Somatic efferent and ANS
Somatic Efferent
Control
External environment
single somatic efferent neuron
Acetlycholine
…is over skeletal muscles.
This division of the PNS responds to some change in the external environment.
Extends from the CNS to the effector (skeletal muscle) … is the NT released at the synapse (motor endplate.)
Autonomic nervous system
(visceral efferent)
Regulates visceral activities
No conscious control
Stable internal environment
Organs of the thoracic and abdominal regions; sweat and sebaceous glands, etc.
…over visceral activities.
Autonomic nervous system
Regulated by centers in
2 efferent neurons
One from CNS to ganglion
One to visceral effector
Acetlycholine (ACh) or norepinephrine (Ne)
CNS
Brain stem and cord
preganglionic postganglionic
Are the NTs released at the synapses.
preganglionic postganglionic ganglion
Structure of the ANS
Visceral efferent neurons organized into
Nerves (neurons)
Ganglia
Plexuses
Entirely motor
Pre- or postganglionic nerves.
Where the pre- or postganglionic neurons form a synapse; this is where the postganglionic soma is located.
Tangles of visceral efferent nerves.
1) Efferent neurons
preganglionic
Soma in brain or cord Myelinated axons
Synapses with postganglionic neuron
CNS
Postganglionic
autonomic ganglia Unmyelinated axons Synapses with effector
1) Efferent neurons
CNS
Somas are located within autonomic ganglia or target organs are found with postganglionic neurons
Sympathetic
thoracolumbar
helps body respond to stress
1) Efferent neurons
CNS
division of the ANS has its preganglionic somas in the... regions of the cord
This division of the ANS is called the “fight or flight’ division. If the body is under some threat or stress, the sympathetic stimulation goes up.
This causes an increase in heart and respiration rate, sweating, blood flow to the CNS and muscles.
This causes a decrease blood flow to some visceral organs, such as the intestines and the kidneys.
Parasympatheic
craniosacral
active under normal conditions
1) Efferent neurons
CNS
division of the ANS has its preganglionic somas in the... regions of the cord
This division of the ANS is called the “rest and repose” division. The parasympathetic division is stimulated under normal or resting conditions, when you want to cover from stress; build up reserves and maintain the body.
This causes a decrease in heart and respiration rate, sweating, blood flow to the CNS and muscles.
This causes an increase blood flow to some visceral organs, such as the intestines and the kidneys.
Dual innervation
The heart, each visceral organ and gland is innervated by both the sympathetic and parasympathetic divisions of the ANS.
Although each effector is under the control of both divisions, they are not simultaneously stimulated by both.
Which division predominates at any given time is determined by the demands on the body at that time.
2) Autonomic ganglia
a) sympatheic trunk or chain ganglia (
paravertebral or lateral ganglia)
Sympathetic division
Preganglionic fibers are short
Located close and lateral to the spinal cord. Stimulate primarily...
2) Autonomic ganglia
b) prevertebral ganglia (collateral ganglia)
Sympathetic division
Preganglionic fibers are short
Located anterior to the spinal cord. Stimulate primarily...
b) prevertebral
ganglia (collateral
ganglia)
Largest
Celiac
Superior mesenteric ganglia
inferior mesenteric ganglia
Some examples of prevertebral ganglia
Postganglionic fibers from this ganglion innervate organs of the abdomen; liver, gallbladder, stomach, pancreas, spleen.
Innervate the small intestine and part of the large.
Innervate most of the large intestine, kidney, bladder and reproductive organs.
2) Autonomic ganglia
c) terminal ganglia
Parasympathetic division
Preganglionic fibers are very long
Located within target visceral organs. Stimulate primarily...
3) Plexuses
Interlaced networks
Solar plexus or Celiac
plexus
Similar to the plexuses of the somatic
efferent PNS.
Tangles of visceral efferent nerve fibers.
Postgangionic fibers from the celiac ganglion pass through here.
Physiology of the ANS
Autonomic fibers release NT at synapse
Cholinergic
Adrenergic
…fibers release Ach at the synapse.
The preganglionic fibers of the sympathetic division are cholinergic. Ach is released to bind to the postsynaptic (postganglionic) neuron. …fibers release norepinephrine (NE) at the synapse.
Responses
Catechol-O-methyl transferase
NE tends to stimulate the effectors.
This enzyme, found in the synaptic gap, breaks down NE.
It has a similar function as acetylcholinesterase, but works at a slower rate.
As a result some NE tends to diffuse out of the synapse into the surrounding tissues, where it may exert an effect.
So the effects of sympathetic stimulation are more wide spread and last longer the parasympathetic stimulation.
Responses
Parasympathetic:
Both pre- and postganglionic fibers are cholinergic.
As Ach is rapidly broken down by acetylcholinesterase, it does not have a chance to diffuse from the synapse.
Visceral Autonomic Reflexes
smooth muscle
cardiac muscle
gland secretion
…similar to somatic reflexes. Target organs are...
Such as digestive system, vessels, reproductive.etc. Heart
Salivary, sweat, etc.
receptor
afferent neuron association neuron
visceral efferent preganglionic neuron
visceral efferent postganglionic neuron
visceral effector
Visceral sensations
conscious sensations
Control by higher centers
Hypothalamus
Cerebral cortex
Visceral sensations reach the conscious
levels of the mind if the a voluntary action is required to deal with the sensation; as in
urination or defecation.
For example; if hypothalamus determines that the the water content of the blood is too low, it will send signals to the higher brain centers to provide a sensation of thirst.
The cerebrum will respond to the thirst
sensation by stimulating drinking behaviors; a voluntary action.
