Physiology 3120 Lecture Notes - Lecture 8: Somatic Nervous System, Sympathetic Ganglion, Muscle Spindle

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Physiology 3120
Dr. Hore
Lecture 8
Autonomic Nervous System (ANS)
Motivational States: Hypothalamus Coordinates Responses:
- Endocrine
- Behavioural
- ANS
Definition of Autonomic Nervous System
- The portion of the nervous system that controls visceral functions (aka vegetative functions)
(has to do with the inner organs of the body and their coordination)
- Three divisions: Sympathetic, Para-sympathetic, Enteric (gut)
o Historically there was only 2, the SYN and the PSYN but now there is another division
that has been identified the enteric nervous system (2 nerve plexors in the gut)
Overall function
- Essential for control of individual organ function and for Homeostasis
- Operates in background (like house keeping)
o Fixing things up internally without bothering consciousness with it
o If I was to sit up from a chair, one function of the ANS is to control BP
o When you stand up, the blood in the system can go to the legs and there can be up to a
40% decrease in cardiac output
o This has the potential of the heart not having enough oxygenated blood to pump to the
brain and consequently there is the risk of fainting
o In the simple task of standing up, before the legs start to contract, if it’s a fast getting up
movement, the ANS has already produced constriction to the arteries to keep the BP
high as you are making that contraction movement to stand up
o As you are getting up, if there is any increase in blood pooling and decrease in CO, that
will be detected by receptors in the cardiovascular ANS tha twill result in feedback
responses that will maintain that constriction
- Stand up, blood to legs, 40% decrease in cardiac output, decrease to brain, faint.
- Feedback & Feedforward
o This is a feedward mechanism blood vessesls constricting before you make an action
(stand up)
o The feedback effect is the maintaining of the constriction `
Special Visceral Functions
- Heart Rate
- Blood Pressure and Blood Flow
- Body Temperature
- Airway Resistance
- Gastrointestinal Motility
- Secretion by Glands
- Bladder Motility
- Sexual Function
ANS exerts its action by controlling
- Smooth Muscle
- Cardiac Muscle
- Glands
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o Salivary, Sweat, Adrenal Medulla,
o Digestive, Prostate, Pancreas, etc
- It does not directly innervate skeletal muscles
Compared to Somatic Nervous System, the ANS
- Controls Internal Environment
o The somatic nervous system interacts with the external world
- Largely Involuntary
o The somatic nervous system is largely voluntary (there are some involuntary things like
stretch reflex, VOR, VPR but most of the activity is voluntary)
- Regulates intrinsically active organs (gut, heart)
- Dual Innervation (one excitatory; other inhibitory)
o There is just one somatic nervous system that has alpha motoneurons and skeletal
muscle
o ANS has dual innervation, one is excitatory and one is inhibitory to a particular organ
- Denervation of organ No atrophy
o If you were to cut a nerve to a skeletal muscle, you would get atrophy but if you were to
cut the nerve supply to the gut, it would not atrophy
o Most of the structures that receive innervation from the ANS, if you cut their axons,
there is no atrophy of that organ it will change its function somewhat but in a not
obvious way
Autonomic Reflex Arc
- the axon of the preganglion is myelinated and it falls in the B fiber category
- there are pregangionlic and post ganglionic axons
- preganglionic are myelinated B and postganglionic are C
- here are the sensory receptors - we can have pressure/stretch receptors (not muscle spindles
but still signal stretch in different organs in the body) or oxygen receptors or nociceptors
- there is an afferent pathway that comes into a preganglionic autonomic nerve in the spinal cord
- the axon of this preganglionic is myelinated and it falls in the B fiber category
- there is then a ganglion (a group of cells for which there can be a synaptic connection)
- SO preganglionic axons are myelinated and size B and the postganglionic axons are
unmyelinated and size C and they go to the effector organ
- if you electrically stimulate here and record a compound nerve then we get this A band with
alpha, beta, gamma, delta all myelinated with C fiber
- pregangionlic autonomic nerve has these myelinated nerves in the B category
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Document Summary

The portion of the nervous system that controls visceral functions (aka vegetative functions) (has to do with the inner organs of the body and their coordination) Three divisions: sympathetic, para-sympathetic, enteric (gut: historically there was only 2, the syn and the psyn but now there is another division that has been identified the enteric nervous system (2 nerve plexors in the gut) Essential for control of individual organ function and for homeostasis. Operates in background (like house keeping: fixing things up internally without bothering consciousness with it, when you stand up, the blood in the system can go to the legs and there can be up to a. If i was to sit up from a chair, one function of the ans is to control bp. 40% decrease in cardiac output brain and consequently there is the risk of fainting: this has the potential of the heart not having enough oxygenated blood to pump to the.

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