Ch. 9 - Skeletal Muscle Tissues and Organization

What do humans rely on muscles for?

Many physiological processes and virtually all dynamic interactions with the environment.

What are the three types of muscle tissue?

Skeletal muscle, cardiac muscle, and smooth muscle

What is skeletal muscle?

Voluntary, striated muscle attached to bones that produces body movement

What is cardiac muscle?

Involuntary, striated muscle found only in the heart that pumps blood

What is smooth muscle?

Involuntary, non-striated muscle found in the walls of organs and blood vessels.

What four basic properties do muscle tissues share?

Excitability, contractility, extensibility, and elasticity

What is excitability?

The ability of muscle cells to respond to stimuli.

What is contractility?

The ability of muscle to shorten and generate force

What is extensibility?

The ability of muscle to stretch over a range of lengths.

What is elasticity?

The ability of muscle to return to its original length after stretching

What type of organs are skeletal muscles?

Contractile organs attached directly or indirectly to bones.

What are the major functions of skeletal muscles?

Produce skeletal movement, maintain posture, support soft tissue, regulate materials entering/exiting the body, and maintain body temperature.

How do skeletal muscles produce skeletal movement?

By contracting and pulling on bones.

How do skeletal muscles maintain posture and body position?

By stabilizing joints and resisting gravity.

How do skeletal muscles support soft tissue?

By supporting organs and protecting internal structures

How do skeletal muscles regulate entering and exiting materials?

By controlling openings such as sphincters

How do skeletal muscles help maintain body temperature?

Muscle contractions produce heat.

What are the three connective tissue layers of skeletal muscle?

Epimysium, perimysium, and endomysium

What is the epimysium?

Dense irregular connective tissue that surrounds the entire muscle

What does the epimysium connect to?

Deep fascia.

What is the perimysium?

Connective tissue that divides muscles into bundles called fascicles.

What structures are found in the perimysium?

Blood vessels and nerves

What is the endomysium?

Connective tissue that surrounds individual muscle fibers.

What does the endomysium do?

Binds muscle fibers together.

What are myosatellite cells?

Stem cells that assist with muscle repair and regeneration

What do tendons connect?

Muscle to bone.

What forms tendons?

Convergence of epimysium, perimysium, and endomysium

What are aponeuroses?

Flattened sheets of tendon that connect muscles to bones or other muscles.

What is a neuromuscular junction?

The site where a motor neuron communicates with a skeletal muscle fiber

How many neuromuscular junctions does each muscle fiber have?

One

What is the motor end plate?

The specialized region of the muscle membrane where the nerve communicates with the muscle.

What is a muscle fiber?

A muscle cell

How long can muscle fibers be?

Up to 30–40 cm

Are muscle fibers multinucleated or single nucleated?

Multinucleated

Where are nuclei located in skeletal muscle fibers?

Just beneath the sarcolemma

What is the sarcolemma?

The plasma membrane of a muscle fiber

What is sarcoplasm?

The cytoplasm of a muscle fiber.

What are myoblasts?

Embryonic cells that fuse to form muscle fibers.

What are myosatellite cells?

Stem cells responsible for muscle repair.

What are transverse tubules (T tubules)?

Extensions of the sarcolemma that conduct electrical impulses into the muscle fiber.

What is the role of T tubules?

Trigger muscle contraction

What structures in the sarcoplasm are responsible for muscle contraction?

Myofibrils.

What surrounds each myofibril?

The sarcoplasmic reticulum

What does the sarcoplasmic reticulum store?

Calcium ions (Ca²⁺)

What is a sarcomere?

The functional contractile unit of a muscle fiber

About how many sarcomeres are found in one myofibril?

About 10,000

What are the two types of myofilaments?

Actin (thin filaments) and myosin (thick filaments)

What is the Z line (Z disc)?

The boundary of a sarcomere that anchors actin filaments

What is the I band?

Region containing only thin filaments.

What is the A band?

Region containing thick filaments.

What is the H band?

Region containing only thick filaments

What is the M line?

The center of the sarcomere where myosin filaments are anchored

What are thin filaments made of?

Actin, tropomyosin, and troponin

What is the function of tropomyosin?

Covers myosin binding sites on actin.

What is the function of troponin?

Binds calcium and moves tropomyosin to allow contraction

What are thick filaments composed of?

Myosin

What are the parts of a myosin molecule?

Tail and globular head.

What are cross-bridges?

Myosin heads that bind to actin during contraction

What happens when a muscle contracts?

It shortens.

What two things are required for muscle contraction?

ATP and calcium ions

What triggers muscle contraction?

A nerve impulse

What causes contraction at the molecular level?

Interaction between actin and myosin filaments

What happens to the overlap zone during contraction?

It becomes larger.

What happens to the A band during contraction?

It remains the same length

What happens to the Z lines during contraction?

They move closer together.

What happens to the H band during contraction?

It becomes smaller.

What happens to the I band during contraction?

It becomes smaller

What neurotransmitter is released at the neuromuscular junction?

Acetylcholine

What happens after acetylcholine is released?

The muscle fiber depolarizes.

What does the sarcoplasmic reticulum release?

Calcium ions

What does calcium allow?

Actin and myosin to bind

What is a motor unit?

A motor neuron and all muscle fibers it controls

What type of motor units provides precise control?

Small motor units.

What type provide less precise control but greater strength?

Large motor units.

What determines muscle tension?

Frequency of stimulation and number of motor units activated.

What is a muscle twitch?

A single contraction in response to a single stimulus.

What is the all-or-none principle?

A muscle fiber contracts fully or not at all.

What is recruitment?

Increasing force by activating more motor units.

What is muscle tone?

Continuous partial contraction of resting muscles.

What does muscle tone stabilize?

Bones and joints.

What is muscle hypertrophy?

Enlargement of muscle fibers due to exercise.

What increases during hypertrophy?

Mitochondria, glycolytic enzymes, glycogen reserves, and myofibrils.

What is muscle atrophy?

Reduction in muscle size due to disuse.

What happens during atrophy?

Muscle fibers shrink and weaken

What can reduce the effects of atrophy?

Physical therapy.

What are the three types of skeletal muscle fibers?

Fast fibers, slow fibers, and intermediate fibers.

What are characteristics of fast fibers?

Large diameter, many myofibrils, high glycogen, few mitochondria, fatigue quickly

What metabolism do fast fibers use?

Anaerobic glycolysis.

Where are fast fibers commonly found?

Eye and hand muscles

What are characteristics of slow fibers?

Small diameter, slow contraction, many mitochondria, fatigue resistant.

What metabolism do slow fibers use?

Aerobic metabolism.

What gives slow fibers their red color?

High myoglobin content

What are characteristics of intermediate fibers?

Features between fast and slow fibers with moderate fatigue resistance.

How can skeletal muscles be classified?

By shape or fiber arrangement.

What are parallel muscles?

Fibers run parallel to the muscle’s long axis.

What are convergent muscles?

Broad origin with a narrow insertion.

What are pennate muscles?

Fibers arranged at angles to a tendon.

What are the types of pennate muscles?

Unipennate, bipennate, and multipennate

What are circular muscles?

Muscles that surround openings

What is the origin of a muscle?

The attachment that remains stationary