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Topic 8: Grey Matter
8.1 Nervous System Structure and Function
8.1.3 Action Potentials
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What is the threshold membrane potential for an action potential to occur?
−
55
m
V
- 55 mV
−
55
mV
Stages of the action potential in the correct order
1️⃣ Depolarization
2️⃣ Repolarization
3️⃣ Hyperpolarization
During depolarization, voltage-gated sodium channels open, allowing
N
a
+
Na^{ + }
N
a
+
ions to rush into the cell.
During hyperpolarization, the membrane potential dips below the
resting
potential.
What happens to the membrane potential during repolarization?
Decreases to -70 mV
The resting membrane potential is typically around
−
70
m
V
- 70 mV
−
70
mV
.
Leak channels allow
K
+
K^{ + }
K
+
ions to flow out of the cell, contributing to the negative resting membrane potential.
What ratio of
N
a
+
Na^{ + }
N
a
+
to
K
+
K^{ + }
K
+
ions does the sodium-potassium pump maintain?
3
N
a
+
3 Na^{ + }
3
N
a
+
out to
2
K
+
2 K^{ + }
2
K
+
in
Match the ion with its approximate concentration inside and outside the neuron:
N
a
+
Na^{ + }
N
a
+
↔️ 15 mM inside, 150 mM outside
K
+
K^{ + }
K
+
↔️ 150 mM inside, 5 mM outside
What causes the membrane potential to dip below the resting potential during hyperpolarization?
K
+
K^{ + }
K
+
channels stay open
During repolarization,
K
+
K^{ + }
K
+
ions flow out of the cell.
Arrange the stages of the action potential based on ion movement
1️⃣
N
a
+
Na^{ + }
N
a
+
rushes in
2️⃣
K
+
K^{ + }
K
+
flows out
3️⃣
K
+
K^{ + }
K
+
continues to flow out
The membrane potential during an action potential typically starts from a resting potential of
-70 mV
Order the stages of an action potential:
1️⃣ Depolarization
2️⃣ Repolarization
3️⃣ Hyperpolarization
During depolarization, voltage-gated sodium channels open, allowing
N
a
+
Na^{ + }
N
a
+
ions to flow into the cell.
During repolarization, voltage-gated potassium channels open, allowing
K
+
K^{ + }
K
+
ions to flow out
Hyperpolarization occurs because potassium channels remain open, causing the membrane potential to dip below
-70 mV
Match the stage of action potential with its corresponding ion movement and membrane potential:
Depolarization ↔️
N
a
+
Na^{ + }
N
a
+
in,
+
+
+
30
m
V
30 mV
30
mV
Repolarization ↔️
K
+
K^{ + }
K
+
out,
−
70
m
V
- 70 mV
−
70
mV
Hyperpolarization ↔️
K
+
K^{ + }
K
+
continues out, below
−
70
m
V
- 70 mV
−
70
mV
The resting membrane potential of a neuron is typically around
-70 mV
The uneven distribution of ions inside and outside the neuron contributes to the
resting membrane potential
.
Leak channels allow
K
+
K^{ + }
K
+
ions to flow out of the cell, contributing to the negative potential
The sodium-potassium pump transports 3 Na^{ + }</latex> ions out and
2
K
+
2 K^{ + }
2
K
+
ions in.
The concentration of
K
+
K^{ + }
K
+
ions inside the neuron is significantly higher than outside, approximately 150 mM
The concentration of
N
a
+
Na^{ + }
N
a
+
ions is higher outside the neuron than inside.
The action potential consists of three main stages: depolarization, repolarization, and
hyperpolarization
Match the stage of action potential with its corresponding ion movement and membrane potential:
Depolarization ↔️
N
a
+
Na^{ + }
N
a
+
in,
+
+
+
30
m
V
30 mV
30
mV
Repolarization ↔️
K
+
K^{ + }
K
+
out,
−
70
m
V
- 70 mV
−
70
mV
Hyperpolarization ↔️
K
+
K^{ + }
K
+
continues out, below
−
70
m
V
- 70 mV
−
70
mV
Ion channels are essential for establishing and maintaining the
resting membrane potential
.
Leak channels, such as those for K^{ + }</latex>, contribute to the stable resting membrane potential around
-70 mV
Order the types of action potential conduction from slowest to fastest:
1️⃣ Continuous conduction
2️⃣ Saltatory conduction
Saltatory conduction occurs in myelinated axons and is faster than
continuous conduction
.
During the absolute refractory period, no new action potential can be generated because sodium channels are open or
inactivated
Refractory periods ensure unidirectional propagation of
action potentials
.
When the membrane potential reaches the resting level again, the potassium channels remain
open
What are the two types of refractory periods?
Absolute and relative
The refractory periods ensure that
action potentials
travel in one direction along the axon.
An action potential occurs when the membrane potential reaches a threshold of
−
55
m
V
- 55 mV
−
55
mV
Stages of an action potential
1️⃣ Depolarization
2️⃣ Repolarization
3️⃣ Hyperpolarization
During depolarization, what ion rushes into the cell?
N
a
+
Na^{ + }
N
a
+
During repolarization, voltage-gated potassium channels open, allowing
K
+
K^{ + }
K
+
During hyperpolarization, the membrane potential briefly dips below the
resting potential
.
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