6.5 Neurons and Synapses Flashcards
What are the sections of a neuron?
Dendrites
Axon
Soma
What is a soma?
Neuron cell body containing the nucleus, organelles, where essential metabolic process occur to maintain cell survival
What may surround the axon?
Myelin sheath
Define resting potential
The difference in charge across the membrane when a neuron is not firing
Usually, the inside of the neuron is more negative than the outside (approximately –70 mV)
How is resting potential maintained?
Actively controlled by the sodium potassium pumps
3 Na+ expelled and 2K+ admitted (some of which will leak back out)
Creates an electrochemical gradient where the interior is relatively more negative
Define active potential
Rapid changes in charge across the membrane that occur when a neuron is firing
What are the three stages of action potential?
Depolarisation
Repolarisation
Refractory period
What occurs during depolarisation?
In response to a signal from the dendrite Na+ channels open causing an influx and causing membrane potential to become positive
What occurs during repolarisation?
The potassium channels open causing a passive efflux of potassium causing cell potential to become negative again
What occurs during the refractory period?
Resting potential is actively restored so the neuron can fire again
How does a nerve impulse travel down an axon?
Channels in the axon are voltage gated so depolarisation happens in segments down the axon
What is the threshold potential?
The minimum level needed to open voltage gated ion channels (~-55mV_
What will a stronger electrical signal cause in nerve impulses?
Assuming the threshold limit was reached on each occasion, a stronger impulse does not change the electrical signal generated
What does an oscilloscope measure?
Membrane potential over time
What is the advantage of myelination?
Improves the speed of electrical transmission
What is the disadvantage of myelination?
Takes up significant space
What is the difference between grey and white matter?
Grey matter does not have myelination
Describe the chemical transfer across a synaptic gap
AP reaches the axon terminal triggering Ca2+ channels to open
Ca2+ diffuses in and promotes neurotransmitter containing vesicles to bind with the cell membrane (exocytosis)
Neurotransmitters bind to receptors in the post synaptic membrane and open ligand-gated channels
This generates an electrical impulse in the post synaptic neuron
What happens to neurotransmitter released in the synapse?
Either recycled or degraded
What is a graded potential?
Changes in membrane potential that vary in size
What are the two types of neurotransmitter?
Excitatory
Inhibitory
What do excitatory neurons cause?
Opening ligand-gated Na+ or Ca2+ channels (depolarisation)
What do inhibitory neurons cause?
Opening ligand-gated K+ or Cl- channels (hyperpolarisation)
Which cells produce Myelin?
Glial cells
Schwann in the PNS
Oligodendrocytes in the CNS
Via which mechanism do myelin sheaths increase speed of electrical transmission?
Saltatory conduction
What are the nodes of Ranvier
The gaps between myelin sheaths
