Parts of the Neuron
What part of the neuron receives inputs?
dendrite
What happens during the resting state in a neuron? (what channels are open? what is the potential?)
the neuron is at its resting membrane potential (-70mV), sodium and potassium channels are closed
what maintains the cell's resting membrane potential?
the sodium-potassium pump
Do all animals have myelin on their neurons?
no, only vertebrates
What part of the neuron is responsible for integration of inputs?
soma
What happens during initial depolarization? (what channels are open? what is the membrane potential?)
when a graded potential from the dendrites reaches the axon hillock, it causes a voltage-gated sodium channel to open, sodium will flow in to the cell down its concentration gradient and the membrane potential slowly gets less negative until it reaches a threshold
What is sodium's (Na+) equilibrium potential?
62 mV
What is the purpose of a myelin sheath on the axon? (2 answers)
- speeds up transmission of the action potential
- saves energy in the form of ATP (only need to maintain resting potential with sodium-potassium pump at nodes of Ranvier)
What part of the neuron propagates signals via action potentials?
axon
What happens during the rising phase of the action potential? (what channels are open? what is the membrane potential?)
after the membrane potential reaches a threshold, more voltage-gated sodium channels open and sodium flows into the cell and quickly depolarizes, membrane potential becomes positive as it approaches the sodium equilibrium potential
What is potassium's (K+) equilibrium potential?
-90 mV
Why do very small invertebrates not need myelin?
their bodies are small enough that passive propagation of membrane potential is enough to transmit neuronal signals, the signal will not experience significant decay over that distance
What part of the neuron transmits signals (aka outputs) to neighboring neurons?
axon terminals
What happens during the falling phase of the action potential? (What channels are open? What is the membrane potential?)
at the peak voltage sodium channels will close due to their inactivation loop, potassium channels will open allowing potassium to flow out of the cell and repolarize
What is the normal resting potential of a neuron?
-70 mV (but can vary, inside of cell will always be negative compared to outside)
What roles do glial cells serve in neurons?
What cell types make up the myelin sheath?
glial cells, specifically oligodendrocytes (CNS) and schwann cells (PNS)
What happens in the undershoot? (What channels are open? What is the membrane potential?)
potassium channels are still open at first so membrane potential will undershoot its resting potential as it tries to achieve potassium's equilibrium potential, eventually potassium channels will close and the sodium potassium pump will return the cell to its resting potential
By the Nernst equation, if the concentration of an ion is higher outside the cell than inside, will its equilibrium potential be positive or negative?
negative (log [ion out]/[ion in] is negative if denominator is larger)
what is the length constant (λ)?
the length over which the voltage signal decays to 1/e