1. Functions of (Skeletal) Muscles
Movement
2. Posture and Muscle Tone
3. Heat Production

2. Muscles move bones by pulling on them
Movement
Muscles move bones by pulling on them
Length of skeletal muscle shortens as muscle fibers
contract moves bones (levers)
Usually only insertion (more movable) bone moves
at end of muscle
Shortening of muscle pulls insertion bone towards
origin (more stationary) bone
Origin bone stays in place while insertion bone moves towards it.
Origin and Insertion can change depending on activity

6. Voluntary Muscle Movement Smooth Results from muscles working in pairs
Prime Movers, and Synergists / Antagonists
Prime Mover  main muscle responsible for mvmt
Synergists  help prime movers
Antagonists  work opposite of prime movers &
synergists

7. As prime movers & synergists contract
opposing antagonists relax
When antagonist muscles contract, they produce movement opposite to prime movers & synergists

8. Example: biceps brachii (prime mover)
brachialis (synergist/helper)
triceps brachii (antagonist)
Example: triceps brachii (prime mover)
biceps brachii & brachialis
(antagonists)
Combined movement  smooth

9. Muscle tone maintains posture through
Tonic Contractions  don’t move body
parts but keeps them in position
Few muscle fibers shorten, muscle as a whole doesn’t shorten so no mvmt occurs
Good posture  body parts help in position that favor best function
Good posture: good appearance
head/chest held high
chin, abdomen, buttocks in
knees slightly bent

10. Important for body to maintain constant Body Temperature
Heat Production
Important for body to maintain constant Body Temperature
Metabolic Rxs / Cellular Fxs
 maintain homeostasis
Hypothermia ↓ BT
Fever/Hyperthermia↑ BT
Affects cellular activity/homeostasis (enzyme/protein Fx impaired)
Muscle contraction produces most of heat required to maintain BT
Sweat releases heat
*integument
Sudoriferous/Eccrine sweat glands

11. Motor Unit = motor neuron + muscle cells attached to it
Muscle cells stimulated by nervous impulse that enters muscle fiber through motor neuron
Neuromuscular Junction: Point of contact between motor neuron & muscle fiber
Nerve impulses pass through neuromuscular junction and cause release of neurotransmitters (chemicals) that cause muscle to shorten/contract
The contractile system for muscles is organized into a number of distinct parts, each of which is controlled by a single motor neuron and each motor neuron controls a large number of muscle fibers.

12. Action potential/impulse

13. Fatigue When muscles stimulated repeatedly w/out adequate rest
 strength of contraction ↓
Prolonged periods of exercise
ATP stores are depleted
O2 can’t keep up, muscles produce
lactic acid through
(anaerobic respiration/glycolysis)
O2 debt repaid by rapid breathing

14. Systems that play an essential role in movement
Respiratory
Circulatory
Excretory
Nervous
Muscular
Skeletal
Muscle functions rely on other systems. No part of the body lives by or for itself!
Now, can you explain HOW?

15. Muscle Stimulus
Muscle cell stimulated contracts completely
ALL OR NONE
All cells in a muscle don’t contract simultaneously
Principle of Graded Response
Sub-minimal Stimulus  no contraction
Minimal or Threshold Stimulus  strength of contraction ↑ according to graded response
Maximal Stimulus  every muscle cell/fiber in entire muscle responds (from all or none)
??Supramaximal Stimulus  no additional effect on contraction b/c all muscle fibers already contracting

16. 5 Types of Skeletal Muscle Contraction
1. Tonic Contraction  muscle tone & posture
(no movement)

17. Isometric Contraction  ↑ tension w/in muscle but no ↓ in muscle length
Results in larger muscles
No movement
No muscle shortening
But ↑ internal tension

18. 3. Isotonic Contraction  Produces movement at
joint and muscle shortens
Ex. walking, running, breathing, lifting, twisting
Insertion end of muscle moves toward
point of origin
(except for facial isotonic contractions)

19. Steps of a Twitch Contraction
Twitch Contraction  quick, jerky contraction
1/10th second delay in response to stimulus
Muscles don’t shorten at stimulation but fraction of a second later
Reaches peak contraction then gradually resumes former length
Steps of a Twitch Contraction
stimulus  latent delay  contraction  relaxation

20. Tetanic Contractions (tetanus)
More sustained than twitch
Produced by series of stimuli bombarding muscle in rapid succession (~ 30 / minute)
Bacteria from puncture wound  tetanus or “lock jaw” results in severe cramping, almost continuous tetanic muscle contractions
Clostridium tetani (gram + bacillus, anaerobic)