The central nervous system (CNS) consists of the brain and spinal cord. The CNS receives sensory input and directs motor output. The brain is divided into the forebrain, midbrain, and hindbrain. The forebrain includes the cerebral hemispheres and diencephalon. The hindbrain contains the brainstem, cerebellum, and medulla. The spinal cord transmits nerve impulses between the brain and body and mediates reflexes. The cerebrum contains gray matter on the surface and white matter internally. It is divided into four lobes and performs higher-level functions like thought and memory.

1. Chapter 11
Central nervous system
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2. Functional organization of Nervous System
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3. • CNS - consists of the brain and spinal cord
- receives input from sensory neurons & directs the
activity of motor neurons that innervate muscles &
glands
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4. CNS
Brain
 Fore brain
 Cerebral hemispheres
 Diencephalon
 Brain stem
 Midbrain
 Pons
 Medulla
 Cerebellum
 Spinal cord
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5. Major levels of CNS function
• The three major levels of CNS function are:
– Spinal cord
• Processes reflexes
• Transmits nerve impulses to and from brain
– Brainstem
• Receives sensory input and initiates motor output
• Controls life-sustaining processes (e.g., respiration,
circulation, digestion)
– Cerebrum and cerebral cortex
• voluntary initiation of movement, final sensory
perception, conscious thought, language, personality
traits
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6. The brain
• The integrative portion of the nervous system
• Function - receive, process, and store sensory information
- plan and orchestrate the appropriate motor response
• Protection:
– Cranium (skull) -encases the brain
– Meninges - dura mater, arachnoid mater & pia mater
(protection and nourishment)
– Blood -brain barrier (limits access of blood borne materials
into the vulnerable brain tissue)
– Cerebrospinal fluid (CSF)- shock-absorber & exchange of
materials b/n the neural cells and the IF surrounding the brain
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7. Cerebrum
• Most highly developed in humans (make up about 80%)
• Has two hemispheres- left and right
• Composed of two types of tissue
1. Gray matter
– contains the cell bodies of neurons
– on the outer surface of the cerebrum
– forms the cerebral cortex
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8. 2. White matter
– composed of the myelinated axons of neurons
– in the core of the cerebrum
– These axons organized into units referred to as tracts
– Three types of tracts:
A. Projection tracts
Ascending - carry sensory impulses from lower regions of
the brain or spinal cord to the cortex
Descending –carry motor nerve impulses from the cerebral
cortex to lower regions of the brain or spinal cord
B. Association tracts
- transmit nerve impulses within the same hemisphere
C. Commissural tracts (example, corpus callosum)
- transmit impulses from one hemisphere to the other
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10. Cerebral cortex
• Outer shell of gray matter
• Highly folded (convoluted )
• A convolution formed by these folds is referred to as a gyrus
• Each gyrus is separated from another by a sulcus (shallow
groove, or a fissure)
• Importance :increase the SA of the cerebral cortex
providing space for a greater number of neurons
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11. • Both hemispheres of the cerebrum consist of four lobes
1. Frontal lobes
- Located in the anterior portions of the hemispheres
- responsible for:
» voluntary motor activity
» speaking ability
» higher intellectual activities
2. Parietal lobes
- posterior to the frontal lobes
- receive and process sensory input
3. Occipital lobes
- located posteriorly
- carry out the initial processing of visual input
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12. 4. Temporal lobes
- located laterally
- process auditory (sound) information
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13. Functional regions of the cerebral cortex
Somatosensory cortex
• located in the postcentral gyrus
• Contains the terminations of ascending pathways that transmit
nerve impulses concerning temperature, touch, pressure, pain,
and proprioception (awareness of body position)
• the site for initial cortical processing & perception of these
types of inputs
• Neurons - are highly organized
- each section of the cortex innervating specific body
parts in a sequential manner
• The size of the region of the cortex devoted to different parts of
the body is quite disproportionate
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14. – Large portions of the cortex innervate the the face, tongue,
and hands
– The trunk of the body and the legs are not densely
innervated with sensory neurons
• Somatosensory cortex localizes the source of sensory input
and perceives the level of intensity of the stimulus
• The ascending sensory pathways cross from one side of the
CNS to the other
- sensory input from the left side of the body is
transmitted to the somatosensory cortex of the right cerebral
hemisphere and visa versa
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15. • Additionally, special senses areas are involved with the initial
processing of a specific type of stimulus
– primary visual cortex (sight)
– primary auditory cortex (hearing)
– primary olfactory cortex (smell)
– primary gustatory or taste cortex
• Each surrounded by a “higher order” sensory area or a
unimodal association area
Unimodal association area
-integrates information from a single sensory modality
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16. Posterior parietal cortex
• Located posterior to the somatosensory cortex
• Serves as its unimodal association area
• Further process of somatosensory input
• Integration of information from the somatosensory cortex
with visual inputs occur
- important for planning complex movements and for hand
(proprioception)–eye (visual) coordination
Multimodal sensory association areas
- process, integrate, and interpret more than one sensory
modality
- link these data to the planning of movement
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17. Prefrontal association area
• located in the most anterior region of the frontal lobe
• involved primarily with motor integration (memory and
planning of motor activity); long-term planning and judgment;
personality traits; and behavior.
Posterior association area
• located at the junction of the parietal, temporal, and occipital
lobes
• integrates somatic, auditory, and visual stimuli for complex
perceptual processing
• involved primarily with visuospatial localization, language,
and attention
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18. Limbic association area
• Partially located in each of the temporal, parietal & frontal
lobes
• concerned with emotional expression and memory storage
 Multimodal sensory association areas then project to the
multimodal motor association areas
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19. Multimodal motor association areas
• located in the frontal lobes
• Include premotor cortex and the supplementary motor cortex
 Important in programming complex sequences of movements
and in orienting the body and limbs toward a specific target,
respectively
• Transmit impulses by way of association tracts to neurons of the
primary motor cortex
Primary motor cortex
• Located in the precentral gyrus
• Initiates voluntary contractions of specific skeletal muscles
• Impulses transmit by way of descending projection tracts to
the spinal cord, where they innervate the alpha motor neurons
(which innervate skeletal muscles)
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20. Similarity with somatosensory cortex
 Neurons are highly organized, with each section of the cortex
innervating specific body parts in a sequential manner
 The size of the region of the primary motor cortex devoted to
different parts of the body is quite disproportionate
– Large portions of the primary motor cortex innervate the
muscles of the hands as well as muscles responsible for
speech and eating
– Little cortex is devoted to motor pathways terminating in
the trunk of the body or the lower extremities
 The projection tracts cross from one side of the CNS to the
other
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22. 22

