LAB 10: GENERAL AND SPECIAL SENSES Last Lab!Agenda • Quiz • General Senses (Exercise 23) • Touch, Pain, Temperature, Pressure, Propioception • Special Senses (Exercise 24) • Vision, Hearing, Smell, Taste, Equilibrium • Preceptor Presentation • Cow Eye Dissection • Practical InformationReminder: TCEs • Link is live now on d2l • Remember, if 80% students complete survey, “free” question on the practicalGeneral vs. Special Senses • General (Somatic and Visceral) • Somatic – tactile (touch, pressure, itch, ect.), pain and proprioceptive sensations • Visceral – sensations coming from internal organs • Sensory receptors are located throughout the body surface (dermal layers) • Special • Modified receptors that function to perceive a specific stimulus • Sensory receptors are typically localized to a specific functional area (e.g. retina)Cutaneous Receptors • Nociceptors – Pain Receptors; free nerve endings in the epidermis. Detect chemical or physical damage • Merkel Discs – Touch receptors; free nerve endings in stratum basale. • Meissner’s Corpuscle – Touch receptors; encapsulated; rapidly adapting and responsive to onset of touch • Ruffini Corpuscle – Touch/strech receptors; encapsulated; deep in dermis. Sensative to strech (e.g. of limbs/digits) • Hair Root Plexus – Touch receptors; free nerve endings; detect movement on skin that moves hair follicles • Pacinian Corpuscle – Pressure receptor; encapsulated; rapidly adaptingFirst-order sensory neuron with free nerve endings!Cold!stimulus!First-order sensory neuron with encapsulated nerve endings!Pressure!stimulus!Sensory receptor synapses with first-order sensory neuron!Sugar!molecule!Receptor!potential!Triggers!Release of!neurotransmitter from sensory receptor!Dendrite!Triggers!Nerve!impulses!Propagate!into CNS!Axon!Neurotransmitter!Synaptic vesicle!Gustatory (taste)!receptor!Dendrite!Encapsulated!nerve ending!Generator!potential!Free nerve endings!(dendrites)!Axon!Nerve!impulses!Triggers!Propagate!into CNS!Axon!Merkel (tactile) disc (type I cutaneous mechanoreceptor)!Meissner corpuscle!(corpuscle of touch)!Ruffini corpuscle (type II cutaneous mechanoreceptor)!Hair root plexus!Pacinian (lamellated) corpuscle!Epidermis!Dermis!Subcutaneous layer!Nociceptor!(pain receptor)!Soma%c'Sensory'Receptors0Other Sensory Receptors - Proprioception • Muscle Spindle – Detect muscle stretch; activated in patellar and Achilles tendon reflexes • Golgi Tendon Organ – Detect force in the muscle; found in the tendons of skeletal muscle • Joint Kinesthetic Receptors – Detect pressure in the capsules of joints; responsive to acceleration and deceleration of joints during movementProprioceptors Muscle Spindle Golgi Tendon OrganPhenomenon of Somatic Sensation • Itch • Stimulation of free nerve endings • Typically caused by certain chemicals often resulting in local inflammation (bradykinin) • Vibration • Result of rapid and repetitive sensory signals • Meissner corpuscle detect low-frequency while Pacinian corpuscle detech high frequency • Tickle • Free nerve ending stimulation • Can’t tickle yourself…due to cerebellar inputNociception • Painful stimuli are carried to the CNS via nociceptive afferent fibers • A-fibers (myelinated) and C-fibers (unmyelinated) • A-fibers carry “fast pain” and C-fibers carry “slow pain” • Fast - Acute, sharp or pricking • Slow - Chronic, burning, aching or throbbing • Referred Pain • Results from nociceptive activation in the visceral organs • Typically feel pain elsewhere than from where the stimulus actually arises (e.g. cardiac pain felt in left upper limb) • Visceral organ involved and area to which the pain is referred are served by same segment of spinal cordSoma%c'Sensa%on'Tests'Review0Heart!Lung and diaphragm!Heart!Pancreas!Stomach!Ovary!Urinary!bladder!Liver and gallbladder!Stomach!Liver and gallbladder!Kidney!Liver and gallbladder!Gallbladder!Small intestine!Ovary!Kidney!Ureter!(b) Posterior view!(a) Anterior view!Testing General Senses • Density and Location of Touch/Temperature Receptors • Adaptation of Touch • Adaptation of Temperature • Two-Point Discrimination • Tactile Localization • “Referred” PainDensity and Location of Touch and Temperature Receptors • Only testing touch receptors • Follow instructions • What happened? • More tactile receptors than thermoreceptors in the the skin • More cold than hot receptors in the skin • Sensitivity of cold receptors vs hot receptorsAdaption of Touch Receptors (Not Tested) • Touch receptors adapt to constant stimulus by decreasing the number of action potentials they send over timeAdaption of Temperature Receptors • Follow instructions • What happened? • Temperature receptors adapt to a constant stimulus by decreasing the number of action potentials they send over time. • Hand in hot bath adapts faster than cold because it is closer to body temperature • Temperature receptors only adapt if temperature is not extreme • Too hot or too cold; nociceptors activated • Past as certain range, nociceptors will become active (C-fibers)Temperature ReceptorsTwo-Point Discrimination • Follow instructions • What happened? • Areas with smaller receptive field, have a greater receptor density, and are better able to discriminate between two points • These areas are more highly represented in primary somatosensory cortex (homunculus) • Why would you be able to feel two close points on an area like the back? (low receptor density)Tactile Localization • Follow instructions • What happened? • Test involves sensory and motor components • Being able to match the same spot requires integration and proprioception • The receptive field/receptor density concept is the same as the two point discriminationReferred pain • Follow instructions • What happened? • Initially sensation of cold at the elbow but eventually digits IV and V begin to hurt • The ulnar nerves serves that part of the hand, so pain is referred to the hand even though “damage” is at elbowSoma%c'Sensa%on'Tests'Review01. Density and location of touch and temp receptors • More tactile