bio 168 neural integration ii: the autonomic nervous system and higher order functions chapter 16

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BIO 168

NEURAL INTEGRATION II: THE AUTONOMIC

NERVOUS SYSTEM AND HIGHER ORDER

FUNCTIONS

CHAPTER 16

created by Dr. C. Morgan

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TOPICS

Introduction and Overview of the ANS

The Sympathetic Division

The Parasympathetic Division

Sympathetic / Parasympathetic Interactions

Integration and Control

Higher Order Functions

Brain Chemistry and Behavior

Aging and the Nervous System

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Introduction and Overview Objectives

Review the role of the autonomic nervous system division.

Compare the organization of the ANS with the SNS.

Examine the structural and functional plan of the ANS.

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Introduction and Overview

If you were unable to think or voluntarily move a muscle, you would continue to survive because your autonomic nervous system (ANS) takes care of vital functions

without your conscious awareness or control.

Although both the ANS and SNS generate efferent output to effectors, there are important structural differences.

In the SNS, lower motor neurons control skeletal muscles.

In the ANS, there is a second visceral motor neuron that originates from a synapse in a ganglion outside the CNS.

All autonomic nerves are motor although some may also carry visceral sensory information.

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Introduction and Overview (cont)

Fig. 1

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Fig. 2 a

SNS plan

Upper motor neuron in the cortex.

Lower motor neuron in the brain stem or

spinal cord.

All cell bodies are within the CNS.

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ANS plan

Preganglionic neuron

cell body in CNS

Postganglionic neuron

cell body outside CNS


Fig. 2 b

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ANS has two subdivisions: sympathetic and parasympathetic, usually with opposing effects if they innervate the same structure or organ.

The sympathetic division directs your “fight-or-flight” or crisis responses (protective) with widespread, global output.

The parasympathetic division directs your “rest and repose” ongoing visceral responses with localized output.

In the sympathetic division, sensory input is consciously perceived but in the parasympathetic division it is not consciously perceived.

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The ANS also includes a huge network of neurons and their processes contained within the wall of the digestive tract.

This extensive network is sometimes called the enteric nervous system (ENS).

This network has as many neurons as the spinal cord and a large variety of neurotransmitters are used.

Reflexes within the digestive tract are initiated and controlled locally without commands from the CNS.

The ANS does influence the activities along the digestive tract.

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TOPICS









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Sympathetic Division Objectives

Examine the structural arrangement of sympathetic ganglia and their fibers.

Using an illustration, explore the distribution of the sympathetic innervation.

Discuss the sympathetic chain ganglia and their branching fiber arrangements.

Describe the characteristics of sympathetic activation.

Discuss neurotransmitter substances and sympathetic function.

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Sympathetic Division

Sympathetic Division Plan

Fig. 3 12

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Sympathetic Division (cont)

Preganglionic fibers of the sympathetic division are associated with spinal segments T1 to L2.

Cell bodies of preganglionic neurons are located in the lateral gray horns of the spinal cord gray matter.

Preganglionic neurons synapse with neurons located in ganglia outside the CNS.

These ganglia are found in three locations:

*in bilateral sympathetic chains adjacent to the spinal column

*in peripheral collateral ganglia associated with effectors in the abdominopelvic cavity

*in the adrenal medullae tissue proper

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Sympathetic Division

Fig. 5

bilateral divergence

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The sympathetic chain includes 3 cervical, 10 – 12 thoracic, 4 – 5 lumbar, 4 – 5 sacral, and 1 coccygeal ganglion.

Do not become confused—the cell bodies of preganglionic neurons lie in the spinal cord between T1 and L2 but the sympathetic chain ganglia extend along cervical to sacral segments.

There is substantial divergent branching of preganglionic fibers (ascending and descending) so that numerous synapses from neuron collaterals may occur along the chain.

It is these fiber branches that produce the chain-like links between the sympathetic (bead-like) ganglia.


