Chapter 7—The Nervous System Part 3

1. Chapter 7—The Nervous SystemPart 3

2. Cerebellum Figure 7.15a

3. Protection of the Central Nervous System • Scalp and skin • Skull and vertebral column • Meninges • Cerebrospinal fluid (CSF) • Blood-brain barrier Figure 7.16a

4. Protection of the CNS Figure 7.17a

5. Meninges • 3 connective membranes • Dura mater • Leathery = hard mother • Double-layered external covering • Periosteum – attached to inner surface of the skull • Meningeal layer – outer covering of the brain • Folds inward in several areas to attach to cranial cavity

6. Meninges • Arachnoid layer = weblike = spider • Middle layer • Web-like – span the subarachnoid space to attach to pia matter • Pia mater = gentle mother • Internal layer • Clings to the surface of the brain

7. Meninges

8. Cerebrospinal Fluid (CSF) • Found in subarachnoid space • Similar to blood plasma composition • Formed by the choroid plexus – capillaries hanging from roof of ventricles • Forms a watery cushion to protect the brain • Circulated in arachnoid space, ventricles, and central canal of the spinal cord • Absorbed into venous blood in dural sinuses

9. Ventricles and Location of the CSF Figure 7.17a–b

10. Circulation of the Cerebrospinal Fluid Figure 7.17c

11. Blood Brain Barrier • Includes the least permeable capillaries of the body • Excludes many potentially harmful substances • Brain could not handle fluctuations of chemicals in blood • Only water, glucose, essential amino acids can pass in • Useless as a barrier against some substances, including • Fats and fat solublemolecules • Respiratory gases • Alcohol • Nicotine • Anesthesia

12. Spinal Cord • Extends from the foramen magnum of the skull (from medulla oblongata) to the region of T12, L1 vertebrae • 31 pair of spinal nerves arise from the spinal cord • Approximately 17” long • 2-way conduction pathway to brain Figure 7.18

13. Below T12 is the caudaequina(a collection of spinal nerves) • Because vertebrae grow faster than cord, cord doesn’t reach end of vertebral column • Enlargements occur in the cervical and lumbar regions • Serve upper & lower limbs • Major reflex center • Covered by meninges

14. Spinal Cord Anatomy Figure 7.20 (1 of 2)

15. Spinal Cord Anatomy Figure 7.20 (2 of 2)

16. Spinal Cord Anatomy • Internal gray matter - mostly cell bodies • Dorsal (posterior) horns – association or interneurons & sensory neurons • Anterior (ventral) horns – motor neurons of somatic (voluntary) • Gray matter surrounds thecentral canal • Central canal is filled with cerebrospinal fluid • Exterior white matter – conduction tracts • Dorsal,lateral, ventral columns • Dorsal & ventral roots fuse into spinal nerves • Central Canal filled with cerebrospinal fluid Figure 7.19

17. Spinal Cord Anatomy • Meningescover the spinal cord • Spinal Nerves leave at the level of each vertebrae • Dorsal root – cell bodies of sensory neurons • Associated with the dorsal root ganglia – collections of cell bodies outside the central nervous system • Ventral root – motor neurons of somatic system • Contains axons

18. Spinal Cord Anatomy Figure 7.21

19. Peripheral Nervous System (PNS) • Nerves and ganglia (= groups of neurons cell bodies) outside the central nervous system • Nerve = bundle of neuron fibers • Neuron fibers are bundled by connective tissue

20. PNS: Structure of a Nerve • Endoneuriumsurrounds each fiber • Groups of fibers are bound into fascicles by perineurium • Fascicles are bound together by epineurium Figure 7.20

21. PNS: Classification of Nerves • Mixed nerves • Both sensory and motor fibers (all spinal nerves are mixed) • Sensory (afferent) nerves • carry impulses toward the CNS • Motor (efferent) nerves • carry impulses away from the CNS

22. PNS: Cranial Nerves • 12 pairs of nerves that mostly serve the head and neck • Only the pair of vagus nerves extend to thoracic and abdominal cavities • Numbered in order, front to back • Most are mixed nerves, but three are sensory only: • Optic, olfactory, vestibulocochlear

23. PNS: Cranial Nerves • I Olfactory nerve – sensory for smell • II Optic nerve – sensory for vision • IIIOculomotor nerve – motor fibers to eye muscles • IVTrochlear – motor • V Trigeminal nerve – sensory for the face; motor fibers to chewing muscles • VIAbducens nerve – motor fibers to eye muscles • VII Facial nerve – sensory for taste; motor fibers to the face • VIIIVestibulocochlear nerve – sensory for balance and hearing fiber to eye muscles

24. Cranial Nerves • IX Glossopharyngeal nerve – sensory for taste; motor fibers to the pharynx • X Vagus nerves – sensory and motor fibers for pharynx, larynx, and viscera • XI Accessory nerve – motor fibers to neck and upper back • XII Hypoglossal nerve – motor fibers to tongue

25. PNS: Spinal Nerves • There are a pair of spinal nerves at the level of each vertebrae for a total of 31 pairs • Spinal nerves are formed by the combination of the ventral and dorsal roots of the spinal cord • Spinal nerves are named for the region from which they arise

26. PNS: Spinal Nerves Figure 7.22a

27. Anatomy of Spinal Nerves • Spinal nerves divide soon after leaving the spinal cord • Only 1/2” long • Dorsal rami– serve the skin and muscles of the posterior trunk • Ventral rami– forms a complex of networks (plexus) for the anterior & limbs • Ramicontain motor & sensory fibers • Damage to spinal nerve causes loss of sensation & paralysis • Plexus – complex network of nerves • See Table 7.2 for detailed info regarding Spinal Nerves Plexuses

28. PNS: The Spinal Nerves

29. PNS: Autonomic Nervous System (ANS) • The involuntary branch of the nervous system • Regulates activities of cardiac & smooth muscles & glands • Maintains homeostasis • Motor subvision of the PNS • Consists of only motor nerves • Divided into two divisions • Sympathetic division • Parasympatheticdivision

30. PNS: Differences Between Somatic and Autonomic Nervous Systems • Nerves • Somatic – one motor neuron (nerves controlling skeletal muscles) • Cell body in CNS; axon in spinal nerves extend to muscle • Autonomic – preganglionic and postganglionic nerves • 2 motor nerves: • 1stin brain or cord (preganglionic), • 2nd is outside CNS (postganglionic), extends to organ it serves

31. Differences Between Somatic and Autonomic Nervous Systems • Effector organs • Somatic – skeletal muscle • Autonomic – smooth muscle, cardiac muscle, and glands • Neurotransmitters • Somatic – only usesacetylcholine • Autonomic – uses acetylcholine, epinephrine, or norepinephrine • Autonomic divided into: • Sympathetic – mobilizes body during extreme situations • Parasympathetic– allows us to unwind & conserve energy

32. Comparison of Somatic and Autonomic Nervous Systems Figure 7.24

33. PNS: Anatomy of the Sympathetic Division • Originates from T1 through L2 • Ganglia are at the sympathetic trunk (near the spinal cord) • Short pre-ganglionic neuron and long postganglionic neuron transmit impulse from CNS to the effector • Norepinephrine and epinephrine are neurotransmitters to the effector organs

34. PNS: Anatomy of the Parasympathetic Division • Originates from the brain stem and S1 through S4 • Terminal ganglia are at the effector organs • Always uses acetylcholine as a neurotransmitter