The Central Nervous System - PowerPoint Presentation

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The Central Nervous System

Prepared by I

Gede

Purnawinadi

,

S.Kep

.,

M.Kes

.

Slide2

Organization of the Nervous System

Central nervous system (CNS

)

Brain and spinal cordIntegration and command center Peripheral nervous system (PNS)Paired spinal and cranial nervesCarries messages to and from the spinal cord and brain

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Organization of the Nervous System

The two principal cell types of the nervous system are:

Neurons

– excitable cells that

transmit electrical

signals

Neuroglia

-

supporting cells

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Functional:

Sensory

(afferent) — transmit impulses

toward the CNSMotor (efferent) — carry impulses away from the CNSInterneurons (association neurons) — shuttle signals through CNS pathwaysNeuron Classification

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Neuroglia

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BrainSpinal cord

Central Nervous System:

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Hair, skin, cranium

Meninges

Cerebrospinal fluid

Blood brain barrierCNS Protection

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Meningeal Layers

Meningeal layer of the brain cushion and protect delicate neural tissue

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Cerebrospinal Fluid

Shock absorbing medium

Provides a optimum and

stable environment for

generating

nerve

impulses

Provides a

medium for the exchange of nutrients and wastes between blood and nervous

tissue

Formed by

selective transport

across ependymal cells

Volume

125-150 ml

and is replaced > 3 times/day, flow maintained by

10 mmHg

paressure

gradient

Path: ventricles



subarachnoid space, reabsorbed into blood in

dural

sinuses through arachnoid villi

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Extensive capillaries & sinuses

Tight junctions promoted by astrocyte

Limits permeability for most molecules

except O2, CO2, alcohol, steroids, H2OProtects brain: hormones & circulating chemicalsProtects CNS from chemical fluctuationsPrevents entry of harmful substancesPrevents entry of molecules that could act as neurotransmitters

Brain receives 15% of blood pumped by heart

Brain responsible for about half of body’s glucose consumption

Membrane transporters move glucose from plasma into the brain interstitial fluid

Blood Brain Barrier

Figure 9-6: The blood-brain barrier

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The Central Nervous System (CNS)

The

central nervous system (CNS)

consists of the brain and spinal cord, which occupy the dorsal body cavity. The CNS is the integrating and command center of the nervous system. It interprets sensory input and dictates

motor responses

based on past experience, reflexes, and current conditions.

The Brain

:

t

he average

adult man’s brain

has a mass of about

1600 g

(3.5

lb

); that of a

woman averages

1450 g

(3.2

lb

).

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Brain Development

(a)

Formation of

two major flexures by week 5 of development causes the telencephalon and diencephalon to angle toward the brain stem. Development of the cerebral hemispheres at (b) 13 weeks, (c) 26 weeks, and (d) birth.

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Trillion interneurons fill the brain

Up to 200,000 synapses each

Levels of complexity

Cerebral cortexBasal nucleiThalamusHypothalamusCerebellum

Brain

stem

Brain Organization

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Hypothalamus

Brain stem

Cerebral cortex

Thalamus

(medial)

Basal nuclei

(lateral to thalamus)

Cerebellum

Spinal cord

Midbrain

Pons

Medulla

Brain component

Cerebral cortex

Basal nuclei

Thalamus

Hypothalamus

Cerebellum

Brain stem

(midbrain, pons,

and medulla)

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Major Functions

Brain component

1. Sensory perception

2. Voluntary control of movement

3. Language

4. Personality traits

5. Sophisticated mental events, such as thinking memory,

decision making, creativity, and self-consciousness

1. Inhibition of muscle tone

2. Coordination of slow, sustained movements

3. Suppression of useless patterns of movements

1. Relay station for all synaptic input

2. Crude awareness of sensation

3. Some degree of consciousness

4. Role in motor control

1. Regulation of many homeostatic functions, such as temperature

control, thirst, urine output, and food intake

2. Important link between nervous and endocrine systems

3. Extensive involvement with emotion and basic behavioral patterns

1. Maintenance of balance

2. Enhancement of muscle tone

3. Coordination and planning of skilled voluntary muscle activity

1. Origin of majority of peripheral cranial nerves

2. Cardiovascular, respiratory, and digestive control centers

3. Regulation of muscle reflexes involved with equilibrium and posture

4. Reception and integration of all synaptic input from spinal cord;

arousal and activation of cerebral cortex

5. Role in sleep-wake cycle

Cerebral cortex

Basal nuclei

Thalamus

Hypothalamus

Cerebellum

Brain stem

(midbrain, pons,

and medulla)

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Cerebral Hemispheres

The cerebral hemispheres form the

superior part of the brain

.Together they account for about 83% of total brain mass and are the most conspicuous parts of an intact brain.

