Introduction to the Nervous System & Neuron Physiology

Vocabulary flashcards covering major terms and concepts from the lecture on nervous system organization, neuron structure, membrane potentials, signal conduction, and synaptic transmission.

Nervous System

Body system that uses electrical and chemical signals to coordinate sensation, movement, and behavior.

Endocrine System

Glandular system that communicates via hormones released into the bloodstream for long-distance regulation.

Central Nervous System (CNS)

The brain and spinal cord, enclosed by the cranium and vertebral column.

Peripheral Nervous System (PNS)

All nervous tissue outside the CNS; consists of nerves and ganglia.

Nerve

Bundle of nerve fibers (axons) wrapped in fibrous connective tissue in the PNS.

Ganglion

Knot-like swelling in a nerve where neuron cell bodies are concentrated.

Sensory (Afferent) Division

PNS subdivision that carries information from receptors to the CNS.

Somatic Sensory Division

Afferent fibers that convey signals from skin, muscles, bones, and joints.

Visceral Sensory Division

Afferent fibers that convey signals from thoracic and abdominal viscera.

Motor (Efferent) Division

PNS subdivision that transmits commands from CNS to effectors.

Somatic Motor Division

Efferent fibers that innervate skeletal muscles; produces voluntary movements and somatic reflexes.

Visceral Motor Division (Autonomic Nervous System)

Efferent fibers that regulate glands, cardiac muscle, and smooth muscle; involuntary.

Sympathetic Division

ANS branch that prepares body for action; increases heart rate, respiration; inhibits digestion and urination.

Parasympathetic Division

ANS branch that calms the body; slows heart and breathing; stimulates digestion and urination.

Neuron

Fundamental nerve cell specialized for communication by electrical and chemical signals.

Excitability (Irritability)

Neuron property of responding to environmental changes (stimuli).

Conductivity

Neuron ability to transmit electrical signals rapidly to distant cells.

Secretion

Release of neurotransmitter when an electrical signal reaches a neuron's axon terminal.

Sensory Neuron

Neuron that detects stimuli and transmits information toward the CNS.

Interneuron

Neuron entirely within CNS that connects pathways and performs integration; ~90 % of all neurons.

Motor Neuron

Neuron that sends signals from CNS to muscles or glands (effectors).

Neurosoma (Cell Body)

Control center of the neuron containing nucleus and most organelles.

Dendrite

Branching process of a neuron that receives signals from other cells.

Axon (Nerve Fiber)

Long process that conducts impulses away from the cell body toward other cells.

Axon Hillock

Cone-shaped region of cell body where the axon originates; trigger zone for action potentials.

Axon Terminal

Distal swelling of an axon that forms a synapse and houses synaptic vesicles.

Multipolar Neuron

Neuron with one axon and multiple dendrites; most common type in CNS.

Bipolar Neuron

Neuron with one axon and one dendrite; found in retina, olfactory epithelium, inner ear.

Unipolar Neuron

Neuron with a single process that splits into peripheral and central fibers; sensory neurons of skin and organs.

Anaxonic Neuron

Neuron with many dendrites but no axon; roles in retina, brain, adrenal gland.

Electrical Potential

Difference in charge across a membrane; cells are polarized at rest (~-70 mV in neurons).

Electrical Current

Flow of charged particles, chiefly ions, across the membrane via channels.

Resting Membrane Potential (RMP)

Stable voltage of an unstimulated neuron (about ‑70 mV) due to ion gradients and membrane permeability.

Local Potential

Small, graded change in membrane voltage near the site of stimulation that may depolarize or hyperpolarize.

Depolarization

Shift of membrane potential toward 0 mV (less negative) typically due to Na⁺ influx.

Hyperpolarization

Shift of membrane potential to more negative values than RMP, making firing less likely.

Action Potential

Rapid, all-or-none reversal of membrane polarity triggered at threshold and propagated along axon.

Threshold

Critical membrane voltage (~-55 mV) required to open voltage-gated channels and start an action potential.

All-or-None Law

Principle that action potentials occur at full amplitude if threshold is reached, or not at all.

Refractory Period

Time after an action potential when a neuron resists re-excitation.

Absolute Refractory Period

First phase when no stimulus can initiate a new action potential (Na⁺ channels inactivated).

Relative Refractory Period

Second phase when only strong stimuli can evoke another spike (K⁺ efflux ongoing).

Continuous Conduction

Sequential opening of voltage-gated channels along unmyelinated fibers; slower signal propagation.

Saltatory Conduction

Rapid impulse transmission in myelinated fibers where action potentials leap between nodes of Ranvier.

Node of Ranvier

Gap between myelin segments rich in voltage-gated channels; site of action potential regeneration.

Myelin Sheath

Insulating lipid layer around axons formed by glial cells; increases conduction speed.

Synapse

Junction where a neuron communicates with another cell via neurotransmitter release.

Presynaptic Neuron

Neuron that releases neurotransmitter at a synapse.

Postsynaptic Neuron

Neuron that responds to neurotransmitter at a synapse.

Neurotransmitter

Chemical messenger released by neurons to stimulate or inhibit adjacent cells.

Axodendritic Synapse

Synaptic connection between an axon terminal and a dendrite.

Axosomatic Synapse

Synaptic connection between an axon terminal and a neuron’s soma.

Axoaxonic Synapse

Synaptic connection between the axon of one neuron and the axon of another; often modulatory.