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Note to Self

• Despite what you think you can get through this chapter in 1 class period, or one with only a few slides left over The Brain and Cranial Nerves

Chapter 14

Organization of the Brain• The brain is divided into six major regions

– Cerebrum– Diencephalon– Mesencephalon

P– Pons– Cerebellum– Medulla oblongata

• In addition, the brain contains a layer of gray matter on the surface of the cerebellum and cerebrum called the neural cortex

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• The brain forms from three swellings (the primary brain vesicles) at the tip of the developing neural tube

• The prosencephalon forms the telencephalon

Embryology of the brain

(cerebrum) and diencephalon• Mesencephalon (midbrain)• The rhombencephalon forms the metencephalon

(cerebellum and pons) and myelencephalon (medulla oblongata)

• Summarized in table 14-1 p 451

Ventricles of The Brain

• During development the nueroceol expands to form chambers that, in the mature brain, are called ventricles

• In the mature brain the ventricles are filled• In the mature brain, the ventricles are filled with cerebrospinal fluid (CSF) which circulates from the ventricles and central canal of the brain into the subarachnoid space

Protection and support of The Brain

• The brain is protected from mechanical forces by

1. The bones of the cranium2 The cranial meninges2. The cranial meninges3. The Cerebrospinal Fluid

• In addition, the neural tissue of the brain is isolated from general circulation by the blood-brain barrier

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Cranial Meninges

• The cranial meninges are continuous with those of the spinal cord, they do, however, h di i i i l d f i lhave distinctive anatomical and functional characteristics

Dura Mater• The cranial dura mater consists of outer and inner

fibrous layers• The outer layer fuses with the periosteum of the

cranial bones, thus there is no epidural space• The inner layer of the dura mater extends via duralThe inner layer of the dura mater extends via dural

folds into the cranial cavity which provide support and stabilization to the brain

• The three largest dural folds are the falx cerebri (between the hemispheres), the tentorium cerebelli (above the cerebellum), and the falx cerebelli (below the cerebellum)

The Arachnoid

• The cranial arachnoid covers the brain, providing a smooth surface that does not follow the folds of the brain

• This membrane is in contact externally with• This membrane is in contact externally with the inner epithelium of the dura mater.

• Internally, the subarachnoid space separates the arachnoid from the pia mater

Pia Mater

• The pia mater is closely appressed to the surface of the brain

• It is anchored to the brain by astrocytes and extends into every fold of the brainextends into every fold of the brain

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Cerebrospinal Fluid

• Cerebrospinal fluid (CSF) completely surrounds and bathes the exposed surfaces of the CNS

• The CSF has several functions, including, g– Cushioning the neural structures– Supporting the brain, the brain is almost neutrally

buoyant while ‘floating’ in the CSF– Transporting nutrients, chemical messengers, and

waste products

Circulation of CSF• Inside the brain, the choroid plexus in the third

ventricle, contains ependymal cells that produce about 500 ml of CSF per day

• CSF reaches the subarachnoid space via two lateral apertures and one medial aperture in the roof of the p pfourth ventricle

• The CSF then flows within the subarachnoid space around the brain, spinal cord, and cauda equina

• CSF then is absorbed into the venous circulation at arachnoid granulations

• The entire volume of CSF is replaced roughly every eight hours

Blood Supply To The Brain• The brain has a high demand for energy, but no

energy or oxygen reserves• As a result, the brain has an extensive circulatory

supply• Arterial blood enters the brain via the internal carotidArterial blood enters the brain via the internal carotid

arteries and vertebral arteries and venous blood leaves via the internal jugular veins which drain the dural sinuses

• A cerebrovascular accident, or stroke, occurs when the blood supply to a portion of the brain is interrupted.

The blood-brain barrier

• The blood-brain barrier isolates neural tissue from general circulation

• This barrier exists because the endothelial cells lining the capillaries of the CNS are connected g pby tight junctions that prevent the diffusion of non-lipid soluble compounds into the interstitial fluid of the CNS

• Such a restriction is necessary to prevent uncontrolled stimulation of neurons in the brain by circulating hormones

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The blood-brain barrier

• The blood-brain barrier is an incomplete barrier in some areas

• Parts of the hypothalamusi i l d• Pituitary gland

• Pineal gland• Choroid plexus• (read excerpt p456 in Martini)

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• The blood-brain barrier remains intact throughout the CNS, with four exceptions:

1. In portions of the hypothalamus, the capillary endothelium is extremely permeable Thisendothelium is extremely permeable. This permeability exposes hypothalamic nuclei to circulating hormones and permits the diffusion of hypothalamic hormones into the circulation

