Peripheral Nervous System

1. Peripheral Nervous System Ch. 13

2. Sensory receptors: • Classified according to location and type of stimulation • Location: Exteroceptors - stimulation arising outside of the body (touch, pain, and temperature) Interoceptors - stimulation arising inside the body (chemical messengers, stretching of tissue, and internal temperature)

3. Proprioceptors - respond to internal stimuli, but located only in skeletal muscle, tendons, joints, and ligaments and C.T. covering bones and muscles. Stimulus detected: - Mechanoreceptors (touch, pressure, vibrations) - Thermoreceptors (temperature) - Photoreceptors (light) - Chemoreceptors (smell, taste, blood chemistry) - Nociceptors (pain)

4. Nerves: Nerve consists of parallel bundles of peripheral axons enclosed by connective tissue coverings: - Epineurium - Perineurium (surrounds fascicle) - Endoneurium (surrounds axon)

6. Direction of transmission: - Mixed nerves - contain both sensory and motor fibers and transmit to and away from CNS - Sensory nerves - contain sensory fibers carrying impulses toward the CNS - Motor nerves - contain sensory fibers carrying impulses away from the CNS • PNS nerves classified as cranial or spinal

7. Regeneration of a severed nerve: 1- Separated ends seal off and swell 2- Axon and myelin sheath (of injured site) disintegrates 3- Schwann cells and macrophages migrate to site to phagocytize debris 4- Neurilemma remains intact and schwann cells proliferate 5- Axon "sprouts", guided by schwann cells, gap to original contact

9. Cranial nerves: • 12 pairs • Classified as sensory, motor or mixed • First two pairs attach to the forebrain • Remaining ten pairs attach to the brainstem

12. Olfactory nerve (I) • Sensory • Sense of smell • Olfactory bulbs that terminate into filaments piercing the cribriform plate of the ethmoid bone. • Clinical: person is asked to identify an odor • Anosmia: lack of smell

14. Optic nerve (II) • Sensory • Vision • Not a true nerve but an extension of the brain • Begins at the retina, converges at the optic chiasma, partial crossing over of the fibers to enter the thalamus. Optic radiations take impulse to the visual cortex in the occipital lobe.

16. Oculomotor Nerve (III) • Motor • Motor fibers to the 4 of the six eye muscles • Eyeball movement • Pupil constriction

18. Trochlea Nerve (IV) • Motor • Movement of one eye muscle: superior oblique muscle • Downward and lateral movement of the eyeball.

19. Trigeminal nerve (V) • Mixed • Largest cranial nerve • Sensory to the face, controls muscles of mastication (temporalis and masseter) • Three divisions: V1- Ophthalmic division V2- Maxillary division V3- Mandibular division • Nucleus located in the pons

22. Abducens (VI) • Motor • Innervates the lateral rectus muscle of the eye • Moves eyeball laterally

25. Facial Nerve (VII) • Mixed • Exits at the stylomastoid foramen • Controls muscles of facial expression • Controls lacrimal and salivary glands • Taste of anterior 2/3 of tongue • Bell’s palsy; unilateral facial paralysis

27. Vestibulocochlear Nerve (VIII) • Sensory • Vestibulo branch: equilibrium • Cochlear branch: hearing • Travels through the internal acoustic meatus

29. Glossopharyngeal Nerve (IX) • Mixed • Fibers emerge from medulla and exit the jugular foramen. • Innervates part of the tongue and pharynx • Taste for bitter on the posterior 1/3 of the tongue (Bitter Back 9) • Swallowing and gag reflex

31. Vagus (X) • Mixed • Only cranial nerve to extend below the head and neck into thorax and abdomen • Heart rate, breathing and digestive function. • Sensory from the viscera • Recurrent laryngeal nerve branches innervate larynx (voice box)

35. Spinal Accessory Nerve (XI) • Motor • Innervates trapezius and sternocleidomastoid muscle • Clinical: ask patient to shrug shoulders against resistance

37. Hypoglossal Nerve (XII) • Motor • Tongue movements: swallowing and speech.

39. Oh, oh, oh, to touch and feel very green vegetables- AH Or On occasion our trusty truck acts funny- very good vehicle anyhow

40. Spinal nerves • 31 pairs of spinal nerves • Mixed nerves - (8) Cervical - cervical and brachial plexus - (12) Thoracic - intercostal nerves and cervical and lumbosacral enlargement - (5) Lumbar - lumbar plexus - (5) Sacral - sacral plexus - (1) Coccygeal

42. Branches (one passing through intervertebral foramen): • dorsal ramus: deep muscles and skin of the dorsal surface of the trunk • ventral ramus: muscles and structures of the upper and lower limbs and the lateral and ventral trunk

43. Formation of Spinal Nerves

44. Formation of Spinal Nerves

46. Brachial plexus • Arises from spinal nerves C4-T1 Serves the arm and shoulder Median nerve: Flexor muscles of the anterior forearm and small muscle in hand (thenar eminence). Radial nerve: extensor muscle of posterior forearm and triceps brachii

47. Musculocutaneous nerve: biceps brachii Axillary nerve: deltoid