5. Located immediately after the spinal cord
All the nerve fibers that relay signals between the spinal cord, cortex, and cerebellum
pass through the brainstem.
Run through the core of the brainstem and consisting of loosely arranged neuron cell
bodies intermingled with bundles of axons is the reticular formation.
The reticular formation is involved mainly in the mechanisms that regulate sleep and
wakefulness and focus attention (consciousness).
The brainstem contains nuclei involved in processing information for 10 of the 12 pairs
of cranial nerves.
Parts of brain stem: a) Medulla oblongata b) Pons c) Midbrain
Introduction
6. Medulla Oblongata
Externally resembles the spinal cord, except for two triangular elevations (pyramids)
on its inferior side and an oval enlargement (olive) on each lateral surface.
Most of the fibers decussate through its pyramidal region
Serves as relay center
The gray matter consists of several important nuclei for the cranial nerves and
sensory relay.
◦ CN IX, CN XI, CN XII, CN X and CN VIII.
◦ The nucleus gracilis and the nucleus cuneatus
◦ The inferior olivary nuclei and the accessory olivary nuclei of the olive mediate impulses
passing from the forebrain and midbrain through the inferior cerebellar peduncles to the
cerebellum.
◦ Three other nuclei within the medulla oblongata function as autonomic centers for
controlling vital visceral functions.
◦ 1. Cardiac center 2. Vasomotor center 3. Respiratory center.
◦ Other nuclei of the medulla oblongata function as centers for reflexes involved in sneezing,
coughing, swallowing, and vomiting.
6
Decussation
7. Pons
◦ A rounded bulge on the inferior surface of the brain,
between the midbrain and the medulla oblongata
◦ Serves as relay center that consists of
◦ The surface transverse fibers that connect with the cerebellum
through the middle cerebellar peduncles.
◦ The deeper longitudinal fibers are part of the motor and
sensory tracts that connect the medulla oblongata with the
tracts of the midbrain.
◦ Has pontine nuclei
◦ CN V, CN VI, CN VII, and the vestibular branches of the CN VIII.
◦ Other nuclei are apneustic and pneumotaxic areas.
7
8. Midbrain
Is the short section of the brain stem between the diencephalon and
the pons
CN III & CN IV
Consists of
◦ The corpora quadrigemina (four rounded elevations on the
posterior portion of the midbrain) which are:
Superior colliculi: it involves in the visual reflex by controlling
extraocular muscles
Inferior colliculi: it involves in the auditory reflex
◦ The cerebral peduncles are a pair of cylindrical structures
composed of ascending and descending projection fiber tracts that
support and connect the cerebrum to the other regions of the
brain.
◦ The red nucleus. It connects the cerebrum and the cerebellum.
Functions in reflexes concerned with motor coordination and
maintenance of posture.
8
11. • Diffused mass of neurons and nerve fibers forming
an ill-defined meshwork of reticulum in the central
portion of the brainstem. i.e poorly differentiated
• loosely arranged neuron cell bodies intermingled with
bundles of axons
Various nuclei: 1) Nuclei of medullary reticular formation
2) Nuclei of pontine reticular formation
3) Nuclei of midbrain reticular formation
• It receives and integrates input from all regions of
the central nervous system and processes a great
deal of neural information.
Introduction to Reticular formation
12. AFFERENT & EFFERENT CONNECTIONS OF RETICULAR FORMATION
Reticular
Formation
Reticular
Formation
Cerebellum
Red Nucleus
Thalamus,
Hypothalamus
Spinal Cord
Cortex
Substantia Nigra
Tectum
EFFERENT CONNECTION TO THE
RETICULAR FORMATION
AFFERENT CONNECTION TO THE
RETICULAR FORMATION
Cortex
Thalamus
Corpus Striatum
Cerebellum
Spinal Cord
Sensory
Pathways
(Touch, pain,
temperature,
kinesthestic
sensation)
Optic, auditory
olfactory and
taste pathways
14. ASCENDING RETICULAR ACTIVATION SYSTEM - ARAS
Receives fibers from the sensory pathways via long
ascending spinal tracts.
Alertness, maintenance of attention and wakefulness.
Emotional reactions, important in learning processes.
Tumour or lesion – sleeping sickness or coma.
15. DESCENDING RETICULAR ACTIVATION SYSTEM - DRAS
INHIBITORY
• Smoothness and accuracy of
voluntary movements;
• Reflex movements;
• Regulates muscle tone;
• Maintenance of posture;
• Control of vegetative functions.
FACILITATORY
• Maintain the muscle tone;
• Facilitates autonomic functions;
• Activates ARAS.
