AUTONOMIC NERVOUS SYSTEM

CHAPTER 3CHAPTER 3AUTONOMIC NERVOUS SYSTEMAUTONOMIC NERVOUS SYSTEM

By Hermizan Bin HalihanafiahBy Hermizan Bin Halihanafiahhermizanhalihanafiah@gmail.comhermizanhalihanafiah@gmail.com

INTRODUCTION

The peripheral nervous system, or PNS, consists of the cranial nerves, spinal nerves and ganglia.

The peripheral nervous system subdivided into:

1. Autonomic nervous system: - sympathetic nervous system - parasympathetic nervous system2. Somatic nervous system

The autonomic nervous system (ANS or visceral nervous system) is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls function.

Responsible for control of “involuntary” or visceral bodily function:

Cardiovascular Respiratory Digestive Urinary Reproductive functions Key role in the bodies response to stress

AUTONOMIC NERVOUS SYSTEM

General function of the autonomic nervous system.

The autonomic nervous system (ANS) regulates the activities of cardiac muscle, smooth muscle, and glands.

It is classically divided into two subsystems:

SYMPATHETIC NERVOUS SYSTEM:Allow body to function under stressFight or flightPrimes body for intense skeletal muscle activity

PARASYMPATHETIC NERVOUS SYSTEMMaintenance functions Rest-and-digest Counterbalances sympathetic function

AUTONOMIC NERVOUS SYSTEM

“Fight or flight”Sympathetic

Parasympathetic “Rest and Digest”

In general nerve impulses from one division of the ANS stimulate the organ to increase its activity (excitation), and another part inhibit the organs activity (inhibition).

Structurally, ANS includes:

a. autonomic sensory neurons (afferent)

b. integrating centers in the CNS

c. autonomic motor neurons (efferent)

AUTONOMIC NERVOUS SYSTEM

Comparison Somatic and Autonomic Nervous System

Characteristics Somatic nervous system

Autonomic nervous system

Sensory neuron Somatic senses and special senses

Mainly from interoceptors 9located in blood vessel, visceral organ, nervous system that monitor internal environment)

Effector Skeletal muscle Cardiac, smooth muscle and glands

Control of motor neuron

Voluntary control from cerebral cortex, with contribution from basal ganglia, cerebellum, brainstem and spinal cord.

Involuntary control from hypothalamus, lymbic system, brain stem and spinal cord; limited control from cerebral cortex.

Comparison Somatic and Autonomic Nervous System

Characteristics Somatic nervous system

Autonomic nervous system

Motor neuron (efferent) pathway

One motor axon from CNS to effector

Two neuron pathway:

One motor axon fromCNS to autonomicganglion(preganglionic)One motor axon fromautonomic ganglionto effector(postganglionic)

Characteristics Somatic nervous system

Autonomic nervous system

Location of ganglion

Motor in CNS. Sensory in dorsal root.

Autonomic ganglion outside CNS. Preganglionic and sensory shared with somatic nervous system.

Neurontransmitter Acetylcholine (Ach): always excitatory

Sympathetic postganglionic neurons release Norepinephrine (NE), to sweat gland release ACH. All parasympathetic postganglionic neurons release ACh.

ANATOMY OF AUTONOMIC MOTOR PATHWAYS

OVERVIEWa.   PREGANGLIONIC NEURONS (type B)

b.   AUTONOMIC GANGLIAc.   POSTGANGLIONIC NEURONS (type C)

ANATOMY OF AUTONOMIC MOTOR PATHWAYS

a. Preganglionic neurons:Its cell body located within gray matter of the CNS

(brain or spinal cord)Its myelinated axon exits the CNS.The preganglionic axon passes from the CNS

in a spinal or a cranial nerve. The preganglionic axon terminates in a

ganglion.

b. Autonomic ganglion.A ganglion is a collection of nerve cell bodies

located in a specific site within the body, but outside the CNS.

c. Postganglionic neurons:The cell body located in an autonomic ganglion.The location of the ganglion is dependent upon

the division of the ANS to which the neuron belongs and which organ it will innervate.

The axons of a postganglionic unmylinated fiber.The postganglionic axon passes from the

ganglion to the effector (cardiac muscle, smooth muscle, or gland) is either stimulated or inhibited.

