INTRODUCTION TO THE NERVOUS SYSTEM

Functions of the Nervous System

Organization of the Nervous System

Nervous Tissue: Support Cells & Neurons  Support cells in the CNS are grouped together as “neuroglia”  Function: to support, insulate, and protect neurons

1. Astrocyte

2. Microglial Cells

3. Ependymal Cells

4. Oligodendrocytes

Anatomy of a Neuron

Structure of Schwann Cells

Where are the Neuron Cell Bodies?  Most neuron cell bodies are found in the central nervous system  Gray matter—cell bodies in clusters called “nuclei”  White matter – dense collections of myelinated fibers called “tracts”  Ganglia—collections of cell bodies in the peripheral nervous system

Neuron Classification

Functional Classification of Neurons Free nerve endings Meissner’s corpuscles Lamellar corpuscles Proprioceptors Golgi tendon Muscle spindle

Structural Classification of Neurons  Multipolar neurons—many extensions from the cell body

Structural Classification of Neurons  Bipolar neurons—one axon and one dendrite

Structural Classification of Neurons  Unipolar neurons—have a short single process leaving the cell body

Nerve Impulses  Also known as “Action Potentials”  All-or-Nothing  If the action potential starts, it is propagated (carried) over the entire axon  Impulses travel faster when fibers have a myelin sheath

What is an “Action Potential”?  It starts with a neuron at “resting potential”

What is an “Action Potential”?  A stimulus causes Na+ to come in through a small patch of membrane

What is an “Action Potential”?  The action potential “propagates”

What Happens at the End of the Neuron?  There is transmission of a signal across the synapse Axon terminal Vesicles Synaptic cleft Action potential arrives Synapse Axon of transmitting neuron Receiving neuron

What Happens at the End of the Neuron?

How Does the Neuron Get Back to “Normal”?  Through the process of “repolarization”