Physiology of Central nervous system

1. Arba Minch
College of Health Science
Department of Pharmacology
Human Physiology
Neurophysiology
By Zelalem K. (MSc in Medical Physiology)
The Central Nervous
System
6/16/2023 CNS 1

2. Objectives
o At the end of this chapter the student will be able to:
1. Define the central nerves system
2. List sensory & motor functions of brain
3. Enumerate the organs of the brain
4. Discuss functions of CNS
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3. Outlines
 Introduction
 Organization & function of the CNS
 Sensory & motor functions of CNS
 Cerebrum
 Basal ganglia
 Cerebellum
 Brain steam
 Limbic system
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4. Introduction
o Central nervous system (brain & spinal cord)
 A system devoted to information processing
 Protected by bony structures, membranes & fluid.
 Heir, skin, skull, meninges and CSF protect brain.
o Brain is held in the cranial cavity of the skull and it consists of:
 Cerebrum, cerebellum & brain stem.
o The peripheral nerves involved are:
 12 cranial nerves & 31 spinal nerves.
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5. NS: a system that controls all of the activities of the body.
o It is made up of: brain, spinal cord, nerves & senses.
The brain The spinal cord
The nerves
The senses
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6. Nervous System
CNS
PNS
Spinal Cord
White mater (myelin sheath)
Gray mater (Cell bodies)
Brain
Myelencephalon: Medulla oblongata
Metencephalon
Pons
Cerebellum
Mesencephalon: Mid-brain
Diencephalon
Thalamus
Hypothalamus
Telencephalon Basal ganglia
Cerebral Cortex
Frontal
Parietal
Temporal
Occipital
Dorsal root ganglia
Peripheral nerves
Cranial nerves = 12 pairs
Spinal nerves
Cervical = 8x2
Thoracic = 12x2
Lumbar = 5x2
Sacral = 5x2
Coccygeal = 1x1
31 pairs
Organization of the CNS
SNS PaNS
Autonomic NS
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7. Organization of the NS…
Central nervous system [brain & SC]
Integrative & control centers
Peripheral nervous system [CN & spinal nerves]
Communicates between CNS & rest of body
Sensory division
Impulse from receptor to CNS
Motor division
Impulse from CNS to effector
ANS
To visceral organs.
SNS
To skeletal muscles.
Sympathetic Division
“Excites”
Parasympathetic Division
“Retards”
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8. Spinal cord
o Extend from brain stem
o Has central grey & peripheral white
portion.
o Here, sensory and motor nerve fibers
separate into dorsal and ventral root.
o Spinal nerves are 31 pairs:
 8 … Cervical
 12 … Thoracic
 5 … Lumbar
 5 … Sacral
 1 … Coccygeal
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10. o The spinal cord has two -functions:
1. Common passageway for ascending & descending tracts.
o Neurons in the white matter of the SC transmit:
i. Sensory signals from peripheral regions to the brain
ii. Motor signals from the brain to peripheral regions
2. Center for reflexes.
o Neurons in the gray matter of the SC:
 Integrate incoming sensory information & respond with motor
impulses that control muscles or glands.
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11. Spinal cord
Gray matter
 Contains nerve cell bodies.
 Divided into dorsal + ventral horns.
Dorsal horn
o Orderly arrangement of sensory relay
neurons that receive input from the
periphery.
Ventral horn
o Contains groups of motor neurons +
interneurons.
White matter
o Ascending + descending tracts of
myelinated axons.
o Ascending pathways carry sensory
information to the brain.
o Descending pathways carry motor
commands + modulatory signals from the
brain to the muscles.
Neuroscience
Organization of the central nervous system
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12. Spinal cord tracts …
Ascending tracts
o Carry information related to: touch, pain,
temperature, 2 point discrimination, position &
vibration
o Gracile tract: below T6
o Cuneat tract: above T7
o Example
 Spinothalamic tracts: fast pain, temperature & crude
touch
 Dorsal column tracts: position & vibration
Descending tracts
o Carry information associated with
motor activity like:
 Posture
 Balance
 Muscle tone
 Somatic reflex
 Visceral reflex
o Example
 Lateral column tracts
 Ventromidial column
 Ventral column tracts
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13. Reticulospinal tract/Pontine
 Control of breathing.
 Emotional motor system (monoaminergic NT: 5-HT,
NA, DA).
 Control the lateral horn cells  visceral
functions/ANS; increase autonomic sensitivity
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14. Rubrospinal tract
 Facilitates flexor motor neurons in upper limbs
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15. Lateral tectospinal tract
 Responsible for orienting the head and neck during eye
movements.
 Concerned with directing the eye and turning the head
towards a light source (visuospinal reflexes).
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16. Ventral tectospinal tract
 Concerned with turning the head
to direct the ears towards a sound
source (audiospinal reflexes).
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17. Medial vestibulospinal tract
o Facilitate stretch reflex and skeletal
muscle tone.
o Mediate some postural reflexes.
(Corticonuclear tract)
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19. Brain regions
1. Cerebrum
 Four lobes, BG and LS
2. Diencephalon
 Thalamus
 Hypothalamus
 Epithalamus
 Mamilary body
 OC
3. Brainstem
 Midbrain
 Pons
 Medulla oblongata
4. Cerebellum Cerebellum
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20. Cerebrum
o Largest portion of the brain (80% by mass).
o Responsible for higher mental functions concerning:
Perception of fine sensation
Learning
Memory
Speech
Judgment
Planning
o Corpus callosum:
Major tract of axons that functionally interconnects right & left
cerebral hemispheres.
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21. Commissural Fibers
Corpus callosum
Commissural fibers
Motor functions
Cerebral cortex
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Commissural fibers

