THE AUTONOMIC NERVOUS SYSTEM.pptx

7/28/2019 THE AUTONOMIC NERVOUS SYSTEM.pptx

1/20

THE AUTONOMICNERVOUS SYSTEM


2/20

Introduction

The autonomic nervous system controls the autonomic

functions of the body i.e. those initiated in the brain below the

level of the cerebrum. Although stimulation does not occur

voluntarily, the individual may be conscious of its effects. For

example, an increase in heart rate.


3/20

Effector organs

The effects of the autonomic activity are rapid and the effector

organs are:

smooth muscle cardiac muscle

glands


4/20

Efferent nerves

The efferent (motor) nerves of the autonomic nervous system

arise from the brain and emerge at various levels between the

midbrain and the sacral region of the spinal cord.

Many travel within the same nerve sheath as peripheral nerves.


5/20

Divisions

The autonomic nervous system has two divisions:

Sympathetic - stressful situations

Parasympathetic - during rest

They work in an opposing manner, thereby maintaining balance

of involuntary functions.


6/20

The sympathetic outflow


7/20

The parasympathetic outflow


8/20

Efferent neurones

Each division of the autonomic nervous system has two efferent

neurones between the central nervous sytem and the effector

organs:

Preganglionic neurone

Postganglionic neurone


9/20

Sympathetic nervous system

The sympathetic nervous system (SNS) is part of the autonomic

nervous system (ANS).The sympathetic nervous system

activates what is often termed the fight or flight response. Like

other parts of the nervous system, the sympathetic nervous

system operates through a series of interconnected neurons.Sympathetic neurons are frequently considered part of the

peripheral nervous system (PNS), although there are many that

lie within the central nervous system (CNS). Sympathetic

neurons of the spinal cord (which is part of the CNS)communicate with peripheral sympathetic neurons via a series

of sympathetic ganglia. Within the ganglia, spinal cord

sympathetic neurons join peripheral sympathetic neurons

through chemical synapses.


10/20

Sympathetic neurons

Spinal cord sympathetic neurons are therefore called presynapticneurons, while peripheral sympathetic neurons are called

postsynaptic (or postganglionic) neurons. At synapses within the

sympathetic ganglia, preganglionic sympathetic neurons release

acetylcholine, a chemical messenger that binds and activates

nicotinic acetylcholine receptors on postganglionic neurons. In

response to this stimulus, postganglionic neurons principally release

noradrenaline (norepinephrine). Prolonged activation can elicit the

release of adrenaline from the adrenal medulla. Once released,

noradrenaline and adrenalinebind adrenergic receptors on peripheral

tissues. Binding to adrenergic receptors

causes the effects seen during the

fight-or-flight response.

These include:

Pupil dilation

Increased sweating

Increased heart rate

Increased blood pressure


11/20

Sympathetic neurones

Two efferent neurones make up the sympathetic nervous system (SNS):

The preganglionic neurone has its cell body in the lateral column of grey

matter in the spinal cord between the levels of the first thoracic and 2nd or 3rd

lumbar vertebrae. The nerve fibre of the cell leaves the cord by the anterior

root and terminates at a synapse in one of the ganglia either in the lateral

chain of sympathetic ganglia or passes through it to one of the paravertebralganglia. Acetylcholine is the neurotransmitter at sympathetic ganglia.

The postganglionic neurone has its cell body in a ganglion and terminates in

the organ or tissue supplied. Noradrenline (norepinephrine) is usually the

neurotransmitter at sympathetic effector organs. The major exception is that

there is no parasympathetic supply to the sweat glands, the skin and bloodvessels of skeletal muscles. These structures are supplied by only

sympathetic postganglionic neurones, which are known as sympathetic

cholinergic nerves and usually have acetylcholine as their neurotransmitter.


12/20

Sympathetic nerves

Sympathetic nerves originate inside the vertebral column, toward themiddle of the spinal cord in the intermediolateral cell column (or

lateral horn), beginning at the first thoracic segment of the spinal cord

and are thought to extend to the second or third lumbar segments.

Because its cells begin in the thoracic and lumbar regions of the

spinal cord, the CNS is said to have a thoracolumbar outflow. Axons

of these nerves leave the spinal cord in the ventral branches (rami) of

the spinal nerves, and then separate out as 'white rami' (so called

from the shiny white sheaths of myelin around each axon) which

connect to two chain ganglia extending alongside the vertebralcolumn on the left and right. These elongated ganglia are also known

as paravertebral ganglia or sympathetic trunks. In these hubs,

connections (synapses) are made which then distribute the nerves to

major organs, glands, and other parts of the body.


13/20

Parasympathetic nervous system

Two neurones are involved in the transmission of impulses from

the source to the effecter organ. The neurotransmitter at both

synapses is aetylcholine:

Preganglionic - long in comparison to its counterpart in the SNS

and has its cell body in the brain or the spinal cord. Those

originating in the brain are the cranial nerves III, VII, IX and X

arising from nuclei in the mid-brain and brain stem, and their

nerve fibres terminate at or near effector organs

Postganglionic - usually very short and has its cell body eitherin a ganglion or in the wall of the organ supplied


14/20

Functions of the autonomic

nervous system

involved in many complex involuntary reflex activities

depends on sensory input to the brain or spinal cord, and or

motor output

reflex action is rapid contraction, or inhibition on contraction ofinvoluntary (smooth and cardiac) muscles or glandular

secretion

activities are coordinated subconsciously in the brain

some sensory input does not reach consciousness - may resultin temporary inhibition of reflex action


15/20

Stimulation

Sympathetic stimulation

allows the body to function under stress

Fight or Flight

Parasympathetic stimulation

controls vegetative functions

feed or breed or rest and response

constant opposition to sympathetic system


16/20

Effects of autonomic stimulation -

sympathetic


17/20


18/20


19/20


parasympathetic

Cardiovascular system

decreases the rate and force of the heart beat

constricts the coronary arteries, reducing the blood supply to the

cardiac muscle

Respiratory system

contraction of the smooth muscle in the airway walls leading to

bronchoconstriction


20/20


parasympathetic

Digestive and urinary systems

the liver

the stomach and small intestine

the pancreas urethral and anal sphincters

Eye

contraction of the circular muscle fibres of the iris causes thepupil to constrict

the eyelids tend to close, giving the appearance of sleepiness

the ciliary muscles contract to facilitate near vision.

THE AUTONOMIC NERVOUS SYSTEM.pptx

Documents

Transcript of THE AUTONOMIC NERVOUS SYSTEM.pptx