The Senses

Sensory Receptors General senses of touch Temperature Pressure Pain Special senses: Taste, Sight, Hearing Smell, Equilibrium

Types of Receptors Chemoreceptors Pain receptors or nociceptors Thermoreceptors Mechanoreceptors Photoreceptors

Somatic or Body Senses associated with skin, muscles, joints, and viscera three groups exteroceptive senses – senses associated with body surface; touch, pressure, temperature, pain proprioceptive senses – senses associated with changes in muscles and tendons visceroceptive senses – senses associated with changes in viscera

Touch and Pressure

Sensitivity to Temperature Warm receptors temperatures above 25 C (77 F) unresponsive to temperature above 45 C (113 F) Cold receptors temperature between 10 C (50 F) and 20 C (68 F) Pain receptors below 10 C above 45 C

Pain free nerve endings, widely distributed,stimulated by tissue damage,do not adapt Acute pain fibers: thin, myelinated, conduct impulses rapidly Chronic pain fibers : thin, unmyelinated, conduct impulses more slowly

Regulation of Pain Thalamus aware of pain Cerebral Cortex judges intensity of pain locates source or pain produces motor response to pain produces emotions to pain Pain Inhibiting Substances enkephalins-Met-enkephalin is Tyr-Gly-Gly-Phe-Met. Leu-enkephalin has Tyr-Gly-Gly-Phe-Leu. serotonin endorphins

Stretch Receptors Found in muscles and tendons: Can shut down contraction if it endangers the body. Can also be turned off during fight or flight response

Smell Olfactory receptors are in the roof of the nasal cavity Neurons with long cilia Chemicals must be dissolved in mucus for detection Impulses are transmitted via the olfactory nerve Interpretation of smells is made in the cortex Contain 1000 genes that code for the sense of smell, but only a few hundred are active???? WHY

Olfaction

Taste Taste Buds: organs of taste, located on papillae of tongue, roof of mouth, linings of cheeks and walls of pharynx The tongue is covered with projections called papillae Taste buds are found on the sides of papillae Gustatory cells are the receptors (Chemoreceptor) Have gustatory hairs (long microvilli) Hairs are stimulated by chemicals dissolved in saliva Sensory impulses from taste receptors travel along cranial nerves; facial nerve, glossopharyngeal nerve, and vagus nerve, to medulla oblongata then to the thalamus and to the gustatory cortex (for interpretation)

Taste

Hearing The ear houses 2 senses hearing and equilibrium. mechanoreceptors 3 Sections External Middle Inner Functions to collect and translate vibration in the air

The Ear External Ear Auricle external auditory meatus tympanic membrane- Middle Ear tympanic cavity auditory ossicles- malleus, incus, and stapes

Cont……. oval window- stapes vibrates against it to move fluids in inner ear eustachian tube or Auditory- connects middle ear to throat: Inner Ear osseous labyrinth- bony canal in temporal bone filled with perilymph membranous labyrinth- tube within osseous labyrinth filled with endolymph

Cont… 3 Parts of Labyrinths cochlea functions in hearing semicircular canals functions in equilibrium vestibule functions in equilibrium

Cochlea Scala vestibuli- upper compartment, Scala tympani- lower compartment, Cochlear duct- membranous labyrinth in cochlea Vestibular membrane- separates cochlear duct from scala vestibuli Basilar membrane- separates cochlear duct from scala tympani

Organ of Corti group of hearing receptor cells (hair cells) on upper surface of basilar membrane different frequencies of vibration move different parts of basilar membrane particular sound frequencies cause hairs of receptor cells to bend nerve impulse generated

Overview of Hearing

Equilibrium Equilibrium has two functional parts Static equilibrium Dynamic equilibrium Static Maculae – receptors in the vestibule Report on the position of the head Send information via the vestibular nerve Anatomy of the maculae Hair cells are embedded in the otolithic membrane Otoliths (tiny stones) float in a gel around the hair cells Movements cause otoliths to bend the hair cells

Dynamic Equilibrium Crista ampullaris – receptors in the semicircular canals Tuft of hair cells Cupula (gelatinous cap) covers the hair cells Action of angular head movements The cupula stimulates the hair cells An impulse is sent via the vestibular nerve to the cerebellum

Eye Muscles Superior rectus- rotates eye up and medially Inferior rectus- rotates eye down and medially Medial rectus- rotates eye medially Lateral rectus- rotates eye laterally Superior oblique- rotates eye down and laterally Inferior oblique- rotates eye up and laterally

Eye Structure and Function 3 layers- outer fibrous tunic, middle vascular tunic, inner nervous tunic 1. Outer- Cornea- anterior portion transparent, light transmission, light refraction Sclera- posterior portion, opaque, protection 2. Middle- Iris- anterior, pigmented, controls light intensity Ciliary body- anterior, pigmented, holds lens, moves lens for focusing Choroid coat- provides blood supply, pigments absorb extra light Anterior of eye filled with aqueous humor. Lens-Transparent, lies behind iris, largely composed of lens fibers, elastic, held in place by suspensory ligaments of ciliary body

Cont.. 3. Inner- retina contains visual receptors continuous with optic nerve ends just behind margin of the ciliary body composed of several layers fovea centralis –produces sharpest vision optic disc – blind spot vitreous humor – thick gel that holds retina flat against choroid coat

How We See Photoreceptors: Rods- long, thin projections, contain light sensitive pigment called rhodopsin, hundred times more sensitive to light than cones, provide vision in dim light, produce colorless vision, produce outlines of objects Cones- short, blunt projections, contain light sensitive pigments called erythrolabe(Red Light), chlorolabe(Green Light), and cyanolabe(Blue Light), provide vision in bright light, produce sharp images, produce color vision

References Jack Brown M.S. Biology Shier,David, Jackie Butler, Ricki Lewis: Hole’s Human Anatomy and Physiology 10 th edition: 2004: McGraw-Hill Marieb, Elaine: Essentials of Human Anatomy and Physiology 7 th edition. 2003: Pearson Education Inc: Benjamin Cummings pub. Microsoft Encarta Encyclopedia 2004