clarification about adrenaline please

[Oh_Gee]

from GS-2. I thought that in the sympathetic system, the preganglionic nerve releases Ach onto the postganglionic nerve which then releases Norepinephrine on the muscle nerve. Am i wrong?

"15) The temporary increase in the sarcolemma's permeability to Na+ and K+ ions that occurs at the motor end plate of a neuromuscular junction is immediately preceded by:


a.The release of acetylcholine from the motor neuron into the synaptic gap.
b. The release of adrenaline from the motor neuron into the synaptic gap.
c. The passage of a nerve impulse along the axon of a motor neuron.
d. The release of noradrenaline from a sensory neuron into the synaptic gap.

To answer this question you must know that acetylcholine is an excitatory neurotransmitter that is important in motor neurons. Acetylcholine must cause an action potential in the following cell to continue the signal to the appropriate muscle. Action potentials start with the membrane becoming temporarily more permeable to sodium ions, causing depolarization of the membrane. Therefore, the post-synaptic membrane (motor end plate; BIO 5.1F) will become more permeable to the positive ions immediately following acetylcholine being released from the pre-synaptic membrane and reaching receptors on the post-synaptic membrane by diffusion."

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[Cawolf]

You are correct about the sympathetic nervous system - but wrong about this question.

This sounds like a question about a motor neuron innervating a neuromuscular junction.

There is no ganglion involved in this signal pathway - I suggest reviewing.

I would say the best takeaway is that acetylcholine is the neurotransmitter involved in voluntary muscle stimulation.

 

[The Brown Knight]

Agreed with the above post.
Also, at the neuromuscular junction, if the muscle cell depolarizes, the motor neuron ALWAYS releases Ach, which is THE excitatory neurotransmitter of the neuromuscular junction (at least for MCAT purposes)
Furthermore, epinephrine and norepinephrine (correct me if I'm wrong) are released by the adrenal medulla when the medullary cells are directly innervated by the sympathetic nervous system; the released epinephrine/norepinephrine goes into the BLOODSTREAM. I don't think it acts as a neurotransmitter at the neuromuscular junction.

 

[Oh_Gee]

i think i'm just starting to lose it...
what pathway do muscles work by? (from brain to muscle cell)

 

[The Brown Knight]

keep it simple!
brain --> spinal cord --> motor neuron --> muscle; Ach being main neurotransmitter at NM junction
and instead of memorizing where epinephrine/norepinephrine join the part, understand their systemic effects when they are released - e.g. preventing bloodflow to renal/digestive systems; promoting bloodflow to heart, muscle, and brain; bronchodilation, pupillary dilation, etc.

 

[Oh_Gee]

do you think i should know which part of the spinal column? like L1

 

[Czarcasm]

i think i'm just starting to lose it...
what pathway do muscles work by? (from brain to muscle cell)

I'm sorry to throw this at you, but I really think if you sit down and study this, it'll really help. There are two divisions of the nervous system in the body, Central NS (CNS) and Peripheral NS (PNS). CNS includes the brain and spinal cord. PNS is basically everything outside of that. We divide neuronal information into 3 pathways: Sensory (Transmission of Information) --> CNS (Integration of Information)--> Motor (Response). Furthermore, the motor division is subdivided into 2 divisions: Somatic and Autonomic (and Enteric but that's not really important).

Somatic division pertains to Skeletal Muscle which is under conscious control.
Autonomic Division is under unconcious control and mainly modulates visceral organs. It's further subdivided into: Parasympathetic and Sympathetic divisions.

The last piece of information worth knowing that may be helpful, especially for questions like these is this:

Somatic Neuron (1 neuron)
-------------------------> nAchR (Skeletal)

Parasympathetic Neuron (2 neurons: 1 presynaptic, 1 postsynaptic)
----------------------------> nAchR--> mAchR (Visceral Organs)

Sympathetic Neuron (2 neurons: 1 presynaptic, 1 postsynaptic)
---------> nAchR---------> adrenergicR (Visceral Organs)
----------->nAchR (neurochromaffin cells in adrenal medulla): mainly releases neurohormone epinephrine (little norepinephrine) into blood, travels to adrenergic receptors.

nt for nAchR is Ach (opens ion channel: Na+ influx)
nt for mAchR is also Ach (metabotropic: acts via 2nd messenger cascade)
nt for adrenergicR is norepinephrine (metabotropic: acts via 2nd messenger cascade)