Neurons

Brain and Spinal Cord

What is in the CNS?

PNS

neurons that connect the CNS to the rest of the body.

Somatic Nervous System

Part of the PNS responsible for voluntary movements that are consciously controlled.

Autonomic Nervous System

Part of the PNS that oversees involuntary movements.

Sensory Neurons

Neurons that carry information to the CNS.

Motor Neurons

Neurons responsible for carrying information from the CNS to the body.

Myelin

A layer of fat that insulates neurons (axon) and allows for faster conduction of impulses.

White Matter

Regions of the CNS that are made up primarily of myelinated axons.

CNS Myelin

Myelin in the CNS is made by oligodendrocytes.

Schwann Cells

Myelin in the PNS

Neurilemma

The outermost layer of myelin that surrounds a nerve fiber in the PNS.

Role of Myelin in Conduction

Myelin keeps action potential from continuously spreading across the cell membrane, insulating against current spread and speeding up conduction.

Saltatory Conduction

A mechanism where action potentials jump from sheath to sheath along myelinated axons, reducing the number of action potentials needed.

Dendrites

Extensions of a neuron that conduct impulses toward the cell body.

Axon

Extension of a neuron that carries impulses away from the cell body.

Nerves

Bundled neuron fibers in the PNS.

Tracts

Bundled neuron fibers in the CNS.

Endoneurium

Connective tissue that surrounds each individual nerve fiber.

Perineurium

Connective tissue that surrounds a bundle of nerve fibers known as a fascicle.

Epineurium

Connective tissue that surrounds the entire nerve.

Mixed nerves

Nerves containing both sensory and motor fibers.

Neuroglia

Support cells in the nervous system, which include Schwann cells.

Astrocytes

Star-shaped support cells in the CNS that have various functions.

Oligodendrocytes

Cells that provide myelin sheath for the CNS.

Microglia

Cells that remove pathogens and dead neurons in the CNS.

Ependymal

Cells that provide a barrier between fluids and CNS nervous tissue.

Spinal Cord

The central pathway for sensory and motor impulses to travel to and from the brain.

Ascending Tracts

Neural pathways that carry information to the brain.

Descending Tracts

Neural pathways that carry information from the brain.