CHAPTER 8 CONT….

MUSCLE PHYSIOLOGY

What are muscles?

MuscleAn organ composed of specialized cells

that use the chemical energy stored in nutrients to contract.

Muscle ActionsProvide muscle tonePropel body fluids and foodGenerate heart beatDistribute heat

3 Types of MusclesSkeletal, smooth, cardiac

SKELETAL SMOOTH CARDIAC

LOCATION (40% of body mass)Attached to bone

Surrounds digestive organs and blood vessels

In heart

CONTRACTIONS

Voluntary Involuntary involuntary

STRIATED Yes No yes

Structure of Skeletal MuscleMUSCLE (COVERED BY EPIMYSIUM)

FASCICLES (COVERED BY PERIMYSIUM)

MUSCLE FIBERS(COVERED BY ENDOMYSIUM)

MYOFIBRILS

THICK AND THIN FILAMENTS(MYOSIN) (ACTIN)

Fascia: layers of fibrous connective tissue that separates individual muscles and hold it in position; forms the tendon and attaches to bone’s periosteum

(aponeuroses: broad sheets of connective tissue that may attach to bone or other muscles)

o Sarcoplasmic reticulum :

o activates muscle contraction mechanism when the fiber is

o stimulated.

Actin and Myosin: Protein filaments. The organization of these produces the alternating light and dark striations.

(form repeating pattern units called sacromeres.)

I band: light band composed of actin attached to Z lines.

A band: dark band composed of myosin overlapping actin.

H zone: has only myosin.

M line: holds myosin in place.

Skeletal Muscle Contractiono

Motor Neuron: conducts impulse from brain and brings it to the muscle fiber.

Neuromuscular Junction: connection between neuron and muscle.

Neurotransmitter: chemicals at ends of connection that stimulates fiber.

Stimulus for Contraction

1. Neurotransmitter (acetylcholine) is released at end of motor neuron.

2. Acetylcholine diffuses into muscle fiber.

3. Sarcolemma is stimulated and impulse travels deep into the sarcoplasmic reticulum.

4. Ca+2 ions diffuse from sarcoplasmic reticulum into sarcoplasm.

Sliding Filament Theory

1. When Ca+2 is present, actin binding sites are exposed.

2. Myosin cross-bridges form a link at binding site.

3. Myosin cross-bridges bend to pull on actin.

4. Linkage breaks.5. Myosin cross-bridges forms to next

binding site.

Relaxation of Muscle1. Acetylcholinesterase decomposes

acetylcholine and the sarcolemma is no longer stimulated.

2. Ca+2 is transported back to sarcoplasmic reticulum.

3. Linkages between actin and myosin break.

4. Filaments slide apart.5. Muscle fiber relaxes.

Muscle ResponsesWhen one muscle fiber (cell) reached its threshold

stimulus and contracts it is called a twitch.

MYOGRAM

All - Or - Nothing (but muscles vary)

A. Normal contractionB. Summation contraction: series of

stimuli with increasing frequency.C. Tetanic contraction: sustained

contraction that lacks relaxation. (tetanus)

SMOOTH & CARDIAC CONTRACTIONSEssentially same as skeletal, difference

include: (pg 190)SMOOTH CARDIAC

Fibers can stimulate each other

2 neurotransmitters (acetylcholine & norepinephrine) and hormones for stimulation

Contracts and relaxes slowly

Produces more Ca+ in transverse tubules which makes twitches longerContracts as a functional unit

Single nuclei Single nuclei

Self-exciting, rhythmic Self-exciting, rhythmic

Slow Twitch Fibers (fatigue resistant) & Fast Twitch Fibers (fatigable)Normal person ½ & ½Sprinter 80% fast twitchMarathoner 90% slow twitch

Fatigue: caused by an interruption in

1.Blood supply2.Lack of acetylcholine3.Accumulation of lactic acid due to lack of O2

Cramp: sustained involuntary contraction from changes in extracellular fluid.

Muscle tone: Partial sustained muscle contractionImportant in maintaining posture

Muscle Strain: muscle fiber can be overstretched or even torn.

Muscle pull: tendon of muscle tears away from bone.Shin splints: soreness due to straining the tibialis

anteriorRigor mortis: partial contraction that fixes joints; actin

and myosin remain linked until decomposition.Tendinitis: inflammation of tendon.Muscle hypertrophy: forcefully exercised muscle that

causes increased size and shape.Muscle atrophy: unused muscle caused decrease in

size and strength.Muscular dystrophies: missing or abnormal dystrophin

(protein that holds fibers together); muscle will weaken and degenerate.

Myoma: tumor composed of muscle tissueMyositis: inflammation of skeletal muscle tissue

Botox: toxin injected into the facial skin to temporarily smooth wrinkles preventing muscles from contraction. It prevents acetylcholine from being released. Too much can cause a frozen faceAlso causes botulism which is a serious form

of food poisoning

Muscle movementsMuscle is connected to bone or connective

tissue at 2 main points.Origin: attachment to the immovable or less

movable bone.Insertion: attachment to movable bone

Moves toward origin during contraction

Some muscles have interchangeable origins and insertions: (rectus femoris)Muscles can only pull (not push) as they contract.Prime mover: muscle that has main responsibility

for a movement. (biceps)Antagonist: muscle that opposes or reverses

movement. (triceps)