Chapter 15 Sense Organs SENSORY RECEPTORS Sensory receptors

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Chapter 15: Sense Organs

Chapter 15: Sense Organs

SENSORY RECEPTORS Sensory receptors allow the body to respond to stimuli caused by changes

SENSORY RECEPTORS Sensory receptors allow the body to respond to stimuli caused by changes in our internal or external environment Receptor response General function: responds to stimuli by converting them to nerve impulses Different types of receptors respond to different stimuli

CLASSIFICATION OF RECEPTORS Classification by location (Table 15 -1) Exteroceptors Visceroceptors (interoceptors) On or

CLASSIFICATION OF RECEPTORS Classification by location (Table 15 -1) Exteroceptors Visceroceptors (interoceptors) On or near body surface, sense pressure, touch, pain, temperature Located internally, often within body organs, or viscera. Sense pressure, stretch, chemical changes, hunger, thirst) Proprioceptors: special type of visceroceptor Location limited to skeletal muscle, joint capsules, and tendons Provide information on body movement, orientation in space, and muscle stretch

SENSORY RECEPTORS (cont. ) Distributions of receptors Receptors for special senses of smell, taste,

SENSORY RECEPTORS (cont. ) Distributions of receptors Receptors for special senses of smell, taste, vision, hearing, and equilibrium are grouped into localized areas or complex organs General sense organs of somatic senses are microscopic receptors widely distributed throughout the body in the skin, mucosa, connective tissue, muscles, tendons, joints, and viscera

SENSORY RECEPTORS- Firing nerves Receptor potential The potential that develops when an adequate stimulus

SENSORY RECEPTORS- Firing nerves Receptor potential The potential that develops when an adequate stimulus acts on a receptor; a graded response When a threshold is reached, an action potential in the sensory neuron’s axon is triggered Impulses travel over sensory pathways to the brain and spinal cord, where they are interpreted as a particular sensation or initiate a reflex action Adaptation: a functional characteristic of receptors; receptor potential decreases over time in response to a continuous stimulus, which leads to a decreased rate of impulse conduction and a decreased intensity of sensation (Figure 15 -1)

Sensory Receptors- sense of touch/feeling Stretch receptors Ø Ø Found in muscles Tell the

Sensory Receptors- sense of touch/feeling Stretch receptors Ø Ø Found in muscles Tell the body information about muscle length and strength in a contraction Touch and pressure receptors Found in the skin Can sense crude and light stimuli (getting punched vs being tickled/caressed)

SENSE OF SMELL Olfactory receptors Olfactory sense organs consist of epithelial support cells and

SENSE OF SMELL Olfactory receptors Olfactory sense organs consist of epithelial support cells and olfactory sensory neurons (Figure 15 -6) Olfactory cilia: located on olfactory sensory neurons that touch the olfactory epithelium lining the upper surface of the nasal cavity Olfactory cells: chemoreceptors; gas molecules or chemicals dissolved in the mucus covering the nasal epithelium stimulate the olfactory cells Olfactory epithelium: located in most superior portion of the nasal cavity Olfactory receptors: extremely sensitive and easily fatigued

SENSE OF SMELL (cont. ) Olfactory pathway: when the level of odorproducing chemicals reaches

SENSE OF SMELL (cont. ) Olfactory pathway: when the level of odorproducing chemicals reaches a threshold level, the following occur (Figure 15 -7): Receptor potential and then action potential are generated and passed to the olfactory nerves in the olfactory bulb The impulse then passes through the olfactory tract and into the thalamic and olfactory centers of the brain for interpretation, integration, and memory storage

SENSE OF TASTE Taste buds: sense organs that respond to gustatory (taste) stimuli; associated

SENSE OF TASTE Taste buds: sense organs that respond to gustatory (taste) stimuli; associated with papillae Chemoreceptors stimulated by chemicals dissolved in the saliva Gustatory cells: sensory cells in taste buds; gustatory hairs extend from each gustatory cell into the taste pore Taste buds are similar structurally; functionally, each taste bud responds most effectively to one of five primary taste sensations: sour, sweet, bitter, umami, and salty Adaptation and sensitivity thresholds differ for each primary taste sensation

SENSE OF TASTE (cont. ) Neural pathway for taste Taste sensation begins with a

SENSE OF TASTE (cont. ) Neural pathway for taste Taste sensation begins with a receptor potential in the gustatory cells of a taste bud; an action potential is generated and activated, which then transmits the sensory input to the brain Glossopharyngeal nerve, facial nerve, and vagus nerve are used Nerve impulses are carried to the medulla oblongata, relayed into the thalamus, and then relayed into the gustatory area of the cerebral cortex in the parietal lobe of the brain

SENSES OF HEARING AND BALANCE: THE EAR

SENSES OF HEARING AND BALANCE: THE EAR

SENSES OF HEARING AND BALANCE: THE EAR (cont. ) Sense of hearing Sound is

SENSES OF HEARING AND BALANCE: THE EAR (cont. ) Sense of hearing Sound is created by vibrations Ability to hear sound waves depends on volume, pitch, and other acoustic properties Sound waves must be of sufficient amplitude to move the tympanic membrane and have a frequency capable of stimulating the hair cells in the organ of Corti (spiral organ) (Figure 15 -13) Basilar membrane width and thickness varies throughout its length

