nurophysiology for undergraduate students

1. For BScStudents
Dereje.E(MSc)
AU-CMHS,AUG 2023
CENTRAL NERVOUS SYSTEM
1

2. Divisions of the Nervous System
2

4. Overview of the NS…
 The NS is an intricate, highly organized network
of billions of neurons & even more neuroglia.
 Human brain has an estimated number of 1011
Neurons and 1014 Synapses.
 Principal cell types that make up the nervous
system are:
– Neurons &
– Neuroglial cells

5. Overview function of the NS…
Neurons
 Functional, signal conducting cells specialized for:
– Sensory function
– Generation of thought
– Storage of memory
– Integrates idea
– Coordinates muscular activities

6. 6
Overview of the NS…
Neuroglia
 Supporting cells.
 20x outnumber neurons.
(the guy to the right had an
inordinate amount of them)
 Can multiply after maturation.
 Potential causes of glioma.
(brain tumour)

7. 7
The Neuroglia
 Non neural cells found in association with neurons.
 Provide supporting functions to the nervous system.
 They are:
1. Microglial cells
2. Astrocytes
3. Oligodendrocytes
4. Ependymal cells
5. Schwann cells
6. Satelite cells

8. 8
The Neuroglia…
1. Microglial cells
 Specialized immune cells that act as the
macrophages of the CNS.
 Why is it important for the CNS to have its own
army of immune cells?
2. Astrocytes
 Star-shaped, abundant & versatile.
 Provide nourishment to the CNS & involved in
the formation of the blood brain barrier (BBB).

9. 9
The Neuroglia
3. Oligodendrocytes
 Produce myelin sheath which provides electrical
insulation for certain neurons in the CNS.
4. Ependymal cells
 Low columnar epithelial cells that line ventricles of
the brain & the central canal of the spinal cord.
 Some are ciliated which facilitates the movement
of cerebrospinal fluid (CSF).

10. 10
Neuroglia…cont’d
5. Schwann cells
• Form myelin sheaths around the larger nerve
fibers in the PNS.
• Vital to neuronal regeneration.
6. Satellite cells
• Small cells that line the exterior surface of the PNS.
• Regulate the external chemical environment.

11. Neuroglia…cont’d
11

12. NEURON
 Defined as the structural and functional unit
of NS.
 Similar to any other cell in the body, having
nucleus and all the organelles in cytoplasm.
 However, it is different from other cells by
two ways:
1. Has axon and dendrites
2. Neuron does not have centrosome.
3. So, it cannot undergo division.

13. 13
Neurons
• There are different types of neurons but most have certain
structural and functional characteristics in common:
– Cell body (soma)
– One or more specialized, slender processes
(axons/dendrites)
– An input region (dendrites/soma)
– A conducting component (axon)
– A secretory (output) region (axon terminal)

14. 14
Soma
• Contains nucleus plus most normal organelles.
• Biosynthetic center of the neuron.
• Contains a very active & developed rough
endoplasmic reticulum (RER) which is responsible
for the synthesis of neurotransmitters (NTs).
– neuronal RER is referred to as the Nissl body.
• Contains many bundles of protein filaments
(neurofibrils) which help to maintain the shape,
structure, and integrity of the cell.

15. 15
Neuronal Processes
 Clusters of somata in the:
– CNS are known as nuclei
– PNS are known as ganglia
 Armlike extensions emanating from every neuron.
– Tracts = Bundles of processes in the CNS
– Nerves = Bundles of processes in the PNS
 2 types of processes that differ in structure and
function:
– Dendrites and Axons

16. 16
Dendrites
 Thin, branched processes whose main function is to
receive incoming signals.
 Effectively increase the surface area of a neuron to
increase its ability to communicate with other
neurons.
 Convey info towards the soma thru the use of
graded potentials.
Neuronal Processes…

