Module 3 Lecture 9: ANS and Somatic Nervous System

Question 1

What is each adrenal gland composed of?

Answer 1

• Inner adrenal medula = secretes epinephrine and norepinephrine
• Surrounding adrenal cortex = secretes steroid hormones

Question 2

What are adrenal glands to sympathetic ganglion?

Answer 2

Modified version of post sympathetic ganglion whose cell bodies don’t have axons

Question 3

If adrenals glands don’t have axons how do they pass their hormones?

Answer 3

Directly sends it to the blood

Instead of post ganglionic we have adrenal medulla

Question 4

The adrenal medulla contains high amounts of epinephrine compared to norepinephrine (80%:20%). What’s the reason behind this high number?

Answer 4

The adrenal medulla expresses high amounts of the enzyme (phenyl-N-methyltransferase) which converts norepinephrine to epinephrine

Question 5

What are cholinergic receptors?

Answer 5

Receptors that bind to ACh (Acetylcholine)

Question 6

What are the two Cholinergic receptors?

Answer 6

Nicotinic and Muscarinic

Question 7

What is nictonic? Where is it found and what is it responsible for?

Answer 7

Nicotnic is a cholinergic receptor (binds ACh) and it is found on postganglionic cell bodies in all autonomic ganglia.
* Nicotnic is directly responsible for the influx/efflux of sodium because the ACh binding to it opens up the receptor to let Na+ as well as K+ in and out

Question 8

What is muscarinic? Where can it be found and what is it responsible for?

Answer 8

Muscarinic is a metabotropic receptor (sends secondary messengers when a NT binds to the receptor) that binds ACh
* It can be found on effector cell membranes (smooth muscle, cardiac muscle, glands)
* ACh can have varying affects on target organs depending on what subtype of muscarinic receptor.

Question 9

What are adrenergic receptors?

Answer 9

Adrenergic receptors bind cathecholamines such as epinephrine & norepinephrine (receptors commonly known as cathecholamine receptor)
* Metabotropic receptors like Muscarinic so it deals with secondary messengers & is coupled to G-proteins

Question 10

What are examples of catecholamine receptors & explain how it works?

Answer 10

Beta 1 is an example of a cathecholamine receptor.
* Beta 1 when it binds Norepinephrine or Epinephrine to itself it opens up
* However, it does not allow for direct import of ions, rather it sends signals (secondary messengers) that cause some sort of intracellular effect
* I.e. Increasing the heart rate due to the secondary messengers

Question 11

What secondary messengers are utilized in beta receptors? Alpha receptors?

Answer 11

• Beta receptors: cAMP (Cyclic-AMP)
• Alpha receptors: Ca2+

Secondary messengers will cause different end effects based on what receptor they respond to

Question 12

What are agonist drugs?

Answer 12

Works in the same way as a NT to bind to a receptor in do the same actions as a NT

Question 13

What are antagonist drugs?

Answer 13

Antagonist drugs act in an opposing manner by blocking the binding site of a NT to inhibit its response

Question 14

Example of an antagonist drug and its consequence?

Answer 14

Atropin = blocks the muscarinic receptor (ACh reelased by parasympathetic postganglion fibres)
* Effects output of PNS so that HR does not decrease, rather increases

Question 15

What is a motor neuron?

Answer 15

Specific to the Somatic Nervous System; it is one long neuron that runs from the cell body to the effector

Question 16

Where can motor neurons be found?

Answer 16

Cell bodies of motor neurons are found in the ventral horn of the spinal cord & brainstem for head muscles

Question 17

How is the Somatic N.S. different from the Autonomic N.S.?

Answer 17

Its one neuron rather than 2 neuron chain and the NT that goes to the effector is ACh only

Binds to Nicotinic Receptors

Question 18

Level of activity of the motor neuron & its output to skeletal muscle fibres is determined by what?

Answer 18

Balance of EPSP and IPSP

Question 19

If a nerve to nerve is a synapse, then what is a motor neuron to a muscle fibre called?

Answer 19

Junction

Question 20

What is the neuromuscular junction?

Answer 20

Link between each axon terminal of a motor neuron & skeletal muscle fibres

Note: Motor neurons are myelinated

Question 21

What is a terminal button?

Answer 21

The axon terminal of the motor neuron but it is quite enlarged

Question 22

What is the motor end plate?

Answer 22

Found on the muscle fibre and this is the place of contact for a motor neuron axon terminal to release its vesicles to
* Motor end plates have a lot of ACh receptors

Question 23

Explain how the Neuromuscular junction works and the process of releasing ACh

Answer 23

1. Action potential is propagated along the motor neuron to the axon terminal (If enough EPSP and IPSP is induced of course)
2. This local action potential triggers the opening of Ca2+ voltage gated channels to allow the influx of Ca2+
3. Ca2+ rushing in means ACh is released by exocytosis in vesicles
4. ACh binds to receptors on the motor end plate of the muscle fibre
5. Binding of receptors opens up non-specific channels, leading to large movement of Na+ ions into the muscle fibre
6. This results in an End-Plate Potential (EPP) which are graded potentials which results in local depolarization across the muscle fibre
7. Local flow of current (graded potentials) results in Na+ channels across the muscle fibre to open and let sodium in
8. This results in another action potential being propagated across the muscle fibre
9. Muscle cell response is terminated after ACh is terminated by Acetyhcholinerase

Question 24

What are key differences between NM junction and Nerve where the action potential travels down?

Answer 24

• NM Junction has the motor neuron axon terminal propagate its action potential down the middle of the fibre - Allows current of graded potential to flow down both sides of the muscle fibre unlike the nerve which the action potential travels down the axon in one direction
• When the action potential is generated in the muscle fibre, since it is in the middle it travels down both directions

Question 25

Key difference between EPSP of Nerve to Nerve and EPP of Nerve to Muscle Fibre and why?

Answer 25

1 EPSP cannot generate an action potential down a postsynaptic nerve but 1 EPP can always generate an action down a muscle fibre
* Because the terminal button is so large, this results in more ACh being released which results in more sodium influx into the end motor plate which will induce an action potential