NS 2 - AP and synaptic activity Flashcards
(18 cards)
List 4 chars of a gp
Most changed at site of stim, decr w/ distance
Involves DP and hp as graded changes
Effects spread passively b/c of local current
Stronger stim = greater change of mp and incr area affected
List 3 phases of GP
RP
- DP
- na channel opens causes gp
- rest membrane exposed
- mp rises
DP
- mp at 0mv
- prod local current
- Change is ipt stim
HP
- increase in negativity by k channel opening
- k channel opening cause k to leave
Define graded potential and list 2 of its effects
Local potential, any stim can open gated channel.
Effects at cell dendrite and triggers function(exocytosis)
Effects MEP and release Ach to syn cleft
How is Na-K exchange powered
By maintaining k and na concentrations
1 ATP : 3 na
W/o ATP the neurons don’t function
Explain 2 ways of initiating and AP
Initial stim
- graded DP (-10 to -15mv) large enough to change RP to threshold of voltage gated channel to -60 to 55mv
All or none
- if the stim exceeds threshold, the AP is the same
- ap either triggered or not
Define propagation and Describe the 2 ways an ap can be propagated
Movement of ap generated at axon hillock through entire length of the axon
1 ) Continuos - unmyelinated
- affects 1 segment at a time
- 4 steps
- > 1st ap segment DP to +30mv
- > DP of 2nd segment to threshold by local current , develops ap
- > 1st segment enters refractory
- > local current DP next segment, cycle repeats
2) saltatory - myelinated
- 5 steps
- > ap travel along myelinated axon
- > faster, uses less energy
- > myelin insulates axon and prevents continuos propagation
- > local current “jumps” bw nodes
- > DP only at nodes
Explain an ap’s effects on the membrane
Propagated change in mp
Links gp at cell body with MEP actions
Affects entire excitable membrane
List and describe 4 steps in generation and propagation of an ap
1) DP cell to threshold of -60mv by GP
2) activation of na channel = rapid DP = na rush into cytoplasm
- causes membrane to change from negative to positive
- membrane at +10 mv
3) inactivation na, activation of K channel
- membrane more positive to +30mv
- RP begins
4) Return to normal (Repolarisation)
- k channel close
- membrane return to -70mv
- HP to -90mv
- ap over
Discuss the refractory phase, and explain the time period when it occurs
From beginning of ap to return of resting state during which membrane will not respond normally to additional stim
Relative
- mp almost normal
- large enough stim can still activate ap
- during DP and HP
Absolute
- no ap possible b/c na channels are inactivated
- during HP of membrane
List 3 ways axons are classified by, explain 3 ways axon diameter and propagation affects its speed and finally describe the 3 types of axons
Classified by diameter, myelination, speed of ap
1) Ion movement related to cytoplasm concentration
2) axon diameter affects ap speed b/c larger diameter= decr resistance to movement across cytoplasm
Axon types
1) type a
- myelinated
- larger diameter
- high speeds of 140m a sec
- involve balance, touch, motor impulses
2) type b
- myelinated
- medium diameter
- 18m a sec
- involve sense info and peripheral factors
3) type c
- unmyelinated
- small diameter
- 1m a sec
- involve muscles, glands
Lost and describe 2 types of synapses
Electrical = direct physical contact b/w cells. Synapses locked together at gap junctions
- eye, ganglia of brain, cilia
- allow ions pass b/w cells
- produce continuous local current, and play role in ap propagation
Chemical = across gap junction by neurotransmitter
- in synapses b/w neurons
- cells not in direct contact
- ap may or may not be propagated. Depends on amount of NT produced and sensitivity of PoSyn cell
Explain synaptic fatigue and synaptic delay
Fatigue = NT can’t recycle fast enough. Synapse remains inactive until Ach replenished
Delay = b/w arrival of ap at SynapticTerminal and it’s effect on the PoSyn membrane
List and describe the 2 classes of NT
NT’s effect is Ach activation which promotes AP, or inhibiting cardiac NMJ. Depends on RECEPTOR not TRANSMITTER
Excitatory NT = DP of the PoSyn membrane, promo AP
Inhibitory NT = HP of PoSyn, suppress AP
List 4 kinds of NT
NE = excitatory or DP effect Dopamine = CNS NT, Excite and inhibit Serotonin = attention, emotions, stress GABA = inhibitory
Discuss Neuromodulators
Similar to NT, but slower and has long term effects.
ST release chems either alone or w/ NT
neuropeptide = NM binds to receptor.
Opioids are NP.
- endorphins
- entrophins
- endomorphins
- dynomorphins
Discuss 3 ways that NT and NM work
Direct ionotropic effect
- ach
- on membrane channel
- through open/ closed gated channels
Indirect G protein
- 2nd messenger
- activate Adenylyl cyclase
- enzyme activates CAMP
Indirect via intracellular enzymes
- lipid soluble gas
- bind to enzymes in brain cells
Discuss PoSyn Potential in detail.
- definition
- 2 types
- action
- effects
- facilitation
Definition- gp in PoSyn cell IRT NT
Action depends on frequency of AP, rate of generation of AP
Types
- Excitatory PoSyn Potential (EPSP)
- > graded DP of PoSyn membrane
- > accumulation can cause Facilitation and incr. mp
- Inhibitory PoSyn potential (IPSP)
- > graded HP of PoSyn membrane
Effects
- inhibition = neuron receive IPSP to inhibit prod of ap b/c stim to reach threshold is incr.
- Summation = 1x EPSP is insufficient to trigger ap. EPSP combo w/ IPSP
- > temporal = rapid, repeated multiple stim at 1 synapse
- > spatial = degree of DP depends on synapses active. Many stim at multiple locations
Facilitation = small stim to trigger ap
- RMP almost at threshold
- EPSP accumulation
- results from EPSP summation or drugs eg: nicotine to tigger PoSyn ach receptor and dopamine
Define neuronal pools and list the 5 types as well as when they will stop
Functional group of inter connected neurons
Diverge = spread of stim
Converge= from multiple to single
Serial process = info move sequentially to synapse
Parallel = simultaneous process diverge first then multiple response
Reverberation = feedback until synaptic fatigue
Will stop when
- negative feedback
- until synaptic fatigue
