Saddle Joint

Joint allowing movement in two planes (e.g., thumb).

Anatomy

Sagittal Plane

Anatomical plane dividing left and right sides.

Anatomy

Saliva

Digestive fluid secreted in mouth.

Physiology

Salivary Glands

Glands producing saliva (parotid, submandibular, sublingual).

Anatomy

Saltatory Conduction

Rapid nerve impulse jumping between nodes of Ranvier.

Physiology

Sarcolemma

Muscle fiber cell membrane.

Anatomy

Sarcomere

Contractile unit of muscle fibers.

Anatomy / Physiology

Sarcopenia

Age-related loss of muscle mass and function.

Pathophysiology

Sarcoplasm

Cytoplasm of a muscle fiber.

Anatomy

Sarcoplasmic Reticulum

Organelle storing and releasing calcium in muscles.

Physiology

Scoliosis

Abnormal lateral curvature of spine.

Anatomy / Pathophysiology

Sebaceous Gland

Skin gland secreting sebum (oil).

Anatomy

Sebum

Oily secretion for skin/hair lubrication.

Physiology

Second Messenger

Molecule transmitting signals inside cells (e.g., cAMP).

Biochemistry

Secondary Survey

Detailed patient evaluation after initial assessment.

First Aid / ACLS

Seizure

Abnormal electrical activity in brain.

Pathophysiology

Selective Attention

Focusing on specific stimulus while ignoring others.

Psychology

Semicircular Canals

Inner ear structures for balance.

Anatomy

Semilunar Valves

Heart valves (aortic, pulmonary).

Anatomy

Semimembranosus

Hamstring muscle aiding knee flexion.

Anatomy

Semitendinosus

Hamstring muscle aiding hip extension/knee flexion.

Anatomy

Sensation

Process of detecting physical stimuli.

Psychology

Sensory Adaptation

Reduced sensitivity during constant stimulation.

Physiology

Sensory Neuron

Nerve cell transmitting sensory input.

Neuroscience

Septum

Dividing wall between two chambers (e.g., heart, nose).

Anatomy

Serum

Clear component of blood after clotting.

Physiology

Shock

Circulatory failure leading to inadequate perfusion.

First Aid / Pathophysiology

Shoulder Abduction

Arm movement away from body’s midline.

Anatomy

Shoulder Adduction

Arm movement toward body’s midline.

Anatomy

Shoulder Press

Strength exercise for deltoids/triceps.

Strength & Conditioning

Shunt

Passage diverting blood or fluid flow.

Medicine

Sigmoid Colon

Part of large intestine leading to rectum.

Anatomy

Signal Transduction

Process of converting signals into cellular response.

Biology

Silent Ischemia

Reduced blood supply without symptoms.

Pathophysiology

Sinus Arrhythmia

Normal variation in heart rhythm with breathing.

ECG

Sinus Bradycardia

Slow heart rhythm originating in SA node.

ECG

Sinus Rhythm

Normal heart rhythm.

ECG

Sinus Tachycardia

Fast heart rhythm from SA node.

ECG

Sinusoidal Wave

Waveform describing oscillations.

Physics

Sit-and-Reach Test

Flexibility test of hamstrings/lower back.

Exercise Testing

Skeletal Muscle

Voluntary, striated muscle tissue.

Anatomy

Skinfold Measurement

Method for estimating body fat percentage.

Exercise Testing

Sleep Apnea

Breathing interruptions during sleep.

Pathophysiology

Sleep Cycle

Progression through sleep stages (REM/NREM).

Psychology

Sliding Filament Theory

Model of muscle contraction via actin-myosin sliding.

Physiology

Slow-Twitch Fibers (Type I)

Endurance muscle fibers using oxidative metabolism.

Exercise Physiology

Small Intestine

Organ for nutrient absorption.

Anatomy

Smooth Muscle

Involuntary, non-striated muscle tissue.

Anatomy

Snellen Chart

Vision test using standardized letters.

Medicine

Sodium (Na⁺)

Electrolyte essential for nerve/muscle function.

Chemistry / Physiology

Sodium-Potassium Pump

Membrane protein maintaining electrochemical gradients.

Physiology

Somatic Nervous System

Division of PNS controlling voluntary movement.

Anatomy

Somatization

Psychological distress expressed as physical symptoms.

Psychology

Somatosensory Cortex

Brain area processing touch/proprioception.

Neuroscience

Somatotype

Classification of body type (ectomorph, mesomorph, endomorph).

Exercise Physiology

Somnolence

Drowsiness or sleepiness.

Physiology

Spasm

Sudden involuntary muscle contraction.

Pathophysiology

Spatial Awareness

Perception of body in space.

Motor Behavior

Specificity Principle

Training adaptations are specific to the stimulus.

