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1. CENTRAL NERVOUS SYSTEM
(BRAIN AND SPINAL CORD)
Ravish Yadav

2. MAJOR PARTS OF THE BRAIN
• The adult brain consists of four major parts:
• Brain Stem,
• Cerebellum,
• Diencephalon And
• Cerebrum.
• The brain stem is
• Continuous with the spinal cord
• Consists of
• Medulla oblongata
• Pons
• Midbrain
• Posterior to the brain stem
• The cerebellum.
• Superior to the brain stem
• Is the diencephalon
• Consists of
• Thalamus,
• Hypothalamus
• Epithalamus.
• Supported on the diencephalon and brain stem is
• The cerebrum, the largest part of the brain.

4. PROTECTIVE COVERINGS OF THE BRAIN
• The cranium and the cranial meninges
• Surround and protect the brain.
• The cranial meninges are
• Continuous with the spinal meninges
• Have the same basic structure
• Bear the same names:
• The outer dura mater,
• The middle arachnoid mater, and
• The inner pia mater.
• However, the cranial dura matter has two layers; the spinal dura mater has
only one.
• The two dural layers around the brain are
• Fused together
• Except where they separate to enclose the dural venous sinuses
• That drain venous blood from the brain and deliver it into the internal jugular veins.

6. • Blood vessels that
• Enter brain tissue pass along the surface of the brain,
• They penetrate inward,
• They are sheathed by a loose-fitting sleeve of pia mater.
• Three extensions of the dura mater
• Separate parts of the brain.
(1) The falx cerebri
• Separates the two hemispheres (sides) of the cerebrum.
(2) The falx cerebelli
• Separates the two hemispheres of the cerebellum.
(3) The tentorium cerebelli
• Separates the cerebrum from the cerebellum.

8. VENTRICLES OF THE BRAIN
• Within the brain there are
• Four irregular-shaped cavities, or ventricles
• Containing cerebrospinal fluid (CSF).
• They are:
• Right and left lateral ventricles
• Third ventricle
• Fourth ventricle.

10. THE LATERAL VENTRICLES
• These cavities lie
• Within the cerebral hemispheres,
• One on each side of the median plane
• Just below the corpus callosum.
• They are separated from each other by
• A thin membrane, the septum lucidum, and
• Lined with ciliated epithelium.
• They communicate with the third ventricle
• By interventricular foramina.

11. THE THIRD VENTRICLE
• A cavity situated below the lateral ventricles
• Between the two parts of the thalamus.
• It communicates with the fourth ventricle
• By a canal, the cerebral aqueduct or aqueduct of the midbrain.

12. THE FOURTH VENTRICLE
• A diamond-shaped cavity
• Situated
• Below and behind the third ventricle,
• Between the cerebellum and pons.
• It is continuous
• Below with the central canal of the spinal cord
• Communicates with the subarachnoid space
• By foramina in its roof.
• Cerebrospinal fluid
• Enters the subarachnoid space
• Through these openings and
• Through the open distal end of the central canal of the spinal cord.

13. BRAIN BLOOD FLOW
• Blood flows to the brain
• Mainly via the internal carotid and vertebral arteries
• The internal jugular veins
• Return blood from the head to the heart.
• In an adult, the brain represents
• Only 2% of total body weight,
• But consumes about 20% of the oxygen and glucose used even at rest.
• Neurons synthesize
• ATP almost exclusively from glucose via reactions that use oxygen.
• When activity of neurons and neuroglia increases in a region of the brain, blood
flow to that area also increases.
• Even a brief slowing of brain blood flow may cause unconsciousness.
• Because virtually no glucose is stored in the brain, the supply of glucose also must
be continuous.
• If blood entering the brain has
• A low level of glucose, mental confusion, dizziness, convulsions, and loss of consciousness may
occur.

14. BLOOD–BRAIN BARRIER (BBB)
• Protects brain cells
• From harmful substances and pathogens
• By preventing passage of many substances from blood into brain tissue.
• Consists mainly of tight junctions
• That seal together the endothelial cells of brain capillaries,
• Along with a thick basement membrane around the capillaries.
• A few water-soluble substances, such as glucose, cross the BBB
• By active transport.
• Other substances, such as creatinine, urea, and most ions,
• Cross the BBB very slowly.
• Still other substances—proteins and most antibiotic drugs—
• Do not pass at all from the blood into brain tissue.
• However, lipid-soluble substances, such as oxygen, carbon dioxide, alcohol,
and most anesthetic agents,
• Easily cross the blood–brain barrier.
• Trauma, certain toxins, and inflammation can
• Cause a breakdown of the blood–brain barrier.

15. CEREBROSPINAL FLUID
• Cerebrospinal fluid (CSF) is
• A clear, colorless liquid
• That protects the brain and spinal cord from chemical and physical injuries.
• It also carries
• Oxygen, glucose, and other needed chemicals
• From the blood to neurons and neuroglia.
• CSF continuously circulates
• Through cavities in the brain and spinal cord and around the brain and spinal cord in
the subarachnoid space.
• The total volume of CSF is
• 80 to 150 mL in an adult.
• CSF contains
• Glucose, proteins, lactic acid, urea, cations (Na, K, Ca2, Mg2), and anions (Cl and
HCO3);
• It also contains some white blood cells.

