BMS1052 Lecture Notes - Lecture 5: Resting Potential, Saltatory Conduction, Demyelinating Disease

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Week 2- Lecture 5 -Synaptic transmission (& integration)
Learning objectives
Describe the structure and function of electrical synapses
Describe the structure of chemical synapses
Identify ways in which chemical synapses can be classified
Describe the steps through which a chemical synapse ultimately leads to changes in
the membrane potential of the post-synaptic neuron
Electrical and chemical synapses
Myelination and saltatory conduction
Nodes spaced by 0.2-2 mm.
AP jump from node to node: diffusion acts quickly over short distances within the axon.
Separation of nodes is limited by diffusion distance. If they were separated by too much,
the ao erae potetial o’t get past NaV threshold.
Saltatory (Latin to leap) conduction is faster jumps. (ions jump from one permeable
myelinated thig to the other) gaps etee ust ot e too large or ios a’t jup.
Multiple sclerosis demyelinating disease. Early symptoms problems with vision and
peripheral control dependent on precisely timed signals in sensory and motor nerves.
Remember the myelinating glia?
Oligodendrocytes and Schwann cells wrap axons in myelin.
The fatty myelin sheathes are insulating they prevent ions crossing the membrane.
Ion channels are concentrated in the Nodes of Ranvier.
Role of Na/K-ATPase: maintaining the resting membrane potential (and the concentration
gradient) no role during action potential, but it helps to reset na and k conc after action
potential
The sodium-potassium pump actively transports Na and K across the membrane
Powered by ATP (the pump is an enzyme converting ATP to ADP)
Pushes Na+ out of the cell (against its concentration gradient)
Pushes K+ into the cell (against its concentration gradient)
2 types of synapses- electrical, chemical
Electrical synapses direct electrical coupling between cytosol of two neurons gap
junctions
Chemical synapses electrical signals are converted into a chemical signal
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The molecular structure of gap junctions (electrical synapses). Gap junction is a large, non
selective channel allows any molecules and ions to pass through.
Gap junction 6 connexin subunits,
form a connexon in each cell membrane.
Non-selective channel ions, small molecules.
They are bidirectional
Not good for computations
Good for occasions where you need precise synchronisation of multiple neurons
commonly found in motor system of vertebrates
Classifying the types of chemical synapses
Chemical synapses:
slow but computationally powerful connections bigger than electrical
Basic properties:
- pre- and postsynaptic (dendrite) membranes are separated by a cleft 20-50 nm wide.
- Presynaptic element contains neurotransmitter-filled vesicles (50 nm)
- Some neurons also contain larger vesicles called secretory granules (100 nm)
- Presapti atie zoes - location of specialised proteins that bind vesicles,
releasing neurotransmitter
Different ways of classifying chemical synapses axon location
a) Axo-dendritic most common type can be on dendrite spines or shaft
b) Axo-somatic commonly inhibitory
c) Axo-axonic can modulate a signal before transmission
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Document Summary

Week 2- lecture 5 -synaptic transmission (& integration) Describe the structure and function of electrical synapses. Identify ways in which chemical synapses can be classified. Describe the steps through which a chemical synapse ultimately leads to changes in the membrane potential of the post-synaptic neuron. Ap jump from node to node: diffusion acts quickly over short distances within the axon. Separation of nodes is limited by diffusion distance. If they were separated by too much, the(cid:374) a(cid:454)o(cid:374) (cid:373)e(cid:373)(cid:271)ra(cid:374)e pote(cid:374)tial (cid:449)o(cid:374)"t get past nav threshold. Saltatory (latin to leap) conduction is faster jumps. (ions jump from one permeable myelinated thi(cid:374)g to the other) gaps (cid:271)et(cid:449)ee(cid:374) (cid:373)ust (cid:374)ot (cid:271)e too large or io(cid:374)s (cid:272)a(cid:374)"t ju(cid:373)p. Early symptoms problems with vision and peripheral control dependent on precisely timed signals in sensory and motor nerves. Oligodendrocytes and schwann cells wrap axons in myelin. The fatty myelin sheathes are insulating they prevent ions crossing the membrane. Ion channels are concentrated in the nodes of ranvier.

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