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Biology 218 – Human Anatomy Session: Section: Days / Time: Instructor: Lecture Outline Adapted from Martini Human Anatomy 7th ed. FALL 52999 MW 5:00 PM – 9:20 PM RIDDELL Chapter 18 The Nervous System General and Special Senses Introduction Sensory information arrives at the CNS Information is “picked up” by sensory receptors Sensory receptors are the interface between the nervous system and the internal and external environment General senses Refers to temperature, pain, touch, pressure, vibration, and proprioception Special senses Refers to smell, taste, balance, hearing, and vision Receptors Receptors and Receptive Fields Free nerve endings are the simplest receptors These respond to a variety of stimuli Receptors of the retina (for example) are very specific and only respond to light Receptive fields Large receptive fields have receptors spread far apart, which makes it difficult to localize a stimulus Small receptive fields have receptors close together, which makes it easy to localize a stimulus. Receptors Interpretation of Sensory Information Information is relayed from the receptor to a specific neuron in the CNS The connection between a receptor and a neuron is called a labeled line Each labeled line transmits its own specific sensation Interpretation of Sensory Information Classification of Receptors Tonic receptors Always active Photoreceptors of the eye constantly monitor body position Phasic receptors Normally inactive but become active when necessary (for short periods of time) Touch and pressure receptors of the skin (for example) Receptors Central Processing and Adaptation Adaptation Reduction in sensitivity due to a constant stimulus Peripheral adaptation Receptors respond strongly at first and then decline Central adaptation Adaptation within the CNS © 2012 Pearson Education, Inc. Page 1 of 11 493714648 Biology 218 – Human Anatomy Lecture Outline Adapted from Martini Human Anatomy 7th ed. Session: Section: Days / Time: Instructor: FALL 52999 MW 5:00 PM – 9:20 PM RIDDELL Consciously aware of a stimulus, which quickly disappears The General Senses Classification of the General Senses One classification scheme: Exteroceptors: provide information about the external environment Proprioceptors: provide information about the position of the body Interoceptors: provide information about the inside of the body The General Senses Classification of the General Senses Another classification scheme: Nociceptors: respond to the sensation of pain Thermoreceptors: respond to changes in temperature Mechanoreceptors: activated by physical distortion of cell membranes Chemoreceptors: monitor the chemical composition of body fluids The General Senses Nociceptors Known as pain receptors Associated with free nerve endings and large receptor fields. This makes it difficult to “pinpoint” the location of the origin of the pain Three types Receptors sensitive to extreme temperatures Receptors sensitive to mechanical damage Receptors sensitive to chemicals The General Senses Nociceptors Fast pain: Sensations reach the CNS fast Associated with pricking pain or cuts Slow pain: Sensations reach the CNS slowly Associated with burns or aching pains Referred pain: Sensations reach the spinal cord via the dorsal roots Some visceral organ pain sensations may reach the spinal cord via the same dorsal root The General Senses Thermoreceptors Found in the dermis, skeletal muscles, liver, and hypothalamus Cold receptors are more numerous than hot receptors Exist as free nerve endings These are phasic receptors Information is transmitted along the same pathway as pain information © 2012 Pearson Education, Inc. Page 2 of 11 493714648 Biology 218 – Human Anatomy Session: Section: Days / Time: Instructor: Lecture Outline Adapted from Martini Human Anatomy 7th ed. FALL 52999 MW 5:00 PM – 9:20 PM RIDDELL The General Senses Mechanoreceptors Receptors that are sensitive to stretch, compression, twisting, or distortion of the plasmalemmae There are three types Tactile receptors Baroreceptors Proprioceptors The General Senses Mechanoreceptors Tactile receptors Provide sensations of touch, pressure, and vibrations Unencapsulated tactile receptors: free nerve endings, tactile disc, and root hair plexus Encapsulated tactile receptors: tactile corpuscle, Ruffini corpuscle, and lamellated corpuscle The General Senses Mechanoreceptors Unencapsulated tactile receptors Free nerve endings are common in the dermis Tactile discs are in the stratum basale layer Root hair plexus monitors distortions and movements of