Chapter 12 Senses Nervous System III - Senses Sensory Receptors • specialized cells or multicellular structures that collect information from the environment General Senses • stimulate neurons to send impulses along sensory fibers to • receptors that are widely distributed throughout the the brain body Sensation • skin, various organs and joints • a feeling that occurs when brain becomes aware of sensory Special Senses impulse • specialized receptors confied to structures in the head Perception • eyes and ears • a person’s view of the stimulus; the way the brain interprets the information 1 2 Receptor Types Sensations Chemoreceptors Sensation • respond to changes in chemical concentrations occurs when the brain becomes aware of sensory impulses Pain receptors (Nociceptors) • respond to tissue damage Perception Thermoreceptors occurs when the brain interprets sensory impulses • respond to changes in temperature Mechanoreceptors Projection • respond to mechanical forces process in which the brain projects the sensation back to the apparent source Photoreceptors • respond to light 3 it allows a person to pinpoint the region of 4 stimulation 1 Sensory Adaptation General Senses • ability to ignore unimportant stimuli • senses associated with skin, muscles, joints, and viscera • involves a decreased response to a particular stimulus • three groups from the receptors (peripheral adaptations) or along the CNS pathways leading to the cerebral cortex (central • exteroceptive senses – senses associated with body surface; adaptation) touch, pressure, temperature, pain • sensory impulses become less frequent and may cease • visceroceptive senses – senses associated with changes in viscera; blood pressure stretching blood vessels, ingesting a meal • stronger stimulus is required to trigger impulses • proprioceptive senses – senses associated with changes in 5 muscles and tendons 6 Touch and Pressure Senses Touch and Pressure Receptors Free nerve endings Meissner’s corpuscles • common in epithelial • Small, oval masses of flattened tissues connective tissue cells in connective • simplest receptors tissue cells in a connective tissue • sense itching sheath with 2 or more sensory nerve fibers branching into each corpusule Pacinian corpuscles • abundant in hairless portions of • Relatively large, ellipsoidal skin; lips structures composed of connective • detect fine touch; distinguish tissue fivers and cells between two points on the skin • common in deeper subcutaneous tissues, tendons, and ligaments • detect heavy pressure and vibrations 7 8 2 Sense of Pain Temperature Senses • free nerve endings Warm receptors • sensitive to temperatures above 25oC (77o F) • widely distributed • unresponsive to temperature above 45oC (113oF) • nervous tissue of brain lacks pain receptors Cold receptors • sensitive to temperature between 10oC (50oF) and 20oC • stimulated by tissue damage, chemical, mechanical forces, (68oF) or extremes in temperature Pain receptors • adapt very little, if at all • respond to temperatures below 10oC • respond to temperatures above 45oC 9 10 Visceral Pain Referred Pain • may occur due to sensory impulses from two regions following a common nerve pathway to brain • pain receptors are the only receptors in viscera whose stimulation produces sensations • pain receptors respond differently to stimulation • not well localized • may feel as if coming from some other part of the body • known as referred pain 11 12 3 Regulation of Pain Impulses Pain Nerve Pathways Thalamus Chronic pain fibers Acute pain fibers • allows person to be aware • C fibers • A-delta fibers of pain • thin, myelinated • thin, unmyelinated Pain Inhibiting Substances • conduct impulses more • enkephalins • conduct impulses Cerebral Cortex slowly • serotonin rapidly • judges intensity of pain • associated with dull, • endorphins • associated with • locates source of pain aching pain sharp pain • produces emotional and • difficult to pinpoint • well localized motor responses to pain 13 14 Proprioceptors Visceral Senses • mechanoreceptors-respond to mechanical stress on Receptors are found on internal organs tissues Free nerve endings • send information to spinal cord and CNS about body position and length and tension of muscles Lamellated corpuscles • Main kinds of proprioreceptors • Pacinian corpuscles – in joints • muscle spindles – in skeletal muscles* • Golgi tendon organs – in tendons* *stretch receptors-respond to stretching in a tissue 15 16 4 Special Senses Sense of Smell • sensory receptors are within large, complex sensory Olfactory Receptors organs in the head • chemoreceptors • respond to chemicals dissolved in liquids • smell in olfactory organs Olfactory Organs • taste in taste buds • contain olfactory receptors and supporting epithelial