The Senses Chapter 10

Senses General senses – Receptors widely distributed throughout body – Skin, various organs & joints Special senses – Specialized receptors confined to structured in the head – Eyes, ears, nose, mouth

Sensation Sensory receptors – Specialized structures that collect info from environment – Stimulate neurons to send impulses to brain Perception – Person’s view of stimulus; interpretation

Different Types of Receptors Chemoreceptors Pain receptors Thermoreceptors Mechanoreceptors Photoreceptors

Sensory Impulses Stimulation of receptor causes local change in receptor potential Current is generated that reflects intensity of stimulation Membrane potential may generate an action potential Peripheral nerves transmit impulses to CNS

Perception Projection – Process in which brain projects sensation back to its apparent source

Sensory Adaptation Ability to ignore unimportant stimuli Decreased response to a stimulus from receptor, or along the pathway leading to the cerebral cortex Sensory impulses become less frequent and may cease Stronger stimulus is required to trigger impulse

General Senses (of skin, muscles, joints, viscera) Exteroceptive senses – Associated with body surface (touch, pressure, temperature, pain) Viseroceptive senses – Associated with changes in viscera Proprioceptive senses – Associated with changes in muscles and tendons

Touch & Pressure Free nerve endings – Epithelial tissue; simple; sense itching Tactile (Meissner’s corpuscles) – Abundant in hairless areas (skin, lips) – Detect fine touch (between two points on skin) Lamellated (Pacinian) corpuscles – Common in deeper subcutaneous areas – Heavy pressure, vibrations

Epidermis Dermis (a) (b) (c) Section of skin Free nerve endings Epithelial cells Sensory nerve fiber Epithelial cells Tactile (Meissner’s) corpuscle (touch receptor) Sensory nerve fiber Lamellated (Pacinian) corpuscle (pressure receptor) Connective tissue cells Sensory nerve fiber

Sense of Pain Where do we have them? – Not in brain – lacks pain receptors Stimulated by tissue damage, chemical, mechanical forces, or extremes in temperature Adapt very little if at all

Pain Pain receptors respond differently to stimulation, not well localized Referred pain – may feel as if coming from other part of body Phantom limb pain

Appendix Ureter Lung and diaphragm Heart Stomach Pancreas Colon Kidney Urinary bladder Liver and gallbladder Small intestine Ovary (female) Liver and gallbladder

Regulation of Pain Impulses Thalamus – awareness of pain Cerebral cortex – judges intensity & location of pain, and responds to pain Pain inhibitors: – Enkephalins – Serotonin – Endorphins

Special Senses Smell – olfactory organs Taste – taste buds Hearing & equilibrium – ears Sight – eyes

Smell Chemoreceptors respond to chemicals dissolved in liquids Olfactory organs cover different parts of nose Nasal cavity Cilia (b) (a) Cribriform plate Superior nasal concha Olfactory bulb Olfactory tract Nerve fibers within the olfactory bulb Olfactory receptor cells Columnar epithelial cells Cribriform plate

Olfactory Stimulation Olfactory organs located high in nasal cavity above the usual pathway of inhaled air Receptors undergo sensory adaptation quickly Sense of smell drops 50% within a second after stimulation

Taste Taste buds located on tongue papillae, roof of mouth, linings of cheeks, walls of pharynx Taste receptors are chemoreceptors – Taste cells, taste hairs (microvilli) Papillae (a) (b) Connective tissue Sensory nerve fibers Epithelium of tongue Supporting cell Taste pore Taste hair Taste cell Taste buds

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

Hearing Three sections of ear – external, middle, inner Auricle 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

Round window Pharynx Auditory tube Auricle Oval window (under stapes) Cochlea Malleus Incus Stapes External acoustic meatus Semicircular canals Vestibulocochlear nerve Tympanic cavity Tympanic membrane

Auditory Tube Eustachian tube – connects middle ear to throat Maintains equal pressure on both sides of tympanic membrane Closed by valve-like flaps in throat

Inner Ear Made of complex system of labyrinths Within, are hair cells that move with different frequencies of sound, and vibrate different parts of the basilar membrane to generate a nerve impulse

