Muscles

Characteristics and functions of smooth muscle

Smooth muscle is non-striated, involuntary, and found in walls of hollow organs (e.g., intestines, blood vessels). It regulates slow, sustained contractions.

Characteristics and functions of cardiac muscle

Cardiac muscle is striated, involuntary, with intercalated discs. Found in the heart, it contracts rhythmically and is responsible for pumping blood.

Characteristics and functions of skeletal muscle

Skeletal muscle is striated, voluntary, and attached to bones. It enables movement and posture maintenance through rapid, forceful contractions.

How is lactic acid formed during muscle contraction?

Lactic acid is formed from pyruvate during anaerobic respiration when oxygen levels are low, typically during intense exercise.

Structures of the neuromuscular junction and action potential movement

The neuromuscular junction includes the axon terminal, synaptic cleft, and motor end plate. Action potential travels from the neuron, releasing ACh which binds to receptors on the sarcolemma, creating a new action potential in the muscle.

What is a motor unit?

A motor unit consists of a single motor neuron and all the muscle fibers it innervates, responsible for muscle contraction.

What is a neurotransmitter, and which is used in skeletal muscle contraction?

A neurotransmitter is a chemical messenger that transmits signals across synapses. Acetylcholine (ACh) is the neurotransmitter used in skeletal muscle contraction.

Describe an action potential.

An action potential is a rapid, transient electrical signal that travels along a neuron or muscle cell. Once started, it cannot be stopped.

What is depolarization?

Depolarization is the process where the membrane potential becomes less negative, moving towards zero, typically due to sodium ions entering the cell.

Steps of the sliding filament theory of muscle contraction

1) Calcium binds to troponin, uncovering myosin binding sites on actin. 2) Myosin heads attach to actin, forming cross-bridges. 3) The power stroke occurs as myosin heads pivot, pulling the actin filaments. 4) ATP binds to myosin, releasing it from actin, and the cycle repeats.

Functions of skeletal muscle

Skeletal muscle functions include movement, maintaining posture, producing heat, and stabilizing joints.

What is acetylcholinesterase?

Acetylcholinesterase is an enzyme that breaks down acetylcholine in the synaptic cleft, ending the signal for muscle contraction.

Describe a sarcomere and its parts.

A sarcomere is the basic contractile unit of muscle, consisting of myofilaments: actin (thin) and myosin (thick) filaments, along with Z discs, M line, and H zone.

How do structures change during contraction?

During contraction, sarcomeres shorten, Z discs move closer together, the H zone disappears, and actin and myosin overlap increases.

What is a muscle twitch?

A muscle twitch is a single, rapid contraction and relaxation cycle of a muscle fiber in response to a stimulus.

What is a tectonic contraction?

Tetanic contraction is a sustained muscle contraction that occurs when stimuli are repeated at a frequency high enough to not allow the muscle to relax.

Define: Sarcoplasm, Sarcoplasmic Reticulum, Cross Bridge, Sarcolemma

Sarcoplasm: cytoplasm of a muscle fiber; Sarcoplasmic Reticulum: stores calcium ions; Cross Bridge: interaction between myosin and actin during contraction; Sarcolemma: muscle cell membrane.

How is creatine phosphate used in muscle contraction?

Creatine phosphate donates a phosphate group to ADP to quickly regenerate ATP during high-intensity exercise.

How is ATP used in muscle contraction?

ATP powers muscle contraction by providing the energy needed for cross-bridge cycling and detachment.

Describe endomysium, perimysium, and epimysium.

Endomysium surrounds individual muscle fibers; perimysium encloses fascicles (bundles of fibers); epimysium encases the entire muscle.

What is an isometric contraction? Isotonic contraction?

Isometric contraction occurs without muscle length change (e.g., holding a weight steady); Isotonic contraction involves muscles shortening (concentric) or lengthening (eccentric) to produce movement.

What is a fascicle?

A fascicle is a bundle of muscle fibers surrounded by perimysium.

Describe muscle contraction from release of ACh to sliding of the filaments.

ACh is released from the axon terminal, binds to receptors on the sarcolemma, causing depolarization, action potential generation, calcium release from the sarcoplasmic reticulum, and filament sliding.

Discuss the role of actin and myosin in the sliding filament theory.

Actin is the thin filament that serves as a track for myosin heads (thick filaments) to walk along, generating contraction through cross-bridge cycling.

How is calcium used in the neuromuscular junction and muscle contraction?

Calcium ions released from the sarcoplasmic reticulum initiate contraction by binding to troponin, causing tropomyosin to shift and exposing myosin binding sites on actin.

Compare and contrast isotonic contraction and isometric contraction with examples.

Isotonic contraction (e.g., lifting weights) involves changing muscle length, while isometric contraction (e.g., pushing against a wall) involves muscle tension without length change.