1. Function of the Muscular System

2. Characteristics of Muscles
Four common:
Contractibility
Excitability or irritability
Extensibility
Elasticity
Collectively produce a veritable mechanical device capable of complex, intricate movements

3. Contractibility
Quality possessed by no other body tissue; muscle become shorter and thicker causing muscle movement
When a muscle shortens or contracts, it reduces the distance b/t the parts of its contents or the space it surrounds
Contraction of muscles that connect a pair of bones brings the attachment points closer together, thus causing the bone to move
When cardiac muscles contract, they reduce the area in the heart chambers, pumping blood from the heart into the blood vessels
Smooth muscles surround blood vessels and the intestines, causing the diameter of these tubes to decrease upon contraction

4. Excitability or Irritability
Characteristic of both muscle and nervous cells (neurons)
Ability to respond to certain stimuli by producing electric signals called action potentials (impulses)

5. Extensibility Ability to be stretched
When we bend our forearm, the muscles on the back of it are extended or stretched

6. Elasticity
Ability to return to original length when relaxing

7. Muscle Attachments and Functions
A muscle must be able to exert its force upon a moveable object
Must be attached to bones for leverage in order to have something to pull against
MUSCLES ONLY PULL, NEVER PUSH
Muscles are attached to the bones of the skeleton by nonelastic cords called tendons
Bones are connected at __________. pg 125

8. Attachments (figure 7-4 pg 126)
Muscles are attached at both ends
Attachment may be to bones, cartilage, ligaments, tendons, skin, and sometimes to each other
Origin: part of a skeletal muscle that is attached to a fixed structure or bone; it moves least during muscle contraction
Insertion: other end, attached to a movable part; moves the most during a muscle contraction
Belly: central body of the muscle

9. continued Muscles of the body are arranged in pairs
Primer mover: produces movement in a single direction
Antagonist: produces movement in the opposite direction
Known as an antagonist pair

10. Upper Arm (figure 7-4 pg 126)
Upper arm muscles are arranged in antagonist pairs
The muscle located on the front part of the upper arm is the biceps
One end of the biceps is attached to the scapula and humerus (its origin)
When the biceps contract, these 2 bones remain stationary
The opposite end of the biceps is attached to the radius (its insertion); this bone moves upon contraction of the biceps

11. continued The muscle on the back of the upper arm is the triceps
Demonstration pg 126, 2nd paragraph
Another group of muscles, called the synergists, help to steady a movement or stabilize joint activity

12. Movement Muscles move bones by pulling on them
Groups of muscles usually contract to produce a single movement

13. Contraction of Skeletal Muscle
Must be stimulated by nerve impulses to contract
Single contraction is called a twitch
A motor neuron (nerve cell) stimulates all of the skeletal muscles within a motor unit
Motor neuron plus all the muscle fibers it stimulates
Neuromuscular junction: junction b/t the motor neuron’s fiber (axon), which transmits the impulse, and the muscle cell’s sarcolemma (muscle cell membrane)
Gap b/t the axon and the end of the muscle cell is the synaptic cleft

14. continued
When the nerve impulses reach the end of the axon, the chemical neurotransmitter acetylcholine is released
Diffuses across the synaptic cleft (carries impulse across synaptic cleft)
A muscle cell, when stimulated properly, contracts all the way
The muscle cell relaxes until it is stimulated by the next release of acetylcholine
See figure 7-5 page 128

15. Muscle Fatigue Caused by an accumulation of lactic acid in the muscles
During vigorous exercise, the blood is unable to transport enough oxygen
Causes the muscles to contract anaerobically
Which means?
Impedes muscular contraction, causing fatigue and cramps
Oxygen debt: after exercise, the amount of oxygen needed by the muscle to change lactic acid back to glucose
Diaphragm: dome-shaped muscle; separates abdominal and thoracic cavity; aids in breathing

16. Muscle Tone Muscles should be slightly contracted and ready to pull
Achieved through proper nutrition and regular exercise
Muscle contractions may be isotonic or isometric
When muscles contract and shorten (when we walk)
When the tension in a muscle increases but the muscle does not shorten (tensing the abdominals)
Atrophy: muscles that become weak and flaccid; shrink (waste away) from disuse
Hypertrophy: muscles that become enlarged from overexercise; the size of the muscle fiber enlarges

17. How Exercising and Training Change Muscles
Alters size, structure, and strength of a muscle
Muscles that have been injured can regenerate only to a certain degree
If damage is extensive, muscle tissue is replaced by connective (scar) tissue
Causes the muscle to become tougher

18. Effects of Training of Muscle Efficiency
Improved coordination of all muscles involved in a particular activity
Improvement of the respiratory and circulatory system to supply the needs of an active muscular system
Elimination or reduction of excess fat
Improved joint movement involved with that particular muscle activity

19. Effects of Training on Muscle Strength
Capacity to do work
Increased with proper training and can have the following effects on skeletal muscles:
Increase in muscle size
Improved antagonistic muscle coordination, where antagonistic muscles are relaxed at the right moment and do not interfere with the functioning of the working muscle
Improved functioning in the cortical brain region where the nerve impulses that start muscular contraction originate