Somatic vs Autonomic (sympathetic vs parasympathetic)
-somatic muscles are basically those of the musculoskeletal system (those that we can consiously control)
beyond conscious control.
also known as the VISCERAL SYSTEM.
these nerves control smooth muscle, cardiac muscle, fat cells etc (anything not skeletal)
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.
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.
-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 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.
They synapse with:
The postganglionic neuron releases NE neurotransmitters.
They innervate many organs:
The postganglionic neuron releases ACh neurotransmitters.
increased heart rate
contraction of muscles
constriction of blood vessels
secretion of sweat
dilation of bronchi
increased blood sugar
increased blood pressure
dilation of pupils
Effects of Parasympathetic Nerve activation:
Heart rate decrease
contraction of pupils
dilation of peripheral blood vessels
constriction of bronchi