Synapse and Muscle

Question 1

When are neurotransmitters released in to the synaptic cleft?

Answer 1

When the vesicles of the synaptic bouton fuse with the presynaptic membrane.

Question 2

When the release of neurotransmitters diffuse and bind to the receptors on the postsynaptic membrane, this results in?

Answer 2

results in excitatory or inhibitory effects at the postsynaptic membrane.

Question 3

Where do action potential in one neuron gets transmitted to another neuron or an effector tissue?

Answer 3

At the synapses

Question 4

The terminal regions of the axons branches and form what?

Answer 4

synaptic boutons

Question 5

When is myelination of an axon lost

Answer 5

When the bouton is in close contact with a dendrite or cell of anther neuron.

Question 6

Receptors are on which end of the membrane

Answer 6

The postsynaptic membrane for an action depolarized or repolarized

Question 7

Explain the steps of a Generic Synapse

Answer 7

Neurotransmitters molecules are sythetized and packaged in vesicles
An action potential arrives at the presynaptic terminal
Voltage-gated Ca++ opens and Ca++ rushes in

Question 8

What is the purpose of the Axon terminus?

Answer 8

To release neurotransmitters.

In addition to neurotransmitters arriving fro the cell body… NTM are also absorbed and recycled at the axon terminus

Question 9

We don’t want a neurotransmitter hanging around in the synaptic cleft because the signal won’t terminate… How are NTM broken down?

Answer 9

1. Broken down
2. Reabsorb
   Waiting to diffuse away is not practical.
   Nerve agents block the block the breakdown of ACH..

Question 10

What opens or during what phase are VGCC Voltage gated Calcium Channels open

Answer 10

During depolarization

Question 11

The 4 general Means of CA++ regulations are

Answer 11

Two channels and two pumps
Ligand gated Ca++ channel 
Voltage gated Ca++ channel
Ca++ pump uses ATP which changes ADP+Pi
Na++/Ca++ exchanger - 3Na for 2ca

Question 12

What is Ca++ concentration gradients extracellular and intracellular.

Answer 12

Extracellular 10 x-3 1-2 milliMolar

Intracellular 10 x-8 8-50 nanoMolar

Question 13

NTM are ligands and they activate receptors opening ion channels via 3 different modes of operation. What are the major modes of actions?

Answer 13

Ligand gated channel e.g. nicotinic AChR, ligand gated cation Na- and K+ channel found at NMJ.. Fastest

Direct G-protien coupling e.g. muscarinic AChR M2. Parasympathetic innervation of the heart.

Second Messenger coupling: Slowest eg Muscarinic AChR M1 e.g. innervation of sweat glands.

Question 14

Where are ligand gated cation Na+ and K+ channel found

Answer 14

At NMJ

Question 15

Chemical Synaptic transmission may result in either excitatory or inhibitory effects at the postsynaptic membrane. Explain explain the changes that happen in Excitatory postsynaptic potential EPSP and Inhibitory Postsynaptic Potential IPSP..

Answer 15

EPSP is depolarization due to Ca++ and Na++ going into the cell and K+ leaving.
IPSP is a hyperpolarizing change in local potential. This happen when Cl- moves in to the cell.

Question 16

What is Temporal and Spatial and when does action potential happens

Answer 16

An action potential happens when the temporal and spatial summation of local potentials reaches the threshold for action potential generation.
Neurons are subject to multiple inhibitory and stimulatory signals that produce local potential changes, which are subject to both temporal and spatial summation. The sum of these influences determines whether an action potential is produced

Question 17

Synapses with few muscle fibers for

Answer 17

control fine

for example the eye

Question 18

synapses with alot of muscle fibers for

Answer 18

strength

Question 19

Corticospinal deals with which function of the body

Answer 19

Moving a muscle

Question 20

Where do the upper motor neuron synapse

Answer 20

in the spinal cord.

Crosses through the pyramid of the medulla without synapse.

Question 21

Where the lower motor neuron hits the muscle fiber

Answer 21

Motor end plate

Question 22

At the neuromuscular junction, the axon of a motor nerve synapses with skeletal muscle at a site known as the

Answer 22

motor endplate.