22. Cerebral Cortex
o 3 functional areas:
1. Motor: control voluntary motor
functions.
2. Sensory: allow for conscious
recognition of stimuli.
3. Association: integration.
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23. 6/16/2023 23
Motor cortex
Sensory cortex
Auditory cortex
Visual cortex
Motor functions
Cerebral cortex
Cerebral cortex…

24. Cerebral cortex…
III
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25. 6/16/2023 25
Motor functions
Cerebral cortex
Prefrontal cortex
Lateral orbitofrontal
Ventromedial

26. Cerebral cortex …
o Each hemisphere contains 4 lobes:
 Frontal, parietal, occipital, temporal and
limbic
o Has an outer cortex of gray matter
surrounding an interior that is mostly white
matter.
o The surface is marked by ridges called gyrus
separated by grooves called sulcus.
 Each gyrus contains one or more
functional areas called Brodmann´s areas.
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27. Sensory, motor & association map
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28. Functions of lobes of the brain
1. Frontal lobe = conscious thought
2. Parietal lobe = plays important roles in
integrating sensory information from
various senses
3. Occipital lobe = sense of sight; lesions
can produce visual hallucinations.
4. Temporal lobe = senses of smell and
sound.
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29. Temporal lobe
1. Auditory areas
 Areas- 41 & 42
 Receive sensory fibers from Cochlea
o 1ry auditory center
2. Auditory association
 Areas 20, 21 & 22
 Interpretation of auditory information.
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30. Occipital lobe
1. Visual sensory area (area-17)
 Primary visual area responsible for
vision and coordination of eye
movements.
2. Visual association (area-18)
 It is concerned with interpretation
of visual impulses into meaningful
written words.
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31. Motor function of the cerebral cortex
o Located in the frontal lobe, in front of
the central sulcus.
o Have 3 functional areas:
1. Primary motor area: area 4
2. Premotor area: areas 6, 8, 44, & 45
3. Prefrontal motor association area:
areas 9, 10 & 11
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32. The primary motor cortex
o Location:
Precentral gyrus in the frontal lobe.
o Body representation:
Inverted (head-down) & crossed (opposite side) manner.
The face area is bilaterally represented.
o The area of representation is proportional to the degree of fine
movement of the part.
e.g. large areas for heads and muscles of speech and small area for trunk
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34. 6/16/2023 34
Motor functions
Cerebral cortex
Motor Homunculus: why the hand & face are over-represented???

35. Function of area-4
1. Initiation of voluntary, fine, discrete movement of limbs (hands, fingers)
on opposite side.
2. Facilitation of stretch reflex
i.e. Facilitation of skeletal muscle tone & tendon jerk
Effect of lesion to area-4
1. Flaccid paralysis in the opposite side of the body.
2. Loss of deep & cutaneous reflexes in the opposite side.
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36. The premotor cortex (area-6, 8, 44 & 45)
Area – 6
o Location: lies anterior to area 4
o Body representation: crossed &
inverted
o Connections
 To area-4
 Sensory areas via sub cortical fibers
 Thalamic nuclei
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37. Function of area-6
1. Cooperates with area-4 in control of coordinated voluntary movement.
 Isolated stimulation of area-6 initiates coordinated gross (not fine)
movement in the opposite side of the body (flexion, extension).
2. Contains the following functional areas:
 Broca´s area
 Frontal eye field area
 Head rotation area
 Hand skill area
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38. o Broca´s area (areas-44 & 45)
 Word formation area (speech center).
 Lesion results in aphasia (condition in which someone is unable to speak)
o Frontal eye field area (area-8)
 Located above the Broca´s area connected to the visual center in the
occipital lobe.
 Controls movement of eye & eyelid.
 Lesion: fixation (locking) of the eye on specific objects
o Head rotation area = directs the head to objects.
o Hand skill area = controls skilled movements.
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39. Function of area-6 ...
3. Inhibition of stretch reflex (suppresses muscle tone) and grasp reflex.
4. Controls complex movement like
 Facial expression, jaws, tongue, larynx, pharynx & respiratory
muscles.
5. Initiates automatic (involuntary) movement performed subconsciously
(swinging movement of arms during walking).
6. Involved in the control of the ANS
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40. Effect of lesion to area-6
1. Muscle paresis in the opposite side.
2. Increase in muscle tone & muscle rigidity.
3. Exaggerated tendon jerk.
4. Appearance of grasp reflex.
5. Failure of vocalization (motor aphasia)
6. Motor apraxia: inability to perform complex movements; facial, jaws,
tongue…
7. Agraphia: failure of writing skills.
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41. The prefrontal motor association cortex (areas 9, 10, 11)
Location
 Anterior part of the frontal lobe
 It is called the organ of mind
 Prefrontal cortex
Connections with
 HT
 Thalamus
 Limbic system
 Motor areas
 Temporal
 Occipital lobes
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42. Function of area 9,10,11
1. Involved in higher intellectual functions of the brain;
 Planning, intelligence & elaboration of thought.
2. Due to its connection with hippocampus, it is involved in the storage
of recent memory.
3. Due to its connection with hypothalamus, it is involved in the control
of the ANS.
4. Due to its connection with the limbic system, it is involved in control
of emotional behaviors.
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43. 6/16/2023 43
 Functions:
• Important for higher order processing + for integrating +
interpreting motor information and activity…
• Play a role in anticipating or ‘planning’ a voluntary movement…
• It gives us our ‘personality’ and lets us adjust our behavior to moral
and social norms…
• Executive function: play a role in planning + problem solving as well
as directing + maintaining attention on a particular situation or task.
• Working memory + our morality + thought + judgment + attention…
• Prioritizing and focusing on relevant themes rather than irrelevant
details…
• Allows us to make deliberate decision about our behavior and adapt it to
specific situations… (Goal-directed motor behavior…).
Motor functions
Cerebral cortex