Sympathetic Preganglionic Neurons

In the Sympathetic Division (thoracolumbar division):

The cell bodies in the lateral horns of the gray matter

in the 12 thoracic segments (T1-T12) and the first two

(L1-L2) lumbar segments of the spinal cord. Therefore, the sympathetic division is called the thoracolumbar division.

Their axons travel in the spinal nerves of these segments, known as the thoracolumbar outflow.

Parasympathetic Preganglionic Neurons

In the Parasympathetic Division (craniosacral division)

cell bodies arise from the nuclei of cranial nerves in the brainstem III, VII, IX, and X and in the lateral gray matter of the second through fourth sacral segments (S2-S4) of the spinal cord, called the craniosacral division.

The axons of the preganglionic neurons are referred to as the craniosacral outflow.

AUTONOMIC GANGLIA

Two major groups of autonomic ganglia:

1. Sympathetic ganglia (sympathetic division)

i. Sympathetic trunk ganglia (vertebral chain ganglia or paravertebral ganglia)

ii. Prevertebral ganglia

2. Parasympathetic ganglia (pasympathetic division)

i. Terminal ganglia (ciliary ganglion, pterygopalatine ganglion, submandibular ganglion, otic ganglion)

i. Sympathetic trunk ganglia (Vertebral chain ganglia or paravertebral ganglia)

Lie in a vertical row on either side of the vertebrae column.

Extend from the base of the skull to the coccyx. Postganglionic axons from sympathetic trunk

ganglia primarily innervate organs above the diaphragm.

In the neck (specific names) called superior cervical ganglion, middle cervical ganglion, and inferior cervical ganglia.

Most sympathetic preganglionic axons are shorter than sympathetic postganglionic axons because sympathetic trunk ganglia near to the spinal cord.

Sympathetic ganglia

ii. Prevertebral ganglia in the sympathetic division:

Lie anterior to the vertebral column and close to the large abdominal arteries.

In general, postganglionic axons from prevertebral ganglia innervate organs below to the diaphragm.

5 major prevertebral ganglia: i) Celiac ganglion ii) Superior mesenteric ganglion iii) Inferior mesenteric ganglion iv) Aorticorenal ganglion v) Renal ganglion

Sympathetic ganglia

Celiac ganglion – on either side of the celiac trunk, an artery that just inferior to the diaphragm.

Superior mesenteric ganglion – near the beginning of the superior mesenteric artery in the upper abdomen.

Inferior mesenteric ganglion – near to the inferior mesenteric artery in the middle of the abdomen.

Aorticorenal ganglion and renal ganglion – near to the renal artery of each kidney.

Sympathetic trunk ganglia /

paravertebral ganglion

Prevertebral ganglion

Parasympathetic GangliaTerminal ganglia - The parasympathetic

division uses terminal (intramural) ganglia located very close to or within the walls of a viscera organ to be innervated.

Terminal ganglia in the head are the ciliary ganglion, pterygopalatine ganglion, submandibular ganglion and otic ganglion.

Parasympathetic preganglionic axons are longer than parasymapthetic postganglionic axons because terminal ganglia are close to the visceral organ.

Postganglionic Neurons

Because of the locations of ganglia, sympathetic postganglionic fibers are relatively long while parasympathetic postganglionic fibers are

relatively short. 

IN THE SYMPATHETIC DIVISION

Once axons of sympathetic preganglionic neurons pass to sympathetic trunk ganglia, they may connect with postganglionic neurons in one of the following ways:

1. An axons may synapse with postganglionic neurons in the ganglion it first reaches.

2. An axons may ascend or descend to a higher or lower ganglion before synapsing with postganglionic neurons. The network of incoming axons collectively called sympathetic chains.

Sympathetic Postganglionic Neurons

3. Without synapsing, an axons continue through the sympathetic trunk ganglion to end at prevertebral ganglion and synapse with postganglionic neurons there.

4. Without synapsing, an axons may pass through sympathetic trunk ganglion and prevertebral ganglion and extend to the chromaffin cells of adrenal medulla.

Sympathetic Postganglionic Neurons

A single sympathetic preganglionic fiber has many axon collateral.

This explain why many sympathetic responses affect almost the entire body simultaneously.

After exiting to their ganglia, the postganglionic axons typically terminate in several visceral effector.

