NMJ AI Flashcards
What is a motor unit?
A motor neuron and all the muscle fibers it innervates
Each motor neuron activates all the muscle fibers it connects to when stimulated.
What is the role of the neuromuscular junction (NMJ)?
It is the synapse between motor neurons and skeletal muscle cells
Also known as the motor end plate.
What is the motor end plate?
The pre synaptic axon, the postsynaptic membrane of NMJ (the specialized sarcolemma of the muscle fiber), and the synaptic cleft
What neurotransmitter is released at the NMJ?
Acetylcholine (ACh)
ACh is released from presynaptic vesicles in response to action potentials.
What happens when ACh binds to its receptors at the NMJ?
Na+ and Ca2+ flow in, K+ flows out, causing depolarization
This generates an action potential in the muscle membrane.
What is the function of dihydropyridine receptors (DHPR) in excitation-contraction coupling?
They detect action potentials and trigger Ca2+ release from the sarcoplasmic reticulum (SR)
DHPRs are voltage-sensitive receptors.
What is the role of troponin in muscle contraction?
Ca2+ binds to troponin, causing a shape change that moves tropomyosin
This exposes binding sites on actin for myosin cross bridges.
What initiates the power stroke during muscle contraction?
Attachment of myosin cross bridges to actin filaments
Myosin must be activated by ATP hydrolysis first.
What is the importance of ATP in muscle contraction?
ATP allows myosin cross bridges to detach from actin
Contraction cycles can repeat as long as Ca2+ is present.
What happens to Ca2+ after muscle contraction?
Ca2+ is actively pumped back to the sarcoplasmic reticulum
This leads to muscle relaxation.
What enzyme degrades ACh at the NMJ?
ACh esterase (AChE)
It is present in both synaptic cleft and postsynaptic membrane.
What are the characteristics of slow-twitch muscle fibers?
- Red color
- Small size
*Aerobic - Low myosin ATPase activity
- Suited for endurance exercise
Examples include postural muscles and the soleus.
What defines fast-twitch muscle fibers?
- White color
- Large size
- anaerobic
- High myosin ATPase activity
- Suited for explosive activities
Examples include gluteal muscles.
Fill in the blank: The _____ is the specialized area of the membrane of a skeletal muscle fiber that contains ACh receptors.
motor end plate
True or False: Each muscle fiber receives multiple axon terminals from different motor neurons.
False
Each muscle fiber receives only one axon terminal from one motor neuron.
What is the effect of increasing stimulation voltage?
- One motor unit activated
- More motor units activated
- All motor units activated
This leads to increased muscle tension.
What characterizes unfused (or incomplete) tetany?
It involves partial relaxation between stimuli
Muscle tension increases but does not reach maximum.
What is muscle fatigue?
The decline in ability of a muscle to generate force
It can occur after prolonged stimulation or intense exercise.
What is the significance of the T tubules in muscle contraction?
They help spread action potentials deep into the muscle fiber
This stimulates the sarcoplasmic reticulum to release Ca2+.
What structure of the NMJ specifically interacts with the motor neuron axon terminals?
The motor end plate
The terminal of the motor neuron axon that interacts with a fiber is the _________________ terminal
Pre synaptic terminal
The synaptic cleft is filled with _______________ knows as a basal lamina.
Extracellular matrix
Where is the AChE ?
In the extracellular matrix of the synaptic cleft
Is ACh vesicles in the pre or post synaptic axon terminal?
Pre synaptic
Is ACh Receptor nicotinic or muscarinic?
Nicotinic
Is the AChR in the pre or post synaptic membrane?
Post synaptic
What does the AChR function as what channel?
Ligand-gated ion channel
What causes the voltage-gated Na to open and thus the action potential generation?
The depolarization of the sarcolemma
Slow-twitch muscle fibers are Type I or II?
Type I
Type II muscle fibers are (fast/slow) twitch
Fast
