Unit 9: Neural Mechanisms Study Guide

Comprehensive vocabulary flashcards covering nervous system anatomy, neuroglia, membrane potentials, synaptic transmission, and circuit patterns.

Central Nervous System (CNS)

The division of the nervous system consisting of the brain and spinal cord.

Peripheral Nervous System (PNS)

Nerves running from the CNS to the rest of the body, including cranial nerves and spinal nerves.

Sensory (Afferent) Nerves

Nerve pathways that carry sensory information from the body toward the CNS.

Motor (Efferent) Nerves

Nerve pathways that carry signals from the CNS to effector organs, such as muscles and glands.

Somatic Sensory Nerves

Sensory nerve pathways carrying information from the skin, skeletal muscles, and joints.

Visceral Sensory Nerves

Sensory nerve pathways carrying information from the viscera (internal organs).

Somatic Motor Division

The motor subdivision of the PNS that innervates skeletal (voluntary) muscle.

Autonomic Motor Division

The motor subdivision that controls smooth and cardiac muscle, divided into the sympathetic ("fight or flight") and parasympathetic ("rest and digest") systems.

Interneurons (Association Neurons)

Neurons located entirely within the CNS between sensory and motor neurons.

Soma

The neuron cell body containing organelles and Nissl substance.

Dendrites

Receptive regions of a neuron with multiple branches that carry graded potentials toward the soma.

Axon Hillock

The specific region of a neuron where the axon meets the soma.

Axon (Nerve Fiber)

A single neuronal process carrying action potentials away from the soma.

Synaptic Bouton (Terminal)

Structure located at the terminal end of an axon that forms a synapse with another neuron or effector cell.

Schwann Cells

Support cells in the PNS that form myelin sheaths and perform phagocytosis.

Satellite Cells

Support cells in the PNS that surround neuron cell bodies in ganglia and regulate the chemical environment.

Astrocytes

The most abundant glial cells in the CNS; they provide structural framework, nutrient exchange, remove neurotransmitters from synapses, and control the chemical environment.

Oligodendrocytes

Glial cells that form insulating myelin sheaths around neurons in the CNS.

Microglia

Small glial cells that act as immune defense cells in the CNS via phagocytosis.

Ependymal Cells

Glial cells that line chambers in the CNS and function to produce and circulate cerebrospinal fluid (CSF).

Mechanoreceptors

Sensory receptors specialized to convert light, touch, and pressure stimuli into electrical signals.

Chemoreceptors

The most common receptor type; converts chemical changes into electrical signals.

Nociceptors

Sensory receptors specialized to detect and convert pain stimuli into electrical signals.

Resting Membrane Potential (RMP)

The electrical potential across the resting neuron membrane, typically around $-70\,\text{mV}$, caused by continuous leaking of $\text{K}^+$ and higher membrane permeability to $\text{K}^+$ than $\text{Na}^+$.

$\text{Na}^+/\text{K}^+$ Pump

An active transport mechanism that maintains resting membrane potential by pumping $3\,\text{Na}^+$ out and $2\,\text{K}^+$ in for every $1\,\text{ATP}$ consumed.

Depolarization

A shift in membrane potential toward a less negative state (e.g., from $-70\,\text{mV}$ to $-55\,\text{mV}$) caused by $\text{Na}^+$ rushing into the cell, increasing the chance of firing an action potential.

Repolarization

The return of membrane potential toward resting values after depolarization, caused by $\text{Na}^+$ channels closing and voltage-regulated $\text{K}^+$ channels opening, allowing $\text{K}^+$ to exit.

Hyperpolarization

A change making the membrane potential more negative than resting (e.g., $-70\,\text{mV}$ to $-90\,\text{mV}$) due to excessive $\text{K}^+$ outflow or $\text{Cl}^-$ inflow, reducing the likelihood of firing.

Graded Potentials

Short-lived, local electrical signals occurring in dendrites and soma whose strength varies with stimulus strength and can be summated.

Action Potentials

Long-distance, all-or-none, self-propagating electrical impulses generated along axon membranes that peak up to $+30\,\text{mV}$ and cannot be summated.

Threshold

The minimum stimulus strength required to trigger an action potential, typically requiring a $15\text{--}20\,\text{mV}$ change reaching approximately $-55\,\text{mV}$.

Absolute Refractory Period

The time frame during which an action potential is actively being generated and no stimulus can initiate another action potential.

Relative Refractory Period

The phase during repolarization where a stronger-than-normal stimulus is required to initiate a new action potential.

Continuous Conduction (Local Current Flow)

Slow, uninterrupted wave of action potential propagation along unmyelinated axons where each adjacent membrane segment depolarizes.

Saltatory Conduction

Fast propagation of action potentials along myelinated axons where the signal jumps from one Node of Ranvier to the next.

Excitatory Postsynaptic Potential (EPSP)

A graded depolarization caused by $\text{Na}^+$ influx that brings the postsynaptic membrane closer to threshold.

Inhibitory Postsynaptic Potential (IPSP)

A graded hyperpolarization caused by $\text{K}^+$ efflux or $\text{Cl}^-$ influx that moves the postsynaptic membrane further away from threshold.

Temporal Summation

Integration occurring when a single presynaptic axon fires rapid, repeated impulses to a single postsynaptic neuron ("automatic weapon" style).

Spatial Summation

Integration occurring when many different presynaptic axons stimulate a single postsynaptic neuron simultaneously ("firing squad" style).

Facilitation

Subthreshold priming of a neuron by partial excitation, making it easier for subsequent inputs to reach threshold and trigger an action potential.

Divergence

A circuit pattern where one presynaptic neuron synapses with multiple postsynaptic neurons to spread the signal.

Convergence

A circuit pattern where multiple presynaptic neurons feed into a single postsynaptic neuron to concentrate the signal.

Neuromodulators

Chemical substances that cause slow, modulatory adjustments to enhance or inhibit synaptic efficiency by altering neurotransmitter synthesis, release, breakdown, or reuptake.

Agonist

A pharmacological substance that produces a physiological response similar to a natural neurotransmitter (e.g., caffeine).

Antagonist

A pharmacological substance that blocks a neurotransmitter from binding to its receptor, preventing a physiological response (e.g., Novocain).