Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
HUMAN ANATOMY LECTURE FOURTEEN SENSES SENSES • Means of receiving information about environment and body • Sensation - conscious awareness of stimuli received by sensory receptors • Steps to sensation: (1) stimuli detected by sensory receptors (2) action potentials sent to CNS - nerve tracts send action potentials to cerebral cortex and other areas of brain (3) cerebral cortex translates action potentials, creating awareness of stimulus RESPONSES OF SENSORY RECEPTORS • Action potential results from interaction of sensory receptors with stimulus • Primary receptors - axons conduct action potentials in response to stimulation of receptor • Secondary receptors - release of neurotransmitters that bind to receptors on a neuron causing an action potential • Accomodation - decreased sensitivity to a continued stimulus • Proprioceptors - provide information about the precise position and the rate of movement of various body parts, the weight of an object being held, and the range of motion of a joint TYPES OF SENSES General Receptors: • Distributed over most of the body • Primary receptor generates action potential • May be: somatic (body) - touch, pressure, temperature, proprioception, pain visceral (internal) - pain, pressure Special Senses: • Smell, taste, sight, hearing, balance • Primary receptor produces an action potential by releasing a neurotransmitter that binds to the secondary receptor that carries impulse to brain TYPES OF SENSORY RECEPTORS Nociceptors - pain • Detect extreme mechanical, thermal, or chemical (from damaged or inflamed tissue) stimuli • All parts of the body except brain • Free nerve endings with large receptive fields - difficult to detect specific area Thermoreceptors - temperature • Detect changes in temperature • Free nerve endings in dermis, skeletal muscles, liver, hypothalamus Chemoreceptors - chemicals • Smell and taste • Chemicals attach to receptors on the membrane Mechanoreceptors - mechanical stimuli • Compression, bending, stretching of cells, touch, pressure, proprioception, hearing, balance • Bending or stretching of plasma membrane on receptor cell stimulates action potential eg: Tactile/touch receptors – pressure and light touch Proprioceptors – stretch of muscles, changes in body position Baroreceptors – monitor changes in walls of blood vessels, digestive and urinary tracts Electromagnetic Receptors - energy wavelengths • Respond to various wavelengths - electricity, magnetism, light • Photoreceptors - detect light energy Sometimes a sensation is a combination of receptors ie/ wet – no wet receptor = touch, pressure, thermal receptors SENSORY NERVES IN THE SKIN Free Nerve Endings • Simplest, unspecialized, most common • Throughout most of body • Responsible for temperature sensation, pain, tickle, some proprioception TACTILE SENSES Merkel’s Discs • Axonal branches with flattened ends - each associated with a cell within the basal layer of epidermis • Light touch and superficial pressure Hair Follicle Receptors • Very sensitive to light touch • Respond to bending of hair • Not localized sensation Pacinian Corpuscles • Lamellated corpuscles - single dendrite surrounded in layers of corpuscles (like an onion) • Located in deep dermis or hypodermis - sense vibration and deep pressure • Associated with tendons and joints - involved with propreception Meissner’s Corpuscles • Located throughout dermal papillae • Perceive sensations of fine touch and pressure • Two-point discrimination - ability to detect simultaneous stimulation at two points on the skin - used to determined texture (numerous and close on tongue and fingertips) Ruffini’s End Organ • Located in reticular dermis • Sensitive to pressure and distortion of skin • Any pulling on dermis distorts capsular fibers and stretches dendrites • Mainly in fingertips PROPRIOCEPTORS Muscle Spindle • Provide information about length of skeletal muscles • Involved in stretch reflexes when adjusting posture Golgi Tendon Organ • Proprioceptors associated with tendons – located between skeletal muscle and its tendon • Respond to increased tension on tendon during muscle contraction SOMATIC