Scala tympani (SKA-la TIM-pan-e) The inferior spiral-shaped channel
of the bony cochlea, filled with perilymph.
Scala vestibuli (ves-TIB-Q-le) The superior spiral-shaped channel of
the bony cochlea, filled with perilymph.
Schwann cell (SCHVON) A neuroglial cell of the peripheral nervous
system that forms the myelin sheath and neurolemma around a
nerve axon by wrapping around the axon in a jelly-roll fashion.
Sciatica (sT-AT-i-ka) Inflammation and pain along the sciatic nerve;
felt along the posterior aspect of the thigh extending down the
inside of the leg.
Sclera (SKLE-ra) The white coat of fibrous tissue that forms the
superficial protective covering over the eyeball except in the most
anterior portion; the posterior portion of the fibrous tunic.
Scleral venous sinus A circular venous sinus located at the junc-
tion of the sclera and the cornea through which aqueous humor
drains from the anterior chamber of the eyeball into the blood.
Also called the canal of Schlemm (SHLEM).
Sclerosis (skle-RO-sis) A hardening with loss of elasticity of tissues.
Scoliosis (sko'-le-O-sis) An abnormal lateral curvature from the nor-
mal vertical line of the backbone.
Scrotum (SKRO-tum) A skin-covered pouch that contains the testes
and their accessory structures.
Sebaceous gland (se-BA-shus) An exocrine gland in the dermis of the
skin, almost always associated with a hair follicle, that secretes
sebum. Also called an oil gland.
Sebum (SE-bum) Secretion of sebaceous (oil) glands.
Secondary response Accelerated, more intense cell-mediated or
antibody-mediated immune response upon a subsequent expo-
sure to an antigen after the primary response.
Secondary sex characteristic A characteristic of the male or female
body that develops at puberty under the influence of sex
hormones but is not directly involved in sexual reproduction;
examples are the distribution of body hair, voice pitch, body
shape, and muscle development.
Second messenger An intracellular mediator molecule that is pro-
duced in response to a first messenger (hormone or neurotrans-
mitter) binding to its receptor in the plasma membrane of a
target cell. Initiates a cascade of chemical reactions that produce
characteristic effects for that particular target cell.
Secretion (se-KRE-shun) Production and release from a cell or a
gland of a physiologically active substance.
Selective permeability (per'-me-a-BIL-i-te) The property of a mem-
brane by which it permits the passage of certain substances but
restricts the passage of others.
Semen (SE-men) A fluid discharged at ejaculation by a male that consists
of a mixture of sperm and the secretions of the seminiferous tubules,
seminal vesicles, prostate, and bulbourethral (Cowper's) glands.
Semicircular canals (sem-T-SER-ku-lar) Three bony channels (anterior,
posterior, lateral), filled with perilymph, in which lie the mem-
branous semicircular canals filled with endolymph. They contain
receptors for equilibrium.
Semicircular ducts The membranous semicircular canals filled with
endolymph and floating in the perilymph of the bony semicircular
canals; they contain cristae that are concerned with dynamic
Semilunar valve (sem'-e-LOO-nar) A valve between the aorta or the
pulmonary trunk and a ventricle of the heart.
Seminal vesicle (SEM-i-nal VES-i-kul) One of a pair of convoluted,
pouchlike structures, lying posterior and inferior to the urinary
bladder and anterior to the rectum, that secrete a component of
semen into the ejaculatory ducts. Also termed a seminal gland.
Seminiferous tubule (sem'-T-NI-fer-us TOO-bul) A tightly coiled duct,
located in the testis, where sperm are produced.
Sensation A state of awareness of external or internal conditions of
Sensory neurons (NOO-ronz) Neurons that carry sensory informa-
tion from cranial and spinal nerves into the brain and spinal cord
or from a lower to a higher level in the spinal cord and brain. Also
called afferent neurons (AF-er-ent).
Septal defect An opening in the septum (interatrial or interventricu-
lar) between the left and right sides of the heart.
Septum (SEP-tum) A wall dividing two cavities.
Serous membrane (SIR-us) A membrane that lines a body cavity that
does not open to the exterior. The external layer of an organ
formed by a serous membrane. The membrane that lines the
pleural, pericardial, and peritoneal cavities. Also called a serosa
Sertoli cell (ser-TO-le) A supporting cell in the seminiferous tubules
that secretes fluid for supplying nutrients to sperm and the
hormone inhibin, removes excess cytoplasm from spermatogenic
cells, and mediates the effects of FSH and testosterone on sper-
matogenesis. Also called a sustentacular cell (sus'-ten-TAK-u-lar).
Serum Blood plasma minus its clotting proteins.
Sesamoid bones (SES-a-moyd) Small bones usually found in tendons.
Sex chromosomes The twenty-third pair of chromosomes, desig-
nated X and Y, which determine the genetic sex of an individual;
in males, the pair is XY; in females, XX.
Sexual intercourse The insertion of the erect penis of a male into the
vagina of a female. Also called coitus (KO-i-tus).
Shivering Involuntary contraction of skeletal muscles that generates
Shock Failure of the cardiovascular system to deliver adequate
amounts of oxygen and nutrients to meet the metabolic needs
of the body due to inadequate cardiac output. It is characterized
by hypotension; clammy, cool, and pale skin; sweating; reduced
urine formation; altered mental state; acidosis; tachycardia;
weak, rapid pulse; and thirst. Types include hypovolemic, cardio-
genic, vascular, and obstructive.
Shoulder joint A synovial joint where the humerus articulates with
Sigmoid colon (SIG-moyd KO-lon) The S-shaped part of the large
intestine that begins at the level of the left iliac crest, projects
medially, and terminates at the rectum at about the level of the
third sacral vertebra.
Sign Any objective evidence of disease that can be observed or
measured such as a lesion, swelling, or fever.