Download Ch. 35.2

Ch. 35.2
THE NERVOUS SYSTEM
 Nearly all multicellular organisms have
communication systems
 Specialized cells carry messages from one cell
to another.
 NERVOUS SYSTEM CONTROLS AND
COORDINATES FUNCTIONS THROUGHOUT
THE BODY AND RESPONDS TO INTERNAL
AND EXTERNAL STIMULI
Neurons
 Electrical signals are called impulses
 NEURONS  cells that transmit the electrical
impulses
 SENSORY: impulses from sense organs to spinal
cord and brain
 INTERNEURONS: connect sensory ad motor
neurons
Neuron Structure
 Largest part is the CELL BODY  contains the
nucleus and cytoplasm
 Metabolic activity takes place in the cell body
 Short, branched extensions DENDRITES  carry
impulses from the environment or other neurons
TOWARD the cell body
 Long fibers AXON  carry impulses AWAY from
the cell body
 Neurons may have many dendrites by only one
axon
 Form NERVES when axons and dendrites are
clustered together
 Some neurons are surrounded by an insulated
layer
 MYELIN SHEATH
The Nerve Impulse
 Nerve impulse is like electricity through a
wire
 Sodium/potassium pump  ions diffuse
across the cell membrane
 Builds up charges and creates a RESTING
POTENTIAL
Moving Impulse
 Nerve impulse begins when a neuron is
stimulated by another neuron or by its
environment
 The protein channels help ions pass in and
out of the cell
 When positive ions flow in, gains a positive
charge an then switches to a negative charge
 ACTION POTENTIAL
 One impulse causes another impulse at the
next point on the membrane
Threshold
 Strength of impulse is always the same
 Minimum level of a stimulus that is required
to activate a neuron is THRESHOLD
The Synapse
 Neurons make contact with other cells at the
axon terminal
 Neuron transfer impulses to another cell is a
SYNAPSE
 NEUROTRASMITTERS  chemicals used by
a neuron to transmit an impulse across a
synapse to another cell