NMJ AI

Question 1

What is a motor unit?

Answer 1

A motor neuron and all the muscle fibers it innervates

Each motor neuron activates all the muscle fibers it connects to when stimulated.

Question 2

What is the role of the neuromuscular junction (NMJ)?

Answer 2

It is the synapse between motor neurons and skeletal muscle cells

Also known as the motor end plate.

Question 3

What is the motor end plate?

Answer 3

The pre synaptic axon, the postsynaptic membrane of NMJ (the specialized sarcolemma of the muscle fiber), and the synaptic cleft

Question 4

What neurotransmitter is released at the NMJ?

Answer 4

Acetylcholine (ACh)

ACh is released from presynaptic vesicles in response to action potentials.

Question 5

What happens when ACh binds to its receptors at the NMJ?

Answer 5

Na+ and Ca2+ flow in, K+ flows out, causing depolarization

This generates an action potential in the muscle membrane.

Question 6

What is the function of dihydropyridine receptors (DHPR) in excitation-contraction coupling?

Answer 6

They detect action potentials and trigger Ca2+ release from the sarcoplasmic reticulum (SR)

DHPRs are voltage-sensitive receptors.

Question 7

What is the role of troponin in muscle contraction?

Answer 7

Ca2+ binds to troponin, causing a shape change that moves tropomyosin

This exposes binding sites on actin for myosin cross bridges.

Question 8

What initiates the power stroke during muscle contraction?

Answer 8

Attachment of myosin cross bridges to actin filaments

Myosin must be activated by ATP hydrolysis first.

Question 9

What is the importance of ATP in muscle contraction?

Answer 9

ATP allows myosin cross bridges to detach from actin

Contraction cycles can repeat as long as Ca2+ is present.

Question 10

What happens to Ca2+ after muscle contraction?

Answer 10

Ca2+ is actively pumped back to the sarcoplasmic reticulum

This leads to muscle relaxation.

Question 11

What enzyme degrades ACh at the NMJ?

Answer 11

ACh esterase (AChE)

It is present in both synaptic cleft and postsynaptic membrane.

Question 12

What are the characteristics of slow-twitch muscle fibers?

Answer 12

• Red color
• Small size
  *Aerobic
• Low myosin ATPase activity
• Suited for endurance exercise

Examples include postural muscles and the soleus.

Question 13

What defines fast-twitch muscle fibers?

Answer 13

• White color
• Large size
• anaerobic
• High myosin ATPase activity
• Suited for explosive activities

Examples include gluteal muscles.

Question 14

Fill in the blank: The _____ is the specialized area of the membrane of a skeletal muscle fiber that contains ACh receptors.

Answer 14

motor end plate

Question 15

True or False: Each muscle fiber receives multiple axon terminals from different motor neurons.

Answer 15

False

Each muscle fiber receives only one axon terminal from one motor neuron.

Question 16

What is the effect of increasing stimulation voltage?

Answer 16

• One motor unit activated
• More motor units activated
• All motor units activated

This leads to increased muscle tension.

Question 17

What characterizes unfused (or incomplete) tetany?

Answer 17

It involves partial relaxation between stimuli

Muscle tension increases but does not reach maximum.

Question 18

What is muscle fatigue?

Answer 18

The decline in ability of a muscle to generate force

It can occur after prolonged stimulation or intense exercise.

Question 19

What is the significance of the T tubules in muscle contraction?

Answer 19

They help spread action potentials deep into the muscle fiber

This stimulates the sarcoplasmic reticulum to release Ca2+.

Question 20

What structure of the NMJ specifically interacts with the motor neuron axon terminals?

Answer 20

The motor end plate

Question 21

The terminal of the motor neuron axon that interacts with a fiber is the _________________ terminal

Answer 21

Pre synaptic terminal

Question 22

The synaptic cleft is filled with _______________ knows as a basal lamina.

Answer 22

Extracellular matrix

Question 23

Where is the AChE ?

Answer 23

In the extracellular matrix of the synaptic cleft

Question 24

Is ACh vesicles in the pre or post synaptic axon terminal?

Answer 24

Pre synaptic

Question 25

Is ACh Receptor nicotinic or muscarinic?

Answer 25

Nicotinic

Question 26

Is the AChR in the pre or post synaptic membrane?

Answer 26

Post synaptic

Question 27

What does the AChR function as what channel?

Answer 27

Ligand-gated ion channel

Question 28

What causes the voltage-gated Na to open and thus the action potential generation?

Answer 28

The depolarization of the sarcolemma

Question 29

Slow-twitch muscle fibers are Type I or II?

Answer 29

Type I

Question 30

Type II muscle fibers are (fast/slow) twitch

Answer 30

Fast