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

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)