Nerve Cells and Nerve Impulses

Vocabulary flashcards covering cellular anatomy, glial functions, blood-brain barrier mechanisms, resting potential dynamics, and action potential propagation based on Chapter 1.

Neurons

Cells in the nervous system that receive information and transmit it to other cells, numbering approximately $86\text{ billion}$ in the human brain.

Glia

The other major cell component of the nervous system that perform various supportive functions, are smaller and slightly more numerous than neurons, but do not transmit information like neurons.

Santiago Ramón y Cajal

A pioneer of neuroscience who used staining techniques to demonstrate that small gaps separate the tips of one neuron from another, proving the brain is made of individual cells.

Membrane

A structure composed of two layers of fat molecules that encloses the cell, allowing small uncharged chemicals to pass passively while regulating charged ion flow through protein channels.

Nucleus

The organelle inside a cell that contains the chromosomes.

Mitochondrion

The organelle that provides the cell with energy, requiring fuel and oxygen to function.

Ribosomes

Cellular structures that serve as the site of protein synthesis.

Endoplasmic reticulum

A network of thin tubes inside the cell that transports newly synthesized proteins to other locations.

Motor neuron

A type of neuron that conducts impulses from the spinal cord to muscles and glands.

Sensory neuron

A receptor neuron highly sensitive to specific kinds of environmental stimulation, such as light or touch.

Dendrites

Branching fibers that extend from the cell body, narrowing at their tips, lined with specialized synaptic receptors to receive information from other neurons.

Dendritic spines

Short outgrowths found on some dendritic branches that increase the total surface area available for synapses.

Cell body (soma)

The core component of a neuron containing the nucleus, ribosomes, mitochondria, and other general cell structures.

Axon

A long, thin fiber that serves as the information-sending part of a neuron, transmitting electrical impulses toward other neurons, glands, or muscles.

Myelin sheath

An insulating covering composed of fats and proteins found on some vertebrate axons that increases signal speed.

Nodes of Ranvier

Short, unmyelinated interruptions or gaps along the myelin sheath of an axon.

Presynaptic terminal

A swelling at the end bulb of an axon tip that releases chemical signals to cross the junction between neurons.

Afferent axon

An axon that brings incoming information into a specific structure.

Efferent axon

An axon that carries outgoing information away from a specific structure.

Interneurons

Neurons (also termed intrinsic neurons) whose entire structure is located within a single neural structure.

Astrocytes

Glial cells that absorb chemicals from axons to help synchronize neuronal activity, clear waste from dead neurons, dilate local blood vessels, and recycle glutamate into glutamine.

Microglia

Extremely small glial cells that act as an immune defense in the brain, clearing out waste, viruses, fungi, and damaged neurons.

Oligodendrocytes

Glial cells responsible for forming myelin sheaths around neurons in the central nervous system (brain and spinal cord).

Schwann cells

Glial cells responsible for forming myelin sheaths around neurons in the periphery of the body.

Radial glia

Specialized glia that guide neuronal migration and axonal/dendritic outgrowth during embryonic development.

Blood-brain barrier

A protective mechanism composed of tightly joined endothelial capillary cells that restricts most chemicals, viruses, and bacteria from entering the brain.

Active transport

A protein-mediated, energy-requiring process that actively pumps needed substances like glucose across the blood-brain barrier.

Korsakoff's syndrome

A condition characterized by severe memory impairment resulting from chronic thiamine (vitamin B1) deficiency, which prevents neurons from metabolizing glucose.

Resting potential

The steady electrical voltage across a undisturbed neuronal membrane, typically $-70\text{ mV}$, where the interior is more negatively charged than the exterior.

Sodium-potassium pump

An active transport protein complex that exports $3$ sodium ions out of the neuron while importing $2$ potassium ions at the cost of ATP.

Electrical gradient

The difference in electrical charge across the membrane (polarization) that causes positively charged ions like sodium to be attracted to the negative cell interior.

Concentration gradient

The difference in distribution of ions across the membrane, driving ions to move from regions of higher concentration to lower concentration.

Action potential

A rapid electrical impulse generated along an axon that allows long-distance signal transmission.

Hyperpolarization

An increase in the negative electrical charge inside the axon relative to the outside (e.g., changing from $-70\text{ mV}$ to $-80\text{ mV}$).

Depolarization

A decrease in the negative electrical charge inside the axon towards zero (e.g., changing from $-70\text{ mV}$ to $-55\text{ mV}$).

Threshold of excitation

The critical level of membrane depolarization that must be reached to initiate an action potential.

All-or-none law

The principle stating that the amplitude and velocity of an action potential are independent of the strength of the initiating stimulus, provided threshold is met.

Voltage-gated channels

Membrane ion channels whose permeability depends directly on the voltage difference across the membrane.

Axon hillock

A swollen site where the axon exits the cell body, serving as the starting point for action potentials.

Propagation of the action potential

The self-regenerating movement of an action potential down the length of an axon.

Saltatory conduction

The rapid jumping of an action potential from one node of Ranvier to the next along a myelinated axon.

Absolute refractory period

The brief period immediately following an action potential (about $1\text{ ms}$) during which sodium gates are firmly closed and cannot open, preventing another action potential.

Relative refractory period

The phase following the absolute refractory period (lasting about $2\text{--}4\text{ ms}$) when potassium channels are open and an action potential can only be triggered by an above-threshold stimulus.

Local neurons

Small neurons lacking long axons or dendrites that do not obey the all-or-none law and exchange messages with nearby cells using graded potentials.

Graded potentials

Membrane potentials produced in local neurons that vary continuously in magnitude based on stimulus intensity and decay as they travel.