THE NERVOUS SYSTEM
DEFINITION
 the body’s communicator
 electrical & chemical changes
relay messages
 nerves are strings of neurons (special
cells) that pass on messages (neural
impulses) to one another (take messages in
at one end & send message out another end)
PARTS OF A NEURON
 dendrites: branched fibers that RECEIVE
message to pass through cell body (soma)
 message is passed on to axon: single fiber
that carries message after passing through
dendrite & soma along to other neurons
 action potential – electrical charge of the
message
PARTS OF A NEURON, PART II
 terminal buttons are activated at end of axon
& want to pass message along BUT…
 neurons are separated by a synapse (gap) so…
 electrical impulse is converted into chemical
message that activates neurotransmitters –
chemicals that transfer the messages across
synaptic gap
 picked up by dendrites to start all over again!
HOW NEURONS WORK VIDEO
TYPES OF NEURONS
 sensory or afferent neurons – send message
from sensory receptor cells to central nervous
system
 motor or efferent neurons – deliver messages
from CNS to muscles & glands
 interneurons – communicate between neurons
AFFERENT VS. EFFERENT NERVES
TRACTS
ascending tract carries sensory
messages to brain
descending tract carries motor
impulses & messages to the body
(from brain)
2 MAIN BRANCHES OF NERVOUS
SYSTEM
 central nervous system (CNS)=
brain & spinal cord: coordinates all
bodily functions by processing neural
messages & sending commands to body
 peripheral nervous system =
connect CNS to body: smaller branches
of nerves & nerve fibers that
communicate messages between CNS
& body
BREAKDOWN OF PERIPHERAL N.S.
 somatic nervous system controls
voluntary acts (tapping foot, walking, etc)
 autonomic nervous system are
involuntary acts (digestion, breathing, etc.)
BREAKDOWN OF AUTONOMIC N.S.
 sympathetic system – reactions to
emergencies & strenuous activity; “fight or
flight”
 parasympathetic system – conserves
energy, helps body behave normally,
monitors routine activities, & calms body
after sympathetic arousal
BREAKDOWN IMAGE
SPINAL CORD
 CNS sends/receives messages through
spine & PNS
 spinal cord is also responsible for
reflexes that do not involve the brain
(it’s too busy!)(i.e. knee-jerk)
SUMMARY VIDEO