23. Language
• In humans, communication takes place primarily through
language or the use of spoken or written words to convey a
message
• The processing of language requires a large network of
interacting brain areas, both cortical and subcortical
• However, the two predominant cortical areas are Wernicke’s
area and Broca’s area
• In approximately 96% of people, these cortical areas for
language skills are found only in the left hemisphere
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24. Cortical pathway for speaking a word seen or heard.
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25. • Lesion in Wernicke’s area  receptive aphasia
– unable to understand any spoken or visual information
– patient’s speech, while fluent, is unintelligible
• Lesion in Broca’s area expressive aphasia
– able to understand spoken and written language
– unable to express his response
Wernicke’s area -responsible for formulating coherent
patterns of speech
Broca’s area - responsible for the mechanical aspects of
speaking(control the muscles necessary for articulation)
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26. Cerebral hemispheres
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Cerebral Hemispheres
• They are separate, but connected
• Have some degree of specialization
• Left side: words and logic
• Right side: art, music, intuition
• Right and left connected by
nerve fibers: corpus callosum
• Crossover: right half connects
to left side of body and vice versa

27. Basal ganglia
• Consist of four nuclei or masses of gray matter embedded within
the white matter
• Gray matter consists of functional aggregations of neuronal cell
bodies
• Modify ongoing activity in motor pathways
• The basal nuclei play a complex role in controlling movement
1. Inhibit muscle tone (continuous contraction) throughout the
body
2. Select & maintain purposeful motor activity while suppressing
useless or unwanted patterns of movement
3. Helping monitor and coordinate slow, sustained contractions,
especially those related to posture and support
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28. 28