16. • The CSF contributes to homeostasis in three main ways:
1. Mechanical protection
• CSF serves as a shock-absorbing medium
• That protects the delicate tissues of the brain and spinal cord.
2. Chemical protection
• CSF provides an optimal chemical environment
• For accurate neuronal signaling.
• Even slight changes in the ionic composition of CSF within the brain
• Can seriously disrupt production of action potentials and postsynaptic potentials.
3. Circulation
• CSF allows exchange of nutrients and waste products between the blood and nervous
tissue.

17. FORMATION OF CSF IN THE VENTRICLES
• The sites of CSF production are
• The choroid plexuses, in the walls of the ventricles.
• These are covered by ependymal cells
• That form cerebrospinal fluid from blood plasma
• By filtration and secretion.
• The ependymal cells are
• Joined by tight junctions.
• Materials entering CSF
• Passes through the ependymal cells.
• This blood–cerebrospinal fluid barrier
• Permits certain substances to enter the CSF
• But excludes others, protecting the brain and spinal cord
• From potentially harmful bloodborne substances.

19. CIRCULATION OF CSF
• The CSF formed in the choroid plexuses of each lateral ventricle
• Flows into the third ventricle
• Through two narrow, oval openings, the interventricular foramina.
• More CSF is added by
• The choroid plexus in the roof of the third ventricle.
• The fluid then flows through
• The aqueduct of the midbrain (cerebral aqueduct), which
• Passes into the fourth ventricle.
• The choroid plexus of the fourth ventricle
• Contributes more fluid.
• CSF enters the subarachnoid space
• Through three openings in the roof of the fourth ventricle:
• A median aperture and the paired lateral apertures, one on each side.
• CSF then circulates
• In the central canal of the spinal cord and in the subarachnoid space around the
surface of the brain and spinal cord.

22. • CSF is gradually reabsorbed into the blood
• Through arachnoid villi, fingerlike extensions of the arachnoid.
• Normally, CSF is reabsorbed as rapidly as it is formed by the choroid plexuses.
• Because the rates of formation and reabsorption are the same, the pressure
of CSF normally is constant.

24. THE BRAIN STEM
• The part of the brain between the spinal cord and the diencephalon.
• It consists of three structures:
(1) Medulla oblongata
(2) Pons
(3) Midbrain

26. MEDULLA OBLONGATA
•It is continuous with
• The superior part of the spinal cord.
•It forms
• The inferior part of the brain stem.
•The medulla
• Extends to the inferior border of the pons.
•The medulla’s white matter contains
• All sensory tracts and motor tracts
• That extend between the spinal cord and other parts of the brain.
•Some of the white matter
• Forms bulges on the anterior aspect of the medulla.
• These protrusions, called the pyramids,
• Formed by the large corticospinal tracts
• That pass from the cerebrum to the spinal cord.

28. • The corticospinal tracts
• Control voluntary movements of the limbs and trunk.
• Just superior to the junction of the medulla with the spinal cord,
• 90% of the axons in the left pyramid cross to the right side, and
• 90% of the axons in the right pyramid cross to the left side.
• This crossing is called the decussation of pyramids.
• Each side of the brain
• Controls voluntary movements on the opposite side of the body.

29. • The medulla
• Also contains several nuclei.
• Some of these nuclei
• Control vital body functions.
• Examples of nuclei in the medulla
• That regulate vital activities include
• The cardiovascular center and
• The medullary rhythmicity area.
• The cardiovascular center regulates
• The rate and force of the heartbeat and
• The diameter of blood vessels.
• The medullary rhythmicity area of the respiratory center
• Adjusts the basic rhythm of breathing.

30. • Nuclei in the medulla
• Also control reflexes for vomiting, swallowing, sneezing, coughing, and hiccupping.
• The vomiting center of the medulla
• Causes vomiting, the forcible expulsion of the contents of the upper gastrointestinal
(GI) tract through the mouth.
• The deglutition center of the medulla
• Promotes swallowing or deglutition of a mass of food that has moved from the oral
cavity of the mouth into the pharynx (throat).
• Sneezing involves
• Spasmodic contraction of breathing muscles that forcefully expel air through the
nose and mouth.
• Coughing involves
• A long drawn and deep inhalation and then a strong exhalation
• That suddenly sends a blast of air through the upper respiratory passages.
• Hiccupping is caused by
• Spasmodic contractions of the diaphragm
• That ultimately result in the production of a sharp sound on inhalation.

