Somatic vs Autonomic (sympathetic vs parasympathetic)

Subdisivions of the nervous system
The nervous system can be divided into two parts: Somatic and Autonomic
Somatic nervous system
-this part of the nervous system controls voluntary movement and sensation.
-somatic muscles are basically those of the musculoskeletal system (those that we can consiously control)
Autonomic nervous system
This part of the nervous system is self-governing
beyond conscious control.
also known as the VISCERAL SYSTEM.
these nerves control smooth muscle, cardiac muscle, fat cells etc (anything not skeletal)
Journey of an autonomic motor pathway
An autonomic motor nerve has a different pathway/structure to the somatic nerve pathways we have been studying in detail.

An autonomic motor nerve exits the spinal cord (from the ventral side just like the somatic motor nerves) and synapses with an intermediate AUTONOMIC GANGLION before then moving on to stimulate the effector.

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Because of this Autonomic ganglion, the nerve is split into two neurons:
1. PREGANGLIONIC NEURON comes from the ventral root (by a myelinated pathway) and synapses at the autonomic ganglion
2. POSTGANGLIONIC NEURON comes from the autonomic ganglion (by an unmyelinated pathway) and synapses at the effector.

Difference in neurotransmitters released between somatic and autonomic motor neurons.
We have seen that the structure is different for the somatic and autonomic motor pathways:
-Somatic pathway is one myelinated neuron from the ventral root
-automic pathway is one myelinated preganglionic neuron to autonomic ganglion, and one unmyelinated postganglionic neuron to the effector.

ANOTHER KEY DIFFERENCE is the neurotransmitter emitted by the neuron to innervate the effector.
In somatic neurons, this neurotransmitter is always ACh (acetylcholine) to stimulate the muscle.
In autonomic neurons, this neurotransmitter is always ACh to synapse onto the autonomic ganglion, but can be EITHER ACh OR NE (norepinephrine) to either stimulate or relax the muscle.

Sympathetic vs Parasympathetic
Within the Autonomic/Visceral nervous system, there is a further division.
Sympathetic Division = responses associated with exercise, emotion, excitement
Parasympathetic Division = responses associated with repletion, rest, relaxation

Our body has a constant shift between SYMPATHETIC TONE and PARASYMPATHETIC TONE. Both are constantly being balanced.

Sympathetic system (accelerator)
The sympathetic system have a chain of ganglia alongside the vertebral column. neuron.
They synapse with:
spinal nerves
internal organs
blood vessels

The postganglionic neuron releases NE neurotransmitters.

Parasympathetic system (decelerator)
The parasympathetic system nerves arise from the cranial nerves (gloospharyngeal, facial, vagus). They have a LONG preganglionic neurons and a SHORT postganglionic.
They innervate many organs:
digestive tract
reproductive organs

The postganglionic neuron releases ACh neurotransmitters.

Alarm and Relaxation Response
Effects of Sympathetic Nerve activation:
increased heart rate
contraction of muscles
constriction of blood vessels
secretion of sweat
dilation of bronchi
increased blood sugar
increased blood pressure
decreased digestion
decreased salivation
dilation of pupils

Effects of Parasympathetic Nerve activation:
Heart rate decrease
contraction of pupils
increased salivation
dilation of peripheral blood vessels
constriction of bronchi
increased digestion

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