Neural Control & Action Potential
Comprehensive notes, formulas, and practice questions for Neural Control & Action Potential.
Neural Control & Action Potential
Neural Control & Action Potential
What you'll learn
- Structure and types of neurons.
- How an action potential is generated and propagated.
- The role of synapses in signal transmission.
- Overview of the human nervous system organisation.
Key concepts
Neuron Structure
| Part | Function |
|---|---|
| Dendrites | Receive signals from other neurons |
| Cell body (soma) | Contains nucleus; integrates signals |
| Axon | Carries signal away from cell body |
| Myelin sheath | Insulates axon; speeds up conduction |
| Nodes of Ranvier | Gaps in myelin; site of saltatory conduction |
| Synaptic terminals | Release neurotransmitters to next neuron |
Types of Neurons
| Type | Function |
|---|---|
| Sensory (afferent) | Carry signals from sense organs to CNS |
| Motor (efferent) | Carry signals from CNS to muscles/glands |
| Interneurons | Connect sensory and motor; within CNS |
Resting Membrane Potential
At rest, inside of neuron is −70 mV relative to outside.
- High K⁺ inside; high Na⁺ outside.
- Maintained by Na⁺/K⁺ ATPase pump (3 Na⁺ out, 2 K⁺ in per cycle).
- K⁺ leak channels keep inside negative.
Action Potential — Step by Step
| Phase | What happens | Ions |
|---|---|---|
| Resting | −70 mV | K⁺ channels open; Na⁺ channels closed |
| Depolarisation | Stimulus → Na⁺ channels open → inside goes to +30 mV | Na⁺ rushes IN |
| Repolarisation | Na⁺ channels close; K⁺ channels open | K⁺ rushes OUT |
| Hyperpolarisation | Briefly more negative than −70 mV | Extra K⁺ out |
| Recovery | Na⁺/K⁺ pump restores resting potential | Active transport |
Threshold: ~−55 mV. Stimulus must depolarise to threshold for AP to fire (all-or-nothing).
Saltatory Conduction
- In myelinated fibres, AP jumps from node to node → much faster.
- Myelinated: 70–120 m/s; Unmyelinated: 0.5–2 m/s.
Synapse
Gap between two neurons (or neuron and muscle):
- AP reaches synaptic terminal.
- Ca²⁺ channels open → Ca²⁺ enters.
- Vesicles fuse; neurotransmitter released into synaptic cleft.
- Neurotransmitter binds to receptor on postsynaptic membrane.
- Ion channels open → EPSP (excitatory) or IPSP (inhibitory).
- Neurotransmitter removed (reuptake, degradation, diffusion).
Key neurotransmitters:
| NT | Effect |
|---|---|
| Acetylcholine (ACh) | Excitatory (NMJ); inhibitory (heart) |
| Dopamine | Reward, motor control |
| Serotonin | Mood, sleep |
| GABA | Inhibitory |
| Glutamate | Major excitatory in CNS |
Nervous System Organisation
Nervous System
├── Central (CNS): Brain + Spinal cord
└── Peripheral (PNS)
├── Somatic: Voluntary (skeletal muscles)
└── Autonomic
├── Sympathetic: "fight or flight"
└── Parasympathetic: "rest and digest"
Reflex Arc
Stimulus → Receptor → Sensory neuron → Spinal cord → Motor neuron → Effector
- Bypass brain for speed.
- Example: knee-jerk reflex, withdrawing hand from hot object.
Quick check
- What maintains the resting membrane potential of −70 mV?
- What is the threshold potential? What is the "all-or-nothing" principle?
- Describe depolarisation — which ion rushes in and which channels open?
- What is saltatory conduction? Why is it faster?
- Name three neurotransmitters and their effects.
Open the Practice tab for graded questions on Neural Control & Action Potential.
Key Takeaways (TL;DR)
- What you'll learn
- Key concepts
- Quick check
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