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Cerebral Cortex

Each half of cortex divided into four major lobes

Occipital lobe

- carries out initial processing of visual inputTemporal lobe - initial reception of sound sensation, taste, smellParietal lobe - somatosensory processing

Frontal lobe

responsible for

Voluntary motor activity

Speaking ability

Elaboration of thought

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Primary Motor Cortex

Located in the

precentral

gyrusComposed of pyramidal cells whose axons make up the corticospinal tracts Allows conscious control of precise, skilled, voluntary movementsMotor homunculus – caricature of relative amounts of cortical tissue devoted to each motor function

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Primary Somatosensory Cortex

Located in the

postcentral

gyrus, this area:Receives information from the skin and skeletal musclesExhibits spatial discriminationSomatosensory homunculus – caricature of relative amounts of cortical tissue devoted to each sensory function

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Motor and sensory areas of the cerebral cortex

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Brain Function: Cerebral Lateralization

Each lobe has special functions

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Basal Nuclei

Act by modifying ongoing activity in motor pathways

Primary functions

Regulates muscle tone throughout the bodySelecting and maintaining purposeful motor activity while suppressing useless or unwanted patterns of movementHelping monitor and coordinate slow, sustained contractions, especially those related to posture and support

Controls large automatic movement

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Thalamus

Final relay point for ascending sensory information

Coordinates the activities of the cerebral cortex and basal nuclei

Domain-specific information processing

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Hypothalamus

Receives indirect sensory inputs from all sensory systems

Sends neural outputs to various motor control nuclei

Sends neural outputs to sympathetic and parasympathetic nervous systemsSends both neural and hormonal outputs to pituitary

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Hypothalamus

Controls somatic motor activities at the subconscious level

Controls autonomic function

Coordinates activities of the endocrine and nervous systemsSecretes hormonesProduces emotions and behavioral drivesCoordinates voluntary and autonomic functionsRegulates body temperatureCoordinates circadian cycles of activity4Fs: feeding, fighting, fleeing, and reproductive behavior

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Limbic System

Cingulated

gyrus Coordinates sensory input with emotions Emotional responses to pain Basic, inborn behavioral patterns related to survival and perpetuation of the species

Regulates aggressive

behavior

Hippocampus

- sends

memories

out to the appropriate part of the cerebral hemisphere for long-term storage and retrieving them when necessary, Plays important role in

motivation and learning

Amygdala

- involved in

emotional

responses,

hormonal

secretions, and

memory

,

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Cerebellum

Basic functions:

coordination, balance, motor learning,

etc.Vestibulocerebellum – balance and control of eye movementSpinocerebellum – enhances muscle tone and coordinates skilled voluntary movement – important in synchronization and timingReceives input concerning desired action from motor cortexReceives feedback concerning actual action from proprioceptors, vestibular apparatus, eyes

Compares inputs and sends adjustments or corrective signals to motor tracts

Cerebrocerebellum

– planning and initiation of

voluntary activity by providing input to the cortical motor areas also involved in procedural memories

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Brain Stem: Midbrain, Pons & Medulla

An important link between

spinal cord

and higher brain levels, relays motor and sensory impulses between other “higher” parts of the brain and spinal cordMidbrain – eye movement controlPons/MedullaSignal relay

Involuntary functions

Many cranial nerves

enter

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CervicalThoracic

Lumbar

Sacral

Spinal Cord Regions

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Gray matter

: mostly cell bodies

Dendrites & terminals

Spinal reflex integrating centerWhite matterBundles of myelinated axonsAscending tracts – sensoryDescending tracts – motorDorsal roots

Ventral roots

Spinal Cord Organization

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Spinal Cord Organization

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Spinal Cord: Integrating Center

Neural Reflexes: Overview

Stimulus

Sensory receptor

Sensory

(afferent)

neuron

CNS integration

Efferent

(motor)

neuron

Effector

(target

tissue)

Response

(

movement)

Feedback

to CNS

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Neural Reflex

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Patellar Tendon Reflex: Stretch & Reciprocal Inhibition

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Cross Extensor Reflex/Withdrawal Reflex

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