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Sympathetic ganglia locations

(1) Sympathetic chain


both patterns bilateral

sweat glands, blood vessels,

arrector pili muscles,

adipose tissue

via spinal nerves

Fig. 4 a

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(2) Passes through chain to collateral ganglion in abdomen


Long preganglionic neuron fibersFig. 4 b

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(3) Directly in adrenal medullae

Long preganglionic

neuron

Short postganglionic neuroendocrine cells release epinephrine and norepinephrine


Fig. 4 c

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Collateral ganglia

Celiac: stomach, liver, spleen, pancreas

Superior Mesenteric: small intestine

Inferior Mesenteric: large intestine,

kidneys, bladder, sex organs

Postganglionic plexuses

Depresses visceral processes


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Splanchnic nerves are preganglionic fibers that pass through chain ganglia to synapse in collateral ganglia located in the abdominopelvic cavity.

Although splanchnic nerves are bilateral, they serve single ganglia.

The ganglia are named for the nearby artery with which they are associated.

In the adrenal medulla, preganglionic fibers synapse on neuroendocrine cells which secrete epinephrine and norepinephrine when they are depolarized at the synapse.

About 80% of the adrenal output is epinephrine.

Sympathetic visceral motor fibers are able to target specific effectors such as blood vessels in the skin.

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Sympathetic activation is the response of the entire sympathetic division to a crisis situation.

Centers in the hypothalamus direct this response.

*RAS is stimulated causing increased alertness, energy, temporary insensitivity to pain, disregard for danger

*Pons and medulla direct increased cardiovascular and respiratory responses

*Increased muscle tone and perhaps shivering

*Mobilization of energy reserves to support increased metabolism

Sympathetic activation supports a “fight-or-flight” response.

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Postganglionic fibers end in branching telodendria

of telodendria


Fig. 6

Most varicosities release E and NE but some ganglionic neurons release

ACh (sweat glands, smooth muscle of blood vessels in brain and skeletal muscle dilation.

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2 types of E and NE neurotransmitter receptors

Alpha

Alpha 1(1): activates second messenger to excitation

Alpha 2 (2 ): reduces cAMP to inhibit cell activity; may inhibit some parasympathetic synapses

Beta

Beta 1(β1): activates second messenger cAMP to increase cellmetabolism ( muscle and liver responses)

Beta 2 (β2): opposite of beta 1 so decreases responses

action depends on receptors and cellular response


TABLE 1

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The body wall and skeletal muscle blood vessels are only innervated by the sympathetic division.

At most sites, the postganglionic telodendria release ACh which stimulates sweat glands and dilates vasculature in skeletal muscles (muscarinic receptors).

In body wall locations, some sympathetic telodendria release NE (1 receptor response) which acts to constrict

arteries so blood flow is shifted to areas of critical need.

Nitric oxide is also released at a few sympathetic synapses involving blood vessel walls of skeletal muscle and the brain.

Nitric oxide causes immediate vasodilation.

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TOPICS









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Parasympathetic Division Objectives

Examine the organization of the parasympathetic division.

List the general functions of the parasympathetic division.

Discuss the parasympathetic neurotransmitter receptors.

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Parasympathetic Division

little divergence

lateral gray horns

midbrain, pons, medulla

Fig. 7

Organization

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CRANIAL PORTION:

Preganglionic fibers extend from brain stem nuclei to ganglia.

Ganglia associated with cranial nerves III, VII, IX, X

Serves lacrimal and salivary glands; intrinsic eye muscles.

Vagus (75% of all outflow) to thoracic and abdominal organs (terminal ganglia)

SACRAL PORTION:

Preganglionic fibers in spinal cord lateral gray horns (S2-S4) with outflow via distinct pelvic nerves (not ventral roots) to intramural ganglia in walls of visceral organs.

Innervates kidneys, urinary bladder, terminal large intestine, and sex organs.

Parasympathetic Division (cont)

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Preganglionic fibers

Ganglia

Plexuses

Pelvic nerves

Vagus nerve***

Innervation Plan

Fig. 8


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Functions of the parasympathetic division include:

*constriction of pupils and nearby focusing of lens

*digestive system smooth muscular and secretory activity

*promotes hormones secretion supporting anabolic activities

*micturition and defecation reflexes

*airway constriction

*reduction in heart rate and force of contraction

*sexual arousal and sex gland stimulation

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ACh and its receptors

All parasympathetic synapses use ACh

Effects are brief due to AChE and tissue cholinesterase presence.

Effects are restricted to specific targets.