the body surface The General Senses Mechanoreceptors Encapsulated tactile receptors Tactile corpuscle: common on eyelids, lips, fingertips, nipples, and genitalia Ruffini corpuscle: in the dermis, sensitive to pressure and distortion Lamellated corpuscle: consists of concentric cellular layers / sensitive to vibrations The General Senses Mechanoreceptors Baroreceptors Stretch receptors that monitor changes in the stretch of organs Found in the stomach, small intestine, urinary bladder, carotid artery, lungs, and large intestine The General Senses Mechanoreceptors Proprioceptors Monitor the position of joints, tension in the tendons and ligaments, and the length of muscle fibers upon contraction Muscle spindles are receptors in the muscles Golgi tendon organs are the receptors in the tendons The General Senses Chemoreceptors Detect small changes in the concentration of chemicals Respond to water-soluble or lipid-soluble compounds © 2012 Pearson Education, Inc. Page 3 of 11 493714648 Biology 218 – Human Anatomy Lecture Outline Adapted from Martini Human Anatomy 7th ed. Session: Section: Days / Time: Instructor: FALL 52999 MW 5:00 PM – 9:20 PM RIDDELL Found in respiratory centers of the medulla oblongata, carotid arteries, and aortic arch The Special Senses The special senses include: Olfaction (smell) Gustation (taste) Equilibrium Hearing Vision Olfaction (Smell) Olfaction The olfactory epithelium consists of: Olfactory receptors Supporting cells Basal cells Olfaction (Smell) Olfactory Pathways Axons leave the olfactory epithelium Pass through the cribriform foramina Synapse on neurons in the olfactory bulbs Impulses travel to the brain via CN I Arrive at the cerebral cortex, hypothalamus, and limbic system Olfaction (Smell) Olfactory Discrimination The epithelial receptors have different sensitivities and we therefore “detect” different smells Olfactory receptors can be replaced The replacement activity declines with age Gustation (Taste) Gustation The tongue consists of papillae Papillae consist of taste buds Taste buds consist of gustatory cells Each gustatory cell has a slender microvilli that extends through the taste pore into the surrounding fluid Gustation (Taste) Gustation Pathways Dissolved chemicals contact the taste hairs (microvilli) Impulses go from the gustatory cell through CN VII, IX, and X Synapse in the nucleus solitarius of the medulla oblongata The impulses eventually arrive at the cerebral cortex © 2012 Pearson Education, Inc. Page 4 of 11 493714648 Biology 218 – Human Anatomy Session: Section: Days / Time: Instructor: Lecture Outline Adapted from Martini Human Anatomy 7th ed. FALL 52999 MW 5:00 PM – 9:20 PM RIDDELL Gustation (Taste) Gustation Discrimination We begin life with more than 10,000 taste buds The number declines rapidly by age 50 Threshold level is low for gustatory cells responsible for unpleasant stimuli Threshold level is high for gustatory cells responsible for pleasant stimuli Equilibrium and Hearing Equilibrium and Hearing Structures of the ear are involved in balance and hearing The ear is subdivided into three regions External ear Middle ear Inner ear Equilibrium and Hearing The External Ear Consists of: Auricle External acoustic meatus Tympanic membrane Ceruminous glands Equilibrium and Hearing The Middle Ear Consists of: Tympanic cavity Auditory ossicles Malleus, incus, and stapes Auditory tube (pharyngotympanic tube) Equilibrium and Hearing The Inner Ear Consists of: Receptors Membranous labyrinth (within the bony labyrinth) Bony labyrinth Vestibule Semicircular canals Cochlea Utricle Saccule Equilibrium and Hearing The Inner Ear The vestibular complex and equilibrium Part of inner ear that provides equilibrium sensations by detecting rotation, gravity, and acceleration © 2012 Pearson Education, Inc. Page 5 of 11 493714648 Biology 218 – Human Anatomy Lecture Outline Adapted from Martini Human Anatomy 7th ed. Session: Section: Days / Time: Instructor: FALL 52999 MW 5:00 PM – 9:20 PM RIDDELL Consists of: Semicircular canals Utricle Saccule Equilibrium and Hearing The Vestibular Complex and Equilibrium The semicircular canals Each semicircular canal encases a duct The beginning of each duct is the ampulla Within each ampulla is a cristae with hair cells Each hair cell contains a kinocilium and stereocilia These are embedded in gelatinous material called the cupula The movement of the body causes movement of fluid in the canal, which in turn causes movement of the cupula and hair cells, which the brain detects Equilibrium and Hearing The Vestibular Complex and Equilibrium The utricle