THE AUTONOMIC NERVOUS SYSTEM
❖ The peripheral Nervous system is composed of the somatic & Autonomic nervous
systems.
❖ These two systems are chiefly distinguished by the type of effector organs they innervate
and the functions they control.
Feature Somatic Nervous Autonomic Nervous
System System
Function Voluntary motor control Involuntary system
Target organ Skeletal muscles Visceral organs
Neuron type Each pathway has a single Each pathway has two
motor neuron. motor neurons: a
preganglionic and post
ganglionic neuron.
Neurotransmitter Acetylcholine Acetylcholine/noradrenali
ne
Divisions of the ANS
❖ The sympathetic
❖ The parasympathetic
❖ The enteric nervous system
The sympathetic and parasympathetic complement each other in regulation of organ function.
THE SYMPATHETIC SYSTEM
, ❖ The overall function of the sympathetic nervous system is to mobilize the body for
activity.
❖ If a person is exposed to a stressful situation, the sympathetic nervous system is
activated with a response known as “fight or flight.”
❖ It includes arterial pressure, blood flow to active muscles, metabolic rate,
blood glucose concentration, and mental activity.
❖ The sympathetic pathway/ organization. Preganglionic ganglion post ganglion
Effector organs.
preganglionic sympathetic neurons.
➔ Are the first neurons in the sympathetic pathway.
➔ Originate in the thoracolumbar region of the spinal cord (specifically in the thoracic and
lumbar segments)(T1–L3).
➔ The Location of preganglionic neurons in the spinal cord corresponds to the organs they
innervate in the body.
➔ This means that the location in the spinal cord can predict the targets of these neurons in
the periphery. E.g Preganglionic neurons that innervate organs in the thorax, such as the
heart, originate from the upper thoracic segments of the spinal cord while preganglionic
neurons that innervate pelvic organs, like the colon and genitals, originate from the
lumbar spinal cord.
➔ For structures like blood vessels, sweat glands, and muscles that make hair stand up
(pilomotor muscles), the preganglionic neurons synapse with multiple postganglionic
neurons along the sympathetic chain. This arrangement allows for a widespread and
coordinated response that can affect multiple areas of the body simultaneously.
➔ Exit Pathways: These neurons exit the spinal cord through the ventral motor roots and
white rami (the pathways leading to the sympathetic chain).
Ganglion (Synapsing Locations
➔ Some preganglionic neurons synapse (connect) with postganglionic neurons in
the paravertebral ganglia.
➔ The synapses can occur at the same spinal level or at different levels (higher or
lower), allowing for a wide-reaching network that can activate multiple areas
simultaneously.
➔ Location of Ganglia: The ganglia (clusters of nerve cell bodies) in the sympathetic
nervous system are situated close to the spinal cord. They are categorized into
two main groups:
● Paravertebral Ganglia/ Also known as the sympathetic chain,
these ganglia run alongside the spinal column.
● Prevertebral Ganglia: These ganglia are located more distally,
near the target organs.
❖ The peripheral Nervous system is composed of the somatic & Autonomic nervous
systems.
❖ These two systems are chiefly distinguished by the type of effector organs they innervate
and the functions they control.
Feature Somatic Nervous Autonomic Nervous
System System
Function Voluntary motor control Involuntary system
Target organ Skeletal muscles Visceral organs
Neuron type Each pathway has a single Each pathway has two
motor neuron. motor neurons: a
preganglionic and post
ganglionic neuron.
Neurotransmitter Acetylcholine Acetylcholine/noradrenali
ne
Divisions of the ANS
❖ The sympathetic
❖ The parasympathetic
❖ The enteric nervous system
The sympathetic and parasympathetic complement each other in regulation of organ function.
THE SYMPATHETIC SYSTEM
, ❖ The overall function of the sympathetic nervous system is to mobilize the body for
activity.
❖ If a person is exposed to a stressful situation, the sympathetic nervous system is
activated with a response known as “fight or flight.”
❖ It includes arterial pressure, blood flow to active muscles, metabolic rate,
blood glucose concentration, and mental activity.
❖ The sympathetic pathway/ organization. Preganglionic ganglion post ganglion
Effector organs.
preganglionic sympathetic neurons.
➔ Are the first neurons in the sympathetic pathway.
➔ Originate in the thoracolumbar region of the spinal cord (specifically in the thoracic and
lumbar segments)(T1–L3).
➔ The Location of preganglionic neurons in the spinal cord corresponds to the organs they
innervate in the body.
➔ This means that the location in the spinal cord can predict the targets of these neurons in
the periphery. E.g Preganglionic neurons that innervate organs in the thorax, such as the
heart, originate from the upper thoracic segments of the spinal cord while preganglionic
neurons that innervate pelvic organs, like the colon and genitals, originate from the
lumbar spinal cord.
➔ For structures like blood vessels, sweat glands, and muscles that make hair stand up
(pilomotor muscles), the preganglionic neurons synapse with multiple postganglionic
neurons along the sympathetic chain. This arrangement allows for a widespread and
coordinated response that can affect multiple areas of the body simultaneously.
➔ Exit Pathways: These neurons exit the spinal cord through the ventral motor roots and
white rami (the pathways leading to the sympathetic chain).
Ganglion (Synapsing Locations
➔ Some preganglionic neurons synapse (connect) with postganglionic neurons in
the paravertebral ganglia.
➔ The synapses can occur at the same spinal level or at different levels (higher or
lower), allowing for a wide-reaching network that can activate multiple areas
simultaneously.
➔ Location of Ganglia: The ganglia (clusters of nerve cell bodies) in the sympathetic
nervous system are situated close to the spinal cord. They are categorized into
two main groups:
● Paravertebral Ganglia/ Also known as the sympathetic chain,
these ganglia run alongside the spinal column.
● Prevertebral Ganglia: These ganglia are located more distally,
near the target organs.
