1. NERVE CELLS
by Grace Minter

2. OVERVIEW
Definition
Structure
Function

3. BASIC DEFINITION Nerve Cell (Neuron)
the structural and functional unit of the nervous system

4. NEURON STRUCTURE All nerve cells contain 4 distinct regions:
1. Cell body
2. Dendrites
3. Axon
4. Axon terminals

5. STRUCTURE CONTINUED CELL BODY AXON AXON TERMINALS DENDRITES
houses nucleus & is site of protein synthesis and degradation of all neuron proteins and membranes
AXON
specialized for the conduction of an electric impulse or action potential away from the neuronal cell body to axon terminals
AXON TERMINALS
Send chemical signals to dendrites of other neurons
DENDRITES
receive chemical signals from the axon termini of other neurons & convert the signals into electric impulses for delivery to cell body

6. FUNCTIONAL MECHANISM
Neurons function through both electric & chemical signaling
An electric potential exist across the plasma membrane of neurons
the potential is due to the selective permeability of the membrane to differing ions
resting membrane potential  – 60 mV, negative on inside because cell pushes large number of K+ ions out
An electrical impulse results from the sequential opening & closing of ion channels and is converted into a chemical signal for message transmission

7. A CLOSER LOOK
Transmission of an electrical signal (performed by axons):
1. Na+ channels open; influx of Na+ into cell causes depolarization of neuronal membrane
2. Na+ channels close; K+ channels open & release K+ ions into extracellular space, causing hyperpolarization of the membrane
3. K+ channels close & membrane returns to resting potential (– 60 mV)
4. This process spreads across the axon, generating an electric signal to the axon terminals

8. A CLOSER LOOK: PART II
Transmission of a chemical signal through synapses (performed by axon terminal & dendrites):
synapses  sites where neurons send & receive information from other cells
1. electrical impulse generated reaches axon terminals & causes the exocytosis of a chemical neurotransmitter contained within a synaptic vesicle from the presynaptic cell
2. Neurotransmitter travels through synaptic cleft & binds to specific receptors on the dendrites of postsynaptic cell, causing a change in its permeability to ions

9. BRINGING IT TOGETHER

10. SUMMARY NEURON  functional & structural unit of the nervous system
All neurons are composed of a cell body, axon, axon terminals, & dendrites
Neurons function through both electrical and chemical signals in order to transmit messages throughout the body

12. QUESTIONS