3.6.2- Nervous co-ordination Flashcards
Structure & function of myelinated motor neurone= (5)
Dendrites= carry nervous impulse > cell body
Axon= carry nervous impulse AWAY from cell body
Cell body= contains nucleus & organelles in animal cell; proteins and NT synthesised here
schwann cells= wrap around axon to form myelin sheath & insulate axon
Nodes of ranvier= gaps between schwann cells (impulses ‘jump’ between these in myelinated transmission
What is the resting potential?
when a neurone is NOT conducting an impulse, there is a DIFFERENCE between the electrical charge INSIDE & OUTSIDE of neurone; this is the RP
Establishment of a RP= (3)
1) Na+-K+ pumps, AT 3Na+ OUT & 2K+ IN axon
2) This creates an electrochemical gradient; causing K+ to diffuse out & Na+ to diffuse in
3) The membrane is more permeable to K+ so more are moved OUT, resulting in -70mV
All or nothing response
- stimulus- Na+ channels open, membrane MORE permeable to Na+ & they flood in down EC gradient
- Depolarisation- PD reaches threshold (-55mV) & AP formed
- Repolarisation- Na+ channels close & K+ channels open, so K+ diffuse out
- Hyperpolarisation- K+ channels slow to close & PD becomes slightly more - than RP
- Return to RP- K+ channels close & membrane returns to RP
All or nothing principle-
- depolarisation needs to exceed threshold (-55mV) for an AP; if doesn’t reach threshold then nothing
- Stimuli that trigger D to -55mV always peaks at same MAXIMUM voltage; bigger stimuli only increase FREQUENCY of AP
importance of all-or nothing principle
ensures animals only respond to large enough stimuli rather than responding to every slight change in environment
Importance of refractory period (3)
- Ensure discrete/separate impulses produced
- Ensures unidirectionality
- Limits frequency of impulses (important to prevent over reaction to a stimulus)
Factors affecting conduction speed (3)
- Myelination=
>in myelinated- SC so FASTER
>in non-myelinated- has to D along whole axon so SLOWER - Axon Diameter=
Greater AD> greater SA for ion movement across cell m> FASTER - Temperature=
Increase > increase in ek> ions move across m FASTER when have more ek
increase > increases RoR > ATP produced FASTER> AT FASTER
what are synapses?
- gaps between the end of the axon on one neuron & the dendrite of another one
- AP is transmitted as NTs that diffuse across the synapse
cholinergic synaptic transmission- process= (7)
1) AP arrives at synaptic knob D it, causing Ca2+ channels to open
2) Ca2+ diffuse into pre-SN, causing vesicles containing AC to move to & fuse with pre-s-m , releasing AC> cleft
3. AC diffuses across cleft, down conc gradient > post-SM
4. AC binds to R on post-s-m
5. Na+ channels on post-s-m open & Na+ diffuse in, depolarising post-SN
6. AC degraded & released from r (AC> choline + acetate)
7. Na+ channels close & post-s-n can re-establish RP; AC transported back> pre-SN
how does synaptic transmission ensure unidirectionality? (2)
- NT only made in pre-SN
- Can only bind to r on post-sm
Spatial summation
- Many pre-SN share SAME post-SN
- These release sufficient NTs to reach threshold for APs
Temporal summation
- ONE pre-SN releases NTs many times & rapidly
- This causes sufficient NTs so reaches threshold for AP
Inhibitory synapse
- When NTs bind to r, K+ channels & Cl- channels open
- Cause Cl- to move into post-SN & K+ to move out
- This prevents AP formation
neuromuscular junction vs cholinergic synapse (4)
Both Unidirectional
NMJ= only excitatory CS= could be excitatory/ inhibitory
NMJ= Connects motor N > muscles CS= connects N>N
NMJ= end point for AP CS= New AP is generated in next N
NMJ= AC binds to r on muscle f m CS= AC binds to r on post-s-m of N
