Lecture 4: Skeletal Muscle Anatomy, Function, and Biomechanics

Comprehensive practice flashcards covering skeletal muscle types, functional characteristics, microstructural hierarchy, sliding filament contraction mechanism, contraction types, and muscle-to-bone attachment methods.

What is the general definition of a muscle?

A type of tissue that has the ability to contract and produce movement.

What are the three main types of muscle found in the human body?

Smooth muscle, cardiac muscle, and skeletal muscle.

What are the key functional characteristics of smooth muscle tissue?

It is unstriated, under involuntary control, and has a slower rate of contraction.

What are the key functional characteristics of cardiac muscle tissue?

It is striated and under involuntary control.

What are the key functional characteristics of skeletal muscle tissue?

It is striated and under voluntary control.

What is contractility in skeletal muscle tissue?

The ability of the muscle tissue to shorten.

What is excitability in skeletal muscle tissue?

The ability to respond or contract in response to chemical and/or electrical signals.

What is extensibility in skeletal muscle tissue?

The capacity of a muscle to stretch to its normal resting length after contracting.

What is elasticity in skeletal muscle tissue?

The ability of a muscle to return to its original resting length after being stretched.

What four major functional characteristics define skeletal muscle tissue?

Contractility, excitability, extensibility, and elasticity.

What is the sarcolemma?

The plasma membrane of a skeletal muscle fiber.

What process occurs at the sarcolemma to trigger muscle contraction?

Action potential conduction.

What are myofibrils?

Long cylindrical structures lying parallel to the muscle fiber that are attached to the sarcolemma.

How does the shortening of myofibrils lead to the contraction of an entire muscle cell?

Myofibrils attach to the sarcolemma, so when the myofibrils shorten, the entire muscle cell contracts.

What are sarcomeres?

Repeating sections within each myofibril that serve as the functional units of skeletal muscle.

What causes the striated appearance of skeletal muscle myofibrils?

Repeating bands of the proteins actin and myosin.

Which protein forms the thin myofilaments in skeletal muscle?

Actin.

Which protein forms the thick myofilaments in skeletal muscle?

Myosin.

What structure marks the border of a sarcomere?

The Z line.

What is considered the functional unit of skeletal muscle?

The sarcomere.

Do thick and thin myofilaments shorten during muscle contraction according to the sliding filament model?

No, thick and thin filaments do not shorten; they slide past each other.

Toward what line are thin filaments pulled by thick filaments during sarcomere contraction?

Toward the center of the sarcomere, known as the M line.

What happens to the Z lines when a sarcomere contracts?

The Z lines are moved closer together.

What forms a crossbridge during the sliding filament cycle?

The myosin head binding to actin.

What occurs during the power stroke phase of the sliding filament cycle?

The myosin head rotates toward the center of the sarcomere, sliding the thin filament toward the center.

What event weakens the bond between the myosin head and actin to allow detachment?

A new $\text{ATP}$ molecule binding to the myosin head.

What happens to the myosin head when it splits $\text{ATP}$ into $\text{ADP}$ and phosphate?

The myosin head becomes reoriented and energised.

Which two conditions are necessary for the muscle contraction cycle to continue?

$\text{ATP}$ must be available and the $\text{Ca}^{2+}$ level in the sarcoplasm must be high.

Which proteins block the myosin-binding sites on actin in a resting muscle?

Tropomyosin and troponin.

What initiates the signal for calcium release in a muscle fiber?

Neural stimulation from a neuron.

What occurs when calcium ions ($\text{Ca}^{2+}$) bind to troponin?

The blocking of myosin-binding sites on actin is removed, allowing myosin heads to bind.

What type of nerve cell controls individual skeletal muscle fibers?

A motor neuron.

Do muscles push or pull bones to cause skeletal movement?

Muscles pull bone; they do not push bone.

What is muscle tension?

The activation of tension in muscle cells.

Does muscle tension always require a change in muscle length?

No, muscle tension does not mean there is a change in muscle length.

What defines an isometric muscle contraction?

A contraction that occurs when a muscle is actively held at a set length.

What is a practical example of an isometric muscle contraction?

Holding a weight stationary in front of you.

What defines a concentric muscle contraction?

A contraction that occurs when a muscle is actively shortened.

What is a practical example of a concentric contraction?

Performing a bicep curl (lifting phase).

What defines an eccentric muscle contraction?

A contraction that occurs when a muscle is actively lengthened.

What is a practical example of an eccentric contraction?

Lowering a heavy weight back to neutral during a biceps curl.

What are the three main ways muscle attaches to bone?

Sharpey's fibers to periosteum, tendons, and aponeuroses.

What are Sharpey's fibers?

Bundles of collagen fibers within a connective tissue matrix that connect the periosteum to bone.

What is the periosteum?

A fibrous connective sheath on the outside of bones that provides innervation and cells.

What main functional advantage does direct muscle attachment via Sharpey's fibers provide?

Speed.

Where can a good anatomical example of Sharpey's fibers attaching muscle to periosteum be found?

At the attachment of the rotator cuff muscles to the scapula.

What is an aponeurosis?

A thin sheath of fibrous connective tissue (flattened tendon) that connects muscles to bones.

What primary functional advantages are offered by an aponeurosis attachment?

Efficiency and accommodating space constraints, while supporting muscles and providing stability.

Where in the human body are aponeuroses located?

In the abdomen and back.

What is a tendon, and what primary functional advantage does it offer?

A rope-like flexible tissue made of collagen fibers that is specialized for storage of energy and handling tensile stress.