BMS1052 Lecture 20: Lecture 20,21,22
5 May 2018
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Department
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Professor
Lecture 20, 21,22 -Autonomic Nervous system- HCP
Learning outcomes
• Overall role of the autonomic nervous system (ANS) in the functioning of the body as a
whole
– Impacts on all organs Ensures that the organs of the body behave in a manner
conducive to your survival as an individual
– Differs from the motor innervation to skeletal muscle (somatic NS) • ANS complexity
How the ANS can be all things to all organs
– Flexibility• Neurotransmitters • Receptors
Importance of the brain in ANS function – Brain-ANS links– Importance of the spinal cord
ANS dysfunction
Impact of disease, trauma on ANS function and consequences for whole body function
ANS, the young person’s system
Function of ANS
Homeostasis- ph, osmolality, ionic composition, temperature, energy, waste
Nerves fast and discrete
Hormones slow and diffuse
General outline
Central nervous system controls ANS and somatic NS/ sends info, orders to diff parts of the
body
Peripheral nervous system
-Autonomic
-Somatic
Somatic nervous system
Mission statement: to make muscle contract
No intrinsic ability of skeletal muscle to contract
– So, requires an innervation
– Highly specialized
A very simple system
– One nerve input per skeletal muscle fibre
– One neurotransmitter – acetylcholine (ACh)
– One receptor - nicotinic
– Neuromuscular junction
Autonomic nervous system (automatic no need to think about it)
Mission statement: Ensure that you survive today so that you can reproduce tomorrow
• Organs possess intrinsic activity
– Contract (smooth and cardiac muscle), secrete (glands)
– Innervation modulates, not initiates activity
• System very complex, nerves can
– Enhance activity or
– Suppress activity
• Need
-More than one neurotransmitter Hence need more than one nerve type
-More than one receptor
• Delivery of transmitter is
– Slop-on, not individual delivery
– Not discrete
– No specialized synapse
• A junction– No specialized line-up of receptors (diffuse) metabotropic receptors
Skeletal muscle (in somatic NS) will not contract without its nerve. On the other hand, the
autonomic nervous system has smooth and cardiac muscle which already have intrinsic
activity and the ANS modulates them in both directions
ANS in the eye accommodation
Muscle supplied by the SNS
Two divisions of ANS: provide flexibility
The modulatory, up or down, output demands two separate systems, two divisions
• sudden, perhaps stressful, perturbation “flight or fight” sympathetic
• housekeeping “rest and digest” parasympathetic
Flexibility
• Both divisions in most organs
– sympathetic and parasympathetic functionally opposing
It is very rare for both division to be on at the same time. If one division is on the brain will
switch off the other division
Sources of parasympathetic division
Axonal output:
Cranial nerves X & X1 Vagus NERVE (from neck to waist)
In general:
• ANS peripheral circuit consists of two neurons
• Parasympathetic
– preganglionic axons long
– ganglia usually on the wall of the target organ (thus near impossible to surgically
denervate)
– thus postganglionic axons short
• Sympathetic
– preganglionic axons shorter
– ganglia close to spinal cord (sympathetic chain ganglia, especially for
cardiovascular targets) or about half-way to target organ (eg mesenteric, hypogastric
ganglia)
– can surgically denervate (separate postganglionic cell body from terminals)
• Pre-ganglionic/post-ganglionic transmission
– Always acetylcholine (ACh) acting on nicotinic receptors
Both sympathetic and parasympathetic divisions
• For the two neurons
• They communicate in a ganglion (swelling due to presence of cell body of the second
neuron)
• Thus the two cells called
– preganglionic (cell body in the spinal cord), myelinated
– postganglionic (cell body in the ganglion), unmyelinated
• Post-ganglionic neurons communicate with cells of effector tissues
Document Summary
Learning outcomes: overall role of the autonomic nervous system (ans) in the functioning of the body as a whole. Impacts on all organs ensures that the organs of the body behave in a manner conducive to your survival as an individual. Differs from the motor innervation to skeletal muscle (somatic ns) ans complexity. How the ans can be all things to all organs. Importance of the brain in ans function brain-ans links importance of the spinal cord. Impact of disease, trauma on ans function and consequences for whole body function. Homeostasis- ph, osmolality, ionic composition, temperature, energy, waste. Central nervous system controls ans and somatic ns/ sends info, orders to diff parts of the body. No intrinsic ability of skeletal muscle to contract. One nerve input per skeletal muscle fibre. Autonomic nervous system (automatic no need to think about it) Mission statement: ensure that you survive today so that you can reproduce tomorrow: organs possess intrinsic activity.
