Basic Neurophysiology Physiology for Anaesthesia

1. NEUROPHYSIOLOGY I
NPMCN 2024 UPDATE COURSE
Dr John Ogedengbe
Associate Professor of Human Physiology
Department of Human Physiology
Faculty of Basic Medical Sciences,
College of Health Sciences,
University of Abuja, Nigeria

2. INTRODUCTION: BASIC CONCEPTS
Body’s NS is organised into CNS & PNS
Sensory elements of the PNS detect changes in the
Internal & external environ.
They then Send info to the CNS
The CNS receives, process & respond to the info
May generate an output that is sent to effectors
through motor elements of the PNS

3. Neurons and neuroglia are the principal types of
cells found in the nervous sys.
Neurons are commonly called nerve cells
Neuroglia provide structural and metabolic
support for the neurons

4. Nerve impulse is a wave of depolarisation
immediately followed by repolarisation.
This is collectively called an ACTION POTENTIAL.
Changes in ion conductance across the nerve
membranes are responsible for the initiation and
propagation of Action Potential.

5. Functional connection btw a neuron and its
effector cell is called synapse.
Neurons communicate with each other via
synaptic transmission.
Neurotransmitters can be grouped according
to their molecular weight

6. ORGANISATION OF THE NERVOUS
SYSTEM

7. Functional composition of the PNS.

8. C o m p a r i s o n o f S o m a t i c &
A u t o n o m i c N e r v o u s S y s t e m

9. NEUROTRANSMITTERS
They are chemical substances that act
as a mediator for the of nerve impulse
from one neuron to another neuron
through a synapse
Discovered by an Austrian scientist
named Otto Loewi in 1921

10. Criteria For Neurotransmitter
1. It must be found in a neuron
2. It must be produced by a neuron
3. It must be released by a neuron
4. After release, it must act on a target area and
produce some biological effect
5. After the action, it must be inactivated

11. Classification Of Neurotransmitters
Based on Chemical Nature
1. Amino Acids e.g. GABA, glycerine, glutamate, aspartate
2. Amines e.g. Noradrenaline, adrenaline, dopamine,
serotonin, histamine
3. Others: They don’t fit into the above e.g. acetylcholine,
nitric oxide

12. Based on Function
1. Excitatory neurotransmitters e.g. acetylecholine and
noradrenaline. Causes Na ion influx excitatory
postsynaptic potential (EPSP)
2. Inhibitory neurotransmitters e.g gammaaminobutyric
acid (GABA) and dopamine. Causes efflux of K ion
inhibitory postsynaptic potential (IPSP).

14. Inactivation Of Neurotransmitter
1. It can move out of synaptic cleft to the
area where it has no action
2. It is destroyed or disintegrated by specific
enzymes
3. It is engulfed and removed by astrocytes
(macrophages)
4. It is removed by means of reuptake into
the axon terminal.

15. NEUROMODULATORS
These are chemical messenger, which modifies
and regulates activities that take place during the
synaptic transmission. E.g.
 Enkephalins
 Dynorphins
 Endorphins

17. CEREBRAL CORTEX
It is also called pallidum and it consists
of two hemispheres.
Surface area in human beings is 2.2 sq m.
Cerebral hemispheres are separated by a deep
vertical fissure.

19. „
Brodmann Areas
Brodmann area is a region of cerebral cortex
defined on the basis of its cytoarchitecture.
Brodmann areas were originally defined and
numbered in 1909 by Korbinian Brodmann
depending upon the laminar organization of
neurons

21. Frontal Lobe Of Cerebral Cortex
Frontal lobe is divided into two parts:
A. Precentral cortex
B. Prefrontal cortex

22. A. Precentral cortex
Precentral cortex is further divided into three
functional areas
1. Primary motor area
2. Premotor area
3. Supplementary motor area

23. 1. Primary motor area
This extends throughout the precentral gyrus and
the adjoining central sulcus. Areas 4 and 4S are
present here
Special structural feature of this layer is the giant
pyramidal cells called Betz cells in ganglionic
layer.