29. • The activity of the basal ganglia tends to be inhibitory
– Thalamus positively reinforces motor activity in the
cerebral cortex
• Impulses from the basal ganglia modulate this effect
– Through their inputs to the brainstem and, ultimately the
motor neurons in the spinal cord, the basal ganglia inhibit
muscle tone
• Parkinson’s disease (PD): Disorder of the basal ganglia
• associated with a gradual destruction of neurons that release
the neurotransmitter dopamine in the basal nuclei
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30. 1. Increased muscle tone, or rigidity
2. Involuntary, useless, or unwanted movements, such as resting
tremors
For example: Hands rhythmically shaking, making it difficult
or impossible to hold a cup of coffee
3. Slowness in initiating and carrying out different motor
behaviors
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31. Thalamus
• Located between the cerebrum and the brainstem
• Lying along the midline of the brain, it consists of two oval-
shaped masses of gray matter, one in each cerebral hemisphere
1. Serves as a “relay station” for preliminary processing of
sensory input
– ascending tracts transmitting upward from the spinal cord
+ sensory tracts from the eyes and the ears, extending
ultimately to the cerebral cortex, pass through it
– All sensory fiber tracts (except olfactory tracts) transmitting
impulses to the cerebral cortex first synapse with neurons
in the thalamus
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32. 2. acts as a filter for information to the cortex
– prevent or enhance the passage of specific information
depending upon its significance to the individual
3. plays a role in regulation of skeletal muscle contraction by
positively reinforcing voluntary motor activity initiated by
the cerebral cortex
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33. Hypothalamus
• lies beneath the thalamus and above the pituitary gland
• a collection of specific nuclei and associated fibers
• It serves as an important link between the autonomic nervous
system and the endocrine system
• It plays a vital role in maintenance of homeostasis in the body
• Function :
– controls body temperature
– controls thirst and urine output
– controls food intake
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34. – controls anterior pituitary hormone secretion
– produces posterior pituitary hormones
– controls uterine contractions and milk ejection
– serves as a major autonomic nervous system coordinating
center, which in turn affects all smooth muscle, cardiac
muscle, and exocrine glands
– plays a role in emotional and behavioral patterns
– participates in the sleep–wake cycle
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35. Brainstem
• Continuous with the spinal cord
• Consists of the midbrain, and the pons and medulla of the
hindbrain
• Serves as an important connection b/n the brain and spinal
cord
• Medulla:
– contains control centers for subconscious, involuntary
functions, such as cardiovascular activity, respiration,
swallowing, and vomiting
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36. • Pons :
– Serve as a relay for the transfer of information between the
cerebrum and the cerebellum
– Along with the medulla, it also contributes to the control of
breathing
• Midbrain
– Controls eye movement
– Relays signals for auditory and visual reflexes
– Provides linkages between components of the motor system
including the cerebellum, basal ganglia, and cerebrum
• In addition, the brainstem contains a diffuse network of
neurons known as the reticular formation
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37. 37
The brainstem reticular formation and reticular activating system.
• Ascending sensory tracts send axon collateral fibers to the reticular
formation.
• These give rise to fibers synapsing in the intralaminar nuclei of the
thalamus.
• From there, these nonspecific thalamic projections influence widespread
areas of the cerebral cortex and limbic system.

38. • Function:
– Cortical alertness, ability to direct attention, and sleep
– Sleep center may be present in the RF (lower pons-upper
medulla)
• Sleep is produced by:
 Actively, by stimulatory activity of sleep center-
active reticular deactivation
 Passively, by suppression of the influences of the
ascending reticular system-
passive reticular deactivation
– coordination of orofacial motor activities, in particular
those involved with eating and the generation of emotional
facial expressions
– coordination of eating and breathing, blood pressure
regulation, and response to pain
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39. Cerebellum
• Second largest part of brain
• Part of the hindbrain and is attached to the dorsal surface of
the upper region of the brainstem
• It contains outer gray (extensively folded) and inner white
matter
• Needed for motor learning
• Specialized function
– coordinate movement by evaluating differences between
intended movement and actual movement
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40. • Cerebellum’s organization that enable it to carry out this
function
1. It receives extensive sensory input from somatic receptors &
from receptors in the inner ear
2. Output from the cerebellum is transmitted to premotor and
motor systems of the cerebral cortex and the brainstem —
systems
- control spinal interneurons and motor neurons
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41. Cerebellum consists of three functionally distinct parts
• Vestibulocerebellum :
– maintain balance and controls eye movements
• Spinocerebellum:
– enhances muscle tone and coordinates skilled, voluntary
movements
• Cerebrocerebellum:
– plan and initiate voluntary activity by providing input to the
cortical motor areas
– stores procedural memories
• Disorders of the human cerebellum
– Hypotonia(reduced muscle tone)
– Ataxia (defective muscular coordination)
– Intention tremors (inability to stop & start skeletal muscle action
quickly)
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43. Spinal Cord
• Long, slender cylinder of nerve tissue that extends from the
brain stem
• ~ 45 cm long and 2 cm in diameter
• enclosed by the protective vertebral column
• There are a total of 31pairs of spinal nerves:
8 Cervical- sensory perception and motor function of the back
of the head, neck, and arms
12 Thoracic- innervate the upper trunk
5 Lumbar innervate the lower trunk, back, and legs
5 Sacral
1 Coccygeal-
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44. 44