31. • Just lateral to each pyramid is
• An oval-shaped swelling
• Called an olive.
• Within the olive is
• The inferior olivary nucleus,
• Which receives input from the cerebral cortex, midbrain and spinal cord.
• Neurons of the inferior olivary nucleus
• Extend their axons into the cerebellum,
• Where they regulate the activity of cerebellar neurons.
• By influencing cerebellar neuron activity,
• The inferior olivary nucleus provides
• Instructions that the cerebellum uses to make adjustments to muscle activity as you learn new
motor skills.

32. • Nuclei associated with
• Sensations of touch, pressure, vibration, and conscious proprioception
• Located in the posterior part of the medulla.
• These nuclei are
• The right and left gracile nucleus and cuneate nucleus.
• Ascending sensory axons of the gracile fasciculus and the cuneate fasciculus,
• which are two tracts in the posterior columns of the spinal cord, form synapses in
these nuclei.
• Postsynaptic neurons then relay the sensory information
• To the thalamus on the opposite side of the brain.
• The axons ascend to the thalamus
• In a band of white matter called the medial lemniscus,
• Which extends through the medulla, pons, and midbrain.
• The tracts of the posterior columns and the axons of the medial leminiscus are
• Collectively known as the posterior column–medial lemniscus pathway.

36. • The medulla also contains nuclei
• That are components of sensory pathways
• For gustation (taste), audition (hearing), and equilibrium (balance).
• The gustatory nucleus of the medulla is
• Part of the gustatory pathway from the tongue to the brain;
• It receives gustatory input from the taste buds of the tongue.
• The cochlear nuclei of the medulla are
• Part of the auditory pathway from the inner ear to the brain;
• They receive, auditory input from the cochlea of the inner ear.
• The vestibular nuclei of the medulla and pons are
• Components of the equilibrium pathway from the inner ear to the brain;
• They receive sensory information associated with equilibrium from proprioceptors in
the vestibular apparatus of the inner ear.

40. • The medulla contains nuclei associated with five pairs of cranial nerves:
• Vestibulocochlear (VIII) nerves
• Glossopharyngeal (IX) nerves
• Vagus (X) nerves
• Accessory (XI) nerves (cranial portion)
• Hypoglossal (XII) nerves

42. PONS
• The pons (bridge) lies directly superior to the medulla and anterior to the
cerebellum.
• Connects different parts of the brain with one another.
• These connections are provided by bundles of axons.
• The pons consists of nuclei, sensory tracts, and motor tracts.
• There are nuclei within the pons which act as relay stations and some of these
are associated with the cranial nerves.

45. • The pons also contains
• Vestibular nuclei that are components of the equilibrium pathway from the inner ear
to the brain.
• Other nuclei in the pons are the pneumotaxic area and the apneustic area of
the respiratory center.
• Together with the medullary rhythmicity area, the pneumotaxic and
apneustic areas help control breathing.
• The pons also contains nuclei associated with the following four pairs of
cranial nerves :
• Trigeminal (V) nerves
• Abducens (VI) nerves
• Facial (VII) nerves
• Vestibulocochlear (VIII) nerves.

46. MIDBRAIN
• The midbrain is the area of the brain situated around the cerebral aqueduct
between the cerebrum above and the pons below.
• It consists of groups of cell bodies and nerve fibres (tracts) which connect
the cerebrum with lower parts of the brain and with the spinal cord.
• The cell bodies act as relay stations for the ascending and descending nerve
fibres.

48. RETICULAR FORMATION
• In addition to the well-defined nuclei, the brain stem consists of small
clusters of neuronal cell bodies (gray matter) interspersed among small
bundles of myelinated axons (white matter).
• The broad region where white matter and gray matter exhibit a netlike
arrangement is known as the reticular formation.
• Neurons within the reticular formation have both ascending (sensory) and
descending (motor) functions.
• Part of the reticular formation, called the reticular activating system (RAS),
consists of sensory axons that project to the cerebral cortex.

51. FUNCTIONS
• The reticular formation is involved in:
• Coordination of skeletal muscle activity associated with voluntary motor movement
and the maintenance of balance.
• Coordination of activity controlled by the autonomic nervous system, e.g.
cardiovascular, respiratory and gastrointestinal activity.
• Selective awareness that functions through the reticular activating system
(RAS) which selectively blocks or passes sensory information to the cerebral
cortex, e.g. the slight sound made by a sick child moving in bed may arouse his
mother but the noise of regularly passing trains may be suppressed.

52. CEREBELLUM
• The cerebellum is situated behind the pons and immediately below the
posterior portion of the cerebrum occupying the posterior cranial fossa.
• It is ovoid in shape and has two hemispheres, separated by a narrow median
strip called the vermis.
• Grey matter forms the surface of the cerebellum, and the white matter lies
deeply.

55. FUNCTIONS
• The cerebellum is concerned with
• The coordination of voluntary muscular movement, posture and balance.
• Cerebellar activities are not under voluntary control.
• The cerebellum controls and coordinates the movements of various groups of
muscles ensuring smooth, even, precise actions.
• It coordinates activities associated with the maintenance of the balance and
equilibrium of the body.
• The sensory input for these functions is derived from the muscles and joints,
the eyes and the ears.

