Nervous Tissue

The Neuron A neuron is a type of cell type that conducts impulses, or action potentials. The structural components of a neuron are: 1. cell body - the large area filled with cytoplasm and containing a nucleus. 2. dendrites – the many projections from the cell body. 3. hillock – the cone-shaped projection that extends from the cell body and becomes the axon (nerve fiber).

The Neuron 4. Schwann cells- neuroglia cells that cover and wrap around the axon of peripheral nerves. 5. myelin – a fatty white substance found in the Schwann cell. 6. nodes of Ranvier – the gaps that occur between the Schwann cells. 7. telodendria – the distal ends of axons they are usually branched. The telodendria are sometimes referred to as: Axon terminals Synaptic knobs

Neuron

Schwann Cell vs Myelin

Dendrite Cell Body Nucleus Axon Hillock Axon

Axon Terminal or Synaptic knobs Cell Body Nucleus Schwann Cell Myelin Axon Node of Ranvier Telodendria Axon Terminal or Synaptic knobs

The Shapes of Neurons (3)

Unipolar Neuron Associated with “touch” Cell Body Dendrite Axon CNS Have one extension from the cell body that splits to become two long branches. Carry impulses towards the central nervous system.

Bipolar Neuron Has two projections from the cell body. Associated with sight, smell and hearing Dendrite Axon Cell Body Has two projections from the cell body. One process conducts impulses towards the cell body and the other process conducts impulses away from the cell body.

Multipolar Neuron Has multiple projections from the cell body. Associated with skeletal muscles Cell Body Axon Dendrites Has multiple projections from the cell body. Most common type of neuron.

Sensory Neurons Afferent = Toward the CNS These carry sensory information from the body to the CNS (brain and spinal cord) Two subdivisions: 1. Somatic fibers – relay information from the skin, skeletal muscles and joints. 2. Visceral fibers – relay information from internal body organs.

Motor Neurons Efferent = Away from CNS These are neurons that carry information from CNS to the body, specifically, to the: Muscles Glands

“Gray” Matter Brain tissue is made up of millions of neurons. It is gray because there is no myelin protecting the axons

Glial Cells (helper cells) 4 different types of glial cells Associated with neurons Provide supportive to neurons AKA: neuroglia

Supporting Cells in the CNS Astrocytes Star Shaped Many functions Monitor the exchanges between capillaries and neurons Nutrient transfer

Supporting Cells in the CNS Oligodendrocytes Produce the myelin sheath which provides insulation for some neurons in the CNS They do the same thing as the Schwann cells, just at a different location

Supporting Cells in the CNS Microglia Small oval cells with long thorny processes Monitor the health of neurons Specialized immune cells that phagocytize microorganisms and debris