Skeletal and Smooth Muscle

Question 1

Skeletal Muscle

Answer 1

Striated/striped appearance
Actin/myosin
Ca++ binds to troponin
Stimulated by somatic motor neurons
Ca++ comes from SR

Question 2

Smooth Muscle

Answer 2

Smooth appearance
Actin/myosin
Ca++ binds to calmodulin
Stimulated by autonomic neurons, hormones, or other chemicals.
Ca++ comes from extracellular fluid

Question 3

Acetylcholine (Ach)

Answer 3

Bind to nicotinic receptors which allow Na+ to enter muscle cell.

Question 4

describe the processes that take place at the NMJ and
the generation of an end -
plate potential

Answer 4

when an action potential travels down the axon , the depolarization
triggers the opening of Ca Channels on the axon .Ca++ flows
in and stimulates the exocytosis of Ach. Ach travels to cleft
and binds to nicotinic receptors , which open and allow Na+ to
enter muscle cell . This is a motor end plate potential .

Question 5

explain excitation -
contraction coupling in skeletal muscles

Answer 5

when enough EPSPs fire to depolarize the motor neuron to threshold,
an AP is fired depolarizing the axon ,spreading to the terminal .
This voltage changes triggers the opening of voltage-gated bait
channels , causing Ca++ to flow into the axon terminal . Ca++ triggers
exocytosis of synaptic vesicles containing Ach . Ach flows across the synaptic cleft onto the motor end plate of the muscle ,binding to nicotinic Ach receptors which are Na+ channels . These open in response to Ach binding , allowing Na+ to flow into the cell , causing a motor end plate potential .When the potential difference reaches threshold , an AP will fire causing VG Na+ channels to open and depolarize the cell . The depolarization spreads down the muscle into the T tubules and detected by the DHP receptors , which are physically linked to RYR receptors on the SR .
In response, the RYR opens allowing Ca++ to flow out of SR and into sarcoplasm. Ca++ then binds to troponin , which is connected to tropomyosin covering the active site of actin.
Troponin and Ca pull back tropomyosin , exposing active site , allowing myosin to bind using ATP. Forming a crossbridge and pulling actin ,
a power stroke helps to contract the muscle.

Question 6

Skeletal Muscle Relaxation

Answer 6

Ca++ is constantly being pumped back into SR by an ATPase
Repolarization phase of AP allows DHP to reset, which closes RYR, preventing more Ca++ from leaving SR
Decreased Ca++ levels in the cytosol mean less Ca++ bound to troponin
Troponin without Ca++ allows tropomyosin to cover actin binding sites
Myosin cannot bind/form cross-bridges

Question 7

explain the length -
tension relationship in skeletal muscle
*
explain force generation in skeletal muscle

Answer 7

as the sarcomere shortens , more tension is developed until no more crossbridges can form , then
tension begins to decrease. (tension =
force development)

Question 8

describe what a motor unit is and how skeletal muscles can
create graded contractions of varying force

Answer 8

a motor unit is a somatic motor neuron and all the muscle cells it innervates.

Muscles can generate graded contractions by recruiting certain groups / amounts of muscle fibers depending on the need .

Question 9

Single Unit Smooth Muscle

Answer 9

Cells are connected by gap junctions
Signal down neuron affects all cells and leads to all of them contracting as a single unit

Question 10

Multi unit Smooth Muscle

Answer 10

Cells are not connected by gap junctions.
Each cell independently stimulated by a neuron.

Question 11

Actin

Answer 11

binds to myosin to form crossbridges to cause tension to develop

Question 12

ATP

Answer 12

binds to myosin causing it to change position and attach to actin and pull, causing muscles to contract.

Question 13

Ca++

Answer 13

binds to troponin which is connected to tropomyosin which uncovers the actin sites so it can bind to myosin.

Question 14

Ca++ ATPases

Answer 14

transport calcium ions from the cytosol back to the sarcoplasmic reticulum (SR) following muscle contraction

Question 15

DHP receptors

Answer 15

voltage gated calcium channels that detect action potentials and are linked to RYR receptors

Question 16

Myosin

Answer 16

binds to actin allowing for a crossbridge to form

Question 17

Nicotinic receptors

Answer 17

open and allow Na to enter muscle

Question 18

RYR receptors

Answer 18

open allowing calcium to flow our of SR into sarcoplasm

Question 19

Synaptic vesicles

Answer 19

release Ach

Question 20

Tropomyosin

Answer 20

uncovers the actin sites so it can bind to myosin.

Question 21

Troponin

Answer 21

pulls back tropomyosin along with Ca+ to expose actin binding site

Question 22

Voltage-gated Ca++ channels

Answer 22

cause calcium to flow into axon terminal.

Question 23

Voltage-gated Na+ channels

Answer 23

Open and depolarize cell when threshold is reached.

Question 24

Length-Tension in Skeletal Muscle

Answer 24

Tension (or force) development depends on cross-bridge formation.

Question 25

Motor Unit:

Answer 25

A somatic motor neuron and all the muscle cells it innervates.

Question 26

Smooth Muscle contraction

Answer 26

smooth skeletal triggered by hormone , voltage , mechanical strecth calcium induced calcium release . calmodulin activated by Ca+ activates MLCK → phosphorylates myosin * contracts in a spiral , 1b * RELAX : sodium calcium exchanger

Question 27

skeletal muscle contraction

Answer 27

triggered by AP RYR releases Ca++ troponin reveals active site release . contracts toward middle * →← sodium calcium exchanger