44. Effect of lesion to area 9,10,11
1. Mental impairment
2. Lack of initiatives & self control
3. Loss of attention
4. Change in social behavior
5. Disorientation of time and space
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45. Frontal/Temporal/Amygdaloid Lobotomy
• Kluver-Bucy Syndrome
45
Altered emotions (placid):
Reduced fear & aggressiveness
Difficulty of planning and
working towards goals
Oral tendencies to identify
object
Hypemetamorphosis:
irresistible urge to run around
objects touch and taste them
Psychic blindness to choose
food
Altered sexual behavior:
masturbations, heterosexual
and homosexual (low moral
standard)
Phineas Gage…1848

46. Cortical areas controlling autonomic function
1. Limbic system
2. Premotor area (area 6): micturition,
salivation
3. Frontal eye field area (area 8):
lacrimation, pupillary changes
4. Prefrontal areas: through their
connections with hypothalamus
control autonomic functions.
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47. o Sensory function of the cerebral cortex
 The highest center for the perception of fine sensations.
 Somatic sensations (touch, pain, To , pressure, 2 point discrimination,
position, vibration, proprioception and …) perceived in the parietal lobe
 Visual sensation in the occipital lobe.
 Auditory sensations in the temporal lobe.
 Gustatory sensation in cingulate cortex
 Olfaction in olfactory bulb
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48. Somatosensory areas
o Two somatosensory areas are:
1. The primary somatosensory
areas (SI)
2. The secondary somatosensory
areas (SII)
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49. Primary somatosensory areas (SI)
Location:
 Post central gyrus of the
parietal lobe.
 Identified by Brodmann´s
areas 3, 1 & 2
 Final termination of fine
somatosensory pathways
projected from thalamic
nuclei.
1
2 3
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50. Body representation:
 Crossed & inverted
 Each half of the body represented in the
contra lateral cortex.
 Upper half of the face is bilaterally
represented.
 Area of representation in each part is
proportional to the number of receptors
in the part not with its size.
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51. Sensory homunculus: very sensitive area represented in more area
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52. Function of SI
o Perception of the following sensations:
1. Fine touch, tactile localization & discrimination.
2. Localization of pain & temperature.
3. Texture of materials differentiation.
4. Properioception.
5. Transmits sensory information to area SII &
somatosensory association area for farther elaboration of sensory
information.
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53. Secondary somatosensory areas (SII)
Location: behind SI.
 Represented by Brodmann´s area-40
 SII receives signal inputs from SI, thalamic nuclei, visual and auditory
sensory areas.
Function:
 Potentiates the function of SI, but not essential for these functions.
 SI can work without SII, but the other way round is not true.
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54. Somatosensory association area
o Location: (areas 5 & 7)
o Connections: receive sensory impulse from SI , SII , thalamus, visual
cortex & auditory cortex.
o Functions:
1. Combines all sensory signals to give meanings to the sensory input.
2. It is important for stereognosis.
 Effect of lesion to this areas ; astereognosis; failure to identify objects by
their touch, shape, weight & texture.
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55. Sensory areas
o Found in the parietal,
occipital & temporal lobes.
1. Somatosensory cortex.
2. Somatosensory association
cortex.
3. Visual areas.
4. Auditory areas.
5. Olfactory cortex.
6. Gustatory cortex.
7. Vestibular cortex
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56. Language areas
o Wernicke’s area
 Understanding oral
& written words.
o Broca’s area
 Speech production.
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57. Language areas …
o Broca’s area (area 44,45)
Involves articulation of speech.
In damage, (aphasia) but comprehension of
speech is unimpaired.
o Wernicke’s area (area 39,40)
Involves language comprehension.
In damage, language comprehension is destroyed
and speech is rapid without any meaning.
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58. Language areas …
o Angular gyrus:
 Center of integration of auditory, visual
information.
 Damage produces aphasias.
o Arcuate fasciculus (neural pathway)
o To speak intelligibly, words originating in
Wernicke’s area must be sent to Broca’s area.
o Broca’s area sends fibers to the motor cortex which
directly controls the musculature of speech.
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59. Arcuate fasciculus
Motor functions
Cerebral cortex
6/16/2023 59

60. Lateralization
o The fact that certain activities
are almost exclusively dominant
on 1 of the 2 hemispheres.
In most people, the left hemisphere has a more control over language,
math, & logic.
While the right hemisphere is geared towards musical, artistic &
other creative endeavors.
o Most individuals with left cerebral dominance are right-handed.
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LA
TE
RA
LI
ZA
TI
ON

