Explain the Structure of a Typical Neuron. How Do Neurons Transmit Electrical Signals Through Action Potentials?
Structure of a Typical Neuron
A neuron is the fundamental unit of the nervous system, specialized for transmitting signals.
- Cell Body (Soma): Contains the nucleus and organelles; metabolic center of the neuron.
- Dendrites: Branched extensions that receive signals from other neurons and convey them to the cell body.
- Axon: Long projection that transmits electrical signals away from the cell body.
- Axon Terminals: Endings of axons that release neurotransmitters into synaptic clefts.
- Myelin Sheath: Insulating layer around axon (formed by Schwann cells in PNS or oligodendrocytes in CNS) that increases conduction speed.
- Nodes of Ranvier: Gaps in myelin that facilitate saltatory conduction.
Transmission of Electrical Signals
Neurons communicate via electrical impulses known as action potentials.
1. Resting Membrane Potential
Maintained by sodium-potassium pumps, the neuron is polarized at approximately -70 mV.
2. Initiation of Action Potential
When a threshold stimulus depolarizes the membrane, voltage-gated Na⁺ channels open, allowing Na⁺ influx and further depolarization.
3. Propagation
The depolarization travels along the axon. In myelinated axons, the signal jumps from node to node (saltatory conduction), speeding up transmission.
4. Repolarization
Na⁺ channels close and K⁺ channels open, allowing K⁺ to exit, restoring the negative membrane potential.
5. Hyperpolarization and Return to Resting State
Excess K⁺ outflow causes hyperpolarization briefly before the membrane stabilizes via the Na⁺/K⁺ pump.
Neurons thus effectively transmit signals via action potentials, essential for brain activity, reflexes, and muscle movement.