chapter 14: the brain and cranial nerves. copyright 2009, john wiley & sons, inc. major parts of...

Chapter 14: The Brain and

Cranial Nerves

Copyright 2009, John Wiley & Sons, Inc.

Major Parts of the Brain

Brain stem- continuation of the spinal cord; consists of the medulla oblongata, pons and midbrain.

Cerebellum- second largest part of the brain. Diencephalon- gives rise to thalamus,

hypothalamus and epithalamus. Cerebrum- largest part of the brain.

The Brain


Protective Coverings of the Brain The cranium The cranial

meninges: dura mater, arachnoid mater and pia mater.



Three extensions of the dura mater separate parts of the brain:

a. Falx cerebri separate the two cerebral hemispheres.

b. Falx cerebelli separate the two cerebellar hemispheres.

c. Tentorium cerebelli separate the cerebrum from the cerebellum.

Extensions of the Dura Mater



Brain Blood Flow and the Blood-Brain Barrier Brain receives approximately 20% of the total

blood supply. Internal carotid and vertebral arteries carry

blood to the brain. Internal jugular veins return blood from the

brain. Blood-brain barrier (BBB) protects brain from

harmful substances.


Cerebrospinal Fluid (CSF)

Clear fluid. Circulates through cavities in the brain

(ventricles) and the spinal cord (central canal) and also in the subarachnoid space.

Absorbs shock and protects the brain and the spinal cord.

Helps transport nutrients and wastes from the blood and the nervous tissue.


Ventricles

CSF-filled cavities within the brain. Lateral ventricles: cerebral hemispheres. Third ventricle: diencephalon. Cerebral aqueduct: midbrain. Fourth ventricle: brain stem and the

cerebellum.


Formation and Circulation of CSF in the Ventricles Choroid plexuses- networks of capillaries in

the walls of the ventricles. Ventricles are lined by ependymal cells. Plasma is drawn from the choroid plexuses

through ependymal cells into the ventricles to produce CSF.

Formation and Circulation of CSF in the Ventricles


Circulation of CSF

CSF from the lateral ventricles → interventricular foramina → third ventricle → cerebral aqueduct → fourth ventricle → subarachnoid space or central canal.

CSF is reabsorbed into the blood by arachnoid villi.


Medulla Oblongata Pyramids-

Bulges on the anterior aspect of the medulla. Formed by the large corticospinal tracts that pass from the cerebrum to the spinal cord.

A common site for decussation of ascending and descending tracts.


Centers of the Medulla Oblongata Vital centers:

Cardiovascular center-

Respiratory center- Also includes centers for vomiting,

swallowing, sneezing, coughing and hiccupping.

Houses five pairs of cranial nerves, VIII-XII. Portion of the ventricle found here is the

fourth ventricle.



Midbrain or Mesencephalon

Extends from the pons to the diencephalon. Part of the ventricle found here- cerebral

aqueduct. Cerebral peduncles: axons of the corticospinal,

corticopontine and corticobulbar tracts. Tectum- situated posteriorly and contains four

rounded elevations: two superior ones called superior colliculi and two inferior ones called inferior colliculi.

Midbrain or Mesencephalon


Midbrain

Substantia nigra: large area with dark pigments. Help control subconscious muscle activities. Loss of neurons here is associated with Parkinson disease.

Red nucleus: Help control voluntary movements of the limbs.

Contains cranial nerves III-IV.

Midbrain



Reticular formation Extends from the upper part of the spinal

cord, throughout the brain stem, and into the lower part of the diencephalon.

Part of the reticular formation called the reticular activating system (RAS) consists of sensory axons that project to the cerebral cortex.

The RAS helps maintain consciousness.


The Cerebellum

Second largest part of the brain.

The central constricted area is the vermis.

The anterior and posterior lobes control subconscious aspects of skeletal movement.

The flocculonodular lobe on the inferior side contributes to the equilibrium and balance.

The Cerebellum



The Cerebellum

Cerebellar cortex- gray matter in the form of parallel folds called folia.

Arbor vitae- tracts of white matter. Cerebellar peduncles- three pairs: superior,

middle and inferior. Attach cerebellum to the brain stem.

Functions- coordinate movements, regulate posture and balance.

Thalamus

Intermediate mass Several nuclei: Major relay station for

most sensory impulses.


Hypothalamus

Inferior to the thalamus.

Consists of mammillary body, median eminence, infundibulum, and a number of nuclei.



Functions of the Hypothalamus Control of the ANS.

Production of hormones

Regulation of emotional and behavioral patterns, eating and drinking, body temperature, and circadian rhythms.


Epithalamus

Small region superior to the thalamus.

Consists of pineal gland which secretes a hormone called melatonin.

Melatonin induces sleep.