2 types of receptors for ACh

Nicotinic: Excitatory

at all ganglionic synapses

Muscarinic: Excitatory or inhibitory

at parasympathetic neuromuscular and neuroglandular junctions


TABLE 2

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TOPICS









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Sympathetic / Parasympathetic Interactions Objectives

Review the innervation plan of the sympathetic and parasympathetic divisions.

Discuss the anatomy of dual innervation.

Using an illustration, compare the two divisions.

Discuss the concept of autonomic tone.

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The sympathetic division is widespread with innervation to nearly all organs and tissues in the body.

The parasympathetic division innervates only those structures associated with four cranial nerves and with

structures served by the pelvic nerves.

Most vital organs receive innervation from both divisions with effects in opposition to one another.

This is especially important in the digestive tract, the heart, and the lungs.

For the cranial nerves III, VII, IX and X, the postganglionic fibers course along with the cranial nerves while the

sympathetic fibers travel from chain ganglia to some of those same structures.

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Sympathetic / Parasympathetic Interactions (cont)

Sympathetic postganglionic

fibers + parasympathetic

preganglionic fibers form autonomic plexuses.

Fig. 9

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Comparison

Fig. 10

TABLE 2

LocalGlobal

1:32 1:6

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In visceral organs where there is dual innervation, there is a certain amount of background output from each division which is called autonomic tone.

Some regions and organs are innervated by one division only (blood vessels–sympathetic).

Background sympathetic output maintains tone on the peripheral blood vessels so that in order to achieve dilation or constriction, only slight adjustments are needed.

TABLE 3 lists a functional comparison of the ANS divisions.

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TOPICS









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Integration and Control Objectives

Introduce the concept of integrating levels of control.

Discuss long and short visceral reflexes.

Examine higher levels of autonomic control.

Discuss the integration of SNS and ANS activities.

Describe the concept of biofeedback.

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Like the SNS, the ANS is organized into various interacting levels of control.

Visceral reflexes represent the lowest level of interaction.

Visceral reflexes are comparable to somatic polysynaptic reflexes.

Visceral reflexes are either long reflexes or short reflexes.

Long reflexes involve the CNS processing of sensory information with ANS motor commands to visceral effectors over a relatively large area or an entire organ.

Short reflexes bypass the CNS and synapse on interneurons of autonomic ganglia for localized control of effectors.

Short reflexes control activity along small sections of the digestive tract.


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Integration and Control (cont)

Fig. 11 41

Most visceral reflexes are parasympathetic.

TABLE 4

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There are centers in the brain stem that control specific functions via the ANS.

Simple reflexes cause immediate responses to specific stimuli.

Processing centers in the medulla coordinate many complex parasympathetic and sympathetic reflexes.

The medulla controls the cardiovascular, respiratory, salivation, swallowing, vomiting, digestive secretory, peristaltic muscular contraction, and urinary functions.

The hypothalamus regulates the medullary centers.

Because of the widespread interaction of the hypothalamus with other brain nuclei and cortical centers, ANS control and integration becomes very complex.

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Levels of Integration

and autonomic

control

Fig. 12

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SNS and ANS are both under higher system

control.

Sensory input may result in output via the SNS and ANS

simultaneously.

Fig. 13 44

TABLE 5

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Biofeedback is an excellent example of higher center control over some ANS functions.

Biofeedback is a mechanism that involves monitoring of physiological processes which are “fed back” so a person can invoke conscious thoughts to control them.

For example, blood pressure may be monitored.

The person is trained to relax and use mechanisms of stress control to lower blood pressure.

The monitor informs the subject when pressure drops so they are aware of the success of their control effort.

Biofeedback control is used for the management of many disorders.

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TOPICS









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Higher-Order Functions Objectives

Discuss what is meant by higher-order functions.

Describe the types of memories.

Investigate the brain regions involved in memory consolidation and access.

Discuss the cellular mechanisms involved with memory.

Describe the state of consciousness.

Discuss sleep and arousal from sleep.

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Complex cortical interactions

Memory

Conscious activities / learning

Unconscious activities

Higher-Order Functions

Higher-Order functions include:

Because higher-order functions do not involve programmed functions such as reflexes, they are

subject to modification and adjustment over time.

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Higher-Order Functions (cont)

Memories are bits of information stored in the cortex.

Fact memories are specific – red stop sign, smell of pizza, shape of a car versus a truck, etc.

Skill memories are learned motor behavior patterns – how to open a can, how to turn on the shower, etc.