Inhibition: uses serotonin
Excitation: uses acetycholine
16. Functions of Reticular formation
1. Control of muscle tone and reflexes: mediates postural reflexes through alpha and gamma
motor neurons
2. Muscles of facial expression
3. Influence all ascending pathways: Central transmission of sensory impulses
4. Control of Autonomic nervous system: Respiration, Cardiovascular functions
5. Arousal and level of consciousness: Ascending reticular formation system: stimulation will
arouse the sleeping person, mediates alerting responses and consciousness and maintain the
cerebrum in a waking state
6. Influence on the biological clock--Sleep: serotonin-secreting neurons in raphe nuclei mediate
non-REM sleep
7. Control of endocrine nervous system
18. Introduction
Located in the inferioposterior portion of the brain (Hind brain)
Consist of about 50% of all neurons in the brain and receives approx. 200 million input fibres
Constitute 10% of the total brain volume
Like cerebrum, it has two large hemispheres – right & left
Division: Anatomically, Phylogenetically and Functionally
Anatomically
Anterior lobe
Posterior lobe
Flocculonodular lobe
Phylogenetically
Archecerebellum
Paleocerebellum
Neocerebellum
Functionally
Vestibulocerebellum
(flocculonodular & part of vermix)
Spinocerebellum
(vermix & intermediate zones)
Cerebrocerebellum
(lateral zones)
19. Anatomical and Functional Areas of the Cerebellum
Anatomically, the cerebellum is divided into 3 lobes by 2 deep fissures.
◦ (1) the anterior lobe,
◦ (2) the posterior lobe, and
◦ (3) the flocculonodular lobe.-functions with the vestibular system in
controlling body equilibrium.
Functional parts of cerebellum
◦ Functionally cerebellum is organized along the longitudinal axis into:
◦ Vermis- control functions for muscle movements of the axial
body, neck, shoulders, and hips are located in this area.
◦ The intermediate zone of the hemisphere is concerned with
controlling muscle contractions in the distal portions of the upper
and lower limbs, especially the hands, fingers, feet, and toes.
◦ The lateral zone - joins with the cerebral cortex in the overall
timing and planning of sequential motor movements.
Posterolateral
fissure
Primary
fissure
20. Topographical Representation of the Body in the Vermis and Intermediate Zones.
Axial portions of the body lie in the vermis whereas the limbs and facial regions lie in
the intermediate zones.
These topographical representations receive afferent nerve signals from all the
respective parts of the body, as well as from corresponding topographical motor
areas in the cerebral cortex and brain stem.
In turn, they send motor signals back to the same respective topographical areas of
the cerebral motor cortex, as well as to topographical areas of the red nucleus and
reticular formation in the brain stem.
lateral portions do not have topographical representations of the body.
◦ They receive signals almost exclusively from the cerebral cortex, especially the premotor
areas, and from somatosensory and sensory association areas.
21. Neuronal Circuit of the Cerebellum
Input Pathways to the Cerebellum
◦ Afferent cerebral cortex
◦ An extensive and important afferent pathway is the Corticopontocerebellar pathway
◦ originates in the cerebral motor and premotor cortices and also in the cerebral somatosensory cortex.
Other important afferent tracts originate from brain stem.
◦ (1) an extensive Olivocerebellar tract, which passes from the inferior olive to all parts of the
cerebellum and is excited in the olive by fibers from the cerebral motor cortex, basal
ganglia, widespread areas of the reticular formation, and spinal cord. They terminate in
lateral part.
◦ (2) Vestibulocerebellar fibers, some of which originate in the vestibular apparatus and from
the brain stem vestibular nuclei, with almost all of these fibers terminating in the
flocculonodular lobe and fastigial nucleus of the cerebellum
◦ (3) Reticulocerebellar fibers, which originate in different portions of the brain stem reticular
formation and terminate in the vermis).
◦ 4. Tectocerebellar fibers from superior and inferior colliculi
21
22. Afferent Pathways From the Periphery.
Receives direct information from lower part of CNS mainly through:
◦ Dorsal spinocerebellar tract and
◦ enters the cerebellum through the inferior cerebellar peduncle and terminates in the vermis and
intermediate zones of the cerebellum ipsilaterally
◦ Transmit signals that come mainly from the muscle spindles and to a lesser extent from other somatic
receptors throughout the body, such as Golgi tendon organs, large tactile receptors of the skin, and joint
receptors.
◦ Ventral spinocerebellar tract.
◦ enters the cerebellum through the superior cerebellar peduncle, but it terminates in both sides of the
cerebellum.
◦ receive much less information from the peripheral receptors.
◦ excited mainly by:
◦ motor signals arriving in the anterior horns of the spinal cord through the corticospinal and rubrospinal
tracts and
◦ internal motor pattern generators in the cord itself. Thus, this ventral fiber pathway tells the cerebellum
which motor signals have arrived at the anterior horns; this feedback is called the efference copy of the
anterior horn motor drive.
22
23. Outputs from Cerebellum
◦ All outputs from the cerebellum originate from the 3 cerebellar deep
nuclei
◦the dentate (from lateral zone) to thalamus
◦Interposed (from intermediate) to cortex, BG & RF
◦fastigial nuclei (from vermix) to brain stem
All the deep cerebellar nuclei receive signals from:
◦ (1) the deep sensory afferent tracts to the cerebellum (excitatory).
◦ (2) the cerebellar cortex (reach the nuclei later and is inhibitory).
23
24. Major efferent pathways from cerebellum consists of the following
pathways:
◦ 1. output from the vermis which passes through the fastigial nuclei into the medullary
and pontile regions of the brain stem.
◦ This circuit functions in close association with the equilibrium apparatus and brain stem
vestibular nuclei to control equilibrium, as well as in association with the reticular formation
of the brain stem to control the postural attitudes of the body.
◦ 2. output from the intermediate zone which passes through the interposed nucleus to
◦ the ventrolateral and ventroanterior nuclei of the thalamus and then to the cerebral cortex,
◦ to several midline structures of the thalamus and then to the basal ganglia and the red
nucleus and reticular formation of the upper portion of the brain stem.