17. 17
Axons (Myelinated /unmylinated)
 Most neurons have single axon (long up to 1m) process
designed to convey info away from the cell body.
– Originates from a special region of the cell body called the
axon hillock.
 Transmit APs from the soma toward the end of the
axon where they cause NT release.
 Often branch sparsely, forming collaterals.
– Each collateral may split into telodendria which end in a
synaptic knob, which contains synaptic vesicles-
membranous bags of NTs.
Neuronal Processes…

18. 18

19. Neuronal Processes…
Axolemma = axon plasma membrane.
Surrounded by a myelin sheath, a wrapping of lipid
which:
– Protects the axon
– electrically isolates it and
– Increases the rate of AP transmission
• This wrapping is never complete.
• There are gaps where there is no myelin – these
are nodes of Ranvier.
• The myelin sheath is made by ________ in the CNS
and by _________in the PNS.

20. 20
Functional classification of neurons
 There are three classes of neurons:
1. Sensory (afferent) neurons
- conduct impulses from periphery to the center
2. Motor (efferent) neurons
- conduct impulses from CNS to the periphery
3. Interneuron (association neurons)
- integrative
- conduct impulses from sensory to motor area.

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Morphological classification of Neurons
• Structurally neurons are classified into 3 classes:
1. Multipolar neurons
 found in the CNS
 motor in function
2. Bipolar neurons:
 found in retina & inner ear
 sensory in function
3. Unipolar neurons:
 located in the ganglia of
spinal & cranial nerves.
 sensory in function

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Synapse
- The region where there is a transfer of message
from a neuron to the effector cell (postsynaptic
neuron, muscle).
- The junction between 2 cells in which 1 must be
a neuron.
- Two types:
1. Electrical synapse (direct) &
2. Chemical synapse (indirect)

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Synapse…
1. Electrical Synapse
 AP is transmitted
through a gap
junction.
 Very fast transmittance
used for :
– escape responses in
invertebrates.
– coordinated activity of
cardiac muscle cells.

24. 24
Synapse…
2. Chemical Synapses
 Chemical messenger (neurotransmitter) is released from
a neuron into the synaptic cleft.
 NT in the synaptic cleft binds to a receptor on the target
cell.
 Acts slower than electrical synapses because the NT
must diffuse across the synaptic cleft to bind the
receptor.
 Advantages over electrical synapses = one-way direction
of communication; presynaptic cell to postsynaptic cell.

25. Synapse…
25

26. 26
Synaptic Transmission
 There are 3 types of synapses
1. Neuro-neuronal junction (between 2 neurons)
2. Neuro-muscular junction (between neuron & muscle)
3. Neuro-glandualr junction (between neuron & gland)
 There are 3 types of neuroneuronal junctions
(axo-dendritic, axo-somatic & axo-axonic junctions)
 Two modes of transmission (chemical and electrical)
 One neuron will transmit impulse to another neuron or to a
muscle or gland cell by releasing chemicals called
neurotransmitters.

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Components of Axo-Somatic synapse
1. Presynaptic terminal
 contains neurotransmitter
(NT)
2. Synaptic cleft
 contains ECF and
Enzymes
3. Postsynaptic neuron
 contains receptor for the
action of NT

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Mechanism of Chemical Synaptic
Transmission
1. AP reaches the presynaptic axon
terminal of the presynaptic cell &
causes V-gated Ca2+ channels to
open.
2. Ca2+ rushes in, binds to regulatory
proteins & initiates NT release by
exocytosis.
3. NTs diffuse across the synaptic
cleft and then bind to specific
receptors on the postsynaptic
membrane & initiate postsynaptic
potentials.

