Download Laboratory Exercise 11: Anatomy and Physiology of the Brain

Laboratory Exercise 11: Anatomy and Physiology of the Brain
The human brain is the highest development of the nervous system. It retains the primitive reflex centers of
lower animals in the brain stem. Its cerebral cortex allows humans to perform delicate movements, learn to
speak, write, have memory and use judgment to make rational decisions.
A. The Meninges
Protective membranes, the meninges, cover the brain and the spinal cord.
1. Dura mater - an outer thick membrane of dense, fibrous connective
tissue.
2. Arachnoid mater - a middle translucent membrane appears as a spider's web. It is infiltrated with large
blood vessels.
3. Pia mater - an inner fine, transparent membrane. It has a microcirculation for the brain tissue below. The
pia follows every contour of the brain surface.
B. The Gross Anatomy of the Brain
The brain is subdivided into four major regions:
1. Cerebrum
2. Diencephalon
3. Midbrain
4. Hindbrain
Pons
Cerebellum
Medulla oblongata
Forebrain
Brain stem
Cerebrum - largest subdivision of the brain, it comprises 80% of its mass.
Cerebral cortex - outer gray matter. It contains groups of nerve cell bodies (nuclei) for higher intellectual
functions.
Gyri or convolutions - folds of cortex.
Sulci - shallow grooves between gyri.
Cerebral hemispheres - the left and right halves of the cerebrum. They are separated by a deep groove, the
longitudinal fissure.
Corpus Callosum - a group of nerve fibers that connect the two cerebral hemispheres.
Each hemisphere is subdivided by sulci into 4 lobes whose names correspond to the cranial bones above the
lobes. The 5th lobe, the insula, lies medially to the parietal, temporal and frontal lobes.
Ventricles - Cavities within the brain filled with cerebrospinal fluid (CSF). Within each hemisphere is a
lateral ventricle. The third ventricle lies below the thalamus. The fourth ventricle lies in the brain stem.
Central sulcus separates the frontal from parietal lobes.
Lateral sulcus separates the temporal lobe from the frontal lobe.
Parieto-occipital sulcus separates occipital lobe from the parietal lobe.
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Precentral (Motor) Gyrus of the frontal lobe - in the precentral gyrus there is a point-to-point representation
of location of every skeletal muscle. On the precentral gyrus the body parts are not represented in proportion
to their size. More cortical area is devoted to muscles involved in skill, complex, delicate movements, as in
the movement of the fingers than of the muscles of the back.
Postcentral (Sensory) Gyrus of the parietal lobe - in the postcentral gyrus there is a point to point
representation of location of sense organs. On the postcentral gyrus the body parts are not represented in
proportion to their size. More cortical area is devoted to the number of sensory organs in the body part rather
than the size of the body part. A larger portion of the postcentral gyrus receives impulses from the lips and
fingers than from the back or hips.
The representation of the sketetal muscles and sense organs on the pre- and post-central gyri is called a
homunculus.
Inner white matter consists of myelinated nerve tracts to and from the spinal cord.
Cerebral nuclei - scattered paired masses of nerve cell bodies (gray matter) in the white matter of each
hemisphere.
Function: the cerebral nuclei control involuntary actions of the skeletal muscles.
Diencephlon
Thalamus - a large pair an oval masses of gray matter.
Function: The Thalamus contains nuclei that act as relay stations to the postcentral sensory gyrus for
sensations.
Hypothalamus - located below the thalamus.
Function: The hypothalamus controls visceral activities, such as temperature, appetite and water and
electrolyte balance. The hypophysis (pituitary gland) is attached to its inferior surface.
Brain Stem
Midbrain
On ventral surface - Cerebral peduncles - a nerve tract path for impulses to and from the cerebrum and
hindbrain.
On dorsal surface - Corpora quadrigemina - four rounded twin bodies - two upper ones, the superior colliculi,
a visual reflex center; two lower ones, the inferior colliculi, an auditory reflex center. These reflex centers
control movements of the eyes, head, and trunk to visual and auditory stimuli.
Hindbrain
Pons - lies between midbrain and medulla.
Function: The pons provides a nerve tract path between cerebrum and medulla and cerebellum. It also has a
center that controls breathing.
Medulla oblongata - the most inferior part of the brain, connects brain to spinal cord.
Function: It is a control center for vital reflexes through the autonomic nervous system (ANS). For example it
regulates heart rate, blood pressure and breathing.
Cerebellum - subdivided into two hemispheres. It has a gray matter cortex with gyri, below is the white
matter. The white matter is made up of nerve tracts resemble branches of a tree, arbor vitae. The cerebellum
is connected to the brain stem by nerve tracts, cerebellar peduncles.
Function: It controls skeletal muscle contraction for skilled movements, coordination, posture and balance.
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Cranial Nerves
I
olfactory nerves
sense of smell
(sensory)
project from olfactory epithelium to olfactory
bulb of brain
II
optic nerves
sense of sight
(sensory)
project from retina of eye to thalamus
III
oculomotor nerves
eye movement
(motor)
project from mesencephalon (mid-brain) to eye
muscles
IV
trochlear nerves
eye movement
(motor)
project from mesencephalon to eye muscle
V
trigerminal nerves
chewing (motor)
face (sensory)
projects from pons to face
VI
abducens nerves
eye movements
projects from mesencephalon to eye muscles
VII
facial nerves
taste (sensory)
facial expression
(motor)
projects from pons to face
VIII
vestibulocochlear
nerves
balance
(vestibular)
hearing (cochlear)
(sensory)
projects from pons and medulla to inner ear
IX
glossopharyngeal
nerves
taste (sensory)
swallowing (motor)
projects from medulla to mouth
X
vagus nerves
XI
accessory nerves
swallowing,
projects from medulla to back of mouth and head
movement of muscles
in back of head
(motor)
XII
hypoglossal. nerves
tongue movement projects from medulla to tongue
(motor)
sensory and motor
only cranial nerve to leave head and neck region
to thorax and abdomen part of the parasympathetic system
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Name each cranial nerve, indicate by a check mark whether it is sensory, motor or both, and describe the main
function of each.
