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Chapter 13 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 Sensory Receptor Types Mechanoreceptors Chemoreceptors Touch, pressure, & vibrations Chemicals in the internal & Bend or stretch PM of external environment O2 in arterioles Osmoreceptors - changes in [blood solute] Pheromone detection receptor cell = changing permeability Stretch receptors – position of body parts Hair cells - sound waves and H2O movements 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 Sensory Receptor Structures Unencapsulated 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 Encapsulated 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 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 The Working Brain Sensory Adaptation Sensory receptors become less responsive Fewer action potentials Limits reactions to normal background stimuli Shower or hot tub temperature Odors over time 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 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 Cranial Nerves Ventral portion of the brain 1st 2 pairs attach to forebrain Remainders originate on brainstem Numbers Cranial Nerve Function I OLFACTORY Smell (sensory) II OPTIC Vision (sensory) III OCULOMOTOR Eye movement (motor) (medial, inferior, superior rectus muscle & inferior oblique muscle) IV TROCHLEAR Eye movements (motor) (superior oblique muscle) V TRIGEMINAL Temperature, pain, crude touch of face (sensory) & mastication (motor) VI ABDUCENS Eye movement (motor) (lateral rectus muscle) VII FACIAL Taste (2/3 of anterior tongue) (sensory) Facial expressions (motor) VIII VESTIBULOCOCHLEAR Hearing & Equilibrium (sensory) IX GLOSSOPHRAYNGEAL Taste (1/3 of posterior tongue) (sensory) Pharynx (swallowing & gag reflex) (motor) X VAGUS Senses blood pressure (sensory) Stimulate heart rate and digestive organs (motor) XI ACCESSORY Head and neck movement (motor) e.g. trapezius, levator scapula XII HYPOGLOSSAL Tongue movement (motor) 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 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 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 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 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 Reflex Arc Receptor Senses stimulus Sensory neuron (afferents) Message to the CNS Integration center Synapses in CNS http://a248.e.akamai.net/7/248/430/20080327144023/www.mercksource.com/ppdocs/ us/common/dorlands/dorland/images/arc_reflex%20a.(1).jpg 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 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