Fisiologi Integrative Functions Bshb14

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

C h a p t e r

16

Neural Integration: Sensory Pathways and the Somatic Nervous System

and Higher-Order FunctionsPowerPoint® Lecture Slides

prepared by Jason LaPresLone Star College - North Harris

Copyright © 2009 Pearson Education, Inc.,publishing as Pearson Benjamin Cummings

Outline

1. INTRODUCTION

2. SOMATIC SENSORY AND MOTOR PATHWAYS

3. MONITORING BRAIN ACTIVITY : THE EEG

4. HIGHER ORDER FUNCTIONS

5. BRAIN CHEMISTRY AND BEHAVIOUR

6. AGING AND THE NERVOUS SYSTEM


Objective

1. Identify the principal sensory and motor pathways.

2. Compare the components, processes, and functions of the various motor pathways.

3. Explain how we can distinguish among sensations that originate in different areas of the body.

4. Describe the levels of information processing involved in motor control.

5. Discuss how the brain integrates sensory information and coordinates responses.

6. Explain how memories are created, stored, and recalled.

7. Distinguish between the levels of consciousness and unconsciousness, and identify the characteristics of brain activity associated with the different levels of sleep.

8. Describe drug-related alterations in brain function.

9. Summarize the effects of aging on the nervous system.



Introduction

Figure 16-1 An Overview of Neural Integration.


Introduction

Afferent Division of the Nervous System

Receptors

Sensory neurons

Sensory pathways

Efferent Division of the Nervous System

Nuclei

Motor tracts

Motor neurons


Sensory Pathways

First-Order Neuron

Sensory neuron delivers sensations to the CNS

Cell body of a first-order general sensory neuron is located in dorsal

root ganglion or cranial nerve ganglion

Second-Order Neuron

Axon of the sensory neuron synapses on an interneuron in the CNS

May be located in the spinal cord or brain stem

Third-Order Neuron

If the sensation is to reach our awareness, the second-order neuron

synapses on a third-order neuron in the thalamus


Sensory Pathways

Somatic Sensory Pathways

Carry sensory information from the skin and

musculature of the body wall, head, neck, and limbs

Three major somatic sensory pathways

The posterior column pathway

The spinothalamic pathway

The spinocerebellar pathway


Sensory Pathways

Figure 15–4 Sensory Pathways and Ascending Tracts in the Spinal Cord.


Sensory Pathways

Figure 15–5b The Spinothalamic Tracts of the Spinothalamic Pathway.


Somatic Motor Pathways

SNS, or the somatic motor system, controls

contractions of skeletal muscles (discussed

next)

ANS, or the visceral motor system, controls

visceral effectors, such as smooth muscle,

cardiac muscle, and glands (Ch. 16)



Always involve at least two motor neurons

Upper motor neuron

Cell body lies in a CNS processing center

Synapses on the lower motor neuron

Innervates a single motor unit in a skeletal muscle:

– activity in upper motor neuron may facilitate or inhibit

lower motor neuron



Always involve at least 2 motor neurons

Lower motor neuron

Cell body lies in a nucleus of the brain stem or

spinal cord

Triggers a contraction in innervated muscle:

– only axon of lower motor neuron extends outside CNS

– destruction of or damage to lower motor neuron

eliminates voluntary and reflex control over innervated

motor unit



Conscious and Subconscious Motor

Commands

Control skeletal muscles by traveling over

three integrated motor pathways

Corticospinal pathway

Medial pathway

Lateral pathway



Figure 15–8 Descending (Motor) Tracts in the Spinal Cord.



The Corticospinal Pathway Motor homunculus

Primary motor cortex corresponds point by point with specific

regions of the body

Cortical areas have been mapped out in diagrammatic form

Homunculus provides indication of degree of fine motor

control available:

– hands, face, and tongue, which are capable of varied and

complex movements, appear very large, while trunk is relatively

small

– these proportions are similar to the sensory homunculus



Figure 15–9 The Corticospinal Pathway.



The Basal Nuclei and Cerebellum

Responsible for coordination and feedback

control over muscle contractions, whether

contractions are consciously or

subconsciously directed



The Basal Nuclei

Provide background patterns of movement involved in

voluntary motor activities

Some axons extend to the premotor cortex, the motor

association area that directs activities of the primary motor

cortex:

– alters the pattern of instructions carried by the corticospinal

tracts

Other axons alter the excitatory or inhibitory output of the

reticulospinal tracts



The Cerebellum

Monitors

Proprioceptive (position) sensations

Visual information from the eyes

Vestibular (balance) sensations from inner ear as

movements are under way


Higher-Order Functions

Require the cerebral cortex

Involve conscious and unconscious

information processing

Not part of programmed “wiring” of brain

Can adjust over time



Memory Fact memories

Are specific bits of information

Skill memories Learned motor behaviors

Incorporated at unconscious level with repetition

Programmed behaviors stored in appropriate area of brain

stem

Complex are stored and involve motor patterns in the basal

nuclei, cerebral cortex, and cerebellum



Memory

Short–term memories

Information that can be recalled immediately

Contain small bits of information

Primary memories

Long-term memories

Memory consolidation: conversion from short-term to long-

term memory:

– secondary memories fade and require effort to recall

– tertiary memories are with you for life



Figure 16–13 Memory Storage.



