THE NERVOUS SYSTEM

Part One:

The Anatomy

THE C.N.S

• The Central Nervous System is the a major part of the nervous system
• This makes up the brain and the spinal cord.
• Thoughts and directions are created here and sent out.
• Most animals have these

P.N.S

• The Peripheral Nervous System is the other main part
• This portion is made up of sensory and motor neurons
• This connects the C.N.S to the rest of the body.
• There are two subgroups of the P.N.S

EFFERENT AND AFFERENT SYSTEM

• Efferent (motor) nerves send signals out from the C.N.S.
• Afferent (sensory) nerves receive signals from a stimulus.
• There are two main parts of efferent neurons.

THE SOMATIC SYSTEM

• This is one of the major P.N.S efferent subgroups
• This part is what handles all voluntary actions
• This controls things like walking or talking.

THE AUTO-SOMATIC SYSTEM

• This is the second part of the efferent P.N.S
• This portion of controls all the involuntary actions
• These are breathing, and digestion.

THE STRUCTURE

• A neuron is made of 5 main parts.
• These parts are:
• The cell body, the axon, the dendrite,
• The Schwann cells, and the node of ranvier.

THE AXON

• The axon is basically a cable that connects the two ends.
• It allows signals to be transmitted from one end to the next.

NODES OF RANVIER

• An axon is covered by segments of Schwann cells.
• The segments that are not covered are called the nodes of ranvier.
• These segments are the sections that transmit signals along the axon.
• Being broken into segments allows the signals to hop from node to node.
• This process, saltatory conduction, greatly increases the speed of the signal.

THE SCHWANN CELLS

• These cells are responsible for the creation of myelin sheaths.
• These help insulate the axon of a neuron.
• These also help increase the speed of a signal as it pass down the axon.

THE DENDRITES

• The dendrites are what receive and transmit signals.
• They have neurotransmitters that hop from one neuron to another.
• This makes up the flow of information.

CELL BODY

• This part is what at holds the nucleus rand other organelles of the cell.

Part Two:

The Process

OVERVIEW

• The nervous system can be broken down into the following steps.
• Step 1- stimulus and sensory neuron send signal to internueron
• Step 2- Interneuron receives and transmits signal to brain
• Step 3- brains receives signal and sends new signal to motor neuron
• Step 4- motor neuron send signal to muscle and body motion occurs.

The Action Potential

RESTING STATE

• The cell's membrane are lined with sodium/potassium pumps
• They also have gated ion channels
• While at resting state the pump is inactive
• This allows for the inside to maintain a negative potential

DEPOLARIZATION

• The cell receives a stimulus an opens some on the gates
• Na+ enters and increases the +/- ratio
• The more Na+ that enters the more gates open depolarizing the cell
• Once the cell reaches its threshold and is depolarized An action potential is triggered.

RISING PHASE

• More gates open allowing more Na+ to enter
• The inside potential of the cell becomes more positive
• The cell becomes polarized

FALLING PHASE

• The cell opens up more k+ gates that allows potassium to leave the cell
• The sodium gates are closed blocking off the flow of Na+ into the cell
• The cells potential become more negative again.

UNDERSHOOT

• The Na+/K+ pump becomes active
• It allows in 2 K+ ions for every 3 Na+ ions that leave
• The cell then reaches it's original ratio of positive/negative charges
• The cell reenters resting state

TRASMITTION

• During action potential the flow of the depolarization move down the axon
• Eventually it reaches the presynaptic membrane
• This causes voltage- gated channel to open and an influx of Ca+ into the membrane
• The neurotransmitters then exit through the ligland- gated channel

NEUROTASMITTERS

• Depending on the type of transmitter the signal will be passed on or not
• Inhibitory transmitters stop the signal immediately
• An example would be GABA
• Excitatory Transmitters carry the signal on.
• Examples of this are acetylcholine, dopamine, and epinephrine.