◦ This complex circuit mainly helps coordinate the reciprocal contractions of agonist and antagonist muscles in the peripheral portions of the limbs,
especially in the hands, fingers, and thumbs.
◦ 3. output from cerebellar cortex of the lateral zone which passes to the dentate
nucleus, next to the ventrolateral and ventroanterior nuclei of the thalamus, and,
finally, to the cerebral cortex. Coordinates sequential motor activities
24
26. Functional unit of the cerebellum are
mainly two types of fibers
◦ the climbing fiber
◦ A single impulse in it will cause single but prolonged AP in
Purkinje cell followed by weak 2o impulses
◦ Each make about 300 synapses with 5 to 10 Purkinje cells.
After sending branches to several deep
◦ the mossy fiber
◦ Send collaterals to excite the deep nuclear cells, then proceed
to the granule cell layer of the cortex, where they also synapse
with hundreds to thousands of granule cells. In turn, the
granule cells send extremely small axons up to the molecular
layer of the cerebellar cortex.
◦ Each axon bifurcates in the molecular layer, sending a
collaterals (parallel fibers) in opposite directions. The parallel
fibers, run parallel to the folds of the cerebellar cortex (folia)
and synapse with projections of purkinje cells.
◦ 80,000 to 200000 parallel fibers synapse with each purkinje
fiber. Excitation of purkinje fibers by the parallel fibers is weak
and short producing simple spike.
26
27. Functions
◦Cerebellum involves in:
◦ Regulation of movement: cerebellum controls the rate, force, range and direction of
movement.
◦ In the timing of motor activities
◦ In control of rapid, smooth progression from one muscle movement to the next. -
seen during rapid muscular activities such as running, typing, playing the piano, and
even talking.
◦ In the controlling intensity of muscle contraction when the muscle load changes i.e
balance and even eye movement.
◦ To aid the cerebral cortex in planning the next sequential movement a fraction of a
second in advance while the current movement is still being executed
◦ In correcting mistakes which occurred in previous movements.- motor learning.
27
28. Abnormalities of Cerebellum – usually involves deep nuclei
Abnormalities Area affected Description
Ataxia Deep nuclei Uncoordinated movements
Dysmetria Deep nuclei, spinocerebellar tract Inability to predict extent of movements.
Past Pointing Deep nuclei Movement ordinarily
goes beyond the intended mark.
Dysdiadochokinesia Deep nuclei Inability to Perform Rapid Alternating
Movements
Dysarthria— Deep nuclei Failure of Progression in Talking
Intention tremor Deep nuclei Overshooting an intended mark or point and
then vibrating back and forth several times
before settling on the mark.
Cerebellar Nystagmus Usually flocculonodular lobes Tremor of the Eyeballs.
Hypotonia deep cerebellar nuclei, particularly of the
dentate and interposed nuclei
Decreased Tone of the Musculature
28
30. Introduction
Scattered masses of gray matter submerged in subcortical substance of cerebral hemisphere
Structures that assist the motor cortex in performing its functions
Group of nuclei in the brain that are interconnected with the cerebral cortex, thalamus and brain stem
In lower animals, basal nuclei function as motor cortex
31. Components of basal nuclei
Basal nuclei is associated with 5 nuclei. 3 located rostrally while 2 are located dorsally.
(i) Putamen (ii) Caudate (iii) Globus pallidus ( internal & external)
(iv) Subthalamic (v) Substantia nigra (pars reticulata & pars compacta)
Striatum
32.
33. Input to basal ganglia
All the cortical regions
give input to basal nuclei
except primary visual
and primary auditory
cortices.
43. R
enhanced
or diminished
response
Modulation
glu
DA D1-Rs in the direct pathway:
1) increase GluR phosphorylation
2) alters ionic conductances
to amplify cortical input
Direct transmission vs. modulation
Striatal medium spiny neuron
46. Release of DA in substantia nigra, as well as
in striatum is required for control of
movement by the basal nuclei
47. Synaptic DA release
in striatum
Smith and Bolam 1990
modified from Fallon et al. 1978
SNc DA cell
Somatic release
(Jaffe et al. 1998)
Dendritic release
(Geffen et al. 1976;
Rice et al. 1994)
Somatodendritic DA
release in SNc
48. DA neuron
Striatonigral axon
terminal (direct pathway)
GABA
SNr
SNc
SNr output neurons
(GABAergic, tonically active, project to thalamus)
are inhibited by the direct, striatonigral pathway,
leading to disinhibition of the thalamus and facilitation of movement
50. DA neuron
Presynaptic D1 dopamine receptors
enhance striatonigral GABA release
Somatodendritic
dopamine
Striatonigral axon
terminal (direct pathway)
GABA
SNr
SNc
Somatodendritic DA release, therefore, enhances the effect
of the direct striatonigral pathway to facilitate movement
52. Functions of Basal Nuclei
• Basal nuclei are involved in generation of goal-directed voluntary movements:
• Motor learning
• Motor pattern selection
•They modulate the thalamic outflow from the motor cortex
•They help in planning and execution of smooth movement – control timing and
intensity of movement
•They involve in regulation of emotion – limbic loop
•They involve in cognition and learning – associative loop
53.
