Nerve Net

A mesh of neurons that controls simple movements

Cnidarians

• Jellyfish, sea anemones
• Radial Body Plan
• Nerve Net

Flatworms

• Bilateral Body Plan
• Simplest animals with a bilateral nervous system
• They have nerves

Earthworm

• Bilateral Body Plan
• Has a Ganglion

Ganglion

A cluster of nerve cell bodies that function as a local integrating center

Cephalization

The formation of a head

Central Nervous System

The brain and spinal cord

Peripheral Nervous System

Nerves extending through the rest of the body

3 Classes of Neurons

1. Sensory Neurons
2. Interneurons
3. Motor Neurons

Sensory Neurons

• Respond to stimuli and sends info to brain and spinal cord
• Receive the initial stimulus

Interneurons

• Receive sensory input or send impulses to motor neurons
• Located in spinal cord and brain

Motor Neurons

Relay information from the brain ans spinal cord to the body's effectors which carry out the response

Cell Body

• Part of neuron
• Contains the nucleus and other organelles

Dendrite

• Part of neuron
• Short, branched slender extensions of the cell body that receive the stimuli

Axon

• Part of a neuron
• A long, slender extension of the cell body that sends messages to other cells

3 Parts of a Neuron

1. Cell Body
2. Dendrites
3. Axon

Polarized

There is a difference in electrical charge between the outside and the inside of the membrane

A neuron at rest is...

• Polarized - + on outside and - on inside
• Na is on outside and K is on inside

The neuron receives a stimulus that travels into the axon.  What happens next?

Na+ is pumped into the axon from the outside.  If the signal is strong enough more Na+ gates will open and the signal moves down the axon

The signal is received and the Na+ is pumped into the axon.  This causes the axon to become ...

depolarized

After the Na+ is pumped into the cell and the neuron becomes depolarized, then...

K+ is pumped out of the neuron to repolarized the neuron.

Once the stimulus reaches the end of the axon and the Na+ is on the inside and the K+ is on the outside, what happens next?

Na+ and K+ will move back to there original positions so the neuron can receive another signal

Neurotransmitter

Signaling molecules that diffuse across chemical synapses

Chemical Synapse

The narrow gap between the output zone of a neuron and the input of an adjacent cell

When the action potential reaches the end of the axon, what happens next?

Ca+ ions will move into the axon

Why do Ca+ ions move into the axon?

The Ca+ causes the neurotransmitter to be released and carry the action potential across the synapse

What happens after the neurotransmitters have been released and are carrying the action potential across the synapse?

Neurotransmitter will bind with receptro proteins on the surface of the adjacent cell and the action potential is sent on.

Acetylcholine

• A type of neurotransmitter
• Is used between a neuron and a muscle cell

Epinephrine, Norepinephrine

• A type of neurotransmitter
• Helps body respond to stress

Gamma Aminobutyric Acid (GABA)

• A type of neurotransmitter
• Usually an inhibitory neurotransmitter among neurons in the brain

Dopamine

• A type of neurotransmitter
• Affects fine motor control and pleasure seeking behaviors

Serotonin

• A type of neurotransmitter
• Affects mood and memory

Nerves

Long axons of many neurons that communicate between the brain or spinal cord and the rest of the body

Myelin Sheath

Encloses the axon that enhances the rate of action potential

Schwann Cells

The myelin sheath is made up of schwann cells that act as insulators and are separated by gaps of unsheathed axon

Nodes of Ranvier

Gaps of unsheathed axon

Reflex

• Are automatic movements made in response to stimuli
• Sensory neurons synapse directly to motor neurons