falx cerebri, tentorium cerebelli, and falx cerebelli

Brain Protection and Support

Dural Folds Falx cerebri

Projects into the longitudinal fissure between the cerebral

hemispheres

Contains superior sagittal sinus and inferior sagittal sinus

Tentorium cerebelli Separates cerebellum and cerebrum

Contains transverse sinus

Falx cerebelli Divides cerebellar hemispheres below the tentorium cerebelli

Brain Protection and Support

Fig 14-3

The Ventricular System

Fig 14-2

Cerebrospinal Fluid

Cerebrospinal Fluid (CSF)

Surrounds all exposed surfaces of CNS

Interchanges with interstitial fluid of brain

Functions of CSF

Cushions delicate neural structures

Supports brain

Transports nutrients, chemical messengers, and

waste products

Cerebrospinal Fluid Cerebrospinal Fluid (CSF)

Choroid plexus

Specialized ependymal cells and capillaries:

– secrete CSF into ventricles

– remove waste products from CSF

– adjust composition of CSF

Produces about 500 mL of CSF/day

– About 130 mLs within and around the brain and spinal cord

at any given time

– About 20 mLs within the ventricles; Remainder in

subarachnoid space

Cerebrospinal Fluid

Cerebrospinal Fluid (CSF)

CSF circulates

From choroid plexus

Through ventricles

To central canal of spinal cord

Into subarachnoid space around the brain, spinal

cord, and cauda equina

Cerebrospinal Fluid

Cerebrospinal Fluid (CSF)

CSF in subarachnoid space

Arachnoid villi:

– extensions of subarachnoid space

– extend through dura mater to superior sagittal sinus

Arachnoid granulations:

– large clusters of villi

– absorb CSF into venous circulation

Cerebrospinal Fluid

Fig 14-4

Hydrocephalus or “water on the brain” may result from _____.

A.deficient production of CSFB.excessive production of CSFC.blockage of circulation of CSFD.excessive water intakeE.B or C

Arterial Blood Supply

Blood Supply to the Brain

Supplies nutrients and oxygen to brain

Delivered by internal carotid arteries and

vertebral arteries

Removed from dural sinuses by internal

jugular veins

Arterial Blood Supply

Fig 21-22

Arterial Blood Supply

Fig 21-23

Venous Drainage

Fig 21-28

Venous Drainage

Fig 21-28

Cerebrovascular Disease

Cerebrovascular Disease

Disorders interfere with blood circulation to brain

Stroke or cerebrovascular accident (CVA)

Shuts off blood to portion of brain

Neurons die

The brain requires a substantial blood supply. The vessels that deliver blood to the brain are the _____.

A.internal carotid arteriesB.vertebral arteriesC.jugular veinsD.A and B onlyE.A, B, and C

Blood-Brain Barrier

Blood–Brain Barrier

Isolates CNS neural tissue from general circulation

Formed by network of tight junctions between

endothelial cells of CNS capillaries

Lipid-soluble compounds (O2, CO2), steroids, and

prostaglandins can diffuse into interstitial fluid of brain

and spinal cord

Astrocytes control blood–brain barrier by releasing

chemicals that control permeability of endothelium

Blood-CSF Barrier

Blood–CSF Barrier

Formed by special ependymal cells

Surround capillaries of choroid plexus

Limits movement of compounds transferred

Allows chemical composition of blood and CSF to

differ

Blood Brain Barrier

Four Breaks in the BBB Portions of hypothalamus

Secrete hypothalamic hormones

Posterior lobe of pituitary gland Secretes hormones ADH and oxytocin

Pineal glands Pineal secretions

Choroid plexus Where special ependymal cells maintain blood–

CSF barrier

Blood Brain Barrier

Meninges stabilize brain in cranial cavity

Cerebrospinal fluid protects against sudden

movement

CSF provides nutrients and removes wastes

Blood–brain barrier and blood–CSF barrier

Selectively isolate brain from chemicals in blood that

might disrupt neural function

The Brain

Fig 14-1

The Brain Stem

The Brain Stem

Processes information

between

Spinal cord and

cerebrum or cerebellum

Includes

Mesencephalon

(midbrain)

