2 Nervous systemCoordinates and regulates the function of all other body systems2 major divisionCentral Nervous System (CNS)BrainSpinal CordPeripheral Nervous System (PNS)Nervescarry sensory info to the CNSMotor commands from CNS to musclesBoth systems are functionally distinct but they work together and are connected to each
4 Nervous system 2 types of cells Neurons Neuroglia transmit nerve impulses between parts of the nervous systemNeurogliaSupport and nourish neuronsMaintain homeostasisForm myelinHelp in signal transmission
5 Neurons 3 types of neurons Sensory neurons Interneuron Motor neuron Take messages to the CNSSensory receptors detect changes in the environmentInterneuronReceive input from the sensory neurons before communicate to motor neuronMotor neuronTakes message away from CNS to rest of body (organ, muscle or gland)Sensory receptors are specialized endings that detect changes in the environment
6 Central nervous system Peripheral nervous system Fig. 17.1bbrainsensory neuronssensoryreceptorsmotor neuronsskeletalmusclesother motor neuronssmooth musclecardiac muscleglandsCentral nervous systemPeripheral nervous system
7 Neurons Anatomy of a neuron Cell body Dendrites Axon Receive signals from other neurons and send them to cell bodyAxonConducts nerve impulses away from the cell body and send them toward other neurons
8 Neurons Myelin Sheath Formed by Schwann Cells around the axon Gaps between Schwan Cells are called nodes of RanvierMyelin Sheath gives nerves white colourHelps protect and insulate the nerveHelps conduct nerve impulseSchwann cells wrap themselves around an axon
13 cell bodydendritesMotor neuronnode of Ranvierdirection ofconductionaxonnucleus ofSchwann cell(neuroglial cell)effector(muscle)
14 Motor neuron node of Ranvier Interneuron effector (muscle) cell bodydendritesMotor neuronnode of Ranvierdirection ofconductionaxonInterneuroncell bodyeffector(muscle)dendritesaxon terminalcell bodydirection ofconductionsensoryreceptor(in skin)node of RanvieraxonSensory neurondendrites
15 Nerve impulse Nervous system uses a nerve impulse to send information When an axon is not conducting a nerve impulse we call it at resting potentialMore negative inside the axonPositive outside the axonElectrical potential of a neuron
16 Nerve impulse Difference in polarity is due to ion concentration More Na+ ions outside the axonMore K+ ions inside the axonSodium-potassium pumpsActively transport Na+ out of axon and K+ into axon3 Na+ for every 2 K+Why there is a more positive charge outside compared to inside the neuron
17 referenceelectrodeoutside axonrecordingelectrodeInside axon++++++++++axonalmembrane+++++++++inside axonK+Na+gated K+channelgated Na+channeloutside axona. Resting potential: more Na+ outside the axon and more K+ insidethe axon causes polarization.
18 Nerve Impulse Action potential During an action potential Rapid change in polarity across the axonNerve impulseDuring an action potentialDEPOLARIZATIONSodium channels open upSodium enters the axonAxon becomes more positiveREPOLARIZATIONPotassium gates openK+ moves outside of axonAxon returns to original negative chargeDue to concentration gradientNot Sodiium channels will closePotassium opens and it becomes negative again inside the axon
19 ++++++++++direction of impulse++++++++++open Na+channelb. Action potential be gins: depolarization occurs when Na+ gatesopen and Na+ moves inside the axon.
20 ++++++++++direction of impulse++++++++++open K+channelc. Action potential ends: repolarization occurs when K+ gates openand K+ moves outside the axon.
21 Nerve Impulse Refractory period Returns K+ to the inside of cell and Na+ outside through pumpreturning the neuron to its normal polarized state
22 +60+40Na+ movesto insideaxonK+ movesto outsideaxonactionpotential+20depolarizationrepolarizationVoltage (mV)–20–40threshold–60restingpotential123456Time (milliseconds)d. An action potential can be visualized if voltage changes aregraphed over time.