1. DR /Noha Elsayed 2014--2015 Anatomy &Physiology CLS 221 Nervous system

2. objectives Describe the three functions of the nervous system. Describe the structure of a neuron. Explain how a nerve impulse is conducted along a nerve and across a synapse Describe the structure of a nerve, and distinguish between sensory,motor, and mixed nerves.

3. Nervous system Definition It is defined as the system of cells tissues and organs that regulates the body responses to the external and internal responses.

4. Functions of the Nervous System Sensory input— gathering information To monitor changes occurring inside and outside the body Changes = stimuli Integration To process and interpret sensory input and decide if action is needed Motor output A response to integrated stimuli The response activates muscles or glands

5. Functions of the Nervous System

6. Structural Classification of the Nervous System Central nervous system (CNS)  Brain  Spinal cord Peripheral nervous system (PNS) – Nerves outside the brain and spinal cord  Spinal nerves  Cranial nerves

7. Functional Classification of the Peripheral Nervous System Sensory (afferent) division Nerve fibers that carry information to the central nervous system Motor (efferent) division Nerve fibers that carry impulses away from the central nervous system

8. Functional Classification of the Peripheral Nervous System Motor (efferent) division (continued) Two subdivisions Somatic nervous system = voluntary Autonomic nervous system = involuntary

9. Nervous Tissue: Support Cells Support cells in the CNS are grouped together as “neuroglia” Function : to support, insulate, and protect neurons

10. Nervous Tissue: Support Cells 1-Astrocytes  Abundant, star-shaped cells  Form barrier between capillaries and neurons  Control the chemical environment of the brain

11. Nervous Tissue: Support Cells 2-Microglia  Spiderlike phagocytes  Dispose of debris

12. Nervous Tissue: Support Cells 3-Ependymal cells  Line cavities of the brain and spinal cord.  Circulate cerebrospinal fluid

13. Nervous Tissue: Support Cells 4-Oligodendrocytes  Wrap around nerve fibers in the central nervous system.  Produce myelin sheaths.

14. Nervous Tissue: Support Cells Satellite cells Protect neuron cell bodies Schwann cells Form myelin sheath in the peripheral nervous system

15. Nervous Tissue: Neurons Neurons = nerve cells: – Cells specialized to transmit messages Major regions of neurons 1-Cell body— nucleus and metabolic center of the cell 2-Processes —fibers that extend from the cell body

16. Nervous Tissue: Neurons Cell body  Nucleus.  Large nucleolus. Processes outside the cell body  Dendrites—conduct impulses toward the cell body.  Axons—conduct impulses away from the cell body.

17. 3-Axons end in axonal terminals Axonal terminals contain vesicles with neurotransmitters Axonal terminals are separated from the next neuron by a gap Synaptic cleft —gap between adjacent neurons Synapse —junction between nerves

18. Myelin sheath —whitish, fatty material covering axons Schwann cells —produce myelin sheaths in jelly roll–like fashion Nodes of Ranvier —gaps in myelin sheath along the axon

19. Functional Classification of Neurons Interneurons (association neurons)  Found in neural pathways in the central nervous system  Connect sensory and motor neurons

21. Multipolar neurons—many extensions from the cell body

22. Bipolar neurons—one axon and one dendrite

23. Functional Properties of Neurons Irritability Ability to respond to stimuli Conductivity Ability to transmit an impulse

24. Nerve Impulses Resting neuron  The plasma membrane at rest is polarized  Fewer positive ions are inside the cell than outside the cell Depolarization  A stimulus depolarizes the neuron’s membrane  A depolarized membrane allows sodium (Na+) to flow inside the membrane The exchange of ions initiates an action potential in the neuron

25. Nerve Impulses

26. Action potential If the action potential (nerve impulse) starts, it is propagated over the entire axon Impulses travel faster when fibers have a myelin sheath

27. Nerve Impulses Action potential  If the action potential (nerve impulse) starts, it is propagated over the entire axon  Impulses travel faster when fibers have a myelin sheath

28. Transmission of a Signal at Synapses Impulses are able to cross the synapse to another nerve  Neurotransmitter is released from a nerve’s axon terminal  The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter  An action potential is started in the dendrite

29. A-osteocytes. B-Osteoclaset. C-Osseous matrix. D- Haversian system.