Lecture # 21: The Brain and Cranial Nerves (Chapter 14)

Objectives:

2- Name the three coverings of the central nervous system and give the characteristics, location, and function of each.

1- Name the major regions of the brain and give the functions of each.

3- Give the functions of cerebrospinal fluid and explain its formation, circulation, and resorption.

Major Landmarks of the Brain

I-Cerebrum

III- Cerebellum

Spinal cord

Foramen magnum

BRAIN

II- Brain Stem

I- Cerebrum

II- Brain Stem

III- Cerebellum

a-Thalamusb- HypothalamusC- Epithalamus

4- Medulla oblongata

2- Midbrain d- Cerebral pedunclese- Corpora quadrigemina

3- Pons

1- Diencephalon

a

bc

de

Major Landmarks of the Brain

BRAIN

Spinal cord

Foramen magnum

Longitudinal fissureIt separates the right and left hemispheres

Right hemisphere

Left hemisphere

Central sulcus

Frontal lobe Frontal lobe

Occipital lobe

Occipital lobe

Parietal lobe Parietal lobe

Gyrus

Gyrus

Precentral gyrus

Postcentral gyrus

Gyri

Frontal lobe Parietal lobe

Occipital lobe

Temporal lobe

Precentral gyrus

Central sulcus

Postcentral gyrus

I- The Cerebrum

Lateral sulcus

Insula

Cranial Meninges

Skull

Dura mater:

Superior sagittalsinus (contains blood)

Pia mater

Arachnoid mater

Meningeal layer Periosteal layer

SubarachnoidSpace (contains CSF)

Arachnoid villus

Falx cerebri (in longitudinalfissure only)

Lateral ventricles

Third ventricle

Fourth ventricle

Cerebral aqueduct

Central canal

Interventricular foramen

Ventricles and Cerebrospinal Fluid

Septum pelucidum

It separates the lateral ventricles

They communicate the lateral ventricles with the third ventricle

It communicates the third ventricles with the fourth ventricle

Cerebral aqueduct

They connect the fourth ventricle with the sub- arachnoid space

Central canal

Interventricular foramina (foramina of Monro)

Medial aperture

Lateral apertures

The Flow of Cerebrospinal Fluid

Choroid plexus in fourthventricle adds more CSF.

CSF flows out two lateral aperturesand one median aperture.

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

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

CSF is secreted by choroid plexus in each lateral ventricle.

CSF flows throughInterventricular foraminainto third ventricle.

Choroid plexus in thirdventricle adds more CSF.

CSF flows down cerebralaqueduct to fourth ventricle.

Broca area

Primary motor cortex

Motor associationarea

Prefrontal cortex

Primary somestheticcortex

Somestheticassociation area

Primary gustatorycortex

Visual associationarea

Primaryvisual cortex

Primaryauditory cortex

Auditoryassociation area

It is where neurons plan a program for the contraction of muscles required for an action such as dancing, typing or speaking

It contains the primary somatosensory cortex for touch, pain and temperature.

The neurons send signals for precise, finely coordinated limb movements (contralateral)

It interprets the sensory information to making cognitive sense of it

Wernicke areaIt is responsible for the recognition of spoken and written language

It generates a motor program for all the muscles of speech

It receives visual signals

It receives auditory signals

It recognizes the signals received as spoken words, a familiar piece of music, a voice, etc.

It recognizes faces and other familiar objects

It receives gustatory (taste) signals

It gives us a sense of our relationship to the rest of the world, enabling us to think about it and to plan and execute appropriate behavior.

Functional regions of the Cerebral Cortex

Median section

II- The Brain Stem1- Diencephalon

Hypothalamus

1- It is the “gateway to the cerebral cortex” – nearly all sensory input to the cerebrum passes by way of synapses in the thalamic nuclei, filters information on its way to cerebral cortex2- It is involved in emotional functions

Thalamus

1- Hormone secretion. It controls anterior pituitary gland.

