1. Chapter 49
Table of Contents
Section 1 Neurons and Nerve Impulses

2. Chapter 49 What is a neuron? Section 1 Neurons and Nerve Impulses
The scientific name for a nerve cell
is made up of a cell body, dendrites, and axons.
A cell body is the nucleus of a neuron and most of its organelles.
Dendrites extend from the cell body and are covered by a membrane.
The axon is a long membrane-bound projection that transmits information away from the cell body in the form of electrical signals.
These electrical signals are called action potentials

3. More on the axon
The end of an axon is called the axon terminal – It may contact and communicate with:
Muscle cells
A gland cell
Another neuron
Axons are covered by a lipid membrane called the myelin sheath
It insulates the axon
It speeds up the transmission of action potentials
Produced by Schwann cells that surround the axon
Gaps in the myelin sheath are called the Nodes of Ranvier

4. Let’s label a neuron

5. Chapter 49 Neuron Communication Section 1 Neurons and Nerve Impulses
Neurons do not touch each other or other cells
There is a small gap between neurons called a synaptic cleft. That region or junction is called synapses.
This is where neurons communicate
The signaling activity of the nervous system is made up of electrical activity within neurons and chemical flow between neurons.
These synapses do not communicate by touch, but by releasing chemicals, or neurotransmitters, into the synaptic cleft.
At a synapse, the transmitting neuron is called the presynaptic neuron and the receiving cell is called a postsynaptic cell

6. Chapter 49 Nerve Impulses Section 1 Neurons and Nerve Impulses
All cells have an electrical charge inside them that is different from outside the cell
A membrane potential is a difference in the electrical charge across a cell membrane.
A membrane potential can change with an addition or removal of ions within the cell.

7. Ions - Add to notes Atoms with a positive or negative charge
Example: Sodium is Na +1
Example: Potassium is K +1
Example: Calcium is Ca +2
Example: Chlorine is Cl -1

8. So what happens with ions?
Ions move in and out of the cell by passing through proteins that act as ion channels. Whether the ion channels are open or closed affects the membrane potential.
Just like with batteries, membrane potentials are expressed as voltage

9. Chapter 49 Resting Potential
Section 1 Neurons and Nerve Impulses
Chapter 49
Resting Potential
A neuron is at rest when it is not sending or receiving a signal.
When at rest, the neuron is more negatively charged on the inside than on the outside of the cell body.
Inside the cell has negatively charged proteins and K+ ions
Outside the cell, there is an accumulation of Na+
The electric potential across the cell membrane when the neuron is at rest is called the resting potential. It is about -70 millivolts.

10. Resting Potential

11. Chapter 49 Action Potential
Section 1 Neurons and Nerve Impulses
Chapter 49
Action Potential
When a dendrite or cell body is stimulated, the permeability of the neuron’s membrane changes suddenly.
A stimulus triggers the cell membrane to suddenly become permeable to Na+ ions and they rush into the cell
The membrane potential reverses and the neuron’s cell body becomes more positively charged than the exterior of a cell.
This reverse in polarity begins an action potential.

12. Action Potentials continued
Section 1 Neurons and Nerve Impulses
Chapter 49
Action Potentials continued
After the first segment of the neuron is stimulated the segment next to the first will become stimulated.
The action potential will continue away from the cell body.
Soon the voltage gated channels for Na+ close and the voltage gated channels for K+ open.
Soon after being stimulated, the interior of the neuron begins to become more and more negative.
This signals the end of the action potential.

13. Chapter 49 Refractory Period
Section 1 Neurons and Nerve Impulses
Chapter 49
Refractory Period
A neuron cannot generate another action potential until it has returned to its resting potential.
The period in which a neuron cannot send a signal is called the refractory period.
Returning the neuron to its resting potential requires energy.
Neurons need a continuous supply of ATP to keep the sodium potassium pump operating.

14. Sodium Potassium Pump

16. Conduction of a Nerve Impulse
Section 1 Neurons and Nerve Impulses
Chapter 49
Conduction of a Nerve Impulse

17. Chapter 49 Action Potential Section 1 Neurons and Nerve Impulses
Click below to watch the Visual Concept.
Visual Concept

18. Communication Between Neurons
Section 1 Neurons and Nerve Impulses
Chapter 49
Communication Between Neurons
Once an action potential reaches the axon terminal, it releases neurotransmitters into the synaptic cleft. These neurotransmitters bind to receptors proteins and open the ion channels of the new neuron cell.
If enough ion channels are opened, the action potential will continue through the new neuron. If not, the nervous signal will be terminated.
After the neurotransmitters have opened the ion channels, they will be cleared out of the synaptic cleft by being reabsorbed by the neuron that released them or broken down by enzymes.

19. Release of Neurotransmitter
Section 1 Neurons and Nerve Impulses
Chapter 49
Release of Neurotransmitter
Click below to watch the Visual Concept.
Visual Concept

20. Synaptic Transmission
Section 1 Neurons and Nerve Impulses
Chapter 49
Synaptic Transmission