What if you could see neurons in action?
The human nervous system is an incredible network that coordinates all our actions and sensory experiences. But how does it actually work? This interactive simulation lets you explore neurons, action potentials, and the divisions of the nervous system.
In this exploration, you'll discover:
- How neurons transmit information through action potentials
- The structure and function of different neuron types
- How the central and peripheral nervous systems work together
- The role of cranial nerves in controlling bodily functions
Start by selecting a tab below to begin your exploration!
Neuron Structure: The Building Block of the Nervous System
Click on any part of the neuron to learn more Tap neuron parts to learn more
Key Neuron Structures
Neurons are specialized cells that transmit information throughout the body. Click on any part in the diagram or cards below to explore in detail!
Dendrites
Signal Reception
Soma (Cell Body)
Metabolic Center
Axon
Signal Transmission
Myelin Sheath
Insulation Layer
Axon Terminals
Neurotransmitter Release
Action Potential: How Neurons Communicate
Membrane Potential Simulation
The action potential is a rapid electrical signal that travels along a neuron's membrane. Adjust the stimulus strength to see how it affects the neuron's response:
The Action Potential Process
1. Resting Potential (-70mV)
Membrane at equilibrium with selective permeability:
- K⁺ leak channels (PK:PNa = 25:1 ratio)
- Na⁺/K⁺-ATPase pump (3 Na⁺ out, 2 K⁺ in)
- Impermeable intracellular anions (A⁻)
- Goldman-Hodgkin-Katz equation determines Em
2. Depolarization (Threshold: -55mV)
Voltage-gated Nav1.1-1.9 channels activate:
- Positive feedback loop: Na⁺ influx → further depolarization
- Peak at +30 to +40mV (ENa = +60mV)
- Duration: 0.5-2ms (temperature dependent)
- All-or-none (regenerative) response
3. Repolarization
Na⁺ inactivation and K⁺ channel opening:
- Fast Na⁺ inactivation (h-gates close, τ = 0.1-0.2ms)
- Delayed rectifier Kv channels (Kv1.1-1.8) activate
- K⁺ efflux restores electronegativity
- Membrane approaches EK (-90 to -100mV)
4. Afterhyperpolarization (AHP)
Prolonged K⁺ conductance creates undershoot:
- Delayed rectifier K⁺ channels remain open
- Ca²⁺-activated K⁺ channels (SK, BK) contribute
- Membrane reaches -75 to -90mV
- Duration: 2-5ms (varies by neuron type)
5. Recovery & Refractory Periods
Channel kinetics determine excitability:
- Absolute refractory: Na⁺ channels inactivated (1-2ms)
- Relative refractory: Higher threshold due to K⁺ conductance
- Na⁺/K⁺-ATPase restores gradients (metabolically expensive)
- Recovery from inactivation: τ = 1-10ms
Clinical Insights
Action potentials follow the "all-or-none" principle - once threshold (-55mV) is reached, the regenerative process is inevitable and stereotyped.
Medical relevance: Local anesthetics (lidocaine, procaine) block voltage-gated Na⁺ channels, preventing action potential propagation and eliminating pain sensation.
Neuron Types: Specialized for Different Functions
Functional Classification
Neurons are classified based on their function in the nervous system:
Sensory (Afferent) Neurons
Convert external stimuli into electrical signals for the brain. Found in sensory organs and the PNS.
Motor (Efferent) Neurons
Transmit signals from the CNS to muscles and glands to initiate actions and movements.
Interneurons
Connect other neurons within the CNS. They process and integrate information between sensory and motor neurons.
Structural Classification
Neurons can also be classified based on their structure:
Multipolar Neurons
Have one axon and multiple dendrites. Most common type in the CNS. Examples include motor neurons and interneurons.
Bipolar Neurons
Have one axon and one dendrite extending from opposite sides of the soma. Found in sensory pathways like the retina, inner ear, and olfactory system.
Unipolar Neurons
Have a single process that divides into two branches - one functions as a dendrite, the other as an axon. Common in sensory neurons of the PNS.
Function vs. Structure
While there's some correlation between a neuron's structure and function, they're not always directly related:
- Sensory neurons are typically unipolar or bipolar
- Motor neurons are generally multipolar
- Interneurons are almost always multipolar
Nervous System Organization
Central vs Peripheral Nervous System
Central Nervous System (CNS)
Brain: Control center for all body functions, containing ~86 billion neurons
Spinal Cord: Information highway between brain and body, 31 segments
- Protected by bone (skull & vertebrae)
- Surrounded by cerebrospinal fluid
- Blood-brain barrier protection
Peripheral Nervous System (PNS)
All neural tissue outside the CNS
- 12 pairs of cranial nerves (from brain)
- 31 pairs of spinal nerves (from spinal cord)
- Ganglia: Clusters of neuron cell bodies
- Sensory receptors throughout the body
Functional Divisions
Somatic Nervous System:
- Voluntary motor control
- Sensory information processing
Autonomic Nervous System:
- Sympathetic (fight-or-flight)
- Parasympathetic (rest-and-digest)
- Enteric (gut nervous system)
Cranial Nerves: Direct Brain Connections
🧠 Your Brain's Direct Hotlines
Think of cranial nerves as dedicated phone lines between your brain and specific body parts. Unlike spinal nerves that take a detour through the spinal cord, these 12 pairs connect directly to your brainstem - like having a direct line to the CEO!
👁️ Special Senses (I, II, VIII)
Smell, vision, hearing, balance - your connection to the world
👀 Eye Movement (III, IV, VI)
Precise eye control for tracking, reading, depth perception
🗣️ Face & Voice (V, VII, IX, X, XI, XII)
Expression, speech, chewing, swallowing, autonomics
Each nerve has a unique personality and job description. Some are pure sensory (like your smell detector), others are pure motor (like your tongue controller), and some are mixed (doing multiple jobs). Click on any cranial nerve below to explore detailed anatomy and clinical correlations!
I. Olfactory
Smell Sensation
II. Optic
Vision
III. Oculomotor
Eye Movement & Pupil
IV. Trochlear
Eye Rotation (Intorsion)
V. Trigeminal
Facial Sensation & Chewing
VI. Abducens
Lateral Eye Movement
VII. Facial
Facial Expression & Taste
VIII. Vestibulocochlear
Hearing & Balance
IX. Glossopharyngeal
Taste & Swallowing
X. Vagus
Parasympathetic Control
XI. Accessory (Spinal)
Neck & Shoulder Muscles
XII. Hypoglossal
Tongue Movement
Clinical Memory Aids
Names: "On Old Olympus' Towering Top, A Finn And German Viewed Some Hops"
Olfactory, Optic, Oculomotor, Trochlear, Trigeminal, Abducens, Facial, Vestibulocochlear, Glossopharyngeal, Vagus, Accessory, Hypoglossal
Types: "Some Say Marry Money, But My Brother Says Big Brains Matter More"
S = Sensory, M = Motor, B = Both (Mixed)