Chapter 12

 Touch  Taste  Vision  Hearing  Smell

 Somatic senses  Include tactile sensations  Touch, pressure, and vibration  Include thermal sensations  Warmth or cold  Include pain sensations  Include proprioceptive sensations  Joint and muscle position sense and movement of limbs and head  Visceral senses  Information about the conditions within body fluids and internal organs

 Is a conscious or subconscious awareness of external and internal conditions of the body  Stimulus  Change in the environment, capable of activating sensory neurons  Sensory Receptors  Convert the stimulus into electrical signals  Nerve impulse  Conducted along neurons in the neural pathway to the CNS  Integrate  CNS receives impulses and initiates a response

Basis of ClassificationDescription Structure Free Nerve EndingDendrites lacking structural specializations at their ends that are associated with pain, thermal, tickle, itch, and some touch receptors Encapsulated Nerve EndingDendrites enclosed in a connective tissue capsule, such as the corpuscle of touch Separated cellsReceptor cell synapses with first order neurons; located in the retina of the eye (photoreceptors), inner ear (hair cells), and taste buds of the tongue (gustatory receptor cells)

Basis ClassificationDescription Function MechanoreceptorsDetect mechanical pressure; provide sensation of touch, pressure, vibration, proprioception, and hearing and equillibrium, also monitor stretching of blood vessels and internal organs ThermoreceptorsDetect changes in temperature NociceptorsPain receptors that respond to stimuli resulting in physical or chemical damage to tissue PhotoreceptorsDetect light that strikes the retina of the eye ChemoreceptorsDetect chemicals in mouth (taste), nose (smell), and body fluids OsmoreceptorsSense osmotic pressure of body fluids

 Stimulations of sensory receptors in the skin, mucous membranes, muscles, tendons, and joints  Not evenly distributed throughout the body  Areas with high number of nerve endings are:  Lips, tip of tongue, and fingertips

 Sensations associated with  Touch  Pressure  Vibration  Itch  Tickle

 Result of stimulation of tactile receptors in the subcutaneous layer  Types:  Corpuscles of Touch (Meissner corpuscles) (adapt rapidly)  Located on the dermal papillae of hairless skin  Abundant in hands, eyelids, tip of tongue lips, nipples, sole, clitoris and tip of penis  Hair Root plexuses – attached to hair follicle and detect movement of hair shaft  Free nerve ending  Cutaneous mechanoreceptors (slowly adapting touch receptors)  Type I cutaneous mechanoreceptors (Merkel disks)  Type II cutaneous mechanoreceptors (Ruffini Corpuscles)  Sensitive to stretch

 Pressure – is an sensation that is felt over a larger area than touch  Types of receptors  Type I cutaneous mechanoreceptor  Pacinian Corpuscle  Adapt rapidly  Vibration – rapidly repetitive sensory signal from tactile receptors  Types of receptors  Corpuscles of touch – detect lower frequencies  Pacinian corpuscles – detect high frequencies

 Itch – results from a stimulation of free nerve endings by certain chemicals  Often a local inflammatory response  Tickle – results from a stimulation of free nerve endings and pacinian corpuscles  Usually only arises when someone else is touching you

 Detect coldness and warmth  Free nerve endings  Cold receptors – located in the epidermis  Warm receptors – located in the dermis

 Nociecptors – sensory receptors for pain  Free nerve endings  Found in every tissue everywhere except the brain  That is why they can do surgery on your brain while you are awake

 Fast Pain  Occurs very rapidly .1 second after stimuli  Localized  Not found in deep tissue  Slow pain  Occurs rapid  1 second or more after stimuli  Gradually increases in intensity over time  In skin and deep tissue

 Sensations that inform you to the  degree your muscles are contracting,  tension on tendons,  position of joints,  And orientation of head  Proprioreceptors – are the receptors for proprioceptive sensation