chapter 13

1. Chapter 13 The Peripheral Nervous System and Reflex Activity

2. Peripheral Nervous System PNS � all neural structures outside the brain and spinal cord All neural structures outside the brain and spinal cord Sensory receptors Peripheral nerves and associated ganglia Efferent motor endings PNS � all neural structures outside the brain and spinal cord

3. Sensory Receptors Structures specialized to respond to stimuli Activation of sensory receptors results in depolarizations that trigger impulses to the CNS The realization of these stimuli, sensation and perception, occur in the brain

4. Receptor Classification by Stimulus Type Mechanoreceptors � respond to touch, pressure, vibration, stretch, and itch Thermoreceptors � sensitive to changes in temperature Photoreceptors � respond to light energy (e.g., retina) Chemoreceptors � respond to chemicals (e.g., smell, taste, changes in blood chemistry) Nociceptors � sensitive to pain-causing stimuli

5. Receptor Class by Location: Exteroceptors Respond to stimuli arising outside the body Found near the body surface Sensitive to touch, pressure, pain, and temperature Include the special sense organs

6. Receptor Class by Location: Interoceptors Respond to stimuli arising within the body Found in internal viscera and blood vessels Sensitive to chemical changes, stretch, and temperature changes

7. Receptor Class by Location: Proprioceptors Found in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles Respond to degree of stretch of the organs they occupy Constantly �advise� the brain of one�s movements

8. Receptor Classification by Structural Complexity Receptors are structurally classified as either simple or complex Most receptors are simple and include encapsulated and unencapsulated varieties Complex receptors are special sense organs

9. Simple Receptors of the General Senses Involved in Tactile sensation Temperature monitoring Pain �Muscle sense� Are either unencapsulated (free nerve endings) or encapsulated nerve endings

10. Unencapsulated Nerve Endings Free Nerve Endings Located everywhere Respond to pain, temperature, pressure

11. Unencapsulated Nerve Endings Merkel discs Lie in deep layers of epidermis Function as light touch receptors

12. Unencapsulated Nerve Endings Hair follicle receptors Wrap around hair follicles Respond to light touch

13. Encapsulated Nerve Endings Meissner�s corpuscles Found just beneath the epidermis Numerous on sensitive hairless areas

14. Encapsulated Nerve Endings Pacinian corupscles Found everywhere Stimulated by deep pressure

15. Encapsulated Nerve Endings Ruffini�s corpuscles Lie deep in dermis, subcutaneous tissue and joint capsules Respond to deep pressure and stretching

16. Encapsulated Nerve Endings Muscle spindles Found in perimysia of skeletal muscles Detect when a muscle is stretched Initiated a reflex that resists the stretch

17. Encapsulated Nerve Endings Golgi tendon organs Located in tendons, close to muscle insertion. Stimulated when muscle stretches the tendon

18. Encapsulated Nerve Endings Joint kinesthetic receptors Monitor stretch in articular capsules of synovial joints Provide information on joint position and motion

20. Structure of a Nerve Nerve � cordlike organ of the PNS consisting of peripheral axons enclosed by connective tissue Connective tissue coverings include: Endoneurium � loose connective tissue that surrounds axons Perineurium � coarse connective tissue that bundles fibers into fascicles Epineurium � tough fibrous sheath around a nerve

22. Classification of Nerves Sensory and motor divisions Sensory (afferent) � carry impulse to the CNS Motor (efferent) � carry impulses from CNS Mixed � sensory and motor fibers carry impulses to and from CNS; most common type of nerve

23. Regeneration of Nerve Fibers Damage is serious because neurons are amitotic If the soma of a damaged nerve remains intact, damage can be repaired Regeneration involves coordinated activity among: Macrophages � remove debris Schwann cells � form regeneration tube and secrete growth factors Axons � regenerate damaged part

24. Cranial Nerves Twelve pairs of cranial nerves arise from the brain They have sensory, motor, or both sensory and motor functions Each nerve is identified by a number (I through XII) and a name Four cranial nerves carry parasympathetic fibers that serve muscles and glands

25. Cranial Nerve I: Olfactory Origin: Receptors are in nasal cavity Passes through the cribriform plate of the ethmoid bone Fibers run through the olfactory bulb and terminate in the primary olfactory cortex Functions solely by carrying afferent impulses for the sense of smell

26. Cranial Nerve II: Optic Origin: retina of the eye Optic nerves converge at the optic chiasm They continue to the thalamus where they synapse From there, the optic radiation fibers run to the visual cortex Functions solely by carrying afferent impulses for vision

27. Cranial Nerve III: Oculomotor Fibers extend from midbrain to extrinsic eye muscles Functions in raising the eyelid, directing the eyeball, constricting the iris, pupil, and controlling lens shape

28. Cranial Nerve IV: Trochlear Fibers emerge from the dorsal midbrain and innervate the superior oblique muscle Primarily a motor nerve that directs the eyeball

29. Cranial Nerve V: Trigeminal Fibers extend from pons to face and form Mixed cranial nerve 3 divisions: Ophthalmic division: sensory fibers from area surrounding eye Maxillary division: sensory fibers from nasal cavity, upper teeth

30. Cranial Nerve V: Trigeminal Mandibular division: sensory fibers from tongue lower teeth, chin, and motor fibers to muscles of mastication

31. Cranial Nerve VI: Abducens Motor fibers run from pons to extrinsic muscle that abducts eye.

32. Cranial Nerve VII: Facial Fibers leave the pons, travel to the lateral aspect of the face Mixed nerve with five major branches Motor functions include facial expression, and the transmittal of autonomic impulses to lacrimal and salivary glands Sensory function is taste from the anterior two-thirds of the tongue

33. Cranial Nerve VIII: Vestibulocochlear Fibers arise from the hearing and equilibrium apparatus of the inner ear and enter the brainstem at the pons-medulla border Two divisions � cochlear (hearing) and vestibular (balance) Functions are solely sensory � equilibrium and hearing

34. Cranial Nerve IX: Glossopharyngeal Fibers emerge from the medulla, leave the skull via the jugular foramen, and run to the throat Mixed nerve with motor and sensory functions Motor � innervates part of the tongue and pharynx, and provides motor fibers to the parotid salivary gland Sensory � fibers conduct taste and general sensory impulses from the tongue and pharynx

35. Cranial Nerve X: Vagus The only cranial nerve that extends beyond the head and neck Fibers emerge from the medulla via the jugular foramen The vagus is a mixed nerve Most motor fibers are parasympathetic fibers to the heart, lungs, and visceral organs Its sensory function is in taste

36. Cranial Nerve XI: Accessory The accessory nerves are unique in that they are formed by the union of a cranial and spinal root Primarily a motor nerve Supplies fibers to the larynx, pharynx, and soft palate Innervates the trapezius and sternocleidomastoid, which move the head and neck

37. Cranial Nerve XII: Hypoglossal Motor fibers arise from the medulla and innervates both extrinsic and intrinsic muscles of the tongue, which contribute to swallowing and speech

38. I. Olfactory II. Optic III. Oculomotor IV. Trochlear V. Trigeminal VI. Aducens On Occasion, Our Trusty Truck Acts Funny � Very Good Vehicle AnyHow VII. Facial VIII. Vestibulocochlear IX. Glossopharyngeal X. Vagus XI. Accessory XII. Hypoglossal

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