Suzanne D'Anna 1

Muscular Responses

Suzanne D'Anna 2

Threshold Stimulus

any stimulus strong enough to initiate action potential

minimal strength of stimulation needed to cause a contraction

Suzanne D'Anna 3

All-Or-None Response

individual muscle cells contract to their fullest extent when exposed to stimulus of threshold strength

muscle fibers do not partially contract if stimulus is strong enough to initiate an

action potential, a nerve impulse is transmitted along entire neuron at a constant strength

Suzanne D'Anna 4

Twitch Contraction

brief contraction of all the muscle fibers in a motor unit

lasts only a fraction of a second response to a single action potential in

its motor unit myogram is a record of a muscle

contraction

Suzanne D'Anna 5

Myogram (single muscle twitch)

Suzanne D'Anna 6

Myogram

latent period

- delay between the time that the stimulus was applied and the time that the muscle responded

period of contraction

- muscle pulls at its attachments period of relaxation

- muscle returns to its former length

Suzanne D'Anna 7

Tetanus or Tetanic Contraction

state of smooth sustained muscle contraction

muscle is stimulated very rapidly no evidence of relaxation point at which the muscle is unable to relax

before next stimulus results from the addition of Ca+2 released

from sarcoplasmic reticulum

Suzanne D'Anna 8

Twitch

brief muscular contraction followed by relaxation

Suzanne D'Anna 9

Muscle Tone (tonus)

state of continuous partial contraction muscles are never totally relaxed important in maintaining posture loss of tone - body will collapse

Suzanne D'Anna 10

Types of Muscle Contractions

Suzanne D'Anna 11

Isotonic Contractions

same as tone or tension myofilaments slide freely muscles shorten - movement occurs

Example:

- bending, rotating arms, smiling

Suzanne D'Anna 12

Isometric Contractions

muscles do not shorten myofilaments do not move freely

“skidding their wheels” muscles are unable to slide because they

are trying to move something more or less immovable

Example:

- pushing against a wall

Suzanne D'Anna 13

Types of Exercise

Suzanne D'Anna 14

Effect of Exercise on Muscles

amount of work done by a muscle is reflected in the muscle itself

inactivity leads to weakness of muscle

Suzanne D'Anna 15

Aerobic or Endurance

results in stronger, more flexible muscles

greater resistance to fatigue due to increased blood supply to muscles

benefits body metabolism improves digestion, elimination

Suzanne D'Anna 16

Aerobic or Endurance (cont.)

strengthens skeleton heart enlarges - more blood pumped gas exchange in lungs more efficient no increase in muscle size

Suzanne D'Anna 17

Weight Resistance Exercises

increase muscle mass the use of immovable or slightly movable

objects requires little time, every other day increase muscle size - increase strength weight lifting will not increase endurance will increase muscle definition