Flashcards in NEURONS Deck (92)
what is an action potential?
it is the way in which a neuron transports electrical signals
they are a brief change in voltage across the membrane
what is the voltage of a resting potential?
generally -50 to -75mV
which ions are found in a higher concentration inside the neuron axon during resting potential?
which ions are found in a higher concentration outside the neuron axon during resting potential?
Na+ and Cl-
what is the permeability of axon membrane to ions like during resting potential?
K+ moves OUT
Na+ and Cl- move IN
how is the resting potential of an axon maintained?
by Na+/K+ ATPase transporters
ions travel by active transport - requires ATP
expels 3 Na+ and allows 2K+ in
what is the movement of ions during resting potential?
3 Na+ out
2 K+ in
where do action potentials start in a neuron?
in the axon hillock due to depolarisation
what are the stages of an action potential?
what happens during depolarisation?
voltage gated Na+ channels
Na+ enters cells
charge inside axon increases
once threshold potential is reached, lots of Na+ gated channels open - rapid influx of Na+ until +30mV
what is the "all or nothing" response in action potentials?
the threshold potential must be reached for an action potential to occur
what happens during repolarisation?
Na+ voltage gated ion channels close
K+ slow voltage gated channels open and K+ diffuse out of axon
the charge inside decreases
what happens during hyperpolarisation?
repolarisation overshoots and the charge in the axon becomes to negative
this is rectified by leakage channels
K+ voltage gated channels close and the resting potential is restored?
what are the different types of refractory period?
absolute refractory period
relative refractory period
what is the absolute refractory period?
during the absolute refractory period another action potential cannot be generated under any circumstance
what is the relative refractory period?
during the relative refractory period another action potential can be fired if the stimulus is long enough
how are action potentials propagated along axons?
via local currents
these flow following depolarisation and allow depolarisation of adjacent axonal membranes
why can action potentials only travel in one direction?
due to the refractory period
what does propagation of action potentials depend on?
capicitance = ability to store charge - lower charge = greater distance travelled (myelin decreases capicitance)
resistance = number of ion channels open - less channels open = greater distance travelled
what factors affect the speed of action potential propagation?
myelination - myelination increases propagation speed
axon diameter - greater diameter increases propagation speed
what is multiple sclerosis?
- most common disease of nervous system amongst young people
- may be autoimmune
- it is the degeneration of myelin and development of scar tissue - this disrupts and eventually blocks neurotransmission along myelinated axons
what are the symptoms of multiple sclerosis?
- uncontrolled eye movement
- slurred speech
- partial/complete paralysis
- tremor and loss of coordination
- weakness and sensory numbness
how can myelin be viewed histologically?
by staining with osmium
white matter turns black
what is myelin?
- lipid-rich substance surrounding axons
- 70% lipid and 30% protein
- it insulates axons
- are found in schwann cells and oligodendrocytes
- found in concentric circles
where are schwann cells found?
in the PNS
where are oligodendrocytes found?
in the CNS
how many axons can one schwann cell myelinate?
how many axons can one oligodendrocyte myelinate?
up to 50 axons
when does myelination occur?
- begins in utero during 3rd trimester
- progresses rapidly during infancy
- continues through adolescene