Chapter 1: Summary

The brain can be studied by methods that range from genetics and molecular biology to behavioral testing of normal human subjects. In addition to an ever-increasing store of knowledge about the anatomical organization of the nervous system, many of the most notable successes of modern neuroscience have come from understanding nerve cells as the structural and functional unit of the nervous system. Studies of the cellular architecture and molecular components of neurons and glia have revealed much about their individual functions at a remarkably detailed level, providing a basis for understanding how nerve cells are organized into circuits, and circuits into systems that process specific types of information pertinent to perception and action. Among the goals that remain are understanding how basic molecular genetic phenomena are linked to cellular, circuit, and system functions; understanding how these processes go awry in neurological and psychiatric diseases; and understanding the especially complex functions of the brain that make us human.

Chapter 1: Key Terms

action potential

The electrical signal conducted along axons (or muscle fibers) by which information is conveyed from one place to another in the nervous system.

astrocytes

One of the three major classes of glial cells found in the central nervous system; important in regulating the ionic milieu of nerve cells and, in some cases, transmitter reuptake.

axon

The neuronal process that carries the action potential from the nerve cell body to a target.

brain-derived neutrophic factor (BDNF)

One member of a family of neutrophic factors, the best-known constituent of which is nerve growth factor.

central nervous system (CNS)

The brain and spinal cord of vertebrates (by analogy, the central nerve cord and ganglia of invertebrates).

chemical synapses

Synapses that transmit information via the secretion of chemical signals (neurotransmitters).

convergence

Innervation of a target cell by axons from more than one neuron.

cortex

The superficial mantle of gray matter covering the cerebral hemispheres and cerebellum, where most of the neurons in the brain are located.

cranial nerve ganglia

The sensory ganglia associated with the cranial nerves; these correspond to the dorsal root ganglia of the spinal segmental nerves.

dendrite

A neuronal process arising from the cell body that receives synaptic input.

divergence

The branching of a single axon to innervate multiple target cells.

dorsal root ganglia (DRG)

The segmental sensory ganglia of the spinal cord; contain the first-order neurons of the dorsal column/medial lemniscus and spinothalamic pathways.

efferent

An axon that conducts information away from the central nervous system.

electrical synapses

Synapses that transmit information via the direct flow of electrical current at gap junctions.

ganglion (ganglia)

Collections of hundreds to thousands of neurons found outside the brain and spinal cord along the course of peripheral nerves.

gene

Hereditary unit located on the chromosomes; genetic information is carried by linear sequences of nucleotides in DNA that code for corresponding sequences of amino acids.

glia

The support cells associated with neurons (astrocytes, oligodendrocytes, and microglia in the central nervous system; Schwann cells in peripheral nerves; and satellite cells in ganglia). Also known as neuroglia.

gray matter

General term that describes regions of the central nervous system rich in neuronal cell bodies and neuropil; includes the cerebral and cerebellar cortices, the nuclei of the brain, and the central portion of the spinal cord.

interneuron

Technically, a neuron in the pathway between primary sensory and primary effector neurons; more generally, a neuron whose relatively short axons branch locally to innervate other neurons. Also known as local circuit neuron.

local circuit neuron

General term referring to neurons whose activity mediates interactions between sensory systems and motor systems; interneuron is often used as a synonym.

microglial cells

One of the three main types of central nervous system glia; concerned primarily with repairing damage following neural injury.

motor neuron

By usage, a nerve cell that innervates skeletal muscle. Also called primary or α motor neuron.

motor system

A broad term used to describe all the central and peripheral structures that support motor behavior.

myelin

The multilaminated wrapping around many axons formed by oligodendrocytes or Schwann cells.

myotatic reflex

A fundamental spinal reflex that is generated by the motor response to afferent sensory information arising from muscle spindles. The “knee jerk reaction” is a common example. Also called a stretch reflex.

nerve

A collection of peripheral axons that are bundled together and travel a common route.

neuron

Cell specialized for the conduction and transmission of electrical signals in the nervous system.

neuropil

The dense tangle of axonal and dendritic branches, and the synapses between them, that lies between neuronal cell bodies in the gray matter of the brain and spinal cord.

neurotransmitter

Substance released by synaptic terminals for the purpose of transmitting information from one nerve cell to another.

nucleus (nuclei)

Collection of nerve cells in the brain that are anatomically discrete, and which typically serve a particular function.

oligodendrocytes

One of three classes of central neuroglial cells; their major function is to elaborate myelin.

peripheral nervous system

All nerves and neurons that lie outside the brain and spinal cord.

projection neuron

A neuron with long axons that project to distant targets.

receptive field

Region of a receptor surface (e.g., the body surface or the retina) that causes a sensory nerve cell (or axon) to respond.

receptor potential

The membrane potential change elicited in receptor neurons during sensory transduction.

Schwann cells

Neuroglial cells in the peripheral nervous system that elaborate myelin (named after the nineteenth-century anatomist and physiologist Theodor Schwann).

sensory system

Term sometimes used to describe all the components of the central and peripheral nervous system concerned with sensation.

spinal cord

The portion of the central nervous system that extends from the lower end of the brainstem (the medulla) to the cauda equina.

synaptic cleft

The space that separates pre- and postsynaptic neurons at chemical synapses.

synaptic vesicle recycling

A sequence of budding and fusion reactions that occurs within presynaptic terminals to maintain the supply of synaptic vesicles.

white matter

A general term that refers to large axon tracts in the brain and spinal cord; the phrase derives from the fact that axonal tracts have a whitish cast when viewed in the freshly cut material.