Peripheral Nervous System

1. Peripheral Nervous System Chapter 13

2. Sensory Receptor Types • Nociceptors • Respond to excess heat, pressure, or chemicals • Tissue damage • All parts of the body but brain • Thermoreceptors • Temperature of skin and blood • Maintains homeostatic control via the hypothalmus • Photoreceptors • Light absorbing pigments • Light detection

3. Sensory Receptor Types Mechanoreceptors Chemoreceptors • Touch, pressure, & vibrations • Bend or stretch PM of receptor cell = changing permeability • Stretch receptors – position of body parts • Hair cells -sound waves and H2O movements • Chemicals in the internal & external environment • O2 in arterioles • Osmoreceptors - changes in [blood solute] • Pheromone detection

4. Sensory Receptor Locations • Exteroceptors • Stimuli outside the body • Skin and special sense organs • Interoceptors • Stimuli within the body • Chemical messengers, tissue stretch, and temperature • Proprioceptors • Internal stimuli • Monitor position and stretch of joints, tendons, and muscles

5. Sensory Receptor Structures Unencapsulated Encapsulated • Free nerve endings • Most body tissues • Temperature and painful stimuli • Capsaicin and itch • Merkel discs • Deeper epidermal layers • Light touch • Hair follicle receptors • Shaft of hair follicle • Light touch and hair bending • Meissner’s corpuscles • Dermal papillae of sensitive and hairless skin • Discriminative touch • Pacinian corpuscles • Deep in the dermis • Deep pressure initially, vibration • Ruffini endings • Deep dermis and hypodermis • Deep continuous pressure • Muscle spindles • Perimysium of skeletal muscle • Detect muscle stretch & initiate a reflex • Golgi tendon • Insertion tendons • Activation inhibits contracting muscle

6. Sensory Input • All senses trigger the same TYPE of signal • Distinction occurs in activated brain area • Typically graded response, but AP’s possible • Sensory receptors detect sensations and carry to the brain • Awareness of environmental change • Brain constructs perceptions by integrating sensations with other information • Neuronal communication involving multiple brain areas

7. The Working Brain

8. Sensory Adaptation • Sensory receptors become less responsive • Fewer action potentials • Limits reactions to normal background stimuli • Shower or hot tub temperature • Odors over time

9. Decoding Nerves • PNS organ consisting of parallel bundles of axons enclosed by connective tissue layers • Epineurium • Perineurium • Endoneurium • Direction of transmission • Afferents: only to CNS • Dorsal root ganglia • Efferents: only from CNS • Sympathetic & parasympathetic ganglia • Mixed: carry both; most • Classified as cranial or spinal

10. Nerve Fiber Regeneration • Mature neurons don’t divide* • Cell body damage = death • Cut/compressed axons regenerate • Separated ends seal off and swell • Distal end of injury disintegrates • Lack of nutrients • Neurilemma maintained in endoneurium • Schwann cells proliferate & encourage axon growth • Guide ‘sprouting’ axons to original contacts • Greater distance decreases chances • Regrowth never exact = retraining • Extremely rare in CNS

11. Cranial Nerves Ventral portion of the brain 1st 2 pairs attach to forebrain Remainders originate on brainstem

13. Testing Cranial Nerves for Disorders • Olfactory • Smell substances • Anosima • Optic • Eye chart • Anopsias • Oculomotor • Follow object; pupil reflex • Strabismus, double vision, ptosis • Trochlear • See oculomotor • Trigeminal • Close/move jaws; touch face with objects • Abducens • See oculomotor • Facial • Make various faces; tasting substances • Bell’s palsy, loss of taste, can’t close eye • Vestibulocochlear • Tuning fork; distance of sound • Deafness, vertigo, tinnitus • Glossopharyngeal • Swallowing & gag reflex; say ‘ah’ • Vagus • See glossopharyngeal • Horseness, swallowing problems, death • (Spinal) accessory • Move head/shoulders against resistance • Hypoglossal • Stick out, retract, & move tongue to sides

14. Spinal Nerve Anatomy • Roots: medial & afferent OR efferent • Dorsal root: peripheral receptors to spinal cord • Ventral root: ventral horn to skeletal muscles • Branches: laterally pass through intervertebral foramen • Dorsal ramus: dorsal trunk • Ventral ramus: limbs & rest of trunk • Meningeal branch: meninges and blood vessels • Plexus • Criss cross joining of ventral rami • Excludes T2 – T12

15. 31 Pairs of Spinal Nerves • 8 cervical • Cervical plexus • Brachial plexus • 12 thoracic • Intercostal nerves & enlargements • 5 lumbar • Lumbar plexus • 5 sacral • Sacral plexus • 1 coccygeal • Tailbone & perineum

16. Cervical Nerves • Cervical plexus • Phrenic nerve: diaphragm • Irritation causes hiccups • Brachial plexus C5 – C8 • Median nerve: flexor muscles of the anterior forearm and small hand muscles • Carpal tunnel syndrome and suicide attempts • Radial nerve: extensor muscle of posterior forearm and triceps brachii • ‘Saturday night paralysis’ • Ulnar nerve: similar to median nerve • ‘Funny bone’ and paralysis/distortion of medial fingers

17. Lumbosacral Plexus • Innervates lower limbs, buttocks, and pelvic muscles • Lumbar plexus L1 – L4 • Femoral nerve: quadriceps and sartorius • Branches to saphenous • Obturator nerve: adductor muscles • Sacral plexus L4 – S4 • Sciatic nerve: entire lower leg (except anteriomedial thigh) • Tibial: hamstrings • Common fibular nerve: anterior tibialis

18. Reflex Arc • Receptor • Senses stimulus • Sensory neuron (afferents) • Message to the CNS • Integration center • Synapses in CNS • Monosynaptic (single motor or sensory neuron) • Polysynaptic (multiple interneurons) • Motor neuron (efferents) • Message to effectors • Effector • Muscle fibers or glands • Reflexes are rapid, predictable motor responses to a stimulus http://a248.e.akamai.net/7/248/430/20080327144023/www.mercksource.com/ppdocs/us/common/dorlands/dorland/images/arc_reflex%20a.(1).jpg

19. Classifying Reflexes • Somatic: activate skeletal muscle • Spinal: integration center is spinal cord • Stretch: ensures muscle length maintained (knee-jerk reflex) • Crossed extensor: withdrawl from painful stimuli (pin prick) • Superficial: cutaneous stimulation (plantar reflex) • Cranial nerve: integration center is brain stem • Corneal: stimulation causes blinking • Autonomic (visceral): activate smooth or cardiac muscle • Pupillary light: controls diameter of pupil (inside/outside) • Ciliospinal: ipsilateral pupil dilation from pain