1.acetylcholine Neurotransmitter; acts on brain, spinal cord, glands, and muscles.
2.action potential Abrupt, brief reversal in the resting membrane potential of excitable cells.
3.autonomic nerve One of the nerves from central nervous system to smooth muscle, cardiac muscle, and glands of viscera.
4.axon Neuron's signal-conducting zone.5.blood-brain barrier Mechanism that controls which solutes enter cerebrospinal fluid.
6.brain Of most nervous systems, integrating center that receives and processes sensory input and issues coordinated commands for responses by muscles and glands.
7.brain stem Most ancient nerve tissue in the vertebrate hindbrain, midbrain, and forebrain.
8.central nervous system Brain and spinal cord.
9.cerebellum Hindbrain region with reflex centers for maintaining posture and smoothing out limb movements.
10.cerebral cortex Thin surface layer of cerebral hemispheres; receives, integrates, and stores sensory information; coordinates responses.
11.cerebrum Forebrain region that generally deals with olfactory input and motor responses. In mammals, it evolved into the most complex integrating center.12.chemical synapse Thin cleft between a presynaptic neuron and a postsynaptic cell. Neurotransmitter molecules diffuse across it.
13.dendrite Short, slender extension from cell body of a neuron; commonly a signal input zone.
14.drug addiction Dependence on a drug, which assumes an ''essential'' biochemical role in the body following habituation and tolerance.
15.hypothalamus Forebrain center of homeostatic control over the internal environment influences hunger, thirst, sex, other viscera-related behaviors, and emotions.16.interneuron Neuron of brain or spinal cord.
17.limbic system In cerebral hemisphere, centers that govern emotions; has roles in memory.
18.medulla oblongata Hindbrain region with reflex centers for basic tasks; coordinates motor responses with complex reflexes; influences sleeping.
19.memory The capacity to store and retrieve information about past sensory experience.20.motor neuron Neuron that relays signals from brain or spinal cord to muscle or gland cells.
21.nerve Sheathed, cordlike bundle of the axons of sensory neurons, motor neurons, or both.
22.nerve net Simple nervous system in epidermis of cnidarians and some other invertebrates; a diffuse mesh of simple, branching nerve cells interacts with contractile and sensory cells.
23.nervous system Integrative organ system with nerve cells interacting in signal-conducting and information-processing pathways. Detects and processes stimuli, and elicits responses from effectors.
24.neural tube The embryonic and evolutionary forerunner of brain and spinal cord.
25.neurotransmitter Any of a class of signaling molecules secreted by neurons. It acts on cells next to it, then is rapidly degraded or recycled.26.parasympathetic nerve An autonomic nerve. Its signals slow down overall activities and divert energy to basic tasks; they also help make small adjustments in internal organ activity by acting continually in opposition to sympathetic nerve signals.
27.peripheral nervous system All nerves leading into and out from the spinal cord and brain. Includes ganglia of those nerves.
28.pons A hindbrain traffic center for signals between cerebellum and forebrain centers.
29.positive feedback mechanism Homeostatic control; it initiates a chain of events that intensify change from an original condition, then intensification reverses the change.30.reflex Stereotyped, simple movement in response to stimuli. In the simplest reflex arcs, it results from sensory neurons synapsing directly on motor neurons.
31.resting membrane potential Of a neuron and other excitable cells, a voltage difference across the plasma membrane that holds steady in the absence of outside stimulation.32.reticular formation A mesh of interneurons extending from the upper spinal cord, through the brain stem, and into the cerebral cortex; it is a low-level pathway of information flow.
33.sensory neuron Type of neuron that detects a stimulus and relays information about it toward an integrating center.
34.sodium-potassium pump Type of membrane transport protein that, when activated by ATP, selectively transports potassium ions across a membrane against its concentration gradient, and passively allows sodium ions to cross in the opposite direction.35.somatic nerve Nerve leading from a central nervous system to skeletal muscles.
36.spinal cord Part of central nervous system, in a canal inside the vertebral column; site of direct reflex connections between sensory and motor neurons; has tracts to and from the brain.37.stimulus A specific form of energy that activates a sensory receptor able to detect it.
38.sympathetic nerve An autonomic nerve; deals mainly with increasing overall body activities at times of heightened awareness, excitement, or danger; works continually in opposition with parasympathetic nerves to make minor adjustments in internal organ activities.
39.synaptic integration Moment-by-moment combining of all excitatory and inhibitory signals arriving at the trigger zone of a neuron or some other excitable cell.
40.thalamus A forebrain region that is a coordinating center for sensory input and a relay station for signals to the cerebrum.
