{saccule}{}{Part of the membranous labyrinth; contains sensory structure, the macula, that detects static equilibrium.}

{sacral foramen [foramina]}{}{An intervertebral foramen between the fused vertebrae of the sacrum.}

{sagittal plane}{}{A plane that separates the body into right and left halves.}

{saliva}{}{Fluid secreted by salivary glands for the purpose of lubricating ingested food and digesting simple carbohydrates.}

{salivary gland}{}{Gland that secretes saliva into the oral cavity.}

{sarco-}{}{Referring to muscles.}

{sarcolemma}{}{Plasma membrane of a muscle fiber.}

{sarcomere}{}{Part of a myofibril between adjacent Z disks.}

{saturated}{}{Fatty acid in which the carbon chain contains only single bonds between carbon atoms.}

{sebaceous gland}{}{Gland of the skin, usually associated with a hair follicle, that produces sebum.}

{sebum}{}{Oily secretion of sebaceous glands.}

{second messenger}{}{Molecule that is produced in a cell in which an intercellular mediator interacts with a membrane-bound receptor molecule; the intercellular mediator then acts as a signal and carries information to a site within the cell; for example, cyclic AMP.}

{secondary sexual characteristic}{}{Physical characteristics that form as a young human grows into either an adult male or female.}

{secretory vesicle}{}{Membrane-bound cellular package that serves to transport cellular products.}

{semen}{}{Fluid containing sperm cells and secretions discharged from male reproductive tract at ejaculation.}

{semicircular canal}{}{Canal in the petrous portion of the temporal bone that contains sensory organs that detect kinetic or dynamic equilibrium. Three semicircular canals are within each inner ear.}

{seminal fluid}{}{Fluid formed by the male secondary sexual organs to protect and nourish spermatozoa.}

{seminal vesicle}{}{Secretes fluid added to the urethra to form seminal fluid.}

{semipermeable}{}{Describes membrane that allows some molecules through but not others.}

{sensation}{}{Feeling resulting from the brain's interpretation of sensory nerve impulses.}

{sensory [afferent] neurons}{}{Neuron that transmits an impulse from a receptor to the central nervous system.}

{sensory area}{}{Portion of cerebral cortex that receives and interprets sensory nerve impulses.}

{sensory receptor}{}{Specialized structure associated with the peripheral end of a sensory neuron specific to detecting a particular sensation and triggering a nerve impulse in response, which is transmitted to the central nervous system.}

{serosa}{}{Outermost layer of the digestive tract, also called the adventitia.}

{serous membrane}{}{Thin sheet composed of epithelial and connective tissues; lines cavities that do not open to the outside of the body or contain glands but do secrete serous fluid.}

{sex chromosome}{}{X- or Y-chromosome; determines gender of zygote.}

{sex-linked gene}{}{A gene that may have nothing to do with sexual characteristics, but lies on a sex chromosome.}

{shell}{}{Concentric orbitals of electrons around the atom's nucleus.}

{short bone}{}{A small bone whose length is not significantly greater than its width.}

{simple epithelium}{}{Epithelium consisting of a single layer of cells.}

{skeletal muscle}{}{Type of muscle tissue in muscles attached to bones.}

{sliding filament theory}{}{The theory behind the mechanism of muscle contraction; refers to the interactions between actin and myosin.}

{small intestine}{}{Tube connecting the stomach to the large intestine; carries out chemical digestion and absorption of many nutrients.}

{smooth endoplasmic reticulum}{}{Cellular organelle made up of a tubelike network.}

{smooth muscle}{}{Type of muscle tissue in walls of hollow viscera; visceral muscle.}

{solute}{}{Dissolved substance in a solution.}

{solution}{}{Homogenous mixture formed when a solute is dissolved in a solvent.}

{somatic motor nerve}{}{Peripheral nerve that leads to a skeletal muscle.}

{somatic motor nervous system}{}{Motor pathways of the peripheral nervous system that lead to skeletal muscles.}

{spatial summation}{}{Summation of the local potentials in which two or more action potentials arrive simultaneously at two or more presynaptic terminals that synapse with a single neuron.}