61. Thalamus
o 80% of the diencephalon.
o Forms most of the walls of the 3rd ventricle.
o Ovoid mass of gray matter/egg-shaped
structure
o Paired structures, located on both sides of the
third ventricle.
o Connected by interthalamic adhesion
o Each thalamus has 4 groups of nuclei (>50
nuclei).
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62. Significance
 Relay station/‘gatekeeper’, ‘secretary of the cerebral cortex’
 Mediates ALL types of sensations to the cerebral cortex…
(except olfaction).
 Connects cortical areas with each other (integrating, modulating + gating,
bidirectional flow of information, fine tuning…).
 Motor integration (inputs from cortex, cerebellum + basal ganglia).
 Pain modulation (all nociceptive information…).
 Arousal (part of RAS).
Neuroscience
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63. Thalamus as relay…
 Link between sensory receptors and
cerebral cortex for all modalities except
olfaction.
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64. Thalamic nuclei
MGN
LGN
/LP
/DM
/ANT
/VA
/LD
/VL
VPL
VPM
Neuroscience
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65. o The hypothalamus
 Forms the floor + lateral wall of
third ventricle
 Inferior to thalamus.
 Component of the limbic system.
 Weighs  4gm.
 Connected to the pituitary gland by
the pituitary stalk.
Neuroscience
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66. Function of hypothalamus
1. Controls the ANS
 Anterior nuclei acts as a parasympathetic center.
 Posterior nuclei acts as a sympathetic center.
2. Endocrine function
o Controls:
 Adenohypophyseal hormones.
 Neurohypophyseal hormones.
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67. 3. Regulation of body temperature
 Heat losing center (anterior HT)
 Heat gaining center (posterior HT)
 Thermostat center (anterior preoptic area)
4. Regulation of sleep, wakefulness, emotions, sexual arousal, anger,
fear, pain & pleasure.
5. Controls food intake (hunger sensation):
 Feeding center (lateral HT)
 Satiety center (ventromedial HT)
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68. 6. Control of water-electrolyte balance
 Thirst center (lateral HT)
 Osmoreceptors (anterior HT)
7. Control of sexual behavior: libido, sexual activities are controlled by
cerebral cortex, limbic system & HT.
8. Regulates sleep: lesion to posterior HT- Somnolence.
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69. 9. Regulates MR
 By stimulating calorigenic hormones such as
o T3/T4, AD, NA, glucocorticoids.
10. Controls milk letdown and utrine contraction.
o Effect of HT lesion:
 Diabetes inspidus
 Hypo/hyperthermia
 Sleep, emotional & hormonal disturbance
 Hyperphagia
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70.  The hypothalamic nuclei
 Hypothalamic nuclei are classified into five groups:
1. Anterior group
 Preoptic
 Supraoptic Regulates hormone release from posterior pituitary
 Paraventricular
 Suprachiasmatic
 Anterior
2. Middle group
 Arcuate nuclei
 Ventromedial
 Dorsomedial nuclei
(Regulates ANS)
Neuroscience
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71. 3. Posterior group
 Posterior n
 Premammillary n.
 Medial
 Lateral n
4. Lateral zone
 Lateral hypothalamic nucleu (limbic system structures, emotion
control)
5. Periventricular nucleus
 Gray matter adjacent to third ventricle.
(Release of endocrine hormones from anterior pituitary gland).
Neuroscience
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72.  Are deep nuclei of the cerebrum
(masses of gray matter).
 Aid the motor cortex in planning +
generating motor actions.
 Kick starter of the voluntary
movement
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Basal Ganglia

73. 73
Motor functions
Basal ganglia
Basal ganglia and the major components of the motor system…

74. 74
Motor functions
Basal ganglia
Anatomical relations of the basal ganglia to the cerebral cortex + thalamus

75. Motor functions
Basal ganglia
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• Cortico–Basal Ganglia–
Thalamocortical Motor
Circuit
VI
Connections between the cerebral cortex, thalamus, basal
ganglia, cerebellum, brainstem, & spinal cord.

