Fundamentals of the nervous system and nervous tissue (2) Flashcards
Week 4
What is meant by the depolarisation of the membrane?
*The membrane potential moves toward 0mV, the inside becoming less negative (more positive)
What is meant by hyperpolarisation?
The membrane potential becomes more negative
What are the steps of the propagation of an action potential? (4)
- Resting state
- Initiation ( a region of depolarisation)
3.Propagation (The action potential propagation moves steadily along, leaving the membrane behind it in a refractory state) - Prop continuation( The site in a refractory site now returns to its resting state, next site which was a region of depolarisation is now in its refractory state AKA moves along)
Describe saltatory conduction
Action potential, when reaching the axon tail, jumps between the nodes of ranvier as the myelin sheath produces saltory conduction.
What are all action potentials independent of ?
*The stimulus intensity, meaning that all action potentials are alike.
How does CNS tell the difference between a weak stimulus and a strong one?
By the number of impulses (Action potentials) received per second (frequency)
What is a refractory period and when does this happen?
*Time in which neuron cannot trigger another AP
*Happens when the voltage-gated Na+ channels are open, so neuron cannot respond to another stimulus.
What are the two types of refractory periods?
*Absolute and relative
What is the absolute refractory period and what does it enforce?
*The time from opening of Na+ channels until resettling of the channels
*Enforced one way transmission of nerve impulses
when and what happens during the relative refractory period?(3)
*Follows the absolute refractory period
1.Moat Na+ channels have returned to their resting state
2.Some K+ channels still open
3.Repolarization is occurring
(Only very strong stimulus could stimulate an AP)
How are neurons connected to other neurons and effector cells?
*Synapses (junctions that mediate information transfer0
What is a presynaptic neuron?
A neuron that conducts impulses towards the synapse (send information)
What is a postsynaptic neuron?
A neuron that transmits electrical signal away from the synapse (receives information)
Three types of synapse (in terms of place on axon? (3 A’s)
- Axosomatic
- Axodendritic
- Axoaxonal
Two main types of synapses?
Chemical and Electrical
What are chemical synapses specialised for?
The release and reception of chemical neurotransmitters
What are the two parts that make up the chemical synapses?
- Axon terminal of presynaptic neuron: contains synaptic vesicles filled with neurotransmitter.
- Receptor region on postsynaptic neuron’s membrane: receives neurotransmitter
Where is the receptor region normally found?
Usually on dendrite or cell body
What is the axon terminal and receptor region separated by?
The synaptic cleft
What does the transmission across synaptic cleft depend on? (3) and what does it ensure?
1.The release, diffusion, and receptor binding of neurotransmitters
2. Unidirectional communication between neurons
Step undertaken when an AP reaches the axon terminal at the presynaptic neuron. (6)
- AP arrives at axon terminal
- Voltage gated Ca2+ channels open and Ca2+ enters the axon terminal
- Ca2+ entry causes synaptic vesicles to release neurotransmitters by exocytosis (at the membrane of the presynaptic neuron)
- Neurotransmitters diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic membrane
- Binding of neurotransmitter opens ion channels, resulting in graded potentials
- Neurotransmitter effects are terminated by re-uptake through transport proteins, enzymatic degradation of diffusion away from the synapse
What are the two types of
postsynaptic potentials?
- EPSP: excitatory post synaptic potentials
- IPSP: inibitory postsynaptic potentials
What is an EPSP?
- Excitatory postsynaptic potential
-A local depolarisation of the postsynaptic membrane
What is an IPSP?
- Inhibitory postsynaptic potential
-A local hyperpolarisation of the postsynaptic membrane
What does an EPSP do and what occurs during it?
- Brings the neuron closer to AP threshold
- Neurotransmitter binding opens chemically gated ion channels, allowing Na+ and K+ to pass simultaneously
What does an IPSP do and what occurs during it?
- Drives the neuron away from the AP threshold
- Neurotransmitter binding opens chemically gated ion channels permeable to either K+ or Cl-
How is another AP induced (inc EPSP/IPSP)
EPSP/IPSPs can summate (add together) to influence the postsynaptic neuron
What are the two types of summations?
1.Temporal
2.Spatial
What is temporal summation and what happens during it?
- When one or more presynaptic neurons transmit impulses in rapid-fire order
- First impulse produces EPSP, and before it can dissipate another EPSP is triggeres, adding on top of the first one
What is Spatial summation and what happens during it?
- The postsynaptic neuron is stimulated by a large number of terminals simultaneously
- Many receptors are activated, each producing EPSPs which can then add together
What does no summation look like on a graph?
- Two peaks
- 2 stimuli separated in time cause EPSPs that do not add together
What does temporal summation look like on a graph?
- 1 small peak then second highest peak
- 2 excitatory stimuli close in time cause EPSPs that add together (E1 then E1)
What does spatial summation look like on a graph?
- 1 small slope then high peak reached
- 2 simultaneous stimuli at different locations cause EPSPs that add together (E1 +E2)
Location of the graded potential and the action potential on a neuron.
- Cell body and dendrites typically
- Axon hillock and axon
Distance travelled for graded potential and action potential
- Short distance (within cell body axon hillock 0.1-1 mm)
- Long distance ( from trigger zone at axon hillock through entire length of axon, few mm to over a m)
What is spectrophotometry
and what does it show?
- A technique that uses light absorption to measure the concentration of an analyte in solution
- The amount of light absorbed by a solution is related to the analyte concentration