{sperm}{}{Male mature sex cell.}

{spinal nerve}{}{One of 31 pairs of nerves formed by the joining of the dorsal and ventral roots that arise from the spinal cord.}

{spindle fiber}{}{Specialized microtubule that develops from each centrosome and extends toward the chromosomes during cell division.}

{spongy bone [cancellous bone]}{}{Bone that consists of bars and plates separated by irregular spaces.}

{squamous cell}{}{Scalelike, flat.}

{static equilibrium}{}{Maintenance of balance when the head and body are motionless.}

{steroid hormone}{}{Hormone derived from the molecule cholesterol.}

{steroid}{}{Large family of lipids, including some reproductive hormones, vitamins, and cholesterol.}

{stomach}{}{Digestive organ between the esophagus and small intestine.}

{stratified epithelium}{}{Epithelium consisting of more than one layer of cells.}

{stratum basale}{}{Basal or deepest layer of the epidermis.}

{stratum corneum}{}{Most superficial layer of the epidermis consisting of flat, keratinized, dead cells.}

{stratum granulosum}{}{Layer of cells in the epidermis filled with granules of keratohyalin.}

{stratum lucidum}{}{Clear layer of the epidermis found in thick skin between the stratum granulosum and the stratum corneum.}

{stratum spinosum}{}{Layer of many-sided cells in the epidermis with intercellular connections [desmosomes] that give the cells a spiny appearance.}

{subarachnoid space}{}{Space within meninges between arachnoid mater and pia mater.}

{subcutaneous tissue}{}{Tissue under the dermis; same tissue as the hypodermis.}

{submucosa [submucosae]}{}{Layer of connective tissue underneath a mucous membrane.}

{submucosal plexus [plexi]}{}{Nerves lying in the submucosal layer of the digestive tract that form a sympathetic ganglionic plexus.}

{subthalamus}{}{Portion of the diencephalon between the thalamus and the hypothalamus.}

{subthreshold potential}{}{Change in potential across the cell membrane that is below the level needed to produce an action potential; several subthreshold potentials may sum to form a threshold potential.}

{sucrose}{}{Disaccharide composed of glucose and fructose; table sugar.}

{sulcus [sulci]}{}{Furrow or groove on the surface of the brain between the gyri; may also refer to a fissure.}

{summation}{}{Phenomena in which the degree of change in membrane potential directly correlates with stimulation frequency.}

{superficial}{}{Near the surface.}

{superior}{}{Pertaining to a structure that is vertically higher than another structure.}

{supination}{}{Rotation of the forearm [when the forearm is parallel to the ground] so that the anterior surface is up [supine].}

{suprarenal gland}{}{Adrenal gland; endocrine gland superior to the kidney.}

{suture}{}{Junction between flat bones of the skull.}

{sweat gland}{}{Usually means structures that produce a watery secretion called sweat. Some sweat glands, however, produce viscous organic secretions.}

{sympathetic division}{}{Subdivision of the autonomic division of the nervous system characterized by having the cell bodies of its preganglionic neurons located in the thoracic and upper lumbar regions of the spinal cord [thoracolumbar division]; usually involved in preparing the body for physical activity.}

{synapse}{}{Functional membrane-to-membrane contact of a nerve cell with another nerve cell, muscle cell, gland cell, or sensory receptor; functions in the transmission of action potentials from one cell to another.}

{synaptic cleft}{}{Space between the presynaptic and the postsynaptic membranes.}

{synaptic vesicle}{}{Secretory vesicle in the presynaptic terminal containing neurotransmitter substances.}

{syndesmosis}{}{Form of fibrous joint in which opposing surfaces that are some distance apart are united by ligaments.}

{synovial joint}{}{A joint containing synovia [a substance that serves as a lubricant in a joint, tendon sheath, or bursa].}

{synovial membrane}{}{Membrane that produces synovial fluid for joint lubrication.}

{systemic circulation}{}{Vessels that conduct blood between the heart and all body tissues except the lungs.}