PowerPoint Lecture Outlines to accompany Hole’s Human Anatomy and Physiology Eleventh Edition Shier w Butler w Lewis Chapter 12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chapter 12 Nervous System III - Senses General Senses receptors that are widely distributed throughout the body skin, various organs and joints Special Senses specialized receptors confied to structures in the head eyes and ears

Senses Sensory Receptors specialized cells or multicellular structures that collect information from the environment stimulate neurons to send impulses along sensory fibers to the brain Sensation a feeling that occurs when brain becomes aware of sensory impulse Perception a person’s view of the stimulus; the way the brain interprets the information

Pathways From Sensation to Perception (Example of an Apple)

Receptor Types Chemoreceptors respond to changes in chemical concentrations Pain receptors (Nociceptors) respond to tissue damage Thermoreceptors respond to changes in temperature Mechanoreceptors respond to mechanical forces Photoreceptors respond to light

Sensory Impulses stimulation of receptor causes local change in its receptor potential a graded electrical current is generated that reflects intensity of stimulation if receptor is part of a neuron, the membrane potential may generate an action potential if receptor is not part of a neuron, the receptor potential must be transferred to a neuron to trigger an action potential peripheral nerves transmit impulses to CNS where they are analyzed and interpreted in the brain

Sensations Projection process in which the brain projects the sensation back to the apparent source it allows a person to pinpoint the region of stimulation

Sensory Adaptation ability to ignore unimportant stimuli involves a decreased response to a particular stimulus from the receptors (peripheral adaptations) or along the CNS pathways leading to the cerebral cortex (central adaptation) sensory impulses become less frequent and may cease stronger stimulus is required to trigger impulses

General Senses senses associated with skin, muscles, joints, and viscera three groups exteroceptive senses – senses associated with body surface; touch, pressure, temperature, pain visceroceptive senses – senses associated with changes in viscera; blood pressure stretching blood vessels, ingesting a meal proprioceptive senses – senses associated with changes in muscles and tendons

Touch and Pressure Senses Free nerve endings common in epithelial tissues simplest receptors sense itching Meissner’s corpuscles abundant in hairless portions of skin; lips detect fine touch; distinguish between two points on the skin Pacinian corpuscles common in deeper subcutaneous tissues, tendons, and ligaments detect heavy pressure and vibrations

Touch and Pressure Receptors

Temperature Senses Warm receptors sensitive to temperatures above 25oC (77o F) unresponsive to temperature above 45oC (113oF) Cold receptors sensitive to temperature between 10oC (50oF) and 20oC (68oF) Pain receptors respond to temperatures below 10oC respond to temperatures above 45oC

Sense of Pain free nerve endings widely distributed nervous tissue of brain lacks pain receptors stimulated by tissue damage, chemical, mechanical forces, or extremes in temperature adapt very little, if at all

Visceral Pain 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

Referred Pain may occur due to sensory impulses from two regions following a common nerve pathway to brain

Pain Nerve Pathways Chronic pain fibers Acute pain fibers C fibers thin, unmyelinated conduct impulses more slowly associated with dull, aching pain difficult to pinpoint Acute pain fibers A-delta fibers thin, myelinated conduct impulses rapidly associated with sharp pain well localized

Regulation of Pain Impulses Thalamus allows person to be aware of pain Pain Inhibiting Substances enkephalins serotonin endorphins Cerebral Cortex judges intensity of pain locates source of pain produces emotional and motor responses to pain

Proprioceptors mechanoreceptors send information to spinal cord and CNS about body position and length and tension of muscles Main kinds of proprioreceptors Pacinian corpuscles – in joints muscle spindles – in skeletal muscles* Golgi tendon organs – in tendons* *stretch receptors

Stretch Receptors

Summary of Receptors of the General Senses

Special Senses sensory receptors are within large, complex sensory organs in the head smell in olfactory organs taste in taste buds hearing and equilibrium in ears sight in eyes

Sense of Smell Olfactory Receptors chemoreceptors respond to chemicals dissolved in liquids Olfactory Organs contain olfactory receptors and supporting epithelial cells cover parts of nasal cavity, superior nasal conchae, and a portion of the nasal septum

Olfactory Receptors

Olfactory Nerve Pathways Once olfactory receptors are stimulated, nerve impulses travel through olfactory nerves olfactory bulbs olfactory tracts limbic system (for emotions) and olfactory cortex (for interpretation)

Olfactory Stimulation olfactory organs located high in the nasal cavity above the usual pathway of inhaled air olfactory receptors undergo sensory adaptation rapidly 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

Sense of Taste 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

Taste Receptors

Taste Sensations Four Primary Taste Sensations sweet – stimulated by carbohydrates sour – stimulated by acids salty – stimulated by salts bitter – stimulated by many organic compounds Spicy foods activate pain receptors

Taste Nerve Pathways Sensory impulses from taste receptors travel along cranial nerves to medulla oblongata to thalamus to gustatory cortex (for interpretation)

Hearing Ear – organ of hearing Three Sections External Middle Inner

External Ear auricle external auditory meatus tympanic membrane collects sounds waves external auditory meatus lined with ceruminous glands carries sound to tympanic membrane terminates with tympanic membrane tympanic membrane vibrates in response to sound waves

Middle Ear tympanic cavity air-filled space in temporal bone auditory ossicles vibrate in response to tympanic membrane malleus, incus, and stapes oval window opening in wall of tympanic cavity stapes vibrates against it to move fluids in inner ear