Question 23

Stimulation of a motor nerve results in the release of

Answer 23

acetylcholine from vesicles at the presynaptic membrane

Question 24

acetylcholine diffuses and binds to postsynaptic receptors, producing

Answer 24

depolarization of the sarcolemma and leading to an action potential.

Question 25

Stimulation of a motor nerve of NMJ results in the release of

Answer 25

acetylcholine from vesicles at the presynaptic membrane

Question 26

The synapse between a nerve and muscle is termed

Answer 26

Neuromuscular junction (NMJ)

Question 27

What is the function of the enzyme Achetylcholinesterase and where is it located

Answer 27

In the space between pre and postsynaptic
membranes there is the basal membrane.
(AChE) that hydrolizes (breaks down ) ACh to choline gets reabsorb and acetic acid terminating its action.

Question 28

The VGCC at (1) is an N-type Ca++ channel; P/Q-type or R-type may also be present
The cation channel at (2) allows both Na+ and K+ to pass and is responsible for the EPP
The VG Na+ channel at (3) only allows Na+ to pass and is responsible for the muscle fiber action potential
The VGCC at (4) is an L-type Ca++ channel (aka DHP receptor)
The Ca++ channel at (5) is a “Ryanodine” receptor and is physically connected to (4) in skeletal muscle
(4) is on the T-tubule, while (5) is on the SR (sarcoplasmic reticulum)

Answer 28

The VGCC at (1) is an N-type Ca++ channel; P/Q-type or R-type may also be present
The cation channel at (2) allows both Na+ and K+ to pass and is responsible for the EPP
The VG Na+ channel at (3) only allows Na+ to pass and is responsible for the muscle fiber action potential
The VGCC at (4) is an L-type Ca++ channel (aka DHP receptor)
The Ca++ channel at (5) is a “Ryanodine” receptor and is physically connected to (4) in skeletal muscle
(4) is on the T-tubule, while (5) is on the SR (sarcoplasmic reticulum)

Question 29

The VGCC at (1) is an N-type Ca++ channel; P/Q-type or R-type may also be present
The cation channel at (2) allows both Na+ and K+ to pass and is responsible for the EPP (ACh is also release)
The VG Na+ channel at (3) only allows Na+ to pass and is responsible for the muscle fiber action potential
The VGCC at (4) is an L-type Ca++ channel (aka DHP receptor)
The Ca++ channel at (5) is a “Ryanodine” receptor and is physically connected to (4) in skeletal muscle
(4) is on the T-tubule, while (5) is on the SR (sarcoplasmic reticulum)

Answer 29

The VGCC at (1) is an N-type Ca++ channel; P/Q-type or R-type may also be present
The cation channel at (2) allows both Na+ and K+ to pass and is responsible for the EPP
The VG Na+ channel at (3) only allows Na+ to pass and is responsible for the muscle fiber action potential
The VGCC at (4) is an L-type Ca++ channel (aka DHP receptor)
The Ca++ channel at (5) is a “Ryanodine” receptor and is physically connected to (4) in skeletal muscle
(4) is on the T-tubule, while (5) is on the SR (sarcoplasmic reticulum)

Question 30

The post-synaptic response: causes the generation of the end plate potential (EPP).. What causes an EPP

Answer 30

The EPP (or EJP, excitatory junction potential) is an EPSP on a muscle fiber. EPP is caused by the opening of Ach receptors, and propagation on the muscle membrane is electrotonic, i.e. it decreases with distance in contrast to the action potential in nerve & muscle that propagates actively.

Question 31

Why do EPP decreases with distance in contrast to the action potential in nerve & muscle that propagates actively.

Answer 31

This is because AChR channels are only found at the end plate while voltage-gated Na channels are found all along the membrane in muscles.

Question 32

EPP has a reversal potential (membrane voltage at which it changes direction) at ~0 mV. Why?

Answer 32

This is because the AChR channel is permeable to both Na+ and K+ and an equilibrium between the Nernst potential of these ions and their relative flux is reached at ~0mV with equal Na+ entering and K+ leaving the cell.