lecture 15

Question 1

resting membrane potential

Answer 1

• Resting membrane potential is determined by the uneven distribution of ions on the inside versus the outside of the cell and by the membrane’s permeability to different ions.
• When the cell is at rest it is more negative on the inside. The potential can be altered by opening or closing the ion channels.

Question 2

action potential

Answer 2

• A large, long-distance change in membrane potential that spreads rapidly across the cell membrane
• a major change in membrane potential that travels across the surface of the cell
  * change caused by the opening and closing of channels

Question 3

chemically gated ion channel

Answer 3

open in response to a chemical messenger (neurotransmitter). The ions travel through based on the concentration gradient once they open.

Question 4

voltage gated ion channel

Answer 4

opens or closes in response to changes in membrane potential. Some proteins may only let certain ions through.
- can also change due to the chemical response that changes the distribution of ions or the membrane potential

Question 5

neuromuscular junction

Answer 5

• Is a neuron that branches out to send signals for contractions. Muscle contraction relies on it.
  
  • Is when an action potential travels down a somatic motor neuron to the neuromuscular junction.

Question 6

motor unit

Answer 6

• A motor unit is either a few or hundreds of muscle fibers together.
• consisting of a single motor neuron and all the muscle fibers it innervates, working together to generate muscle contraction;

Question 7

synaptic cleft

Answer 7

is a skeletal muscle cell that is a small gap between the axon of one neuron and the dendrites of another one.
- is the neuron that communicates with the cells has acetylcholine neurotransmitters on it (which then will leave and interact with the receptors in the muscle)

Question 8

what is acetylcholine essential for

Answer 8

• is the neurotransmitter that is essential for voluntary muscle contraction

Question 9

describe the function fo acetylcholine in skeletal muscle fiber contraction

Answer 9

• Nerve impulses stimulate the release of the neurotransmitter acetylcholine and into the synaptic cleft via exocytosis
• Ach will then diffuse across the synaptic cleft and bind to receptors embedded in the sarcolemma.
• The enzyme acetylcholinesterase will then work to break down excess Ach into acetic acid and choline
  
  • Choline will then be transported down into the axon to be used again

Question 10

role of acetylcholinesterase

Answer 10

• It is an enzyme that is in the synaptic cleft that will break down excess Ach into acetic acid and choline. The choline will then be sent to the axon to be used again

Question 11

explain how and why concentrations of these ions change just before, during, and after skeletal muscle contraction

Answer 11

• Ach binds to specialized receptors embedded in the sarcolemma, which causes the chemically gated ion channels in the sarcolemma to open
  
  • When Ach goes across and creates the binding that opens the ion gated channels. When this happens, it binds to the receptor and creates a chemical response needed for chemical – gated ion channels to open (calcium and phosphorous)
• The Sodium (NA+) and Potassium (K+) ions will diffuse along their concentration gradients. This is why sodium goes in and potassium goes out.

Question 12

depolarization

Answer 12

• Depolarization occurs when there is a rapid influx of Na+ that causes the interior of the sarcolemma to become less negatively charged (or depolarized) at that location
  
  • K+ exits the cell, but its movement may be slower.
  • When the channels open and sodium flies in it makes the interior more positive and depolarizes it

Question 13

repolarization

Answer 13

• Repolarization is the process in which potassium flows out of the cell and sodium flows out which returns the negative charge to the inside of the membrane. This is further facilitated by the sodium-potassium pump which takes in 3 sodium for every 2 potassium that comes out.

Question 14

the steps to the excitation - contraction coupling

Answer 14

• This is a series of physiological events that converts the electrical signal of an action potential into a mechanical response.
  
  • The action potential travels along the sarcolemma and down the T-tubules, which opens the voltage-gated calcium channels in the sarcoplasmic reticulum. (the calcium then floods out)
  • The released calcium then binds to troponin, which then uncovers the myosin binding sites on the thin filament
  • Then myosin binds with actin to form the cross bridges and begins the contraction process. This allows myosin to bind with actin

Question 15

what is excitation-contraction coupling

Answer 15

This is a series of physiological events that converts the electrical signal of an action potential into a mechanical response.

Question 16

the process of the cross bridge cycle and the role ATP plays

Answer 16

• First Actin and Myosin are separate and ATP binds to the myosin head which then splits and releases energy
• Then the energized myosin head attaches to actin, which forms a cross bridge. This is allowed because the breaking of ATP helps for the cross bridge.
• Third, ADP + P are released, and a power stroke occurs which allows for the head of myosin to bend and pull on actin. It all moves toward the center of the sarcomere and becomes smaller.
• Fourth, the binding of a new ATP allows for myosin’s head to return to its original resting potential and to be released from actin.

Question 17

the role that calcium plays in the process of skeletal muscle contraction

Answer 17

• When calcium is released, it binds to tropomyosin and allows for actin and myosin to interact. The binding of calcium to tropomyosin allows for the binding site to be uncovered.

Question 18

the steps of muscle contraction

Answer 18

1) an action potential arrives at the axon terminal
2) Exocytosis and the release of acetylcholine molecules into the synaptic cleft
3) Acetylcholine binds to receptors embedded in the sarcolemma
4) chemically gated ion channels in the sarcolemma open, allowing diffusion of sodium and potassium ions
5) voltage-gated sodium channels in the sarcolemma open, triggering an action potential
6) voltage-gated calcium channels in the sarcoplasmic reticulum open, releasing calcium
7) calcium ions bind to troponin, shifting the position of tropomyosin
8) the myosin head binds with actin, forming a cross bridge
9) the myosin head pivots and bends, pulling the actin filament toward the M line
10) an input of ATP allows myosin to detach from actin

Question 19

what is the first thing that has to happen before muscle contraction

Answer 19

an action potential

Question 20

if you have acetylcholinesterase but not acetylcholine what happens?

Answer 20

the muscles will never relax and there will be constant muscle contraction; the body will never relax.
- can eventually cause death.