Auditory Tube eustachian tube connects middle ear to throat helps maintain equal pressure on both sides of tympanic membrane usually closed by valve-like flaps in throat

Inner Ear complex system of labyrinths osseous labyrinth bony canal in temporal bone filled with perilymph membranous labyrinth tube within osseous labyrinth filled with endolymph

Inner Ear Three Parts of Labyrinths cochlea semicircular canals functions in hearing semicircular canals functions in equilibrium vestibule

Cochlea Scala vestibuli upper compartment leads from oval window to apex of spiral part of bony labyrinth Scala tympani lower compartment extends from apex of the cochlea to round window

Cochlea Cochlear duct portion of 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

Organ of Corti

Auditory Nerve Pathways

Summary of the Generation of Sensory Impulses from the Ear

Equilibrium Dynamic Equilibrium Static Equilibrium semicircular canals sense rotation and movement of head and body Static Equilibrium vestibule sense position of head when body is not moving

Vestibule Utricle communicates with saccule and membranous portion of semicircular canals Saccule communicates with cochlear duct Mucula hair cells of utricle and saccule

Macula responds to changes in head position bending of hairs results in generation of nerve impulse

Semicircular Canals three canals at right angles ampulla swelling of membranous labyrinth that communicates with the vestibule crista ampullaris sensory organ of ampulla hair cells and supporting cells rapid turns of head or body stimulate hair cells

Crista Ampullaris

Sight Visual Accessory Organs eyelids lacrimal apparatus extrinsic eye muscles

Eyelid palpebra composed of four layers orbicularis oculi - closes skin muscle connective tissue conjunctiva orbicularis oculi - closes levator palperbrae superioris – opens tarsal glands – secrete oil onto eyelashes conjunctiva – mucous membrane; lines eyelid and covers portion of eyeball

Lacrimal Apparatus lacrimal gland lateral to eye secretes tears canaliculi collect tears lacrimal sac collects from canaliculi nasolacrimal duct collects from lacrimal sac empties tears into nasal cavity

Extrinsic Eye Muscles Superior rectus rotates eye up and medially Inferior rectus rotates eye down and medially Medial rectus rotates eye medially

Extrinsic Eye Muscles Lateral rectus rotates eye laterally Superior oblique rotates eye down and laterally Inferior oblique rotates eye up and laterally

Structure of the Eye hollow spherical wall has 3 layers outer fibrous tunic middle vascular tunic inner nervous tunic

Outer Tunic Cornea anterior portion transparent light transmission light refraction Sclera posterior portion opaque protection

Middle Tunic Iris anterior portion pigmented controls light intensity Ciliary body anterior portion pigmented holds lens moves lens for focusing Choroid coat provides blood supply pigments absorb extra light

Anterior Portion of Eye filled with aqueous humor

Lens transparent biconvex lies behind iris largely composed of lens fibers elastic held in place by suspensory ligaments of ciliary body

Ciliary Body forms internal ring around front of eye ciliary processes – radiating folds ciliary muscles – contract and relax to move lens

Accommodation changing of lens shape to view objects

Iris composed of connective tissue and smooth muscle pupil is hole in iris dim light stimulates radial muscles and pupil dilates bright light stimulates circular muscles and pupil constricts

Aqueous Humor fluid in anterior cavity of eye secreted by epithelium on inner surface of the ciliary body provides nutrients maintains shape of anterior portion of eye leaves cavity through canal of Schlemm

Inner Tunic retina contains visual receptors continuous with optic nerve ends just behind margin of the ciliary body composed of several layers macula lutea – yellowish spot in retina fovea centralis – center of macula lutea; produces sharpest vision optic disc – blind spot; contains no visual receptors vitreous humor – thick gel that holds retina flat against choroid coat

Posterior Cavity contains vitreous humor – thick gel that holds retina flat against choroid coat

Major Groups of Retinal Neurons receptor cells, bipolar cells, and ganglion cells - provide pathway for impulses triggered by photoreceptors to reach the optic nerve horizontal cells and amacrine cells – modify impulses

Layers of the Eye

Light Refraction Refraction bending of light occurs when light waves pass at an oblique angle into mediums of different densities

Types of Lenses Convex lenses cause light waves to converge Concave lenses cause light waves to diverge

Focusing On Retina as light enters eye, it is refracted by convex surface of cornea convex surface of lens image focused on retina is upside down and reversed from left to right

Visual Receptors 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, chlorolabe, and cyanolabe provide vision in bright light produce sharp images produce color vision

Rods and Cones

Visual Pigments Rhodopsin light-sensitive pigment in rods decomposes in presence of light triggers a complex series of reactions that initiate nerve impulses impulses travel along optic nerve Pigments on Cones each set contains different light-sensitive pigment each set is sensitive to different wavelengths color perceived depends on which sets of cones are stimulated erythrolabe – responds to red chlorolabe – responds to green cyanolabe – responds to blue

Rod Cells

Stereoscopic Vision provides perception of distance and depth results from formation of two slightly different retinal images

Visual Nerve Pathway

Life-Span Changes Age related hearing loss due to damage of hair cells in organ of Corti degeneration of nerve pathways to the brain tinnitus Age-related visual problems include dry eyes floaters (crystals in vitreous humor) loss of elasticity of lens glaucoma cataracts macular degeneration

Clinical Application Refraction Disorders concave lens corrects nearsightedness convex lens corrects farsightedness