IBDP Bio (2025) - B3.3 HL - Muscle and Motility

Skeletal Muscle

A type of muscle tissue that is under voluntary control and is responsible for movement.

Motor neurons

Nerve cells that transmit signals from the brain and spinal cord to muscles, causing them to contract.

Effector

A muscle or gland that responds to a stimulus from a motor neuron.

Neuromuscular junction

The synapse or junction where a motor neuron meets a muscle fiber.

Neurotransmitter

Chemical messengers that transmit signals across the neuromuscular junction.

Sarcomere

The basic structural and functional unit of a muscle fiber, composed of myofilaments.

Myofibril

Long, thread-like structures within muscle fibers that contain sarcomeres.

Myosin

A protein that forms thick filaments in muscle fibers and is involved in muscle contraction.

Z disc

The boundary between adjacent sarcomeres, anchoring the actin filaments.

Actin

A protein that forms thin filaments in muscle fibers and plays a key role in muscle contraction.

M line

The line in the center of the sarcomere that anchors myosin filaments.

A band

The dark band in a sarcomere that contains both myosin and overlapping actin filaments.

I band

The light band in a sarcomere that contains only actin filaments.

H band

The region in the A band where there are only myosin filaments, not overlapping with actin.

Sarcolemma

The cell membrane surrounding a muscle fiber.

Sarcoplasmic reticulum

A specialized endoplasmic reticulum in muscle cells that stores calcium ions.

Cross bridge

The connection formed between myosin heads and actin filaments during muscle contraction.

Tropomyosin

A protein that blocks the binding sites on actin filaments, preventing contraction when muscles are relaxed.

Troponin

A protein complex that, when bound to calcium, causes tropomyosin to move and expose binding sites on actin.

Power stroke

The movement of the myosin head that pulls the actin filament during muscle contraction.

Antagonistic pair

Two muscles that work against each other to create movement.

Titin

A large protein that helps stabilize the position of myosin filaments in the sarcomere.

Lever

A rigid bar that pivots around a fixed point (fulcrum) to create movement.

Endoskeleton

The internal skeleton of an organism, providing support and protection for internal organs.

Exoskeleton

A hard outer structure that provides support and protection for an organism, typically found in arthropods.

Synovial joint

A type of joint that allows for free movement and contains synovial fluid.

Synovial fluid

The lubricating fluid found in synovial joints that reduces friction between the articular cartilages.

Ligaments

Tissues that connect bones to other bones at a joint.

Articular cartilage

Smooth tissue that covers the ends of bones in a joint, reducing friction.

Tendons

Tissues that connect muscles to bones.

Collagen

A structural protein that provides strength and support to connective tissues.

Flexion

The bending movement that decreases the angle between two body parts.

Extension

The straightening movement that increases the angle between two body parts.

Adduction

The movement of a limb toward the midline of the body.

Abduction

The movement of a limb away from the midline of the body.

Circumduction

The circular movement of a limb, combining flexion, extension, adduction, and abduction.

Rotation

The movement of a body part around its own axis.

Goniometer

An instrument used to measure the range of motion of joints.