Chapter 12: Nervous System Physiology and Anatomy

Comprehensive vocabulary flashcards covering neuroanatomy, glial cells, electrophysiology, action potential dynamics, and synaptic transmission from Chapter 12.

Afferent Neurons

Sensory nerve cells that carry incoming information about the environment toward the brain and spinal cord in the peripheral nervous system (PNS).

Efferent Neurons

Motor nerve cells that exit the central nervous system (CNS) to carry signals to effectors such as muscles and glands.

Interneurons

Integrative neurons located entirely within the CNS that process incoming information and determine how the body responds, making up $>90\%$ of all neurons.

Dendrites

Branch-like extensions of a neuron that receive chemical and electrical incoming signals from other cells.

Axon Hillock

A mound-like region of the neuron cell body where the axon originates; it contains a high density of voltage-gated channels and serves as the initial site of action potential generation.

Nucleus (Nervous System)

A cluster or group of neuronal cell bodies located within the central nervous system (CNS).

Ganglion

A cluster or group of neuronal cell bodies located within the peripheral nervous system (PNS).

Tract

A bundle of nerve fibers (axons) traveling together within the central nervous system (CNS).

Nerve

A cordlike bundle of nerve fibers (axons) located within the peripheral nervous system (PNS).

Neuroglia

Mitotic support cells in the nervous system that protect, support, and nourish neurons, outnumbering neurons by a ratio of $20:1$.

Astrocytes

Star-shaped, most abundant glial cells in the CNS that nourish neurons, help form and maintain the blood-brain barrier, and regulate the chemical environment.

Oligodendrocytes

Glial cells in the CNS that produce myelin sheaths around axons, with individual cells capable of myelinating segments of multiple neighboring axons.

Microglia

Specialized phagocytic macrophages of the CNS that provide immune defense by engulfing bacteria, damaged cellular debris, and foreign material.

Ependymal Cells

Glial cells lining the ventricles of the brain and central canal of the spinal cord that help produce and circulate cerebrospinal fluid (CSF).

Schwann Cells

Glial cells of the PNS that wrap around a single axon segment to form a myelin sheath and assist in nerve fiber regeneration.

Satellite Cells

Glial cells that surround neuron cell bodies within PNS ganglia to provide structural support and regulate the chemical environment.

Myelin

An insulating lipid-and-protein sheath produced by oligodendrocytes and Schwann cells that wraps axons and increases the speed of electrical conduction.

Nodes of Ranvier

Unmyelinated gaps along an axon between adjacent segments of myelin where voltage-gated ion channels are concentrated.

Internodes

The insulated, myelin-covered segments of an axon located between consecutive Nodes of Ranvier.

Saltatory Conduction

The rapid mode of signal conduction in myelinated axons where electrical depolarization jumps from one Node of Ranvier to the next.

Local (Graded) Potentials

Decremental, reversible changes in membrane potential generated by non-voltage-gated channels on dendrites and the cell body that vary in size and can summate.

Action Potential

A rapid, irreversible, all-or-none spike in membrane potential generated by voltage-gated channels at the axon hillock and axon that propagates long distances.

Resting Membrane Potential (RMP)

The stable electrical voltage difference across an unexcited neuron's plasma membrane, typically around $-70\,\text{mV}$, with the interior more negative than the exterior.

Threshold

The critical membrane voltage (approximately $-55\,\text{mV}$) required to trigger the opening of voltage-gated $\text{Na}^+$ channels and fire an action potential.

Depolarization

A shift in membrane potential making the inside of the cell less negative and more positive (rising up to $+30\,\text{mV}$), caused by the influx of $\text{Na}^+$ ions.

Repolarization

The recovery of the membrane potential toward resting negative levels, driven by the inactivation of $\text{Na}^+$ channels and the opening of voltage-gated $\text{K}^+$ channels that allow $\text{K}^+$ efflux.

Hyperpolarization

A temporary drop in membrane potential to a voltage more negative than the resting potential due to delayed closure of voltage-gated $\text{K}^+$ channels.

Sodium-Potassium Pump ($\text{Na}^+/\text{K}^+$ Pump)

An ATP-driven primary active transporter that moves $3\,\text{Na}^+$ out of the cell and $2\,\text{K}^+$ into the cell against their gradients to restore resting ionic distributions.

Absolute Refractory Period

The phase during an action potential when voltage-gated $\text{Na}^+$ channels are either fully open or inactivated, preventing any subsequent stimulus from triggering an action potential.

Relative Refractory Period

The phase following an action potential when voltage-gated $\text{K}^+$ channels are open, requiring an unusually strong stimulus to reach threshold and initiate another action potential.

Chemical Synapse

A junction where a presynaptic neuron releases neurotransmitter molecules across a synaptic cleft to bind receptors on the postsynaptic membrane.

Electrical Synapse

A junction where ions flow directly from one cell to an adjacent cell through gap junctions, providing near-instantaneous transmission.

EPSP (Excitatory Postsynaptic Potential)

A local, depolarizing graded potential usually caused by $\text{Na}^+$ entering the postsynaptic cell, shifting the membrane potential closer to threshold.

IPSP (Inhibitory Postsynaptic Potential)

A local, hyperpolarizing graded potential typically caused by $\text{Cl}^-$ influx or $\text{K}^+$ efflux, shifting the postsynaptic neuron further from threshold.

Temporal Summation

The addition of postsynaptic potentials generated in rapid succession by a single presynaptic neuron at a single synapse.

Spatial Summation

The integration of postsynaptic potentials arriving simultaneously from multiple separate presynaptic neurons onto one postsynaptic cell.

Axodendritic Synapse

A synaptic connection formed between the axon terminal of a presynaptic neuron and a dendrite of a postsynaptic neuron.

Axosomatic Synapse

A synaptic connection formed between the axon terminal of a presynaptic neuron and the soma (cell body) of a postsynaptic neuron.

Axoaxonic Synapse

A synaptic connection formed between the axon terminal of one neuron and the axon of another neuron.