ThalamusHypothalamusEpithalamus

EpithalamusIt contains the pineal gland that helps regulate the sleep-wake cycle

2- It is the major integrating center for the autonomic nervous system3- Thermoregulation4- Hunger center 5- Thirst center that monitors osmolarity of the blood

Median section

II- The Brain Stem2- Midbrain Cerebral peduncles

Corpora quadrigemina

Corpora quadrigemina:Superior culliculi

They mediate visual attention and visually tracking moving objects.

Inferior culliculiThey mediates the reflexive turning of the head in response to a sound

Cerebral peduncles

They contain the substantia nigra, a motor center that relays inhibitory signals preventing unwanted movements.

Degeneration of the neurons of the substantia nigra leads to the muscle tremor of Parkinson’s disease.

Posterolateral view

Median section

Medulla oblongataIt contains:1- Cardiac center (regulates the rate and force of heartbeat)2- Vasomotor center (regulates blood pressure)3- Respiratory centers (regulates the rhythm and depth of breathing)

PonsIt connects the two hemispheres of the cerebellum

II- The Brain Stem3- Pons4- Medulla oblongata

III- The Cerebellum

2- It aids in motor coordination to produce smooth movements

1- It monitors muscle contractions and coordinates postural muscles

Functions:

Thoracic nerves

Cranial and Spinal Nerves

Lumbar plexus

Sacral plexus

Brachial plexus

Cervical plexusCranial Nerves

2- Optic nerve (II)

5- Trigeminal nerve (V)

6- Abducens nerve (VI)

7- Facial nerve (VII)

8- Vestibulocochlear nerve (VIII)

9- Glossopharyngeal nerve (IX)

11- Accessory nerve (XI)

12- Hypoglossal nerve (XII)

10- Vagus nerve (X)

3- Oculomotor nerve (III)

1- Olfactory nerve (I)

4- Trochlear nerve (IV)

Spinal Nerves

Coocygeal plexus

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Optic nerve (II)

Trigeminal nerve (V)

Abducens nerve (VI)

Facial nerve (VII)

Vestibulocochlear nerve (VIII)

Glossopharyngeal nerve (IX)

Accessory nerve (XI)

Hypoglossal nerve (XII)

Vagus nerve (X)

Oculomotor nerve (III)

Olfactory tract

Olfactory bulb

Sensory. It provides for the sense of vision.

Motor. It innervates four of the six extraocular muscles that move the eyes, the muscle that open the eyelid, the muscle that constricts the pupil, and the muscle that changes the shape of the lens for accommodation.

Motor. It innervates the superior oblique muscle of the eye.

Mixed. It provides sensory innervation to the face, and motor innervation to the muscles of mastication.

Motor. It innervates the lateral rectus muscle of the eye.

Mixed. It provides motor innervation to the muscles of facial expression, and sensory innervation to taste to the anterior two thirds of tongue.

Sensory. It provides for the senses of hearing and equilibrium.

Mixed. It provides motor innervation to the muscles of pharynx, and sensory for taste to the posterior third of the tongue.

Mixed. It provides sensory fibers to skin of head and to the pharynx. It provides motor fibers to muscles of speech and swallowing. It innervates most of thoracic and abdominal viscera (parasympathetic nervous system).

Optic chiasm

Trochlear nerve (IV)

Motor. It innervates the muscles that move the tongue.

Motor. It innervates the muscles that move the head and neck (trapezius, sternocleidomastoid).

Three are sensory nerves: Olfactory nerve (smell), optic nerve (vision), and vestibulocochlear nerve (hearing and equilibrium)

Four are mixed nerves: Trigeminal nerve, facial nerve, glossopharyngeal nerve, and vagus nerve.

Five are motor nerves: Oculomotor nerve, trochlear nerve, abducens nerve, hypoglossal nerve, and accessory nerve.

HeadExtrinsic muscles of eyes Tongue