Neuron

Front 1

Neuron

Back 1

A specialized, impulse-conducting cell that is the functional unit of the nervous system, consisting of the cell body and its processes, the axon and dendrites.

Front 2

Dendrite

Back 2

The branching process of a neuron that conducts impulses toward the cell.

Front 3

Axon

Back 3

The appendage of the neuron that transmits impulses away from the cell body.

Front 4

Myelin Sheath

Back 4

A wrapping of myelin around certain nerve axons, serving as an electrical insulator that speeds nerve impulses to muscles and other effectors.

Front 5

Action Potential

Back 5

The change in electrical potential that occurs between the inside and outside of a nerve or muscle fiber when it is stimulated, serving to transmit nerve signals.

Front 6

Threshold

Back 6

The point at which a stimulus is of sufficient intensity to begin to produce an effect.

Front 7

Synapse

Back 7

A region where nerve impulses are transmitted and received, encompassing the axon terminal of a neuron that releases neurotransmitters in response to an impulse, an extremely small gap across which the neurotransmitters travel, and the adjacent membrane of an axon, dendrite, or muscle or gland cell with the appropriate receptor molecules for picking up the neurotransmitters.

Front 8

Neurotransmitters

Back 8

Any of several chemical substances, as epinephrine or acetylcholine, that transmit nerve impulses across a synapse to a postsynaptic element, as another nerve, muscle, or gland.

Front 9

Acetylcholine

Back 9

A white crystalline derivative of choline that is released at the ends of nerve fibers in the somatic and parasympathetic nervous systems and is involved in the transmission of nerve impulses in the body.

Front 10

Endorphins

Back 10

Any of a group of peptides occurring in the brain and other tissues of vertebrates, and resembling opiates, that react with the brain's opiate receptors to raise the pain threshold.

Front 11

Nervous System

Back 11

The system of cells, tissues, and organs that regulates the body's responses to internal and external stimuli. In vertebrates it consists of the brain, spinal cord, nerves, ganglia, and parts of the receptor and effector organs.

Front 12

Central Nervous System

Back 12

The part of the nervous system comprising the brain and spinal cord.

Front 13

Peripheral Nervous System

Back 13

The part of the vertebrate nervous system constituting the nerves outside the central nervous system and including the cranial nerves, the spinal nerves, and the sympathetic and parasympathetic nervous systems.

Front 14

Nerves

Back 14

One or more bundles of fibers forming part of a system that conveys impulses of sensation, motion, etc., between the brain or spinal cord and other parts of the body.

Front 15

Sensory Neurons

Back 15

A nerve cell that conducts impulses from a sense organ to the central nervous system.

Front 16

Motor Neurons

Back 16

A nerve cell that conducts impulses to a muscle, gland, or other effector.

Front 17

Interneurons

Back 17

Any neuron having its cell body, axon, and dendrites entirely within the central nervous system, especially one that conveys impulses between a motor neuron and a sensory neuron.

Front 18

Somatic Nervous System

Back 18

The part of the nervous system that controls voluntary movements in the body, such as those performed by the skeletal muscles. The somatic nervous system also includes the special nerve fibers that help keep the body in touch with its surroundings, such as those involved in touch, hearing, and sight.

Front 19

Autonomic Nervous System

Back 19

The system of nerves and ganglia that innervates the blood vessels, heart, smooth muscles, viscera, and glands and controls their involuntary functions, consisting of sympathetic and parasympathetic portions.

Front 20

Sympathetic Nervous System

Back 20

The part of the autonomic nervous system originating in the thoracic and lumbar regions of the spinal cord that in general inhibits or opposes the physiological effects of the parasympathetic nervous system, as in tending to reduce digestive secretions or speed up the heart.

Front 21

Parasympathetic Nervous System

Back 21

The part of the autonomic nervous system originating in the brain stem and the lower part of the spinal cord that, in general, inhibits or opposes the physiological effects of the sympathetic nervous system, as in tending to stimulate digestive secretions or slow the heart.

Front 22

Reflex

Back 22

Noting or pertaining to an involuntary response to a stimulus, the nerve impulse from a receptor being transmitted inward to a nerve center that in turn transmits it outward to an effector.

Front 23

Neural Networks

Back 23

Any group of neurons that conduct impulses in a coordinated manner, as the assemblages of brain cells that record a visual stimulus.

Front 24

Endocrine System

Back 24

The bodily system that consists of the endocrine glands and the hormones that they secrete.

Front 25

Hormones

Back 25

Any of various internally secreted compounds, as insulin or thyroxine, formed in endocrine glands, that affect the functions of specifically receptive organs or tissues when transported to them by the body fluids.

