A+P - Chapter 6: The Muscular System

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What are the three basic muscle types found in the body?

1. Skeletal muscle

2. Cardiac muscle

3. Smooth Muscle

What does the prefix “myo” and “mys” mean in muscle terminology?

muscle

Where are each muscle type located? (i.e: skeletal, cardiac, smooth)

1. Attached to bones

2. Walls of the heart

3. Mostly in walls of hollow visceral organs

Which of the three muscle types can be voluntarily contracted?

Skeletal

Which muscles of the three muscle types can be involuntarily contracted?

1. Cardiac

2. Smooth

What are the four connective tissue components of skeletal muscle?

Endomysium, perimysium, epimysium, and fascia

What are the three sites of skeletal muscle attachments?

Bones, cartilages, and connective tissue coverings

What are some characteristics of smooth muscle?

• Lack striations

• Spindle-shaped cells

• Single nucleus

• Involuntary contraction

What are some characteristics of cardiac muscle?

• Visible striations

• Single nucleus

• Branching cells

• Joins to another muscle cell at an intercalated disc

• Involuntary contraction

What are the four functions of skeletal muscle?

• Movement production

• Maintaining posture

• Stabilizing joints

• Heat generation

What is the sarcolemma in a skeletal muscle?

specialized plasma membrane

What are myofibrils?

long organelles inside the muscle cell

What gives muscles its striped appearance (striations)?

Myofilaments. Light bands (I bands) and dark bands (A bands)

What is a sarcomere?

contractile unit of muscle fiber

What is the difference between myosin and actin?

Myosin: Thick filaments

Actin: Thin filaments

What are some characteristics of myosin (thick filaments)? What can it do?

• Composed of the protein myosin

• Contains ATPase enzymes

• Possess myosin heads

Heads are also known as cross bridges when they perform what during muscle contraction?

when myosin heads link thick and thin filaments during muscle contraction

What are some characteristics of actin (thin filaments)? What can it do?

• Composed of the contractile protein actin

• Actin Is anchored to the Z disc

What is the “H zone”?

A zone within the A band that lacks actin filaments at rest

What are some characteristics/functions of the sarcoplasmic reticulum? (SR)?

• Specialized smooth endoplasmic reticulum

• Stores and releases calcium (Ca+)

• Surrounds myofibril

What is irritability (responsiveness? What role does it play in muscle stimulation?

the ability to receive and respond to a stimulus

What is contractility? What role does it play in muscle stimulation and contraction?

the ability to shorten when an adequate stimulus is recieved

What does extensibility mean?

ability of muscle cells to be stretched

What does elasticity mean?

ability to recoil and resume resting length after stretching

What stimulates contraction in skeletal muscles?

motor neurons (nerve cells)

What is a motor unit?

one motor neuron and all the skeletal muscle cells stimulated by the given neuron

What is the neuromuscular junction?

the association site of axon terminal of the motor neurons and sarcolemma of a muscle

What is the neurotransmitter? What neurotransmitter stimulates skeletal muscle?

• chemical released by nerve upon arrival of a nerve impulse in the axon terminal

• Acetylcholine (ACh)

What is the synaptic cleft, and what does it do in terms of muscles and nerves?

• Synaptic cleft: gap between nerve and muscle, filled with interstital fluid

• Separates nerves and muscle, they don’t make contact

What six things occur when a nerve impulse reaches the axon terminal of the motor neuron?

1. Calcium channels open, calcium ions enter the axon terminal

2. Calcium ion entry causes (some) synaptic vesicles to release ACh (acetylcholine)

3. ACh diffuses, attaches to receptors on the muscle cell’s sarcolemma

4. Sarcolemma becomes temporarily more permeable to sodium if enough ACh is released

5. Depolorization opens more sodium channels, allowing more sodium ions to enter the cell. Contraction occurs

6. AChE breaks down ACh into acetic acid and choline. Ends muscle contraction

What enters the axon terminal via calcium channels, causing synaptic vessels to release ACh?

Calcium ions (Ca+)

What happens when enough ACh is released and the sarcolemma opens up to more sodium?

Sodium rushes into the cell, potassium exits the cell

Under what two conditions does the muscle cell return to its resting state?

1. Potassium ions diffuse out of the cell

2. Sodium-potassium pump moves sodium and potassium ions back to their original positions

What are the three steps mechanically cause muscle contraction according to the “Sliding Filament Theory”?

• Calcium binds to proteins on thin filaments (actin) exposing myosin-binding sites. Allows myosin heads on the thick filaments to attach.

• Attached heads pivot, sliding thin filaments toward sarcomere center. Contraction occurs

• ATP provides energy for sliding process. Continues as long as Ca+ ions are present.

What are graded responses?

Different degrees of skeletal muscle shortening

What two changes determine the outcome of a graded response?

• Frequency of muscle stimulation

• Number of muscle cells being stimulated at one time

What is a twitch?

A single, brief contraction (not a normal muscle function).