SENSORY CENTER HOMUNCULUS • Size of various regions related to the number of sensory receptors in that area of the body REFERRED PAIN • Sensation in one region of body that is not source of stimulus • Organ pain usually referred to the skin • Both the organ and that region of the skin input to the same spinal segment and converge on the same ascending neurons PHANTOM AND CHRONIC PAIN Phantom Pain • Occurs in people who have appendage amputated or structure removed (such as a tooth) • If sensory pathway is stimulated at any point the action potentials are initiated and move toward CNS – integration in cerebral cortex results in perception of pain that is projected to the site of the receptors in the pathway (even if the receptors are no longer present) Chronic Pain • Not a response to immediate direct tissue injury • Cerebrum and thalamus may malfunction and misinterpret discomfort as pain • Brain may not properly regulate how much pain stimulation is allowed to penetrate to the cerebral cortex ie/ back pain, migraine – associated with frustration, helplessness, depression SPECIAL SENSES • • • • Olfaction Taste Visual Hearing and Balance OLFACTION Olfaction (smell) occurs when airborne molecules (odors) enter the nasal cavity OLFACTORY NEURONS • Dendrites found within the OLFACTORY EPITHELIUM lining superior part of nasal cavity – ends in long cilia extending into surrounding mucus • Odorants dissolved in mucus attach to receptors on cilia which initiate action potential • Axons pass through cribiform plate to OLFACTORY BULBS which extend into OLFACTORY TRACT and synapse with associated neurons in OLFACTORY CORTEX of frontal lobe of brain OLFACTORY NEURONAL PATHWAYS Three regions in frontal lobe affect conscious perception of smell: • Lateral olfactory area - conscious perception of smell • Medial olfactory area - visceral and emotional reactions to odors • Intermediate olfactory area - effect modification of incoming information TASTE/GUSTATION TASTE BUDS • Located on PAPILLAE enlargements on tongue • Consist of TASTE CELLS - each contain hairlike processes called TASTE HAIRS that extend into a TASTE PORE in the epithelium • Dissolved substances bind to receptors on hairs and initiate action potential carried to parietal lobe of cerebral cortex Taste sensations from anterior 2/3’s of tongue carried by facial nerve (VII), posterior 1/3 carried by glossopharyngeal nerve (IX), also vagus nerve (X) Types of Papillae Filiform • Thread-like • Most numerous, provide friction • No taste buds Fungiform • Mushroom shaped • Scattered over tongue • About 5 taste buds on each Foliate • Leaf shaped • In folds of tongue • Most sensitive Vallate • Flat topped • 100 taste buds on each Taste Types Sour • Most sensitive receptors on lateral surface of tongue Salty • Most sensitive receptors on tip of tongue • Anything with Na+ causes action potential Bitter • Most sensitive receptors on posterior of tongue • Highest sensitivity Sweet • Most sensitive receptors on tip of tongue Water • Water receptors (mainly on pharynx) • Processed in hypothalamus to regulate blood volume Umani • Pleasant taste ie/ beef broth, chicken broth, parmesan cheese • Detected by receptors sensitive to amino acids Taste Facts • • • • Texture affects perception of taste Temperature affects taste Very rapid adaptation, both at level of taste bud and within CNS Taste influenced by olfaction - sense of taste is reduced when nose is plugged • Different tastes have different thresholds with acid and bitter being tastes to which we are most sensitive (acids will damage mouth and many poisons are bitter) • Born with over 10,000 taste buds, number reduces dramatically by age 50 VISION ACCESSORY STRUCTURES • Eyebrows - shade, inhibit sweat • Eyelids (palpebrae) - five layers of tissues including a dense connective tissue that maintains shape of lid - blinking keeps eye lubricated - protect eye Palpebral fissure - space between eyelids Canthi - where eyelids meet, lateral and medial Medial canthus - has carnucle with modified sweat and sebaceous glands • Eyelashes - double/triple row of hairs • Ciliary glands (modified sweat glands) empty into follicles of eyelashes • Meiblomian