Equilibrium Static – senses position of head when body not moving Dynamic – senses rotation and movement of head and body

Eye Eyelid – 4 layers: Skin Muscle – closes/opens eyelid CT Conjunctiva – mucous membrane

Lacrimal Apparatus Lacrimal gland – lateral to eye/secretes tears Canaliculi – collects tears Lacrimal sacs – collects from canaliculi Nasolacrimal duct – collects from lacrimal sac/empties tears into nasal cavity Lacrimal gland Lacrimal sac Superior and inferior canaliculi Nasolacrimal duct

Eye Structure Hollow, spherical, wall with three layers: – Outer fibrous tunic – Middle vascular tunic – Inner nervous tunic Ciliary body Retina Choroid coat Sclera Fovea centralis Optic nerve Lens Iris Pupil Cornea Lateral rectus Medial rectus Optic disc Posterior cavity Vitreous humor Posterior chamber Anterior chamber Aqueous humor Suspensory ligaments Anterior cavity

Outer Tunic Cornea – Anterior; transparent – Light transmission and refraction Sclera – Posterior; opaque – Protection

Middle Tunic 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

Ciliary body Retina Choroid coat Sclera Fovea centralis Optic nerve Lens Iris Pupil Cornea Lateral rectus Medial rectus Optic disc Posterior cavity Vitreous humor Posterior chamber Anterior chamber Aqueous humor Suspensory ligaments Anterior cavity

Anterior Eye Filled with aqueous humor Conjunctiva Iris Lens Ciliary process Ciliary muscles Sclera CorneaAnterior chamber Vitreous humor Suspensory ligaments Posterior chamber Ciliary body

Anterior Eye Lens Transparent, biconvex, elastic Behind iris Composed of lens fibers Held in place by ligaments of ciliary body Ciliary Body Forms internal ring around front of eye Has folds and muscles that move the lens Retina Choroid coat Sclera Lens Ciliary processes of ciliary body Suspensory ligaments

Iris CT & smooth muscle Pupil is hole in iris Dim light stimulates muscles that dilate pupil Bright light stimulates muscles that constrict pupil Sympathetic motor nerve fiber In dim light Radially arranged Smooth muscle fibers of the iris Circularly arranged smooth muscle fibers of the iris Pupil In normal light In bright light Parasympathetic ganglion Parasympathetic motor nerve fiber

Aqueous Humor Fluid in anterior cavity of eye Provides nutrients and maintains shape Sclera Iris Lens Aqueous humor Cornea Vitreous humor Ciliary process Ciliary muscles Posterior chamber Ciliary body Scleral venous sinus (canal of Schlemm) Anterior chamber

Inner Tunic Retina – Contains visual receptors, continuous with optic nerve – Several layers – Macula lutea – yellowish spot in retina – Fovea centralis – center of above; produces sharpest vision – Optic disc – blindspot, no visual receptors – Vitreous humor – thick gel; holds retina flat against choroid coat

Retina Focusing 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 Light waves Object Cornea Image Retina

Refraction Disorders Concave lens corrects nearsightedness Convex lens corrects farsightedness Light waves Cornea Lens Retina (a) Eye too long (myopia) (b) Normal eye (c) Eye too short (hyperopia) Point of focus Point of focus Point of focus Light waves Concave lens Convex lens (a) (b) Uncorrected point of focus Corrected point of focus Uncorrected point of focus Corrected point of focus

Visual Receptors Rods Long, thin Light sensitive pigment rhodopsin 100x more sensitive to light than cones Provide vision in dim light Produce colorless vision and outlines of objects Cones Short, blunt Light sensitive pigments— erythrolabe, chlorolabe, cyanolabe Vision in bright light Sharp images, color vision

Cones Rods Rod Cone (c) Many sensory nerve fibers (b) Single sensory nerve fiber (a) Retinal pigment epithelium c: © Frank S. Werblin, PhD.

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

Optic tract Eye Fibers from nasal (medial) half of each retina crossing over Visual cortex of occipital lobe Lateral geniculate body of thalamus Optic chiasma Optic nerve Optic radiations

Aging and the Senses 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

Helpful Videos on Senses 1nslE 1nslE 4JU 4JU