56. • Proprioceptor impulses from the muscles and joints indicate
• Their position in relation to the body as a whole and those impulses from the eyes
and the semicircular canals in the ears provide information about the position of the
head in space.
• Impulses from the cerebellum influence the contraction of skeletal muscle so
that balance and posture are maintained.
• Damage to the cerebellum results in clumsy uncoordinated muscular
movement, staggering gait and inability to carry out smooth, steady, precise
movements.

57. THE DIENCEPHALON
• The diencephalon extends from the brain stem to the cerebrum and
surrounds the third ventricle.
It includes:-
• Thalamus
• Hypothalamus
• Epithalamus

58. THALAMUS
• The thalamus consists of two masses of nerve cells and fibres situated
within the cerebral hemispheres just below the corpus callosum, one on each
side of the third ventricle.
• Consists of paired oval masses of gray matter organized into nuclei with
interspersed tracts of white matter.
• It consists of myelinated axons that enter and leave the various thalamic
nuclei.
• Sensory input from the skin, viscera and special sense organs is transmitted
to the thalamus before redistribution to the cerebrum.

61. FUNCTIONS OF THALAMUS
• The thalamus is
• The major relay station for most sensory impulses
• That reach the primary sensory areas of the cerebral cortex from the spinal cord and
brain stem.
• In addition, the thalamus
• contributes to motor functions
• By transmitting information from the cerebellum and basal ganglia to the primary
motor area of the cerebral cortex.
• The thalamus also
• Relays nerve impulses between different areas of the cerebrum and plays a role in the
maintenance of consciousness.

62. HYPOTHALAMUS
• The hypothalamus is a small part of the diencephalon.
• The hypothalamus is composed of a number of groups of nerve cells (nuclei).
• It is situated below and in front of the thalamus, immediately above the
pituitary gland.
• The hypothalamus is linked to the posterior lobe of the pituitary gland by
nerve fibres and to the anterior lobe by a complex system of blood vessels.
• Through these connections, the hypothalamus controls the output of
hormones from both lobes of the gland.

64. FUNCTIONS OF HYPOTHALAMUS
• Controls many body activities and is one of the major regulators of
homeostasis.
• Sensory impulses related to both somatic and visceral senses arrive at the
hypothalamus, as do impulses from receptors for vision, taste, and smell.
• Other receptors within the hypothalamus itself continually monitor osmotic
pressure, glucose level, certain hormone concentrations, and the
temperature of blood.
• The hypothalamus has several very important connections with the pituitary
gland and produces a variety of hormones.

65. Other functions with which the hypothalamus is concerned include control
of:
• The autonomic nervous system
• Appetite and satiety
• Thirst and water balance
• Body temperature
• Emotional reactions, e.g. pleasure, fear, rage
• Sexual behaviour including mating and child rearing
• Biological clocks or circadian rhythms, e.g. sleeping and waking cycles,
• Body temperature and secretion of some hormones.

66. IMPORTANT FUNCTIONS OF THE HYPOTHALAMUS
• Control of the ANS :
• The hypothalamus controls and integrates activities of the autonomic nervous system,
which regulates contraction of smooth muscle and cardiac muscle and the secretions
of many glands.
• Through the ANS, the hypothalamus is a major regulator of visceral activities, including
regulation of heart rate, movement of food through the gastrointestinal tract, and
contraction of the urinary bladder.

67. PRODUCTION OF HORMONES
• The hypothalamus produces several hormones and has two types of
important connections with the pituitary gland, an endocrine gland located
inferior to the hypothalamus.
• First, hypothalamic hormones known as releasing hormones and inhibiting
hormones are released into capillary networks in the median eminence.
• The bloodstream carries these hormones directly to the anterior lobe of the
pituitary, where they stimulate or inhibit secretion of anterior pituitary
hormones.
• Second, axons extend from the paraventricular and supraoptic nuclei through
the infundibulum into the posterior lobe of the pituitary.
• The cell bodies of these neurons make one of two hormones (oxytocin or
antidiuretic hormone).
• Their axons transport the hormones to the posterior pituitary, where they are
released.

68. Regulation of emotional and behavioral patterns:-
• Together with the limbic system, the hypothalamus participates in expressions of rage,
aggression, pain, and pleasure, and the behavioral patterns related to sexual arousal.
Regulation of eating and drinking:-
• The hypothalamus regulates food intake.
• It contains a feeding center, which promotes eating, and a satiety center, which causes
a sensation of fullness and cessation of eating.
• The hypothalamus also contains a thirst center.
• When certain cells in the hypothalamus are stimulated by rising osmotic pressure of
the extracellular fluid, they cause the sensation of thirst.
• The intake of water by drinking restores the osmotic pressure to normal, removing the
stimulation and relieving the thirst.

