PSYC 1315 1st Edition Lecture 32Outline of Last Lecture The Autonomic Nervous SystemOutline of Current LectureSensory , motor, integrative systems Sensation Conscious and subconscious awareness of changes in the external or internal environment Components of sensation: Stimulation of the sensory receptor → transductionof the stimulus → generation of nerve impulses → integration of sensory input  Classification of Sensory Receptors General sensesSomatic- tactile, thermal, pain and proprioceptive sensationsVisceral- provide information about conditions within internal organs  Special sensesSmell, taste, vision, hearing, and equilibrium or balance.  Types of Sensory Receptors Free nerve endingsPain and thermoreceptors Encapsulated nerve endingsPacinian corpuscles Separate cellsHair cells, photoreceptors and gustatory receptor cells Generator Potential & Receptor Potential Generator potential is produced by free nerve endings, encapsulated nerve endings, and olfactory receptors. When it reaches a threshold, it triggers one or more nerve impulses in the axon of a first-order sensory neuron. Receptor potential triggers the release of neurotransmitter → postsynaptic potential → action potential Neural pathways Afferent pathwaysSensory information coming from the sensory receptors through peripheral nerves to the spinal cord and on to the brain Efferent pathwaysMotor commands coming from the brain and spinal cord, through peripheral nerves to effecter organs Sensory receptor❑ Specialized cell or cell process that monitors specific conditions ❑ Arriving information is a sensation❑ Awareness of a sensation is a perception Classification of Sensory Receptors Based on the Location ExteroceptorsRespond to stimuli originating outside the body InteroceptorsMonitor conditions in the internal environment ProprioceptorsProvide information about body position, muscle length and tension, and position and movement of joints Sensory receptors Each receptor cell monitors a specific receptive field TransductionA large enough stimulus changes the receptor potential, reaching generator potential Classification of Sensory Receptors Based on the Type of Stimulus Mechanoreceptors -responsive to mechanical stimuli Thermoreceptors - detect changes in temperature Nociceptors - respond to painful stimuli Photoreceptors - detect light striking the retina of the eye Chemoreceptors - detect chemicals in the mouth, nose, and body fluids Osmoreceptors - detect the osmotic pressure of body fluids Senses General sensesPainTemperaturePhysical distortionChemical detectionReceptors for general senses scattered throughout the body Special sensesLocated in specific sense organsStructurally complex Adaptation of Sensory Receptors AdaptationReduction in sensitivity in the presence of a constant stimulus Rapidly adapting receptors (phasic)Provide information about the intensity and rate of change of a stimulusReceptors that detect pressure, touch and smell Slowly adapting receptors (tonic)Receptors that detect pain, body position, and chemical composition of the bloodAlways active The general senses Three types of nociceptorProvide information on pain as related to extremes of temperatureProvide information on pain as related to extremes of mechanical damageProvide information on pain as related to extremes of dissolved chemicalsMyelinated type A fibers carry fast painSlower type C fibers carry slow pain Thermoceptors&mechaniceptors Found in the dermis Separate reception for heat and cold MechaniceptorsSensitive to distortion of their membraneTactile receptors (six types)Baroreceptors (pressure)Proprioceptors (three groups) Tactile Sensations Include touch, pressure, vibration, itch and tickle Tactile receptors in the skin are Meissner corpuscles, hair root plexuses, Merkel discs, Ruffini corpuscles, pacinian corpuscles, and free nerve endings  Somatic Sensations Arise from sensory receptors in the skin (cutaneous sensations), muscles, tendons and joints and in the inner ear Show uneven distribution of receptors Four modalitiesTactileThermalPain Proprioceptive. Meissner Corpuscles or Corpuscles of Touch Egg-shaped mass of dendrites enclosed by a capsule of connective tissue Rapidly adapting receptors Found in the dermal papillae of hairless skin such as in the fingertips, hands, eyelids, tip of the tongue, lips, nipples, soles, clitoris, and tip of the penis Hair Root Plexuses Rapidly adapting touch receptors found in hairy skin Free nerve endings wrapped around hair follicles Detect movements on the skin surface that disturb hairs Merkel Discs or Tactile Discs Also known as Type I cutaneous mechanoreceptors Slowly adapting touch receptors Saucer-shaped, flattened free nerve endings Found in the fingertips, hands, lips, and external genitalia Ruffini Corpuscles Also called as Type II cutaneous mechanoreceptors Elongated, encapsulated receptors Located deep in the dermis and in ligaments and tendons Found in the palms of the hands and the soles of the feet Pacinian or Lamellated Corpuscles Large oval structures composed of a multilayered connective tissue capsule that encloses a dendrite Fast adapting receptors Found around joints, tendons, and muscles, in the periosteum, mammary glands, external genitalia, pancreas and urinary bladder Thermal Sensations Thermoreceptors are free nerve endings Two distinct thermal sensationsCold receptorsWarm receptors Pain Sensations Protective Sensory receptors are nociceptors Free nerve endings Two types of painFast - acute, sharp or pricking painSlow - chronic, burning, aching or throbbing pain Referred Pain Pain is felt in or just deep to the skin that overlies the stimulated organ or in asurface area far from the stimulated organ. Proprioceptive Sensations Receptors are proprioceptors Show slow adaptation Allow weight discrimination TypesMuscle spindlesTendon organsJoint kinesthetic receptors Muscle Spindles Interspersed among most skeletal muscle fibers and aligned parallel to them Measure muscle stretching Consist of intrafusal muscle fibersSpecialized muscle fibers with sensory nerve endings and motor neurons called gamma motor neurons. Extrafusal muscle fibersSurrounding