Neurons and Neural Communication Study Pack
Kibin's free study pack on Neurons and Neural Communication includes a 7-section study guide, 25 quiz questions, 30 flashcards, and 5 open-ended Explain review questions. Sign up free to track your progress toward mastery, plus upload your own notes and recordings to create personalized study packs organized by course.
Last updated May 28, 2026
Neurons and Neural Communication Study Guide
Trace the full journey of a neural signal — from resting membrane potential and action potentials to synaptic transmission and neurotransmitter binding — while mastering key structures like the axon, myelin sheath, and glial cells essential for any Psych 101 exam.
Key Takeaways
- •Neurons are electrically excitable cells with three functional regions — dendrites, cell body (soma), and axon — each playing a distinct role in receiving, integrating, and transmitting signals.
- •The resting membrane potential of approximately −70 mV is maintained by the sodium-potassium pump and selective ion channel permeability, creating an electrochemical gradient across the neuron's membrane.
- •An action potential is an all-or-nothing electrical event triggered when membrane depolarization reaches threshold (around −55 mV), causing rapid Na⁺ influx followed by K⁺ efflux to restore the resting state.
- •Myelin sheaths produced by oligodendrocytes (CNS) and Schwann cells (PNS) dramatically increase signal conduction speed through saltatory conduction at nodes of Ranvier.
- •Synaptic transmission converts an electrical signal into a chemical one: arriving action potentials trigger neurotransmitter release from presynaptic vesicles into the synaptic cleft, where neurotransmitters bind to receptors on the postsynaptic membrane.
- •Postsynaptic effects are either excitatory (EPSPs, moving membrane potential toward threshold) or inhibitory (IPSPs, moving it away), and neurons integrate many simultaneous inputs before firing.
- •Glial cells — including astrocytes, microglia, and oligodendrocytes — perform essential support functions such as maintaining ion homeostasis, immune defense, and myelin formation rather than transmitting signals themselves.
Neuron Structure and Functional Regions
A neuron's shape is not arbitrary — each structural region is specialized for a specific step in processing and transmitting information, and understanding that structure is the foundation for understanding how neural communication works.
Dendrites: Input Receivers
- •Dendrites are branching extensions that project from the soma and increase the neuron's surface area for receiving incoming signals from other neurons or sensory stimuli.
- •The number and branching complexity of dendrites vary widely across neuron types, reflecting differences in how many inputs a neuron integrates.
- •Dendritic spines — small protrusions on dendrite surfaces — are sites of synaptic contact and are thought to play a role in synaptic plasticity and learning.
Soma: Integration Center
- •The soma, or cell body, houses the nucleus and carries out essential metabolic functions including protein synthesis for neurotransmitters and ion channel proteins.
- •The soma integrates all excitatory and inhibitory signals arriving from dendrites before any output signal is generated.
Axon and Axon Terminal: Output Pathway
- •The axon is a single elongated projection that carries electrical signals away from the soma; it originates at the axon hillock, the site where action potentials are initiated.
- •Axon length ranges from less than a millimeter to over a meter in motor neurons projecting from the spinal cord to muscles.
- •At the far end, the axon branches into axon terminals (also called terminal boutons), which contain synaptic vesicles filled with neurotransmitters ready for release.
Neuron Classification by Function
- •Sensory neurons (afferent) carry information from sensory receptors toward the central nervous system.
- •Motor neurons (efferent) carry commands from the CNS to muscles and glands.
- •Interneurons, which make up the vast majority of neurons in the brain and spinal cord, connect neurons to one another and are responsible for integration and complex processing.
Resting Membrane Potential and Electrochemical Gradients
Before a neuron fires, it maintains a stable electrical charge difference across its membrane called the resting membrane potential, which is the baseline state from which all neural signaling originates.
Ion Distribution at Rest
- •At rest, the inside of the neuron is negatively charged relative to the outside, producing a resting membrane potential of approximately −70 millivolts (mV).
- •Sodium ions (Na⁺) are concentrated outside the cell, while potassium ions (K⁺) and negatively charged proteins are concentrated inside.