With repetition, skill memories may be become part of your unconscious or programmed behavioral patterns such as eating, driving, swimming, golfing, etc.

Cerebral nuclei and the cerebellum will participate.

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Short–term memories are primary, can be recalled immediately, and last a short time.

Long–term memories are secondary and last much longer—perhaps even a lifetime.

Consolidation converts short term memories to long ones.

There are two types of long–term memories:

*secondary memories that fade with time; difficult to recall

*tertiary memories that are part of your conscious being such as knowing your name, knowing the contours of your body


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Fig. 14

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Memory Storage

Memory is complex

Amnesia is the loss of memory.

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Regions involved in memory:

cerebral cortex — storage for long–term memories with association areas important storage sites

hippocampus + amygdaloid body — convert short–term memories to long–term memories

amygdaloid body — relates memories to emotions

nucleus basalis (near diencephalon) — some role in storage and retrieval

The visual association area helps you remember what a cat looks like, or your best friend; the speech center tells you how to say the word “cat”, the auditory association area tells you what “meow” sounds like and that it is a cat call, etc.


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How memories are consolidated is poorly understood.

How they are retrieved is even less well understood.

What is known: a synapse that is frequently active does increase its output of neurotransmitter to produce a

greater effect on the postsynaptic neuron(s).

Circuits that are repeatedly active release a low level of neurotransmitter that results in facilitation of postsynaptic neurons(s).

Highly active neurons establish increased numbers of synapses with the postsynaptic neuron to produce a greater effect.

A single circuit may correspond to a single long–term memory (memory engram) and take 1 hour to form.

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Consciousness is the degree of wakefulness and alertness.

If you are conscious, you are alert and attentive.

There are gradations in the degree of consciousness.

Sleep is an unconscious state from which you may be awakened by normal sensory stimuli.

There are two levels of sleep, deep sleep (non–REM) and rapid eye movement (REM) sleep.

In NREM sleep, the body relaxes and metabolism slows.

In REM sleep, dreaming occurs; you are less receptive to sensory stimuli (around 2 hours per night).

REM and NREM alternate throughout the night.


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Alpha waves

NREM


Delta waves

Fig. 15

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Arousal from sleep is a function of the RAS

(reticular activating system)

The RAS alerts your thalamus which

stimulates the cortex.

Fig. 16

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TOPICS









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Brain Chemistry and Behavior Objectives

Discuss the importance of understanding the interplay between neurotransmitters.

Discuss the role of drugs or chemicals on behavior.

List several chemical disorders that have been documented to affect behavior.

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We know that all neural communication is chemical and that there are many neurotransmitter substances.

Awake – sleep cycles seem to depend on a balance between serotonin and norepinephrine.

Drugs that block serotonin synthesis or binding induce depression while drugs that prolong the presence of

serotonin (Prozac) are used to treat depression.

Drugs that stimulate NE producing neurons cause excitement while those that inhibit those neurons produce

depression.

Too little dopamine causes Parkinsons’s and excessive dopamine may lead to schizophrenia.

Personality is a mystery.

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Aging and the Nervous System Objectives

Describe some age–related anatomical changes in the nervous system.

Describe some age–related functional changes in the nervous system.

Discuss Alzheimer’s disease.

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The nervous system begins its decline about age 30.

Many individuals over age 65 may exhibit changes in their CNS function as documented below.

Anatomical changes:

*The brain size declines as the cortex is reduced.

*The number of neurons in the cortex declines.

*Blood flow to the brain declines due to atherosclerosis.

*The number of synapses decreases and neurotransmitter quantity likewise declines.

*Neurons may accumulate abnormal deposits consisting of pigments, proteins (amyloid), or neurofibril tangles.

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Aging and the Nervous System (cont)

Functional changes:

*Memory consolidation declines and access declines especially for secondary memories (recent past).

*Sensory processing is less acute.

*Fine motor control is more difficult and reflexes are slower.

Alzheimer’s disease is a progressive loss of higher–order functions that affects 15% of people over 65 and causes 100,000+ deaths / year in the U.S.

There is some evidence that several genes may be responsible for the development of senile dementia, especially Alzheimer’s.

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bio 168 neural integration ii: the autonomic nervous system and higher order functions chapter 16

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sympathetic function

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autonomic nervous system

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