and saccule The utricle and saccule are connected to the ampulla and to each other and to the fluid within the cochlea Hair cells of the utricle and saccule are in clusters called maculae Hair cells are embedded in gelatinous material consisting of statoconia (calcium carbonate crystals) Gelatinous material and statoconia collectively are called an otolith Equilibrium and Hearing Equilibrium Process When you rotate your head: The endolymph in the semicircular canals begins to move This causes the bending of the kinocilium and stereocilia This bending causes depolarization of the associated sensory nerve When you rotate your head to the right, the hair cells are bending to the left (due to movement of the endolymph) When you move in a circle and then stop abruptly, the endolymph moves back and forth causing the hair cells to bend back and forth resulting in confusing signals, thus dizziness Equilibrium and Hearing Equilibrium Process (cont.) When you move up or down (elevator movement): Otoliths rest on top of the maculae When moving upward, the otoliths press down on the macular surface When moving downward, the otoliths lift off the macular surface When you tilt side to side: When tilting to one side, the otoliths shift to one side of the macular surface Equilibrium and Hearing The Cochlea © 2012 Pearson Education, Inc. Page 6 of 11 493714648 Biology 218 – Human Anatomy Session: Section: Days / Time: Instructor: Lecture Outline Adapted from Martini Human Anatomy 7th ed. FALL 52999 MW 5:00 PM – 9:20 PM RIDDELL Consists of “snail-shaped” spirals Spirals coil around a central area called the modiolus Within the modiolus are sensory neurons The sensory neurons are associated with CN VIII Organ of Corti Equilibrium and Hearing The Cochlea (cont.) Each spiral consists of three layers Scala vestibuli (vestibular duct): consists of perilymph Scala tympani (tympanic duct): consists of perilymph Scala media (cochlear duct): consists of endolymph / this layer is between the scala vestibuli and scala tympani There is a basilar membrane between each layer The scala vestibuli and scala tympani are connected at the apical end of the cochlea Sense organs rest on the basilar membrane within the scala media Equilibrium and Hearing The Cochlea The Organ of Corti Also known as the spiral organ Rests on the basilar membrane between the scala media and the scala tympani Hair cells are in contact with an overlying tectorial membrane This membrane is attached to the lining of the scala media Sound waves ultimately cause a distortion of the tectorial membrane, thus stimulating the organ of Corti Equilibrium and Hearing Auditory Pathways Sound waves enter the external acoustic meatus The tympanic membrane vibrates Causes the vibration of the ossicles The stapes vibrates against the oval window of the scala tympani Perilymph begins to move Equilibrium and Hearing Auditory Pathways (continued) As the perilymph moves: Pressure is put on the scala media This pressure distorts the hair cells of the organ of Corti This distortion depolarizes the neurons Vision Vision Accessory structures of the eye Palpebrae (eyelids) Medial and lateral canthus (connect the eyelids at the corners of the eye) Palpebral fissure (area between the eyelids) © 2012 Pearson Education, Inc. Page 7 of 11 493714648 Biology 218 – Human Anatomy Session: Section: Days / Time: Instructor: Lecture Outline Adapted from Martini Human Anatomy 7th ed. FALL 52999 MW 5:00 PM – 9:20 PM RIDDELL Eyelashes (contain root hair plexus, which triggers the blinking reflex) Conjunctiva (epithelial lining of the eyelids) Glands: glands of Zeis, tarsal glands, lacrimal gland, lacrimal caruncle Vision Accessory Structures of the Eye Conjunctiva Covers the inside lining of the eyelids and the outside lining of the eye Fluid production helps prevent these layers from becoming dry Palpebral conjunctiva Inner lining of the eyelids Ocular conjunctiva Outer lining of the eye Vision Accessory Structures Glands All of the glands are for protection or lubrication Glands of Zeis: sebaceous glands / associated with eyelashes Tarsal glands: secrete a lipid-rich product / keeps the eyelids from sticking together / located along the inner margin of the eyelids Lacrimal glands: produce tears / located at the superior, lateral portion of the eye Lacrimal caruncle glands: produce thick secretions / located within the canthus areas Vision Accessory Structures Glands An infection of the tarsal gland may result in a cyst An infection of any of the other glands may result in a sty Vision Accessory Structures Lacrimal glands