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 from senses  passes to cell body (soma) message is passed to axon: long single fiber that carries message myelin sheath – insulates/protects axon; controls speed of impulses action potential – message’s electrical charge

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 (brain can understand these) 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

ascending tract carries sensory messages to brain 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 Additional Nervous System Video Link: https://www.youtube.com/watch?v=x8DjPqdlUbg (1:30min)