Process of Synapses Flashcards
(18 cards)
Structure of
myelinated
motor neurone
- dendrite
- cell body w. nucleus
- axon
- myelin sheath w. Schwann cell
- nodes of Ranvier
- Axon terminal
Resting
potential
- the difference between the
electrical charge inside and
outside the axon - when a neurone
is not conducting an impulse - more positive ions (Na
+/K+ ) outside
axon compared to inside - inside the axon -70mV
How is resting
potential
established
- Sodium potassium pump actively
transports 3 Na+ out of the axon, 2 K+
into the axon - membrane more permeable to K+
(more channels and always open) - K+ diffuses out down conc. gradient
- facilitated diffusion
- membrane less permeable to Na+
(closed Na+ channels) - higher conc. Na+ outside
Action
potential
- Stimulus causes membrane to depolarise
past the threshold (–55 mV) - Voltage-gated Na+ channels open → Na+
diffuses in
→ Inside becomes more positive
(depolarisation) - At +40 mV, Na+ channels close and voltage-
gated K+ channels open - K+ diffuses out, making the inside negative
again (repolarisation) - Hyperpolarisation may occur as K+ channels
are slow to close
Action potential: stimulus
Stimulus causes the membrane to
depolarise past the threshold (–55
mV)
Voltage-gated Na+ channels open →
Na+ diffuses in
→ Inside becomes more positive
(depolarisation)
Action potential:
depolarisation
- When a threshold potential is
reached, an action potential is
generated - more voltage-gated Na+ channels
open - Na+ move by facilitated diffusion
down conc. gradient into the axon - potential inside becomes more
positive
Action potential:
repolarisation
Na channels close, membrane
becomes less permeable it Na+
+
K voltage-gated channels open,
membrane more permeable to K+
+
K diffuses out neuron down conc.
gradient
+
voltage rapidly decreases
Action potential:
hyperpolarisation
K channels slow to close ->
overshoot in voltage
+
too many K+ diffuse out of neurone
potential difference decreases to
-80mV
sodium-potassium pump returns
neurone to its resting potential
Draw a actional potential graph
yeah
All or nothing
principle
- If depolarisation does not
exceed -55 mV threshold, action
potential is not produced - any stimulus that does trigger
depolarisation to -55mV
threshold will always peak at
the same maximum voltage
Importance of all
or nothing
principle
- Ensures that only stimuli above a
threshold trigger an action potential - Prevents response to small,
insignificant stimuli — avoids overload - All action potentials are the same size,
so information is transmitted clearly
→ Stimulus intensity is shown by
frequency, not size, of impulses
Refractory
period
- After an action potential has
been generated, - the membrane
enters a period where it cannot
be stimulated - because Na channels are
recovering and cannot be
opened
Importance of the refectory period
- Ensures discrete impulses
produced - action potentials
separate and cannot be
generated immediately - unidirectional - cannot generate
action potential in refractory
region
-limits number of impulse
transmissions - prevent
overwhelming
Factors affecting
speed of
conductance
Myelination
axon diameter
temperature
How
myelination
affects speed
- With myelination - depolarisation
occurs at Nodes of Ranvier only -> - saltatory conduction
impulse jumps from node-node - in non-myelinated neurones,
depolarisation occurs along full
length of axon - slower
How axon
diameter affects
speed
- Increases speed of conductance
- increases rate
of movement of
ions as more kinetic energy
(active transport/diffusion) - higher rate of respiration as
enzyme activity faster - so ATP is
produced faster - active
transport faster
Saltatory
conduction
- Gaps between myelin sheath
and nodes of Ranvier - action potential can “jump”
from node to node - via saltatory
conduction - action potential
travels faster as depolarisation
across whole length of axon not
required