76. Roles of the basal ganglia in the motor control
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77. o BG: 4 principal structures:
i. Striatum (caudate +
putamen)
ii. Globus pallidus (GPe + GPi).
iii. Substantia nigra
iv. Subthalamic nucleus.
Basal ganglia
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78. o Three large nuclear masses
 Caudate nucleus
Striatum/neostriatum/corpus striatum
 Putamen
Lentiform nucleus
 Globus pallidus/GPi + Gpe
(paleostriatum)
o Two functionally related nuclei:
 Subthalamic nucleus (STN).
 Substantia nigra (SN)
• Pars compacta (SNc)
• Pars reticulata (SNr)
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79. Caudate nucleus
o A tadpole - shaped nucleus
o Its head lies in the floor of the lateral
ventricle.
o Its body arches over the thalamus as a C
shape.
o Tail lying in the roof of the inferior horn of
the lateral ventricle.
o Control of eye movement + cognitive +
affective behavior.
o GABAergic neurons
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80. Putamen
o Most lateral of the BG.
o Anterior limb of the internal capsule
separates caudate and putamen.
o Putamen + caudate nuclei: input nuclei
to the BG.
o Receive mainly excitatory input from
cortical + subcortical structures
o GABAergic neurons
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81. Globus pallidus/GP
o GP: medial to the putamen + lateral to the
thalamus.
o GPe + GPi
o GP is the output nucleus (inhibitory
projections to the thalamus, GABAergic).
o GPi: major output structures of the BG
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82.  Subthalamic nucleus/STN
o A biconvex nucleus, lies inferior to the thalamus + superior to tegmentum of the
midbrain, caudal to the hypothalamus
o Receives afferents from both the cortex + GPe.
o Output is excitatory thru glutamatergic projections to the GPi + SN
o ‘Clock’ of basal ganglia/defines the output rhythm.
 Nucleus accumbens
• The anterior + ventral part of the striatum where the head of the caudate and
putamen are continuous with each other.
• Receives extensive dopaminergic input + an integral part of the limbic system and
reward circuitry.
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83. Substantia nigra
o Located in the rostral midbrain within
the cerebral peduncle at the level of
the superior colliculi.
o Contains dopaminergic neurons that
project to the putamen + caudate +
STN.
o SNc (dopaminergic cells)
o SNr (GABAergic).
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84. Substantia nigra and its connections
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85.  Categories of BG nuclei
o Input nuclei/zones
 Caudate nuclei Ach, GABA
 Putamen Ach, GABA
o Intrinsic nuclei
 Globus pallidus (Gpe)  GABA STN
 Subthalamic nucleus (STN)  Glutamate Gpi, SNc
 Substantia nigra (SNc)  DA Striatum
o Output nuclei
 Globus pallidus (Gpi)  GABA VA,VL &DM
 Substania nigra (SNr)  GABA STN,VA, VL &DM
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86. o Fibers to and from BG
 Corticostriatal fibers fibers from the cortex to the striatum
 Nigrostriatal pathway  the connection between the SN and the
striatum
 Subthalamic fasciculus  the connection between the STN and the
Gpi
 Thalamic fasciculus  is the projection from the Gpi to the thalamus
 Striatopalidal fibers  fibers from the striatum to the Gp
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87. Neurotransmitters in the basal ganglia…
 Fibers from the cerebral cortex  Glu  corpus striatum.
 Fibers from the substantia nigra  DA  corpus striatum.
 Fibers from the corpus striatum  GABA  GP.
 Fibers from the corpus striatum  GABA  SNr.
 Fibers from the brainstem  NA + serotonin + enkephalin  BG
NB
 Excitatory NT:Glu + Ach + NA + DA (D1).
 Inhibitory NT: DA (D2), GABA, serotonin + enkephalin.
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88. 88
Motor functions
Basal ganglia
Red: Excitatory pathways
Gray: Inhibitory pathways
 Inputs: striatum (putamen + caudate) + STN
 Outputs: GPi + SNr
o Thalamic nuclei (VL, VA, CM)
o Brain stem (pedunculopontine nucleus +
superior colliculus (SNr)…brain stem…SC).
The basal ganglia–thalamocortical circuitry.

89. 89
 Neuronal connections of the basal ganglia
o Internal circuits
• Input is well integrated + the output highly regulated.
• Balance of inhibitory + excitatory pathways  thalamus  cortex.
• Thalamus is under tonic inhibition (unless inhibition is removed, there is no
signaling to the cortex).
• Striatum  GP + SNr.
• Output can either decrease or increase the tonic inhibition of the thalamus via
two internal pathways (direct + indirect pathways).
Motor functions
Basal ganglia

90. 90
Motor functions
Basal ganglia
 Inputs
• Input to the basal ganglia is to the striatum (caudate
+ putamen).
• Caudate + putamen each receive input from distinct
cortical + subcortical regions… intralaminar nuclei
of thalamus… dopaminergic + serotonergic
inputs…
Glutamate

91. Motor functions
Basal ganglia
Outputs
• Striatum projects to the output
nuclei via direct and indirect
pathways/GPi + SNr.
• Output from the basal ganglia is
inhibitory via GABAergic
neurons.
• Striatum + SNr  thalamus 
cortex.
• Arise from GPi + SN  VA + VL
nuclei of the thalamus cortex.
91

92. 1.Direct pathway
o Excitatory projections from the cortex  Striatum
o Inhibitory neurons from striatum  GPi.
o GPi inhibitory neurons  thalamus.
o Inhibition of the inhibition releases the tonic inhibition of the thalamus
o The thalamus then sends excitatory fibers to the cortex.
o More cortical output results from increased excitation of the cortex.
o At the same time, the striatum is also influenced by input from the SN.
o DA neurons project to the striatum where they excite (via D1 receptors) inhibitory
neurons, which project to the GPi.
o The SN enhances the excitatory input from the cortex.
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93. 93
The direct pathway
Motor functions
Basal ganglia

94. The direct pathway
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DA
Glu
Glu
GABA
GABA
GABA
Glu

95. 95
Motor functions
Basal ganglia
Direct pathway
Pars compacta

96. 1. Direct pathway…
o Facilitates target-oriented + efficient behavior.
o Disinhibits thalamus from tonic inhibition   thalamocortical
activity.
o More excitation of the cortex and in turn more cortical output,
facilitates movement (positive feedback).
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97. 2. Indirect pathway
o This circuit inhibits the output from the thalamus
o Leading to less excitation of the motor cortex and less motor output
o Puts “brakes” on the direct pathway
o Inhibits the thalamocortical activity ( excitation of the motor cortex +
less motor output (negative feedback).
o Inhibits movement.
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98. The indirect pathway
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99. Motor functions
Basal ganglia
99
Indirect pathway

100. 100
Motor functions
Basal ganglia
The indirect pathway

101. 101
Motor functions
Basal ganglia
Corticostriatal pathway
Nigrostriatal pathway
Subthalamic fasciculus
Thalamic fasciculus
Normal input-output relationships of the basal ganglia
/CM