Nerve Name
Sensory
Motor
Function
I. Olfactory
X
convey impulses related to smell
II. Optic
X
convey impulses related to vision
III. Oculomotor
IV. Trochlear
V. Trigeminal
X
X
M-convey impulses to muscles of chewing
S-convey impulses from sense organs in mouth,
teeth, face, nose for touch, pain, and temperature
X
X
M-convey impulses to muscles of face,
scalp, neck- causes facial expression; impulses to
salivary and tear glands for secretion
S-convey impulses from proprioceptors of face
muscles, taste receptors
VI. Abducens
VII. Facial
VIII. Vestibulocochlear
(auditory)
X
convey impulses related to equilibrium
(balance) and hearing
IX. Glossopharyngeal
X. Vagus
X
X
M-convey impulses to muscles of abdominal and
thoracic viscera, heart, muscles of the pharynx
S-convey impulses from sense organs in
abdominal and thoracic viscera
XI. Accessory
XII. Hypoglossal
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E. Review of Ascending and Descending Pathways between the Cerebral Cortex and Spinal Cord
As a review of ascending and descending pathways in the brain and spinal cord, complete the labeling of the
following figures.
Clinical Application
The axons of pyramidal neurons - the initiators of voluntary movement all cross over to the opposite side of the
body at some point in their descent to the ventral horns of the spinal cord. Stroke victims with frontal cortical
lesions in the right hemisphere will predictably lose motor function on the left side of the body, and vice versa.
Single limb paralysis is termed monoplegia; hemiplegia applies when an entire side of the body is paralyzed.
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CRANIAL NERVES
I. OLFACTORY NERVE
Function: Smell (sensory)
Origin: Receptors of olfactory epithelium
Foramen: Cribriform plate of ethmoid bone
Innervation: Olfactory bulbs
II. OPTIC NERVE
Function: Vision (sensory)
Origin: Retina of the eye
Foramen: Optic canals of sphenoid bone
Innervation: Diencephalon via the optic chiasm
III. OCULOMOTOR NERVE
Function: Eye movements (motor)
Origin: Mesencephalon
Foramen: Superior orbital fissures of sphenoid bone
Innervation: Intrinsic eye muscles
IV. TROCHLEAR NERVE
Function: Eye movements (motor)
Origin: Mesencephalon
Foramen: Superior orbital fissures of sphenoid bone
Innervation: Superior eye muscle
V. TRIGEMINAL NERVE
Function: Face (sensory and motor)
Origin: Ophthalmic (s) - skin of the forehead, eyelid, eyebrow, nose
Maxillary (s) - upper lip, gums, and teeth, cheek
Mandibular (s) - lower lip, gums, and teeth
(m) - motor nuclei of pons
Foramen: Superior orbital fissure
Foramen rotundum
Foramen ovale
Innervation: (s) - as above
(m) - muscles of mastication
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VI. ABDUCENS NERVE
Function: Abducts the eye
Origin: Motor nuclei of pons
Foramen: Superior orbital fissure
Innervation: Lateral eye muscle
VII. FACIAL NERVE
Function: Face (sensory and motor)
Origin: (s) - anterior two thirds of tongue
(m) - motor nuclei of pons
Foramen: Internal acoustic canal through stylomastoid foramen
Innervation: (s) - sensory nuclei of pons
(m) - muscles of facial expression,
tear, nasal mucous, salivary glands
VIII. VESTIBULOCOCHLEAR NERVE
Function: Balance and hearing (sensory)
Origin: Sense organs (receptors) of the inner ear
Foramen: Internal acoustic canals of temporal bone
Innervation: Pons and medulla oblongata
IX. GLOSSOPHARYNGEAL NERVE
Function: Head and neck (sensory and motor)
Origin: (s) - posterior 1/3 of the tongue, carotid arteries of neck
(m) - motor nuclei of medulla oblongata
Foramen: Jugular foramina
Innervation: (s) - sensory nuclei of medulla oblongata
(m) - swallowing Muscles
X. VAGUS NERVE
Function: Thorax and abdomen (sensory and motor)
Origin: (s) - diaphragm, visceral organs in thoracic and abdominopelvic organs
(m) - motor nuclei of medulla oblongata
Foramen: Jugular foramen
Innervation: (s) - medulla oblongata
(m) - muscles of the digestive, respiratory, and cardiovascular systems in the thoracic and
abdominal cavities
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XI. ACCESSORY NERVE
Function: Neck and Upper back (motor)
Origin: Spinal cord and medulla oblongata
Foramen: Jugular foramina
Innervation: Muscles of the larynx; Sternocleidomastiod and trapezius muscles
XII. HYPOGLOSSAL NE RVE
Function: Tongue movements (motor.)
Origin: Motor nuclei of medulla oblongata
Foramen: Hypoglossal canal of occipital bone
Innervation: Muscles of the tongue
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