Kinesiology Ch.2

Key vocabulary terms and concise definitions covering skeletal muscle structure, naming, tissue properties, contraction types, muscle roles, neural control, proprioception, and related concepts from the neuromuscular fundamentals lecture.

Skeletal muscles

Muscles attached to the skeleton; there are about 600, comprising 40–50% of body weight; typically work in agonist/antagonist pairs and in groups for a given joint motion.

Aggregate muscle action

Muscles work in groups rather than independently to achieve a specific joint motion.

Muscle nomenclature

Rules by which muscles are named based on appearance, location, function, shape, size, divisions, and fiber direction.

Gaster (belly)

Central fleshy portion of a muscle that generally increases in diameter as the muscle contracts; the contractile portion.

Tendon

Fibrous connective tissue that connects muscle to bone or other structures; can be shared by two muscles; may have multiple attachments.

Aponeurosis

A sheet- or ribbon-like tendinous expansion that binds muscles together or connects muscle to bone (example: palmar aponeurosis).

Fascia

A sheet or band of fibrous connective tissue that envelopes or binds body parts; can form retinacula near joints to retain tendons.

Parallel muscle

Muscle fibers run parallel to the length of the muscle; allows greater range of motion than pennate counterparts.

Pennate muscle

Muscle fibers run obliquely to tendons; shorter fibers but greater cross-sectional area, increasing potential power.

Flat parallel muscles

Thin, broad muscles originating from broad aponeuroses and spreading force over a broad area (e.g., rectus abdominis, external oblique).

Fusiform parallel muscles

Spindle-shaped with a central belly that tapers to tendons; focus power onto small targets (e.g., brachialis, biceps brachii).

Strap parallel muscles

Uniform diameter with fibers in a long parallel arrangement; concentrate power on small targets (e.g., Sartorius).

Radiate muscles

Triangular or fan-shaped muscles that originate from broad aponeuroses and converge onto a tendon (e.g., pectoralis major, trapezius).

Sphincter (circular) muscles

Endless strap muscles surrounding openings to close them upon contraction (example: orbicularis oris).

Unipennate

Fibers run obliquely from a tendon on one side only.

Bipennate

Fibers run obliquely on both sides from a central tendon.

Multipennate

Several tendons with diagonal fibers between them (example: deltoid).

Irritability/excitability

Muscle property of responsiveness to chemical, electrical, or mechanical stimuli.

Contractility

Ability of a muscle to contract and develop tension against resistance.

Extensibility

Ability of a muscle to be passively stretched beyond its normal resting length.

Elasticity

Ability of a muscle to return to its original length after stretching.

Intrinsic muscles

Muscles located within a body part and acting on it (e.g., intrinsic hand muscles).

Extrinsic muscles

Muscles that originate outside the body part they act on (e.g., forearm muscles attaching to the fingers).

Action (muscle action)

Specific movement of a joint produced by a muscle or muscle group crossing that joint.

Innervation

Nerve supply to a muscle or portion of a muscle; a muscle may be innervated by multiple nerves.

Origin

Proximal attachment; the least movable part of a muscle.

Insertion

Distal attachment; the most movable part of a muscle.

Isometric contraction

Active tension develops but joint angle remains constant.

Isotonic contraction

Contractions with changes in muscle length; includes concentric and eccentric actions.

Concentric contraction

Muscle shortens during contraction to cause movement.

Eccentric contraction

Muscle lengthens while contracting, often controlling movement.

Isokinetic contraction

Dynamic exercise where movement speed is constant; maximal contraction throughout the movement (not a separate type of contraction).

Agonist

Primary or main mover responsible for a movement; may have assisting movers.

Antagonist

Muscles on the opposite side of the joint; relax to allow movement and work with agonists.

Stabilizers

Contract to fixate a region to enable another limb to move effectively (proximal stabilization).

Synergists

Assist agonists by guiding or enhancing their action; not the primary movers.

Neutralizers

Counteract or neutralize the action of another muscle to prevent undesired movements.

Force couples

Two or more forces pulling in different directions to rotate a body part; enhance efficiency (e.g., trapezius and serratus).

Motor unit

A single motor neuron and all the muscle fibers it innervates; functions as a single unit.

All-or-none principle

A motor unit fires maximally or not at all; all fibers in the unit contract together if threshold is reached.

Subthreshold stimulus

A stimulus not strong enough to produce an action potential.

Threshold stimulus

A stimulus strong enough to elicit an action potential in a motor unit.

Recruitment

Process of activating additional motor units to increase muscle force.

Treppe (staircase)

Gradual increase in tension with successive maximal stimuli when there is complete relaxation between contractions.

Muscle length–tension relationship

Maximal force depends on muscle length at the time of contraction; there is an optimal length for force production.

Force–velocity relationship

With greater resistance, shortening velocity decreases; high velocity with light resistance; zero velocity is isometric; further resistance yields eccentric action.

Stretch-shortening cycle

Eccentric pre-stretch followed by immediate concentric contraction, improving total force output via elastic energy and stretch reflex.

Reciprocal inhibition

Antagonist muscles relax to allow agonists to move; mediated by neural mechanisms to enable smooth movement.

Angle of pull

Angle between muscle’s line of pull and the bone; affects rotary vs non-rotary force components; most muscles work at angles <50 degrees; 90 degrees yields full rotary force.

Uniarticular/multiarticular/biarticular muscles

Uniarticular cross and act on one joint; biarticular cross two joints; multiarticular cross three or more joints.

Lombard’s paradox

Concurrent contraction of antagonist muscle groups (e.g., rectus femoris and hamstrings) with different moment arms enabling efficient gait.

Active insufficiency

Muscle shortens to a point where it cannot generate or maintain active tension for all intended actions.

Passive insufficiency

Opposing muscle becomes stretched so it can no longer lengthen enough to allow movement.

Proprioception

Conscious and unconscious sense of body position and movement; kinesthesis is the conscious aspect.

Proprioceptors

Receptors that provide sensory information for proprioception, including muscle spindles, Golgi tendon organs, Pacinian, Ruffini, Meissner, Krause receptors.

Muscle spindles

Proprioceptors in the muscle belly sensitive to stretch and rate of stretch; contribute to stretch reflexes.

Golgi tendon organs (GTO)

Proprioceptors located near the muscle-tendon junction sensitive to muscle tension; initiate inhibitory reflex to prevent damage.

Pacinian corpuscles

Proprioceptors around joints and tissues that respond to rapid changes in joint angle and pressure.

Ruffini’s corpuscles

Proprioceptors in deep skin and joint capsules that respond to slow, sustained changes in joint position.

Meissner’s corpuscles and Krause’s end-bulbs

Touch receptors in skin and subcutaneous tissue contributing to tactile feedback.

Dermatome

Area of skin supplied by a specific spinal nerve.

Myotome

Group of muscles supplied by a specific spinal nerve.

Nerve types (CNS/PNS)

CNS includes brain and spinal cord; PNS includes sensory (afferent) and motor (efferent) divisions; somatic (voluntary) and autonomic (involuntary) nervous systems.

Cranial nerves

12 pairs of nerves arising from the brain that have motor and/or sensory functions.

Spinal nerves

31 pairs of nerves arising from the spinal cord that provide motor and sensory innervation.

Dendrites

Branching projections of a neuron that transmit impulses toward the cell body.

Axon

Long projection of a neuron that transmits impulses away from the cell body.

Neuron classifications

Motor neurons, sensory neurons, and interneurons that process and transmit neural signals.