The part of the brain composed of the midbrain, pons, and medulla oblongata and connecting the spinal cord with the forebrain and cerebrum.

The part of the nervous system which in vertebrates consists of the brain and spinal cord, to which sensory impulses are transmitted and from which motor impulses pass out, and which supervises and coordinates the activity of the entire nervous system.

A convoluted ridge between anatomical grooves.

A group of subcortical structures (as the hypothalamus, the hippocampus, and the amygdala) of the brain that are concerned especially with emotion and motivation.

A division of a body organ (as the brain, lungs, or liver) marked off by a fissure on the surface.

The part of the nervous system that is outside the central nervous system and comprises the cranial nerves excepting the optic nerve, the spinal nerves, and the autonomic nervous system.

The study of the conformation of the skull based on the belief that it is indicative of mental faculties and character.

A shallow furrow on the surface of the brain separating adjacent gyri.

A momentary reversal in electrical potential across a plasma membrane (as of a nerve cell or muscle fiber) that occurs when a cell has been activated by a stimulus.

The dorsal portion, composed of right and left hemispheres, of the vertebrate forebrain; the integrating center for memory, learning, emotions, and other highly complex function of the central nervous system.

A long nerve cell process that usually conducts impulses away from the cell body.

Any of the usually branching protoplasmic processes that conduct impulses toward the body of a neuron.

An atom or group of atoms that carries a positive or negative electric charge as a result of having lost or gained one or more electrons.

In a neuron, an insulating coat of cell membrane from Schwann cells that is interrupted by nodes of Ranvier.

A physician skilled in the diagnosis and treatment of disease of the nervous system.

A nerve cell; the fundamental unit of the nervous system, having structure and properties that allow it to conduct signals by taking advantage of the electrical charge across its cell membrane.

A substance (as norepinephrine or acetylcholine) that transmits nerve impulses across a synapse.

The time elapsing between the beginning of the application of a stimulus and the beginning of an organism's reaction to it.

An automatic and often inborn response to a stimulus that involves a nerve impulse passing inward from a receptor to the spinal cord and thence outward to an effector (as a muscle or gland) without reaching the level of consciousness and often without passing to the brain.

The place at which a nervous impulse passes from one neuron to another.

A gland (as the thyroid or the pituitary) that produces an endocrine secretion -- called also ductless gland, gland of internal secretion.

The glands and parts of glands that produce endocrine secretions, help to integrate and control bodily metabolic activity, and include especially the pituitary, thyroid, parathyroid, adrenals, islets of Langerhans, ovaries, and testes.

A gland (as a sweat gland, a salivary gland, or a kidney) that releases a secretion external to or at the surface of an organ by means of a canal or duct.

A protein hormone that is produced especially by the pancreatic islets of Langerhans and that promotes an increase in the sugar content of the blood by increasing the rate of breakdown of glycogen in the liver.

A cell, group of cells, or organ of endothelial origin that selectively removes materials from the blood, concentrates or alters them, and secretes them for further use in the body or for elimination from the body.

Any one of the many circulating chemical signals found in all multicellular organisms that are formed in specialized cells, travel in body fluids, and coordinate the various parts of the organism by interacting with target cells.

The ventral part of the vertebrate forebrain; functions in maintaining homeostasis, especially in coordinating the endocrine and nervous systems; secretes hormones of the posterior pituitary and releasing factors, which regulate the anterior pituitary.

A vertebrate hormone that lowers blood glucose levels by promoting the uptake of glucose by most body cells and the synthesis and storage of glycogen in the liver.

An endocrine gland at the base of the hypothalamus; consists of a posterior lobe, which stores and releases two hormones produced by the hypothalamus, and an anterior lobe, which produces and secretes many hormones that regulate diverse body functions.

The automatic adjustment of the eye for seeing at different distances affected chiefly by changes in the convexity of the crystalline lens.

A defect of an optical system (as a lens) causing rays from a point to fail to meet in a focal point resulting in a blurred and imperfect image.

The small circular area in the retina where the optic nerve enters the eye that is devoid of rods and cones and is insensitive to light.

Any of the conical photosensitive receptor cells of the vertebrate retina that function in color vision.

The transparent part of the coat of the eyeball that covers the iris and pupil and admits light to the interior.

The ability to judge the distance of objects and the spatial relationship of objects at different distances.

A condition in which visual images come to a focus behind the retina of the eye and vision is better for distant than for near objects -- called also�farsightedness.

The opaque muscular contractile diaphragm that is suspended in the aqueous humor in front of the lens of the eye, is perforated by the pupil and is continuous peripherally with the ciliary body, has a deeply pigmented posterior surface which excludes the entrance of light except through the pupil and a colored anterior surface which determines the color of the eyes.

A curved piece of glass or plastic used singly or combined in eyeglasses or an optical instrument (as a microscope) for forming an image by focusing rays of light.

A condition in which the visual images come to a focus in front of the retina of the eye because of defects in the refractive media of the eye or of abnormal length of the eyeball resulting especially in defective vision of distant objects -- called also nearsightedness.

Either of the pair of sensory nerves that comprise the second pair of cranial nerves, arise from the ventral part of the diencephalon, form an optic chiasma before passing to the eye and spreading over the anterior surface of the retina, and conduct visual stimuli to the brain.

The opening in the iris, which admits light into the interior of the vertebrate eye; muscles in the iris regulate its size.

The deflection from a straight path undergone by a light ray or a wave of energy in passing obliquely from one medium (as air) into another (as water or glass) in which its velocity is different.

The sensory membrane that lines most of the large posterior chamber of the vertebrate eye, is composed of several layers including one containing the rods and cones, and functions as the immediate instrument of vision by receiving the image formed by the lens and converting it into chemical and nervous signals which reach the brain by way of the optic nerve.

Any of the long rod-shaped photosensitive receptors in the retina responsive to faint light.