physiology brain bloc 16

8/12/2019 Physiology Brain Bloc 16

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PHYSIOLOGY OF HIGHERFUNCTION OF BRAIN

Integrative teaching bloc 16

Dr. Swanny, MSc


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Objectives Describe the functions of the different areas of the

brain.

Distinguish between different types of memory and

describe the roles of different brain regions inmemory.

Describe the location of the hypothalamus andexplain the significance of this region.

Explain the role of the limbic system in the controlof behavior and emotion.


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Introduction

HIGHER FUNCTION OF BRAIN

Neurobehavioral function.

What is the part of brain?

What is the function ?

How is the mechanism ?


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Neuronal part of brain

CEREBRAL CORTEX :

the functional part of cerebral cortex a

thin layer of neurons 2 to 5 mm inthickness covering the surface of all

convolutions of cerebrum a total area

of one quarter square meter contains

about 100 billions neurons.


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Function of cerebral cortex

1. Intellectual

2. Learning

3. Memory


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Behavioral and motivational

The control of behavior is the function of

ENTIRE nervous system wakefulness,

sleep cycle.

Brain control the level of activity.

Motivational drives control of learning

process, feeling of pleasure and

punishment performed by basalregions of brain LIMBIC SYSTEM.


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Behavioral State System: Emotion and Motivation

The link between

emotions and

physiological

functionsThe amygdala is the

center of emotion

in the brain

Stimulus to Cerebrum-

creates perception,

limbic createsemotion, cerebrum

becomes aware of

emotion while

hypothalus

stimulates multiple

responses


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Behavioral/Cognitive State : Motivation

Defined as internal signals that shape voluntary behavior (related to

survival or emotions)

Some states known as drives create increased arousal, goal-

oriented behavior, and disparate behavior to achieve the goal. Works with autonomic and endocrine responses to maintain

homeostasis

Motivated behaviors stop

Satiety

Pleasure is related to addictive behaviors which can be changed ifgiven a different motivation.


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Behavioral State System: Moods

Similar to emotions but longer-lasting- related to senseof being, not purely psychological, related to sense ofwell-being and proper neurotransmitter function

Mood disorders

Fourth leading cause of illness worldwide today

Depression

Sleep and appetite disturbances

Alteration of mood and libido

Antidepressant drugs alter synaptic transmissionallow a neurotransmitter to remain at the synapselonger, change the receptor, or the amount of NTreleased.


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Cognitive State: Learning and Memory

Learning has two broad types

Associativelinks two stimuli or a stimulus to a behavior

Nonassociative- change behavior due to repeated exposure

Habituationdo not respond to an irritant stimulus, filters outinsignificant stimulus

Sensitization- enhanced response to irritant stimulus, helps avoidharmful stimuli

Memory has several types

Short-term and long-term- combined by working memory, consolidationturns short-term into long term. Changes in synaptic connections arerequired

Reflexive and declarative- requires unconscious (procedural) or

conscious recall (infer, compare, evaluate). Declarative can becomereflexive


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Brain Function: Language

Cerebral processing of spoken and visual language

Damage to Wernickes causes receptive aphasia- unable to

understand spoken or visual information

Damage to Brocas area causes expressive aphasia- can

understand information but cannot speak or write in proper

order, are aware of mistakes


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Functional Divisions - Cerebrumprimary sensory or motor areas

secondary sensory or motor areas

association cortex


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Functional Divisions - Cerebrum

primary sensory areas

somatosensory cortex - postcentral gyrusvisual cortex - occipital

auditory cortex - temporal

olfactory cortex - olfactory bulb

gustatory - part of somatosensoryprimary motor area - precentral gyrus


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Cortical Areas


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Organization of nerve fibers within

layer of cortex

1. Molecular layer

2. External granular layer

3. Pyramidal cells layer4. Internal granular layer

5. Large pyramidal cell layer

6. Fusiform or polymorphic cells.


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Granular/ stellate cell short axon,

function as intracortical interneurons.

Pyramidal and fusiform cells

long nervefibers give rise to almost all output

fibers from cortex. They also give rise to

most of large subcortical association fiber

bundles that pass from one major part ofbrain to the other.


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Function of fibers

Horizontal fibers extend between

adjacent areas of cortex.

Vertical fibers

to and from cortex to lowerareas of brain and to spinal cord or to

distant regions of cerebral cortex through

the long association bundles.


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Sensory,

association,

and motor

cortex

Layer IV vs.

Layer V


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Layer I, II and III perform most of theintracortical association functions.

Layer IV incoming sensory signals

terminate in this layer.

Layer V, VI output signals leave cortexfrom neurons located in these layer. Thevery large fibers to brain stem and cordarises in layer V. The fibers to thalamusarises from neuron in layer VI.


