Human Nervous System notes+
practice Q&A
SUMMARY
1–10: Neuron Structure & Function
Q1: What is the main function of dendrites?
A: Receive incoming signals from other neurons or sensory
receptors.
R: Dendrites are branched extensions that increase surface area
for receiving synaptic input and conducting graded potentials
toward the cell body.
Q2: Which part of the neuron typically contains the nucleus?
A: Cell body (soma).
R: The soma houses the nucleus and most organelles; it integrates
incoming signals and generates the axon hillock’s initial segment.
Q3: What is the role of the axon hillock?
A: Site where action potentials are initiated if threshold is reached.
R: The axon hillock has the highest density of voltage-gated
sodium channels, making it the spike-initiation zone.
Q4: How does myelin sheath affect impulse speed?
A: It increases conduction velocity via saltatory conduction.
R: Myelin insulates the axon, forcing action potentials to “jump”
between Nodes of Ranvier, greatly speeding transmission
compared to unmyelinated axons.
,Q5: What cells produce myelin in the CNS?
A: Oligodendrocytes.
R: Oligodendrocytes extend processes to wrap around multiple
CNS axons; each cell myelinates several axons.
Q6: What cells produce myelin in the PNS?
A: Schwann cells.
R: Each Schwann cell myelinates a single segment of one PNS
axon; they also aid in axonal regeneration.
Q7: Name the gaps between myelin segments.
A: Nodes of Ranvier.
R: These unmyelinated gaps contain voltage-gated Na⁺ channels
and are the only places where action potentials regenerate in
myelinated axons.
Q8: Which organelle is responsible for neurotransmitter
packaging?
A: Synaptic vesicles.
R: Synaptic vesicles, derived from the Golgi apparatus and
endocytosis, store neurotransmitters and fuse with the
presynaptic membrane upon Ca²⁺ entry.
Q9: What is the typical resting membrane potential of a neuron?
A: −70 mV.
R: Maintained by the Na⁺/K⁺ ATPase (3 Na⁺ out, 2 K⁺ in) and
higher K⁺ permeability, making the inside negative relative to
outside.
Q10: Which ion is most permeable at rest?
A: Potassium (K⁺).
, R: Leak K⁺ channels are open at rest, allowing K⁺ to exit down its
concentration gradient, contributing most to the resting potential.
11–20: Action Potential
Q11: What triggers depolarization?
A: Opening of voltage-gated sodium channels.
R: A threshold stimulus causes Na⁺ channels to open; Na⁺ rushes
in, making the membrane potential less negative (moves toward
+30 mV).
Q12: What is the threshold potential?
A: Approximately −55 mV (varies by neuron).
R: At this level, enough Na⁺ channels open to produce a
regenerative, all-or-none action potential.
Q13: What happens during repolarization?
A: Na⁺ channels inactivate; voltage-gated K⁺ channels open,
allowing K⁺ efflux.
R: K⁺ leaving restores the negative interior; repolarization ends
when potential returns near −70 mV.
Q14: Define the absolute refractory period.
A: Period when a second action potential cannot be initiated, no
matter the stimulus strength.
R: Caused by inactivation of Na⁺ channels; ensures unidirectional
propagation and limits firing rate.
Q15: What is the relative refractory period?
A: A stronger-than-normal stimulus can trigger an action
practice Q&A
SUMMARY
1–10: Neuron Structure & Function
Q1: What is the main function of dendrites?
A: Receive incoming signals from other neurons or sensory
receptors.
R: Dendrites are branched extensions that increase surface area
for receiving synaptic input and conducting graded potentials
toward the cell body.
Q2: Which part of the neuron typically contains the nucleus?
A: Cell body (soma).
R: The soma houses the nucleus and most organelles; it integrates
incoming signals and generates the axon hillock’s initial segment.
Q3: What is the role of the axon hillock?
A: Site where action potentials are initiated if threshold is reached.
R: The axon hillock has the highest density of voltage-gated
sodium channels, making it the spike-initiation zone.
Q4: How does myelin sheath affect impulse speed?
A: It increases conduction velocity via saltatory conduction.
R: Myelin insulates the axon, forcing action potentials to “jump”
between Nodes of Ranvier, greatly speeding transmission
compared to unmyelinated axons.
,Q5: What cells produce myelin in the CNS?
A: Oligodendrocytes.
R: Oligodendrocytes extend processes to wrap around multiple
CNS axons; each cell myelinates several axons.
Q6: What cells produce myelin in the PNS?
A: Schwann cells.
R: Each Schwann cell myelinates a single segment of one PNS
axon; they also aid in axonal regeneration.
Q7: Name the gaps between myelin segments.
A: Nodes of Ranvier.
R: These unmyelinated gaps contain voltage-gated Na⁺ channels
and are the only places where action potentials regenerate in
myelinated axons.
Q8: Which organelle is responsible for neurotransmitter
packaging?
A: Synaptic vesicles.
R: Synaptic vesicles, derived from the Golgi apparatus and
endocytosis, store neurotransmitters and fuse with the
presynaptic membrane upon Ca²⁺ entry.
Q9: What is the typical resting membrane potential of a neuron?
A: −70 mV.
R: Maintained by the Na⁺/K⁺ ATPase (3 Na⁺ out, 2 K⁺ in) and
higher K⁺ permeability, making the inside negative relative to
outside.
Q10: Which ion is most permeable at rest?
A: Potassium (K⁺).
, R: Leak K⁺ channels are open at rest, allowing K⁺ to exit down its
concentration gradient, contributing most to the resting potential.
11–20: Action Potential
Q11: What triggers depolarization?
A: Opening of voltage-gated sodium channels.
R: A threshold stimulus causes Na⁺ channels to open; Na⁺ rushes
in, making the membrane potential less negative (moves toward
+30 mV).
Q12: What is the threshold potential?
A: Approximately −55 mV (varies by neuron).
R: At this level, enough Na⁺ channels open to produce a
regenerative, all-or-none action potential.
Q13: What happens during repolarization?
A: Na⁺ channels inactivate; voltage-gated K⁺ channels open,
allowing K⁺ efflux.
R: K⁺ leaving restores the negative interior; repolarization ends
when potential returns near −70 mV.
Q14: Define the absolute refractory period.
A: Period when a second action potential cannot be initiated, no
matter the stimulus strength.
R: Caused by inactivation of Na⁺ channels; ensures unidirectional
propagation and limits firing rate.
Q15: What is the relative refractory period?
A: A stronger-than-normal stimulus can trigger an action