Brain Regions Involved in Memory Consolidation

and Access

Amygdaloid body and hippocampus

Nucleus basalis

Cerebral cortex



Amygdaloid body and hippocampus

Are essential to memory consolidation

Damage may cause

Inability to convert short-term memories to new

long-term memories

Existing long-term memories remain intact and

accessible



Nucleus Basalis

Cerebral nucleus near diencephalon

Plays uncertain role in memory storage and retrieval

Tracts connect with hippocampus, amygdaloid body,

and cerebral cortex

Damage changes emotional states, memory, and

intellectual functions



Cerebral cortex Stores long-term memories

Conscious motor and sensory memories referred to

association areas

Occipital and temporal lobes Special portions crucial to memories of faces, voices, and

words

A specific neuron may be activated by combination of

sensory stimuli associated with particular individual; called

“grandmother cells”



Cerebral cortex

Visual association area

Auditory association area

Speech center

Frontal lobes

Related information stored in other locations

If storage area is damaged, memory will be incomplete



Cellular Mechanisms of Memory Formation and

Storage

Involves anatomical and physiological

changes in neurons and synapses

Increased neurotransmitter release

Facilitation at synapses

Formation of additional synaptic connections



Increased Neurotransmitter Release

Frequently active synapse increases the

amount of neurotransmitter it stores

Releases more on each stimulation

The more neurotransmitter released, the

greater effect on postsynaptic neuron



Facilitation at Synapses Neural circuit repeatedly activated

Synaptic terminals begin continuously releasing

neurotransmitter

Neurotransmitter binds to receptors on postsynaptic

membrane

Produces graded depolarization

Brings membrane closer to threshold

Facilitation results affect all neurons in circuit



Formation of Additional Synaptic Connections

Neurons repeatedly communicating

Axon tip branches and forms additional synapses on

postsynaptic neuron

Presynaptic neuron has greater effect on

transmembrane potential of postsynaptic neuron




Storage

Basis of memory storage

Processes create anatomical changes

Facilitate communication along specific neural circuit

Memory Engram

Single circuit corresponds to single memory

Forms as result of experience and repetition




Storage

Efficient conversion of short-term memory

Takes at least 1 hour

Repetition crucial

Factors of conversion

Nature, intensity, and frequency of original stimulus

Strong, repeated, and exceedingly pleasant or unpleasant

events likely converted to long-term memories



Cellular Mechanisms of Memory Formation and Storage Drugs stimulate CNS

Caffeine and nicotine are examples:– enhance memory consolidation through facilitation

NMDA (N-methyl D-aspartate) Receptors:– linked to consolidation– chemically gated calcium channels– activated by neurotransmitter glycine– gates open, calcium enters cell– blocking NMDA receptors in hippocampus prevents long-

term memory formation



States of Consciousness

Many gradations of states

Degree of wakefulness indicates level of

ongoing CNS activity

When abnormal or depressed, state of

wakefulness is affected




Deep sleep

Also called slow-wave sleep

Entire body relaxes

Cerebral cortex activity minimal

Heart rate, blood pressure, respiratory rate, and

energy utilization decline up to 30%




Rapid eye movement (REM) sleep

Active dreaming occurs

Changes in blood pressure and respiratory rate

Less receptive to outside stimuli than in deep sleep

Muscle tone decreases markedly

Intense inhibition of somatic motor neurons

Eyes move rapidly as dream events unfold




Nighttime sleep pattern

Alternates between levels

Begins in deep sleep

REM periods average 5 minutes in length;

increase to 20 minutes over 8 hours



Sleep

Has important impact on CNS

Produces only minor changes in physiological

activities of organs and systems

Protein synthesis in neurons increases during sleep

Extended periods without sleep lead to disturbances

in mental function 25% of U.S. population experiences sleep disorders



Figure 16–14 Levels of Sleep.

