Understanding the Nervous System: Anatomy & Physiology Overview

1. ANATOMY & PHYSIOLOGY UNIT V NERVOUS & AUTONOMIC NERVOUS SYSTEM

2. Organization • Structural Divisions • Central Nervous System (CNS) • Brain • Spinal cord • Peripheral Nervous System (PNS) • Nerves connecting CNS to the rest of the body

3. Functions • Sensory function: • Afferent nerves carry information to CNS • Integrative function: • Processing information brought to CNS • Integrates everything & makes a plan • Motor function: • Efferent nerves carry information to all skeletal muscles & glands to carry out plan

4. Neuroglia (Glial) • Most abundant nerve cells • Located in CNS • Support, protect, insulate, nourish, care for neurons • “Nerve glue” • Some participate in phagocytosis; others assist in secretion of cerebrospinal fluid (CSF) • Do not conduct nerve impulses

5. Glial Cell Types • Astrocytes • Most abundant of glial cells • Support neurons • Form protective barrier around neurons of CNS • Blood-brain barrier • Ependymal • Line inside cavities of brain • Assist in CSF formation

6. Neuron • Information transmission • Many shapes & sizes • 3 types • Sensory (afferent): information to CNS • Motor (efferent): information from CNS • Interneuron – only in CNS; connects sensory & motor neurons

7. Neuron Structure • Dendrites • Receive information from other neurons • Cell body • Contains nucleus • Receives information from dendrites • Axon • Extension transmits info away from cell body • End become terminals storing a chemical neurotransmitter

8. Myelin Sheath • Layer of white fatty material encasing most long nerve fibers of CNS & PNS • Protects & insulates axon • White matter – myelin • Gray matter – unmyelinated fibers, cell bodies, interneurons • Nodes of Ranvier – exposed axon membrane • Formation differs between CNS & PNS

9. PNSMyelin Sheath formation • Schwann cells • Special cells surrounding axon; forms the myelin • Schwann cells nuclei & cytoplasm are located in outermost layer and called neurilemma • Neurilemma helps in nerve regeneration

10. CNSMyelin Sheath formation • Oligodendrocytes • Type of glial cell; forms myelin • No Schwann cell = no neurilemma = inability of CNS to regenerate

11. Nerve Impulse • Electrical signal, conveys info along a neuron • Action potential (electrical impulse) • Process of polarization, depolarization, & repolarization

12. Nerve Impulse – What is it?

13. Nerve Impulse – What causes it? • Potassium (K+)chief intracellular ion • Sodium (Na+) chief extracellular ion • Changes from (+) & (-) due to specific ions moving across cell membrane

14. What causes it? POLARIZATION • “Resting State” • K+ ions “leak” (diffuse) out of cell so takes positive charge with • Excess negative charged ions trapped in the cell • Resting membrane potential

15. What causes it? DEPOLARIZATION • Neuron stimulated =Changes neuron membrane =Allows Na+ into cell = Inside now positive • K+ pumped in by ATP

16. What causes it? REPOLARIZATION • Neuron membrane changes again = No more of Na+ into cell = Allows K+ to diffuse out of cell • K+ leaving takes positive charge and leaves negative charge **outward movement of K+ causes repolarization** • Eventually ATP drives out the Na+

17. Nerve Impulse – What causes it to move & why? • Nerve impulse moves along length of neuron • Each impulse depolarizes the adjacent membrane; moves wave-like • Saltatory Conduction • Impulse “jumps” from node of Ranvier to next node = increases speed of impulse • Myelinated fibers are fast conduction nerve fibers

18. Neurotransmitter • Chemical substance • Stored in tiny vesicles at axon terminals • Transmit signals across neuron synapse • Acetylcholine, norepinephrine • Epinephrine, serotonin, endorphins

19. Synapse Transmission • Synapse ---junction / space called synaptic cleft • Neurotransmitter acetylcholine (ACh) carry information from 1 neuron across the cleft to the next neuron • Receptive sites on dendrites allow ACh to bind (attach) • ACh is inactivated by acetylcholinesterase, an enzyme located in same area as the receptor sites

20. 4 Brain divisions

21. Largest • Right & left hemispheres • Corpus callosum • Large fiber tract of white matter bands joins 2 hemispheres

22. Cerebral cortex – outermost part • Thin layer gray matter • Primarily cell bodies & interneurons • Allows higher mental tasks • Bulk of cerebrum • White matter directly below cortex • Primarily myelinated axons forming connections between parts of brain & spinal cord

23. Basal nuclei – gray matter patches • Scattered throughout white matter • Neurotransmitter dopamine • Regulate body movement & facial expression

24. Cerebrum Markings • Gyrus / gyri • Elevations folded into the surface • Increases the amount of cerebral cortex • Sulcus / sulci • Grooves separating gyri • Fissure • Deep sulcus

25. Sulci / Fissures • Separate cerebrum into lobes • Central sulcus • Separates frontal lobe from parietal lobe • Lateral sulcus (fissure) • Separates temporal lobe from frontal & parietal lobes • Longitudinal fissure • Separates right & left hemisphere

26. 4 Lobes of Cerebrum

27. Frontal Lobe • Front of brain • Primary motor cortex • Anterior to central gyrus • Control voluntary muscle movement • Broca’s area • Left hemisphere frontal lobe • Motor speech role • Personality development, emotional & behavioral expression, perform high level tasks Decussation – crossing of fibers

