Senses: Chapter 10

Types of Receptors Chemoreceptors Pain receptors Thermoreceptors Respond to changes in chemical concentrations Pain receptors Respond to tissue damage Thermoreceptors Respond to temperature changes Mechanoreceptors Respond to changes in pressure or movement Photoreceptors Respond to light

Sensation and Projection Brain: Sensations come from here Impulses are interpreted based on what area of the brain they end up in Brain projects the sensation back to the sensor so the person feels the sensation at the sensor Sensory Adaptation: Ability of the PNS or CNS to block sensory impulses that it deems unimportant or has become used to

Somatic senses Sensors are widely spread throughout body and are fairly simple Include: Touch Pressure Temperature Pain

Touch and Pressure Three kinds of receptors 1) Free nerve endings Sensations of touch and pressure 2) Meissner’s corpuscles Provide sensations of light touch, usually located in regoins of skin without hair 3) Pacinian corpuscles Respond to heavy pressure, located in deeper tissues

Temperature Receptors Warm and cold receptors in skin Free nerve endings Receptors adapt very fast Pain receptors Extreme temperatures and injury stimulate these

Pain Receptors Sensations arise from free nerve ending throughout body except brain Pain receptors adapt poorly Visceral pain Refers pain to areas on the skin

Special senses Sensations arise from specially adapted sensors Includes: Smell Taste Hearing Equilibrium Sight

Smell Olfactory receptors are located in small patches along the roof of the nasal cavity They are chemoreceptors Incoming gases must dissolve in the mucous covering the nasal cavity Dissolved particles interact with the cilia and may stimulate an action potential

Taste Taste buds Located primarily on tongue, although some found on roof of mouth and sides of the throat Each taste bud has many gustatory receptors and tiny cilia projections These are chemoreceptors Incoming foods must be dissolved in saliva to be tasted

Areas of the Tongue Four main taste areas: Sweet - concentrated on the tip of the tongue Sour - concentrated along the margins of the tongue Bitter - concentrated along the back of the tongue Salty - spread throughout

The Outer Ear Sound waves are directed into the ear by the external auricle They travel down the external acoustic meatus Bounce against tympanic membrane (eardrum) and make the eardrum move

The Middle Ear Occurs in the tympanic cavity Has three small auditory ossicles/bones Vibrations at the tympanic membrane cause the three bones to vibrate The final bone vibrates against the oval window of the inner ear The bones amplify the sound Eustachian tube Connects middle ear to throat, equalizes pressure for eardrum, often where earaches occur

Inner Ear Includes two labyrinths: Two parts to the labyrinth: 1) Osseous labyrinth - bony canals 2) Membranous labyrinth - membrane-bound tube inside the bony canals Perilymph separates the two Endolymph is found inside the membranous labyrinth Two parts to the labyrinth: 1) Semicircular canals - used in equilibrium 2) Cochlea – organ for hearing

Inner Ear (cont) Vibrations at the oval window cause vibrations in the perilymph of the scala vestibuli Vibrations pass through vestibular membrane into endolymph Vibrations than pass through basilar membrane to perilymph of scala tympani Organ of Corti Found in basilar membrane, contains hearing sensors with hairs; vibrations cause hairs to move Animation

Equilibrium Two divisions: 1) Static Equilibrium - senses posture while at rest Occurs in vestibule Position of head is determined by hairs on the macula, hairs respond to shifting of otoliths 2) Dynamic Equilibrium – maintaining balance during movement Occurs in the semicircular canals, in particular the ampulla Movements cause the perilymph to stimulate hairs in the ampulla

Sight Visual receptors located in eye Accessory organs aiding eye: Eyelids Lacrimal apparatus Gland that produces tears to cleanse and protect eye and ducts to carry the tears to the nasal cavity Muscle Moves the eye

The Eye Posterior portion Sclera Choroid coat Retina Vitreous humor Tough fibrous covering Choroid coat Contains melanocytes to help darker the inside of the eye Retina Thin complex inner layer that is continuous with the optic nerve and contains the receptors Vitreous humor Jelly-like fluid filling internal eye

The Eye (cont) Anterior portion Cornea Aqueous humor Iris Lens Transparent covering Aqueous humor Fluid that is made between the iris and lens but can move to between the cornea and the iris through the pupil Iris Pigmented layer containing smooth muscle to control size of pupil Lens Layer that focuses the image on the retina; can change shape to change focus

The Retina Contains two types of receptors: Fovea centralis Optic disc 1) Rods Black-and-white vision; more indistinct image; pigment is rhodopsin 2) Cones Color vision; refined image; pigments are sensitive to red, green, and blue hues Fovea centralis Part of retina containing high concentration of cones; area with sharpest focus Optic disc Area of retina with connection to optic nerve; lacks receptors (blindspot)

Eye Dissection Cow's Eye Dissection