Action Potentials/Neurons

What are the main parts of a neuron and their functions?

Soma (metabolic center), dendrites (input), axon (signal transmission), initial segment (impulse initiation)

What are the basic characteristics of neurons?

Rapid, precise communication; morphological and functional asymmetry; electrical and chemical excitability

What are principal/projecting neurons?

Neurons with long axons forming fiber tracts in the CNS (e.g., motor neurons)

What are intrinsic neurons?

Neurons with short axons, common in cerebral and cerebellar cortices (e.g., interneurons)

What are the functions of astrocytes?

Support neurons, clean debris, transport nutrients, regulate extracellular space, digest dead neurons

What do microglia do?

Digest dead neurons, similar to astrocytes

What is the role of oligodendroglia?

Provide myelin insulation in the CNS

What do Schwann cells do?

Provide myelin insulation in the PNS

What is the function of satellite cells?

Provide physical support to neurons in the PNS

What are the three types of ion channels?

Leak channels, ligand-gated channels, voltage-gated channels

What is conductance in ion channels?

The ability of ions to move through a channel; higher conductance = more open channels

What maintains the resting membrane potential?

Na⁺/K⁺ ATPase pump and potassium leak channels

What is the typical resting membrane potential of a neuron?

Approximately -71 mV

Why is the resting membrane potential negative?

Due to high intracellular K⁺ and impermeable anions (A⁻) inside the cell

What are graded potentials?

Local changes in membrane potential that decay over distance; proportional to stimulus strength

What are action potentials?

All-or-none electrical impulses triggered when threshold is reached; do not decay over distance

What are the three states of voltage-gated Na⁺ channels?

Closed, open, and inactivated

What are the two states of voltage-gated K⁺ channels?

Closed and open

What happens during stimulus reception?

Na⁺ channels open, depolarization to threshold (~-55 mV), AP begins

What occurs during rapid depolarization?

More Na⁺ influx, membrane potential rises to +30 mV

What happens during channel inactivation?

Na⁺ channels inactivate, K⁺ channels open, absolute refractory period begins

What occurs during repolarization?

K⁺ efflux restores membrane potential toward rest

What is hyperpolarization?

Membrane potential overshoots to ~-90 mV; relative refractory period begins

How does the membrane return to rest?

K⁺ channels close, Na⁺/K⁺ ATPase restores -70 mV

What is EPSP?

Excitatory postsynaptic potential; depolarizes membrane toward threshold

What is IPSP?

Inhibitory postsynaptic potential; hyperpolarizes membrane away from threshold

What is temporal summation?

Overlapping graded potentials from the same source

What is spatial summation?

Graded potentials from different locations on the cell

What is the role of the axon hillock?

Integrates EPSPs and IPSPs to determine if threshold is reached

What is continuous conduction?

Occurs in unmyelinated axons; channels distributed along the entire membrane

What is saltatory conduction?

Occurs in myelinated axons; AP jumps between Nodes of Ranvier

What factors affect conduction speed?

Axon diameter and membrane resistance (myelin increases resistance and speed)

What two functions do membrane proteins perform to maintain RMP?

Ion pumping (Na⁺/K⁺ ATPase) and selective permeability (leak channels)

Where are Na⁺ ions more abundant?

Outside the neuron

At potassium equilibrium potential, which direction does K⁺ move?

No net movement; forces are balanced

Why is RMP negative despite high intracellular K⁺?

K⁺ efflux and impermeable intracellular anions

What effect would lack of ATP have on membrane potential?

Loss of gradient; membrane potential would collapse

How would elevated extracellular Na⁺ affect RMP and AP?

RMP may become less negative; AP amplitude may increase

How does myelin contribute to homeostasis?

Increases conduction speed and energy efficiency

If Cl⁻ equilibrium potential is -65 mV, is Cl⁻ channel activity excitatory or inhibitory?

Inhibitory; it hyperpolarizes the membrane