Chapter 7—The Nervous System Part 1

1. Chapter 7—The Nervous SystemPart 1

2. General Functions of the Nervous System • Sensory input – Gathering Information • Monitor changes occurring inside and outside the body • Changes = stimuli • Integration of stimuli • To process and interpret sensory input and decide if action is needed • Motor output—Responding to Stimuli • Sending instructions to activate muscles or glands

3. General Functions of the Nervous System

4. Structural Classification of the Nervous System • Central nervous system (CNS) • Brain • Spinal cord • Peripheral nervous system (PNS) • Nerves that extend from the brain and spinal cord • Spinal nerves—carry impulses to & from the spinal cord • Cranial nerves—carry impulses to & from brain • Carry impulses from sensory receptors to CNS & from CNS to appropriate muscles & glands

5. Functional Classification of the Peripheral Nervous System • Sensory (Afferent) Division • Nerve fibers that carry information to the central nervous system • Somatic – fibers from skin, muscles & joints • Visceral – fibers from internal organs Figure 7.1

6. Functional Classification of the Peripheral Nervous System • Motor (efferent) division • Nerve fibers that carry impulses away from the central nervous system • To effector organs, muscles, glands Figure 7.1

7. Functional Classification of the Peripheral Nervous System • Motor (efferent) division • Two subdivisions • Somatic nervous system = voluntary (skeletal muscle) • Autonomic nervous system = involuntary (smooth & cardiac muscle, glands) • 2 parts: sympathetic & parasympathetic Figure 7.1

8. Organization of the Nervous System Figure 7.2

9. Nervous Tissue—Structure & Function Nervous tissue made of 2 kinds of cells: Supporting cells = neuroglia (aka glial cells) Cannot transmit nerve impulses Can divide Most brain tumors are gliomas Function – to support, insulate, and protect neurons Neurons

10. Nervous Tissue: Support Cells of CNS • Astrocytes(half of neural tissue) • Abundant,star-shaped cells • Brace neurons • Form barrier between capillaries and neurons • Control the chemical environment of the brain Figure 7.3a

11. Nervous Tissue: Support Cells • Microglia • Spider-likephagocytes • Dispose of debris, including bacteria & dead brain cells Figure 7.3b–c

12. Nervous Tissue: Support Cells • Ependymal Cells • Line cavities of the brain and spinal cord • Circulatecerebrospinal fluid • Cushions CNS tissue

13. Nervous Tissue: Support Cells • Oligodendrocytes • Wrap around nerve fibers in the central nervous system • Producemyelinsheath that insulates nerve fibers Figure 7.3d

14. Nervous Tissue: Support Cells of PNS • Satellite Cells • Cushion & protect neuron cell bodies • Schwann Cells • Form myelin sheath in the peripheral nervous system Figure 7.3e

15. Nervous Tissue: Neurons • Neurons = Nerve Cells • Cells specialized to transmit messages • Major regions of neurons • Cell Body – nucleus and metabolic center of the cell • Processes – fibers that extend from the cell body • Nerve fibers covered in whitish, fatty material = myelin • Protects & insulates & increases transmission rate of nerve impulse

16. Cell Body Nissl substance Specialized rough endoplasmic reticulum Neurofibrils Intermediate cytoskeleton Maintains cell shape Nucleus Large nucleolus Neuron Anatomy Figure 7.4a

17. Neuron Anatomy • Extensions outside the cell body (can be 3-4’ long) • Dendrites – conduct impulses toward the cell body • Axons – conduct impulses awayfrom the cell body • Neuron has 100’s of dendrites, but only 1 axon Figure 7.4a

18. Figure 7.4a–b

19. Axons and Nerve Impulses • 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

20. Nerve Fiber Coverings • Myelin sheath—whitish, fatty material covering axons • Schwann cells – produce myelin sheaths that form in jelly-roll like fashion around nerve • Found in PNS only • Neurilemma – cytoplasm on outside • Nodes of Ranvier – gaps in myelin sheath along the axon Figure 7.5

21. Neuron

22. Neuron Cell Body Location • Most neuron cell bodies are found in the central nervous system • Gray matter – cell bodies and unmyelinated fibers • Nuclei – clusters of cell bodies within the gray matter of the central nervous system • White matter – myelinated fibers • Ganglia – collections of cell bodies outside the central nervous system

23. Functional Classification of Neurons • Sensory (Afferent) Neurons • Cell bodies in gangliaof PNS • Carry impulses from the sensory receptors to CNS • Cutaneous sense organs (skin) • Proprioceptors – detect stretch or tension (muscle) • Motor (Efferent) Neurons • Cell bodies in CNS • Carry impulses from the central nervous system to viscera, muscles, glands

24. Functional Classification of Neurons Free nerve endings (pain & temperature receptors) Meissner’s Corpuscles (touch receptors Golgi Tendon Organ (proprioceptors) Muscle Spindle (proprioceptor) Lamellara Corpuscles (deep pressure receptors)

25. Functional Classification of Neurons • Interneurons(Association Neurons) • Cell bodies inCNS • Found in neural pathways in the central nervous system • Connect sensory and motor neurons

26. Neuron Complex Figure 7.6

27. Structural Classification of Neurons • Multipolar neurons – many extensions from the cell body (all motor & association neurons) Figure 7.8a

28. Structural Classification of Neurons • Bipolar neurons – one axon and one dendrite • Rare in adults • In special sense organs (eye, nose) Figure 7.8b

29. Structural Classification of Neurons • Unipolar neurons – have a short, single process leaving the cell body • Axon conducts nerve impulses both toward & away from cell body • In PNS ganglia Figure 7.8c

30. Functional Properties of Neurons • Irritability – ability to respond to stimuli & convert it into a nerve impulse • Conductivity – ability to transmit an impulse • Resting Neuron (Baseline Anatomy): • The plasma membrane (of a neuron) at rest is polarized • Fewer positive ions are inside the cell than outside the cell (K+ inside, Na+outside)

31. Starting a Nerve Impulse • Depolarization – a stimulus depolarizes the neuron’s membrane • A depolarized membrane allows sodium(Na+) to flow insidethe membrane • The exchange of ions initiates an action potential(aka “nerve impulse”) in the neuron Figure 7.9a–c

32. Nerve Impulses

33. The Action Potential • If the action potential (nerve impulse) starts, it is propagated over the entire axon (all or none) • Impulses travel faster when fibers have a myelin sheath • Saltatory conduction – impulse can’t flow through myelin sheath, so it jumps across from node to node

34. Nerve Impulses

35. Repolarization • Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane • Restores electrical conditions at membrane to polarized or resting state • The sodium-potassium pump restores the original configuration (Na+ outside, K+ inside) • This action requires ATP

36. Nerve Impulses

37. 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 startedin the next dendrite

38. Transmission of a Signal at Synapses Figure 7.10