PoH: How Nerves Work Flashcards
Which part of a neurone receives information?
Dendrite
Which part of a neurone triggers the action potential?
The initial segment/Axon hillock
Which part of a neurone contains the nucleus
Cell body/Soma
Which part of a neurone sends action potentials?
Axon
Which part of a neurone releases neurotransmitter?
The axon’s presynaptic terminals
Where is a motor/efferent neurone’s cell body?
Ventral horn of spinal cord
What type of neurone can have a bipolar of pseudounipolar shape?
Afferent/sensory
What type of neurone can have a multipolar or anaxonic shape?
Interneurone
What type of neurone can have a multipolar (but not anaxoniac) shape?
Efferent/motor neurone
What do sensory/afferent neurones do?
Detect a stimulus and send a signal to the CNS
What 3 things could a motor/efferent neurones target?
A muscle, gland or neurone
What is an action potential?
Transmitting a signal over a long distance
What is a graded potential
Deciding whether an action potential should be fired
Define resting membrane potential
It keeps cell ready to respond. Most cells have a RMP where the inside is negative relative to the outside – determined by the size of the initial concentration gradient
What causes RMP?
Leaky K+ channels in most neurones
Leaky K+, Na+ and Cl- channels in most other cells
Provide a value for RMP in most neurones, and a value for most other cells
-70 mV in neurones (due to leaky K+ channels)
-90 mV in other cells (due to leaky K+, Na+ and Cl- channels)
Can graded potentials summate?
Yes
Can action potentials summate?
No
Do graded potentials have a threshold?
No
Do action potentials have a threshold?
Yes
What channels mediate graded potentials?
Ligand-gated channels
What channels mediate action potentials?
Voltage-gated channels
Do graded potentials have various or fixed amplitude?
Various
Do action potentials have various or fixed amplitude?
Fixed
Do graded potentials decay as they travel?
Yes
Do action potentials decay as they travel?
No - they’re self propogating
Where are action potentials evoked?
At the initial segment
Do graded potentials have a refractory period?
No
Do action potentials have a refractory period?
Yes
When is equilibrium reached for leaky K+ channels?
When the gradient is equal and opposite to the concentration gradient
Define electrogenic and explain how it relates to RMP
It makes the inside of the cell slightly negative
It relates to RMP due to the sodium-potassium pump where 3 Na+ is exchanged for 2 K+. The inequal amount leads to the inside of the cell being negative
What does the Nernst Equation tell us?
The equilibrium potential is the membrane potential at which the electrical gradient is equal and opposite to the concentration gradient
What does the Goldman-Hodgkin-Katz Equation let us predict?
The equilibrium potential generated by several ions
Do the following refer to graded or action potentials: Decremental, summate, depolarising/hyperpolarising
Graded
What is Excitatory Post Synaptic Potential (EPSP)?
It makes it more likely to generate an action potential
What receptors do fast ESPS use and what’s their mechanism?
Ionotrophic receptors - they depolarise a neurone’s membrane, making it more likely to fire an action potential
What receptors do slow EPSPs use and what’s their mechanism?
Metabotrophic receptors - they close leaky K+ channels, so only the sodium-potassium pump leads to change
What are Inhibitory Post-Synaptic Potentials?
They make it less likely to generate an action potential
What receptors do fast IPSPs use and what’s their mechanism?
Ionotrophic receptors - hyperpolarise neurone’s membrane, making it less likely to fire an action potential
What receptors do slow IPSPs use and what’s their mechanism?
Metabotrophic receptors - open leaky K+ channels so only sodium-potassium pump leads to change
Do ionotrophic receptors provide fast or slow EPSP/IPSPs?
Fast
Do metabotrophic receptors lead to fast or slow EPSP/IPSP?
Slow
Explain synaptic integration
Each neuron has 100s of excitatory and inhibitory synapses, evoking fast/slow EPSPs/IPSPs, each one is only a few mV high. Adding them together pushes the cell to threshold and fires an action potential or keeps cell away from threshold and tells it to shut up. The concept of synaptic integration is the summation of the synaptic inputs to decide if the initial segment will reach threshold.
What 3 types of synapses can be found on a neurone’s dendrites?
Axo-dendritic synapse
Axo-somatic synapse
Axo-axonic synapse
Name 2 types of summation
Temporal summation and spatial summation
Name the 5 types of nerve fibres
Aa, aB, Ay, Ad, C
What 2 features of neurones can speed up an action potential?
Large axons and myelination
What type of nerve fibre is useful for proprioception and motor neurones?
Aa/Largest myelinated - it’s got the fastest velocity
What type of nerve fibre is useful for pressure and touch?
AB/Large myelinated
What type of nerve fibre is useful for warmth and slow pain?
C/Unmyelinated - it’s got the slowest velocity
Name two types of demyelinating disease
MS (in CNS) and Guillain-Barre syndrome (in PNS)
What effect do demyelinating diseases have on neurones?
They attack the myelin sheath, leading to:
Decreased membrane resistance (more current leaks out)
Increased membrane capacitance (more current wasted charging up the membrane)
Define end plate potential
The voltage which causes depolarisation of muscle fibres, caused by neurotransmitters binding to the postsynaptic membrane in the neuromuscular junction
Is neuromuscular transmission graded?
No
What are post junctional folds at the NMJ?
Increase the number of voltage-gated Na+ channels
What diffuses across the synaptic cleft?
ACh
Name the type of channel and ion that opens at the presynaptic terminal at the NMJ
Voltage-gated Ca2+ channel
What receptors does ACh bind to?
Nicotinic
What cleans up ACh at the NMJ?
Acetylcholinesterase
ACl is the only one acting at the NMJ. What receptors can it bind to?
Cholinergic, nicotinic and ionotrophic
Name 5 amine neurotransmitters
Adrenaline
Noradrenaline
Dopamine
Serotonin (5HT)
Histamine
Name 3 amino acid neurotransmitters and whether they’re excitatory or inhibitory
Glutamate - excitatory
GABA - inhibitory
Glycerine - inhibitory
Name 3 peptide neurotransmitters
Endorphins
Cholecystokinin
Substance P
Name 2 purine neurotransmitters
ATP
Adenosine
Name a gas acting as a neurotransmitter
Nitric oxide
What 5 types of neutotransmitters are there in the CNS?
Amines
Amino acids
Peptides
Purines
Gases
What type of receptor is a fast EPSP/IPSP?
Ionotrophic
What type of receptor is a slow EPSP/IPSP?
Metabotrophic
What 2 ways can a synapse connect to other synapses?
Divergence and convergence
Define feedback inhibition and explain its purpose
When an action potential is fired, a collateral branch activates an inhibitory interneuron. It releases inhibitory neurotransmitter, hyperpolarising the original neurone
It prevents repeat firing
What does a polysynaptic reflex have that a monosynaptic reflex doesn’t?
Interneurone(s)
Define synaptic plasticity
Changes in strength of synapses. It can be activity dependent
