NeuronsNeurons

Structure and Function

G.Burgess

NeuronNeuron• Specialized cells that send electric signals as impulses through the body.

NeuronNeuron

NeuronNeuronDendrites: receptor site for stimulus from

axon.

Axon: myelinated branch that leads the neural impulse away from the cell body.

Cell body: location for all metabolic processes

Myelin Sheath: insulating layers of lipid material that allow a stimulus to move quickly through the axon

Node: also called the Node of Ranvier, a space found between the myelin

sheathes on the axon

End brush: the branches off the axon that send a stimulus to a dendrite.

NeuronNeuron

Myelin Sheath•Acts as an insulator for the axon to allow neural impulses to move quickly from the cell body along the axon to the next dendrite.

•Made from many layers of membrane from Schwann cells. These are neural cells that help the axon to receive nutrients and to regenerate.

Myelin Sheath•Between the Myelin sheaths are spaces where the axon is not protected called nodes of Ranvier.

•Axons that are not protected by myelin and do not have nodes of Ranvier send impulses slower than those that are covered.

Resting PotentialResting PotentialThe normal unstimulated

membrane potential of a neuron at rest.

**Potential refers to the voltage or difference in the electrical charge of the cell. Stored energy that can be released to do work.

Resting PotentialResting PotentialNeurons at rest are polarized. The region outside the neuron has a charge opposite to the charge in side the cell.

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

Outside

Inside

NaNa++

Na+

K+

KK++

**Sodium has a more positive charge than potassium.

What causes neurons to beWhat causes neurons to bePolarizedPolarized??

Factors:

1. Differences in concentration of K and Na ions.

-Outside; concentration of Na > K ions

-inside; concentration of Na <K ions

**As a result there is a more positive charge outside the cell than inside the cell. This is caused by the sodium - potassium pump.

What causesWhat causesPolarizationPolarization??

Factors:

2. Potassium ions are able to diffuse through the cell membrane.

3. There are many large negatively charged ions in the cell that are not able to pass through the cell membrane.

What is the Sodium - What is the Sodium - Potassium PumpPotassium Pump

A Type of active transport protein that enables the movement of Na and K in and out of the cell.

How does the How does the sodium potassium sodium potassium

pump work?pump work?1. When gate is open inside the cell,

potassium ions are released and sodium ions are captured.

2. When the gate is opened to the out side of the cell, sodium ions are released and potassium ions are captured.

Action PotentialAction Potential is another name for impulse or electrical charge that moves through the neuron

Action PotentialAction PotentialWhat is needed for an impulse to move

quickly?Myelin sheaths accompanied by nodes of Ranvier

OR

if the neuron does not have any myelin or nodes of Ranvier

axon with a large diameter

ie. squid, earthworm

Types of NeuronsTypes of Neurons1. Sensory neurons: transmit impulses from receptors in sensory organs to the brain

2. Motor neurons: sends impulse from the brain to the muscles

Types of NeuronsTypes of Neurons3.Interneurons: send impulses from sensory neurons to motor neurons.

Groups of neurons that function together are called

What is a nerve What is a nerve impulse?impulse?

An impulse is an electric charge that passes along a cell.

The nerve impulse, also called The nerve impulse, also called action potentialaction potential, moves from , moves from dendrite to cell, body, to axon, to dendrite to cell, body, to axon, to dendrite, to cell body, to axon and dendrite, to cell body, to axon and so on.so on.