Neuron & Nerve Impulses (Exam 3)

Q: What is a neuron?

A: A specialized cell that transmits electrical and chemical signals in the nervous system.

Q: What are the three main parts of a neuron?

A: The cell body (soma), dendrites, and axon.

Q: What is the function of the cell body (soma)?

A: It contains the nucleus and organelles and integrates incoming signals.

Q: What are dendrites?

A: Short, branched extensions that receive signals from other neurons and transmit them toward the cell body.

Q: What is the axon?

A: A long fiber that carries electrical impulses away from the cell body to other neurons or effectors.

Q: What is the axon hillock?

A: The cone-shaped region where the axon joins the cell body and where nerve impulses begin.

Q: What is the myelin sheath?

A: A fatty layer that insulates the axon, increases conduction speed, and prevents signal loss.

Q: What is a Schwann cell?

A: A type of neuroglial cell in the PNS that forms the myelin sheath around axons.

Q: What are nodes of Ranvier?

A: Gaps in the myelin sheath where action potentials are regenerated, enabling faster signal transmission.

Q: What is saltatory conduction?

A: The process where nerve impulses jump from node to node along a myelinated axon, greatly increasing speed.

Q: What are oligodendrocytes?

A: Glial cells in the CNS that form myelin sheaths around multiple axons.

Q: What are astrocytes?

A: Star-shaped glial cells that support neurons, maintain the blood-brain barrier, and regulate nutrient exchange.

Q: What are microglia?

A: Immune-like glial cells in the CNS that remove debris and protect against pathogens.

Q: What are ependymal cells?

A: Cells lining the ventricles of the brain and central canal of the spinal cord that help circulate cerebrospinal fluid (CSF).

Q: What is resting membrane potential?

A: The difference in electrical charge across a neuron’s membrane when it is not transmitting a signal, typically around -70 mV.

Q: What ions are primarily involved in generating resting membrane potential?

A: Sodium (Na⁺) and potassium (K⁺) ions.

Q: What maintains the resting membrane potential?

A: The sodium-potassium pump (Na⁺/K⁺ ATPase), which pumps 3 Na⁺ out and 2 K⁺ in.

Q: What is an action potential?

A: A rapid, temporary change in membrane potential that travels along an axon.

Q: What causes depolarization during an action potential?

A: The opening of voltage-gated sodium channels allowing Na⁺ to enter the neuron.

Q: What causes repolarization?

A: The closing of sodium channels and the opening of potassium channels, allowing K⁺ to exit the neuron.

Q: What is hyperpolarization?

A: When the membrane potential becomes more negative than the resting potential due to excess K⁺ leaving the cell.

Q: What is the refractory period?

A: A short period after an action potential during which a neuron cannot fire another impulse.

Q: What is the threshold potential?

A: The minimum membrane potential (around -55 mV) that must be reached to trigger an action potential.

Q: What is continuous conduction?

A: The slow transmission of nerve impulses along unmyelinated axons, where the impulse travels along every part of the membrane.

Q: What is saltatory conduction and how is it different?

A: It occurs in myelinated axons where impulses jump from node to node, making it much faster than continuous conduction.

Q: What factors affect the speed of nerve impulse transmission?

A: Axon diameter (larger = faster) and myelination (myelinated = faster).

Q: What is the all-or-none principle?

A: Once a neuron reaches threshold, it fires completely

Q: What are graded potentials?

A: Small changes in membrane potential that can summate to reach threshold and initiate an action potential.

Q: What is summation in neurons?

A: The process by which multiple graded potentials combine to reach threshold.

Q: What are excitatory postsynaptic potentials (EPSPs)?

A: Depolarizing changes in membrane potential that move the neuron closer to threshold.

Q: What are inhibitory postsynaptic potentials (IPSPs)?

A: Hyperpolarizing changes that move the neuron farther from threshold, making it less likely to fire.

Q: What is meant by “neurons are excitable cells”?

A: They can generate and transmit electrical impulses in response to stimuli.

Q: What is a synaptic end bulb (axon terminal)?

A: The swollen tip of an axon where neurotransmitters are stored and released.

Q: What is the importance of calcium ions (Ca²⁺) at the synaptic terminal?

A: Calcium influx triggers vesicles to release neurotransmitters into the synaptic cleft.

Q: What is the role of neurotransmitters in neuron communication?

A: They transmit signals across the synaptic cleft from one neuron to another.