102. Connections of BG
1. Cerebral cortex via
I. Caudate circuit
II. Putamen circuit
2. Brainstem via
I. Extrapyramidal tracts
 Vestibular nuclei
 Reticular formation
 Tectum
 Red nucleus
 Olivary nucleus
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103. Connection of BG to cerebrum
Caudate circuit
o From association area +M1 + M2+
sensory association area
Caudate nucleus
Globus pallidus
VLNT
Motor association area
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104. Role of caudate circuit
o Convert motor thoughts, ideas and plans to motor action
 What pattern of movement will be used
o Determines the time and scale movement
 To what extent the movement will be fast
 For how long the movement will last
o Damage to caudate circuit
 Disorganized motor activity; wearing neck tie before a shirt
 Failure to scale a contra lateral side (when drawing)
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105. Putamen circuit
Motor Association +M1+ M2
Putamen
Globus pallidus
VLNT
M1 + M2
Accessory circuit that involve STN
and SN
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106.  Role of putamen circuit
o Storage of motor circuit of familiar actions
 Signature, writing, lighting candle
o Damage to this circuit
 Motor apraxia; inability to carry out familial movements in the absence
of motor paralysis
 Inability to write or draw figures with a fixed scale
o Excluding the contralateral side of the body from any motor plans.
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107. Clinical correlates
 Two characteristic features of lesions of BG
1. Involuntary movements during rest
 Disappear during sleep
  with nervous excitement
2. Change in muscle tone
Hyperkinetic
Hypokinetic
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108. 1. Parkinsonism/Parkinson disease, paralysis agitans (James Parkinson in 1817)
o Cause:
 Lesion in the substantia nigra/SNc
 Combination of environmental and genetic factors
• Exposure to environmental toxins, such as pesticides
• Parkin gene mutation on chromosome 6
A. Hypokinetic disorders
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109. Parkinson’s disease/hypokinetic
 Due to the effect on direct and indirect path way
 Is difficulty to initiate movement
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110.  Features
Tremor/4 - 8 Hz
 Due to lack inhibition of Ach interneuron's, leads to AP reverberating circuit
 Pill-rolling movement of the hands.
 Mandibular tremor.
 Other prominent motor features include a shuffling gait, flexed posture,
reduced facial expression, decreased blinking, and small handwriting.
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111.  Rigidity
o In both muscle groups, flexors > extensors
o Lead-pipe rigidity.
o Cog-wheel rigidity (‘catches’ or ‘clicks’ during bending)
 Cause
o Lack of cortical inhibition to reticular formation
o Facilitation of the -motor neurons due to lack of dopamine
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112. 2. Akinesia
 Lose of movement
 No DA  basal ganglia locked in the sate of excitation
 Mask face (no facial expresion).
 Slow monotonous, low volume speech.
o Treatment: medical and surgical
 Medical (Ach inhibtors, DA (L-dopa))
 Surgical (Destruction of the ventrolateral nucleus of thalamus)
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113. 1. Chorea: lesion in the caudate nucleus
o Features:
 Involuntary, rapid, purposeless 'dancing' movements during rest.
 Due to rapid leaking of motor program
 Facilitatory role of caudate is lost
 Loss of caudate circuit functions.
o Types:
 Sydenham chorea (children, 5-15y, F > M).
 Huntington chorea (genetic, a defect on chromosome 4, affecting the
gene that codes for the protein huntingtin), damage caudate n.
 Chorea gravidarum /chorea of the contraceptive pills.
B. Hyperkinetic disorders
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114. Huntington’s disease/hyperkinetic
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115. 2. Athetosis: lesion in the putamen
o Features:
 Involuntary, spasmodic, slow writing movements/mobile spasm.
 Motor program leak slowly
 Artistic movement
 Inhibitory function of putamen is lost
 Loss of putamen circuit functions.
3. Hemiballismus/Ballism: HTN or DM infarction in the subthalamus
o Features:
 Sudden, involuntary, strong, spasmodic movements in hip and shoulder.
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116. Cerebellum
o Lies inferior to the cerebrum &
occupies the posterior cranial
fossa.
o 2nd largest region of the brain
 10% of the brain by volume,
but contains 50% of neurons.
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117. The cerebellum controls your
Balance Posture
Motor Skill
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118. Cerebellum...
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119. Cerebellum: functional parts
o Vestibulocerebellum [archicerebellum]
 It is the oldest part of the cerebellum.
 It consists of flocculonodular lobe.
 It is mainly connected to the vestibular apparatus.
 Function: controls equilibrium & posture
o Spinocerebellum [paleocerebellum]
 It comprises vemis & paravermal parts.
 It receives signal from muscle spindle & golgi tendon organs.
 Function: concerned mainly with control of muscle tone.
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120. o Cerebrocerebellum (neocerebellum]
It includes the lateral cerebellar hemispheres.
It is the newest part
Connected to cerebrum.
Function: control of skilled voluntary movements initiated by
cerebral cortex.
Ex playing piano, writing, driving…
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121. Cerebellar connections
o Tracts that link the cerebellum with the brain
stem, cerebrum, & spinal cord leave the
cerebellar hemispheres as the superior, middle, &
inferior cerebellar peduncles.
1. SCP carries instructions from cerebellar
nuclei to the cerebral cortex.
2. MCP connects pontin nuclei to the
cerebellum.
3. ICP connects the cerebellum & the medulla
oblongata
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122. Cerebellar connections …
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123. Functions of cerebellum
1. Control of posture & equilibrium.
2. Control of muscle tone
3. Control of voluntary movement
a. Planning
 Cerebrocerebellum is concerned with the intention & plan of movement.
b. Timing of movement
 Cerebellum determines the start & termination of sequential movement.
c. Damping of movement
 Ending of movement without oscillation.
d. Ballistic movement
 Rapid & short movement such as typing.
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124. Cerebellar syndrome
o Produced by lesion to the cerebellar nuclei.
o Appeared on the same side of the lesion.
o There are three main types:
1. Atonia: marked decrease in muscle tone
2. Asthenia: lack of strength
3. Ataxia: incoordination of voluntary movements
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125. 3. Ataxia
Manifestation:
a. Dysmetria: inability to adjust a motor act to a certain distance.
• A motor act may overshoot or stop short of the intended point (hypometria).
• It is caused by failure of the timing & damping function of the cerebellum.
b. Dysarthria: difficulty in producing clear speech.
c. Rebouned phenomenon: manifested by an overshooting of a limb when a
resistance is removed.
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126. The Brain Stem [Mid brain; Pons; Medulla]
o Extended between the spinal cord &
sub cortical structures (thalamus,
HT, BG).
o Connected with cerebellum by
cerebellar peduncles.
o Contents:
1. Ascending & descending tracts
2. Vital controlling centres
3. Reticular formation
4. Nuclei of cranial nerves
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127. Midbrain
o Contains both sensory & motor tracts &
important nuclei
1. Superior colliculi: involved in visual reflexes.
 The reflex center for the movement of eyes
& head in response to visual stimuli.
2. Inferior colliculi: relay centers for auditory
information.
o The reflex center for the movement of head
& neck in response to auditory stimuli.
3. Red nucleus: works with BG & cerebellum to
coordinate muscle movement
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128. Pons
o Contains: tracts & several nuclei
of CN V, VI, VII.
o Pontin nucleus: which is a relay
station for impulses discharged
from the cerebral cortex to the
cerebellum via cortico-ponto-
cerebellar tract.
o Apneustic & pneumotaxic
respiratory centers.
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129. Medulla oblongata
o Contains ascending & descending tracts &
vital controlling centres:
 Cardiovascular , respiratory,
swallowing, vomiting center and
salivatory nuclei.
o Is the origin of cranial nerves (CN VIII to XII)
o Other nuclei with specific functions are:
o Olivatory nuclei: regulation of muscle
tone
o Vestibular nuclei: regulation of muscle
tone, posture & equilibrium.
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Midial lemniscus

