Flashcards in Nervous System Physiology Part Two Deck (19):
What are glial cells made up of?
Mostly lipids, so they do not conduct and electrical charge and provide insulation for the electrical current.
What are the Nodes of Ranvier?
The open membrane of the axon between two glial cells, they produce salutatory conduction. Ensures that the signal moves in a few jumps from the hillock to the terminal, speeding up the action potential.
Where are the sodium channels located on the axon?
On the Nodes of Ranvier.
Do (most) invertebrates have myelinated axons?
No, most invertebrates have non-myelinated axons and therefore experience continuous conduction and have much slower conduction than vertebrates. The conduction velocity will increase with axon diameter because the electrical current encounters less resistance.
How does the Signal Travel to an Effector Cell?
Via synaptic transmission, the axon terminals form synapses with the dendrites of another neuron.
What are the two types of synaptic transmission?
1. Electrical (ions flow from cell to cell, uses electrical current, found in cardiac muscles and some invertebrate neurons)
2. Chemical (neurotransmitters, this is the majority of neurons' transmission choice)
How does an Electrical Synapse work?
Axon terminal → gap junctions → postsynaptic cell membrane. There is a continuous connection through the gap junction, so ions can travel continuously between the cells. Very fast.
How does a Chemical Synapse work?
The neurotransmitters are enclosed in vesicles and travel across the synaptic cleft. The Neurotransmitters are released by exocytosis and bind to postsynaptic receptors with ligated ion channels (chemically gated, not voltage gated). The neurotransmitter gets reabsorbed into the presynaptic cell.
How many classes of neurotransmitters are there?
What is Acetylcholine?
Choline derived, it will depolarize the postsynaptic membrane. It's excitatory to skeletal muscles and is found in the CNS, PNS, and vertebrate neuromuscular junction. It stimulates skeletal muscle conraction.
What is GABA?
Gamma aminobutric acid, causes repolarization in the postsynaptic membrane. It's inhibitory and found in the CNS and invertebrate neuromuscular junctions.
What does Acetylcholine act via?
For stimulating skeletal muscle contraction: A nicotinic receptor, a chemical-gated sodium channel, allows sodium currents to move in (depolarization).
For inhibiting cardiac muscle contraction: A muscarinic receptor, causes repolarization.
What are the two classes of receptor proteins?
1. Ionotropic Receptor (e.g. nicotinic receptor)
2. Metabotropic Receptor
What is an Ionotropic Receptor?
A chemically/ligand gated ion channel. Response of the post-synaptic cell depends on ion. Has different subunits, each of the subunits can bind to a natural and foreign compound.
What is the Nicotinic Receptor?
A sodium channel, acetylcholine stimulates by depolarization.
What is the GABA receptor?
A chlorine channel, GABA inhibits by hyperpolarization.
What is a Metabotropic Receptor?
It requires a signalling cascade, linked indirectly with an ion channel. Does not trigger the ion channel directly when bonded with the neurotransmitter, instead triggers a signally cascade witch will phosphatize. Example: muscarinic receptor.
What does a sodium channel cause?
It lets the sodium flow inward and causes a depolarizing or excitatory post-synaptic potential.