Neuron/Membrane Potential
If a resting neuron (Vm = -70 mV, EK = -90 mV, ENa = +60 mV) suddenly becomes highly permeable to Na+, this will happen to the membrane potential, and this type of electrical event will be triggered.
The membrane potential will depolarize toward ENa (+60 mV), and an action potential will be triggered if the depolarization reaches threshold.
Increasing Na+ permeability allows positive Na+ ions to enter the cell, making the inside more positive (depolarization). If this depolarization reaches the threshold (~ -55 mV), it initiates an action potential.
This brief, approximately 1 millisecond period after voltage-gated Na+ channels open is critical for preventing another action potential from immediately firing.
What is the absolute refractory period?
This property of graded potentials allows multiple sub threshold signals from the same or different synapses to combine and potentially trigger an action potential.
What is summation (temporal and/or spatial)?
Although part of the peripheral nervous system, the cell bodies of these sensory neurons cluster just outside the spinal cord in a structure called a ganglion
What are dorsal root ganglion neurons?
In a neuron at rest, the membrane potential is -70 mV. The equilibrium potential for Cl⁻ is -65 mV. If Cl⁻ channels open, predict the direction of net Cl⁻ movement and explain why
Cl⁻ will flow into the cell.
Vm (-70 mV) is more negative than ECl (-65 mV). Since Cl⁻ is negatively charged, the electrical force (opposite charges attract) will pull Cl⁻ into the cell. The chemical force is weak because Cl⁻ concentrations inside and outside are similar.
Although both Na+ and K+ voltage-gated channels respond to depolarization, only this channel type undergoes inactivation to contribute to the refractory period.
What are voltage-gated sodium channels?
Opening Cl- channels at a postsynaptic membrane typically produces this type of graded potential, decreasing the likelihood of an action potential?
What is hyperpolarization (inhibitory postsynaptic potential)?
This fluid not only cushions the brain but also maintains correct extracellular ion concentrations and provides nutrients, and is found in the ventricles and surrounding the CNS.
What is cerebrospinal fluid (CSF)?
A drug blocks all K+ leak channels in a neuron. Predict the effect on the resting membrane potential and explain the reasoning in terms of driving forces.
The resting membrane potential will become more positive (depolarize).
Normally, K+ leak channels allow K+ to exit, keeping the inside negative. Blocking them reduces K+ efflux, so the negative charge inside decreases, moving Vm away from EK.
This "jumping" process allows action potentials to travel faster along myelinated axons by regenerating the signal only at specific gaps in the myelin sheath.
What is saltatory conduction?
This region of the neuron acts as the integrator, summing all excitatory and inhibitory inputs to determine whether an action potential will fire.
What is the axon hillock (initial segment)?
In a spinal cord cross-section, this type of matter is located centrally, contains neuron cell bodies and dendrites, and is the primary site of local processing.
What is gray matter?
A neuron has Vm = -80 mV. ENa = +60 mV, EK = -90 mV. If only Na+ channels open, describe the direction of net Na+ movement and whether Vm moves toward ENa or EK.
Na+ will flow into the cell, and Vm will move toward ENa (+60 mV).
The membrane is much more negative than ENa, so the electrical and chemical forces both drive Na+ into the cell, causing depolarization toward ENa.
At this axonal region, a high concentration of voltage-gated Na+ channels ensures that a sufficiently strong graded potential triggers an action potential.
What is the initial segment (axon hillock or trigger zone)?
If a GABA receptor agonist binds to a postsynaptic inotropic receptor, this is the expected effect on the postsynaptic membrane potential.
What is hyperpolarization?
Lesions in this region between the parietal and temporal lobes can leave a patient fluent in speech but unable to comprehend language?
What is Wernicke's area?
Under resting conditions, the membrane is slightly permeable to Na+ but highly permeable to K+. If the membrane suddenly becomes equally permeable to both ions, predict whether Vm will become more positive, more negative, or stay the same, and explain why.
Vm will become more positive (depolarize).
At rest, Vm is close to EK because K+ dominates. Increasing Na+ permeability allows more Na+ to enter, pulling Vm toward ENa (+60 mV), making it less negative.
In a demyelinating disease like multiple sclerosis, loss of this glial-derived structure allows action potential conduction and can lead to neuronal degeneration.
What is myelin?
Unlike inotropic receptors, these receptors work through G proteins and second messengers to produce slower, longer-lasting effects, including enzyme activation or gene expression changes.
What are metabotropic receptors (GPCRs)?
Glucose can cross this barrier due to specialized transporters, while most polar molecules cannot; astrocytes contribute to its selective permeability.
What is the blood-brain barrier?