1. April 22 2015 The Neuron & Nerve Impulses
The Nervous System
April
The Neuron & Nerve Impulses

2. Nervous Tissue Two Types Neurons Neuroglia Nerve impulse conduction
AP (action potential)
Neuroglia
Support & nourish neurons

3. The Neuron
Three Main Parts
1. Cell Body
2. Dendrites
3. Axon

4. Cell Body
Nucleus
Organelles such as mitochondria, lysozomes

5. Dendrites Many branched extensions off of cell body
RECEIVE SIGNALS/INPUTS

6. Axon Long & thin extension off cell body
Conducts nerve impulses toward another neuron, a muscle fiber, or a gland cell (effector cells)
Axons end by dividing into many fine processes called axon terminals
Nerve impulses travel from cell body to the axon terminals

7. Axon Myelin Sheath Most axons are surrounded by the myelin sheath
Myelin sheath is made up of lipids & proteins
Insulates the axon of the neuron
Increases the speed of the signals that travel down the axon

8. The Synapse
The site where two neurons meet (or a neuron meets an effector cell) is called a Synapse

9. Neuroglia These cells are smaller than neurons Much more numerous
Do not conduct impulses
Six types of neuroglia cells

10. Action Potentials
Cells, like neurons, have a difference in the charge within their plasma membrane versus the charge outside
The voltage across the plasma membrane when the neuron is not conducting an AP is the resting membrane potential
At rest, the inside of the neuron has a negative charge and the outside of the neuron has a positive charge
The flow of ions is the current carried between cells in living tissues
Electrical charge Voltage = the difference of electric potential between two points

11. Ion Channels Potassium (K+) and Sodium (Na+) 2 types of Ion Channels
Leakage Channels
Gated Channels
Leakage channels – small, constant stream of ions
Gated channels – open in response to a change in membrane potential

12. Generation of Action Potentials
A stimulus causes a change in the resting membrane potential
If the resting membrane potential reaches a critical level (threshold) an action potential begins
Two Phases 1. Depolarization – the negative membrane potential becomes less negative, passes 0, and become positive 2. Repolarization – the membrane/neuron is returned to its resting potential
Remember the neuron is usually negatively charged compared to outside

13. Ion Channels During A.P. First opens voltage-gated Na+ channels
Na+ rush into the cell
Voltage-gated K+ channels open more slowly
K+ open as Na+ channels close
K+ ions flowing out of the cell allow repolarization
Remember the neuron is usually negatively charged compared to outside

14. “All-or-none principal”
As long as a stimulus meets the threshold, an action potential will occur
A stronger stimulus does not cause a larger action potential
Size of AP is always the same
Remember the neuron is usually negatively charged compared to outside

15. Conduction of Nerve Impulses
Nerve impulses travel from the area where the axon arises, down the axon, to the axon terminals
At the end of each axon terminal is a synaptic end bulb
The synaptic bulb of one neuron meets (but does not touch) a dendrite of another at the SYNAPSE
Remember the neuron is usually negatively charged compared to outside

16. The Synapse
Depolarization causes a series of events that results in the release of neurotransmitters from the axon terminal into the synaptic cleft
The neurotransmitters bind to receptors on the dendrites
Neurotransmitters cause gates to open in the post-synaptic neuron, and the signal continues
Remember the neuron is usually negatively charged compared to outside