5. Autonomic Nervous System Flashcards
(30 cards)
Name the divisions of the Autonomic Nervous System
has three divisions: the sympathetic, the parasympathetic, and the enteric.
What type of system is the ANS?
a general visceral efferent (GVE) motor system
What does the ANS control?
controls and regulates smooth muscle, cardiac muscle, and glands. (Vegetative functioning PS and Fight or Flight S)
What usually accompanies the GVE fibres and what system are they a part of?
General visceral afferent (GVA) fibers run with GVE fibers.
They are considered to be part of the visceral nervous system, not the autonomic nervous system.
Describe the neuronal structure of the ANS
Consists of two types of projection neurons: preganglionic neurons and postganglionic neurons
(sympathetic ganglia have interneurons).
What is the final common pathway?
A motor pathway representing the point beyond which the neural code can no longer be altered.
Why is the role of interneurones unique in the ANS?
In the case of the ANS the interneurone stretches out to the periphery to establish communication with the ganglia (little brains) that regulate target organs.
Which experiment showed the signaling across the synapse to be chemical?
Otto Loewi’s Experiment
Describe Otto Loewi’s Experiment.
Before Loewi’s experiments, it was unclear whether signalling across the synapse was bioelectrical or chemical. Loewi’s famous experiment, published in 1921, largely answered this question. According to Loewi, the idea for his key experiment came to him in his sleep. He dissected out of frogs two beating hearts: one with the vagus nerve which controls heart rate attached, the other heart on its own. Both hearts were bathed in a saline solution (i.e. Ringer’s solution). By electrically stimulating the vagus nerve, Loewi made the first heart beat slower. Then, Loewi took some of the liquid bathing the first heart and applied it to the second heart. The application of the liquid made the second heart also beat slower, proving that some soluble chemical released by the vagus nerve was controlling the heart rate. He called the unknown chemical Vagusstoff. It was later found that this chemical corresponded to Acetylcholine (Kandel, et al. 2000).
What did Henry Dale Establish?
That Acetylcholine is found in the spleen and then it turned out to be a ubiquitous transmitter
How does chemical and electrical signal transmission differ?
Electrical stimulation does not amplify the signal , whereas chemical transmission acts as an amplifier which stimulates the target cels/tissues/
Which neurotransmitter is used in the preganglionic and postganglionic neurones?
It varies between each division of the ANS.
Sympathetic. PreG = Acethylcholine (Ach), PostG = Noradrenaline (some blood vessels and sweat glands receive cholinergic (Ach) symp innervation).
Parasympathetic. PreG + Post G = Acetylcholine (Ach)
What will the effect of excessive concentrations of neurotransmitter be to the receptor?
It will render the receptor inactive due to overstimulation.
What are the two categories of Ach receptors?
Nicotinic and Muscarinic
From where does outflow from the parasympathetic ns come?
From
Cranial Nerves: III, VII, IX, X
Sacral Outflow: S2, S3, S4 (Pelvic Splanchnic Nerves)
Describe the typical structure of the postganglioic neurone in the parasympathetic system?
Typically, they are embedded in the target organ and so are very short. There are some exceptions.
From where does outflow from the sympathetic NS come?
Essentially thoracic outflow from the spinal cord via a paravertabral ganglionic chain
Often the postG nerves have the same name as the arteries they follow.
Two chains, fairly symmetrical on either side of the body.
The two symph chains join in the ganglion empire at the base of the tail
Where do the preganglionic neurons of the sympathetic NS originate?
Always originate in the CNS within the lateral horn/intermediolateral cell column of the spinal cord.
The lateral horn is present only at spinal cord levels T1-L2,3 meaning that every preganglionic sympathetic neuron originates at these levels. There are no exceptions to this rule
What are the possible courses of preganglionic fibres of the sympathetic NS?
- SAME SEGMENTAL OUTFLOW Travel to sympathetic chain ganglion at the same level, entering via the white ramus communicans, synapsing and then the postganglionic fibres leave via the grey (unmyelinated) ramus communicans to course with the spinal nerve or independent splanchnic nerve.
- DIFFERENT SEGMENTAL OUTFLOW Travel to sympathetic chain ganglion but travel up/down chain to ganglion at different segmental level and then synapse… etc/
- OUTFLOW TO DIFFERENT PREVERTEBRAL GANGLION. Bypass sympathetic ganglion to synapse at prevertebral ganglion in the periphery.
Describe the autonomic control of the pupil
PSNS = Constricts pupil (miosis) Contracts for near vision (accommodation). CNIII via ciliary ganglion to muscles of dilation. SNS = Dilates pupil (mydriasis). From high toracici cord, enters symp chain, travel to top , forms synaptic contact in superior cervical ganglion, makes route and arrives at muscles of dilation for pupil.
Describe the location and innervation of postganglionic fibres of the SNS?
●● located in the sympathetic trunk (paravertebral ganglia) and in prevertebral (collateral) ganglia.
●● in the sympathetic trunk, project via gray communicating rami to spinal nerves and innervate blood vessels, arrector pili muscles, and sweat glands.
●● in prevertebral ganglia, project to abdominal and pelvic viscera.
Describe the autonomic control of salivation?
Parasympathetic stimulation evokes a copious flow of saliva. In contrast, sympathetic stimulation produces either a small flow, which is rich in protein, or no flow at all
What is Hexamethonium Man?
A synthetic Acetylcholine for nicotinic receptors only. Also selective for autonomic ganglia (as opposed to motor neuron receptors which also use Acetylcholine).
However Hexamethonium toxic since activates all ganglia, administering it is the equivalent of disabling the entire autonomic nervous system.
Name the drug with effectively disables the entire autonomic nervous system?
Hexmethonium Man