54. Hypokinetic disorders
• insufficient direct pathway output
• excess indirect pathway output
Hyperkinetic disorders
• excess direct pathway output
• insufficient indirect pathway
output
Pathophysiology of Basal nuclei
If there is damage to basal nuclei, there would be difficulties in the initiation of
voluntary movement, specifically damage to the Globus pallidus which results
into inability to maintain posture - Athetosis
Parkinson’s disease
Huntington’s disease
Hemiballism
55. Parkinson’s Disease: decreased dopamine from SN
decreased inhibition of the inhibition excessive inhibitory
output classic signs of PD (hypokinesia, bradykinesia) – via
decreased thalamic signals to cortex decreased
corticospinal outflow.
Huntington’s Disease: decreased striatal (GABA, encephaline)
output and decreased inhibition of Gpe enhanced excitatory
effects of indirect path decreased inhibition via direct path
hyperkinesis.
Hemiballism: similar mechanism (subthalamic n. lesion).
57. Introduction
Like basal nuclei, limbic system is dominant in lower animal
Connect with neocortex in performing higher functions – learning and memory and behaviour
It has direct connection with olfactory – smell function
Anatomically refers to areas surrounding the diencephalon (limbus = border) and bordering the cerebral
cortex.
58. Components of limbic system
Amygdaloid body
Hippocampus
Cingulate gyus
Parahippocampal gyrus
Hypothalamus
Mamillary bodies
Anterior nucleus of thalamus
Septal nuclei
Parts of basal nuclei
59. Papez Circuit
Mammillary bodies
Other hypothalamic nuclei
Septal nuclei
Substantia innominata
(Basal nucleus of Meynert)
Hippocampal Formation
(hippocampus
and dentate gyrus)
Anterior Thalamic
nuclear group
Cortex of Cingulate Gyrus
Parahippocampal Gyrus
Neocortex
Fornix
Mammillothalamic
tract
There is a
prolonged
afterdischarged
following
stimulation.
61. Functions of Limbic System
Study of functions of limbic system is based on 3 methods:
• Electrical stimulation of specific location
• Destruction of some tissues located in site
• Surgical removal of specific part (Ablation)
• Perception of smell
• Involves in control of autonomic nervous system
• Regulation of endocrine gland
• Control of circadian rhythm
• Principal role in Behavior
• Principal role in memory
62. Specific functions
It involves in the control of Emotional Behavior which include Fear, Rage, Placidity or
Docility
Fear: if the amygdaloid nuclei is stimulated , the individual will exhibit fear. Lesion of amygdaloid nuclei will
abolish fear at the usual stimuli and also abolish ANS responses like sweating and pupillary dilatation.
Placidity: if there is lesion in the piriform cortex, hippocampus and cingulate gyrus it will lead to placidity or
docility.
Rage: In normal human being the stimulation and determination of rage lies between fear & docility
It involves in the control of Motivation drive: Motivation lies between reward and punishment
(approach & avoidance systems)
Reward: stimulation of reward centre give a sense of relaxation, pleasure, contentment and serenity. The centre
include nucleus accumben, medial forebrain bundle, lateral and ventromedial nuclei of hypothalamus
Punishment: stimulation of punishment centre make the individual feel persecuted, fear, displeasure and pain.
The center include central gray area at midbrain, some nuclei of hypothalamus and thalamus and some parts of
amygdaloid and hippocampus.
63. It involves in the regulation of sexual behavior which include
coordination of copulation, learning of sexual activities, seeking out for
partner. Piriform cortex plays vital role
Regulation of maternal behavior which include protection and affection
for younger ones. Lesion in the cingulate gyrus and retrosphenial part of
limbic system leads to depression in maternal behavior.
It involves in the regulation of feeding behavior which include licking of
lips, moving of mouth. Stimulation leads to overfeeding (hyperphargia)
and sometime indiscriminate injection of all food. Lesion of amygdaloid
leads to it. When satiety centre is stimulated there will be ceasation of
feeding – anorexia nervosa.
64. Pathophysiology of limbic system
Voracious appetite: Increased (perverse) sexual activity
Docility: Loss of normal fear/anger response
Memory loss: Damage to hippocampus
Kluver-Bucy Syndrome: Results from bilateral destruction of amygdala.
Characteristics:
Increase in sexual activity.
Compulsive tendency to place objects in mouth.
Decreased emotionality.
Changes in eating behavior.
Visual agnosia.
69. Concept of cerebral hemisphere dominance
Wernicke’s area more developed in one hemisphere, responsible for
verbal symbolism and related intelligence. Dominance is related to
Language
95% of population has a left dominant hemisphere.
Wernicke’s area can be as much as 50% larger in the dominant
hemisphere.
Non-dominant side related to other forms of sensory intelligence (music,
sensory feelings).
Damage to dominant Wernicke’s area leads to dementia.