4562. Capillaries in the posterior lobe of the pituitary

gland, which is continuous with the floor of the hypothalamus, are highly permeable. At this site, the hormones ADH and oxytocin, produced by hypothalamic neurons are released into theby hypothalamic neurons, are released into the circulation

3. Capillaries in the pineal gland are also permeable. The pineal gland is located on the posterior, superior surface of the diencephalon. Capillary permeability here allows pineal hormones into the general circulation

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4. Capillaries at the choroid plexus are extremely permeable. Although the capillary characteristics of the blood-brain barrier are lost there, the transport activities of the ependymal cells in the choroid plexus maintain the blood-CSF barrier

The Medulla Oblongata

• The medulla oblongata is continuous with the spinal cord

• All communication between the brain and spinal cord passes through the medullaspinal cord passes through the medulla oblongata

• It is a center for the coordination of complex autonomic reflexes and visceral function

• See 14-6 a & b and table 14-2

Reminder Slide

• A collection of neuron cell bodies with a common function is a center

• A center with a discrete boundary is termed a nucleusnucleus

• The neural cortex is a thick layer of gray matter covering the surface of the brain

• Bundles of axons in the CNS are termed tracts• Tracts in the spinal cord form columns

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The Medulla Oblongata

• The medulla oblongata contains three important groups of nuclei

• Autonomic nuclei controlling visceral activities (heart rate peripheral bloodflowactivities (heart rate, peripheral bloodflow, respiratory movements)

• Sensory and motor nuclei of cranial nerves • Relay stations along sensory and motor

pathways

The Pons

• The pons contains four groups of components• Sensory and motor nuclei of cranial nerves• Nuclei involved with the control of respiration• Nuclei and tracts that process and relay

information to/from the cerebellum• Ascending, descending and transverse tracts• And see table 14-2

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The Cerebellum

• The cerebellum is an automatic processing center and has two primary functions

• Adjusting the postural muscles of the body (balance and equilibrium)(balance and equilibrium)

• Programming and fine tuning movements controlled at the subconscious levels

The Mesencephelon

• The tectum or roof of the mesencephelon, or midbrain, contains two pairs of sensory nuclei called the corpora quadrigemina

• These nuclei, the superior and inferior , pcolliculi, process visual and auditory sensation respectively, and control movement of the eyes, head, and neck in response to those stimuli

• And see table 14-4

Table 14-4 Components and Functions of the Midbrain

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The Diencephalon

• The diencephalon is composed of – The epithalamus– The hypothalamus– The thalamus

• The epithalamus is the roof of the diencephalon superior to the third ventricle

• The posterior portion of the epithalamus contains the pineal gland, an endocrine gland that secretes melatonin

The Thalamus• The thalamus is the final relay point for ascending

sensory information that will be projected to the sensory cortex

• It acts as a filter, passing only a small portion of the arriving informationarriving information

• The left and right thalamus are separated by the third ventricle

• Each thalamus consists of a rounded mass of thalamic nuclei that project information to specific regions of the sensory cortex

The Hypothalamus

• The hypothalamus extends from the area superior to the optic chiasm to the posterior margins of the mamillary bodies

• Immediately posterior to the optic chiasm, a y p p ,narrow stalk, the infundibulum connects the floor of the hypothalamus to the pituitary gland

• The hypothalamus contains important control and integrative systems with numerous functions

• Controls somatic motor activities at the subconscious level

• Controls autonomic function (HR, BP, Resp, Dig)• Coordinates activities of the endocrine and nervous

The Hypothalamus

systems• Secretes hormones (ADH and Oxytocin)• Produces emotions and behavioral drives (hunger, thirst)• Coordinates voluntary and autonomic functions• Regulates body temperature• Coordinates circadian cycles of activity

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The Limbic System• The limbic system includes nuclei and tracts along

the border between the cerebrum and diencephalon• Its functions include

– Establishing emotional statesLi ki h i f i f h b l i h– Linking the conscious functions of the cerebral cortex with the unconscious functions of the brain stem

– Facilitating memory retrieval and storage• The limbic system is known as the motivational

system because it provides desire to perform the complex tasks that the complexity of our brains makes possible

