Potentials Flashcards
What are the 2 ways in which hyper-polarisation can occur?
Fast/slow EPSP : Ionotropic - opening Cl- channels so it flows in. Metabotropic - opening K+ channels so more flows out
What is hyperpolarisation?
Cell charge becomes negative - lower than -70mV
What is depolarisation?
Cell charge becomes more positive - higher than -70mV. -55mV is threshold.
What are the 2 ways in which depolarisation can occur?
Fast/slow IPSP : Ionotropic - allow Na+ in rapidly. Metabotropic - close leaky K+ channel so slowly depolarises
What does IPSP and EPSP refer to?
Inhibitory/Excitatory post synaptic potential
What is a generator potential?
Graded potential that is generated by any sense - touch, heat
What is the ionic basis of graded potentials?
Ions must flow in/out the cell for a graded potential to occur. This includes Na+, K+ and Cl-. These can cause depolarisation or hyperpolarisation
What does summate mean in regards to graded potentials?
2 or more graded potentials can ‘add together’ to form a larger graded potential, which could reach threshold, or to inhibit an action potential by decreasing the depolarisation.
What are 3 examples of graded potentials?
Sensory receptors (generator potential), postsynaptic potential and end-plate potential
Describe synaptic integration
Multiple synapses of different forms - excitatory and inhibitory - interacting with one another to depolarise or hyper polarise an axon hillock. Can be axo-dendritic synapse, axo-somatic synapse or axo-axonic synapse
Explain the difference between axo-dendritic, axo-somatic and axo-axonic synapses
Axo-dendritic - directly on dendrite, excitatory.
Axo-somatic - directly on soma - inhibitory.
Axo-axonix - synapses onto pre-synaptic terminal of axo-dendritic synapse - inhibits it
Explain the ionic basis of an action potential (to increase)
Threshold (55mV) reached, voltage-gated Na+ channels open and it rushes into cell, taking cell to +40mV.
Explain how a cell returns after an action potential
From 40mV, voltage gates Na+ channels close and voltage gated K+ channels open, exiting. This takes cell towards -90mV (K+ equilibrium potential) and channel stays open for long time. Cell is hyper polarised but slowly returns to rest
How can an action potential be sped up?
Myelination or Larger axon diameter
What are some consequences of demyelination?
Multiple sclerosis in CNS - slower impulses
What does the term ‘self propagating’ refer to in regards to an action potential?
Each section passes the impulse forward, depolarising along the axon with the same strength
What does the term ‘refractory period’ refer to?
The period after an action potential when another action potential cannot be triggered, as the cell is in a state of hyperpolarisation
What does ‘decremental’ mean in regards to graded potentials?
The potential decreases as it moves along the membrane - if threshold isn’t met
What does ‘graded’ mean in regards to graded potentials?
A larger stimulus will lead to a larger graded potential and more depolarising. Very large stimulus can reach threshold
Which type of neuron will have the highest velocity vs lowest?
Myelinated with large diameter = fastest velocity, e.g. motor neurone.
Un-myelinated with small diameter = slowest velocity
What is the neuromuscular junction?
Where a pre-synaptic motor neutron, synaptic cleft and post-synaptic plate/end plate meet
Explain the whole formation of an action potential at a neuromuscular junction
Motor neuron has action potential. Na+ flows to pre-syn terminal, causing voltage-gates Ca2+ channels to open. Ca2+ releases proteins causing vesicle exocytosis of ACh. Diffuses across syn-cleft and some binds to ACh inotropic receptor. Now open so anything with 1+ can flow in. Na+ rushes in, so post synaptic plate reached threshold, opening voltage gated Na+ channels, causing action potential at end plate. Remaining ACh broken down by ACh-esterase
What are the 2 types of synaptic connectivity and what are the benefits?
Divergence allows one neutron to synapse multiple muscle fibres. Convergence means one cell can be influenced by many others, e.g. several rods converging to one axon in the retina
Monosynaptic vs Polysynaptic pathways?
Monosynaptic has one synapse - e.g. sensory - motor. Polysnaptic has +1, e.g. sensory - interneuron - interneuron - motor (3 synapses)
How many neurotransmitters are present in the neuromuscular junction?
Only 1 - Acetylcholine
What is the process of synaptic transmission in the CNS?
Same as neuromuscular junction, but more complex as there are different pathways, no. of synapses and many different neurotransmitters.
Which 5 types of molecules are CNS neurotransmitters?
Amines, amino acids, peptides, purines, gasses
Spatial vs Temporal summation?
Temporal is one neuron summating into another. Spatial is multiple neurons summating into another