71. 71
Brain Organization and Handedness
Close to 90% of people are right-handed and close to 10% are left-handed and a small number
are ambidextrous (use both hands)
95% of right-handers process speech primarily in the left hemisphere
◦ left-handers: around 65% in left hemisphere, 15-20% in right hemisphere, 15-20% in both
More than 90% of people are born with the left hemisphere area that controls the movement
of the right hand is bigger
◦ They tend to use the right hand, this area grows and become dominant
Left handed people have their right cerebral hemisphere area that controls the
movement of the left hand bigger
◦ If they use the left hand then this area grow and become dominant
◦ They still can convert and the younger the more easier if they start to use their right
hand instead and then they become right handed
◦ Same applies for using the legs
72. Intellectual Functions of the Prefrontal Association Area
This area is responsible for calling forth stored information and using it to
obtain a goal
It also responsible for concerted thinking in a logical sequence
◦ damage causes an inability to keep tract of simultaneous bits of information, easily distracted
It is area where thought is elaborated
◦ prognosticate, plan, consider consequences of motor actions before they are performed
◦ correlate widely divergent information, control one’s activities
◦ Personality trait and behavior that confines to values and manners of the culture
73. 73
Language areas
Located in a large area surrounding the left (or language-dominant) lateral sulcus
Major parts and functions:
◦ Wernicke’s area – involved in sounding out unfamiliar words –sensory aspect
of speech- damage cause sensory aphasia (Receptive aphasia)
◦ Broca’s area – speech preparation and production- motor aspect of speech –
damage cause motor aphasia (expressive aphasia)
◦ Both Wernicke’s and Broca’s area damage cause global aphasia
◦ Lateral prefrontal cortex – language comprehension and word analysis
◦ Lateral and ventral temporal lobe – coordinate auditory and visual aspects of
language
74. 74
1. primary auditory area
recognition of the
sound as a word
2. interpretation of the
word and the thought
that the word expresses
in Wernicke’s area
3. formation of the
word that expresses a
particular thought
4. transmission via the
arcuate fasciculus to
Broca’s area
5. activation of motor programs
in Broca’s area for control of
word formation
6. transmission of signals to motor
cortex to control speech muscles
Pathways for Auditory Communication
75. Pathways for Visual Communication
1. receive the visual input in
primary visual area
2. processing of the visual
information in the parietal-
temporal-occipital association
cortex, the angular gyrus region
3. visual input reaches full
level of interpretation in
Wernicke’s area
4. then to Broca’s area for
motor formation of the word
5. transmission of signals to motor
cortex to control speech muscles
76. 76
Sensory Aspects of Communication
Destruction of the
visual and auditory
association areas
results in an inability
to understand the
written or spoken
word.
Wernicke's aphasia
Corpus callosum - connects the
two hemispheres and allows
transfer of information.
Damaged cause bizarre types of
anomalies
77. Thoughts formation
Thought can be defined as an idea, plan, an intellectual function, perception or awareness as a
product of mind.
Neural mechanism for thought is not known.
Most likely it is a specific pattern of simultaneous neural activity in many brain areas.
Destruction of cerebral cortex does not prevent one from thinking. - However, depth of thought and
level of awareness may be less.
Holistic theory of thought
“Thought results from a pattern of stimulation of many parts of the nervous
system at the same time in an orderly sequence.”
It involves cerebral cortex, and lower areas such as thalamus, limbic system, and upper
reticular formation of the brain stem.
The lower areas are believed to determine the general nature of the thought, giving it such
qualities as pleasure, displeasure, pain, comfort, crude modalities of sensation, localization to
gross areas of the body. Some basic thoughts depend almost entirely on lower centers.
Specific stimulated areas of the cerebral cortex determine discrete characteristics of the thought, such as
(1) specific localization of sensations (2) the feeling of the texture (3) visual recognition of shapes
78. Speech formation
When a thought is expressed verbally, it is called the speech. Speech is defined as the expression of thoughts by
production of sound, bearing a definite meaning.
If it is expressed by visual symbols, it is known as writing. If visual symbols or written words are expressed
verbally, that becomes reading.
Mechanism of Speech Production
Speech depends upon coordinated activities of central speech apparatus and peripheral speech apparatus.
• Central speech apparatus consists of higher centers, i.e. the cortical and subcortical centers.
• Peripheral speech apparatus includes larynx or sound box, pharynx, mouth, nasal cavities, tongue and lips.
It functions in coordination with respiratory system, with the influences of motor impulses from respective motor areas of
the cerebral cortex.
Development of speech involves integration of three important areas of cerebral cortex:
1. Wernicke area- Speech understanding
2. Broca area - Speech synthesis
◦ develops the pattern of motor activities required to verbalize the words. The pattern of motor activities is sent to motor
area.
◦ responsible for the movements of tongue, lips and larynx.
3. Motor area – Activation of peripheral speech apparatus
78
79. Learning
Learning is the neural mechanism by which a person changes his or her
behavior as a result of experiences.
Memory is the mechanism for storing what is learned.