The Cerebrum

• The cerebrum is the largest region of the brain.• Conscious thought and all intellectual

functions originate in the cerebral hemispheresh f h b i i l d i• Much of the cerebrum is involved in

processing somatic sensory and motor information

• See figure 14-12 p 469

Figure 14-12a The Brain in Lateral View

FRONTALLOBE

Central sulcus

OCCIPITALLOBE

PARIETAL LOBE

Lateral sulcus

Pons

Medulla oblongata

TEMPORAL LOBE

Lateral view, cadaver brain

Cerebellum

LOBE

Figure 14-12b The Brain in Lateral View

FRONTALLOBE

Precentralgyrus

Centralsulcus

Postcentralgyrus

PARIETAL LOBE

OCCIPITALLOBE

Lateral sulcus

Pons

LOBE

TEMPORALLOBE

Cerebellum

Medulla oblongata

Lateral view

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• Surface contains gyri (folds) and sulci (fissures)

• A longitudinal fissure separates two cerebral hemispheres

The Cerebral Cortex

cerebral hemispheres• The central sulcus separates frontal and

parietal lobes• The temporal and occipital lobes are also

bounded by sulci

The Cerebral Cortex• Each lobe contains functional regions whose

boundaries are less clearly defined• Some things to keep in mind• Each cerebral hemisphere receives sensory

i f i f d d d hinformation from and sends motor commands to, the opposite side of the body

• The 2 hemispheres have different functions even though they appear identical

• The assignment of specific functions to specific regions of the cerebral cortex is imprecise

White matter of the Cerebrum

• The interior of the cerebrum is principally composed of white matter

• The axons are classified as: A i i fib hi h i f• Association fibers, which interconnect areas of the cerebral cortex within a single hemisphere– Shorter arcuate fibers connect adjacent gyri– Longer longitudinal fasciculi connect the frontal

lobe and other lobes of the same hemisphere

Figure 14-13a Fibers of the White Matter of the Cerebrum

Arcuate fibers

Longitudinalfasciculi

Lateral view

White matter of the Cerebrum

• Commisural fibers interconnect the cerebral hemispheres– Includes the corpus callosum and anterior

commisurecommisure• Projection fibers link the cerebral cortex and

the diencephalon, brain stem, cerebellum, and spinal cord

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Longitudinalfissure

Corpuscallosum

Projectionfibers ofinternalcapsule

Anteriorcommissure

Anterior view

Basal Nuclei

• The basal nuclei are involved with the subconscious control of skeletal muscle and the coordination of learned movements

• They do not initiate the movement but rather• They do not initiate the movement but rather control the general pattern and rhythm, especially for movements of the trunk and proximal limb muscles

Basal Nuclei

• The basal nuclei are masses of gray matter that lie within each hemisphere.

• They are embedded in the white matter of the cerebrum, and radiating projection fibers and , g p jcommissural fibers travel between them

• The principal nuclei are:– The caudate nucleus– The lentiform nucleus– The globus palidus– The putamen

Motor and Sensory areas of the Cortex

• The central sulcus separates the motor and sensory areas of the cortex

• The surface of the pre-central gyrus of the frontal lobe is the primary motor cortexp y

• Nuerons here direct voluntary movement by controlling somatic motor neurons in the brain stem and spinal cord

• Specific regions of the primary motor cortex correspond to specific skeletal muscles

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FRONTAL LOBE

Prefrontal cortex

Gustatory cortex

Insula

Lateral sulcus

Olfactory cortex

Somatic motor associationarea (premotor cortex)

Primary motor cortex(precentral gyrus)

Central sulcus Primary sensory cortex(postcentral gyrus)

PARIETAL LOBE

TEMPORALLOBE

OCCIPITAL LOBE

Somatic sensoryassociation area

Visual association area

Visual cortex

Auditory cortex

Auditory association area

Major anatomical landmarks on the surface ofthe left cerebral hemisphere. The lateral sulcushas been pulled apart to expose the insula.

Regions of the cerebral cortex as determinedby histological analysis. Several of the47 Brodmann areas are shown for comparisonwith the results of functional mapping.

Generalinterpretivearea

Frontal eye field

Speechcenter

Prefrontalcortex

The left hemisphere generally contains thegeneral interpretive area and the speech center.The prefrontal cortex of each hemisphere isinvolved with conscious intellectual functions.

