Lecture 6 – Central Nervous System, Action Potentials, and Neurons

These question-and-answer flashcards review the anatomy of neurons, function of glial cells, mechanisms of action potentials and synaptic transmission, and major neurotransmitter types covered in Lecture 6.

What are the two major divisions of the nervous system?

The Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

Which structures make up the Central Nervous System?

The brain and spinal cord.

What primary role does the CNS serve?

It acts as the control center, receiving information and determining appropriate responses.

What is the specialized function of neurons?

To receive and transmit neural impulses (action potentials) as electrical and chemical signals.

Which part of a neuron contains the nucleus and most organelles?

The cell body (soma).

What are dendrites?

Branched extensions that receive impulses and carry them toward the cell body.

What is the function of an axon?

To transmit neural signals away from the cell body toward another neuron, muscle, or gland.

What are collateral branches of an axon?

Secondary branches that extend from the main axon.

What takes place at synaptic terminals?

Release of neurotransmitters that communicate with the next cell.

Define a nerve.

A bundle of axons in the PNS wrapped in connective tissue.

What is a ganglion?

A cluster of neuronal cell bodies in the PNS.

What is a bundle of axons called in the CNS?

A pathway or tract.

What are nuclei in the CNS?

Clusters of neuronal cell bodies within the CNS.

Which cells form myelin sheaths in the PNS?

Schwann cells.

What is the main function of a myelin sheath?

To speed conduction of nerve impulses by insulating axons.

What are the gaps between segments of myelin called?

Nodes of Ranvier.

What type of conduction occurs along myelinated axons?

Saltatory conduction.

Which part of the Schwann cell aids in regeneration of damaged PNS axons?

The neurilemma.

What disorder is characterized by deterioration of CNS myelin?

Multiple sclerosis.

Which glial cells form myelin sheaths in the CNS?

Oligodendrocytes.

Give two key functions of astrocytes.

They support and protect neurons and regulate extracellular fluid by removing excess K⁺.

What do ependymal cells do?

Line CNS cavities and produce/circulate cerebrospinal fluid (CSF).

What is the primary role of microglia?

Phagocytosis of bacteria and cellular debris in the CNS.

What is a synapse?

The junction between two neurons where information is transmitted across a small gap (synaptic cleft).

List the five basic steps of neural signaling in order.

Reception, Transmission (afferent), Integration, Transmission (efferent), Response by effectors.

Define resting membrane potential.

The voltage difference across a neuron’s membrane when it is not transmitting an impulse.

What is the typical resting potential of a neuron?

Approximately –70 mV.

Which two ions chiefly determine resting membrane potential?

Sodium (Na⁺) and potassium (K⁺).

How many ions does the sodium-potassium pump move and in which directions?

It pumps 3 Na⁺ out of the cell and 2 K⁺ into the cell.

What event initiates an action potential?

Opening of voltage-gated Na⁺ channels when a stimulus reaches threshold.

During an action potential, what causes depolarization?

Rapid influx of Na⁺ into the neuron.

What happens during repolarization of an axon?

Na⁺ channels close and K⁺ channels open, allowing K⁺ to exit and restore negativity inside the membrane.

What is the absolute refractory period?

A period during which a neuron cannot generate another action potential, no matter the stimulus strength.

Define the relative refractory period.

A timeframe when a second action potential is possible but requires a stronger-than-normal stimulus.

What is continuous conduction and where does it occur?

Step-by-step propagation of action potentials along unmyelinated axons.

What does the all-or-nothing principle state?

An action potential either occurs fully or not at all once threshold is reached.

In synaptic terminology, which neuron sends the signal?

The presynaptic neuron.

What substances carry signals across a synapse?

Neurotransmitters.

Which neurotransmitter is crucial for memory formation and logical thinking?

Acetylcholine.

Name the three catecholamine neurotransmitters.

Norepinephrine, epinephrine, and dopamine.

Which neurotransmitter imbalance is linked to depression, ADHD, and schizophrenia?

Serotonin (and catecholamines).

What amino acid neurotransmitter is the main inhibitor in the CNS?

GABA (gamma-aminobutyric acid).

What is the function of endorphins and enkephalins?

They act as natural opioids, blocking pain signals by binding to brain receptors.

Which gaseous neurotransmitter acts as a retrograde messenger?

Nitric oxide (NO).

Which ion’s influx at the synaptic terminal triggers neurotransmitter release?

Calcium ions (Ca²⁺).

Name two mechanisms that quickly remove neurotransmitters from the synaptic cleft.

Enzymatic breakdown and reuptake into the presynaptic terminal.

What is an excitatory postsynaptic potential (EPSP)?

A change that depolarizes the postsynaptic membrane, bringing it closer to threshold.

What is summation in neural signaling?

The additive effect of multiple EPSPs to reach threshold and trigger an action potential.

What is an inhibitory postsynaptic potential (IPSP)?

A hyperpolarization that moves the membrane potential farther from threshold, decreasing likelihood of firing.