It is the ability of previous experiences to modify the inborn reactions
or create new ones or
It is the acquisition of knowledge or skills as a result of experiences and
consequently it can alter behavior on basis of this experiences
Learning is the process by which we acquire knowledge about the world
(Eric Kandel, 2000)
Learning refers to a more or less permanent change in behavior which
occurs as a result of practice (Kimble, 1961)
80. Types
1. Associative
(Relation of one stimulus to
another)
a. Classic conditioning
b. Operant conditioning
2. Non-associative
(ignore or react )
a. Habituation
b. Sensitization
81. Associative Learning
In this type of learning, the subject learns about the relationship that can associate one stimulus to another
It is a conditioned process which results in the formation of learned responses called conditioned reflexes
Conditioned reflex is an automatic response to a stimulus (conditioned stimulus) which did not previously evoke
response acquired by repeatedly associating this stimulus with another stimulus (unconditioned stimulus)
a) Classic Conditioning
This type of conditioned reflexes was 1st described by Pavlov (Russian Physiologist)
He noticed that his experimental dogs salivate just on seeing the animal house keeper who used to feed. Some
sort of association had developed in the brains of these animals between visual stimuli related to seeing the
housekeeper (conditioned stimulus) and food ingestion (unconditioned stimulus for salivation when food is
placed in mouth)
82. b) Operant Conditioning
In this type of conditioning the subject is taught to perform some voluntary action in response to a particular
stimulus (visual or sound stimulus) that alert him to perform the learned action in order to obtain reward to
avoid punishment
Alerting signal acts as conditioned stimulus whereas pleasant or unpleasant event that follow performance of
learned response represents unconditioned stimulus. E.g car driver and traffic light
83. Non-associative Learning
In this type of learning, the subject learns whether to ignore or react to a certain stimulus
It is a simple way of learning that does not need association between 2 stimuli
It is 2 types;
A) Habituation B) Sensitization
Habituation
It is a gradual decrease in the response to stimulus when it is frequently repeated. It is simple and widespread
Examples:
A loud and unexpected sound produces looking towards the source of sound, change in heart rate, and change in
blood pressure. If the sound turns to be insignificant, its repetition results in little or no response
Sensitization
It is a potentiation in the response to stimulus (painful or pleasant) when it is frequently repeated. It is simple and
widespread
Examples:
One normally ignore stray dogs by habituation, but if he is bitten, he will become more attentive and develop
aversion reaction to them for long time .
84. Memory
Memory is the process by which that knowledge of the world is encoded,
stored, and later retrieved (Kandel, 2000)
It is the ability of the brain to store information and recall it at later time
Memory is a phase of learning
learning has three stages:
1. acquiring, wherein one masters a new activity . . . or memorizes verbal material . . .
2. retaining the new acquisition for a period of time; and
3. remembering, which enables one to reproduce the learned act or memorized material
87. Sensory Memory
•Duration: very short (about 0.5 seconds)
•Capacity: very small (15-20 bits). Entry into storage: automatic during perception. Access to storage: very
rapid
1. Vision: iconic memory 2. Hearing: echoic memory
•Mechanism:
•1. Stimulation of reverberating circuits → repeated activation of neurons
•2. Synaptic sensitization if sensory experience coupled with painful stimuli
•3. Post-tetanic potentiation: multiple stimuli at presynaptic terminal →↑ Ca content
in presynaptic terminal →↑ release of neurotransmitters
•Mechanism of forgetting:
1. Fading (spontaneous and gradual decline in the amount of information)
2. Extinction (spont. disappearance of information from memory)
88. Short-term Memory
Duration: (min to hours) Capacity: Small bits of information Entry into storage: verbalization
Recall or access to storage: rapid
Mechanism:
Made by formation of temporary memory traces
Memory trace: is a newly developed pathway or signal transmission resulting from facilitation
of new synapses → creation of new circuits in the brain
This occurs by
1. Long term potentiation of synapses
2. Changes in physical properties of postsynaptic membrane → ↑ sensitivity to chemical transmitters
Mechanism of forgetting: New information replaces old
89. Long-term potentiation of synapse
1. The binding of glutamate to its NMDA receptors
and simultaneous depolarization of the
postsynaptic membrane causes the NMDA
receptor channels to open.
2. This opening of the NMDA receptor channels
allows Ca2+ to enter.
3. The entry of Ca2+ into the postsynaptic neuron
causes long-term potentiation in that neuron.
4. The entry of Ca2+ into the postsynaptic neuron
also activates nitric oxide synthase, causing nitric
oxide production.
5. The nitric oxide then acts as a retrograde
messenger, diffusing into the presynaptic neuron
and somehow causing it to release more
neurotransmitter.
90. Long-term Memory
Duration: (hours to years ) Capacity: Very large, Information stored according to its significance
Entry into storage: practice or and punishment or reward
Recall or access to storage: slow
Mechanism:
Made by formation of memory engrams (long-lasting memory traces) formed by structural changes in
presynaptic terminals
memory engrams made up by;
1. increase in number of vesicles
2. increase in number of presynaptic terminals
3. increase in release sites of chemical transmitters
4. generation of new receptor sites
5. long term potentiation
Engrams remain for long time up to several years
Formation of new engrams requires protein synthesis
Mechanism of forgetting:
1. Proactive inhibition by previously stored materials (more common)
2. Retroactive inhibition by subsequently stored material
91. Permanent Memory
Duration: (permanent)
Capacity: Very large
Entry into storage: very frequent practice
Recall or access to storage: very rapid (recall not affected by brain injury (like name, write, and read)
Mechanism:
Advanced stage of long-term(permanent engrams)
Mechanism of forgetting :
No forgetting
92. Phases of memory
Encoding-information for each memory is assembled from the different
sensory systems and translated into whatever form necessary to be
remembered. This is presumably the domain of the association cortices and
perhaps other areas.
Consolidation-converting the encoded information into a form that can be
permanently stored. The hippocampal and surrounding areas apparently
accomplish this.
