Somatic and special senses Ch. 15

Introduction Sensory receptors - make it possible for the body to respond to stimuli caused by changes occurring in the internal or external environment Different types of receptors respond to different stimuli General function—responds to stimuli by converting them to nerve impulses Sensations Sensory adaptation - receptor potential decreases over time in response to a continuous stimulus Receptors for special senses of smell, taste, vision, hearing, and equilibrium are grouped into localized areas or into complex organs

Receptors and sensations Types of receptors Chemoreceptors activated by amount or changing concentration of certain chemicals; e.g., taste and smell Pain receptors - Nociceptors—activated by intense stimuli that may damage tissue; the sensation produced is pain Thermoreceptors — activated by changes in temperature Mechanoreceptors activated when “deformed” to generate receptor potential Proprioceptors -Location limited to skeletal muscle, joint capsules, and tendons Provide information on body movement, orientation in space, and muscle stretch Photoreceptor— found only in the eye; respond to light stimuli if the intensity is great enough to generate a receptor potential

Somatic senses Touch and pressure Free ends of dendrites Called nociceptors Receptors for pain Meissner’s corpuscles sense touch large and superficial Pacinian corpuscles Respond to deep pressure/stretch Deep dermis and joint capsules Stretch receptors Found in tendons and muscles Once stretched, the muscle shortens

Temperature senses Organs of Ruffini - also called Ruffini’s corpuscles Deep in dermis Sense heat - 85 - 120 degrees Bulbs of Krause - sense cold

Sense of pain Free nerve endings Visceral pain Referred pain Pain nerve fibers - Chronic/acute Regulation of pain impulse - awareness of pain - thalamus. Impulse conducted to cerebral cortex - judges intensity and location of pain. Endorphins provide natural pain control. Serotonin inhibits release of pain impulses in spinal cord.

Special senses - receptors are in specialized organs Smell - olfactory sense Taste - gustatory sense Hearing - auditory sense Static equilibrium - balance when stationary Dynamic equilibrium - balance when moving Sight - sense of vision

Sense of smell

Sense of smell Olfactory receptors Cilia in nasal cavity chemoreceptors Olfactory organs - epithelial supporting tissue Nerve pathways Action potential to olfactory nerves in olfactory bulb Thalamic and olfactory centers in brain

Sense of taste

Sense of taste Taste receptors - chemoreceptors Taste sensations Taste hairs portrude from taste pores Chemicals dissolved in saliva Taste sensations Sweet Sour Salt Bitter Nerve pathways Facial, glossopharyngeal, vagus nerves to medulla oblongata to gustatory cortex in cerebrum.

Sense of hearing

Sense of hearing External ear Middle ear Inner ear - Auricle or pinna - visible - collects sound External auditory meatus - tube Middle ear in temporal bone- contains ossicles Malleus - attached to tympanic membrane Incus - attached to malleus and stapes Stapes - attached to chochlea Inner ear - semicircular canals - equilibrium Cochlea - hearing Organ of corti - located in the cochlear duct. Contains supporting cells and hair cells

Sense of hearing Nerve pathways - sound waves move tympanic membrane Movement of membrane moves ossicles which move oval window which create waves which bend hairs. Hearing - stimulation of auditory area in cerebral cortex. Range of hearing 20-20,000 decibels, whisper 40 db, rock concert 120 db, pain, 140 db

Causes and types of hearing loss

Sense of equilibrium - two types Static equilibrium—ability to sense the position of the head relative to gravity or to sense acceleration or deceleration Dynamic equilibrium—needed to maintain balance when head or body is rotated or suddenly moved; able to detect changes both in direction and rate at which movement occurs

Static Equilibrium Stability of head when body is motionless Utricle and Saccule - location for static equilibrium sense Macula - movement provides information about head position Otoliths located in macula, gravity shifts them, bending hair cells. Nerve fibers send message to brain Body is restored to normal position.

Dynamic equilibrium Cristae ampullaris, located in semicircular canal Cupula - gelatinous cap in which hairs are embedded, moves with flow of endolymph (fluid) Semicircular canals placed at right angles - detect motion in all directions When cupula moves, hair cells are bent, sending action potential to medulla oblongata and then other areas for interpretation.

Sense of balance and equilibrium

Visual accessory organs Eyelid - palpebrae voluntary muscle and skin, lined with mucous membrane called conjunctiva. Eyelashes and eyebrows - give some protection agains foreign objects entering eye Lacrimal gland -secret tears. Tears are drained from surface of eyeball.

Extrinsic muscles of the eye Attach to outside of eyeball and bones of the orbit

Structure of the eye Outer tunic Middle tunic Cornea - transparent portion that lies over the iris. Sclera - tough outer coat Middle tunic Choroid coat - vascular and pigmented Ciliary body - attaches to iris Iris - colored part of the eye Lens - held in place by suspensory ligaments and ciliary muscles. Has elasticity - shape is adjustable.

Inner tunic and cavities/chambers Retina - innermost coat of eyeball Contains receptors Macula lutea Fovea centralis Optic disk Cavities - anterior and posterior chamber Anterior cavity contains anterior/posterior chambers Filled with aqueous humor - watery fluid - involved in bending light Posterior cavity - right behind lens. Filed with Vitreous humor - semisolid, maintains intraocular pressure.

Overview of the eye

Light refraction and the process of seeing Refraction - Light waves bent Accomplished by cornea, lens, aqueous humor Accomodation of the lens - increase in curvature for near vision. Pupil constricts controlling the entering of light

Visual receptors - undergo changes that generate nerve impulses Rods - black and white vision Rhodopsin - photo pigment Breaks down into opsin and retinal Energy is required to reform rhodopsin Cones - color vision Three types

Visual Pigments Rhodopsin Isodopsin Opsin, retinal Erythrolabe - red Chlorolabe - green Cyanolabe - blue

Visual nerve pathways Optic nerves Optic chiasma cross over Thalamus Visual cortex of occipital lobe