24. Function of area 4
Area 4 is the center for movement, as it sends all
efferent (corticospinal) fibers of primary motor area.
It activates the lower motor neurons in the spinal
cord: both α-motor neurons and γ-motor neurons

25. Activation of α-motor neurons causes
contraction of extrafusal fibers of the muscles.
Activation of γ-motor neurons causes
contraction of intrafusal fibers leading to
increase in muscle tone.
stimulation leads to discrete isolated
movements in the opposite side of the body

26. Effect of lesion of area 4
Paralysis occurs in contralateral side
Complete paralysis is rare
More severe if area 6 is also affected

27. Area 4S
It is called suppressor area.
It scrutinizes and suppresses the extra
impulses produced by area 4 and inhibits
exaggeration of movements

29. 2. Premotor Area
This includes areas 6, 8, 44 and 45.
Giant pyramidal cells are absent in the ganglionic
layer.
The premotor area is concerned with control of
postural movements by sending motor signals to
axial muscles (muscles near the midline of the
body).

30. Functions of area 6:
i. Coordination of movements initiated by area 4.
It helps to make the skilled movements more
accurate and smooth.
ii. The cortical center for extrapyramidal system.
Lesion leads to loss of skilled movement,
grasping reflex

31. Function of area 8:
i. Conjugate movement of eyeballs.
ii. It is also responsible for opening and closing
of eyelids, pupillary dilatation and lacrimation.
Lesion leads to the eyes turning to the affected
side. Conjugate movements of eyes are lost

32. Broca area:
Broca area is the motor area for speech.
It includes areas 44 and 45
Broca area is present in left hemisphere (dominant
hemisphere) for right-handed people
Function of Broca area:
Broca area is responsible for movements of
tongue, lips and larynx, which are involved in
speech.
Lesion leads to aphasia

33. 3. Supplementary Motor Area
Situated in medial surface of frontal lobe rostral to
primary motor area
Exact function of this area is not well known
It is suggested that it is concerned with
coordinated skilled movements
Lesion in this area leads to the head and eyeballs
turn towards the affected side.

34. B. PREFRONTAL CORTEX OR
ORBITOFRONTAL CORTEX
It is the anterior part of frontal lobe of cerebral
cortex.
Areas present in prefrontal cortex are 9, 10, 11,
12, 13, 14, 23, 24, 29 and 32.
Areas 12, 13, 14, 23, 24, 29 and 32 are in medial
surface
Areas 9, 10 and 11 are in lateral surface.

35. Functions of prefrontal cortex
1. Short-term memories are registered here.
2. Center for planned actions
3. This area is the seat of intelligence; so, it is also
called the organ of mind
4. It is responsible for the personality of the
individuals
5. Responsible for the various autonomic changes
during emotional conditions, because of its
connections with hypothalamus and brainstem.

36. Bilateral lesion or removal of prefrontal cortex in
human beings does not cause paralysis.
It causes lack of initiation and loss of mental
alertness.

38. PARIETAL LOBE
Parietal lobe extends from central sulcus and
merges with occipital lobe behind and temporal
lobe below
Parietal lobe is divided into three functional
areas:
A. Somesthetic area I
B. Somesthetic area II
C. Somesthetic association area

39. PARIETAL LOBE
It is involved in the analysis of:
touch,
pressure,
pain,
knowledge of space position,
the sensation of the environment etc.

41. SOMESTHETIC AREA I
It is also called somatosensory area I or primary
somesthetic or primary sensory area.
It is present in the posterior lip of central sulcus, in
the postcentral gyrus
It has three areas, which are called areas 3, 1 and 2
Receives sensory fibers from thalamus

42. Functions of Somesthetic Area I
Perception and integration of cutaneous and
kinesthetic sensations
Area 1 is concerned with sensory perception. Areas 3
and 2 are involved in the integration of these
sensations.
Sends sensory feedback to the premotor area
Concerned with the movements of head and
eyeballs
Responsible for recognizing the discriminative
features of sensations

43. Functions of Somesthetic Area II
Receives sensory impulses from
somesthetic area I and from thalamus
Though the exact role of this area is not
clear, it is concerned with perception of
sensation

44. Functions of Somesthetic Association
Area
This area is concerned with synthesis of various
sensations perceived by somesthetic area I.
Thus, it forms the center for combined
sensations like stereognosis
Lesion of this area causes astereognosis

45. TEMPORAL LOBE
Temporal lobe of cerebral cortex includes
three functional areas:
A. Primary auditory area
B. Secondary auditory area or auditopsychic
area
C. Area for equilibrium.