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Mechanism of…cont’d
4. NT-Receptor interaction results in either EPSP/IPSP.
• When the NT-R combination triggers the opening of
ligand gated Na-channels, this leads to membrane
depolarization, EPSP.
e.g. Ach on Nicotinic receptor
• When the NT-R combination triggers the opening of
ligand gated K or Cl-channels, this leads to
membrane hyperpolarization, IPSP.
e.g. GABA on GABAb receptor

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Excitatory Vs Inhibitory Synapses
1. Excitatory
- more likely to have action potential
- depolarization
2. Inhibitory
- less likely to have action potential
- hyperpolarization
- membrane stabilization

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1. Excitatory Synapses
• Depolarizes postsynaptic cell
– brings membrane potential closer
to threshold by opening or
closing ion channels
• Opens channels that are equally
permeable to Na and K
– causes depolarization because of
the stronger force of Na to flow
into the cell.
• Depolarization=EPSP (excitatory
postsynaptic potential)

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2. Inhibitory Synapses
• Neurotransmitter binds to
receptor, channels for either K
or Cl open
hyperpolarizes the cell
• If K channels open
– K moves out  IPSP
(inhibitory postsynaptic
potential)
• If Cl channels open, either
– Cl moves in  IPSP
– Cl stabilizes membrane
potential

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Neurotransmitter Removal
 Why do we want to
remove ACh from the
neuro-muscular junction?
 How was ACh removed
from the NMJ?
 NTs are removed from the
synaptic cleft via:
– Enzymatic degradation
– Diffusion
– Reuptake

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Properties of synaptic transmission
 Unidirectional conduction
 Synaptic delay (0.5 -1.0m/s)
 Fatigue
- Decrease in response of postsynaptic neurons after repetitive
stimulation by the presynaptic neurons
 Synaptic potentiation (facilitation)
- Increase in postsynaptic responses caused by previous post
synaptic stimulation

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 PH
- Alkalosis ↑ Synaptic transmission
- Acidosis ↓ Synaptic transmission
 Hypoxia ↓ Synaptic transmission
 Drugs
- Caffeine, Theophylline, Theobromine
↑Synaptic transmission
- Strychnine
↑ Synaptic transmission
- Hypnotics, Anesthetics, tranquilizers
↓ Synaptic transmission
Factors Affecting Synaptic transmission

36. Nervous System
 Controls all activities of the body.
 It is quicker than other control system.
 Primarily, nervous system is divided
into two parts:
1. Central nervous system
2. Peripheral nervous system.

37. „
Central Nervous System
 CNS includes brain and spinal cord.
 It is formed by neurons and supporting cells
called neuroglia.
 The CNS contains more than 100 billion neurons.
 Brain and spinal cord are arranged in two layers,
– Gray matter consists of somata, dendrites, and
unmyelinated axons.
– White matter consists primarily of myelinated
axons.

38. Cont.……
 In brain, white matter is placed in the inner part and
gray matter in outer part.
 In spinal cord vis versa,
 Brain is situated in the skull.
 It is continued as spinal cord in the vertebral canal
through the foramen magnum.
 surrounded by three layers of meninges
– Dura mater
– Arachnoid mater and
– Pia mater

39. Cont.…
 The space between arachnoid mater and pia
mater is known as subarachnoid space.
 This space is filled with a fluid called
cerebrospinal fluid (CSF).

40. 40
Brain Regions
 Cerebrum
 Diencephalon
- Thalamus
- Hypothalamus
 Brainstem
- Midbrain
- Pons
- Medulla ob.
 Cerebellum
Cerebellum

41. Spinal cord
 lies loosely in the vertebral canal. It
 foramen magnum up to the lower border of first
lumbar vertebra.
 Covered by meninges
– Pia matter
– Dura matter and
– Arachnoids

42. Spinal Cord
 The spinal cord has two functions:
1. Common passageway for ascending and descending
tracts.
 Neurons in the white matter of the spinal cord transmit
 sensory signals from peripheral regions to the brain
 motor signals from the brain to peripheral regions.
2. Centre for Spinal Cord reflexes.
 Neurons in the gray matter of the spinal cord integrate
incoming sensory information and respond with motor
impulses that control muscles (skeletal, smooth, or
cardiac) or glands.
42