Pons

Medulla oblongata

The Medulla Oblongata

The Brain Stem

Medulla oblongata

Connects brain to spinal

cord

Relays information

Regulates autonomic

functions:

– heart rate, blood pressure,

respiration and digestion

The Medulla Oblongata

The Medulla Oblongata

Allows brain and spinal cord to communicate

Coordinates complex autonomic reflexes

Controls visceral functions

Nuclei in the Medulla

Autonomic nuclei: control visceral activities

Sensory and motor nuclei: of cranial nerves

Relay stations: along sensory and motor pathways

The Medulla Oblongata

Autonomic Nuclei of the Medulla Oblongata Reticular formation

Gray matter with embedded nuclei

Regulates autonomic functions

Reflex centers Control peripheral systems:

– cardiovascular centers:

» cardiac center

» control blood flow through peripheral tissues

– respiratory rhythmicity centers

sets pace for respiratory movements

The Medulla Oblongata

Relay Stations of the Medulla Oblongata

Nucleus gracilis and nucleus cuneatus

Pass somatic sensory information to thalamus

Solitary nucleus

Receives visceral sensory information

Olivary nuclei (olives)

Relay information about somatic motor commands

The Medulla Oblongata

Fig 14-6

The Medulla Oblongata

Fig 14-6

The medulla oblongata regulates _____.

A.blood pressureB.food intakeC.respirationD.both A and BE.both A and C

The Pons

The Pons

Connects cerebellum to brain stem

Links to mesencephalon, diencephalon, cerebrum

and spinal cord

Is involved in somatic and visceral motor

control

The Pons

Fig 14-6

The Pons

The Pons Nuclei involved with respiration

Apneustic center and pneumotaxic center: – modify respiratory rhythmicity center activity

Nuclei and tracts Process and relay information to and from

cerebellum Ascending, descending, and transverse tracts:

– transverse fibers (axons):

» link nuclei of pons with opposite cerebellar hemisphere

The Pons

Fig 14-6

The Pons contains:

A.sensory and motor nuclei for four cranial nerves.B.nuclei concerned with the control of respiration.C.tracts that link the cerebellum with the brain stem.D.All of the above

The Mesencephalon

The Brain Stem

Mesencephalon

Also called midbrain

Processes sight, sound, and associated reflexes

Maintains consciousness

The Mesencephalon

Structures of the Mesencephalon

Tectum

Two pairs of sensory nuclei (corpora quadrigemina):

– superior colliculus (visual)

– inferior colliculus (auditory)

Tegmentum

Red nucleus (many blood vessels)

Substantia nigra (pigmented gray matter)

The Mesencephalon

Fig 14-8

The Mesencephalon

Structures of the

Mesencephalon

Cerebral peduncles

Nerve fiber bundles on

ventrolateral surfaces

Contain:

– descending fibers to cerebellum

– motor command fibers

Damage to the superior colliculi would interfere with the reflex ability to _____.

A.express rageB.voluntarily move the armC.react to a bright lightD.react to loud noisesE.maintain proper posture

The Cerebellum

Cerebellum

Second largest part of brain

Coordinates repetitive body

movements

Two hemispheres

Covered with cerebellar

cortex

The Cerebellum

Functions of the Cerebellum

Adjusts postural muscles

Fine-tunes conscious and subconscious

movements

The Cerebellum

Structures of the Cerebellum Folia

Surface of cerebellum Highly folded neural cortex

Anterior and posterior lobes Separated by primary fissure

Cerebellar hemispheres: Separated at midline by vermis

Vermis Narrow band of cortex

Flocculonodular lobe Below fourth ventricle

The Cerebellum

Structures of the Cerebellum

Purkinje cells

Large, branched cells

Found in cerebellar cortex

Receive input from up to 200,000 synapses

Arbor vitae

Highly branched, internal white matter of cerebellum

Cerebellar nuclei: embedded in arbor vitae:

– relay information to Purkinje cells

The Cerebellum

Structures of the Cerebellum

The peduncles

Tracts link cerebellum with brain stem, cerebrum, and spinal

cord:

– superior cerebellar peduncles

– middle cerebellar peduncles (links cerebellum with pons)

– inferior cerebellar peduncles

The Cerebellum

Disorders of the Cerebellum

Ataxia

Damage from trauma or stroke

Intoxication (temporary impairment)

Disturbs muscle coordination

The Cerebellum

Fig 14-7

The Cerebellum

Fig 14-7

Overseeing the postural muscles of the body and making rapid adjustments to maintain balance and equilibrium are functions of the _____.

A.cerebrumB.mesencephalonC.cerebellumD.ponsE.medulla oblongata

The Diencephalon

Diencephalon

Located under cerebrum

and cerebellum

Links cerebrum with

brain stem

Two divisions

Thalamus

Hypothalamus

The Diencephalon

Diencephalon Thalamus

Relays and processes sensory information

Hypothalamus Hormone production Emotion Autonomic function

Pituitary gland Major endocrine gland Connected to hypothalamus Via infundibulum (stalk) Interfaces nervous and

endocrine systems

The Diencephalon

The Thalamus Filters ascending sensory information for primary

sensory cortex

Relays information between basal nuclei and cerebral

cortex

The third ventricle Separates left thalamus and right thalamus

Interthalamic adhesion (or intermediate mass):

– projection of gray matter

– extends into ventricle from each side

The Diencephalon

The Thalamus

Thalamic nuclei

Are rounded masses that form thalamus

Relay sensory information to basal nuclei and

cerebral cortex

The Diencephalon

Five Groups of Thalamic Nuclei

Anterior group

Anterior nuclei

Part of limbic system (emotions)

Medial group

Provides awareness of emotional states

Ventral group

Relays sensory information from basal ganglia and

cerebellum

The Diencephalon

Five Groups of Thalamic Nuclei

Posterior group

Pulvinar nucleus (sensory)

Lateral geniculate nucleus (visual)

Medial geniculate nucleus (auditory)

Lateral group

Affects emotional states

Integrates sensory information

The Diencephalon

Fig 14-9

The Diencephalon

The Hypothalamus Mamillary bodies

Located in posterior hypothalamus

Process olfactory and other sensory information

Control reflex eating movements

Infundibulum A narrow stalk

Connects hypothalamus to pituitary gland

Tuberal area Located between the infundibulum and mamillary bodies

Helps control pituitary gland function

The Diencephalon

Fig 14-10

The Diencephalon

Fig 14-10

The Diencephalon

Eight Functions of the Hypothalamus

Provides subconscious control of skeletal muscle

Controls autonomic function

Coordinates activities of nervous and endocrine

systems

Secretes hormones

Antidiuretic hormone (ADH) by supraoptic nucleus

Oxytocin (OT; OXT) by paraventricular nucleus

The Diencephalon

Eight Functions of the Hypothalamus

Produces emotions and behavioral drives

The feeding center (hunger)

The thirst center (thirst)

Coordinates voluntary and autonomic functions

Regulates body temperature

Preoptic area of hypothalamus

Controls circadian rhythms (day–night cycles)

Suprachiasmatic nucleus

JoJo begins to experience mood swings and disturbed thirst and hunger. Imaging studies indicate that a brain turmor is the likely cause of these disorders. In what part of the brain is the tumor most likely located?