- •This unequal distribution is maintained partly by the selective permeability of the membrane — leak channels allow K⁺ to move more freely than Na⁺ at rest.
Sodium-Potassium Pump
- •The sodium-potassium pump (Na⁺/K⁺-ATPase) actively transports 3 Na⁺ out of the cell and 2 K⁺ into the cell per cycle, consuming ATP to counteract ion leakage and preserve the concentration gradients.
- •This pump is essential for sustaining the resting potential over time; without it, ions would gradually equilibrate and the neuron would lose the ability to fire.
Significance of the Resting Potential
- •The resting potential represents stored electrochemical energy — a readiness to respond — analogous to a compressed spring awaiting release.
- •Disruptions to this baseline (either depolarization toward zero or hyperpolarization further negative) determine whether a neuron will fire an action potential.
Action Potentials: Generation and Propagation
An action potential is the primary electrical signal neurons use to transmit information over long distances, and its reliable, stereotyped nature is central to the nervous system's ability to encode and transmit information.
Threshold and Depolarization
- •When enough excitatory input accumulates to depolarize the axon hillock to approximately −55 mV (the threshold), voltage-gated Na⁺ channels open rapidly.
- •Na⁺ rushes into the cell down its concentration and electrical gradients, driving the membrane potential sharply positive, reaching about +30 to +40 mV at the peak.
- •This event is all-or-nothing: either the threshold is reached and a full action potential fires, or nothing happens — there is no partial action potential.
Repolarization and Hyperpolarization
- •Shortly after Na⁺ channels open, they inactivate automatically, stopping Na⁺ influx.
- •Voltage-gated K⁺ channels open with a slight delay, allowing K⁺ to rush out of the cell, repolarizing the membrane back toward its resting potential.
- •K⁺ channels close slowly, causing a brief undershoot below −70 mV called the afterhyperpolarization, during which the neuron is in its refractory period and cannot fire again.
Absolute and Relative Refractory Periods
- •During the absolute refractory period, Na⁺ channels are inactivated and no action potential can be triggered regardless of stimulus strength.
- •During the relative refractory period (the afterhyperpolarization phase), a stronger-than-normal stimulus can trigger a new action potential, which is how neurons encode stimulus intensity through firing rate.
Propagation Along the Axon
- •Action potentials do not travel like an electrical current in a wire; instead, each segment of the axon membrane regenerates the signal by triggering the next adjacent segment.
- •In unmyelinated axons, this propagation is continuous and relatively slow.
- •In myelinated axons, the signal jumps between nodes of Ranvier in a process called saltatory conduction, which dramatically increases conduction velocity and energy efficiency.
Myelin and Signal Conduction Speed
Myelin is a lipid-rich insulating sheath around many axons that fundamentally changes how fast and efficiently action potentials travel, and damage to myelin has serious neurological consequences.
Myelin Formation by Glial Cells
- •In the central nervous system, oligodendrocytes wrap their membrane extensions around axons to form myelin; a single oligodendrocyte can myelinate segments of multiple axons simultaneously.
- •In the peripheral nervous system, Schwann cells form myelin by wrapping around a single axon segment; each Schwann cell covers one internode.
- •Myelin increases the electrical resistance of the axon membrane and decreases capacitance, forcing ionic current to travel along the interior of the axon rather than leaking out.
Nodes of Ranvier and Saltatory Conduction
- •Nodes of Ranvier are small gaps between adjacent myelin segments where voltage-gated ion channels are densely concentrated.
- •Action potentials are regenerated only at these nodes, causing the signal to 'jump' from node to node — a process called saltatory conduction (from the Latin saltare, to leap).
- •This mechanism increases conduction velocity from roughly 0.5–2 m/s in unmyelinated fibers to up to 120 m/s in heavily myelinated axons.
Clinical Relevance of Myelin Damage
- •Multiple sclerosis (MS) is an autoimmune disease in which the immune system attacks and degrades myelin in the CNS, disrupting action potential conduction.
- •Symptoms of MS — including muscle weakness, coordination problems, and sensory disturbances — reflect the loss of reliable, high-speed neural communication in affected pathways.
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