69. Control of body temperature:-
• The hypothalamus also functions as the body’s thermostat.
• If the temperature of blood flowing through the hypothalamus is above normal, the
hypothalamus directs the autonomic nervous system to stimulate activities that
promote heat loss.
• When blood temperature is below normal, by contrast, the hypothalamus generates
impulses that promote heat production and retention.
Regulation of circadian rhythms and states of consciousness:-
• The suprachiasmatic nucleus of the hypothalamus serves as the body’s internal
biological clock because it establishes circadian rhythms, patterns of biological activity
(such as the sleep–wake cycle) that occur on a circadian schedule (cycle of about 24
hours).

70. EPITHALAMUS
• A small region superior and posterior to the thalamus.
• Consists of the pineal gland and habenular nuclei.
• The pineal gland is considered part of the endocrine system because it
secretes the hormone melatonin.
• Melatonin appears to contribute to the setting of the body’s biological clock,
which is controlled by the hypothalamus.
• As more melatonin is liberated during darkness than in light, this hormone is
thought to promote sleepiness.
• The habenular nuclei, are involved in olfaction, especially emotional
responses to odors.

72. THE CEREBRUM
• This is the largest part of the brain.
• It occupies the anterior and middle cranial fossae.
• It provides us with the ability to read, write, and speak; to make calculations
and compose music; and to remember the past, plan for the future, and
imagine things that have never existed before.
• Consists of an outer cerebral cortex, an internal region of cerebral white
matter and gray matter nuclei deep within the white matter.

73. CEREBRAL CORTEX
• The cerebral cortex is a region of gray matter that forms the
outer rim of the cerebrum contains billions of neurons.
• The folds are called gyri or convolutions.
• The deepest grooves between folds are known as fissures;
the shallower grooves between folds are termed sulci.
• the longitudinal fissure, separates the cerebrum into right
and left halves called cerebral hemispheres.
•The falx cerebri is formed by the dura mater that separates
the two hemispheres.
• The hemispheres are connected internally by the corpus
callosum , a broad band of white matter containing axons
that extend between the hemispheres.

76. • For descriptive purposes each hemisphere of the cerebrum is divided into
lobes which take the names of the bones of the cranium under which they lie:
• Frontal, Parietal, Temporal,Occipital lobes
• The boundaries of the lobes are marked by deep sulci (fissures).
• These are the central, lateral and parieto-occipital sulci.
• The central sulcus separates the frontal lobe from the parietal lobe.
• The lateral sulcus separates the frontal lobe from the temporal lobe.
• The parieto- occipital sulcus separates the parietal lobe from the occipital lobe.

79. CEREBRAL WHITE MATTER
•The cerebral white matter consists primarily of
myelinated axons in three types of tracts:-
1. Association tracts:-
• Contain axons that conduct nerve impulses between gyri in
the same hemisphere.
2. Commissural tracts:-
• Contain axons that conduct nerve impulses from gyri in one
cerebral hemisphere to corresponding gyri in the other cerebral
hemisphere.
• Three important groups of commissural tracts are the corpus
callosum (the largest fiber bundle in the brain, containing about
300 million fibers), anterior commissure, and posterior
commissure.

80. 3. Projection tracts:-
• Contain axons that conduct nerve impulses from the cerebrum to lower parts of
the CNS (thalamus, brain stem, or spinal cord) or from lower parts of the CNS to the
cerebrum.
• An example is the internal capsule, a thick band of white matter that contains both
ascending and descending axons.

82. FUNCTIONAL AREAS OF THE CEREBRUM
• The main areas of the cerebrum associated with sensory perception and
voluntary motor activity.
• Specific types of sensory, motor, and integrative signals are processed in
certain regions of the cerebral cortex.
Sensory areas:-
• Receive sensory information and are involved in perception, the conscious awareness
of a sensation.
Motor areas:-
• Control the execution of voluntary movements.
Association areas:-
• Deal with more complex integrative functions such as memory, emotions, reasoning,
will, judgment, personality traits, and intelligence.

85. SENSORY AREAS
• Sensory information arrives mainly in the posterior half of both
cerebral hemispheres, in regions behind the central sulci.
• In the cerebral cortex, primary sensory areas receive sensory
information that has been relayed from peripheral sensory
receptors through lower regions of the brain.
• The postcentral (sensory) area
• The sensory speech area
• The auditory (hearing) area
• The olfactory (smell) area
• The taste area
• The visual area

86. Sensory areas of the cerebrum
The postcentral (sensory) area:-
• This is the area behind the central sulcus.
• Here sensations of pain, temperature, pressure and touch, knowledge of muscular
movement and the position of joints are perceived.
• The sensory area of the right hemisphere receives impulses from the left side of the
body and vice versa.
• The size of the areas representing different parts of the body is proportional to the
extent of sensory innervation.
• e.g. larger region of the somatosensory area receives impulses from the lips and
fingertips than from the thorax or hip.