Motor and Sensory areas of the Cortex

• The surface of the post-central gyrus of the parietal lobe contains the primary sensory cortex

• Neurons here receive sensory info from• Neurons here receive sensory info from receptors for touch, pressure, pain, vibration, taste, or temperature

• We are aware of these sensations only when the thalamus relays it

Figure 14-15a Motor and Sensory Regions of the Cerebral Cortex

FRONTAL LOBE

Prefrontal cortex

Gustatory cortex

Somatic motor associationarea (premotor cortex)

Primary motor cortex(precentral gyrus)

Central sulcus Primary sensory cortex(postcentral gyrus)

PARIETAL LOBE

OCCIPITAL LOBE

Somatic sensoryassociation area

Visual association area

Visual cortex

Major anatomical landmarks on the surface ofthe left cerebral hemisphere. The lateral sulcushas been pulled apart to expose the insula.

Insula

Lateral sulcus

Olfactory cortexTEMPORALLOBE

Visual cortex

Auditory cortex

Auditory association area

Motor and Sensory areas of the Cortex

• Sensations of light, sound, smell, and taste arrive at other areas of the cerebral cortex

• The visual cortex is in the occipital lobeh di d lf i i h• The auditory and olfactory cortices are in the

temporal lobe• The gustatory cortex lies in the anterior portion

of the insula, a covered region of the cortex near the frontal lobe

Figure 14-15a Motor and Sensory Regions of the Cerebral Cortex

FRONTAL LOBE

Prefrontal cortex

Gustatory cortex

Somatic motor associationarea (premotor cortex)

Primary motor cortex(precentral gyrus)

Central sulcus Primary sensory cortex(postcentral gyrus)

PARIETAL LOBE

OCCIPITAL LOBE

Somatic sensoryassociation area

Visual association area

Visual cortex

Major anatomical landmarks on the surface ofthe left cerebral hemisphere. The lateral sulcushas been pulled apart to expose the insula.

Insula

Lateral sulcus

Olfactory cortexTEMPORALLOBE

Visual cortex

Auditory cortex

Auditory association area

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Association Areas• The sensory and motor regions of the cortex are

connected to nearby association areas• Association areas are regions of the cortex that

interpret incoming data and coordinate a motor responseresponse

• The somatic sensory area monitors activity in the primary sensory cortex

• The visual association area monitors the patterns of activity in the visual cortex and interprets the results; the ability to read is governed by this area

Association Areas

• The auditory association area monitors sensory activity in the auditory cortex, word recognition occurs here

• The somatic motor association area or• The somatic motor association area or premotor cortex is responsible for the coordination of learned movements

• The premotor cortex relays the instructions to the primary motor cortex

Figure 14-15a Motor and Sensory Regions of the Cerebral Cortex

FRONTAL LOBE

Prefrontal cortex

Gustatory cortex

Somatic motor associationarea (premotor cortex)

Primary motor cortex(precentral gyrus)

Central sulcus Primary sensory cortex(postcentral gyrus)

PARIETAL LOBE

OCCIPITAL LOBE

Somatic sensoryassociation area

Visual association area

Visual cortex

Major anatomical landmarks on the surface ofthe left cerebral hemisphere. The lateral sulcushas been pulled apart to expose the insula.

Insula

Lateral sulcus

Olfactory cortexTEMPORALLOBE

Visual cortex

Auditory cortex

Auditory association area

Integrative Centers

• Integrative centers are areas that receive information from many association areas and direct extremely complex motor activities

• The prefrontal cortex performs abstract p pintellectual functions, such as predicting the consequences of possible responses

• Feelings of frustration, tension and anxiety are generated in the prefrontal cortex as it makes predictions about future situations and consequences

Integrative Centers

• The general interpretive area or Wernicke’s area receives information from all of the sensory association areas and plays an important role in personality by integratingimportant role in personality by integrating sensory data and coordinating access to visual and auditory memories

• Wernicke’s area is typically restricted to the left hemisphere

Integrative Centers

• The speech center or Broca’s area lies along the edge of the premotor cortex in the same hemisphere as the general interpretive area (left)(left)

• The speech center regulates the pattern of breathing and vocalization needed for speech

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Figure 14-15b Motor and Sensory Regions of the Cerebral Cortex

Generalinterpretivearea

Frontal eye field

Speechcenter

Prefrontalcortex

The left hemisphere generally contains thegeneral interpretive area and the speech center.The prefrontal cortex of each hemisphere isinvolved with conscious intellectual functions.

