The Nervous System

1
The Nervous System

• The nervous system controls and coordinates
  functions throughout the body and responds to
  internal and external stimuli.

2
Neurons

• Messages carried by the nervous system are
  electrical signals called impulses.
• Impulses are transmitted by neurons

3
3 Types of Neurons

• Based on the direction in which an impulse
  travels
• Sensory neurons carry impulses from the sense
  organ s to the spinal cord
• Motor neurons carry impulses from the brain and
  the spinal cord to muscles and glands
• Interneurons connect sensory and motor neurons
  and carry impulses between them

4
Neurons (nerve cells)
5
Parts of a neuron

• Cell body The largest part of the neuron,
  contains the nucleus and cytoplasm
• Dendrites short branches off the cell body that
  carry impulses from the environment or from other
  neurons toward the cell body.

6

• Axon long fiber that carries impulses away from
  the cell body
• Myelin sheath insulating membrane located on
  the axon
• has gaps in it called nodes, these nodes speed up
  the rate the impulse moves

7
The Nerve ImpulseThe resting impulse

• The resting neuron has a positive charge outside
  the cell and a negative charge inside the cell.
• This is caused by sodium and potassium pump which
  pumps sodium out and potassium into the cell.
• Potassium can leak out of the cell faster than
  sodium which leaves a negative charge on the
  inside of the cell.

8

• This leaves a positive charge outside the cell
  and a negative charge inside the cell membrane.
• Resting potential the electrical charge across
  the cell membrane of a neuron in its resting
  state
• http//highered.mheducation.com/sites/0072495855/
  student_view0/chapter2/animation__how_the_sodium_p
  otassium_pump_works.html

9
The Moving Impulse

• An impulse begins when a neuron is stimulated by
  another neuron or by the environment.
• The impulse travels down the axon away from the
  cell body and toward the axon terminals
• Na flows into the cell reversing the resting
  potential

10
Action potential

• Action potential the change from a negative to
  a positive charge along the axon
• As the impulse passes the K gates open up an
  allow K to flow out
• This restores the resting potential
• http//highered.mheducation.com/sites/0072495855/
  student_view0/chapter14/animation__the_nerve_impul
  se.html

11
Threshold

• The strength of an impulse is always the same
• It either happens or it doesnt
• Threshold the minimum level of a stimulus that
  is required to activate a neuron.

12
The Synapse

• At the end of the neuron, the impulse reaches an
  axon terminal.
• This is where the neuron touches another cell.
• The neuron can pass the impulse along to another
  cell.
• This location is called a synapse.

13
Neurotransmitters

• The chemicals used by neurons to transmit an
  impulse across a synapse to another cell