88. • The primary somatosensory area allows you to pinpoint where somatic
sensations originate, so that you know exactly where on your body to swat
that mosquito.
The sensory speech area:-
• This is situated in the lower part of the parietal lobe and extends into the temporal
lobe.
• It is here that the spoken word is perceived.
• There is a dominant area in the left hemisphere in right handed people and vice versa.

89. The auditory (hearing) area:-
• This lies immediately below the lateral sulcus within the temporal lobe.
• The cells receive and interpret impulses transmitted from the inner ear by the
cochlear (auditory) part of the vestibulocochlear nerves (8th cranial nerves).
The olfactory (smell) area:-
• This lies deep within the temporal lobe
• Where impulses from the nose via the olfactory nerves (1st cranial nerves) are
received and interpreted.

90. The taste area:-
• This is thought to lie just above the lateral sulcus in the deep layers of the sensory
area.
• This is the area where impulses from special nerve endings in taste buds in the
tongue and in the lining of the cheeks, palate and pharynx are perceived as taste.
The visual area:-
• This lies behind the parieto-occipital sulcus and includes the greater part of the
occipital lobe.
• The optic nerves (2nd cranial nerves) pass from the eye to this area which receives
and interprets the impulses as visual impressions.

91. MOTOR AREAS OF THE CEREBRUM
• Motor output from the cerebral cortex flows mainly from the anterior part
of each hemisphere.
• Among the most important motor areas are the following:-
• THE PRECENTRAL (MOTOR) AREA
• THE PREMOTOR AREA
• MOTOR (BROCA’S) SPEECH AREA
• THE FRONTAL AREA

92. THE PRECENTRAL (MOTOR) AREA
•This lies in the frontal lobe immediately anterior to the
central sulcus.
•The cell bodies are pyramid shaped (Betz's cells) and
they initiate the contraction of skeletal muscles.
•A nerve fiber from a Betz's cell passes downwards
through the internal capsule to the medulla oblongata
where it crosses to the opposite side then descends in
the spinal cord.
•At the appropriate level in the spinal cord the nerve
impulse crosses a synapse to stimulate a second neuron
which terminates at the motor end-plate of a muscle
fiber.

93. • This means that the motor area of the right hemisphere of the cerebrum
controls voluntary muscle movement on the left side of the body and vice
versa.
• The neuron with its cell body in the cerebrum is the upper motor neuron
and the other, with its cell body in the spinal cord, is the lower motor
neuron.
• In the motor area of the cerebrum the body is represented upside down,
i.e. the cells nearest the vertex control the feet and those in the lowest part
control the head, neck, face and fingers.
• The sizes of the areas of cortex representing different parts of the body are
proportional to the complexity of movement of the body part, not to its
size.
• In comparison with the trunk, the hand, foot, tongue and lips are
represented by large cortical areas.

96. THE PREMOTOR AREA
• This lies in the frontal lobe immediately anterior to the motor area.
• The cells are thought to exert a controlling influence over the motor area,
ensuring an orderly series of movements.
• For example, in tying a shoe lace or writing, many muscles contract but the
movements must be coordinated and carried out in a particular sequence.
• Such a pattern of movement, when established, is described as manual
dexterity (skill in performing tasks).

97. MOTOR (BROCA’S) SPEECH AREA
• Located in the frontal lobe close to the lateral cerebral sulcus.
• This group of nerve cells controls the movements necessary for speech.
• It is dominant in the left hemisphere in right-handed people and vice versa.

98. THE FRONTAL AREA
•This extends anteriorly from the premotor
area to include the remainder of the frontal
lobe.
•It is a large area and is more highly
developed in humans than in other animals.
•It is thought that communications between
this and the other regions in the cerebrum
are responsible for the behaviour, character
and emotional state of the individual.

99. ASSOCIATION AREAS
• Association areas are connected with one another by association tracts.
Include the following:
• Somatosensory association area
• Visual association area
• Facial recognition area
• Auditory association area
• Orbitofrontal cortex
• Wernicke’s (posterior language) area
• Common integrative area
• Prefrontal cortex (frontal association area)
• Frontal eye field area

100. Somatosensory association area:-
• Receives input from the primary sensory area, as well as from the thalamus and
other parts of the brain.
Functions:-
• Permits you to determine the exact shape and texture of an object by feeling it and to
sense the relationship of one body part to another.
• The storage of memories of past somatic sensory experiences, enabling you to
compare current sensations with previous experiences.
Visual association area:-
• Receives sensory impulses from the primary visual area and the thalamus.
• Functions :- It relates present and past visual experiences and is essential for
recognizing and evaluating what is seen.

101. Facial recognition area:-
• Receives nerve impulses from the visual association area.
• Functions :- This area stores information about faces, and it allows you to recognize
people by their faces.
Auditory association area:-
• Receives nerve impulses from the primary auditory area in the temporal cortex,
• Functions :- Allows to recognize a particular sound as speech, music, or noise.
Orbitofrontal cortex:-
• Receives sensory impulses from the primary olfactory area.
• Functions:- This area allows to identify odors and to discriminate among different
odors.

