Chapter 12: Nervous System Study Guide

Comprehensive vocabulary flashcards focusing on nervous system functions, subdivisions, neuron anatomy, glial cell types, axonal transport, membrane physiology, and signal propagation.

Stimuli

Changes in the external and internal environment that are monitored by specialized nervous structures called receptors.

Effectors

Tissue types including skeletal, cardiac, and smooth muscle, as well as glands, that receive motor input from the nervous system.

Central Nervous System (CNS)

Anatomical subdivision of the nervous system consisting of the brain and spinal cord, which carries out processing and integrative functions.

Peripheral Nervous System (PNS)

Nervous system subdivision including nerves and bundles of neuron processes that provides pathways for signal input and output between the CNS and the body.

Sensory Nervous System

Also known as the afferent nervous system; it receives information from receptors and transmits it toward the CNS.

Somatic Sensory Neurons

Neurons that detect stimuli we consciously perceive, such as information from the skin, joints, skeletal muscles, and eyes.

Visceral Sensory Neurons

Neurons that detect stimuli we do not consciously perceive, such as structural changes within blood vessels or internal organs.

Motor Nervous System

Also known as the efferent nervous system; it initiates and transmits motor output away from the CNS to effectors.

Somatic Motor Neurons

Neurons that transmit motor output from the CNS to voluntary skeletal muscles for conscious control.

Autonomic Motor Neurons

Neurons that transmit motor output without conscious control to cardiac muscle, smooth muscle, and glands.

Neurons

Specialized cells that function in transmitting electrical signals ($graded and action potentials$) and the release of neurotransmitters.

Glial cells

Also called neuroglia; smaller cells found in the CNS and PNS that support and protect neurons and are capable of cell division.

Astrocytes

The most abundant CNS glial cells; they help form the blood-brain barrier, regulate interstitial fluid composition, and provide structural support.

Ependymal cells

Epithelial cells that line fluid-filled spaces in the CNS and form the choroid plexus to help produce CSF.

Microglia

The smallest percentage of CNS glial cells; they are phagocytic cells that respond to infection.

Oligodendrocytes

Large CNS glial cells that insulate axons to form the myelin sheath; they are specifically targeted by multiple sclerosis.

Satellite cells

Flat cells that surround neuronal cell bodies in a ganglion to insulate the cell body and regulate nutrient and waste exchange.

Neurolemmoocytes

Also known as Schwann cells; PNS glial cells that insulate axons to form the myelin sheath.

Excitability

The ability of a neuron to respond to a stimulus (such as chemical or stretch) by initiating ion movement across the plasma membrane.

Conductivity

The propagation of voltage changes along the plasma membrane as voltage-gated channels open sequentially.

Secretion

The release of neurotransmitters from the synaptic knob in response to conductive activity.

Chromatophilic substance

Also called Nissl bodies; dark-staining ribosomes within the cell body that account for the gray matter of the brain and spinal cord.

Axon hillock

The triangular, cone-shaped region of the cell body from which the axon typically emanates.

Axolemma

The plasma membrane of an axon.

Synaptic knobs

Slightly expanded tips at the extreme ends of axon terminal extensions containing synaptic vesicles with neurotransmitters.

Neurofibril nodes

Also called Nodes of Ranvier; the uninsulated regions of the axon located between the myelin sheaths.

Neurofilaments

Intermediate filaments specific to neurons that aggregate into bundles called neurofibrils to maintain shape and provide structural support.

Tau

A protein that stabilizes microtubules of the neuron cytoskeleton; it is associated with Alzheimer disease.

Anterograde Transport

The movement of materials from the neuronal cell body toward the synaptic knobs.

Retrograde Transport

The movement of materials from the synaptic knobs toward the neuronal cell body.

Fast Axonal Transport

Movement along microtubules powered by motor proteins like kinesin and dynein that split ATP; it occurs in both anterograde and retrograde directions.

Slow Axonal Transport

Also called axoplasmic flow; moves materials only in the anterograde direction from the cell body toward the knobs.

Multipolar neuron

The most common structural category of neuron, possessing multiple processes extending from the cell body (many dendrites and one axon).

