Physiology 3120 Lecture Notes - Lecture 28: Alpha Motor Neuron, Parasympathetic Nervous System, Autonomic Nervous System
2 May 2018
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Human Physiology Lecture 28
Autonomic Nervous System (ANS) 1
November 20 2017
- Motivational States: Hypothalamus Coordinates Responses:
o Endocrine system
o Behavioural changes
o ANS
o Coordinates responses & motivational states in the limbic system, and coordinates it in 3
basic ways
- ANS via the hypothalamus it implicates these motivational drives and states coming from the limbic
system
- Definition of Autonomic Nervous System;
o The portion of the nervous system that controls visceral (vegetative) functions
▪ Inner organs in the body and their coordination & function
o Three divisions: Sympathetic, Para-sympathetic, Enteric (gut)
▪ Enteric: two nerve plexus in the gut (separate part of the ANS)
- Overall function of the ANS:
o Essential for control of individual organ function and for Homeostasis
o Operates in background (house keeping)
▪ Fixing things internally without bothering consciousness
- Stand up from seated position; blood to legs, 40% decrease in cardiac output, decrease to brain, faint.
o Prevented by feedforward arteriole constriction
o ANS control blood pressure
o When you stand up, the blood in the system can go to the legs so that there is a decrease up
to 40% in the cardiac output – has the potential for the heart to not have sufficient
oxygenated blood to pump to the brain
▪ Risk of fainting
o In that task of standing up, before the legs start to contract (if it is fast getting up movement),
the ANS has already produced construction to the arteries to keep the blood pressure high as
you are making that contraction movement to stand up
o Example of feed forward mechanism; Blood vessels constricting before making a motor
action
o If there was any decrease in cardiac output, increase in blood pooling; it is recognized by
receptors in cardiac ANS
▪ Cause feedback responses that maintain that constriction
- BOTH Feedback & Feed forward associated with the ANS
Specific Visceral Functions performed by the ANS
- Heart Rate
- Blood Pressure and Blood Flow
- Body Temperature
- Airway Resistance (in bronchioles)
- Gastrointestinal Motility
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- Secretion by Glands
- Bladder Motility
- Sexual Function
ANS exerts its actions by controlling;
- Smooth Muscle (arterioles, gut muscle, etc.)
- Cardiac Muscle
- Glands:
o Salivary, Sweat, Adrenal Medulla, Digestive, Prostate, Pancreas, etc.
- DOES NOT DIRECTLY INNERVATE SKELETAL MUSCLE FIBERS
Compared to Somatic Nervous System, the ANS
- Controls Internal (rather than external) environment
- Largely Involuntary
- Regulates intrinsically active organs (gut, heart)
- Dual Innervation (one excitatory; other inhibitory) to a particular organ
o Parasympathetic excites, the sympathetic inhibits – always going to be opposite
- Denervation of organ – No atrophy
o In contrast, if you cut the sympathetic and parasympathetic nerve to the gut it would NOT
atrophy
o If you cut the axon from the ANS to the organ, no atrophy of the organ occurs
o It will change its function but not in obvious ways
- SNS:
o Alpha motor neuron going to skeletal muscle fibers
o Interacts with external world
o Largely voluntary
▪ But some is involuntary; Stretch reflex, VOR, VPR, etc.
o One alpha motor neuron
o Denervation of organ (e.g. gut, heart)– atrophy
▪ If you were to cut a nerve to a skeletal muscle, it would atrophy
SNS
ANS
Interacts with external world
Controls internal environment
Voluntary
Involuntary
One alpha motor neuron
Dual innervation – one excitatory, one
inhibitory to a particular organ
Denervation of organ – atrophy
Denervation of organ – no atrophy
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Autonomic Reflex Arc
- Reflex arc in the ANS
- Sensory Receptors:
o Stretch or pressure receptors (sensory receptors)
▪ STRETCH RECEPTORS NOT MUSCLE SPINDLES (& not as elaborate as muscle
spindles)
▪ Stretch receptors in different organs of the body
o Oxygen receptor
o Nociceptors
- Note: oxygen receptor and nociceptors seen in the SNS too
- Afferent pathway that comes into a preganglion autonomic nerve in the spinal cord
- Axon of the preganglionic axon is myelinated and it falls in the B fiber category
- Ganglion – group of cells where there can be a synaptic connection
- Preganglionic axons: myelinated B fiber
- Postganglionic axons: unmyelinated C fiber
- Unmyelinated axons go to the effector organ (smooth, cardiac muscle or glands)
I. Impulses are initiated in a variety of visceral (sensory) receptors: pressure/stretch receptors (GI
tract, bladder, heart), oxygen receptors (carotid bodies), and nociceptors
II. They are relayed via afferent sympathetic and parasympathetic nerves to the CNS
III. The sensory information is processed at various levels within the CNS (spinal cord, brain stem,
hypothalamus and portions of the cerebral cortex).
IV. Information is then transmitted via efferent pathways to visceral effectors (smooth muscle, cardiac
muscle and glands)
V. The efferent pathway is made up of a preganglionic axon and a postganglionic axon.
VI. The preganglionic axons have their cell bodies within the CNS; their axons (mostly myelinated B
fibers) synapse on the cell bodies of postganglionic neurons that are located in ganglia outside the
CNS; the axons of the postganglionic neurons (mostly unmyelinated C fibers) end on the visceral
effectors.
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find more resources at oneclass.com
Document Summary
Motivational states: hypothalamus coordinates responses: endocrine system, behavioural changes, ans, coordinates responses & motivational states in the limbic system, and coordinates it in 3 basic ways. Ans via the hypothalamus it implicates these motivational drives and states coming from the limbic system. Definition of autonomic nervous system: the portion of the nervous system that controls visceral (vegetative) functions. Inner organs in the body and their coordination & function: three divisions: sympathetic, para-sympathetic, enteric (gut, enteric: two nerve plexus in the gut (separate part of the ans) Overall function of the ans: essential for control of individual organ function and for homeostasis, operates in background (house keeping, fixing things internally without bothering consciousness. If there was any decrease in cardiac output, increase in blood pooling; it is recognized by receptors in cardiac ans: cause feedback responses that maintain that constriction. Both feedback & feed forward associated with the ans. Glands: salivary, sweat, adrenal medulla, digestive, prostate, pancreas, etc.