Part of the lacrimal apparatus The lacrimal apparatus consists of: Lacrimal glands (produce tears) Lacrimal canaliculi Lacrimal sac Nasolacrimal duct Vision Accessory Structures Lacrimal glands (continued) Tears are produced by the lacrimal glands Flow over the ocular surface Flow into the nasolacrimal canal (foramen) This foramen enters into the nasal cavity © 2012 Pearson Education, Inc. Page 8 of 11 493714648 Biology 218 – Human Anatomy Session: Section: Days / Time: Instructor: Lecture Outline Adapted from Martini Human Anatomy 7th ed. FALL 52999 MW 5:00 PM – 9:20 PM RIDDELL Therefore, when you sob heavily, tears flow across your eye and down your face and also through the nasolacrimal canal into your nose and out, resulting in a “runny” nose Vision The Eyes Consist of: Sclera Cornea Pupil Iris Lens Anterior cavity Posterior cavity Three tunics: (1) fibrous tunic, (2) vascular tunic, and (3) neural tunic Retina Vision The Eyes The Fibrous Tunic (outer layer) Makes up the sclera and cornea Provides some degree of protection Provides attachment sites for extra-ocular muscles The cornea is modified sclera Vision The Eyes The Vascular Tunic (middle layer) Consists of blood vessels, lymphatics, and intrinsic eye muscles Regulates the amount of light entering the eye Secretes and reabsorbs aqueous fluid (aqueous humor) Controls the shape of the lens Includes the iris, ciliary body, and the choroid Vision The Vascular Tunic The iris Consists of blood vessels, pigment, and smooth muscles The pigment creates the color of the eye The smooth muscles contract to change the diameter of the pupil Vision The Vascular Tunic The ciliary body The ciliary bodies consist of ciliary muscles connected to suspensory ligaments, which are connected to the lens The choroid Highly vascularized © 2012 Pearson Education, Inc. Page 9 of 11 493714648 Biology 218 – Human Anatomy Session: Section: Days / Time: Instructor: Lecture Outline Adapted from Martini Human Anatomy 7th ed. FALL 52999 MW 5:00 PM – 9:20 PM RIDDELL The innermost portion of the choroid attaches to the outermost portion of the retina Vision The Eyes The Neural Tunic (inner layer) Also called the retina Made of two layers: (pigmented layer – outer layer) / (neural layer – inner layer) Retina cells: rods (night vision) and cones (color vision) Vision Cavities and Chambers of the Eye Anterior cavity Anterior chamber Posterior chamber Filled with fluid called aqueous fluid Posterior cavity Vitreous chamber Filled with fluid called vitreous fluid Vision Cavities and Chambers of the Eye Aqueous fluid Sometimes called aqueous humor Secreted by cells at the ciliary body area Enters the posterior chamber (posterior of the iris) Flows through the pupil area Enters the anterior chamber Flows through the canal of Schlemm Enters into venous circulation Vision Cavities and Chambers of the Eye Vitreous fluid Gelatinous material in the posterior chamber Sometimes called vitreous humor Supports the shape of the eye Supports the position of the lens Supports the position of the retina Aqueous humor can flow across the vitreous fluid and over the retina Vision Aqueous fluid If this fluid cannot drain through the canal of Schlemm, pressure builds up This is glaucoma Vitreous fluid If this fluid is not of the right consistency, the pressure is reduced against the retina The retina may detach from the posterior wall (detached retina) © 2012 Pearson Education, Inc. Page 10 of 11 493714648 Biology 218 – Human Anatomy Session: Section: Days / Time: Instructor: Lecture Outline Adapted from Martini Human Anatomy 7th ed. FALL 52999 MW 5:00 PM – 9:20 PM RIDDELL Vision Visual Pathways Light waves pass through the cornea Pass through the anterior chamber Pass through the pupil Pass through the posterior chamber Pass through the lens The lens focuses the image on some part of the retina This creates a depolarization of the neural cells Signal is transmitted to the brain via CN II Vision Visual Pathways The retina There are rods and cones all over the retina 100% cones in the fovea centralis area The best color vision is when an object is focused on the fovea centralis 0% rods or cones in the optic disc area If an object is focused on this area, vision does not occur Vision Visual Pathways The retina (cont.) The cones require light to be stimulated (that’s why we see color) At night (still has to be at least a small amount of light), the cones deactivate and the rods begin to be activated (that’s why we can see at night but we can’t determine color at night) © 2012 Pearson Education, Inc. Page 11 of 11 493714648