A.Prefrontal cortexB.Postcentral gyrusC.Basal nucleiD.HypothalamusE.Reticular formation

The Limbic System

The Limbic System

Is a functional grouping that

Establishes emotional states

Links conscious functions of cerebral cortex with

autonomic functions of brain stem

Facilitates memory storage and retrieval

The Limbic System

Components of the Limbic System Amygdaloid body

Acts as interface between the limbic system, the

cerebrum, and various sensory systems

Limbic lobe of cerebral hemisphere Cingulate gyrus

Dentate gyrus

Parahippocampal gyrus

Hippocampus – storage and recall of long-term

memories

The Limbic System

Components of the Limbic System Fornix

Tract of white matter Connects hippocampus with hypothalamus

Anterior nucleus of the thalamus Relays information from mamillary body to

cingulate gyrus

Reticular formation Stimulation or inhibition affects emotions (rage,

fear, pain, sexual arousal, pleasure)

The Limbic System

Fig 14-11

The Limbic System

Fig 14-11

Which of the following is not a function of the limbic system?

A.Contains cerebral and diencephalic componentsB.Functions in maintaining homeostasis in cold weatherC.Located between the border of the cerebrum and diencephalonD.Links conscious functions of the cerebral cortex with unconscious functions of the brain stemE.Functions in emotions, learning, and memory

The Brain

Cerebrum (Cortex)

Largest part of brain

Controls higher mental

functions

Divided into left and right

cerebral hemispheres

The Brain

Cerebrum

Neural cortex

Also called cerebral cortex

Folded surface increases surface area

Elevated ridges (gyri)

Shallow depressions (sulci)

Deep grooves (fissures)

The Cerebrum

The Cerebrum

Is the largest part of the brain

Controls all conscious thoughts and

intellectual functions

Processes somatic sensory and motor

information

The Cerebrum

Gray matter

In cerebral cortex and

basal nuclei

White matter

Deep to basal cortex

Around basal nuclei

The Cerebrum

Structures of the Cerebrum Gyri of neural cortex

Increase surface area (number of cortical neurons)

Insula (island) of cortex Lies medial to lateral sulcus

Longitudinal fissure Separates cerebral hemispheres

Lobes Divisions of hemispheres named after overlying

skull bones

The Cerebrum

Structures of the Cerebrum

Central sulcus divides

Anterior frontal lobe from posterior parietal lobe

Lateral sulcus divides

Frontal and Parietal lobe from temporal lobe

Parieto-occipital sulcus divides

Parietal lobe from occipital lobe

The Cerebrum

Fig 14-12

The Cerebrum

Fig 14-12

The Cerebrum

Fig 14-12

The Cerebrum

Three Functional Principles of the Cerebrum

Each cerebral hemisphere receives sensory

information from, and sends motor commands to, the

opposite side of the body

The two hemispheres have different functions,

although their structures are alike

Correspondence between a specific function and a

specific region of cerebral cortex is not precise

The Cerebrum

White Matter of the Cerebrum

Association fibers

Commissural fibers

Projection fibers

The Cerebrum

White Matter of the Cerebrum Association fibers

Connections within one hemisphere:

– arcuate fibers: » are short fibers

» connect one gyrus to another

– longitudinal fasciculi: » are longer bundles

» connect frontal lobe to other lobes in same hemisphere

The Cerebrum

White Matter of the Cerebrum

Commissural fibers

Bands of fibers connecting two hemispheres:

– corpus callosum

– anterior commissure

The Cerebrum

White Matter of the Cerebrum

Projection fibers

Pass through diencephalon

Link cerebral cortex with:

– diencephalon, brain stem, cerebellum, and spinal cord

Internal capsule:

– all ascending and descending projection fibers

The Cerebrum

Fig 14-13

The Cerebrum

Fig 14-13

The Cerebrum

The Basal Nuclei

Also called cerebral nuclei

Are masses of gray matter

Are embedded in white matter of cerebrum

Direct subconscious activities

The Cerebrum

Structures of Basal Nuclei

Caudate nucleus

Curving, slender tail

Lentiform nucleus

Globus pallidus

Putamen

The Cerebrum

Fig 14-14

The Cerebrum

Fig 14-14

The Cerebrum

Fig 14-14

The Cerebrum

Functions of Basal Nuclei

Involved with

The subconscious control of skeletal muscle tone

The coordination of learned movement patterns

(walking, lifting)

Which of the following is NOT one of the basal nuclei?

