Lecture Exam 4 Flashcards
(9 cards)
How does action potential propagate in unmyelinated axons?
In unmyelinated axons, the action potential travels by continuous conduction, where every segment of the axon membrane sequentially depolarizes as the action potential moves down the axon. This method is slower because each part of the membrane needs to be activated in turn.
How does action potential propagate in myelinated axons?
In myelinated axons, action potentials conduct through saltatory conduction, where the action potential ‘jumps’ from one node of Ranvier to the next. The myelin sheath acts as an insulator, speeding up transmission.
What happens when the action potential reaches the axon terminal?
The arrival of the action potential at the axon terminal causes the membrane to depolarize, opening voltage-gated calcium (Ca²⁺) channels.
What triggers the release of neurotransmitters at the axon terminal?
The influx of Ca²⁺ into the axon terminal triggers the release of neurotransmitters stored in synaptic vesicles.
What occurs during exocytosis of neurotransmitters?
Synaptic vesicles fuse with the membrane of the axon terminal, releasing neurotransmitters into the synaptic cleft.
What happens to neurotransmitters after they are released?
Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynaptic cell, affecting it based on the type of cell.
What are the effects of neurotransmitter binding in different cell types?
In a muscle cell, it triggers contraction; in a gland cell, it may lead to secretion; in another neuron, it causes a graded potential, which could be excitatory or inhibitory.
How is the signal terminated in synaptic transmission?
Neurotransmitters are removed through enzymatic degradation, reuptake by the presynaptic neuron or glial cells, or diffusion away from the synapse.
Why is the termination of neurotransmitters important?
It ensures that the postsynaptic cell is only influenced by the presynaptic cell as long as neurotransmitters are present in the synaptic cleft, providing precise control over signal transmission.
