Biology Terms

Words	Meaning
Stimuli	Detectable changes in the internal or external environment that which influences or causes a temporary increase of physiological activity or response in the whole organism or in any of its parts. It can evoke a response or has an influence on a system to act.
Receptor	A sensory nerve terminal that responds to stimuli of various kinds. An organ having nerve endings (in the skin or viscera or eye or ear or nose or mouth) that respond to stimulation.
Sclera	The tough white outer coat of the eyeball, covering approximately the posterior five sixths of its surface and continuous anteriorly with the cornea and posteriorly with the external sheath of the optic nerve. Composed mainly of type i collagen arranged in bundles and proteoglycans.
Cornea	The transparent structure forming the anterior part of the fibrous tunic of the eye.
Conjunctiva	a clear membrane that coats the inner aspect of the eyelids and the outer surface of the eye.
Vitreous humour	The gel-like substance that fills the eyeball between the lens and the retina.
Aqueous humour	a transparent liquid contained in the anterior and posterior chambers of the eye, produced by the ciliary process it passes to the venous system via the canal of schlemm.
Suspensory ligament	A series of delicate meridional fibres arising from the inner surface of the orbiculus ciliaris that run in bundles between, and in a very thin layer over, the ciliary processes; at the inner border of the corona, the fibres diverge into two groups that are attached to the capsule on the anterior and posterior surfaces of the lens close to the equator; the spaces between these two layers of fibres are filled with aqueous humor.
Choroid	middle layer of the vertebrate eye, between retina and sclera. Well vascularised and also pigmented to throw light back onto the retina (the tapetum is an irridescent layer in the choroid of some eyes). Not to be confused with the choroid plexus, a highly vascularised region of the roof of the ventricles of the vertebrate brain that secretes cerebrospinal fluid.
Retina	light sensitive layer of the eye.
Lysozyme	An enzyme found in saliva and sweat and tears that destroys the cell walls of certain bacteria.
Fovea	a relatively small cup-shaped depression or pit.
Accomodation	adjustment, especially that of the eye for various distances resulting in pupil constriction or dilatation.
The Central Nerve System	Pertaining to the brain, cranial nerves and spinal cord. It does not include muscles or peripheral nerves.
Neurons	An excitable cell specialised for the transmission of electrical signals over long distances. Neurons receive input from sensory cells or other neurons and send output to muscles or other neurons.
Neurotransmitter	Any of a group of substances that are released on excitation from the axon terminal of a presynaptic neuron of the central or peripheral nervous system and travel across the synaptic cleft to either excite or inhibit the target cell.
Homeostasis	The ability of the body or a cell to seek and maintain a condition of equilibrium or stability within its internal environment when dealing with external changes
Antagonistic muscle	A muscle that opposes the action of another; the biceps and triceps are antagonistic muscles.
Voluntary muscle	Striated muscle that can be controlled voluntarily. A muscle that is connected at either or both ends to a bone and so move parts of the skeleton; a muscle that is characterized by transverse stripes
Involuntary muscle	A muscle that contracts without conscious control and found in walls of internal organs such as stomach and intestine and bladder and blood vessels (excluding the heart).A type of muscle that is not consciously controlled by an organism and reacts 'involuntarily' to nerve system signals.
Coordination	The harmonious functioning of interrelated organs and parts, applied especially to the process of the motor apparatus of the brain which provides for the co-working of particular groups of muscles for the performance of definite adaptive useful responses.
Cerebrum	The portion of the brain (frontal lobes) where thought and higher function reside.
Cortex	the outer layer of an organ or other body structure, as distinguished from the internal substance.
Medulla	The inner part of an organ. A white fatty substance that forms a medullary Sheath around the axis cylinder of some nerve fibers.
Reflex arc	Physiol the neural pathway over which impulses travel to produce a reflex action, consisting of at least one afferent (receptor) and one efferent (effector) neuron
Excretion	The process, act or function of discharging or ejecting waste product of metabolism, especially from the system of an organism.
Glomerulus	A small intertwined group of capillaries in the malpighian body; glomeruli filter blood during urine formation.
Renal capsules	Suprarenal capsules, two small bodies of unknown function in front of, or near, the kidneys in most vertebrates. Also called renal capsules, and suprarenal bodies.
Nephron	Any of the small tubules that are the excretory units of the vertebrate kidney.A structure deriving from the bowmans [[capsule of the Kidney responsible for blood filtration.
Osmoregulation	The process of regulating water potential in order to keep fluid and electrolyte balance within a cell or organism relative to the surrounding.
Homeostasis	The ability of the body or a cell to seek and maintain a condition of equilibrium or stability within its internal environment when dealing with external changes
Dermis	Mesodermally derived connective tissue underlying the epithelium of the skin.
Vasodilation	The increase in the internal diameter of a blood vessel that results from relaxation of smooth muscle within the wall of the vessel. This causes an increase in blood flow, but a decrease in systemic vascular resistance.
Vasoconstriction	The diminution of the calibre of vessels, especially constriction of arterioles leading to decreased blood flow to a part.
Negative feedback	A feedback in which the system responds in an opposite direction to the perturbation.