43. Spinal cord
 Ascending fibers of spinal cord
 Anterior spinothalamic tract
– crude touch like itching and tickling
 Lateral spinothalamic tract
– sensations of pain and temperature
 Ventral spinocerebellar
– subconscious kinesthetic sensation (proprioceptive
impulses from muscles, tendons and joints)

44. Spinal cord
 Dorsal spinocerebellar tract
– subconscious kinesthetic sensation
– This tract is uncrossed
– Lesion affects on the same side
 Spinotectal tract is concerned with
– spinovisual reflex
 Fasciculus gracilis and fasciculus cuneatus
– are together called ascending posterior column tracts.
– Fasciculus gracilis contains the fibers from lower
extremities and lower parts of the body
– Fasciculus cuneatus contains fibers from upper part of
the body,
– Both terminate in the medulla oblongata

45. Spinal cord
 Tracts of the posterior white column convey impulses
of following sensations:
– Fine (epicritic) tactile sensation
– Tactile localization
– Tactile discrimination
– Sensation of vibration
– Stereognosis and
– to differentiate the weight of different objects

46. Spinal cord
Descending tracts
 These tracts carry motor impulses from brain to spinal cord.
 Descending tracts of spinal cord are of two types:
A. Pyramidal tracts
 cerebral cortex towards spinal cord
 For voluntary motor activity
B. Extrapyramidal tracts.
 position of head and body during angular and linear
acceleration.
 maintenance of muscle tone, respiration and diameter
of blood vessels
 reflex movements

47. 47
Brain Regions
 Cerebrum
 Diencephalon
- Thalamus
- Hypothalamus
 Brainstem
- Midbrain
- Pons
- Medulla ob.
 Cerebellum
Cerebellum

48. Brainstem
 Is the part of brain formed by;
– medulla oblongata
– pons and
– midbrain.
 Contains;
– ascending and descending tracts between brain
and spinal cord
– centers for regulation of vital functions

49. Medulla oblongata
 Is the lowermost part of brain.
 Functions of medulla
– Respiratory centers, which maintain normal rhythmic
respiration.
– Vasomotor center controls blood pressure and heart rate.
– Deglutition center regulates the pharyngeal and
esophageal stages of deglutition.
– Vomiting center induces vomiting
– Salivatory nuclei control the secretion of saliva
– Nuclei of 12th, 11th, 10th cranial nerves are located in the
medulla oblongata.

50. Pons
 A bridge between medulla and mid brain
 Nuclei of 8th, 7th, 6th and 5th cranial nerves
are located in pons
 Connects cerebellum with cerebral cortex.
 Pneumotaxic and apneustic centers for
regulation of respiration

51. MIDBRAIN
 Lies between pons and diencephalon.
 It consists of two parts:
A. Tectum
B. Cerebral peduncles.
 Tectum is formed by two structures:
1. Superior colliculus-light reflex
2. Inferior colliculus-auditory reflexes

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Diencephalon
• Forms the central core of
the forebrain
• 3 paired structures:
1. Thalamus
2. Hypothalamus
3. Epithalamus
 All 3 are gray matter

53. 53
Thalamus…
– Composes 4/5 of the diencephalon.
– Forms most of the walls of the 3rd ventricle.
– Acts as relay center through which all sensory information
(except olfactory) passes to the cerebrum.
• Lateral geniculate nuclei:
–Relay visual information.
• Medial geniculate nuclei:
–Relay auditory information.
• Intralaminar nuclei:
–Activated by many sensory modalities.
–Projects to many areas.
»Promotes alertness and arousal from sleep.

