Biology 250: Human Anatomy

1. Biology 250: Human Anatomy Spring 2005 Nervous System II

4. Organization of Nervous System • 2 Major Components: • Central Nervous System (CNS) • Brain & Spinal Cord • Integrating and Command center • Peripheral Nervous System (PNS) • Nerves that extend from the brain and spinal cord • Outside of the CNS

6. Spinal Cord • Two-way communication to/from brain • Protected by bone, meninges, CSF • Epidural Space: between vertebrae / dura • Spinal cord ends at L1 • Conus Medullaris • Cauda Equina – extends beyond L1 • Safe for spinal taps

10. Spinal Cord Anatomy • Gray Matter – composed of cell bodies • Dorsal Horn : receives sensory input • Anterior Horn : delivers motor output • White Matter – composed of nerve fibers • Ascending : up to higher centers • Descending : down to lower centers • Transversely : cross over the different sides • Spinal Nerve – directly off of spinal cord

13. Spinal Cord Anatomy (Cont.) Spinal Cord Enlargements: • Cervical Enlargement • Site of Brachial Plexus • Nerves for the upper limbs • Lumbar Enlargement • Site of Lumbar Plexus • Nerves for the lower limbs

15. Spinal Cord Trauma • Paralysis – loss of motor function • Paraplegia: lower limbs affected • Quadriplegia: all limbs affected • Paresthesias – loss of sensation • Poliomyelitis – inflammation of SC (viral) • Destruction of anterior horn motor neurons • Amyotrophic Lateral Sclerosis (ALS) • Lou Gehrig’s Disease • Destruction of anterior horn motor neurons

16. Peripheral Nervous System • All neural structures outside Brain & SC • Mostly Sensory Receptors & Nerves • Responsible for voluntary movement

17. Functions of PNS • Subdivisions of PNS: • Sensory (Afferent) Division • Sends sensory info from body to CNS • Motor (Efferent) Division • Sends commands from CNS to body • Somatic Nervous System (Voluntary) • Autonomic Nervous System (Involuntary) • Sympathetic, Parasympathetic

19. Supporting Cells of PNS • Satellite Cells – surround neuron bodies • Function is Unknown • Schwann Cells • From Myelin Sheaths around peripheral nerves • Function similar to oligodendrocytes

21. Sensory Receptors Stimulus Type: • Mechanoreceptors - mechanical forces • Thermoreceptors – temperature change • Photoreceptors – light energy • Chemoreceptors – chemical changes • Nociceptors – pain receptors

22. Sensory Receptors (Cont.) Location Type: • Exteroceptors • Stimuli outside the body • Interoceptors • Stimuli within the body • Proprioceptors • Within the muscles, tendons, ligaments • Equilibrium, balance, body position

23. Nerve Connective Tissue • Endoneurium • Surrounds each individual axon • Perineurium • Surrounds each bundle (Fascicle) • Epineurium • Surrounds the entire nerve

25. Cranial Nerves • Olfactory: Smell • Optic: Sight • Oculomotor: Eye Movement • Trochlear: Eye Movement • Trigeminal: Facial sensation, Mastication muscles • Abducens: Eye Movement

26. Cranial Nerves (Cont.) • Facial: Facial expression • Vestibulocochlear: Hearing, Balance • Glossopharyngeal: Taste, Swallowing • Vagus: Sensation from most organs • Spinal Accessory: SCM, Trapezius • Hypoglossal: Tongue movement

27. Spinal Nerves • Arise from the spinal cord • Supply all parts of body except head, neck • 8 pairs of Cervical Nerves (C1-C8) • 12 pairs of Thoracic Nerves (T1-T12) • 5 pairs of Lumbar Nerves (L1-L5) • 5 pairs of Sacral Nerves (S1-S5) • 1 pair of Coccygeal Nerves (C0)

28. Spinal Nerves (Cont.) • C1-C7: exit Superior to vertebrae for which they are named. • C8: (no C8 vertebrae) • Exits Inferior to C7 vertebrae • All other Spinal Nerves • Exit Inferior to the vertebrae for which they are named

30. Spinal Nerves (Cont.) • All skin innervated by spinal nerves • Except C1; no skin innervation • Dermatome • Term used to describe the distribution of spinal nerves on the skin • Has been specifically mapped

33. Major Peripheral Nerves Upper Limb Nerves: • Axillary Nerve: controls Deltoid Muscle • Musculocutaneous Nerve: • Controls Biceps, Coracobrachalis, Brachalis • Median Nerve: muscles of anterior forearm • “Carpal Tunnel” • Ulnar Nerve: intrinsic hand muscles • “Funny Bone” • Radial Nerve: muscles of posterior forearm

35. Major Peripheral Nerves (Cont.) Lower Limb Nerves: • Femoral Nerve: muscles of anterior thigh • Sciatic Nerve: muscles of posterior thigh • “Sciatica” • Fibular (Peroneal) Nerve: • Muscles of anterior, lateral compartments of lower leg • Tibial Nerve: • Muscles of posterior compartment of lower leg

38. Stretch Reflex • “Knee-Jerk Reflex” Striking the patellar tendon causes: • Stretching of Quadriceps Muscles • Stimulates the muscle spindles • Mechanoreceptors, proprioceptors • Contraction of Quadriceps Muscles • Inhibition of Hamstring Muscles

40. Autonomic Nervous System (ANS) • Also called Involuntary Nervous System • No conscious control • Affects many of the organs • 2 Major Sub-Divisions: • Parasympathetic Division • Sympathetic Division

41. Parasympathetic Division • Most active in non-stressful situations • “Resting and Digesting” System • Concerned with keeping body energy low • BP, HR, RR are low • GI Tract is active • Skin is warm • No need for blood to go to skeletal muscle

42. Sympathetic Division • Most active in stressful situations • “Fight-or-Flight” System • Concerned with providing extra energy • BP, HR, RR are high • GI activity is halted • Blood diverted to skeletal muscles