Neuronal Signaling

What structures make up the central nervous system?

The brain and spinal cord.

Define the peripheral nervous system.

All nerves and ganglia outside the brain and spinal cord.

In which direction does sensory information travel?

From peripheral receptors toward the central nervous system.

Where does motor output travel from the central nervous system?

To peripheral muscles and glands.

Define neuronal excitability.

The ability to respond to stimuli by generating electrical signals.

What does neuronal conductivity allow?

Propagation of electrical signals along the cell membrane.

Why is neuronal loss often difficult to replace?

Mature neurons are amitotic and generally cannot divide.

Which neuron type has many dendrites and one axon?

A multipolar neuron.

What sensory roles are typical of bipolar neurons?

They serve smell and vision pathways.

What information do unipolar neurons commonly carry?

Touch, pain, and temperature signals to the central nervous system.

Which glial cell helps form the blood-brain barrier?

An astrocyte.

How do oligodendrocytes differ from Schwann cells?

Oligodendrocytes myelinate multiple central axons; Schwann cells myelinate one peripheral axon.

What is the immune function of microglial cells?

They phagocytose pathogens and cellular debris in the central nervous system.

Which glial cells produce cerebrospinal fluid?

Ependymal cells.

What is the role of satellite cells in ganglia?

They protect neuron cell bodies and regulate nutrient-waste exchange.

Define voltage in neuronal membranes.

Electrical potential energy from separated ions across a membrane.

What does membrane resistance oppose?

The flow of electrical charge.

Which neuronal segment receives neurotransmitter signals?

The receptive segment: dendrites and cell body.

What is the axon hillock's primary function?

It sums inputs to determine whether threshold is reached.

Which neuronal segment conducts action potentials?

The conductive segment, or axon.

What is a typical neuronal resting membrane potential?

Approximately -70 mV.

Why does potassium strongly influence resting membrane potential?

Numerous potassium leak channels allow potassium to diffuse outward.

What ions does the sodium-potassium pump transport per ATP?

Three sodium ions out and two potassium ions in.

How does an EPSP affect action-potential threshold?

It depolarizes the membrane, moving it closer to threshold.

How does an IPSP affect action-potential threshold?

It hyperpolarizes the membrane, moving it farther from threshold.

Define spatial summation in neurons.

Simultaneous inputs at different synapses combine at the axon hillock.

What causes temporal summation at a synapse?

Rapid repeated firing by one presynaptic neuron.

What triggers an action potential at the axon hillock?

Net graded potentials reaching threshold open voltage-gated sodium channels.

What ion movement causes action-potential depolarization?

Rapid sodium influx through voltage-gated sodium channels.

What ion movement drives action-potential repolarization?

Potassium efflux through voltage-gated potassium channels.

Why does hyperpolarization follow neuronal repolarization?

Potassium channels close slowly, allowing excess potassium efflux.

Which conduction type occurs in unmyelinated axons?

Continuous conduction.

Why is saltatory conduction faster than continuous conduction?

Signals depolarize only nodes, skipping myelinated segments.

How does larger axon diameter affect conduction velocity?

It increases velocity by reducing internal resistance.

How do graded potentials differ from action potentials in amplitude?

Graded potentials vary and decay; action potentials are all-or-none.

Why cannot action potentials be summated?

Refractory periods prevent overlapping action potentials.

What opens when an action potential reaches an axon terminal?

Voltage-gated calcium channels.

How does calcium entry promote neurotransmitter release?

It triggers synaptic-vesicle exocytosis into the synaptic cleft.

What happens after neurotransmitter binds a postsynaptic receptor?

Ligand-gated ion channels open, producing a graded potential.