OP - 6+7+8 Flashcards
What are the types of cells of the nervous system? Both CNS and PNS
Neurons
Nuroglia:
–>CNS:
- oligodendrocytes (form myelin sheath around axons)
- microglia (removes cell debris, waste, pathogens)
- astrocytes (form blood brain barrier)
- ependymal cells (assist in producing and circulating cerebrospinal fluid
–>PNS:
- schwann cells (form myelin sheath)
- satellite cells (surround neuron cell bodies in ganglia)
What are interneurons?
Multipolar neurons located entirely within the CNS G
Ganglion
Grouping of neuron cell bodies outside the CNS
Nucleus
Grouping of neuron cell bodies within the CNS
Tract
Grouping of axons that interconnect regions of the CNS
Why cant ppl with parkinsons be treated with dopamine - what do they have to be treated with instead?
Because the blood-brain barrier has capillaires with very tight junctions that prevent the flow of many substances
Have to be treated with a dopamine precursor called L-dopa
What maintains resting memb potential and how?
The Na/K pump
Pumps 3 Na out for every 2 K pumped in
thus Na conc. in ECF > than K
and K in ICF > than Na
**all cells have resting memb potential - only some excitable
does the amplitude and frequency of APs change?
Not amplitutde
only frequency
Why does K+ leave the cell slowly (from ICF–>ECF) and why does Na move in rapidly?
Higher K+ in the ICF than the ECF thus due to conc gradient it moves out
However the inside of the cell is -ve and since K+ is positive there is attraction between the two
But effect of conc gradient is larger acc. to Nernst equation
Higher Na+ in the ECF than the ICF thus Na+ moves into cell
Inside is -ve thus attracts Na+ into the cell
Thus strong pull on Na+ to move into the cell
What does the Nernst equation let us calculate?
It allows us to calculate the equilibrium potential for an ion – which is the membrane potential at which there is no net flux/change in the conc. of ions in the ECF and the ICF
what is potential difference and current +units
Potential diff is the diff in charge between two point (V, mV)
Current is the movement of charge (ions) (A, pA)
axon hillock?
Generation and propagation of an AP
- In resiting condition - sodium voltage gated channels on the membrane are closed
- A release of some neurotransmitters or other substances due to a stimulus can cause binding to receptors on the membrane of the dendrites and cause the receptors to open
- Since sodium is high in the ECF, sodium moves in thru these receptor channels
- The entry of Na raises the membrane potential – these are known as graded potentials
- HYPOPOLARIZATION: When there are a sufficient amount of graded potentials IN THE AXON HILLOCK for the membrane to reach its threshold potential, the voltage gated Na channels on the cell memb. open and an AP can be generated in the AXON as follows:
- DEPOLARISATION: Once threshold is reached the neuron depolarises
– causes opening of Na+ voltage gated channels
– leads to a rapid influx of sodium into the cell membrane
– Resulting in the membrane potential becoming more positive until it reaches overshoot phase of extreme positivity.
—- Na channels close 1msec later during refractory period
-REPOLARISATION: K+ channels open after overshoot phase
– Results in K+ from the ICF moving into ECF (K+ conc. is higher in ICF)
– results in the membrane potential becoming more negative
– K+ channels open at +30mV and close soon after RMP is re-established
HYPERPOLARISATION: Repolarisation leads to this - memb. potential more -ve than resting memb. potential
– K+ leak channels allow for resting memb. potential value to go back up to -70mV.
When do the diff channels involved open and close
Na channels:
- Open when threshold pot. reached
- clsoe 1 msec later during refractory period once depolarisation is over
K channels:
- Open during repolaristaion after depolarisation is complete at +30mV
- After hyperpolarisation
- K+ leak channels help establish RMP
Absolute and relative refractory periods
Absolute:
- No new action potential can be generated during this period
- Extends from the entire depolarisation phase (as all Na+ channels are open thus max. inflow is already occurring - no Na+ channels free to generate a new AP) and during part (2/3rds) of the repolarization phase (Na+ channels are completely closed)
Relative refractory period:
- A new action potential can be generated only if the new stimulus is stronger than the previous one (during period after hyperpolarisation)
