Communication in the Nervous System Starting out small- what are Neurons and their parts?

Starting out Small to Understand the Big  We have a general idea of the nervous system’s structure- now onto the details  The Nervous System- made up in part of neurons  Nerve cells  Brain communication specialists  Transmitting info to, from, within the CNS

How are they held together?  Neurons are held in place by glia, or glial cells (from the Greek word for “glue”)  Make up 90% of the brain’s cells  What do they do?  Provide neurons with nutrients  Insulate neurons  Protect the brain from toxic agents  Remove cellular debris when neurons die  Communicate chemically with each other and neurons –(so without glial cells, neurons are unemployed)  Glial cells can give neurons the “go-ahead” to start “talking” with each other

Really, the Neurons are the Stars of the Nervous System’s Show!  Neurons are the building blocks of the nervous system  They are shaped more like snowflakes than blocks though  Delicate and differing from one another in size and shape  In a giraffe, a neuron that runs from the spinal cord down the animal’s hind leg may be 9 feet long!  In the Human Brain, neurons are microscopic  How many are there? Nobody knows!  Estimate: 100 BILLION  About the same number as there are stars in our galaxy

The structure of the Neuron  The Neuron has three main parts:  Dendrites, Cell Body, Axons  Dendrites- look like small branches of a tree (“dendrite” actually means “little tree” in Greek  They act like antennas, receiving messages from as many as 10,000 other nerve cells  They transmit these messages to the cell body (and do a little processing of those messages  Cell Body- shaped roughly like a sphere or pyramid  It keeps the neuron alive  Play a key role in deciding if a neuron should transmit a message to other neurons (depending on the inputs from other neurons)

The Structure of the Neuron Cont.  Axons and Dendrites give Neurons the catcher and batter roles.  Axon- (from the Greek word “axle”)  The axon transmits messages away from the cell body to other neurons/muscle/gland cells  They commonly divide at the end into axon terminals (branches – look more veiny than dendrites)  In adult human beings- axons may be 4 thousandths of an inch to a foot in length  Many axons, esp. big ones, are covered in a fatty layer called the myelin sheath (in the CNS are made up of glial cells) And the constrictions in this covering, called nodes, divide it into segments making it look like a string of sausage links. The myelin sheath prevents adjacent cells from interfering with each other, and speed up neural impulses.  Multiple Sclerosis- loss of the myelin sheath causes erratic nerve signals- leading to loss of sensation/paralysis

Getting on my Nerves  In the PNS the fibers of individual neurons, (axons and dendrites) are connected together in bundles called Nerves  Like lines of a telephone cable  The human body has 43 pairs of peripheral nerves (one for each pair on the left side of the body, other on the right)  Most of these nerves enter or leave the spinal cord  12 pairs are in the head – cranial nerves- connecting directly to the head= they are involved in smell, hearing, and vision (Chapter 6 stuff)

OMG so what do these look like all together?

Wait, where are the glial cells?

Different kinds of Neurons  THERE ARE MORE THAN 200 TYPES IDENTIFIED IN MAMMALS!  Here are 4 you will have to identify What do each of these look like to you?