Neuron Structure Quiz

Neuron Structure

• The axon hillock is the point where the axon originates from the cell body and is crucial for initiating action potentials.
• Axon collaterals are secondary branches that extend from the main axon allowing one neuron to send signals to multiple target neurons/muscle cells.
• The myelin sheath, formed by oligodendrocytes in the CNS and Schwann cells in the PNS, insulates the axon, increasing electrical signal transmission speed.
• Nodes of Ranvier are gaps in the myelin sheath where ion channels are concentrated.
• Axon terminals (synaptic buttons) are the distal endings of the axon responsible for releasing neurotransmitters into the synaptic cleft. They contain synaptic vesicles filled with neurotransmitters.
• The synapse is the junction for information transfer between two neurons or between a neuron and a target cell (e.g., muscle or gland). It includes the pre-synaptic membrane, synaptic cleft, and postsynaptic membrane.

Action Potentials

• An action potential is a rapid change in voltage across a cell membrane, initiated at the axon hillock and propagated down the axon.
• A single cell is a neuron.
• A nerve is a bundle of axons from many neurons.
• Axonal transport moves proteins, organelles, and materials along the axon for neuronal maintenance, function, and survival.

Anterograde Transport

• Anterograde transport moves cargo from the cell body (soma) to the axon terminal using kinesin as the motor protein.
• Kinesin proteins consist of heavy chains with motor domains at the N-terminus and light chains associated with the heavy chains at the C-terminus.
• Kinesin motor domains bind to microtubules and "walk" along them by hydrolyzing ATP to power movement.
• Light chains bind to cargo, ensuring specific materials are transported.

Retrograde Transport

• Retrograde transport moves cargo from the axon terminal back to the cell body using dynein as the motor protein.
• Dynein uses a similar mechanism to kinesin with heavy and light chains.

Axonal Transport and Diseases

• Drugs affecting microtubule assembly/disassembly (e.g., colchicine, vincristine, vinblastine, taxol) can cause peripheral polyneuropathy.
• Toxins/pathogens can be endocytosed at the axon terminal and transported retrogradely to the soma. (e.g., Tetanus toxin)
• Axonal transport impairment is implicated in degenerative diseases like Alzheimer's, Huntington's, motor neuron disease, amyotrophic lateral sclerosis, and Parkinson's.

Neurotransmission

• Neurons communicate with targets through chemical or chemo-electric neurotransmission using neurotransmitters stored in axon terminal vesicles.

Neuron Types

• Dendritic arbor refers to the branched dendrite structure of a neuron, increasing surface area for synaptic connections.
• Neurites are projections from the cell body including axons and dendrites.
• Bipolar neurons have the cell body between the dendrites and axon terminals, often serving as sensory receptors.
• Multipolar neurons have one axon originating from the cell body and multiple dendritic projections.
• Pseudounipolar neurons have a single process that bifurcates into a peripheral branch receiving sensory input and a central branch transmitting sensory information to the CNS.

Neuron Functions

• Projection neurons have long axons and are usually excitatory in the CNS.
• Interneurons have shorter axons and can be excitatory or inhibitory (usually inhibitory) in the CNS.

Synapse Types

• Axo-somatic synapses are between axon terminals and the soma of the postsynaptic neuron, strongly influencing the postsynaptic neuron's ability to fire.
• Axo-dendritic synapses are located on dendrites.
• Axo-axonic synapses are between axon terminals of the presynaptic neuron and the axon terminal/hillock of the postsynaptic neuron, modulating the release of neurotransmitters.

Test your knowledge on the structure of neurons with this quiz. It covers key components such as axon hillock, myelin sheath, and synapse, along with their functions. Perfect for students studying neuroscience or biology.