46. Primary Auditory Area
Primary auditory area includes:
1. Area 41
2. Area 42
3. Wernicke’s area.

47. Functions of Primary Auditory Area
Areas 41 and 42 are concerned only with the
perception of auditory sensation (sound).
Wernicke’s area is responsible for the
interpretation of auditory sensation and
sending information to Broca area

49. Functions of Secondary Auditory Area
This includes area 22
It is concerned with interpretation of auditory
sensation along with Wernicke’s area.
Also concerned with storage of memories of
spoken words

50. Functions of Area For Equilibrium
Area for equilibrium is in the posterior part
of superior temporal gyrus
It is concerned with the maintenance of
equilibrium of the body.
Stimulation of this area causes dizziness,
swaying, falling and feeling of rotation

51. Lesion in Temporal Lobes
1. Aphasia
2. Auditory disturbances e.g. tinnitus, auditory
hallucinations with sounds like buzzing, ringing or
humming.
3. Disturbances in smell and taste sensations
4. Dreamy states: The patients are not aware of their
own activities and have the feeling of unreality
5. Visual hallucinations associated with hemianopia

52. OCCIPITAL LOBE
Occipital lobe is called the visual cortex
It is divided into three:
1. Primary visual area (area 17)
2. Secondary visual area or visuopsychic area
(area 18)
3. Occipital eye field (area 19).

53. Functions of Occipital Lobe
1. Primary visual area (area 17) is concerned
with perception of visual sensation
2. Secondary visual area (area 18) is concerned
with interpretation of visual sensation and
storage of memories of visual symbols
3. Occipital eye field (area 19) is concerned with
reflex movement of eyeballs.

54. Lesion In The Occipital Lobe
Lesion in the upper or lower part of visual
cortex results in hemianopia.
Bilateral lesion leads to total blindness.

55. Basal Ganglia
 Basal ganglia are the
scattered masses of
gray matter
submerged in
subcortical
substance of
cerebral hemisphere

56. FUNCTIONS OF BASAL GANGLIA
1. CONTROL OF MUSCLE TONE
 It decrease the muscle tone by inhibiting gamma motor neurons
through descending inhibitory reticular system in brainstem
 Thus, lesion leads to increase muscle tone, leading to rigidity
2. CONTROL OF MOTOR ACTIVITY
i. Regulation of Voluntary Movements: These are initiated by
cerebral cortex but controlled by basal ganglia
ii. Regulation of Conscious Movements: I.e. Cognitive control.
Fibers in connection with cerebral cortex are concerned with
regulation of conscious movements
iii. Regulation of Subconscious Movements

57. 3. CONTROL OF REFLEX MUSCULAR ACTIVITY
 Basal ganglia are responsible for the coordination and
integration of impulses for particularly visual and
labyrinthine reflexes
4. CONTROL OF AUTOMATIC ASSOCIATED MOVEMENTS
 Eg the swing of the arms while walking, appropriate facial
expressions while talking or doing any work.
5. ROLE IN AROUSAL MECHANISM
 Globus pallidus and red nucleus are involved in arousal
mechanism because of their connections with reticular
formation.

58. 6. ROLE OF NEUROTRANSMITTERS IN THE FUNCTIONS
OF BASAL GANGLIA
1. Dopamine - substantia nigra to corpus striatum
2. Gammaaminobutyric acid (GABA) - corpus striatum &
substantia nigra
3. Acetylcholine - cerebral cortex to caudate nucleus &
putamen
4. Substance P - globus pallidus reaching substantia nigra
5. Enkephalins - globus pallidus reaching substantia nigra
6. Noradrenaline - basal ganglia and reticular formation
7. Glutamic - subthalamic nucleus to globus pallidus &
substantia nigra.

60. CEREBELLUM
The cerebellum sits astride the main sensory and
motor systems in the brainstem
It is connected to the brainstem on each side by:
superior peduncle
middle peduncle, and
inferior peduncle.
The cerebellum weighs only 10% as much as the
cerebral cortex, but its surface area is about 75% of
that of the cerebral cortex.

