Human Physiology Chapter 9: Muscle And Muscle Tissue Part 3

Front 1

What is a muscle twitch?

Back 1

A muscle twitch is the response of a muscle to a single, brief threshold stimulus

Front 2

What sets off a muscle twitch?

Back 2

A muscle AP

Front 3

Is a muscle twitch a slow or fast mechanical response? How long does it last?

Back 3

Slow mechanical response lasting 10-200 msec

Front 4

From fast to start, which 3 muscles twitch quickly that we looked at?

Back 4

1. Extraocular muscle
2. Gastrocnemius
3. Soleus

Front 5

What is the latent period?

Back 5

The latent period is very brief and begins the moment muscle is stimulated

Front 6

What happens during the latent period?

Back 6

It is the time when excitation-contraction coupling occurs and slack is taken up in muscle

Front 7

What is the contraction period?

Back 7

The contraction period is the time when the muscle shortens and develops tension

Front 8

What is the relaxation period?

Back 8

The relaxation period is the time when calcium is pumped back into the SR and muscles lose tension

Front 9

If a muscle could only twitch, contractions would be what?

Back 9

Weak and jerky

Front 10

Muscle responses are graded by what two things?

Back 10

1. Change in frequency of stimulation
2. Change in strength of stimulus

Front 11

A single stimulus results in what?

Back 11

A single brief weak contraction

Front 12

In order to for a wave summation and tetanus to occur, what must happen?

Back 12

Increase in frequency of stimulus and neurons fire a volley of APs

Front 13

What is the effect of increasing frequency of stimulus?

Back 13

Calcium becomes more available from SR and the muscle does not have time to relax between stimuli and twitches summate

Front 14

Low stimulation frequency causes what kind of tetanus?

Back 14

Unfused (incomplete) tetanus

Front 15

High stimulation frequency causes what kind of tetanus?

Back 15

Fused (complete) tetanus

Front 16

What is recruitment?

Back 16

Recruitment is multiple motor unit summation

Front 17

As stimulus strength increases, what occurs?

Back 17

Muscle contracts more vigorously

Front 18

Why does the muscle contract more vigorously when stimulus strength increases?

Back 18

Increases due to recruitment of motor units thus more and more muscle fibers are being stimulated

Front 19

What is a motor unit?

Back 19

A motor unit is a motor neuron and all the muscle fibers it innervates

Front 20

A sustained tetanic contraction results from what?

Back 20

Increasing the frequency of stimulus

Front 21

What is the net result of weak stimulus strength recruiting motor units?

Back 21

Stimulus strength eventually recruits the maximum number of motor units

Front 22

How many fibers are in one motor unit?

Back 22

4 to several hundred

Front 23

Where are fibers in a motor unit located?

Back 23

Located throughout the muscle

Front 24

When a motor neuron fires APs, what occurs in a motor unit?

Back 24

ALL fibers in its unit contract in unison

Front 25

Small motor units in muscles control what? Examples?

Back 25

Fine movements like in eyes or fingers

Front 26

Large motor units in muscles control what? Examples?

Back 26

Large weight-bearing muscles like in thighs and hips

Front 27

What is spastic paralysis?

Back 27

Muscle stays contracted

Front 28

What is flaccid paralysis?

Back 28

Muscle stays relaxed

Front 29

What is Acetylcholinesterase?

Back 29

It is an enzyme that breaks down ACh

Front 30

Where does AChE naturally occur?

Back 30

It naturally occurs at the motor end plate

Front 31

What is the normal way a muscle relaxes when a neuron stops firing?

Back 31

AChE degrades ACh

Front 32

When AChE degrades ACh, what happens?

Back 32

It turns off EPPs, muscle APs, and muscle contraction

Front 33

As long as ACh stays bound, what will happen?

Back 33

Channels stay open and EPPs continue (stays contraction)

Front 34

What are AChE inhibitors?

Back 34

Toxic chemicals in nerve gases and pesticides

Front 35

What do AChE inhibitors cause?

Back 35

Inhibit the action of AChE and prevent ACh breakdown

Front 36

What is the effect on muscle contraction when AChE inhibitors interfere?

Back 36

Muscle stays contracted. Unable to relax

Front 37

What is Myasthenia Gravis?

Back 37

Autoimmune disease

Front 38

What does myasthenia gravis do?

Back 38

The immune system destroys 80% of cholinergic receptors at motor end plate

Front 39

What is the effect of myasthenia gravis?

Back 39

Muscle contractions become weak and brief

Front 40

What are some symptoms of myasthenia gravis?

Back 40

Droopy eyelids, profound muscle weakness

Front 41

How might a myasthenia patient be helped by taking AChE inhibitors?

Back 41

Inhibitor would prolong the action of ACh on the remaining channels so contractions can last

Front 42

When 80% of cholinergic receptors are destroyed, EPPs may not be what?

Back 42

EPP may not be large enough to set off muscle AP or muscle contraction

Front 43

What is the most potent toxin known?

Back 43

Botulinum Toxin (Botox)

Front 44

What is botulinum toxin? What does it act on and cause?

Back 44

It is a neurotoxin that acts on motor neuron to prevent secretion of ACh.

Front 45

What is the effect of the botulinum toxin on muscle contraction?

Back 45

Muscle stays relaxed. Unable to contract.

Front 46

What are three medical uses for the botulinum toxin?

Back 46

1. Relax muscles causing crossed eyes
2. Relieve muscle spasms in stroke victims
3. Paralyze facial muscles to reduce wrinkles

Front 47

What is the Tetanus toxin? What does disease does it cause?

Back 47

Tetanus is a neurotoxin that causes the disease Tetanus (lockjaw)

Front 48

How does the Tetanus toxin travel through the body?

Back 48

Tetanus travels up motor neurons and enters the CNS

Front 49

What does the tetanus toxin cause?

Back 49

It inhibits inhibitory interneurons and causes massive contractions in opposing muscles

Front 50

Where does black widow spider venom act?

Back 50

Acts at the NMJ

Front 51

What does black widow spider venom enhance?

Back 51

Enhances ACh secretion from motor neuron

Front 52

What is the effect of black widow spider venom on muscle contraction?

Back 52

Muscle stays contracted, unable relax

Front 53

Black widow spider venom particularly affects what kind of motor neurons that secrete ACh?

Back 53

It particularly affects parasympathetic motor neurons to contract smooth muscle in digestive organs

Front 54

What is the result of being bit by a black widow spider?

Back 54

Massive abdominal cramps

Front 55

What is Curare?

Back 55

It is a poison from the tubocurarine plant

Front 56

Where does Curare act?

Back 56

Curare acts at NMJ

Front 57

Curare is used by who and for what?

Back 57

Used by South American Indians for blow-dart poison

Front 58

What does curare do?

Back 58

Curare blocks cholinergic receptors on motor end plate and ACh cannot bind

Front 59

What is the effect of curare on muscle contraction?

Back 59

Muscle stays relaxed, unable to contract

Front 60

What are two medical uses of curare?

Back 60

1. Relax muscles during anesthesia and intubation
2. Relief of abdominal muscles after black widow spider bite

Front 61

What is hypocalcemia?

Back 61

Low blood calcium (ECF)

Front 62

What does hypocalcemia cause?

Back 62

Causes muscle spasms

Front 63

What are the muscle spasms caused by hypocalcemia called?

Back 63

Hypocalcemic tetany

Front 64

How does LOW calcium cause INCREASED muscle contraction?

Back 64

Motor neurons become more excitable and spontaneously fires APs that set off muscle contraction