102. Wernicke’s area:-
• Functions:- Interprets the meaning of speech by recognizing spoken words.
• It is active as you translate words into thoughts.
• Also contribute to verbal communication by adding emotional content, such
as anger or joy, to spoken words.
Common integrative area
• Bordered by somatosensory, visual, and auditory association areas.
• It receives nerve impulses from these areas and from the primary gustatory
area, primary olfactory area, the thalamus, and parts of the brain stem.
• Functions :-
• This area integrates sensory interpretations from the association areas and
impulses from other areas, allowing the formation of thoughts based on a
variety of sensory inputs.
• It then transmits signals to other parts of the brain for the appropriate
response to the sensory signals it has interpreted.

103. Prefrontal cortex (frontal association area):-
• This area has numerous connections with other areas of the cerebral cortex,
thalamus, hypothalamus and cerebellum.
• Functions:-
• Concerned with the makeup of a person’s personality, complex learning abilities, recall of
information, initiative, judgment, foresight, reasoning, intuition, mood, planning for the future, and
development of abstract ideas.
Frontal eye field area
• Functions:-
• It controls voluntary scanning movements of the eyes—like those you just used in reading this
sentence.

104. ANATOMY OF CRANIAL
NERVES

105. INTRODUCTION
There are 12 pairs of cranial nerves in our body
These are called as cranial nerve because the originated directly from the
brain; inside the cranium
There names are
Olfactory nerve
Optic nerve
Oculomotor nerve
Trochlear nerve
Trigeminal nerve
Abducens nerve
Facial nerve
oVestibulocochlear nerve
oGlossopharangial nerve
oVagus nerve
oAccessory nerve
oHypoglossal nerve

106. NAMES OF CRANIAL NERVES
 Ⅰ Olfactory nerve
 Ⅱ Optic nerve
 Ⅲ Oculomotor nerve
 Ⅳ Trochlear nerve
 Ⅴ Trigeminal nerve
 Ⅵ Abducent nerve
 Ⅶ Facial nerve
 Ⅷ Vestibulocochlear nerve
 Ⅸ Glossopharyngeal nerve
 Ⅹ Vagus nerve
 Ⅺ Accessory nerve
 Ⅻ Hypoglossal nerve

108. CLASSIFICATION OF CRANIAL NERVES
•Sensory cranial nerves: contain only afferent (sensory)
fibers
• ⅠOlfactory nerve
• ⅡOptic nerve
• Ⅷ Vestibulocochlear nerve
•Motor cranial nerves: contain only efferent (motor) fibers
• Ⅲ Oculomotor nerve
• Ⅳ Trochlear nerve
• ⅥAbducent nerve
• Ⅺ Accessory nerv
• Ⅻ Hypoglossal nerve
•Mixed nerves: contain both sensory and motor fibers---
• ⅤTrigeminal nerve,
• Ⅶ Facial nerve,
• ⅨGlossopharyngeal nerve
• ⅩVagus nerve

109. I. Olfactory nerves (sensory)
• These are the nerves of the sense of smell.
• Their nerve endings and fibres originate in the upper part of the mucous
membrane of the nasal cavity, pass upwards through the cribriform plate of
the ethmoid bone and then go to the olfactory bulb.
• The nerves then proceed backwards as the olfactory tract, to the area for the
perception of smell in the temporal lobe of the cerebrum.

110. OLFACTORY NERVE

111. CRANIAL NERVE I: OLFACTORY

112. II. Optic nerves (sensory)
• These are the nerves of the sense of sight.
• The fibres originate in the retinae of the eyes and they combine to form the
optic nerves.
• They then pass through the optic foramina of the sphenoid bone into the
cranial cavity and join at the optic chiasma.
• The nerves proceed backwards as the optic tracts to the lateral geniculate
bodies of the thalamus.
• Impulses pass from these to the centre for sight in the occipital lobes of the
cerebrum and to the cerebellum.
• In the occipital lobe sight is perceived, and in the cerebellum the impulses
from the eyes contribute to the maintenance of balance, posture and
orientation of the head in space.

113. II. OPTIC NERVE

114. CRANIAL NERVE II: OPTIC

115. III. OCCULOMOTOR NERVE
 Component: Motor
 Function:
 Raises upper eyelid
 Turns eyeball upward, downward and
medially
 Constricts pupil
 Opening to the Skull: Superior orbital fissure
 Origin: Anterior surface of the midbrain

116. III. OCULOMOTOR NERVES (MOTOR)
• These nerves arise from nerve cells near the cerebral aqueduct.
• They supply:
• Four extraocular muscles, which move the eyeball, i.e. the superior, medial
and inferior recti and the inferior oblique muscle
Intraocular muscles:
— Ciliary muscles which alter the shape of the lens, changing its refractive
power.
— Circular muscles of the iris which constrict the pupil.
— The levator palpebrae muscle which raises the upper eyelid.

