what type of nerve fibres constitute post ganglionic PARAsympathetic outflow?...somehow none of books mention?

Question

another one...pressure on pressure senstive nerves causes stimulation(A beta fibres)...pressure on motor nerves (A alpha) causes their inhibition. how do you explain this discrepency...is there somthing like pressure acts as a stimulant for sensory nerves and inhibitor for motor?
as far as my knowledge goes A type fibres are most succeptible to inhibiton by pressure.
and one more..compression of a nerve trunk( as in diseased states..) causes loss of cutaneous sensations first and then motor paralysis when compressed to extreme states...why is this when A fibres should be inhibited first and here pressure is causing inhibition of sensory fibres too..
this was in my mind for a long time...help me clear this..thanks

Answer 1

The post ganglionic parasympathetic outfow is by multipolar neurons.

The sensations from the nerve are carried from the nerve terminal to the CNS. The beta fibers carries the pressure input from their terminal end to the CNS. The sensations are picked up at the end of the nerve not in the middle of the axon. Any pressure at the middle of the sensory axon will block the impulses from traveling to the CNS and any pressure on the middle of the motor nerve will block the impulses from the CNS.
When you compress the nerve whether it is motor or sensory, the impulses are always blocked from conducting.

The pressure on the pressure sensitive nerve at some mid point of the nerve does not cause stimulation, but if blocks the impulses from conducting. The pressure at the terminal of that beta fibers at the region where it supplies only causes the stimulation.

For the second part of your question, it takes different amount of pressure to block the conduction in different nerves.

Answer 2

The motor nerves are efferent nerves involved in muscular control. The cell body of the efferent neuron is found in the central nervous system where it is connected to a single, long axon and several short dendrites projecting out of the cell body itself. This axon then forms a neuromuscular junction with the effectors. The cell body of the motor neuron is satellite-shaped. The motor neuron is present in the grey matter of the spinal cord and medulla oblongata, and forms an electrochemical pathway to the effector organ or muscle.Pressure on these nerves obstructs the neurochemical impulses . So motor and glandular inhibition occurs.
The structure of an afferent neuron contains a single long dendrite and a short axon; the shape of the cell body of an afferent neuron is smooth and rounded. Just outside the spinal cord, thousands of afferent neuronal cell bodies are aggregated in a swelling in the dorsal root known as the dorsal root ganglion. The impulses or messages carried along these fibers originally and naturally carry messages of pain and pressure. So on pressure more vollies of impulses are generated at pressure points aggravating the effect.
The effects are roughly comparable to flow of fluids along and against gravity. For nervous impulses "gravity" is centripetal ie towards CNS.