Module 5: Muscles

Question 1

3 kinds of muscle cells

Answer 1

skeletal, smooth, cardiac

Question 2

3 principle functions of muscles

Answer 2

movement, heat production, body support and posture

Question 3

describe the structure of muscles

Answer 3

whole muscle, fascicle, muscle cell, myofibril, thick and thin myofilaments (surrounded by sarcoplasmic reticulum )

Question 4

sarcoplasmic reticulum

Answer 4

the mesh like substance containing calcium ions that surrounds myofillaments

Question 5

sarcolema

Answer 5

plasma membrane that surrounds the muscle cell

has t-tubules (how the action potential reaches the contractile proteins)

Question 6

thin myofilaments

Answer 6

has the protein molecules: actin
troponin A (actin), C (Ca++), and T (tropomyonin)
tropomyonin - the protein molecule that covers the myosin binding sites at rest

Question 7

actin

Answer 7

the globular protein

each actin molecule has a special binding site for the other contractile protein myosin

Question 8

thick myofilaments

Answer 8

protein: myosin

Question 9

Myosin

Answer 9

has a long bendable tail and two heads that attach to myosin binding sites on actin and ATP

Question 10

excitation-contraction coupling

Answer 10

Excitation-contraction coupling = when an action potential from a cell membrane excites a muscle cell to produce a muscle contraction

Action potential comes

Action potential spread out over sarcolemma down t tubules and into the core of the muscle

Action potential comes close to SR and will open Ca++ channels

Ca++ released from terminal cisternae of the SR

Ca++ binds to troponin C on the thin myofilaments, causing tropomyosin to uncover the myosin binding site on actin

Question 11

relaxation of muscle

Answer 11

Action potential stops

Ca++ stops getting released

Special calcium pumps draws Ca++ back into the SR

Up concentration gradient

Requiring ATP

Without Ca++ present, tropomyosin covers the myosin binding sites

Myosin will be unable to bind to actin and power strokes will not occur

Question 12

rigor mortis

Answer 12

death occurs and there is no more ATP in the muscle cells. myosin cannot release from actin. Ca++ is released from the degrading sarcoplasmic reticulum

Question 13

Motor unit

Answer 13

motor neuron and the muscle cells/fibers it causes to contract
One motor neuron contacts several muscles

Each muscle cell is innervated by only one motor neuron

Large motor unit – motor nerve comes in contact with a lot of muscle cells (200)

Small motor unit – the motor neuron contacts only a few muscle cells

Question 14

recruitment of motor units

Answer 14

more muscles are added so the task can be completed (ex, heavier objects need more motor units to be active than holding something light)

Question 15

muscle twitch

Answer 15

smallest muscle contraction

Twitch 10 to 100 milliseconds. Action potential 2ms

Question 16

summation of twitch contraction

Answer 16

When an action potential is stimulated before the muscle is fully relaxed the tension in the twitch would be doubled

Increase the force of contraction by increasing the number of action potentials per second that travel down the nerve (increase frequency)

High frequencies of action potentials = maximal titanic contraction