| A | B |
|---|
| neuron | a nerve cell, that can transmit a nervous impulse |
| dendrite | an extension of the nerve cell body that can receive input from synapses with the axon terminals of other neurons |
| myelin | a fatty substance that lines some axons, insulating them and speeding up impulse conduction |
| Schwann cell | a cell that wraps around a nerve fiber to form the insulating myelin sheath |
| Theodor Schwann | the German physiologist who discovered the Schwann cells lining axons |
| axon | a long extension of the neuronal cell body that carries outgoing impulses |
| resting potential | the electric potential across a nerve cell membrane when the neuron is not firing (normally about -60 millivolts) |
| action potential | a travelling wave of depolarization and repolarization along the axon of a neuron |
| synapse | a junction where the axon terminals of one neuron meet the dendrites or cell body of another neuron or muscle cell |
| neurotransmitter | a chemical substance that transmits nerve impulses across a synapse |
| CNS: central nervous system | the brain and the spinal cord |
| PNS: peripheral nervous system | all of the nervous system except the brain and spinal cord |
| cerebrum | the large upper part of the brain, consisting of the two hemispheres, containing four lobes |
| the four lobes of the cerebrum | frontal, parietal, temporal, and occipital |
| cerebellum | a part of the brain located just behind the brain stem; it helps with coordination of movement |
| gray matter | nervous tissue consisting mostly of neuronal cell bodies |
| white matter | nervous tissue consisting mostly of myelinated axons |
| autonomic nervous system | this part of the PNS directs the involuntary functions of the internal organs |
| somatic nervous system | this part of the PNS involves the control of skeletal muscles |
| retina | the layer of photoreceptors and neurons at the back of the eye |
| iris | the colored part of the eye, with a hole in the center; it regulates how much light enters the eye |
| cochlea | the spiral-shaped structure in the middle ear that contains the hair cells that detect sound vibrations |
| optic nerve | the nerve that connects the retina with the brain |
| rods | the photoreceptive cells in the retina that are sensitive to dim light, but not to color |
| cones | the photoreceptive cells in the retina that are sensitive to color, but not to dim light |
| lens | the nearly spherical body in the eye that focuses light rays onto the retina |
| eardrum | the tympanic membrane which vibrates and transmits sound to the middle ear |
| semicircular canals | a set of three loops in the inner ear that sense head movement and orientation, and hellp with balance |
| olfactory receptors | receptors that detect odors in the nose |
