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Nervous System.

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Presentation on theme: "Nervous System."— Presentation transcript:

1 Nervous System

2 Nervous system Coordinates and regulates the function of all other body systems 2 major division Central Nervous System (CNS) Brain Spinal Cord Peripheral Nervous System (PNS) Nerves carry sensory info to the CNS Motor commands from CNS to muscles Both systems are functionally distinct but they work together and are connected to each

3 Basic Divisions of the Nervous System

4 Nervous system 2 types of cells Neurons Neuroglia
transmit nerve impulses between parts of the nervous system Neuroglia Support and nourish neurons Maintain homeostasis Form myelin Help in signal transmission

5 Neurons 3 types of neurons Sensory neurons Interneuron Motor neuron
Take messages to the CNS Sensory receptors detect changes in the environment Interneuron Receive input from the sensory neurons before communicate to motor neuron Motor neuron Takes 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. 17.1b brain sensory neurons sensory receptors motor neurons skeletal muscles other motor neurons smooth muscle cardiac muscle glands Central nervous system Peripheral nervous system

7 Neurons Anatomy of a neuron Cell body Dendrites Axon
Receive signals from other neurons and send them to cell body Axon Conducts 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 Ranvier Myelin Sheath gives nerves white colour Helps protect and insulate the nerve Helps conduct nerve impulse Schwann cells wrap themselves around an axon

9 Neurons

10 axon node of Ranvier myelin sheath

11 Sensory neuron cell body direction of conduction node of Ranvier sensory receptor (in skin) axon dendrites

12 axon cell body Interneuron dendrites axon terminal

13 cell body dendrites Motor neuron node of Ranvier direction of conduction axon nucleus of Schwann cell (neuroglial cell) effector (muscle)

14 Motor neuron node of Ranvier Interneuron effector (muscle)
cell body dendrites Motor neuron node of Ranvier direction of conduction axon Interneuron cell body effector (muscle) dendrites axon terminal cell body direction of conduction sensory receptor (in skin) node of Ranvier axon Sensory neuron dendrites

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 potential More negative inside the axon Positive outside the axon Electrical potential of a neuron

16 Nerve impulse Difference in polarity is due to ion concentration
More Na+ ions outside the axon More K+ ions inside the axon Sodium-potassium pumps Actively transport Na+ out of axon and K+ into axon 3 Na+ for every 2 K+ Why there is a more positive charge outside compared to inside the neuron

17 reference electrode outside axon recording electrode Inside axon + + + + + + + + + + axonal membrane + + + + + + + + + inside axon K+ Na+ gated K+ channel gated Na+ channel outside axon a. Resting potential: more Na+ outside the axon and more K+ inside the axon causes polarization.

18 Nerve Impulse Action potential During an action potential
Rapid change in polarity across the axon Nerve impulse During an action potential DEPOLARIZATION Sodium channels open up Sodium enters the axon Axon becomes more positive REPOLARIZATION Potassium gates open K+ moves outside of axon Axon returns to original negative charge Due to concentration gradient Not Sodiium channels will close Potassium opens and it becomes negative again inside the axon

19 + + + + + + + + + + direction of impulse + + + + + + + + + + open Na+ channel b. Action potential be gins: depolarization occurs when Na+ gates open and Na+ moves inside the axon.

20 + + + + + + + + + + direction of impulse + + + + + + + + + + open K+ channel c. Action potential ends: repolarization occurs when K+ gates open and K+ moves outside the axon.

21 Nerve Impulse Refractory period
Returns K+ to the inside of cell and Na+ outside through pump returning the neuron to its normal polarized state

22 +60 +40 Na+ moves to inside axon K+ moves to outside axon action potential +20 depolarization repolarization Voltage (mV) –20 –40 threshold –60 resting potential 1 2 3 4 5 6 Time (milliseconds) d. An action potential can be visualized if voltage changes are graphed over time.

23 Nerve impulse

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