Strength & Conditioning

Sphenoid Bone

Skull bone forming part of eye socket.

Anatomy

Sphincter

Circular muscle controlling passage of substances.

Anatomy

Sphygmomanometer

Device measuring blood pressure.

Medicine

Spinal Cord

CNS structure transmitting neural signals.

Anatomy

Spinal Nerve

Peripheral nerve arising from spinal cord.

Anatomy

Spinal Shock

Temporary loss of function after spinal injury.

Pathophysiology

Spiral Fracture

Bone fracture twisting along its axis.

Sport Injury

Spirometry

Test measuring lung volumes/capacity.

Exercise Testing

Splanchnic Nerves

Nerves supplying abdominal organs.

Anatomy

Spleen

Organ filtering blood and supporting immunity.

Anatomy

Splenius Capitis

Neck muscle aiding extension/rotation.

Anatomy

Splenius Cervicis

Neck muscle aiding rotation and extension.

Anatomy

Spondylolisthesis

Forward slippage of vertebra.

Pathophysiology

Spondylosis

Degeneration of spinal vertebrae/discs.

Pathophysiology

Sport Psychology

Study of mental factors affecting performance.

Sport Psychology

Sprain

Ligament injury due to overstretching.

Sport Injury

Sprint Interval Training (SIT)

High-intensity training using repeated sprints.

Exercise Physiology

Squamous Cell

Flat epithelial cell type.

Biology

Squat Exercise

Lower body strengthening movement.

Strength & Conditioning

Stamina

Ability to sustain prolonged effort.

Exercise Physiology

Standard Deviation

Measure of data variability.

Sociology / Research

Standard Error

Statistical measure of sampling error.

Sociology

Stapes

Smallest bone in human body (middle ear).

Anatomy

Static Balance

Maintaining equilibrium without movement.

Motor Behavior

Static Stretching

Flexibility exercise with held positions.

Exercise Prescription

Statin

Drug lowering cholesterol levels.

Medicine

Stem Cell

Undifferentiated cell capable of specialization.

Biology

Sternocleidomastoid

Neck muscle aiding head rotation/flexion.

Anatomy

Sternum

Breastbone protecting heart/lungs.

Anatomy

Stiffness

Resistance of a tissue to deformation.

Biomechanics

Stimulant

Substance increasing nervous system activity.

Physiology

Stimulus

Environmental change triggering a response.

Psychology

Stoke Volume (SV)

Blood ejected by ventricle per beat.

Physiology

Stomach

Organ digesting food with acid/enzymes.

Anatomy

Strain

Muscle or tendon injury from overstretching.

Sport Injury

Stratum Corneum

Outermost skin layer of dead keratinocytes.

Anatomy

Strength

Ability to exert maximal force.

Strength & Conditioning

Stress Fracture

Small bone crack from repetitive stress.

Sport Injury

Stress Response

Physiological reaction to challenges/threats.

Psychology / Physiology

Stroke

Sudden interruption of blood flow to brain.

Pathophysiology

Stroke Volume

Volume of blood pumped per heartbeat.

Physiology

Subarachnoid Space

Space containing cerebrospinal fluid around brain/spinal cord.

Anatomy

Subclavian Artery

Major artery beneath the clavicle.

Anatomy

Sublimation

Defense mechanism redirecting impulses to acceptable outlets.

Psychology

Submaximal Exercise

Exercise below maximum effort capacity.

Exercise Physiology

Subscapularis

Rotator cuff muscle stabilizing shoulder.

Anatomy

Substrate-Level Phosphorylation

ATP production directly in glycolysis/Krebs cycle.

Biochemistry

Sudden Cardiac Arrest

Unexpected heart stoppage.

ACLS / Pathophysiology

Sulcus

Groove or depression on brain surface.

Anatomy

Superior Vena Cava

Vein returning blood to right atrium.

Anatomy

Supination

Outward rotation of forearm/foot.

Anatomy

Supplement

Nutrient or compound taken to enhance health.

Nutrition

Supraspinatus

Rotator cuff muscle aiding abduction.

Anatomy

Synapse

Junction where neurons communicate.

Neuroscience

Synaptic Vesicle

Structure storing neurotransmitters.

Neuroscience

Syncope

Temporary loss of consciousness due to low blood flow.

Pathophysiology

Synergist Muscle

Muscle assisting agonist in movement.

Anatomy

Synovial Fluid

Lubricating fluid in joints.

Anatomy

Synovial Joint

Freely movable joint with synovial cavity.

Anatomy

Systemic Circulation

Blood flow through body excluding lungs.

Physiology

Systole

Heart contraction phase.

Physiology

Systolic Blood Pressure (SBP)

Maximum arterial pressure during contraction.

Physiology