Sympathetic Postganglionic Neurons

SYMPATHETIC DIVISION

IN THE PARASYMPATHETIC DIVISION

Axons of preganglionic neurons of the parasympathetic division pass to the terminal ganglia near or within a visceral effector.

In the ganglion, the presynaptic neuron usually synapse with 4 or 5 postsynaptic neurons, all of which supply a single visceral effector, allowing parasympathetic response to be localized to a single effector.

Postganglionic Neurons

EFFECTS OF SYMPATHETIC NERVOUS SYSTEM

The sympathetic system prepares the body to meet emergency demands and is primarily involved with processes that expend energy.  During physical or emotional stress, the sympathetic division dominates the parasympathetic system, initiating a series of activities known as the fight-or-flight response.

In addition, there is activation of the adrenal medulla, causing secretion of norepinephrine and epinephrine as hormones to greatly heighten the response.

Cardiovascular SystemIncreasing heart beatIncrease blood supply to cardiac muscle

(dilate the coronary artery)Raised peripheral resistance and blood

pressure by constricting the small artery the skin. In this way increase blood supply is available for highly active tissue, such as skeletal muscle, heart and brain.

Constrict the blood vessel in secretory glands of digestive system

Accelerates blood coagulation because of vasoconstriction.

Respiratory system

Causes smooth muscle relaxation and therefore dilatation of the airways, especially bronchioles.

Allowing a greater amount of air to enter the lungs at each inspiration, and increase the respiratory rate.

Deal with ’fight and flight’ situation.

Digestive and urinary system

Liver increase conversion of glycogen to glucoseStomach and small intestine; smooth muscle

contraction (peristalsis) and secretion of digestive juices are inhibited, delaying digestion and the tone of sphinxter muscle is increased.

Adrenal gland; stimulated to secrete adrenaline and noradrenaline which potentiate and sustain the effect of sympathetic stimulation

Urethral and anal sphincter; muscle tone increase, inhibit micturition and defecation.

Bladder walls relaxesMetabolic rate increase

EyeDilating the pupilOpening the eyes open wide and giving the

appearance of alertness and excitement

SkinIncrease sweat secretion, leading to

increased heat loss from the bodyContract the arrector pili muscle on the skinConstrict the peripheral blood vessel

increasing blood supply available to active organs, e.g heart and skeletal muscle.

The parasympathetic nervous system is an energy conservation-restorative system.  It regulates those activities that conserve and restore body energy during times of rest and digest.

The parasympathetic nervous system dominates over sympathetic activity in the glands and smooth muscle of the gut, stimulating glandular secretion and the gut movements necessary for food to be digested and absorbed.

Salivation, lacrimation, urination, and defecation, all controlled by the parasympathetic nervous system.

EFFECTS OF PARASYMPATHETIC NERVOUS SYSTEM

 Cardiovascular SystemDecrease the rate and force of the heartbeatConstrict the coronary artery reducing the

blood supply to cardiac muscle

RespiratoryProduces contraction of smooth muscle in

airway walls causing their constriction, e.g. bronchioles and bronchi

EyeConstricting the pupilThe eyelids tend to closed, giving the

appearance of sleepiness.

Digestive and urinary systemLiver: conversion of glucose to glycogen and

secretion of bile are increased.Stomach and small intestine: Motility and

secretion are increased together with the rate of digestion and absorption of food.

Pancreas: secretion of pancreatic juice and the hormone insulin are increase.

Urethral and anal sphincter: relaxation in urethral and anal sphincter, micturition and defecation occurs.

Neurotransmitters are chemicals which transmit signals from a neuron to a target cell across the synapes.

The postganglionic neurons use different neurotransmitters and the effectors bear different receptors.

The hypothalamus regulates the balance of sympathetic versus parasympathetic activity or tone.

 In general, we are in parasympathetic tone, except during states of emergency when we immediately switch to sympathetic tone.

Neurotransmitter (Autonomic Nervous system)

At a sympathetic nervous system:

Preganglionic neurons use Acetylcholine (ACh) as a neurotransmitter.

Most postganglionic neurons utilize noradrenaline (norepinephrine)—with the major exception that postganglionic neurons innervating sweat glands use acetylcholine.

At the parasympathetic nervous system:

all preganglionic neurons and all postganglionic parasympathetic neurons uses Acetylcholine (ACh) as its neurotransmitter

NEUROTRANSMITTER