Front 26

Adrenal Glands

Back 26

One of a pair of ductless glands, located above the kidneys, consisting of a cortex, which produces steroidal hormones, and a medulla, which produces epinephrine and norepinephrine.

Front 27

Pituitary Glands

Back 27

A small, somewhat cherry-shaped double structure attached by a stalk to the base of the brain and constituting the master endocrine gland affecting all hormonal functions in the body, consisting of an anterior region ((anterior pituitary) or (adenohypophysis)) that develops embryonically from the roof of the mouth and that secretes growth hormone, LH, FSH, ACTH, TSH, and MSH, a posterior region ((posterior pituitary) or (neurohypophysis)) that develops from the back of the forebrain and that secretes the hormones vasopressin and oxytocin, and an intermediate part (pars intermedia) derived from the anterior region but joined to the posterior region, that secretes the hormone MSH in lower vertebrates.

Front 28

Lesion

Back 28

An injury; hurt; wound.

Front 29

Brainstem

Back 29

The portion of the brain that is continuous with the spinal cord and comprises the medulla oblongata, pons, midbrain, and parts of the hypothalamus, functioning in the control of reflexes and such essential internal mechanisms as respiration and heartbeat.

Front 30

Medulla

Back 30

a.
The marrow of the bones.
b.
The soft, marrowlike center of an organ, as the kidney or adrenal gland.

Front 31

Reticular Formation

Back 31

A network of neurons in the brainstem involved in consciousness, regulation of breathing, the transmission of sensory stimuli to higher brain centers, and the constantly shifting muscular activity that supports the body against gravity.

Front 32

Thalamus

Back 32

The middle part of the diencephalon through which sensory impulses pass to reach the cerebral cortex.

Front 33

Cerebellum

Back 33

A large portion of the brain, serving to coordinate voluntary movements, posture, and balance in humans, being in back of and below the cerebrum and consisting of two lateral lobes and a central lobe.

Front 34

Limbic System

Back 34

A ring of interconnected structures in the midline of the brain around the hypothalamus, involved with emotion and memory and with homeostatic regulatory systems.

Front 35

Amygdala

Back 35

A ganglion of the limbic system adjoining the temporal lobe of the brain and involved in emotions of fear and aggression.

Front 36

Hypothalamus

Back 36

A region of the brain, between the thalamus and the midbrain, that functions as the main control center for the autonomic nervous system by regulating sleep cycles, body temperature, appetite, etc., and that acts as an endocrine gland by producing hormones, including the releasing factors that control the hormonal secretions of the pituitary gland.

Front 37

Cerebral Cortex

Back 37

The furrowed outer layer of gray matter in the cerebrum of the brain, associated with the higher brain functions, as voluntary movement, coordination of sensory information, learning and memory, and the expression of individuality.

Front 38

Glial Cells

Back 38

Any of the cells making up the glia, such as the star-shaped cells called astrocytes.

Front 39

Frontal Lobes

Back 39

The anterior part of each cerebral hemisphere, in front of the central sulcus.

Front 40

Parietal Lobes

Back 40

The middle part of each cerebral hemisphere behind the central sulcus.

Front 41

Occipital Lobes

Back 41

The most posterior lobe of each cerebral hemisphere, behind the parietal and temporal lobes.

Front 42

Temporal Lobes

Back 42

The lateral lobe of each cerebral hemisphere, in front of the occipital lobe.

Front 43

Motor Cortex

Back 43

The region of the cerebral cortex concerned with transmitting impulses to the voluntary muscles.

Front 44

Sensory Cortex

Back 44

The region of the cerebral cortex concerned with receiving and interpreting sensory information from various parts of the body.

Front 45

Association Areas

Back 45

Any of the regions of the cerebral cortex of the brain connected by numerous nerve fibers to all parts of both cerebral hemispheres and coordinating such higher activities as learning and reasoning.

Front 46

Aphasia

Back 46

The loss of a previously held ability to speak or understand spoken or written language, due to disease or injury of the brain.

Front 47

Brocha's Area

Back 47

A cerebral area, usually in the left inferior frontal gyrus, associated with the movements necessary for speech production.

Front 48

Wernicke's Area

Back 48

A portion of the left posterior temporal lobe of the brain, involved in the ability to understand words.

Front 49

Plasticity

Back 49

The capability of being molded, receiving shape, or being made to assume a desired form.

Front 50

Corpus Callosum

Back 50

A great band of deeply situated transverse white fibers uniting the two halves of the cerebrum in humans and other mammals.

Front 51

Split Brain

Back 51

Having, involving, or pertaining to a severed corpus callosum.