neuromuscular junctions

Question 1

what are the three types of muscle tissue ?

Answer 1

cardiac, smooth, skeletal

Question 2

which muscle tissue is multinucleated ?

Answer 2

Skeletal

Question 3

Name a function of skeletal muscle

Answer 3

causes movement
stops movement
prevent excess movement
of the bones and joints, maintaining skeletal stability and preventing skeletal structure damage or deformation.

Question 4

what is the connective tissue that each muscle is wrapped in called ?

Answer 4

epimysium,

Question 5

what are the functions of epimysium

Answer 5

epimysium,
which allows a muscle to contract and move powerfully while maintaining its structural integrity. The epimysium also
separates muscle from other tissues and organs in the area, allowing the muscle to move independently

Question 6

what are the three types of connective tissues that help support muscles called ?

Answer 6

epimysium, perimysium,endomysium

Question 7

what is the purpose of endomysium ?

Answer 7

The endomysium contains the extracellular fluid and nutrients to support the muscle
fiber. These nutrients are supplied via blood to the muscle tissue.

Question 8

What is the sarcolemma

Answer 8

The plasma

membrane of muscle fibers

Question 9

what is the sarcoplasm

Answer 9

the cytoplasm of muscle fibers

Question 10

what is the sarcoplasmic reticulum

Answer 10

the specialized

smooth endoplasmic reticulum, which stores, releases, and retrieves calcium ions (Ca++)

Question 11

What is the sarcomere ?

Answer 11

Each packet of these microfilaments(actin and myosin ) and their regulatory
proteins, troponin and tropomyosin (along with other proteins)
or
the smallest contractile unit of a muscle cell

Question 12

what is a summary of excitation-contraction coupling ?

Answer 12

for a skeletal
muscle fiber to contract, its membrane must first be “excited”—in other words, it must be stimulated to fire an action
potential. The muscle fiber action potential, which sweeps along the sarcolemma as a wave, is “coupled” to the actual
contraction through the release of calcium ions (Ca++) from the SR. Once released, the Ca++ interacts with the shielding
proteins, forcing them to move aside so that the actin-binding sites are available for attachment by myosin heads. The
myosin then pulls the actin filaments toward the center, shortening the muscle fiber.

Question 13

which neurotransmitter is present at neuromuscular junctions ?

Answer 13

acetyl choline

Question 14

what happens before excitation-contraction coupling ?

Answer 14

Signaling begins when a neuronal action potential travels along the axon of a motor neuron, and then along the individual
branches to terminate at the NMJ. At the NMJ, the axon terminal releases a chemical messenger, or neurotransmitter,
called acetylcholine (ACh). The ACh molecules diffuse across a minute space called the synaptic cleft and bind to
ACh receptors located within the motor end-plate of the sarcolemma on the other side of the synapse. Once ACh binds,
a channel in the ACh receptor opens and positively charged ions can pass through into the muscle fiber, causing it to
depolarize, meaning that the membrane potential of the muscle fiber becomes less negative (closer to zero.)
Muscle Tissue

As the membrane depolarizes, another set of ion channels called voltage-gated sodium channels are triggered to open.
Sodium ions enter the muscle fiber, and an action potential rapidly spreads (or “fires”) along the entire membrane to initiate
excitation-contraction coupling.

Question 15

The receptors on the motor end plate are nicotinic acetylcholine receptors. How can these best be described and what type of ion passes through when acetylcholine binds to them?

Answer 15

ligand gated ion channels and sodium is the ion that passes through

Question 16

What is responsible for the high concentration of calcium ions in the sarcoplasmic reticulum, and what allows its release?

Answer 16

the calcium pump pumps calcium against its concentration gradient into the sarcoplasmic reticulum which is released by voltage-gated calcium channels

Question 17

What must happen to the calcium ions surrounding the muscle fibers to allow muscle relaxation?

Answer 17

it needs to be sequestered back into the sarcoplasmic reticulum

Question 18

What is an agonist?

Answer 18

A ligand that binds to a receptor mediating its activity (i.e. mimicking the original ligand/molecule/neurotransmitter)

Question 19

What is an antagonist?

Answer 19

A ligand that binds to a receptor blocking its activity

Question 20

How can both agonists and antagonists to nicotinic acetylcholine receptors both result in muscle relaxation.

Answer 20

an antagonist blocks the receptor, not allowing depolarization of the motor end plate. In this case there is no depolarization to cause calcium release from the sarcoplasmic reticulum so no muscle contraction is initiated. In contrast, whilst an agonist activates the receptor causing an initial depolarization it also stays bound to the receptor stopping further depolarisations causing the released calcium ions to be sequestered and muscle relaxation to occur.

Question 21

Why are drugs that cause non-reversible inhibition of enzymes (such as acetylcholinesterase) a bad starting point for developing therapeutics?

Answer 21

their action cannot be reversed causing permanent effect and therefore modulation and fidelity is completely lost and will most likely result in severe (life threatening) side effects. Sarin nerve gas being a case in point

Question 22

describe in terms of a sarcomere, why, for the majority of our skeletal muscles, the tension or force is maximum approximately halfway through the range of contraction.

Answer 22

The contraction of our muscles is mediated by the cross-bridge cycling between myosin and actin. When the muscle (and therefore the sarcomere) is at its most stretched the h-zone is at its largest. At this point not all the thick filament (composed of myosin molecules) are overlapping the thin filaments (actin, tropomyosin, and troponin) which means that less force can be developed through the cross bridge cycling. At the mid point of the contraction range, the h-zone is smaller, and all the myosin heads are overlapping actin molecules – allowing for maximum tension to be developed. At the final point of the contraction range, there is no more h-zone, there is no further room for the thick filaments to move (i.e. at the z-line) and even some of the thin filaments overlap, losing some of the capacity for cross-bridge cycling hence no more tension can be developed.