Body Systems• All our body systems

work together to maintain homeostasis within our bodies.

• Nervous• Circulatory (includes

respiration)

• Lymphatic• Digestive• Excretion (includes

integumentary)• Endocrine• Immune

Nervous System

• Our nervous system allows us to understand what is happening around us as well as within us.

• It allows us to develop inferences to explain the observations we make using our five senses.

• It is a network of cells (called neurons) that send electrical messages (called impulses) to and from our cells, tissues, and organs.

Neurons

Neuron parts* Parts of the neuron include:1. Cell body, 2. dendrites, 3. axon,and 4. axon terminals.* The axons are covered with a myelin sheath. There are nodes separating the Schwann cells that make up the myelin sheath. As the impulse travels along the axon, it travels from node to node; thereby, increasing the speed at which an impulse can travel down a nerve cell.

1.

2.

3.

4.

Movement of an Impulse

• Without nodes

• http://www.ship.edu/~cgboeree/actionpot.html

• With nodes

The cell body of a neuron: note that in

contains all the cell organelles

found in eukaryotic

cells

Types of Neurons• Sensory Neurons:

carry impulses from our senses and our body to our CNS.

• Motor Neurons: carry impulses from our CNS to our body (either another neuron, gland cell, or a muscle cell).

• Interneurons: connect sensory and motor neurons.

Example of a Motor Neuron

Sensory Neuron

• Typically the cell body of a sensory neuron is found protruding from the middle of the axon.

How is an electrical impulse sent along a neuron: Resting Potential

• Sodium/Potassium pumps actively pump (3) Na+ out of the cell and (2) K+ into the cell.

• Na+ channels are closed so Na+ are not able to move into the cell.

• This generates a separation of charges so that the inside of the cell is relatively – and the outside is relatively +.

• The cell will remain in this state (at rest) until it is stimulated.

Inside of cell

Outside of cell

How is an electrical impulse sent along a neuron: Action Potential

• A nerve impulse starts when a stimuli such as light waves (eye), chemicals in scents or food (nose or tongue) , pressure (touch/organs), sound waves (ear), or another chemical, disturbs a neuron in its resting potential.

• This causes Na+ channels to open and the Na+ diffuse (flood) into the cell leading to a more positive charge inside than outside.

• This sudden reversal of charges (or voltage) causes other sodium channels nearby to open and the action potential continues down the neuron.

Action Potential

At rest. As the action potential passes, potassium gates open, allowing K+ ions to flow out.

At the leading edge of the impulse, the sodium gates open. The membrane becomes more permeable to Na+ ions and an action potential occurs.

The action potential continues to move along the axon in the direction of the nerve impulse.

How is an electrical impulse sent along a neuron: Repolarization

• The sodium/potassium pumps return the cell to a resting state by actively pumping (3) Na+ out of the cell and (2) K+ into the cell.

• http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/ion_pump/ionpump.html

An action potential will continue down a neuron until it reaches the axon terminal.

Direction of a nerve impulse: travels from the dendrites to the axon terminal

• At the axon terminal of a neuron there is either 1. another neuron, 2. a gland cell, or 3. a muscle cell.* However, neurons don’t actually touch

other cells regardless if that cell is another neuron, a gland cell, or a muscle cell.

Synapse: The space between neurons (because neurons don’t touch).

Synapse Animation

• Here’s what happens at the synapse:

• http://www.tvdsb.on.ca/westmin/science/sbioac/homeo/synapse.htm

Neurotransmitters

Na+ channel open

• They trigger Na+ channels to open so the sodium ions diffuse into the neuron.

http://www.ship.edu/~cgboeree/actionpot.html

The red dot are neurotransmitters sitting on the sodium channels

Na+ channel closed

The black dots are Na+ ions

Examples of neurotransmitters

• Acetylcholine: Neuron to muscle

• Muscle Contractions; stimulates neurons

• Dopamine: Neuron to neuron

• Associated with the pleasure center of the brain; involved in feelings of enjoyment in regards to food and sex.

• Certain drugs cause the release of dopamine or inhibit its reuptake.

• Serotonin: Neuron to neuron

• Involved in sexuality and appetite.

• An imbalance can lead to depression and bipolarism.