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Brain Function: complex processing and responses


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Hemispheric Dominance (Lateralization)

90% of humans are right handed - left hemisphere is dominant for

handedness

many animal species also show handedness

98% of humans - comprehension of spoken and written word and

motor control of speech is in the left hemisphere


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Hemispheric Dominance - Humanleft hemisphere

(analytical)

speech

writing

main language center

calculation

right hemisphere

(creative)

spatial construction

nonverbal ideation

simple language

comprehension


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Hemispheric Dominancehemispheric damage in the adult nearly

permanent loss

damage in the child (up to age 3 yrs) results in

functions being assumed to variable extents by the

other hemisphereplasticity

some hemispheric differences are present before

birth, so anatomically predetermined

class demo


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MemoryEncoding, sorting, storage, retrieval, and

transfer of acquired verbal and nonverbal

sensory experiences, concepts, andsensorimotor behavioral patterns.

Memory is the substrate for all higher

mental functions and the prerequisite for

learning and adaptive behavior.


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Memory & LearningLearning: the process by which we and

other animals acquire knowledge about the

world.

Memory: the retention or storage of that

knowledge.


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Alternate Definitions

Learning: the acquisition of an altered

behavioral response due to an environmental

stimulus.

Memory: the process through which learned

information is stored.

Recall: the conscious or unconscious

retrieval process through which this alteredbehavior is manifest.


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Classification of Memory Formsclassified by how information is

stored and recalled:

explicit (declarative) memory

implicit (procedural) memory


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Explicit/Declarative Memorystorage (& retrieval) of material that is available

to the conscious mind

"what" the world is aboutknowledge of people, places, and things that

are available to the conscious mind

involves evaluation, comparison, and inference

can be recalled by a deliberate act ofrecollectingbirth date, Social Security

Number

from single or multiple trials


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Implicit/Procedural Memorynot available to the conscious mind

involves skills and associations that are

acquired and retrieved at an unconscious level"how" to do things

motor or perceptual skills unavailable to

conscious mind

acquired slowly through repetitionexpressed primarily by improved performance

signing your name or riding a bicycle


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Implicit/Procedural Memory (cont.)motor memory: physical acts learned through

multiple repetitions to the point where

conscious thought is not required for theirperformance

other typesemotions associated with a

memory, etc.


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Subdivisions of Human Memory


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Time Domains of Memoryboth explicit and implicit memories have

short-term forms and long-term (nearly

permanent) forms (more below)consolidation from short-term to long-term

requires protein synthesis (and sleep!)

recently acquired memories are more easily

disrupted than older oneslong-term memories gradually diminish with

time, especially with disuse


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Time Domains (3) of Memory1. immediate memorylasts a few seconds, large

capacity, all sensory modalities, awareness of

environment

2. short-term memory - seconds to minutes; e.g.

strings of digits; limited storage capacity, then

either lost or transferred to more stable memory

forms; rapid retrieval

working memory - form of short-term conscious

memory used to carry out sequential actions toward

a goal, i.e. searching for a lost object; not stored.


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Time Domains of Memory3. long-term memory - days, weeks, or a lifetime;

requires transfer (consolidation) from short- term;

depends on changes in synaptic strength or

synapse numbers; vast capacity, rapid recall

intermediate-term memory - name used by some to

describe the memories that overlap short-term and

long-term memory


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Time Domains of MemoryConsolidation of memory from short-term to long-

term:

hippocampus is required for memory

consolidation

requires protein synthesis

requires sleepREM and possibly SWSat least

in animals


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Short-term

memory store

Long-term

memory store

Search and read out

Simplified Model of Memory

Processes During Learning

Input

Output

consolidation


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Proposed Anatomic Correlates of Memory

explicitimmediate: prefrontal cortex and dorsal

medial thalamus or primary & secondarysensory cortex

short-term: hippocampus and temporal

lobe, mammillary bodies, midlinediencephalic structures

long-term: diffuse throughout the cerebrum


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Anatomic Correlates of Memoryimplicit motor: cerebellum, basal ganglia,

secondary motor cortex

emotion-associated: amygdala


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Mechanisms of Memoryimmediate and short-termreverberating circuits (minutes)

altered electrical excitabilitychanges in[Ca++] and altered ionic conductances due

to neurotransmitters (minutes to hours)

transient changes in receptors

long-term potentiation (LTP)long-term depression (LTD)


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Dendritic Spines: Young vs. Old Animals


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Long-Term Potentiation (LTP)

strengthening the synaptic connections between

activated neurons, especially in the hippocampus,

cerebral cortex

postsynaptic potential amplitudes are increased by

tetanic stimulation of the presynaptic terminal

(50 Hz, 1 sec)

enhanced response can last for minutes to hours to

days, perhaps longer

can selectively enhance one input to a neuron

without changing the strength of other inputs


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Long-Term Potentiation


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Long-Term Depression (LTD)

weakening of established synaptic

connections between activated neurons

"turning off" LTPresults from reversing the biochemical

pathways that produced LTP

activated by low frequency activation of the

same or different presynaptic terminal

seen especially in cerebellum


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Long-Term Depression


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Ca++

Trigger of Both LTP & LTD


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Memory DisordersAmnesia (or pathological forgetting)

Anterograde amnesiaRetrograde amnesia

Hyperthymestic syndrome


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Memory DisordersAnterograde amnesia- deficit in registration

and storage of new recent or long-term

memories

Korsakoff syndrome (chronic alcoholics)

damage to mammillary bodies & medial

thalamus, confabulationKlver-Bucy syndromebilateral lesion of

hippocampal/temporal lobe; patient H.M.

head trauma and/or impaired consciousness


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Memory DisordersRetrograde amnesia- deficit in ability to

retrieve memories

head trauma

impaired consciousness

Alzheimer's disease

electroconvulsive therapy

Clinical amnesia cases typically show a mix

of anterograde and retrograde amnesia


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Memory DisordersHyperthymestic syndrome- deficit in ability

to forget or suppress memories

Details of events going back 30 years

Patient describes being consumed by the

"burden" of memories that were "non-

stop, uncontrollable and totallyexhausting."