Storage-the actual deposition of the memories into the final resting places–
this is though to be in association cortex.
Retrieval-memories are of little use if they cannot be read out for later use.
Less is known about this process.
93. Encoding of memory
Hippocampus
store
Mamillary
body
Orbitofrontal
cortex
Basal forebrain
Meynerts Nucleus
Amygdala
store
(Temporal lobe)
Neocortex
store
All bits
Select important information
(reward or punishment)
Cholinergic projections
Cholinergic projections
Cholinergic projections
It means classification and
placing memory items in their
proper memory stores in brain
94. Consolidation of memory
It means the process of conversion of
STM to LTM
It takes from 5 min to 2 hrs
It is interrupted by
1. Deep anaesthesia
2. Brain concussion
3. Electroconvulsive therapy
Brain regions involve are:
• Hippocampus
• Anterior & lateral temporal lobe,
• Medial temporal lobe
• Amygdala
95. Pathophysiology of Memory
1. Amnesia -Loss of memory
Types:
i. Anterograde amnesia: Failure to establish new long-term memories.
◦ It occurs because of lesion in hippocampus.
ii. Retrograde amnesia: Failure to recall past remote long-term memory.
◦ It occurs in temporal lobe syndrome. Can be due to damage to thalamus.
2. Dementia- Progressive deterioration of intellect, emotional control, social behavior and
motivation associated with loss of memory.
◦ It is an age-related disorder. Usually, it occurs above the age of 65 years.
Causes
◦ Most common (~75%) is Alzheimer disease (progressive neurodegenerative disease)
◦ Others- hydrocephalus, Huntington chorea, Parkinson disease, viral encephalitis, HIV infection,
hypothyroidism, hypoparathyroidism, Cushing syndrome, alcoholic intoxication, poisoning by high dose of
barbiturate, carbon monoxide, etc
95
96. Intelligence
Intelligence can be defined as higher comprehension levels of brain function. It
also means intellectual capacity of humans for intellectual functions - learning,
understanding, reasoning and all mental activities
A major share of our sensory experience is converted into its language
equivalent before being stored as memory and before being processed for other
intellectual purposes.
Therefore, the Wernicke’s/knowing general interpretative / the tertiary
association area is very important.
◦ This area is confluence of the different sensory interpretative areas which is involve in interpreting
the complicated meanings of different patterns of sensory experiences. Its destruction leads to loss
main intellectual functions.
98. The brain is constantly involved in the control of a huge range of activities both
when awake and during sleep. Its activity can be monitored indirectly by placing
electrodes on the scalp. If this is done in such a way as to minimize electrical
interference from the muscles of the head and neck, small oscillations are seen that
can reflect the overall activity of the brain. These electrical oscillations are known as
the electroencephalogram or EEG.
Electroencephalography is the study of electrical activities of brain.
Electroencephalograph is the instrument used to record EEG
Significance of EEG
Diagnosis of neurological disorders and sleep disorders.
1. Epilepsy, which occurs due to excessive discharge of impulses from cerebral cortex
2. Disorders of midbrain affecting ascending reticular activating system
3. Subdural hematoma during which there is collection of blood in subdural space
Introduction
99. Procedure of recording EEG
The electrodes called scalp electrodes from the instrument are placed over
unopened skull or over the brain after opening the skull or by piercing into
brain. Electrodes are of two types, unipolar and bipolar electrodes. While
using bipolar electrodes, both the terminals are placed in different parts of
brain.
When unipolar electrodes are used, the active electrode is placed over
cortex and the indifferent electrode is kept on some part of the body away
from cortex.
100. EEG waves
Alpha wave
Alpha wave consists of rhythmical waves, which appear at a frequency of 8 to 12 waves/second
with the amplitude of 50 µV. Alpha waves are synchronized waves. It is obtained in inattentive
brain or mind as in drowsiness, light sleep or narcosis with closed eyes. It is abolished by visual
stimuli or any other type of stimuli or by mental effort.
Beta wave
Beta wave includes high frequency waves of 15 to 60 per second but, the amplitude is low, i.e. 5 to
10 µV. Beta waves are desynchronized waves. It is recorded during mental activity or mental
tension or arousal state. It is not affected by opening the eyes. During higher mental activity, the
frequency waves of 30 to 100 per second appear.
101. Delta wave
Delta wave includes waves with low frequency and high amplitude of 1 to 5 per second and 20 to 200 µV
respectively. It is common in early childhood during waking hours. In adults, it appears mostly during deep
sleep. Presence of delta waves in adults during conditions other than sleep indicates the pathological process
in brain like tumor, epilepsy, increased intracranial pressure and mental deficiency or depression. These
waves are not affected by opening the eyes.
Theta Waves
Theta waves are obtained generally in children below 5 years of age. These waves are of
low frequency and low voltage waves. Frequency of theta waves is 4 to 8 per second and
the amplitude is about 10 µV.
102. Introduction to Sleep
Sleep is the natural periodic state of rest for mind and body with closed eyes characterized by
partial or complete loss of consciousness.
It is common experience that people are active during the day and sleep at night. In some other
animals, the pattern is reversed. This cyclical variation in activity is called the sleep-wakefulness
cycle.
Sleep is defined as unconsciousness from which the person can be aroused by sensory stimuli .
