Nervous Tissue: Neurons and Neuroglia
Nervous Tissue Communication
Learning Outcomes
Distinguish between neurons and neuroglia.
Describe the structure of a neuron.
Nervous Tissue
Central component of the nervous system (see section 14.1).
Consists of two cell types: neurons and neuroglia.
Serves three primary functions:
Sensory input.
Integration of information.
Motor output.
Neurons
Specialized cells with three parts:
Dendrites: Extensions that receive signals from sensory receptors or other neurons.
Cell body: Contains most of the cell's cytoplasm and the nucleus.
Axon: Extension that conducts nerve impulses (see Fig. 4.6).
Myelin: A white, fatty substance covering some axons.
Fiber: Refers to an axon, along with its myelin (if present).
Nerves: Fibers bound by connective tissue outside the brain and spinal cord.
Nerve Function
Conduct signals from sensory receptors to the spinal cord and brain.
Integration or processing occurs in the spinal cord and brain.
Sensation: Occurs only in the brain.
Conduct signals from the spinal cord and brain to muscles, glands, and other organs.
Triggers responses from tissues (e.g., muscle contraction, gland secretion).
Achieves a coordinated response to the original sensory input.
Biology in Your Life: Multiple Sclerosis (MS)
MS: An autoimmune disease where the immune system targets the myelin covering of neurons.
Results in scrambled signals traveling along the neurons.
Leads to a variety of symptoms.
Risk factors: genetic susceptibility and exposure to unidentified environmental factors.
Neuroglia
Cells that outnumber neurons nine to one.
Take up more than half the volume of the brain.
Primary function: support and nourish neurons.
Research: Investigating their direct contribution to brain function.
Do not have long extensions (axons or dendrites).
Evidence suggests they communicate among themselves and with neurons.
Examples of Neuroglia in the Brain
Microglia.
Astrocytes.
Oligodendrocytes.
Function will be explored further in section 14.1.