Chedy - theme 7 Flashcards
Synapse:
Junction where a nerve terminal meets a neuron, muscle cell, or gland.
Three types of synapses:
Electrical, chemical, neuromuscular***
Electrical synapse:
Pre/postsynaptic membranes are connected by channels (gap junctions) that pass electrical current. Voltage changes in the presynaptic cell induce voltage changes in post.
Chemical synapses:
Neurotransmitters. Endogenous agents transmit signals from a neuron to a target cell across a synapse where they bind with receptors on the postsynaptic membrane. Synthesized from simple precursors. Packaged in vesicles that release their contents upon an action potential. May also follow electrical gradients into the synaptic cleft.
ACh:
A small polyatomic cation ester of acetic acid and choline. ACh is the only neurotransmitter in the motor division of the somatic nervous system. Excitatory in skeletal muscle; inhibitory in cardiac tissue.
Mechanism of ACh in neuromuscular system:
Binds to nicotinic ACh receptor (nAChR), a receptor located on muscle fiber membranes. Depolarizes the fiber, causing a cascade that results in muscle contraction.
How contraction is propagated along muscles:
God this is fucking complicated
Action potential reaches the end of a motor neuron. Voltage-dependent calcium channels open, allowing calcium to enter the neuron. Calcium tells vesicles to release Ntransmitters by exocytosis. ACh binding to receptors opens nonspecific cation channels, leading to lots of Na+ coming into the cell and a little K+ moving out, producing current. The current opens adjacent voltage-gated Na+ channels. Na+ comes in and initiates an action potential (if it reaches the necessary level). ACh is eventually destroyed by ACh-esterase on the endplate membrane, terminating the muscle’s response.
The principal Ntransmitter in all autonomic ganglia is:
ACh. ACh is the only Ntransmitter that matters. All hail ACh.