Coma, on the other hand , is a state of loss of consciousness from which the person cannot be
aroused.
Loss of wakefulness
A fundamental function for physical and mental health
Not loss of conciousness; only a “shift”
An unconcious state which can be in part modified by sensory stimulations sleep centres
103. Sleep centers
1. Raphe nuclei in lower pons and medulla
– Targets (efferents): Reticular formation,
thalamus, neocortex, hypothalamus, limbic
system, dorsal roots of spinal cord
– Neurotransmitter: Serotonin (5HT)
2. Medullary synchronization area” in nuc.
tractus solitarius level: May stimulate the Raphe
nuclei?
3. Diencephalic sleep areas: Rostral of
hypothalamus especially the suprachiasmatic area,
Intralaminar and anterior thalamic nuclei
4. Basal forebrain sleep area: Preoptic area and
Broca’s diagonal band.
*low freq stimulation (8/s) leads to sleep; while
high freq. causes to wake up
104. • Adenosine - Inhibits the specific cholinergic neurons of RAS which stimulates the cortex
• PgD2-Increases tendency to sleep when released from medial preoptic area of hypothalamus
• PgE2-wakefulness
• IL-1
sleep inducing factor
Muramil Peptide
Rythmic stimulation of mechanoreceptors (10 Hz or lower)
Possible mechanisms of sleep-wake cycle
• Wakefulness: Excitatory effects of RAS and thalamus
Stimultion of RAS reinforced by the positive feedback from cortex and peripheral nervous system
RAS gets “tired” during the day.
• Sleep: Diminished RAS activity allows sleep centers to inhibit RAS - - - - and drowsiness begin...
• Sleep-Wake Cycle: Circadian rhythm of Biological clock
• Suprachiasmatic nucleus – Biological clock. - Related to natural light dark cycle
1. Retinohypothalamic pathway-Pineal gland-Melatonin
2. Humoral fototransduction-circulating receptors?
3. Intergeniculate pathway?
Some factors known to interfere with sleep
105. Types
1. Slow-wave sleep (NonREM): has 4 Phases
2. Paradoxal/desynchronized sleep (REM- Rapid Eye Movements)
Slow-Wave (nonREM) Sleep
Entrance to sleep
• Takes appr. 90 minutes with 5-20 minutes intervals
• Peripheral vessel tone and vegetative body functions decrease
• Muscle tone decreases
• 10-30% decrease in blood pressure, respiration rate and basal metabolism
• Spinal reflexes can be elicited but strech (deep tendon) reflexes are absent.
Dreams cannot be remembered
• Theta and delta waves in EEG
• Duration and frequency decrease with age
Phases of Sleep
107. Phase-1 nonREM
• Transition period between wakefulness and sleep; takes approximately 1-15
minutes.
• Eyes closed and relaxed...
• Light sleep, hallucination-like visions...
• α (alpha) waves weaken, slower θ (delta) waves emerge.
Phase-2 nonREM
First stage of the real sleep; takes about 20 minutes...
• Sleep spindles: 12-14 Hz sharp waves appear for 1-2 seconds...
• Slow eye movements...
• Hard to awaken...
• Fragments of dreams?
108. Phase-3 nonREM
• Half-way deep sleep
• Body temperature and blood pressure decreases
• Harder to awaken
• Low frequency δ (theta) waves
• Sleep spindles are decreased
• No slow eye movements
Phase-4 nonREM
• Deepest sleep; takes about 30-40 mins.
• δ (theta) waves predominate
• Most reflexes are intact; muscle tone slightly decreased
• Sleep-walking; sleep-talking; snoring and bedwetting generally occurs at this
stage.
109. REM Sleep
• 5-30 minutes with 90 minute-intervals
• Active dreaming (dreams are remembered)
• Active body movements
• More difficult to wake up with sensory stimulations
• Waking up in the morning generally coincides with the last REM period.
• Decrease in muscle tone (except respiratory and eye muscles)
• Irregularity in heart and respiration rate.
• 20% increase in brain metabolism
• Atonia in neck muscles
• Rapid eye movements
• Beta waves in EEG
paradoxal sleep, =desynchronized sleep
Possible causes of REM Sleep
• ACh neurons in rostral reticular formation
• Lateral tegmentum -> lateral geniculate body -> occipital cortex:
Ponto-geniculo-occipital spikes in EEG
110.
111. • Helps the maintenance of normal activity level of CNS.
• Helps to maintain the “balance” between the different parts of the
CNS.
• Increased sympathetic activity and muscle tone during the awake
period decreases with sleep...
• Body temperature drops, energy loss decreases
• Growth hormone and cortisol secretion
• Phosphate excretion from kidneys increase
• Melatonin secretion increases
• Skin and tissue repair
Physiological effects of sleep
112. • Insomnia: Disturbances in sleep onset or maintenance
• Fatal Familial Insomnia: Unable to sleep, emotional instability, hallucinations,
stupor- coma and death
Sleep deprivation
• Prolonged wakefulness may result in irritability, confusion and psychotic
symptoms
• Fatigue, prostration, depression...
• Unability to direct attention
• Hypersensitivity to pain
• Visceral problems including anorexia and distruption of excretion
• Defects in skin repair: Collagen fibres loose their flexibility and may display
color changes
Sleep Disorders
