IB Biology: Muscle Structure, Contraction, and Movement Adaptations

Mobility

The ability of an organism to locomote and move from one location to another.

Motility

A characteristic of all organisms whereby they independently move using metabolic energy.

Sessility

A trait by which an organism is fixed in its location and unable to move.

Streamlining

Marine animals are shaped to minimize water resistance by reducing drag and friction through smooth + hairless skin and tapering towards the rear.

Adapted limbs

Marine limbs form flippers to allow for steering, and their fluked tails with up-and-down movement provides increased thrust.

Airways in marine mammals

The mouth and lungs are not connected (like in humans), and the blowhole enables them to breathe.

Motor unit

Includes the motor neuron, muscle fibres and the neuromuscular junctions that connect them.

Muscle fibers

Composed of myofibrils.

Neuromuscular junction

A synapse connecting the axon terminal of a motor neuron and the sarcolemma of a muscle fiber using acetylcholine (Ach) as the neurotransmitter.

Action potential

Transmitting the action potential to the muscle causes Ca2+ ions to be released from the sarcoplasmic reticulum, initiating muscle contraction.

Sarcomere

The functional unit of muscles.

Muscle contraction

The shortening of muscle fibers, which involves the cross-bridge cycle.

Cross-bridge cycle

The process involving the binding of myosin to actin, leading to muscle contraction.

Ca2+ ions

Calcium ions that bind to troponin to change the conformation of tropomyosin, exposing myosin binding-sites on actin filaments.

ATP hydrolysis

The process that produces ADP + Pi and releases energy for myosin to move into a high energy state.

Power stroke

The action where the myosin head bends, sliding the actin towards the H-zone.

Antagonistic muscles

Muscles that work in pairs, where one muscle contracts while the other relaxes.

Titin

connects myosin filaments with the Z-line, stores potential energy, and prevents overstretching of the sarcomere.

Exoskeleton

The external skeleton found in arthropods, such as spiders and crabs.

Endoskeleton

The internal skeleton found in vertebrates.

Synovial fluid

The fluid found in synovial joints that lubricates and nourishes the cartilage.

Cartilage

The flexible tissue that covers the ends of bones at joints, providing cushioning.

Ligaments

Tissues that connect bones to other bones at joints.

Tendons

Tissues that connect muscles to bones.

Range of motion

The extent of movement possible at a joint, determined by the type of joint.

ball-and-socket joint

A type of joint that allows movement in multiple directions, such as the hip joint.

Internal intercostal muscles

contract while external intercostals relax, moving the ribcage inwards and downwards.

External intercostal muscles

contract while internal intercostals relax, moving the ribcage outwards and upwards.

Acetylcholine

functions in muscle contraction.

Sliding filament theory

describes the process of muscle contraction at the molecular level.

Motor units

composed of a motor neuron and the muscle fibers it innervates.

ATP

provides the energy necessary for muscle contraction.

Evolutionary advantages of locomotion

include improved access to resources and escape from predators.

Adaptations of marine animals for swimming

include streamlined bodies and specialized fins.

Function of the musculoskeletal system

moves, supports, and protects the human body.

Peristalsis

the movement of internal parts of the body in response to stimuli, such as in the digestive system.

Skeletal Muscles

Muscles in the body that are attached to the skeleton and aid movement

Striated Muscle

Skeletal muscle

Muscle Fibres

Striated muscle cells are bundled up into fibres, which are highly specialised cell-like units.

Contractile Proteins

Each muscle fibre contains an organised arrangement of contractile proteins in the cytoplasm.

Sarcoplasmic Reticulum (SR)

The specialised endoplasmic reticulum that stores calcium and conveys signals to all parts of the fibre at once.

Sarcoplasm

The specialised cytoplasm called the sarcoplasm contains mitochondria and myofibrils.

Mitochondria

The mitochondria carry out aerobic respiration to generate the ATP required for muscle contraction.

Myofibrils

bundles of actin and myosin filaments, which slide past each other during muscle contraction.

Thick Filaments

made of myosin.

Thin Filaments

made of actin.

H Band

contains only thick myosin filaments.

I Band

contains only thin actin filaments.

A Band

contains areas where only myosin filaments are present and areas where myosin and actin filaments overlap.

M Line

serves as an attachment for myosin filaments.

Z line

Attachment for actin filaments

Sliding Filament Model

The thick filaments within a myofibril are made up of myosin molecules

Myosin

Fibrous protein molecules with a globular head

Actin

Globular protein molecules that link together to form a chain

Tropomyosin

A fibrous protein twisted around two actin chains

Troponin

A protein attached to the actin chains at regular intervals

Cross-bridges

Formed by myosin heads binding with sites on the actin filaments during muscle contraction

Isometric contraction

A muscle contraction without motion, maintaining posture by both muscles contracting at joints

Spring-like properties of titin

The many folds in the titin molecule that aid muscle contraction

Chemical energy storage in titin

Titin stores chemical energy within its structure when stretched

Overstretching prevention

The presence of titin prevents overstretching of the muscle

Energy release from titin

During muscle contraction, titin proteins recoil, releasing stored chemical energy

Sarcomere shortening

Occurs during muscle contraction as Z lines are pulled closer together

Muscle relaxation

The process where the sarcomere lengthens and titin is stretched out

Skeletal Muscle

contracts when it receives an impulse from a motor neurone via the neuromuscular junction.

Motor Unit Activation

During a low intensity muscle contraction, a low number of motor units are activated; for a high intensity contraction, more motor units receive impulses.

Chitin

Exoskeletons are made of polysaccharides called .

Skeleton as Levers

The presence of pivot points means that skeletons act as levers transferring the size and direction of force.

Synovial joints

The most common type of joint characterized by a joint cavity filled with lubricating synovial fluid which reduces friction.

Flexion

A movement that decreases the angle between two body parts.

Extension

A movement that increases the angle between two body parts.

Rotation

A movement around an axis.

Abduction

The movement of a limb away from the body.

Adduction

The movement of a limb towards the body.

Knee joint

A hinge joint that allows flexion and extension.

Elbow joint

A hinge joint that allows flexion and extension.

Hip joint

A ball and socket synovial joint that allows flexion, extension, rotation, sideways and backwards movement.

Shoulder joint

A joint that allows abduction, adduction, flexion, and extension.

Articulation

The connection between the bones of the femur (the ball) and the pelvis (the socket) in the hip joint.

Effectors

Muscles that are stimulated by nerve impulses from motor neurones to bring about movement.

Inhalation

The process where the external intercostal muscles contract to pull the ribs up and out, increasing the volume of the chest cavity.

Exhalation

The process where the external intercostal muscles relax, allowing the ribs to drop down and in, decreasing the volume of the chest cavity.

Diaphragm

A muscle that also relaxes and contracts during ventilation, but is not part of an antagonistic muscle pair.

Goniometer

A simple tool that measures the distance and direction that a joint can move in degrees.

Potential Energy in Muscles

The stretching of internal intercostal muscles results in stored potential energy within the titin protein of the sarcomere.

Intercostal Muscles

Muscles that work antagonistically to facilitate breathing.

Rib Cage Movement

The movement of the rib cage in opposite directions is due to the contraction and relaxation of intercostal muscles.

Locomotion

The movement or the ability to move from one place to another.

Flippers

Adapted front limbs of marine mammals used mainly for steering.

Fluke

The adapted tail of marine mammals capable of up and down movement used for propulsion.

Blowhole

An evolutionary adaptation in marine mammals allowing periodic breathing between dives, which can be sealed to prevent water entry.