neuron projection terminus

Definition

Target type: cellularcomponent

The specialized, terminal region of a neuron projection such as an axon or a dendrite. [GOC:jl]

The neuron projection terminus, also known as the axon terminal or synaptic bouton, is a specialized structure at the end of a neuron's axon responsible for transmitting signals to other neurons or target cells. It's a highly complex cellular compartment, characterized by the following features:

**1. Synaptic Vesicles:**
- Abundant, small membrane-bound sacs filled with neurotransmitters, the chemical messengers that transmit signals across synapses.
- These vesicles are clustered near the presynaptic membrane, the portion of the axon terminal facing the target cell.
- They undergo exocytosis, releasing neurotransmitters into the synaptic cleft, the narrow space between the presynaptic and postsynaptic membranes.

**2. Presynaptic Membrane:**
- Specialized membrane of the axon terminal facing the target cell.
- Contains a high density of voltage-gated calcium channels, which open in response to an action potential arriving at the terminal.
- Calcium influx triggers the fusion of synaptic vesicles with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft.

**3. Synaptic Cleft:**
- The narrow gap between the presynaptic and postsynaptic membranes.
- It's filled with extracellular matrix, which helps regulate the diffusion of neurotransmitters and other molecules.
- Neurotransmitters diffuse across the cleft, binding to receptors on the postsynaptic membrane of the target cell.

**4. Postsynaptic Density:**
- A dense protein structure on the postsynaptic membrane of the target cell.
- Contains receptors for neurotransmitters, as well as other signaling molecules and enzymes involved in signal transduction.
- Upon binding to neurotransmitters, these receptors trigger changes in the postsynaptic cell, leading to a response.

**5. Cytoskeleton:**
- A network of protein filaments that provides structural support and helps transport materials within the axon terminal.
- Microtubules and microfilaments ensure the precise positioning of synaptic vesicles and other organelles.

**6. Mitochondria:**
- Provide energy for the metabolic processes occurring within the axon terminal.
- They are essential for maintaining the high energy demands of neurotransmitter synthesis, vesicle cycling, and signal transduction.

**7. Enzymes and Proteins:**
- The axon terminal contains numerous enzymes and proteins involved in:
- Neurotransmitter synthesis
- Vesicle trafficking
- Receptor regulation
- Signal transduction pathways

**8. Synaptic Scaffolding Proteins:**
- A network of proteins that organize and maintain the structure of the synapse.
- They provide anchors for receptors, enzymes, and other signaling molecules, ensuring their proper localization and function.

These intricate components of the neuron projection terminus work in a coordinated manner to ensure efficient and reliable communication between neurons. The process involves the release of neurotransmitters from the presynaptic terminal, their diffusion across the synaptic cleft, and their binding to receptors on the postsynaptic cell. This intricate interplay ultimately leads to changes in the target cell's activity, contributing to the complex functions of the nervous system.'
"

Proteins (5)

Compounds (41)