Muscle Physiology Test

Name the functions of the muscle

1. Movement of the body and its parts

2. Maintains posture

3. Generates heat

4. Stabilizing joints

Name the characteristics of the skeletal muscle

Location: Most are attached by tendons to bones

Shape: Long, cylindrical, multinucleate, visible striations

Regulation contraction: Voluntary, subject to conscious control

Speed contraction: Slow to fast

Rhythmic: no rhythmic contraction

Name the characteristics of the smooth muscle

Location: Found mainly in the walls of hollow organs (ex.stomach, bladder, respiratory passageway)

Shape: No striations, spindle-shaped cell, single nucleus

Regulation contraction: involuntary

Speed contraction: Very slow

Rhythmic: Yes, in some

Name the characteristics of the cardiac muscle

Location: Only in the heart

Shape: striations, single nucleus, joined to another muscle cell at an intercalated disc

Regulation contraction: involuntary

Speed contraction: slow

Rhythmic: Yes

Name the muscle

Smooth

Name the muscle

Skeletal

Name the muscle

cardiac

Name the wrappings of the skeletal muscle

1. Muscle fiber

2. Endomysium

3. Fascicle

4. Perimysium

5. Epimysium

6. Tendons

What does the endomysium wrap?

Surrounds and supports each individual muscle fiber (muscle cell) within the skeletal muscle (inside)

What does the perimysium wrap?

Bundles of muscle fibers, that are the fascicles (around)

What does the epimysium wrap?

The entire skeletal muscle

Microscopic anatomy of skeletal muscle

Cells are multinucleated

The nuclei are beneath the sarcolemma

What is the sarcoplasmic reticulum?

It is found beneath the sarcolemma

For storage of calcium

*Calcium is key for muscle contraction*

What are myofibrils?

Bundles of myofilaments

Myofibrils are aligned to give distinct bands I band: light band

A band: dark band

What are sarcomeres?

A contractile unit of a muscle fiber

Explain the organization of the sarcomeres

Thick filaments= myosin filaments, composed of the protein myosin, has ATPase

Thin filaments: actin filaments

Composed of the protein actin

Continuation of the sarcomere

Myosin filaments have heads, extension or cross bridges

Myosin and actin overlap somewhat

At rest there is a bare zone that lacks actin filaments

Name the properties of the skeletal muscle

Irritability: ability to receive and respond to a stimulus

Contractility: ability to shorten when an adequate stimulus is received

Extensibility: stretch

Elasticity: Recoil

Why do skeletal muscles have to stimulated?

Skeletal muscles must be stimulated by a nerve to contract

A motor unit

One neuron and the muscle cells stimulated by that neuron

What is the neuromuscular junction and what does it consist of?

An association site of nerve and muscle

Synaptic cleft: gal between nerve and muscle

*The nerve and muscle do not make contact, area between nerve and muscle is filled with interstitial fluid

Name the transmission of nerve impulse to muscle

1. Neurotransmitter, chemical released by nerve upon arrival of nerve impulse

2. The neurotransmitter for skeletal muscle is acetylcholine (aCh)

3. The neurotransmitter attaches to receptors on the sarcolemma (plasma membrane)

4. Sarcolemma becomes permeable to sodium

Continuation of transmission

5. Sodium rushing into the cell generated an action potential

6. Once started, muscle contraction cannot be stopped

What is the sliding filament theory

An activation by nerves causes myosin heads (cross bridges) to attach to binding sites on the thin filament

Myosin heads then bind to the next site of the thin filament

This action causes a sliding of the myosin along the actin

The result is that the muscle is contracted

Basic steps of the neuromuscular junction

1. Message sent

2. Neurotransmitter

3. Depolarization

4. Calcium + Troponin= Actin exposed

5. Actin + Myosin= contraction

6. Relaxation

Nervous sys. Sends message to the effector organ

1. Neurotransmitter released ACh

2. ACh binds to sarcolemma of muscle fiber

3. ACh initiates opening of sodium-potassium

Depolarization

Cause: the binding of ACh to sodium-potassium channels, opening of channels + movements of sodium and potassium across sarcolemma

Involves the movement of charges

More sodium moves in and potassium moves out

Imbalance of charges =electrical current (action potential)

SR and Calcium

Cause: depolarization

Action potential across the SR causes the release of calcium

Once calcium is released from membrane of SR

The calcium binds with troponin

Troponin- tropomyosin conformation

Troponin and tropomyosin no longer cover actin binding sites thus exposing the sites

Myosin interacts with actin

Cause: Troponin and tropomyosin unveils actin (binding sites exposed)

Actin exposed

Myosin releases inorganic phosphate and ADP

Inorganic phosphate + ADP= ATP

Myosin changes conformation

Myosin binds actin

Myosin and actin slide towards each other and a contraction occurs

Relaxation

ATP binds back with myosin

Myosin detaches and repositions

Troponin and tropomyosin cover up actin

Calcium moves back into SR

Repolarization= sarcolemma stable again

Contraction of skeletal muscle

Muscle fiber contraction is “all or none”

Within a skeletal muscle, not all fibers may be stimulated during the same interval

Different combinations of muscle fiber contractions may give differing responses

Muscle response to strong stimuli

Muscle force depends upon the number of fiber stimulated

Muscles can continue to contract unless they run out of energy

Energy for muscle contraction

muscles used stored ATP for energy

Bonds of ATP are broken to release energy

Only 4-6 seconds worth of ATP is stored by muscles

After this time, other pathways must be utilized to produce ATP

Direct phosphorylation

Muscles cells contain creatine phosphate (CP)

CP is a high energy molecule

After ATP is depleted, ADP is left

CP transfers energy to ADP, to regenerate ATP

CP supplies are exhausted in about 20 seconds

Anaerobic glycolysis

Reaction that breaks down glucose without oxygen

Glucose is broken down to pyruvic acid to produce some ATP

Pyruvic acid is converted to lactic acid

Anaerobic glycolysis continued

This reaction is not as efficient but is fast

Huge amounts of glucose are needed

Lactic acid produces muscle fatigue

Muscle fatigue and oxygen debt

When a muscle is fatigued, it is unable to contract

The common reason for muscle fatigue is oxygen debt

Oxygen must be repaid to tissue to remove oxygen debt

Oxygen is required to get rid of accumulated lactic acid

Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less

What are two types of muscle contractions?

Isotonic contractions and Isometric

What are the differences between the two types of muscle contraction?

Isotonic contractions: myofilaments are able to slide past each other during contractions, the muscle shortens

Isometric contractions: tension in the muscles increases

The muscle is unable to shorten

Muscle tone

Some fibers are contracted even in a relaxed muscle

Different fibers contract at different times to provide muscle tone

The process of stimulating various fibers is under involuntary control