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1 Neurons and Synapses Types of Neurons SensoryMotor Interneurons.

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Presentation on theme: "1 Neurons and Synapses Types of Neurons SensoryMotor Interneurons."— Presentation transcript:

1 1 Neurons and Synapses Types of Neurons SensoryMotor Interneurons

2 2 Spinal Cord Brain Sensory Neuron Sensory Neurons zINPUT From sensory organs to the brain and spinal cord. Drawing shows a somatosensory neuron Vision, hearing, taste and smell nerves are cranial, not spinal

3 3 Spinal Cord Brain Sensory Neuron Motor Neuron Motor Neurons zOUTPUT From the brain and spinal cord To the muscles and glands.

4 4 Spinal Cord Brain Sensory Neuron Motor Neuron Interneurons zInterneurons carry information between other neurons only found in the brain and spinal cord.

5 5 Structures of a neuron

6 6 The cell body yRound, centrally located structure yContains DNA yControls protein manufacturing yDirects metabolism yNo role in neural signaling zContains the cells Nucleus

7 7 Dendrites zInformation collectors zReceive inputs from neighboring neurons zInputs may number in thousands zIf enough inputs the cells AXON may generate an output

8 8 Dendritic Growth zMature neurons generally cant divide zBut new dendrites can grow zProvides room for more connections to other neurons zNew connections are basis for learning

9 9 Axon zThe cells output structure zOne axon per cell, 2 distinct parts ytubelike structure branches at end that connect to dendrites of other cells

10 10 Myelin sheath zWhite fatty casing on axon zActs as an electrical insulator zNot present on all cells zWhen present increases the speed of neural signals down the axon. Myelin Sheath

11 11 How neurons communicate zNeurons communicate by means of an electrical signal called the Action Potential zAction Potentials are based on movements of ions between the outside and inside of the cell zWhen an Action Potential occurs a molecular message is sent to neighboring neurons

12 12 Ion concentrations Cell Membrane in resting state K+ Na+ Cl- K+ A- Outside of Cell Inside of Cell Na + Cl-

13 13 The Cell Membrane is Semi- Permeable

14 14 Resting Potential zAt rest the inside of the cell is at -70 microvolts zWith inputs to dendrites inside becomes more positive zif resting potential rises above threshold an action potential starts to travel from cell body down the axon zFigure shows resting axon being approached by an AP

15 15 Depolarization ahead of AP zAP opens cell membrane to allow sodium (NA+) in zinside of cell rapidly becomes more positive than outside zthis depolarization travels down the axon as leading edge of the AP

16 16 Repolarization follows zAfter depolarization potassium (K+) moves out restoring the inside to a negative voltage zThis is called repolarization zThe rapid depolarization and repolarization produce a pattern called a spike discharge

17 17 Finally, Hyperpolarization Repolarization leads to a voltage below the resting potential, called hyperpolarization zNow neuron cannot produce a new action potential This is the refractory period

18 18 Neuron to Neuron zAxons branch out and end near dendrites of neighboring cells zAxon terminals are the tips of the axons branches zA gap separates the axon terminals from dendrites zGap is the Synapse Cell Body Dendrite Axon

19 19 Synapse zaxon terminals contain small storage sacs called synaptic vesicles yvesicles contain neurotransmitter molecules Sending Neuron Synapse Axon Terminal

20 20 Neurotransmitter Release zAction Potential causes vesicle to open zNeurotransmitter released into synapse zLocks onto receptor molecule in postsynaptic membrane

21 21 Locks and Keys zNeurotransmitter molecules have specific shapes positive ions (NA+ ) depolarize the neuron negative ions (CL-) hyperpolarize zWhen NT binds to receptor, ions enter zReceptor molecules have binding sites

22 22 Some Drugs work on receptors zSome drugs are shaped like neurotransmitters zAntagonists : fit the receptor but poorly and block the NT ye.g. beta blockers zAgonists : fit receptor well and act like the NT ye.g. nicotine.

23 23 Summary z3 types of neurons zThe cell membrane zIon movements zAction potentials zSynapse zNeurotransmitters zReceptors and ions zAgonists and antagonists

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