28. Parietal Lobe • Located behind central sulcus • Reading, speech, taste • Primary somatosensory area • Receives general sensory info from body • Experience temperature, pain, light touch, an awareness of where your body is • Fibers cross

29. Temporal Lobe • Inferior to lateral sulcus (fissure) • Primary auditory cortex • Controls hearing • Olfactory area • Controls smell • Sensory info from taste buds

30. Occipital Lobe • Back of the brain • Visual cortex • Interprets sight • Visual reflexes & vision related functions

31. Diencephalon • Beneath cerebrum & above brain stem • Thalamus • Relay station • Sorts out information • Hypothalamus • Directly below thalamus • Regulate body processes & autonomic nerves • Controls pituitary gland

32. Cerebellum • Protrudes from under occipital lobe at skull base • Coordinates voluntary muscle activity • Integrate information to produce smooth muscle response

33. Brain Stem • Connects spinal cord to higher brain structures • White matter include sensory & motor tracts • Nuclei – exert effects on vital functions • 3 components : midbrain, pons, medulla oblongata

34. Midbrain • Extends from lower diencephalon to pons • Relays sensory & motor information

35. Pons • Extends from midbrain to medulla oblongata • Bridge tracts for info to & from brain structures • Regulates breathing rate & rhythm

36. Medulla Oblongata • Connects pons to spinal cord • Relay for sensory & motor information • Vital center • Important nuclei control heart rate, BP, resp. • Emetic (vomiting) center • Extremely sensitive to certain drugs

37. MeningesBrain & Spinal cord protection

38. Cerebrospinal Fluid (CSF)3rd protective layer of CNS • Formed from blood within brain • Clear fluid similar to plasma composition • Approx. ¼ cup circulates in an adult HOW IS IT FORMED? • 4 ventricles; 2 lateral, third, & fourth • Choroid plexus • Grapelike collection of blood vessels & ependymal cells suspended from roof of ventricles • Forms CSF

39. CSF – 2 PATHS • Leaves ventricles via 2 paths: • Central canal: hole in center of spinal cord eventually draining into subarachnoid space at base of spinal cord • Foramina: tiny holes in which CSF flows from fourth ventricles into subarachnoid spaces that encircles brain Eventually, CSF flows into arachnoid villi, into blood within dural sinuses, cerebral veins, to heart

40. Spinal Cord • Continuation of brain stem • Tube-like structure within spinal cavity • 17 inches long Same 3 protective measures as the brain • Bone • Meninges • CSF

41. GrayvsWhite GRAY MATTER • Butterfly shape, • Centrally located around central canal • Primarily cell bodies & interneurons • 2 projections • Dorsal horns (posterior) • Ventral horns (anterior) WHITE MATTER • Primarily myelinated axons grouped into nerve tracts • Sensory(ascending) • Carry information from periphery up spinal cord toward brain • Motor(descending) • Carry information from brain down spinal cord toward periphery

42. Spinal Nerves • Attached to spinal cord by 2 roots • Dorsal root • Ventral root • Roots are “packaged” together to form a spinal nerve Functions • Sensory pathway • Motor pathway • Reflex center

43. reflex Reflex • Involuntary response to a stimulus • Many occur at level of the spinal cord not the brain Reflex arc • Nerve pathway • Sensory receptor stimulated • Afferent neuron to spinal cord • Integrating center • Efferent neuron to muscle • Effector organ responds

44. Spinal Nerves 31 Pairs • 8 pairs cervical • 12 pairs thoracic • 5 pairs lumbar • 5 pairs sacral • 1 pair coccygeal

45. Spinal Nerves • Caudaequina • Lumbar & sacral nerves extend length of spinal cavity before exiting vertebrae through the foramina (tiny holes) • Dermatome • Distribution of dorsal root of spinal nerves innervating particular area of skin; named from the nerve it serves

46. Nerve Plexuses(networks) Cervical Plexus Brachial Plexus Lumbosacral Plexus C1 – C4 Muscles and skin of neck Phrenic nerve – diaphragm contraction C5 – C8 , T1 Muscles and skin of shoulder, arm, forearm, wrist, and hand; Axillary, ulna & radial nerves T12 , L1 – L5 , S1 to end Muscles and skin of lower abdominal wall, external genitalia, buttocks, lower extremities Sciatic nerve – entire leg & foot

47. Autonomic Nervous System (ANS) • Motor neurons within spinal nerves • Innervate smooth muscle, cardiac muscle & glands automatically & without conscious intervention • Motor pathway involves 2 neurons & 1 ganglion (cell body) between each neuron

48. ANS Motor pathway • Cell body of neuron #1 located in CNS • Axon (preganglionic fiber) of neuron #1 leaves CNS & extends to ganglion (cell body) of neuron 2 • Axon (postganglionic fiber) of neuron #2 leaves ganglion & extends to the organ • Postganglionic fibers secrete different neurotransmitters = different effects on organs

49. ANS Divisions Sympathetic & parasympathetic • Function automatically • Innervate all internal organs

50. Sympathetic Nervous System Fight or flight • All body systems effected • Norepinephrine (noradrenalin) --Neurotransmitter secreted by postganglionic (adrenergic) fibers