Neurons and Nerve Impulses

Dendrites

Receive incoming signals and carry them toward the cell body.

Cell body (Soma)

Integrates incoming signals and supports neuron functions.

Nucleus

Houses DNA and maintains neuron function.

Axon

Carries the nerve impulse (action potential) away from the cell body.

Myelin sheath

Insulates the axon and speeds up nerve impulse conduction.

Nodes of Ranvier

Gaps in the myelin sheath where action potentials are regenerated.

Axon terminals

Release neurotransmitters to communicate with other cells.

Sensory (afferent) neurons

Carry information from receptors to the CNS.

Motor (efferent) neurons

Carry commands from the CNS to muscles or glands.

Interneurons

Connect neurons within the CNS for processing.

Multipolar neurons

Many dendrites, one axon; most common neuron type.

Bipolar neurons

One dendrite and one axon; found in sensory organs.

Unipolar neurons

Single process that divides into axon and dendrite; common in PNS sensory neurons.

Astrocytes (CNS)

Support neurons, maintain blood–brain barrier, regulate environment.

Oligodendrocytes (CNS)

Form myelin sheath around CNS axons.

Microglia (CNS)

Immune defense cells of the CNS.

Ependymal cells (CNS)

Produce and circulate cerebrospinal fluid.

Schwann cells (PNS)

Form myelin sheath around PNS axons.

Satellite cells (PNS)

Support neuron cell bodies in ganglia.

Action potential

Rapid, temporary reversal of membrane potential that travels along the axon.

Threshold

Minimum stimulus needed to trigger an action potential (about –55 mV).

Depolarization

Na⁺ channels open, Na⁺ rushes in. Charge: inside goes from –70 mV → +30 mV (becomes positive).

Repolarization

K⁺ channels open, K⁺ exits. Charge: inside goes from +30 mV → –70 mV (returns toward resting).

Hyperpolarization

Excess K⁺ leaves (or Cl⁻ enters). Charge: inside goes below resting, around –80 to –90 mV. neuron cant fire another action potential easily

Refractory period

Time when neuron cannot fire or needs stronger stimulus.

Afferent Division (Sensory Division)

Carries sensory information from receptors to the CNS; includes somatic and visceral sensory pathways.

Efferent Division (Motor Division)

Carries motor commands from the CNS to muscles and glands; includes the somatic (skeletal muscles) and autonomic (smooth/cardiac muscle, glands) systems.

Which two factors are most important in determining the rate of action potential conduction?

if the myelin sheath is present or absent and the diameter of the axon

mechanically gated channels

Channels that open when the membrane is physically deformed

chemically gated channels

Channels that open when a neurotransmitter or chemical binds to them.

voltage gated channels 

open and close due to changes in transmembrane potential or the charge changes