54. Hypothalamus
 The hypothalamus (hypo- under)
is the small portion of the
diencephalon that lies below the
thalamus and above the pituitary
gland.
 Although its size is small, the
hypothalamus controls many
important body activities, most of
them related to homeostasis.
 The chief functions of the
hypothalamus are as follows:-

55. 55
Function of Hypothalamus
• Controls the ANS
• Influences HR, BP, resp. rate, GI motility, pupillary
diameter.
• Can you hold your breath until you die?
 Anterior nuclei acts as a parasympathetic center
 Posterior nuclei acts as a sympathetic center
• Endocrine function
– Controls adenohypophyseal hormones
Releases hormones that influence hormonal secretion from the
anterior pituitary gland.
– Controls neurohypophyseal hormones
 Releases oxytocin and vasopressin
– Controls adrenal medulla

56. Function of Hypothalamus
• Regulation of body temperature
 The heat losing center (anterior HT)
 Heat gaining center (posterior HT
• Contributes to the regulation of sleep, wakefulness,
emotions, sexual arousal, anger, fear, pain, and pleasure.
• Controls food intake (hunger sensation):
 Feeding center (lateral HT),
 Satiety center (ventromedial HT)
56

57. 57
Function of Hypothalamus
 Control of water-electrolyte balance
 Thirst center (lateral HT, OVLT)
 Osmoreceptors (anterior HT, SFO)
 Control of sexual behavior: libido, sexual activities are
controlled by cerebral cortex, limbic system and HAT.
 Relation to sleep:
 Lesion to posterior HT leads to somnelence.
 Hypothalamic neurons project on RAS where sleep center is
located.
Effect of HT lesion:
 Diabetes inspidus, hypo-/hyperthermia, sleep disturbance,
hormonal disturbance, hyperphagia, emotional diturbance

58. 58
Epithalamus
• Located above the thalamus.
• Contains the pineal gland which releases melatonin.
 Because the pineal gland secretes the hormone melatonin, it
is part of the endocrine system.
 Melatonin promotes sleepiness and contributes to the setting
of the body’s biological clock.
• Contains a structure called the habenula – involved in food
and water intake.

59. 59
Cerebellum
 Lies inferior to the cerebrum and
occupies the posterior cranial fossa.
 2nd largest region of the brain.
 10% of the brain by volume,
but it contains 50% of its
neurons.

60. 60
Cerebellum
 The 2 cerebellar hrs. are
separated by a shallow groove
called vermis
 In the vermis, most motor
function of cerebellum
controlling movt of axial body;
neck, shoulder, & lips are
located.
 The intermediate zone of
cerebellar h. controls muscle
movt of upper and lower limbs.
 The lateral zone of cerebrall h.
controls timing & planning of
sequential motor movts.
Anterior
lobe
Posterior
lobe
Flocculnodular
lobe
Vermis
Primary fissure

61. 61
Functional Parts of Cerebellum
1. 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 and posture
2. Spinocerebellum/paleocerebellum:
 It comprises vemis and paravermal (medial) parts
 It receives signal from muscle spindle and Golgi tendon organs
 Function: it is concerned mainly with control of muscle tone
3. Cerebrocerebellum/pontocerebellum/neocer.
 It includes the lateral cerebellar hemispheres
 It is the newest part, connected to cerebrum
 Function: Concerned w/t control of skilled voluntary movts
initiated by cerebral cortex

62. 62
Afferent Cerebellar Connections
A. From the brain
1. Tecto-cerebellar fibers: originate from the tectum (sup. & inf.
Colliculus) in the MB --- SCP --- different parts of the
cerebellum.
 Transmit visual and auditory signals to the cerebellum.
2. Cortico-ponto-cerebellar fibers: Started from motor,
somatosensory & association areas---pontin relay nuclei---
MCP---contra lateral cerebro-cerebellum.
 They transmit signals from the cerebral cortex to the
cerebellum to produce intended motor plan of movt.
3. Olivo-cerebellar pathway: Originates from the inf. Olive---
ICP---to all parts of cerebellum.
 Inf. Olive is stimulated by fibers from the motor cortex, BG,
RF & the spinal cord about muscle tone and movts.

63. 63
Afferent Cerebellar connections (cont´d)
4. Vestibulo-cerebellar tract: originates from the vestibular
apparatus--- vestibular nuclei---ICP---vestibulocerebellum.
 Transmits signals about body posture and equilibrium.
5. Reticulo-cerebellar pathway: Originates from the different
parts of RF---MCP & ICP---Spinocerebellum (vermis).
 Transmits signals of various sensations particularly muscle
tone and movts.

