Receptors, graded potentials Flashcards
define excitable cells:
cells which experience momentary change in membrane potential
membrane potential symbol:
Vm
change in Vm represents:
electrical signal
where is electrical signals used:
directly - electrical synapse
indirectly - chemical synapse
- communicating w other cells
change in membrane potential process:
polarisation - depolarisation - repolarisation - hyperpolarisation
Vm: polarisation
anytime Vm not at 0mV, change separation exists
Vm: depolarisation
change in Vm making it less polarised (less -ve) than at RMP
Vm: repolarisation
Vm returns to RMP after depolarised
Vm: hyperpolarisation
change in Vm makes membrane more polarised (more -ve) than at RMP
RMP: generated by
uneven distribution of +ve and -ve charges across cell membrane (semi permeable)
RMP: governed by
- concentrations of mostly K+ and Na+ in ICF and ECF
- relative permeability (P) of membrane to K and Na
- any change in relative permeability will have dramatic effect on:
Vm as electrical forces generated by movement of few charged ions DOMINATES chemical forces
how does permeability of membrane change? and effects Vm
when ion channels open and close
- cause Vm more -ve (hyperpolarise) or +ve (depolarise)
list types of gated channels:
- ligand gated
- mechanically gated
- thermally
- voltage-gated
neurotransmitter released by: and thus
pre-synaptic cell
- activates ligand gated ion channels of post-synpatic cell -> open
- ions move across post-synaptic cell (change to Vm)
electrical signals: graded potentials
- small (few mV) rapid changes in membrane potential
- excitatory (depolarising) or inhibitory (hyperpolarising)
- spreads rapidly away from site of generation
- dissipates quickly, short distances
electrical signals: action potentials
- triggered by EXCITATORY (depolarising) graded potentials -> reach threshold potential (typically -55mV)
- fixed and large (100mV) dynamic change in Vm
- regenerative, travels far without decrement (decreasing size)
- spreads slower
electrical signals: polarity of Vm depends on
- type of cell
- type of stimulus
- type of ion channel that opens/closes in response to stimulus
electrical signals: graded potential- hyperpolarisation (Y)
- ligand binds to K ion channel and opens it
- K flow out of cell DOWN electrochemical gradient = Y
electrical signals: graded potential- depolarisation (Z)
- ligand binds to Na ion channel and opens it
- Na flows into cell DOWN electrochemical gradient = Z
define electronic spread:
graded potentials spread out from origin (or active area) by passive flow of charges
flow of charges aka
current
graded potential magnitude:
- proportional to stimulus strength
- stronger stimulus = more ion channels open = more charged ions move across membrane
- can also add up if overlaps and becomes stronger
summation: (integration) most excitable cells receive stimulation from
more than one source:
- multiple synaptic inputs
- multiple membrane channels
- repetitive stimulation
