Smooth - no striations, involuntaryvisceral organs

Skeletal - striated, voluntary, tires easily, powerful

Cardiac - striated, involuntaryintercalated disks

Endomysium - connective tissue that surrounds the muscle fibers

Perimysium - fibrous membrane that forms a bundle of fibers called fascicles

Epimysium - covers the entire muscle and blends into the strong cord-like tendons

Fascia – connective tissue that surrounds the muscle just outside the epimysium and tendon

Fig 10-3 p281

Muscle Functions

1. Movement and regulation of body fluids (heart- blood, bladder- urine)

2. Maintains posture

3. Stabilizes joints

4. Generates heat

Microscopic Anatomy of Skeletal Muscle

Long ribbon like Organelles made up of myofilaments

cytoplasmCell membrane

Microscopic Anatomy of Skeletal Muscle I band - (light)A band - (dark)Z line - midpoint in the

I band H zone - portion of A band where thick and thin filaments don’t overlap

Give striped appearance

Sarcomere - tiny contractile units in myofibrils of skeletal muscle between the Z lines.

p313 Box 11-1

myosin

actin

I. Myofilaments-Thick filaments p315 Fig 11-4

Myosin filaments - made mostly of the protein myosin and also contain ATPase enzymes

*Make up the length of the Dark A band

Myosin heads - small projections or cross bridges that link the thick and thin filaments together during contraction

-Thin Filaments p315 Fig 11-4

Actin filaments - contain actin (contractile protein) and regulatory proteins (tropomyosin and troponin)that prevent myosin head from binding to actin.

Skeletal Muscle Activity p316 Fig 11-5

Motor unit - a motor neuron and the skeletal muscle cells it stimulates

Neuromuscular junction -nerve muscle connection

Synaptic cleft - gap between nerve endings and muscle cells

Skeletal Muscle Activity

What Happens During Muscle Contraction?????

1. Nerve impulse reaches axon terminaland a neurotransmitter acetylcholine ACh is released across synapse

2. ACh attaches to receptors on membrane of muscle (sarcolemma)

3. Causes sarcolemma to become permeable to Na+ ions

4. This creates an action potential or electrical current that travels the cellto cause it to contract

Skeletal Muscle Activity p317 Fig 11-7

What Happens During Muscle Contraction?????

5. SR releases Ca+ into the sarcoplasm where it binds to troponincausing the tropomyosin molecules to shift exposing the active sites on actin.

6. Myosin heads bind to actincausing the actin and myosin filaments to slide (ATP)

7. Muscle fibers shorten as it contracts

Pearson Muscle Contraction

SR - membraneous channels that surround each myofibril, and store Ca+ and release on demand.

Skeletal Muscle Activity

What Happens During Muscle Relaxation?????

1. Cholinesterase breaks down ACh

2. Ca+ ions diffuse back into SR and tropomyosin returns to its original position.

3. Actin and Myosin filaments are broken and slide apart

4. Muscle relaxes

Energy Sources for Muscle Contraction

ATP must be regenerated continuously b/c muscles store only 4-6 seconds worth of ATP

1) Creatine Phosphate (CP) - CP & ADP result in a transfer of a phosphate group to make ATP

2) Aerobic respiration - 1 glucose 36 ATP *slow and requires continuous O2 and nutrients

3) Anaerobic - glycolysis 2 ATP w/out O2

*lactic acid buildup

Oxygen Debt – is the amt of extra oxygen required by muscle tissue to convert accumulated lactic acid to glucose in the liver and to restore supplies of ATP and creatine phosphate following vigorous exercise.

Muscle Fatigue - is due to the accumulation of lactic acid and can cause the muscle to lose its abilityto contract (exhaustion produced by strenuous activity)

The Muscle Response - Contraction

Threshold stimulus - is the minimal stimulus needed to elicit a muscular contraction

All or None Response - when a muscle fiber contracts it always contracts to the fullest extent

Muscle Twitch

Myogram is a recording of a muscle contraction

•Latent period - time between when the stimulus is applied and when it responds

•Period of contraction •Period of relaxation

Sustained Contraction - when a muscle is unable to complete relaxation period before next stimulus

•Response to rapid series of stimuli

•Tetanic contraction is forceful and sustained, and has partial or lacks partial relaxation (smooth)

•Tonic contraction is responsible for muscle tone (response to nerve impulses from spinal cord sending continual, partialstimuli). Responsible for posture.

*If sustained contraction is lost body will collapse(loss of consciousness)

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