This topic covers the structure and function of neurons, as well as the process of neurotransmission including action potentials, synaptic transmission, and the role of neurotransmitters in communication between neurons.
Neurons & Neurotransmission – Study Notes
| Component | Main Function |
|---|---|
| Central Nervous System (CNS) | Brain + spinal cord; integrates information and generates responses. |
| Peripheral Nervous System (PNS) | Sensory (afferent) and motor (efferent) nerves that connect the CNS to the rest of the body. |
| Neurons | Specialized cells that transmit electrical and chemical signals. |
| Structure | Description | Key Role in Transmission |
|---|---|---|
| Cell Body (Soma) | Contains nucleus, organelles, and most cytoplasm. | Generates the resting membrane potential; integrates incoming signals. |
| Dendrites | Branch‑like extensions (often many). | Receive excitatory or inhibitory inputs from other neurons. |
| Axon | Long, thin process that can be myelinated. | Conducts action potentials away from the soma toward terminals. |
| Myelin Sheath | Lipid‑rich layers formed by Schwann cells (PNS) or oligodendrocytes (CNS). | Increases conduction speed via saltatory propagation. |
| Nodes of Ranvier | Gaps in myelin. | Concentrate voltage‑gated Na⁺ channels; allow regeneration of the action potential. |
| Axon Terminals (Synaptic Boutons) | Swellings at the end of the axon. | Release neurotransmitter into the synaptic cleft. |
| Synapse | Junction between a presynaptic terminal and a postsynaptic element (neuron, muscle, gland). | Site of chemical communication. |
Typical value: –70 mV (inside negative).
Main contributors:
Nernst equation (for a single ion):
[ E_{ion}= \frac{RT}{zF}\ln\frac{[ion]{\text{out}}}{[ion]{\text{in}}} ]
[ V_m = \frac{RT}{F}\ln\frac{P_{K}[K^+]{\text{out}} + P{Na}[Na^+]{\text{out}} + P{Cl}[Cl^-]{\text{in}}}{P{K}[K^+]{\text{in}} + P{Na}[Na^+]{\text{in}} + P{Cl}[Cl^-]_{\text{out}}} ]
| Phase | Membrane Change | Ion Movements | Key Channels |
|---|---|---|---|
| Depolarization | Membrane potential rises toward 0 mV. | Voltage‑gated Na⁺ channels open → Na⁺ influx. | Na⁺ channels (fast, inactivating). |
| Repolarization | Return toward negative values. | Voltage‑gated K⁺ channels open → K⁺ efflux; Na⁺ channels inactivate. |