64. 64
Function of Cerebellum
1. Control of posture and equilibrium
 It is the function of the vermis and archicerebellum
 Cerebellum compares signals coming from the vestibular
apparatus and proprioceptive signals from periphery to
maintain posture and equilibrium.
2. Control of muscle tone
 Generally the neocerebellum is facilitatory to muscle tone,
while the paleocerebellum is inhibitory.
 The former is dominant.
 Cerebellar output signals through reticulspinal tract,
vestibulospinal tract, rubrospinal tract increase muscle tone.

65. Function of Cerebellum
65
3. Control of voluntary movt
 Cerebellum influences voluntary movt through the following
functions:
 Planning: Cerebrocerebellum is concerned with the intention
& plan of movt.
 Timing of movt: Cerebellum determines the start and
termination of sequential movts.
 Damping of movt: ending of movt without osscillation.
 Ballistic movt: rapid & short movts such as typing.

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Cerebellar Syndrome
 Produced by lesion to the cerebellar nuclei.
 Cerebellar syndrome appeared on the same side of the
lesion.
 There are three main types
1. Atonia/Atetonis/Hypotonis: marked decrease in muscle tone
due to loss of the excitatory effects of dentate nucleus and
interposituse nuclei on muscle tone.
Manifestation: Flaccid feel of muscle and Pendular kneejerk
2 Asthenia: Lack of strength
Manifestation: Muscle weakness due to difficulty in initiating
and maintaining muscle contraction.
3. Ataxia: Incoordination of voluntary movts.
 Cerebellar ataxia is manifested by:-

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Cerebellar syndrome (cont´d)
• The cerebellum can be permanently damaged by trauma
or stroke or temporarily affected by drugs such as
alcohol.
• These alterations can produce ataxia – a disturbance in
balance.

68. 68
Cerebrum
• Largest portion of brain (80% mass).
• Most developed in man
• Responsible for higher mental functions, concerning
perception of
 Fine sensation
 Learning
 Memory
 Speech
 Judgment and planning.

69. Cerebral cortex
 It consists of two hemispheres.
 Connected by Corpus callosum
 Surface of the cerebral cortex is characterized
by sulci and gyri
– Sulcus is a slight depression
– groove and gyrus is a raised ridge.
 Cerebral cortex consists of gray matter that
surrounds the deeper white matter.

70. Lobes of cerebral cortex
1. Frontal
2. Parietal
3. Occipital
4. Temporal lobe.

71. Lobes of cerebral cortex
 Lobes of each hemisphere are demarcated by four
main fissures and sulci:
1. Central sulcus- between frontal and parietal lobes
2. Parieto-occipital sulcus- between parietal and
occipital
lobe
3. Sylvian fissure or lateral sulcus- between parietal
and temporal lobes
4. Callosomarginal fissure -between temporal lobe
and limbic area.

72. Cerebral hemisphere
 Right hemisphere is called representational
hemisphere
 it is associated with;
– Artistic and visuospatial functions like;
– Judging the distance,
– Determining the direction,
– Recognizing the tones, etc.
 Lesion in representational hemisphere causes
only mild effects like astereognosis.

73. Cerebral hemisphere
 Left hemisphere is the dominant hemisphere
 About 75% of the right-handed persons.
 Lesion in dominant hemisphere leads to
language disorders.

74. Wernicke’s area
When Wernicke's area in the dominant hemisphere of
an adult person is destroyed:-the person normally loses
almost all intellectual functions associated with
language or verbal symbolism.
Such as:-
the ability to read,
the ability to perform mathematical operations, and
even the ability to think through logical problems.
– Lateral prefrontal cortex is also used for language
comprehension and complex word analysis
74

75. 75
Broca’s Area
• Typically found in only one
hemisphere (often the left), anterior
to the inferior portion of the
premotor cortex.
• Directs muscles of tongue, lips, and
throat that are used in speech
production.
• Involved in planning speech
production and possibly planning
other activities.
• Involves articulation of speech.
• In damage, comprehension of
speech is impaired.

