1. Neurons & Neuroglia

Neuron

A specialized excitable cell that receives, processes, and transmits information using electrical and chemical signals

Excitable tissue

Tissue capable of responding to a stimulus by generating electrical signals due to changes in membrane potential

Primary function of neurons

To conduct electrical signals rapidly along the cell membrane in response to a stimulus

Electrical signaling in neurons involves

Changes in electrical potential across the cell membrane due to ion movement

Dendrites

Branched extensions of a neuron that receive incoming signals from other neurons

Cell body (soma)

The region of the neuron containing the nucleus and most organelles responsible for cell maintenance

Axon

A long projection that conducts action potentials away from the cell body toward target cells

Trigger zone (axon hillock)

The region where graded potentials are integrated and action potentials are initiated

Direction of signal transmission in neurons

From dendrites to cell body to axon terminal

Sensory (afferent) neurons

Neurons that carry information from sensory receptors to the central nervous system

Motor (efferent) neurons

Neurons that transmit signals from the central nervous system to muscles or glands

Interneurons

Neurons that lie entirely within the central nervous system and integrate information between sensory and motor neurons

Multipolar neurons

Neurons with multiple dendrites and one axon commonly found in the CNS

Neuroglia

Non-excitable supporting cells of the nervous system that protect, insulate, and assist neurons

Primary role of neuroglia

To support, protect, nourish, and regulate the environment of neurons

Do neuroglia generate action potentials?

No neuroglia do not generate electrical impulses

Astrocytes

CNS glial cells that provide structural support regulate extracellular ions and contribute to the blood-brain barrier

Microglia

Immune cells of the CNS responsible for phagocytosis and defense against pathogens

Ependymal cells

CNS glial cells that line ventricles and the central canal and help produce cerebrospinal fluid

Oligodendrocytes

CNS glial cells that form myelin sheaths around axons

Schwann cells

PNS glial cells that form myelin sheaths around peripheral axons

Schwann cells vs oligodendrocytes

Schwann cells myelinate axons in the PNS whereas oligodendrocytes myelinate axons in the CNS

Satellite cells

PNS glial cells that surround neuron cell bodies in ganglia and regulate the chemical environment

Myelin

A lipid-rich insulating substance wrapped around axons

Effect of myelin on conduction speed

Myelin increases conduction speed by reducing ion leakage

Nodes of Ranvier

Gaps between myelin segments where voltage-gated sodium channels are concentrated