A.Caudate nucleusB.Globus pallidusC.PutamenD.HippocampusE.Amygdaloid body

The Cerebrum

Motor and Sensory Areas of the Cortex Central sulcus separates motor and sensory

areas

Motor areas Precentral gyrus of frontal lobe:

– directs voluntary movements

Primary motor cortex:– is the surface of precentral gyrus

Pyramidal cells:– are neurons of primary motor cortex

The Cerebrum

Motor and Sensory Areas of the Cortex

Sensory areas

Postcentral gyrus of parietal lobe:

– receives somatic sensory information (touch, pressure,

pain, vibration, taste, and temperature)

Primary sensory cortex:

– surface of postcentral gyrus

The Cerebrum

Special Sensory Cortexes Visual cortex

Information from sight receptors

Auditory cortex Information from sound receptors

Olfactory cortex Information from odor receptors

Gustatory cortex Information from taste receptors

The Cerebrum

Fig 14-15

The Cerebrum

Association Areas

Cortical regions that interpret sensory information or

coordinate motor responses

Sensory association areas

Monitor and interpret arriving information at sensory areas of

cortex

Somatic motor association area (premotor cortex)

Coordinates motor responses (learned movements)

The Cerebrum

Sensory Association Areas

Somatic sensory association area

Interprets input to primary sensory cortex (e.g., recognizes

and responds to touch)

Visual association area

Interprets activity in visual cortex

Auditory association area

Monitors auditory cortex

The Cerebrum

Integrative Centers

Are located in lobes and cortical areas of both

cerebral hemispheres

Receive information from association areas

Direct complex motor or analytical activities

The Cerebrum

General Interpretive Area

Also called Wernicke area

Present in only one hemisphere

Receives information from all sensory association

areas

Coordinates access to complex visual and auditory

memories

The Cerebrum

Other Integrative Areas

Speech center Is associated with general interpretive area

Coordinates all vocalization functions

Prefrontal cortex of frontal lobe Integrates information from sensory association

areas

Performs abstract intellectual activities (e.g.,

predicting consequences of events or actions)

The Cerebrum

Fig 14-15

The Cerebrum

Interpretive Areas of Cortex

Brodmann areas

Patterns of cellular organization in cerebral cortex

Fig 14-15

The Cerebrum

Hemispheric Lateralization

Functional differences between left and right

hemispheres

Each cerebral hemisphere performs certain

functions that are not ordinarily performed by

the opposite hemisphere

The Cerebrum

The Left Hemisphere In most people, left brain (dominant hemisphere)

controls Reading, writing, and math

Decision making

Speech and language

The Right Hemisphere Right cerebral hemisphere relates to

Senses (touch, smell, sight, taste, feel)

Recognition (faces, voice inflections)

The Cerebrum

Fig 14-16

The Cerebrum

Monitoring Brain Activity

Brain activity is assessed by an

electroencephalogram (EEG)

Electrodes are placed on the skull

Patterns of electrical activity (brain waves) are

printed out

The Cerebrum

Four Categories of Brain Waves Alpha waves

Found in healthy, awake adults at rest with eyes closed Beta waves

Higher frequency Found in adults concentrating or mentally stressed

Theta waves Found in children Found in intensely frustrated adults May indicate brain disorder in adults

Delta waves During sleep Found in awake adults with brain damage

The Cerebrum

Fig 14-16

The Cerebrum

Synchronization A pacemaker mechanism

Synchronizes electrical activity between hemispheres

Brain damage can cause desynchronization

Seizure Is a temporary cerebral disorder Changes the electroencephalogram Symptoms depend on regions affected

The neural cortex is found on the surface of the _____.

A.cerebral hemispheresB.ponsC.cerebellumD.all of the aboveE.a and C only