The Cerebrum

“seat of intelligence” Cerebral cortex- gray matter. Gyri- Sulci- Longitudinal fissure- Cerebral hemispheres-

The Cerebrum



Lobes of the Cerebrum

Four lobes: frontal lobe, parietal lobe, temporal lobe and occipital lobe.

Central sulcus- separates the frontal and parietal lobes.

Precentral gyrus- primary motor area. Postcentral gyrus- primary somatosensory

area.

Cerebral white matter

Commissural tracts- Corpus callosum:

Association tracts- Projection tracts-



Basal Ganglia

Three nuclei deep within each cerebral hemisphere make up basal ganglia.

They are globus pallidus, putamen, and caudate nucleus.

Help initiate and terminate movements, suppress unwanted movements and regulate muscle tone.

Basal Ganglia



The Limbic System

A ring of structures on the inner border of the cerebrum and floor of the diencephalon.

Includes cingulate gyrus, hippocampus, dentate gyrus, amygdala, mammillary bodies, thalamus, and the olfactory bulb.

“emotional brain” as it governs emotional aspects of behavior.

Also involved in olfaction and memory.

The Limbic System



Functional Organization of the Cerebral Cortex: Sensory Areas Primary somatosensory area- postcentral

gyrus. Primary visual area- occipital lobe. Primary auditory area- temporal lobe. Primary gustatory area- base of the

postcentral gyrus. Primary olfactory area- temporal lobe.

Functional Organization of the Cerebral Cortex: Sensory Areas


Functional Organization of the Cerebral Cortex: Motor Areas Primary motor area-

precentral gyrus. Broca’s speech area-

left cerebral hemisphere.



Functional Organization of the Cerebral Cortex: Association Areas Somatosensory association area- posterior to

primary somatosensory area. Visual association area- occipital lobe. Auditory association area- temporal lobe. Wernicke’s area- left temporal and parietal

lobes. Prefrontal cortex- anterior portion of the

frontal lobe.


Hemispheric Lateralization

Brain Waves

Electroencephalogram: Recording of the electrical activity within the brain.

Alpha waves Beta waves Theta waves Delta waves



Cranial Nerves

12 pairs.

Sensory, motor and mixed nerves.

Name as well as roman numeric numbers to identify the nerves.

Olfactory (I) Nerve

Sensory nerve. Sense of smell. Olfactory cells

converge to become olfactory nerve.


Optic (II) Nerve

Sensory nerve. Ganglion cells in the

retina of each eye join to form an optic nerve.

Nerve of vision.


Oculomotor (III) Nerve

Motor cranial nerve. Originates in the

midbrain. Supply extrinsic eye

muscles to control movements of the eyeball and upper eyelid.


Trochlear (IV) Nerve

Motor cranial nerve. Smallest of the 12

cranial nerves. Origin: midbrain. Controls movement of

the eyeball.


Trigeminal (V) nerve

Largest cranial nerve. Mixed nerve. Three branches:

opthalmic, maxillary and mandibular. Deal with sensation of touch, pain and temperature.

Motor axons supply muscles of mastication.


Abducens (VI) Nerve

Motor cranial nerve. Originates from the

pons. Cause abduction of

the eyeball (lateral rotation).


Facial (VII) Nerve

Mixed cranial nerve. Sensory portion

extends from the taste buds of the anterior two-thirds of the tongue.

Motor portion arises from the pons and deal with facial expression.


Vestibulocochlear (VIII) Nerve Sensory cranial

nerve. Originates in the inner

ear. Vestibular branch

carries impulses for equilibrium.

Cochlear branch carries impulses for hearing.


Glossopharyngeal (IX) Nerve

Mixed cranial nerve. Sensory axons carry

signals from the taste buds of the posterior one-third of the tongue.

Motor neurons arise from the medulla and deal with the release of saliva.


Vagus (X) Nerve

Vagus (X) Nerve Mixed cranial nerve. Distributed from the head and neck into the

thorax and abdomen. Sensory neurons deal with a variety of

sensations and stretching. Motor neurons arise from the medulla and

supply muscles of the pharynx, larynx, and soft palate that are involved in swallowing and vocalization.


Accessory (XI) Nerve

Motor cranial nerve. Divided into cranial

accessory and spinal accessory nerves.

Supplies sternocleidomastoid and trapezius muscles to coordinate head movements.


Hypoglossal (XII) Nerve

Motor cranial nerve. Conduct nerve

impulses for speech and swallowing.


chapter 14: the brain and cranial nerves. copyright 2009, john wiley & sons, inc. major parts of...

Documents

john wiley sons

brain ventricles

brain blood flow

bloodbrain barrierbrain

bloodbrain barrier bbb

cerebral hemispheres

ventricle cerebral aqueduct

total blood supply