L18 - nerve cells & excitability: resting memb potential Flashcards
what is a neurone?
- nerve cell
- most in CNS (brain + spinal cord)
- post mitotic cells (fully differentiated and unable to divide)
cell body of neurone
- aka soma
- cytoplasm
- nucleus
- mitochondria
- LACK OF CENTRIOLES (used in cell division)
dendrites
- branches on cell body
- send electrochemical signals to cell body + axon
axon
- transports A.P across from cell body to terminals
nerve fibre
- some axons are very long
- myelin sheath covers axons so A.P can jump from node to node to get past quicker
- saltatory conduction
- Schwann cells produce this lipid
- when axon is covered with this it is known as nerve fibre
how do nerve cells communicate with each other?
- through dendrites and axons
- to terminals
multipolar neurone
- one axon
- lots of dendrites
- most common
bipolar neurone
- 2 axons which come out from each side of cell body
unipolar neurone
cell body is extended off axon (cell bodies still in the middle)
anaxonic neurone
- no axon
afferent neurone
carries sensory information from the body’s periphery to the central nervous system (CNS)
efferent neurone
carries signals from the central nervous system (CNS) to muscles, glands, and organs in the body
interneurone
neurone which transmits impulses between other neurones, especially as part of a reflex arc
excitable cell
- neurone is an excitable cell
- cell that can be electrically excited to produce A.P
examples of excitable cells
- neurones
- muscular cells
- some endocrine cells
examples of non-excitable cells
red blood cells
what is resting membrane potential?
electrical charge across plasma membrane (inside is more negative than outside)
what can resting membrane potential do in excitable cells?
change via stimulation
resting membrane potential of excitable cells
-50mV to -85mV
selective permeability of lipid membrane
- lipid soluble molecules easily pass
- charged ions/ proteins can’t without carrier/ transporter
- so Na+, K+, Cl- can’t pass
electrical gradient
gradient based of charge
as you increase conc of oppositely charged ions, what happens?
increase in forces of attraction
facilitated diffusion
- ions diffuse down conc gradient
- selectively permeable to diff ions
- the one that doesn’t need to open and close
- memb spanning protein
active transporters (pump)
- moves ions against conc gradient
-na+/k+ channel - uses atp to open and close
K+ channels are usually…
leaky
Na+/K+ pump to maintain excitability
- maintains conc of Na+ and k+
- 2K+ IN
- for every 3Na+ OUT
- always working
what is RMP in most neurones?
around -70mV (use this one when u see a graph)
distribution of charged ions
- conc of ions inside and outside are diff
- ions move down conc gradient
- movement restricted by memb
why is cell membrane more permeable to K+ than Na+?
- due to K+ leak channels
- no Na+ leak channels
- so Na+ cannot return to cell
what happens when the Na+/K+ pump works?
- as the Na+/K+ pumps transport K+ into the cell, the conc of K+ increases
- memb potential becomes more negative
- so conc gradient of K+ increases
- K+ begins to diffuse out to area of lower K+ conc
- RMP established when the diffusion of K+ out of the cell is balanced by the rate of K+ influx from the pump
- once this inward rate of K+ flow from the pumps balances rate of K+ flow out of the cell through the leak channels a resting membrane potential stabilizes at approximately -70mV.
equilibrium potential (Eion), Nernst equation
Eion = RT/ zF x logn [ion]outside / [ion]inside
- R= gas constant, 8.314
- absolute temp
- F - faradays constant
- z = valency of ion
[ion] outside = ionic conc on outside of cell
calculating resting memb potential (Vm), goldman equation
look at ppt