119. IV. TROCHLEAR NERVE
 Component: Motor
 Function: Assisting in turning eyeball downward
and laterally
 Opening to the Skull: Superior orbital fissure
 Origin: Posterior surface of the midbrain

120. IV. TROCHLEAR NERVES (MOTOR)
• These nerves arise from nerve cells near the cerebral aqueduct.
• They supply the superior oblique muscles of the eyes.

121. IV. TROCHLEAR NERVE

122. V. TRIGEMINAL NERVES (MIXED)
• These nerves contain motor and sensory fibres and are among the largest of
the cranial nerves.
• They are the chief sensory nerves for the face and head (including the oral
and nasal cavities and teeth), receiving impulses of pain, temperature and
touch.
• The motor fibres stimulate the muscles of mastication.
• There are three main branches of the trigeminal nerves.
• V1. Ophthalmic Nerve
• V2. Maxillary Nerve
• V3. Mandibular Nerve

123. V. TRIGEMINAL NERVE

124. CRANIAL NERVE V: TRIGEMINAL

125. V. TRIGEMINAL NERVES (MIXED)
Ophthalmic nerves:-
• Sensory only
• Supply the lacrimal glands, conjunctiva of the eyes, forehead, eyelids,
anterior aspect of the scalp and mucous membrane of the nose.
Maxillary nerves:-
• Sensory only
• Supply the cheeks, upper gums, upper teeth and lower eyelids.
Mandibular nerves:-
• Contain both sensory and motor fibres.
• They supply the teeth and gums of the lower jaw, pinnae of the ears, lower
lip and tongue.
• The motor fibres supply the muscles of mastication.

126. V1. OPHTHALMIC NERVE
Infratrochlear

127. V1. OPHTHALMIC NERVE

128. V2. MAXILLARY NERVE

129. V3. MANDIBULAR NERVE

130. VI. ABDUCENT NERVES (MOTOR)
• These nerves arise from a group of nerve cells lying under the floor of the
fourth ventricle.
• They supply the lateral rectus muscles of the eyeballs.
• Function:-Lateral rectus muscle turns eyeball laterally.
• Origin: Medulla oblongata
• Opening to the Skull: Superior orbital fissure

131. VI. ABDUCENT NERVE

132. VII. FACIAL NERVES (MIXED)
• These nerves are composed of both motor and sensory nerve fibres.
• The motor fibres supply the muscles of facial expression.
• The sensory fibres convey impulses from the taste buds in the anterior two-
thirds of the tongue to the taste perception area in the cerebral cortex.

133. VII. FACIAL NERVE

134. CRANIAL NERVE VII: FACIAL

135. VIII. Vestibulocochlear (auditory) nerves
(sensory)
• These nerves are composed of two distinct sets of fibres, vestibular nerves
and cochlear nerves.
Vestibular Nerves:-
• Arise from the semicircular canals of the inner ear and convey impulses to
the cerebellum.
• They are associated with the maintenance of posture and balance.
Cochlear Nerves:-
• Originate in the organ of Corti in the inner ear
• It convey impulses to the hearing areas in the cerebral cortex where sound
is perceived.

136. CRANIAL NERVE VIII: VESTIBULOCOCHLEAR

137. IX. GLOSSOPHARYNGEAL NERVES (MIXED)
• These nerves arise from nuclei in the medulla oblongata.
• The motor fibres stimulate the muscles of the tongue and pharynx and the
secretory cells of the parotid (salivary) glands.
• The sensory fibres convey impulses to the cerebral cortex from the posterior
third of the tongue, the tonsils and pharynx and from taste buds in the
tongue and pharynx.
• These nerves are essential for the swallowing.

138. CRANIAL NERVE IX: GLOSSOPHARYNGEAL

139. X. VAGUS NERVES (MIXED)
• Have a more extensive distribution than any other cranial nerves.
• They arise from nerve cells in the medulla oblongata and other nuclei, and
pass down through the neck into the thorax and the abdomen.
• These nerves form an important part of the parasympathetic nervous
system.
• The motor fibres supply the smooth muscles and secretory glands of the
pharynx, larynx, trachea, heart, oesophagus, stomach, intestines, pancreas,
gall bladder, bile ducts, spleen, kidneys, ureter and blood vessels in the
thoracic and abdominal cavities.
• The sensory fibres convey impulses from the lining membranes of the same
structures to the brain.

140. CRANIAL NERVE X: VAGUS

141. XI. ACCESSORY NERVES (MOTOR)
• These nerves arise from cell bodies in the medulla oblongata and in the
spinal cord.
• The fibres supply the sternodeidomastoid and trapezius muscles.
• Branches join the vagus nerves and supply the phanyngeal and laryngeal
muscles.

142. CRANIAL NERVE XI: ACCESSORY

143. XII. HYPOGLOSSAL NERVES (MOTOR)
• These nerves arise from cells in the medulla oblongata.
• They supply the muscles of the tongue and muscles surrounding the hyoid
bone and contribute to swallowing and speech.

144. CRANIAL NERVE XII: HYPOGLOSSAL