Hole's Human Anatomy & Physiology - Chapter 10: Nervous System I

Comprehensive vocabulary flashcards detailing the anatomical, physiological, and neurochemical principles of the nervous system from Chapter 10 of Hole's Human Anatomy & Physiology.

Central Nervous System (CNS)

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

Peripheral Nervous System (PNS)

The division of the nervous system consisting of cranial nerves and spinal nerves that connects the central nervous system to the rest of the body.

Somatic Nervous System

A subdivision of the motor (efferent) division of the PNS that transmits voluntary commands from the CNS to skeletal muscles.

Autonomic Nervous System

A subdivision of the motor (efferent) division of the PNS that transmits involuntary commands from the CNS to viscera, including smooth muscle, cardiac muscle, and glands.

Neuroglia

Non-excitable support cells of the nervous tissue that protect, insulate, nourish, and support neurons without conducting nerve impulses.

Chromatophilic substance (Nissl bodies)

Membranous packets consisting of rough endoplasmic reticulum situated within the cytoplasm of a neuron's cell body (soma).

Axon hillock

The specialized, cone-shaped elevation of a neuron's cell body from which the axon arises.

Myelin sheath

An insulating, lipid-rich coating formed around certain axons in the nervous system by layered membranes of Schwann cells or oligodendrocytes.

Nodes of Ranvier

Narrow gaps in the myelin sheath between adjacent neuroglial cells along the length of an axon.

White Matter

Tissue regions in the central nervous system that consist predominantly of bundles of myelinated axons.

Gray Matter

Tissue regions in the central nervous system containing neuron cell bodies, dendrites, and unmyelinated axons.

Multipolar neuron

A neuron with multiple processes arising from its cell body—one axon and many dendrites—accounting for approximately $99\%$ of all neurons in the body.

Bipolar neuron

A neuron possessing only two cellular extensions protruding from opposite sides of the cell body: one dendrite and one axon; found in specialized sensory organs of the eyes, ears, and nose.

Unipolar (pseudounipolar) neuron

A neuron characterized by a single process extending from the cell body that bifurcates into a peripheral process and a central process, functioning together as a single axon.

Sensory (afferent) neuron

A neuron that carries sensory impulses from peripheral receptors toward the central nervous system.

Interneuron

A multipolar neuron confined entirely within the brain or spinal cord that forms connections between other neurons to relay and integrate information.

Motor (efferent) neuron

A neuron that conducts impulses out of the central nervous system to effectors such as muscles or glands.

Astrocytes

Star-shaped neuroglial cells in the CNS that link neurons to capillaries, contribute to the blood-brain barrier, regulate ion and neurotransmitter levels, and form scar tissue following injury.

Oligodendrocytes

Glial cells in the central nervous system with fewer processes than astrocytes that wrap around axons to produce myelin sheaths and secrete nerve growth factors.

Microglia

Small phagocytic neuroglial cells scattered throughout the CNS that provide structural support and engulf cellular debris and pathogens.

Ependyma

Ciliated cuboidal or columnar epithelial-like glial cells lining the ventricles of the brain and the central canal of the spinal cord that help regulate cerebrospinal fluid.

Schwann cells

Peripheral neuroglia whose lipid-rich membranes wrap around axons to form myelin sheaths and assist in guiding axon regeneration after injury.

Satellite cells

Small, cuboidal glial cells that surround and support neuron cell bodies within peripheral ganglia, regulating the surrounding ionic microenvironment.

Neurilemma

The outermost sheath of Schwann cell cytoplasm and organelles surrounding the myelin layers in peripheral nerves that facilitates axon regeneration.

Resting membrane potential

The electric potential difference across an undisturbed, inactive neuron membrane, typically measuring approximately $-70\,\text{mV}$ with the cytoplasmic face negative relative to the outside.

Sodium-potassium pump

An ATP-driven membrane transport protein that actively moves $3\,\text{Na}^+$ ions outward and $2\,\text{K}^+$ ions inward against their respective concentration gradients.

Threshold potential

The minimum level of membrane depolarization, approximately $-55\,\text{mV}$, required to open voltage-gated sodium channels at the trigger zone and fire an action potential.

Depolarization

The phase of the action potential during which voltage-gated $\text{Na}^+$ channels open and sodium ions rapidly rush inward, driving the membrane potential up toward $+30\,\text{mV}$.

Repolarization

The recovery phase of the action potential where voltage-gated $\text{Na}^+$ channels close and $\text{K}^+$ channels open, allowing potassium ions to diffuse outward and restore electrical polarity.

Hyperpolarization

A brief period at the conclusion of repolarization when the membrane potential drops slightly below the baseline resting value of $-70\,\text{mV}$ due to continuous potassium efflux.

Action Potential

A sequence of electrical events in an excitable cell involving rapid, transient changes in membrane potential that propagate along the axon.

All-or-None Law

The principle stating that if a neuron responds to a stimulus that reaches threshold, it fires an action potential of constant, maximal strength; otherwise, no action potential occurs.

Absolute refractory period

The initial phase of the refractory period during which voltage-gated $\text{Na}^+$ channels remain unresponsive, rendering the axon incapable of firing another action potential regardless of stimulus intensity.

Relative refractory period

The interval following the absolute refractory period during which membrane repolarization is incomplete and an action potential can only be generated by a stimulus of suprathreshold intensity.

Saltatory conduction

The rapid mechanism of nerve impulse transmission along myelinated axons in which the electrical signal jumps from one Node of Ranvier to the next, reaching speeds up to $120\,\text{m/s}$.

Synapse

The specialized junction where the axon terminal of a presynaptic neuron communicates chemically with a postsynaptic neuron or effector cell.

Synaptic cleft

The narrow extracellular fluid-filled gap that separates the presynaptic membrane from the postsynaptic membrane at a synapse.

Excitatory postsynaptic potential (EPSP)

A local, graded depolarization of the postsynaptic membrane produced when neurotransmitter binding opens chemically gated $\text{Na}^+$ channels, bringing the membrane closer to threshold.

Inhibitory postsynaptic potential (IPSP)

A local, graded hyperpolarization of the postsynaptic membrane caused by neurotransmitter-stimulated opening of $\text{K}^+$ channels, moving the membrane farther from threshold.

Summation

The integration and arithmetic combining of multiple excitatory and inhibitory postsynaptic potentials, typically occurring at the neuron's trigger zone.

Vesicle trafficking

The cycle of membrane exchange wherein synaptic vesicles fuse with the presynaptic membrane to release neurotransmitters by exocytosis and are retrieved via endocytosis.

Neuromodulators

Neuropeptides that modify a neuron's responsiveness to neurotransmitters or modulate the release of neurotransmitters, such as enkephalins inhibiting the release of substance P.

Neuronal pool

A organized functional group of interneurons confined entirely within the CNS that receive, process, and relay specific synaptic inputs to other pools or effectors.

Facilitation

A state in which repeated excitatory subthreshold stimuli cause a presynaptic neuron to release larger quantities of neurotransmitter, bringing the postsynaptic cell closer to firing threshold.

Convergence

A neural wiring pattern where a single postsynaptic neuron receives synaptic inputs from two or more presynaptic neurons, allowing collection and integration of diverse information.

Divergence

A circuit arrangement wherein a single presynaptic neuron divides to form synapses with multiple postsynaptic neurons, amplifying the reach of an incoming nerve impulse.

Agonist

A chemical or pharmacological agent that binds to and activates a specific receptor, mimicking the effect of an endogenous neurotransmitter.

Antagonist

A drug or chemical compound that binds to a neurotransmitter receptor and competitively blocks the endogenous neurotransmitter from binding.