PSYC 1315 1st Edition Lecture 32 Outline of Last Lecture The Autonomic Nervous System Outline of Current Lecture Sensory motor integrative systems Sensation Conscious and subconscious awareness of changes in the external or internal environment Components of sensation Stimulation of the sensory receptor transduction of the stimulus generation of nerve impulses integration of sensory input Classification of Sensory Receptors General senses Somatic tactile thermal pain and proprioceptive sensations Visceral provide information about conditions within internal organs Special senses Smell taste vision hearing and equilibrium or balance Types of Sensory Receptors Free nerve endings Pain and thermoreceptors Encapsulated nerve endings Pacinian corpuscles Separate cells Hair 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 pathways Sensory information coming from the sensory receptors through peripheral nerves to the spinal cord and on to the brain Efferent pathways Motor 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 Exteroceptors Respond to stimuli originating outside the body Interoceptors Monitor conditions in the internal environment Proprioceptors Provide information about body position muscle length and tension and position and movement of joints Sensory receptors Each receptor cell monitors a specific receptive field Transduction A 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 senses Pain Temperature Physical distortion Chemical detection Receptors for general senses scattered throughout the body Special senses Located in specific sense organs Structurally complex Adaptation of Sensory Receptors Adaptation Reduction in sensitivity in the presence of a constant stimulus Rapidly adapting receptors phasic Provide information about the intensity and rate of change of a stimulus Receptors that detect pressure touch and smell Slowly adapting receptors tonic Receptors that detect pain body position and chemical composition of the blood Always active The general senses Three types of nociceptor Provide information on pain as related to extremes of temperature Provide information on pain as related to extremes of mechanical damage Provide information on pain as related to extremes of dissolved chemicals Myelinated type A fibers carry fast pain Slower type C fibers carry slow pain Thermoceptors mechaniceptors Found in the dermis Separate reception for heat and cold Mechaniceptors Sensitive to distortion of their membrane Tactile 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 modalities Tactile Thermal Pain 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 sensations Cold receptors Warm receptors Pain Sensations Protective Sensory receptors are nociceptors Free nerve endings Two types of pain Fast acute sharp or pricking pain Slow 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 a surface area far from the stimulated organ Proprioceptive Sensations Receptors are proprioceptors Show slow adaptation Allow weight discrimination Types Muscle spindles Tendon organs Joint kinesthetic receptors Muscle Spindles Interspersed among most skeletal muscle fibers and aligned parallel to them Measure muscle stretching Consist of intrafusal muscle fibers Specialized muscle fibers with sensory nerve endings and motor neurons called gamma motor neurons Extrafusal muscle fibers Surrounding muscle fibers supplied by alpha motor neurons Tendon Organs Located at the junction of a tendon and a muscle Protect tendons and their associated muscles from damage due to excessive tension Consist of a thin capsule of connective tissue that encloses a few tendon fascicles Joint Kinesthetic Receptors Found within or around the articular capsules of synovial joints Free nerve