THE NERVOUS SYSTEM
THE NERVOUS SYSTEMDEFINITIONthe bodys 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 NEURONdendrites: 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 messagePARTS OF A NEURON,
PART IIterminal 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!
TYPES OF NEURONSsensory 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
TRACTSascending tract carries sensory messages to brain
descending tract carries motor impulses & messages to the
body (from brain)
2 MAIN BRANCHES OF NERVOUS SYSTEMcentral 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
SPINAL CORDCNS sends/receives messages through spine &
PNS
spinal cord is also responsible for reflexes that do not involve
the brain (its too busy!)(i.e. knee-jerk)
