Neurotransmission Flashcards
explain continuous conduction
- AP propagation in unmyelinated axons
- AP’s start at one spot on a membrane but can propagate by stimulating adjacent regions
- one AP stimulates another beside it
- AP’s spread in ONE direction only (because of absolute refractory period)
types of propigation
- Continuous Conduction (unmyelinated axons)
- Saltatory Conduction (myelinated axons)
what is propigation?
spreading of action potentials along the length of the axon
movement of positive ions into the axon is called
local current
why do unmyelinated APs only travel in one direction?
refractory period prevents it from moving back (can’t restimulate that portion of the membrane)
explain saltatory conduction
- AP propagation in myelinated axons
- AP conducted from one node of Ranvier to another
- local current flows between nodes of Ranvier
- voltage gated Na+ channels concentrated at the nodes
- flow of AP much faster because of “leaping effect”
factors that effect propagation speed
- Axon diameter
- more surface area, more voltage gated Na+ channels, faster local current - Amount of myelination
- heavy myelination > light myelination - Temperature
- AP propagate more slowly when cool
3 main types of nerve fibres
- Type A
- large diameter
- myelinated
- 15-120 m/s
- motor neurons supplying skeletal muscle and sensory neurons - Type B
- medium diameter
- lightly myelinated
- 3-15 m/s
- part of ANS - Type C
- small diameter
- unmyelinated
- 2 m/s or less
- part of ANS
what are the 2 types of synapses? describe them
- Electrical
- not found in neurons, only in cardiac and smooth muscle
- junction between two cells
- important for coordinated contractions
- GAP JUNCTION: space between plasma membranes of attached cells
CONNEXONS: cells that connect one cells cytosol to the attach cell’s
- divert local currents to trigger neighbouring cell - Chemical (used in neurons)
- no direct transfer of AP
- NEUROTRANSMITTERS relay info
- presynaptic terminals produce, store and release neurotransmitters from synaptic vesicles
name for cell membrane closely asscociated with presynaptic terminal
post synaptic membrane
name for end of an axon
synaptic end bulb or presynaptic terminal
space between the post synaptic cell membrane and the axon
synaptic cleft
chemical synapse process
- Action potential arrives at presynaptic terminal, voltage gated Ca2+ gates open
- Ca2+ diffuses into the cell, stimulates EXOCYTOSIS of synaptic vesicles. NTs released.
- NTs diffuse across synaptic cleft
- NTs bind to receptor sites and cause ligand gated Na+ channels to open
- Na+ diffused into cell and causes depolarization
if following tissue reaches threshold, AP produces
structure that stores neurotransmitters
synaptic vessicle
3 ways to remove neurotransmitters from synaptic cleft
- Diffusion
- NTs will move down concentration gradient - Enzymatic degradation
- enzymes break down NTs and resulting parts are recycled to be used again as NTs - Uptake by neurons or glial cells
- via NEUROTRANSMITTER TRANSPORTERS that take it back into presynaptic terminal