Hemispheric Lateralization• In most people the left hemisphere contains the

general interpretive and speech centers responsible for language based skills; reading, writing, speaking

• The left hemisphere also is important in performing analytical tasks such as mathematics or logicalanalytical tasks, such as mathematics or logical decision making

• The right hemisphere analyzes spatial relationships and allows the recognition of familiar objects; face recognition. It is also important in interpreting the emotional context of a conversation

Left Cerebral Hemisphere Right Cerebral Hemisphere

LEFT HAND RIGHT HAND

Prefrontalcortex

Prefrontalcortex

Speech centerAnterior commissure

Writing

Auditory cortex

Anterior commissure

Analysis by touch

Auditory cortex

Spatial visualizationand analysis

Visual cortex(left visual field)

General interpretive center(language and mathematical

calculation)

Visual cortex(right visual field)

CORPUSCALLOSUM

The Electroencephalogram

• The activity of neurons generates electrical activity that can be monitored by placing electrodes on the skull

• This electrical activity of the brain is ycommonly monitored to assess brain activity

• A graphical report of such activity is termed and electroencephalogram or EEG

• The electrical patterns observed are termed brain waves

The Electroencephalogram• Apha waves occur in the brains of healthy adults

when they are awake and resting with their eyes closed

• Beta waves are typical of individuals who are concentrating, or under stress, or in a state of gpsychological tension

• Theta waves are observed transiently in sleeping adults, but are common in children and frustrated adults

• Delta waves are normally seen in deeply sleeping adults, infants, and in waking adults with brain damage

Figure 14-17 Brain Waves

Patient being wiredfor EEG monitoring

Alpha waves arecharacteristic ofnormal resting adultsg

Beta waves typicallyaccompany intenseconcentration

Theta waves areseen in children andin frustrated adults

Delta waves occurin deep sleep and incertain pathologicalconditions 0 Seconds 1 2 3 4

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The Cranial Nerves

• Cranial nerves are PNS components that connect directly to the brain rather than to the spinal cord

• The 12 pairs of cranial nerves are named either pby appearance or function of the nerve

• The number assigned to each nerve roughly corresponds to its position along the longitudinal axis of the brain beginning at the cerebrum and moving downwards

Figure 14-18 Origins of the Cranial Nerves

Optic chiasmOlfactory bulb: terminationof olfactory nerve (I)

Olfactory tract

Optic nerve (II)

Infundibulum

Oculomotor nerve (III)

Pons

Optic tract

Mamillary body

Trochlear nerve (IV)

Trigeminal nerve (V)

Abducens nerve (VI)

Facial nerve (VII)Pons

Basilar artery

Vertebral artery

Cerebellum

Medulla oblongata

Spinal cord

Vestibulocochlearnerve (VIII)

Facial nerve (VII)

Glossopharyngealnerve (IX)

Vagus nerve (X)

Hypoglossal nerve (XII)

Accessory nerve (XI)

The Mnemonic

• Oh, Once One Takes The Anatomy Final, Very Good Vacations Are Heavenly

• Old Opie Occasionally Tries Trigonometry And Feels Very Gloomy Vague And y y gHypoactive

• Olfactory, Optic, Oculomotor, Trochlear, Trigeminal, Abducens, Facial, Vestibulocochlear, Glossopharyngeal, Vagus, Accessory, Hypoglossal

• Carry sensory information responsible for the sense of smell

Olfactory nerves (I)

• Synapse within the olfactory bulb

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• Optic nerves (II)– Carry visual information from special

sensory receptors in the eyes• Occulomotor nerves (III)

Cranial nerves II, III, IV

• Occulomotor nerves (III)– Primary source of innervation for 4 of the

extraocular muscles• Trochlear nerves (IV)

– Innervate the superior oblique muscles

• Trigeminal nerves (V)– Mixed nerves (sensory and motor) with ophthalmic,

maxillary and mandibular branches• Abducens nerve (VI)

– Innervates the lateral rectus muscles

Cranial nerves V, VI, VII

Innervates the lateral rectus muscles• Facial nerves (VII)

– Mixed nerves that control muscles of the face and scalp

– Provide pressure sensations over the face – Receive taste information from the tongue

• Vestibulocochlear nerves (VIII)– Vestibular branch monitors balance, position and

movement– Cochlear branch monitors hearing

Cranial nerves VIII, IX

Cochlear branch monitors hearing• Glossopharyngeal nerves (IX)

– Mixed nerves that innervate the tongue and pharynx– Control the action of swallowing

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• Vagus nerves (X)– Mixed nerves that are vital to the autonomic

control of visceral function

Cranial nerves X

control of visceral function

• Accessory nerves (XI)– Internal branches innervate voluntary swallowing

muscles of the soft palate and pharynx– External branches control muscles associates with the

pectoral girdle

Cranial nerves XI, XII

p g• Hypoglossal nerves (XII)

– Provide voluntary motor control over tongue movement