EEG





Arousal and the reticular activating system (RAS)

Awakening from sleep

Function of reticular formation:

– extensive interconnections with sensory, motor, integrative nuclei,

and pathways along brain stem

Determined by complex interactions between reticular formation

and cerebral cortex



Reticular Activating System (RAS) Important brain stem component

Diffuse network in reticular formation

Extends from medulla oblongata to mesencephalon

Output of RAS projects to thalamic nuclei that

influence large areas of cerebral cortex

When RAS inactive, so is cerebral cortex

Stimulation of RAS produces widespread activation of

cerebral cortex



Arousal and the Reticular Activating

System

Ending sleep

Any stimulus activates reticular formation and RAS

Arousal occurs rapidly

Effects of single stimulation of RAS last less than a

minute



Arousal and the Reticular Activating System

Maintaining consciousness

Activity in cerebral cortex, basal nuclei, and sensory and

motor pathways continue to stimulate RAS:

– after many hours, reticular formation becomes less responsive

to stimulation

– individual becomes less alert and more lethargic

– neural fatigue reduces RAS activity



Arousal and the Reticular Activating System

Regulation of awake–asleep cycles

Involves interplay between brain stem nuclei that use

different neurotransmitters

Group of nuclei stimulates RAS with NE and maintains

awake, alert state

Other group promotes deep sleep by depressing RAS

activity with serotonin

“Dueling” nuclei located in brain stem



Figure 16–15 The Reticular Activating System.


Brain Chemistry

Huntington Disease

Destruction of ACh-secreting and GABA-secreting

neurons in basal nuclei

Symptoms appear as basal nuclei and frontal lobes

slowly degenerate

Difficulty controlling movements

Intellectual abilities gradually decline


Brain Chemistry

Lysergic Acid Diethylamide (LSD)

Powerful hallucinogenic drug

Activates serotonin receptors in brain stem,

hypothalamus, and limbic system


Brain Chemistry

Serotonin

Compounds that enhance effects also

produce hallucinations (LSD)

Compounds that inhibit or block action cause

severe depression and anxiety

Variations in levels affect sensory

interpretation and emotional states


Brain Chemistry

Serotonin

Fluoxetine (Prozac) Slows removal of serotonin at synapses

Increases serotonin concentrations at postsynaptic

membrane

Classified as selective serotonin reuptake

inhibitors (SSRIs)

Other SSRIs:

– Celexa, Luvox, Paxil, and Zoloft


Brain Chemistry

Parkinson Disease

Inadequate dopamine production causes motor

problems

Dopamine

Secretion stimulated by amphetamines, or “speed”

Large doses can produce symptoms resembling

schizophrenia

Important in nuclei that control intentional movements

Important in other centers of diencephalon and cerebrum


Aging and the Nervous System

Anatomical and physiological changes

begin after maturity (age 30)

Accumulate over time

85% of people over age 65 have changes

in mental performance and CNS function



Reduction in Brain Size and Weight

Decrease in volume of cerebral cortex

Narrower gyri and wider sulci

Larger subarachnoid space



Reduction in Number of Neurons

Brain shrinkage linked to loss of cortical

neurons

No neuronal loss in brain stem nuclei



Decrease in Blood Flow to Brain

Arteriosclerosis

Fatty deposits in walls of blood vessels

Reduces blood flow through arteries

Increases chances of rupture

Cerebrovascular accident (CVA), or stroke

May damage surrounding neural tissue



Changes in Synaptic Organization of Brain

Number of dendritic branches, spines, and

interconnections decreases

Synaptic connections lost

Rate of neurotransmitter production declines



Intracellular and Extracellular Changes in CNS

Neurons

Neurons in brain accumulate abnormal intracellular

deposits

Lipofuscin

Granular pigment with no known function

Neurofibrillary tangles

Masses of neurofibrils form dense mats inside cell body and

axon



Intracellular and Extracellular Changes in

CNS Neurons

Plaques

Extracellular accumulations of fibrillar proteins

Surrounded by abnormal dendrites and axons



Intracellular and Extracellular Changes in

CNS Neurons

Plaques and tangles

Contain deposits of several peptides

Primarily two forms of amyloid ß (Aß) protein

Appear in brain regions specifically associated with

memory processing



Anatomical Changes

Linked to functional changes

Neural processing becomes less efficient with

age

Memory consolidation more difficult

Secondary memories harder to access



Sensory Systems

Hearing, balance, vision, smell, and taste become

less acute

Reaction times slowed

Reflexes weaken or disappear

Motor Control

Precision decreases

Takes longer to perform



Senility

Also called senile dementia

Degenerative changes

Memory loss

Anterograde amnesia (lose ability to store new memories)

Emotional disturbances

Alzheimer disease is most common


Nervous System Integration

Figure 16–16 Functional Relationships between the Nervous System and Other Systems.







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Fisiologi Integrative Functions Bshb14