76. 76
Memory
 Memory is the ability of the brain to store information and
recall it at a later time.
 It was calculated that 10 neurons are required to store 1 bit
of information
 The total storage capacity of the human brain is about
3x108 bits
 Medial temporal lobe: Consolidates short term into long
term memory.
 Hippocampus is critical component of memory.
 Acquisition of new information, facts and events requires
both the medial temporal lobe and hippocampus.

77. 77
Types of Memory
There are 4 types of memories
I. Sensory memory (immediate memory)
II. Primary memory (short-term memory)
III. Secondary memory (long-term memory)
IV. Tertiary memory (Permanent memory)
Sensory memory
 It is the storage of sensory info for few seconds
 Forgetting starts immediately after the info is acquired.
 A gradual decline in the amount of info is called fading of info.
 The spontaneous disappearance of info from the memory is
called extinction of info.
 Infos in sensory memory can be transferred into primary or
secondary memory.

78. 78
Types of memory (cont´d)
Primary memory
 This is a memory that lasts from a few minutes to few Hrs
 Info enters this memory by verbalization, ie. Describing
the items in words.
 Primary memory is not stored in infants and animals
 The capacity of primary memory is small, but rate of
retrieval is rapid.

79. Types of memory (cont´d)
Secondary memory
 This is a memory that lasts for Hrs, 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, ie. Attentive repetition of information or experience.
 The capacity of secondary memory is very large
 Information are stored according to their significance
 Retrieval is time taking
 Forgetting of info in the secondary memory occurs through
interference, by previously stored info (pro active inhibition) or
subsequently stored info (retro active inhibition).
79

80. 80
Types of memory (cont´d)
Tertiary memory
 This is the permanent memory.
 The info stored never forgotten.
 eg. One´s name, ability to read and write
 Infos in the tertiary memory comes from secondary memory
by years of practice, which consolidates memory.
 Tertiary memory can not be erased by brain injury and
diseases.
 Access to retrieve tertiary memory is rapid

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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 duringVerbalization Practice, reward/ Frequent
Storgae: 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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Memory Disordes
Amnesia (Gr = forgetfulness)
 = It means that inability to remember past experiences.
Types of amnesia:
1. Retrograde amnesia:
2. Antrograde
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, ECT.

83. Memory Disordes (cont´d)
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.
Pschogenic or hysterical amnesia
 A rare condition chara/zed by sudden loss of memory
of all info in the secondary and tertiary memories.
 It is purely functional disorder without any organic
disease.
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Memory Disordes (cont´d)
Alzheimer's disease and Senile dementia
 AD is caused by degeneration of the cholinergic nerve fibers in
the limbic system (basal forebrain, amygdala, and
hippocampus).
 The disease is chara/zed by deterioration of intellectual
abilities as impairment of memories, lack of judgment and
inattentiveness
 The disease occurs at any age.
 In old age, it is called senile dementia
 An anticholinesterase drug, physiostegmin (eserine) produces
improvement but does not stop progression of the disease.

85. Cerebrospinal fluid
 Is the clear, colorless and transparent fluid.
 It circulates through ventricles of brain,
subarachnoid space and central canal of spinal cord.
 It is a part of extracellular fluid (ECF).
SITE OF FORMATION
 CSF is formed by choroid plexuses
 situated within the ventricles.
 Choroid plexuses are tuft of capillary
 CSF is formed by the process of secretion that
involves active transport mechanism.

87. „Functions of cerebrospinal fluid
1. Protective Function
 CSF acts as fluid buffer
 acts like a cushion (countercoup injury).
2. Medium of Exchange
3. Diagnostic purpose
4. To remove weast products