Normal IQ

Two cases reported


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SpeechCommunication or expression of ideas or

information through vocalization of

standardized sounds (and/or words) withaccepted associations


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Speech In Humans - Left Hemisphere (98%)

Broca's area- frontal lobe, secondary

motor cortex area for muscles involved in

speech

Wernicke's areatempero-parietal lobe,

secondary auditory cortex

Arcuate fasciculus- pathway from

Wernicke's area to Broca's area


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Language Areas of the Brain


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Language Areas of the Brain


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Speaking/Repeating a Heard Word1. Primary auditory cortex

2. Wernicke's area

3. Arcuate fasciculus

4. Broca's area

5. Motor cortex


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Speaking a Heard Word


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Speaking a Written Word

1. Visual cortex

2. Angular gyrus

3. Wernicke's area

4. Arcuate fasciculus

5. Broca's area

6. Motor cortex


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Cerebral Cortex:

Outer layer of neurons (1mm thick)

Perception: hearing, vision, olfaction,

muscles & viscera

Reasoning, information integration

Directing voluntary behavior


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Lobes of Cerebral Cortex and Associated

Integration

Frontal: voluntary movement, behavior,

perception Parietaltactile sensory

Occipitalvision

Temporalolfactory, auditory & gustatory


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Cerebral Cortex:

Outer layer of neurons (1mm thick)

Perception: hearing, vision, olfaction,

muscles & viscera Reasoning, information integration

Directing voluntary behavior


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Lobes of Cerebral Cortex and Associated Integration

Frontal: voluntary movement, behavior,

perception

Parietaltactile sensory Occipitalvision

Temporalolfactory, auditory & gustatory

HYPOTHALAMUS &


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HYPOTHALAMUS &

LIMBIC SYSTEM

EMOTION


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EMOTION

Emotionhas been a notoriously difficult conceptto define. Many psychologists argue that anemotion comprises three different elements:

cognitive (thinking) component: an appraisalor judgment

feeling (subjective) component: what a personexperiences privately

action (or, action tendency) component:

either an action or, at least, a tendency to anaction


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Limbic System Functions

Brain Region Effect on Emotion

Cingulate Cortex

Damage: reduced level oftension & anger

Medial Frontal Cortex

Inactivation = impaired abilityto identify angry expressions(but not happy expressions)

Insula

Activated by disgust + primarytaste cortex

Damage: fail to experiencedisgust or recognize otherpeople's retching sound asmeaning nausea or disgust



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RH more sensitive to emotional stimuli than the lefthemisphere (LH). For example, Right amygdala: activated by laughing or crying Right temporal cortex: scanning faces for emotional

expression increases activity RH damage: Difficulty interpreting facial expression

indicating viewing pleasant or unpleasant scene LH damage: Higher than normal ability to interpret facial

expression + greater than even chance to detect lying(60% vs. 50%)

RH inactivation: facts, but not strong emotions, of pastevents remembered

RH > LH activity: associated with shyness LH > RH activity: associated with outgoing & fun-lovingpersonality


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Start (Approach Repeat Behavior) Stop


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Start (Approach, Repeat Behavior), Stop

Signals, Pain and Pleasure

The reward pathway is a neural network inthe middle of the brain that prompts goodfeelings in response to certain behaviors,

such as relieving hunger, quenching thirstor having sex, and it thereby reinforcesthese evolutionarily important drives.However, the circuit also responds to

drugs of abuse, such as heroin, cocaine,amphetamine and nicotine, which seem tohijack the circuitry, altering the behavior ofits neurons.

Complex Pathways of Emotion and Motivation


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Hypothalamus, limbic & cortex integration

Emotions: pleasure, sexual arousal, anger & fear limited

cognitive control"hard to turn off" Motivation: "drives", increase arousal coordinate goal-

oriented behavior

Moods:

Long term emotional states Depression, SSRI



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Complex Pathways of Learning and Memory


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Most Complex Pathways: Language and Personality

Languageexchange complex information

Wernike's area

Broca's area

Personality Genetic components

Experiences

Learning

Memory

Perceptions


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References

1. Text book of medical physiology.

Guyton & Hall.

2. Human PhysiologyDee ungland Silverthorn

3. Neuronal control of mood, emotion and

state of awareness.

Dianna A. Johnson


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THANK YOU

physiology brain bloc 16

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