130. Reticular formation [RF] of the brain stem
o RF contains a dense network of
neurons within medulla, pons &
midbrain.
o Found in the brainstem, extended
between diencephalon & spinal cord.
o The reticular formation contains 2
functional parts
i. Sensory &
ii. Motor reticular formation.
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131. 1. The sensory RF
o Contains sensory neurons, many in number, small in size.
o Occupies the lateral part of RF of medulla & pons.
o Receives afferent inputs from:
 All ascending sensory pathways
 Cerbral cortex: corticofugal fibers
 Cerebellum, BG, vestibular & red nucleus
 Projects short connecting fibers to the motor RF.
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132. 2. The motor RF
o Contains neurons, which are fewer in number & larger in size than
sensory neurons.
o Located in the medial part of medulla & pons.
o The motor division of RF has 2 parts:
I. Inhibitory RF: found in the medulla and lower part of pons
II. Excitatory RF: found in pons and midbrain
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133. I. The inhibitory RF
o Consists of the medial 2/3 of medullary & lower pontin RF.
o Sends a descending inhibitory tract which inhibits the muscle tone & somatic
spinal reflex.
o Contains 2 sleeping centers [medullary & pontin].
 Which inhibit the excitatory RF, particularly the ascending RAS
(reticular activating system).
o Raphe magnus nucleus
 Is part of the inhibitory RF that sends inhibitory fibres down the spinal
cord to inhibit pain conduction.
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134. II. Excitatory RF
o Consists of the medial 2/3 of the pontin and
midbrain RF
o It has an inherent discharge of excitatory
impulses
o It sends excitatory output neurons in 2
directions:
A. Down ward (the descending branch)
B. Up ward (the ascending branch)
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135. A. Down ward
 Arises from pontin RF
 Descend on the same side as ventral reticulospinal tract
 Facilitate skeletal muscle tone & spinal somatic reflex
B. Up ward
 Arise from the pontin & midbrain RF
 Ascend upward to the thalamus & diffuse to all parts of cerebral cortex.
 It is known as reticular activating system (RAS).
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136. Reticular activating system (RAS)
o It is the ascending excitatory RF that arises from the pontin & midbrain
o Ascend the thalamus and cerebral cortex.
o Function of RAS:
1. Controls level of consciousness by exciting cortical neurons.
2. Increases cortical excitability.
3. Maintains wakefulness.
o Inhibition of RAS brings about sleep.
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137. Function of the RF
i. Control of skeletal muscle tone to maintain posture & equilibrium
ii. Facilitates voluntary movements by stimulating α & γ motor neurons.
iii. It modifies pain sensation by the activity of raphe magnus nucleus
iv. Controls excitability of the cerebral cortex.
v. It controls sleep.
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138. The Limbic system
 Forebrain nuclei & fiber tracts that
form a ring around the brain stem.
 Center for basic emotional drives.
 Consists of structures that make
the border between neocortex &
BS.
 Has 2 components
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139. Components of the Limbic system
1. The limbic lobe: (lower, older
part of the cerebral cortex):
 Subcallosal gyrus
 Cingulate gyrus
 Hippocampus
 Fornix
 Entorhinal cortex
 Olfactory bulb.
2. A group of deep structures:
intimately associated with the limbic
lobe:
 Hypothalamus
 Amygdala
 Anterior nucleus of the thalamus
 Septal nuclei in the upper midbrain
also called septal midbrain area
(SMA).
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140. Neuroscience
The limbic system
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141. Function of the limbic system
1. Olfaction
 Oldest function of the limbic system.
 It is concerned with perception, discrimination & coordination of olfactory
sensation.
2. Emotion
 Amygdala & HT control the somatic, autonomic, endocrine & behavioral responses
in state of emotion.
 Stimulation of amygdaloid nuclei produces anger, fear or rage.
 Destruction of amygdaloid nuclei abolishes fear and aggression.
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142. 3. Memory
 It plays an important role in sorting out the information & deciding
which info to be stored in memory as well as for encoding &
consolidation of memory.
 Particularly, hippocampus & amygdala play crucial role in memory &
learning.
4. Motivation:
 It contains the reward & punishment centers which are responsible for
motivation to take or avoid certain actions.
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143. 5. Control of feeding behavior
 LS, particularly the amygdala is concerned with sorting out the type of food into
edible & inedible type.
 Lesion to amygdaloid nuclei results in hyperphagia.
 The subject with amygdaloid lesion tries to eat any available unlike lesion to the
hypothalamic satiety center.
6. Control of the ANS
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144. 7. Control of sexual behavior:
 Sexual behavior in human is largely controlled by the cerebral cortex.
 But the instinctual desire & reaction are the function of LS & HT.
 Lesion to piriform cortex in the periamygdaloid area produces
hypersexuality.
8. Control of the maternal behavior
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145. Memory
o The ability of the brain to store information & recall it at a later time.
o Storage capacity of human brain 3x108 bit
The unit of information is `bit`
The simplest form of sensory experience
e.g. A figure, a sound, smell.
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146. Memory…
o Info flow to the brain.
During quite reading, the rate of info flow to the brain is 40 bits/sec
During mental calculation, it is 12 bits/ sec
During counting it is 3 bits/sec
o An average rate of info flow is 20 bits/sec .
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147. Types of memory
o There are 4 types of memories
1. Sensory memory (immediate memory)
2. Primary memory (short-term memory)
3. Secondary memory (long-term memory)
4. Tertiary memory (permanent memory)
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148. 1. Sensory memory [immediate memory]
o Storage of sensory info for few seconds.
o Forgetting starts immediately after the info is acquired.
o Info in sensory memory can be transferred into primary or secondary
memory.
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149. 2. Primary memory [short-term memory]
 Memory that lasts from a few minutes to few Hrs.
 Info enters this memory by verbalization.
 Primary memory is not stored in infants & animals.
 The capacity of primary memory is small, but rate of retrieval is rapid.
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150. 3. Secondary memory [long-term memory]
 Memory that lasts for hours, days or years.
 Info is introduced into this memory by two means:
1. From the sensory memory, through stimulation of reward or
punishment system.
2. From the sensory and primary memories by practice or rehearsal.
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151. 4. Tertiary memory [permanent memory]
 The info stored never forgotten.
e.g. One´s name, ability to read & write.
 Info in the tertiary memory comes from secondary memory by years of
practice, which consolidates memory.
 Can not be erased by brain injury and diseases.
 Access to retrieve tertiary memory is rapid.
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152. Consolidation of memory
o The transfer of info from the primary short - term memory into the
secondary long - term memory.
o This process takes from 5 min - 2 hrs.
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153. Memory encoding
o Classification & placing of memory items in their proper memory stores
in the brain as part of consolidation process.
o Hippocampus plays a central role in memory encoding.
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154. Characteristics of different types of memories
Characters Sensory Primary Secondary Tertiary
Capacity: Very small Small Very large Large
Duration: Few seconds Several min-hrs Several hrs-yrs Permanent
Entry into Automatic during Verbalization Practice, reward Frequent
Storge: perception punishment practice
Rate of retrieval: Very rapid Rapid Slow Very rapid
Type of Info: Sensory Verbal All forms All forms
Mechanis of Synaptic Long-term Structural and functional
Storage: potentiation potentiation modification of memory traces
Mehanism of Fading & New info Proactive or retro- No forgett-
Forgetting extinction replaces the old active inhibition ing
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155. Memory Disordes
I. Amnesia (Greek = forgetfulness): inability to remember past
experiences.
o Types of amnesia:
1. Retrograde amnesia
2. Antrograde amnesia
3. Psychogenic or hysterical amnesia
II. Alzheimer's disease & senile dementia: deterioration of intellectual
abilities
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156. 1. Retrograde amnesia: inability to recall events occurred shortly before the
onset of brain malfunction without affecting past memories.
 It occurs due to brain concussion (post-traumatic amnesia), anesthesia, etc.
2. Antrograde amnesia: inability to form new memories.
 Consolidated memories before the onset of amnesia are retained.
 Primary memory is functional, but not consolidated.
 Caused by bilateral lesion to hippocampus and related structures involved in
memory encoding.
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157. 3. Psychogenic or hysterical amnesia
 A rare condition characterized by sudden loss of memory of all info in the
secondary & tertiary memories.
 It is purely functional disorder without any organic disease.
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158. II. Alzheimer's disease & Senile dementia
o Caused by degeneration of the cholinergic nerve fibers in the limbic
system.
Basal forebrain, amygdala, hippocampus.
o Characterized by:
Deterioration of intellectual abilities as impairment of memories, lack
of judgment & inattentiveness.
o The disease occurs at any age.
In old age, it is called senile dementia.
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