45. • Spinal nerves associate with the spinal cord by way of two
branches
• Dorsal root-contains afferent, or sensory, neuron
• Ventral root-contains efferent, or motor, neurons
• Function:
– Conducts nerve impulses to and from the brain
– Processes sensory input from the skin, joints, and muscles
of the trunk and limbs and initiates reflex responses to this
input
• Composition:
• Gray matter
• White matter
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46. • Gray matter:
• Nerve cell bodies + unmyelinated interneuron fibers
• Found internally and is surrounded by the white matter
• Has a butterfly or “H” shape
• Divided into three regions:
• Dorsal horn (posterior, toward the back)
• Ventral horn (anterior)
• Lateral horn (at side)
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47. • Contains four types of neurons
1. Second-order sensory neurons
• cell bodies are found in the dorsal horn
• receive input from afferent neurons (first-order sensory
neurons; their cell bodies are found in the dorsal root
ganglia) through the dorsal root
• Function :transmit nerve impulses to higher levels in
the CNS
2. Somatic motor neurons
• cell bodies are found in the ventral horn
• axons exit the spinal cord through the ventral root
• Function: innervate skeletal muscles
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48. 48
Cross-sectional view of the spinal cord

49. • There are two types of motor neurons in the ventral horn
• Alpha motor neurons innervate skeletal muscle fibers
to cause contraction.
• Gamma motor neurons innervate intrafusal fibers of
the muscle spindle, which monitors muscle length
3. Visceral motor neurons
• cell bodies are found in the lateral horn
• axons form efferent nerve fibers of the ANS
• axons of these neurons exit the spinal cord by way of
the ventral root
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50. 4. Interneurons
• in all areas of the spinal cord gray matter
• receive input from: higher levels of the CNS + sensory
neurons entering the CNS thr’ the spinal nerves
• synapse with motor neurons in the ventral horn
• These interconnections are responsible for the integrative
functions of the spinal cord
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51. • White matter:
– Composed of myelinated axons of neurons
– Axons are grouped together to form tracts
• Ascending tracts -carry sensory information toward the
brain
• Descending tracts-carry motor information away from the
brain toward the motor neurons in the lateral or ventral
horns of the spinal cord gray matter
• Both tracts cross from one side of the CNS to the other
• Cross over: in the medulla (most)
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52. Reflex
• Any response that occurs automatically without conscious
effort
• Are specific, predictable, and, furthermore, often purposeful
• Simple, or basic, reflexes are preprogrammed (built-in),
unlearned responses.
Pulling the hand away from a burning hot object
• Acquired, or conditioned, reflexes are learned responses that
require experience or training.
Pianist striking a particular key on seeing a given note on
the music staff
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53. REFLEX ARC
• Neural pathway involved in accomplishing reflex activity
• Includes five basic components:
1. Sensory receptor (e.g. Stretch receptor, pain receptor)
2. Afferent or first-order sensory neuron
3. Integrating center in the spinal cord (synapses)
4. Efferent or motor neuron
5. Effector tissue (skeletal muscle)
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54. 54
• Monosynaptic reflex has a single synapse between afferent
and efferent neurons. E.g. stretch reflex
• Polysynaptic reflex has two or more synapses between
these neurons. E.g. withdrawal reflex

55. 55
Muscle spindle 1a fiber
Muscle
Motoneurone
Motor axon
RECEPTOR
EFFERENT
EFFECTOR
AFFERENT
CENTRAL NEURONE
Components of Reflex Arc

56. Stretch reflex-Knee jerk
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57. Withdrawal reflex
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58. Crossed extensor reflex
• The withdrawal reflex may be accompanied by the crossed-
extensor reflex
• Ensure that the opposite limb will be in a position to bear the
weight of the body as the injured limb is withdrawn from the
stimulus.
• Causes extensor muscles in the opposite limb to contract. The
straightening of the opposite limb provides support for the
body.
• In this case these interneurons influence the activity of the
opposite muscle groups
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59. 59
The crossed extensor reflex coupled with the withdrawal reflex