SENSES OF HEARING AND BALANCE: THE EAR (cont. ) Pathway of sound waves Enter

SENSES OF HEARING AND BALANCE: THE EAR (cont. ) Pathway of sound waves Enter external auditory canal Strike tympanic membrane, causing vibrations Neural pathway of hearing A movement of hair cells against the tectorial membrane stimulates the dendrites that terminate around the base of the hair cells and initiates impulse conduction by the cochlear nerve to the brainstem Impulses pass through “relay stations” in the nuclei in the medulla, pons, midbrain, and thalamus before reaching the auditory area of the temporal lobe

SENSES OF HEARING AND BALANCE: THE EAR (cont. ) Sense of balance Static equilibrium:

SENSES OF HEARING AND BALANCE: THE EAR (cont. ) Sense of balance Static equilibrium: ability to sense head position relative to gravity or acceleration/deceleration (Figure 15 -14) Dynamic equilibrium: needed to maintain balance when the head or body is rotated or suddenly moved; able to detect changes in direction and rate at which movement occurs (Figure 15 -15) Changing head position produces a change of pressure on the otolith-weighted matrix, stimulating the hair cells that stimulate the receptors of the vestibular nerve Vestibular nerve fibers conduct impulses to the brain and sense head position and a change in the pull of gravity

VISION: THE EYE Structure of the eye (Figures 15 -16 to 15 -25) Lacrimal

VISION: THE EYE Structure of the eye (Figures 15 -16 to 15 -25) Lacrimal apparatus: structures that secrete tears and drain them from the surface of the eyeball Eyebrows and eyelashes give some protection against foreign objects entering the eye; cosmetic purposes Eyelids consist of voluntary muscle and skin with a tarsal plate Lined with conjunctiva, a mucous membrane Palpebral fissure: opening between the eyelids Angle or canthus: where the upper and lower eyelids join

VISION: THE EYE (cont. ) Muscles of the eye Extrinsic eye muscles: skeletal muscles

VISION: THE EYE (cont. ) Muscles of the eye Extrinsic eye muscles: skeletal muscles that attach to the outside of the eyeball and bones of the orbit Named according to their position on the eyeball Include the superior, inferior, medial, and lateral rectus muscles and superior and inferior oblique muscles Intrinsic eye muscles: smooth muscles located within the eye Iris: regulates size of pupil Ciliary muscle: controls shape of lens

VISION: THE EYE (cont. ) Layers of the eyeball: three coats of tissues make

VISION: THE EYE (cont. ) Layers of the eyeball: three coats of tissues make up the eyeball (Figure 15 -21) Fibrous layer: outer coat Sclera: tough, white, fibrous tissue Cornea: the transparent anterior portion that lies over the iris; no blood vessels found in the cornea or in the lens Scleral venous sinus (canal of Schlemm): ringshaped venous sinus found deep within the anterior portion of the sclera at its junction with the cornea

VISION: THE EYE (cont. ) Vascular layer: middle coat Contains many blood vessels and

VISION: THE EYE (cont. ) Vascular layer: middle coat Contains many blood vessels and a large amount of pigment Choroid: pigmented membrane lining more than two thirds of the posterior fibrous outer coat Inner layer: incomplete innermost coat of the eyeball Retina: composed of an outer layer of pigmented epithelium (pigmented retina) and an inner layer of nervous tissue (sensory retina)

VISION: THE EYE (cont. ) Cavities and humors Cavities: eyeball has a large interior

VISION: THE EYE (cont. ) Cavities and humors Cavities: eyeball has a large interior space divided into two cavities Humors Aqueous humor: fills both chambers of the anterior cavity; clear, watery fluid that often leaks out when the eye is injured; formed from blood in capillaries located in the ciliary body (Figure 15 -25) Vitreous humor: fills the posterior cavity; semisolid material; helps maintain sufficient intraocular pressure, with aqueous humor, to give the eyeball its shape

VISION: THE EYE (cont. ) The process of seeing Formation of retinal image Refraction

VISION: THE EYE (cont. ) The process of seeing Formation of retinal image Refraction of light rays: deflection, or bending, of light rays produced when they pass obliquely through transparent mediums. The cornea, aqueous humor, lens, and vitreous humor are the refracting media of the eye Accommodation of lens: increase in curvature of the lens to achieve the greater refraction needed for near vision (Figure 15 -26) Constriction of pupil: muscles of iris are important to formation of a clear retinal image Ø Pupil constriction prevents divergent rays from object from entering eye through periphery of the cornea and lens Convergence of eyes: movement of the two eyeballs inward so that their visual axes come together at the object viewed

VISION: THE EYE (cont. ) The process of seeing

VISION: THE EYE (cont. ) The process of seeing

CYCLE OF LIFE: SENSE ORGANS Sensory information is acquired through depolarization of sensory nerve

CYCLE OF LIFE: SENSE ORGANS Sensory information is acquired through depolarization of sensory nerve endings Age, disease, structural defects, and lack of maturation affect ability to identify and respond Structure and function response capabilities are related to developmental factors associated with age Senses become more acute with maturation Sensory capability loss in old age related to structural change in receptor cells or other sense organ structures