MMED2931 Lecture Notes - Lecture 5: Esophagus, Peristalsis, Goose Bumps
4 Jun 2018
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Nervous System lecture 4: Control of visceral organs: Autonomic nervous system
Learning objectives:
1. Sympathetic nervous system: neural pathways, transmitters, and function
2. Parasympathetic nervous system: neuronal pathways, transmitters and function
3. Enteric nervous system
4. Sensory innervation of visceral organs
5. Visceral reflexes and brain control of autonomic activities
Autonomic Nervous System: ANS
- NS controls many body activities aimed at maintaining homeostasis
- If peripheral sensory system detects change in internal or external environment that
threatens homeostasis, CNS makes adjustments by controlling function of visceral
organs & tissues via its peripheral efferent division – ANS (= visceral motor system)
- ANS: responsible for regulating most of bodil futios that at e otrolled
conscious effort. E.g. movements of intestine, heart rate & blood pressure, body
temp, metabolism and energy regulation, focusing & iris adjustments in eye, etc.
- 3 divisions of the ANS:
o Sympathetic NS
o Parasympathetic NS
o Enteric NS
SNS, PNS, ENS:
- Both Sympathetic NS and Parasympathetic NS have ongoing activity or tone. In some
circumstances, activity of one division can dominate the other
- E.g. Spatheti N“ is far ore atie spatheti doiae during body stress
(fight or flight – heart rate and BP, metabolic rates and blood glucose levels, blood
supply to skeletal muscle ALL , but blood supply to gut shut down)
- Paraspatheti N“ usuall assoiated ith rest ad digest state paraspatheti
doiae). Heart rate , digestion, growth, immune responses, energy storage,
etc.
- Sympathetic and parasympathetic NS often (not always) act producing opposite
effects on visceral organs. Some cases effects are just different not opposite
- Most functions related to digestion controlled by ENS (with input from PNS and SNS)
Motor output from CNS:
- Most of iseral orgas reeie a dual autooi otor output fro CN“ – P and S
- To euro autooi patha: pregaglioi ell od is i CN“, postgaglioi
in peripheral ganglia. Autonomic neurons have single preganglionic myelinated axon,
and single postganglionic unmyelinated axon. At the periphery, autonomic axons
branch extensively
find more resources at oneclass.com
find more resources at oneclass.com
Sympathetic NS: basic plan
- Preganglionic sympathetic axons leave middle region of spinal cord to synapse onto
neurons in sympathetic chain ganglia (=paravertebral ganglia) beside spinal cord or
in other large ganglia (prevertebral ganglia – celiac ganglion, superior mesenteric
ganglion, inferior mesenteric ganglion)
- Postganglionic axons go to large number of organs
- Sympathetic NS: neurotransmitters and receptors:
-
-
Sympathetic NS: innervation and function – examples of sympathetic control
- Tonic activity (active almost all the time)
o Tonic constriction of skin, muscle and gut blood vessels (NA from
sympathetic nerves acts via receptors) to cause constriction of arterioles
o Tonic inhibition of gut motility via and receptors
o Tonic inhibition of bladder muscle via receptors
- Phasic activity (sometimes active)
o cardiac output during exercise: NA from sympathetic nerves acts on
receptors to heart rate and F of contraction
o Sweating (when you get hot)
o Lift goose bumps (when you get cold)
o Pupil dilation, etc.
Convergence and divergence of info in ANS: (see CNS for comparison)
- Convergence of inputs onto postganglionic (postsynaptic) neurons:
o Several preganglionic neurons (a & c neurons) in the ANS form
synapses with a single postganglionic neuron (neuron 3 in figure)
o This allows integration and selective activation of neuronal circuitry
- Divergence of outputs of preganglionic (presynaptic) neurons:
o Single preganglionic neuron in the ANS may innervate > 100
postganglionic neurons (neuron b in figure)
o This allows to amplify and distribute central signal with minimal
central representation (i.e. less neurons in CNS)
Sympathetic innervation of adrenal gland:
- Adrenal medulla innervated by preganglionic sympathetic
fibres that release ACh
- Cells of adrenal medulla similar to sympathetic ganglion cells
(have nicotinic receptors) but do not have an axon.
- Instead of releasing neurotransmitter onto a target, they
release (predominantly) adrenaline as a hormone into the
blood
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Nervous system lecture 4: control of visceral organs: autonomic nervous system. Learning objectives: sympathetic nervous system: neural pathways, transmitters, and function, parasympathetic nervous system: neuronal pathways, transmitters and function, enteric nervous system, sensory innervation of visceral organs, visceral reflexes and brain control of autonomic activities. Ns controls many body activities aimed at maintaining homeostasis. If peripheral sensory system detects change in internal or external environment that threatens homeostasis, cns makes adjustments by controlling function of visceral organs & tissues via its peripheral efferent division ans (= visceral motor system) Ans: responsible for regulating most of bodil(cid:455) fu(cid:374)(cid:272)tio(cid:374)s that (cid:272)a(cid:374)(cid:859)t (cid:271)e (cid:272)o(cid:374)trolled (cid:271)(cid:455) conscious effort. E. g. movements of intestine, heart rate & blood pressure, body temp, metabolism and energy regulation, focusing & iris adjustments in eye, etc. 3 divisions of the ans: sympathetic ns, parasympathetic ns, enteric ns. Both sympathetic ns and parasympathetic ns have ongoing activity or tone. In some circumstances, activity of one division can dominate the other.