Bipolar neuron

A neuron with two processes extending from the cell body (one dendrite and one axon), found in the retina and olfactory epithelium.

Unipolar neuron

Also called psuedounipolar; a neuron with a single short process extending from the cell body that branches into a T-shape.

Interneurons

Also known as association neurons; they are located entirely within the CNS and comprise $99\%$ of all neurons.

Nerve

An organ composed of cablelike bundles of axons, connective tissue layers, and blood vessels.

Epineurium

A thick layer of dense irregular connective tissue that encloses and protects the entire nerve.

Perineurium

A layer of dense irregular connective tissue that wraps each fascicle within a nerve.

Endoneurium

A delicate layer of areolar connective tissue that surrounds and electrically insulates each individual axon.

Synapse

The specific location where a neuron is functionally connected to another neuron or an effector.

Synaptic delay

The time required for neurotransmitter release, diffusion across the synaptic cleft, and binding to the postsynaptic receptors.

Pumps

Active transport proteins, such as $Na^+/K^+$ and $Ca^{2+}$ pumps, that maintain concentration gradients by moving substances against them.

Leak channels

Passive channels that are always open, such as those for $Na^+$ and $K^+$.

Voltage-gated channels

Channels that open temporarily in response to changes in voltage at the plasma membrane, including those for $Na^+$, $K^+$, and $Ca^{2+}$.

Voltage-gated Na+ Resting state

The state where the inactivation gate is open and the activation gate is closed, preventing $Na^+$ entry.

Receptive segment

The neuron region including dendrites and the cell body, containing chemically gated cation, $K^+$, and $Cl^-$ channels.

Initial segment

The axon hillock region containing voltage-gated $Na^+$ and $K^+$ channels where integration occurs.

Transmissive segment

The region including the synaptic knobs, containing voltage-gated $Ca^{2+}$ channels and $Ca^{2+}$ pumps.

Voltage

The measure of the difference in electrical charge between two areas, representing potential energy.

Resting membrane potential (RMP)

The electrical charge difference across the plasma membrane of a neuron at rest, typically $-70\,mV$.

Threshold

The minimum positive voltage change, typically $-55\,mV$, required to open voltage-gated channels.

Graded potential

Relatively small, local voltage changes that occur in the receptive segment and weaken with distance.

Action potential

A self-propagating change in membrane potential generated in the conductive segment (axon) when threshold is reached.

Depolarization

A shift in membrane voltage toward zero or a positive value, caused by $Na^+$ rushing into the cell through voltage-gated channels.

Repolarization

The resetting of the membrane potential toward the resting state, caused by $K^+$ flowing out of the cell.

Hyperpolarization

A change that makes the inside of the cell more negative than the RMP, such as moving from $-70\,mV$ to $-80\,mV$.

EPSP

Excitatory postsynaptic potential; a local depolarization of the postsynaptic neuron caused by neurotransmitter binding to chemically gated cation channels.

IPSP

Inhibitory postsynaptic potential; a local hyperpolarization or repolarization that makes the inside of a cell more negative.

Spatial Summation

The addition of graded potentials that occur when multiple presynaptic neurons release neurotransmitters at various locations.

Temporal Summation

The addition of graded potentials that occur when a single presynaptic neuron repeatedly releases neurotransmitters at the same location.

Continuous Conduction

The sequential opening of voltage-gated channels along the entire length of an unmyelinated axon.

Saltatory (Conduction)

The rapid propagation of a nerve signal in myelinated axons, where action potentials are generated only at neurofibril nodes.

Refractory period

A short time after an action potential during which a neuron cannot be stimulated to fire again or requires a stronger stimulus.

Acetylcholine (ACh)

An organic neurotransmitter released at the neuromuscular junction and within the CNS and PNS; can be excitatory or inhibitory.

Monoamines

Neurotransmitters derived from amino acids, including catecholamines (norepinephrine, epinephrine, dopamine) and serotonin.

Neuromodulation

The release of chemicals that locally regulate or alter the response of neurons to neurotransmitters through facilitation or inhibition.

Reverberating circuit

A neuronal pool that utilizes feedback to produce repeated, cyclical stimulation.