Introduction to Neurones, Nerve Conduction and Synaptic Transmission Flashcards
What are the 5 main morphological features of a neuron and what are each of their functions ?
- Dendrites - receive inputs from other neurones and convey graded electrical signals passively to the soma
- Soma - synthetic and metabolic centre. Contains the nucleus, ribosomes, mitochondria and ER. It Integrates incoming signals that are conducted passively to the axon hillock
- Axon hillock and initial segment: site of initiation of the ‘all or none’ AP
- Axon: conducts output signals as action potentials to other neurones (or other cells).
- Synapse: point of chemical (usually) communication between neurones (or other cells)
What are the 4 main types of neurons and how are they classified and where are they usually found ?
- Unipolar neuron - it only has one neurite, these are the neurons of the peripheral autonomic nervous system
- Pseudopolar neuron - it only has one neurite but this bifurcates, these are the dorsal root ganglion (DRG) neurons
- Bipolar neuron - has 2 neurites, these are the retinal neurons
- Multipolar neurons - has 3 or more neurites, these are the LMN’s
Describe how an AP is produced
Voltage gated sodium channels open causing an influx of Na+ into the neuron, this resulting in depolarisation of the neuron with threshold membrane potential met it results in AP produced (rapid influx of Na+ occurs here), Then K+ channels open and cause efflux of K+ into the neuron resulting in hyperpolarisation of the neuron back to the resting membrane potential
What is the value of the membrane potential for each of the following in a neuron:
- Resting membrane potential
- Threshold membrane potential
- Resting membrane potential = -70
- Threshold membrane potential = -60
What is the distance to which an AP spreads along an axon dependent on (as recall that nerve cell membranes are leaky allowing the amplitude of the AP to decrease as it travels)
The distance over which current spreads depends upon membrane resistance (rm) and the axial resistance of the axoplasm (ri) – increasing the ratio rm/ri increases the distance travelled (λ)
The membrane potential change in a passive neuronal process decays exponentially with distance. λ= length constant
Refer to the pic for this point, but essentially rm is the resistance keeping the AP energy from leaving the axon, and ri is the resistance which the AP experiences as it tries to propagate along the axon ==> a high rm and low ri will result in a longer distance travelled by the AP
How do you increase rm and decrease ri to allow an AP to travel further along the axon ?
- Decrease ri (possible by increasing axon diameter)
- Increase rm with myelin sheath produced by either oligodendrocytes or schwann cells
Conduction in myelinated axons is much faster than in nonmyelinated axons of the same diameter
What are the 2 ways in which a synapse can be classified functionally ?
- As an excitatory synapse
- As an inhibitory synapse
What is the main excitatory neurotransmitter in the CNS and how does it produce an excitatory response ?
Gultamate - activates postsynaptic glutamate receptors producing an excitatory (depolarizing) response called the excitatory postsynaptic potential (e.p.s.p)
What are the 2 main inhibitory neurotransmitters in the CNS ?
GABA and glycine - they activate postsynaptic GABAa or glycine receptors producing an inhibitory (hyperpolarizing) response called the inhibitory postsynaptic potential (i.p.s.p.)
What are pre and post synpatic membranes separated by ?
Synpatic cleft
Describe the idea of summation in terms of excitatory postsynpatic potentials (e.p.s.p) and inhibitory postsynpatic potentials (i.p.s.p)
Think essentially mutiple can act on a neuron and its whichever there is more of
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