cells • hearing and equilibrium in ears • cover parts of nasal cavity, superior nasal conchae, • sight in eyes and a portion of the nasal septum 17 18 Olfactory Nerve Pathways Olfactory Stimulation • olfactory organs located high in the nasal cavity above the usual pathway of inhaled air Once olfactory receptors are stimulated, nerve impulses travel through • olfactory receptors undergo sensory adaptation • olfactory nerves olfactory bulbs olfactory rapidly tracts limbic system (for emotions) and olfactory cortex (for interpretation) • sense of smell drops by 50% within a second after stimulation Olfactory Code • hypothesis • odor that is stimulated by a distinct set of receptor cells and its associated receptor proteins 19 20 5 Sense of Taste Taste Receptors 75-80% of taste comes from smell Taste Buds • organs of taste • located on papillae of tongue, roof of mouth, linings of cheeks and walls of pharynx Taste Receptors • chemoreceptors • taste cells – modified epithelial cells that function as receptors • taste hairs –microvilli that protrude from taste cells; sensitive parts of taste cells 21 22 Taste Sensations Taste Nerve Pathways Five Primary Taste Sensations • sweet – stimulated by carbohydrates Sensory impulses from taste receptors travel along • sour – stimulated by acids • cranial nerves to • salty – stimulated by salts • medulla oblongata to • bitter – stimulated by many organic compounds • thalamus to • umani - stimulated by certain amino acids • gustatory cortex (for interpretation) Spicy foods activate pain receptors 23 24 6 Hearing External Ear • auricle Ear – organ of hearing • collects sounds waves • external auditory meatus • lined with ceruminous glands • carries sound to tympanic Three Sections membrane • External • terminates with tympanic • Middle membrane • Inner • tympanic membrane • vibrates in response to sound waves • tympanic reflex-two small skeletal muscles protect the 25 26 ear from loud noices Middle Ear Auditory Tube • tympanic cavity • air-filled space in temporal bone • eustachian tube • auditory ossicles • connects middle ear to • vibrate in response to tympanic throat membrane • helps maintain equal • malleus, incus, and stapes pressure on both sides • oval window of tympanic membrane • opening in wall of tympanic • usually closed by cavity valve-like flaps in throat • stapes vibrates against it to move fluids in inner ear 27 28 7 Inner Ear Equilibrium Three Parts of Labyrinths • cochlea Static Equilibrium Dynamic Equilibrium • functions in hearing • vestibule (utricle • semicircular canals • semicircular canals and saccule) • sense rotation and • functions in • sense position of movement of head and equilibrium head when body is body • vestibule • functions in not moving equilibrium 29 30 Eyelid Sight • palpebra • composed of four layers • skin Visual Accessory Organs • muscle • eyelids • connective tissue • conjunctiva • lacrimal apparatus • orbicularis oculi - closes • extrinsic eye muscles • levator palperbrae superioris – opens • tarsal glands – secrete oil onto eyelashes • conjunctiva – mucous membrane; lines eyelid and covers portion of eyeball 31 32 8 Lacrimal Apparatus Extrinsic Eye Muscles • lacrimal gland Superior rectus • lateral to eye • rotates eye up and • secretes tears medially • canaliculi • collect tears Inferior rectus • lacrimal sac • rotates eye down • collects from canaliculi • nasolacrimal duct and medially • collects from lacrimal sac • empties tears into nasal Medial rectus cavity • rotates eye medially 33 34 Extrinsic Eye Muscles Structure of the Eye Lateral rectus • rotates eye laterally • hollow • spherical • wall has 3 layers Superior oblique • outer fibrous tunic • rotates eye down and • middle vascular tunic laterally • inner nervous tunic Inferior oblique • rotates eye up and laterally 35 36 9 Outer Tunic Middle Tunic Iris Cornea • anterior portion • anterior portion • pigmented • transparent • controls light intensity by controlling the size of the • light transmission pupil • light refraction Ciliary body • anterior portion Sclera • pigmented • posterior portion • holds lens • opaque, white • moves lens for focusing • protection Choroid coat • provides blood supply • pigments absorb extra light 37 38 Anterior Portion of Eye Lens • filled with aqueous humor • transparent • biconvex • lies behind iris • largely composed of lens fibers • elastic • held in place by suspensory ligaments of ciliary body 39 40 10 Ciliary Body Accommodation • forms internal ring around front of eye • changing of lens shape to view objects • ciliary processes – radiating folds • ciliary muscles – contract and relax to move lens 41 42 Inner Tunic Posterior Cavity • retina • contains vitreous humor – thick gel that holds retina • contains visual receptors flat against