62. Function of Principal Afferent Systems
to the Cerebellum
Vestibulocerebellar
Vestibular impulses from labyrinths, direct and via
vestibular nuclei
Dorsal spinocerebellar
Proprioceptive and exteroceptive impulses from body
Ventral spinocerebellar
Proprioceptive and exteroceptive impulses from body

63. Cuneocerebellar
Proprioceptive impulses, especially from head and
neck
Tectocerebellar
Auditory and visual impulses via inferior and superior
colliculi
Pontocerebellar
Impulses from motor and other parts of cerebral
cortex via pontine nuclei
 Olivocerebellar
Proprioceptive input from whole body via relay in
inferior olive

64. Functions of Major Parts of the
Cerebellum
Vestibulocerebellum
Regulates tone, posture and equilibrium by receiving
impulses from vestibular apparatus.
Information regarding gravity, linear movement and
angular acceleration to vestibulocerebellum comes
through vestibulocerebellar tract.
Vestibulocerebellum, in turn, sends signals to spinal
cord via vestibulospinal and reticulospinal tracts.

65. Spinocerebellum
 Regulates tone, posture and equilibrium by receiving sensory
impulses form tactile receptors, proprioceptors, visual receptors
and auditory receptors.
 Tactile and proprioceptive impulses are localized in the
spinocerebellum
 In cerebral cortex, different parts of the body are represented in an
inverted manner.
 But in cerebellum, different parts are represented in upright
manner.

66. Corticocerebellum
 It is concerned with the integration and regulation of well-
coordinated muscular activities.
These include:
i. Damping action
ii. Control of ballistic movements
iii. Timing and programming the movements
iv. Servomechanism
v. Comparator function

67. LIMBIC SYSTEM
The word "limbic" means "border."
Originally, the term "limbic" was used to describe
the border structures around the basal regions of
the cerebrum
But the term limbic system has been expanded to
mean the entire neuronal circuitry that controls
emotional behavior and motivational drives.
A major part of the limbic system is the
hypothalamus, with its related structures.

70. Papez Circiut

71. FUNCTIONS OF LIMBIC SYSTEM
1. OLFACTION
2. REGULATION OF ENDOCRINE GLANDS
3. REGULATION OF AUTONOMIC FUNCTION
4. REGULATION OF FOOD INTAKE
5. CONTROL OF CIRCADIAN RHYTHM
6. REGULATION OF SEXUAL FUNCTIONS
7. ROLE IN EMOTIONAL STATE
8. ROLE IN MEMORY
9. ROLE IN MOTIVATION

72. RETICULAR FORMATION
Reticular formation is a diffused mass of
neurons and nerve fibers, which form an ill-
defined meshwork of reticulum in central
portion of the brainstem.
It is situated in brainstem & extends
downwards into spinal cord & upwards up to
thalamus and subthalamus

73. Afferent
connections of
reticular
formation

74. Efferent
connections
of reticular
formation

75. Functions Of Reticular Formation
Based on functions, reticular formation is
divided into two systems:
A. Ascending reticular activating system
B. Descending reticular system.

77. Functions of ARAS
1. The ARAS is concerned with arousal, alertness,
maintenance of attention and wakefulness. Hence,
it is called Ascending Reticular Activating System.
Stimulation produces wakefulness by generalized
activation of entire brain
2. The ARAS also causes emotional reactions
3. The ARAS plays an important role in regulating the
learning processes and the development of
conditioned reflexes.

78. Fxn of Descending Reticular
System
Descending reticular system includes
reticular formation in brainstem,
reticulospinal tract and reticular formation in
spiral cord
It is divided into two:
1. Descending facilitatory reticular system
2. Descending inhibitory reticular system.

79. Descending facilitatory reticular system
i. Facilitation of somatomotor activities
a. Maintains muscle tone by exciting the gamma motor
neurons in spinal cord;
b. It facilitates the movements of the body.
c. It plays a role in wakefulness and alertness by
activating the ARAS.
ii. Facilitation of vegetative functions
It is the center for facilitation of the autonomic functions
such as cardiac function, blood pressure, respiration,
gastrointestinal function and body temperature.

80. Descending Inhibitory Reticular System
i. Control of somatomotor activities
a. it inhibits the gamma motor neurons
b. It is responsible for smoothness & accuracy
of voluntary movts.
c. It also controls the reflex movements.
ii. Control of vegetative functions.
It is the center for inhibition of several
autonomic functions