glands - sebaceous glands that release sebum (oil) • Conjunctiva - thin transparent mucous membrane over inner surface of eyelid and anterior surface of eye - specialized stratified squamous epithelium Palprbral conjuctiva - covers inside eyelids Ocular (bulbar) conjunctiva covers anterior of eye (except pupil) SAGITTAL SECTION OF THE EYE LACRIMAL APPARATUS • Lacrimal gland - produce tears to moisten, lubricate, wash eye - tears pass through lacrimal ducts then into eye • Lacrimal puncta - two pores that drain tears • Lacrimal canaliculi - canals that tears flow through to the lacrimal sac • Nasolacrimal duct - opens into nasal cavity beneath the inferior nasal conchae EXTRINSIC EYE MUSCLES ANATOMY OF THE EYE • The eyeball is a hollow, fluid-filled sphere with a large posterior compartment and a smaller anterior compartment • The wall of the eye is made up of three layers (tunics): Fibrous tunic - outer layer including sclera and cornea Vascular tunic - middle layer including iris, ciliary body, choroid, Nervous tunic - inner layer including retina FIBROUS TUNIC Sclera – white of eye • firm, white, outer layer continuous with cornea • maintains roundness of eye • protects internal structures and provides muscle attachment points • made up of dense collagenous connective tissue with elastic fibers Cornea • transparent area that allows light to enter the eye • causes light to bend/refract as part of focusing system • avascular • connective tissue matrix containing collagen, elastin fibers and proteoglycans • collagen fibers are small (so transparent) • low water content (water would scatter the light) VASCULAR TUNIC • Middle layer with many blood vessels - branch off internal carotid artery Iris • Contains melanin (colored-part) • Mainly smooth muscle surrounding the pupil – by changing size of pupil controls amount of light entering - parasympathetic stimulation from oculomotor nerve causes circular smooth muscles to contract = constriction - sympathetic stimulation causes radial smooth muscles to contract = dilate Ciliary Body • Produces aqueous humor that fills the anterior chamber • Ciliary muscles control lens shape - ciliary processes attach to suspensory ligaments of lens Choroid • Between sclera and retina • Contains many blood vessels to nourish retina • Contains melanin so appears black - black absorbs light so it is not reflected inside the eye NERVOUS TUNIC Retina • Innermost layer of eye wall • Made up of two layers (1) Pigmented retina - outer pigmented layer - reduces light scattering inside eye (2) Sensory retina - inner layer of rod and cone cells that are sensitive to light - rods are very sensitive to light and function in dim light but don’t do color - cones require more light but do discriminate color (blue, green, or red) • rods and cones synapse with neurons that converge into the optic nerve OPTHALMIC VIEW OF THE RETINA Posterior of the eye is examined with a opthalmoscope • Macula lutea - only cones • Fovea centralis - small pit in center of macula lutea - area of greatest visual acuity, cones tightly packed • Optic disc - white spot - blood vessels enter eye - nerve processes from sensory retina meet and exit eye (optic nerve) COMPARTMENTS OF THE EYE • Two fluid-filled compartments are separated by the lens Anterior Compartment • Filled with aqueous humor - helps maintain pressure within the eye, refracts light and provides nutrients to inner eye - produced by ciliary process and returned to venous circulation through canal of Schlemm that goes around the eye into veins of sclera • Anterior chamber - between cornea and iris • Posterior chamber - between iris and lens Posterior Compartment • Filled with jelly-like vitreous humor that maintains intraocular pressure, holds lens and retina in place THE LENS • Transparent, biconvex • Made of columnar epithelial cells • Surrounded by a highly elastic, transparent capsule • Held by suspensory ligaments attached to ciliary muscles • Changes shape as ciliary muscles contract and relax - when relaxed lens is flat and allows for distance vision - as object moves closer ciliary muscles contract (parasympathitic stimulation) and pull ciliary body toward the lens - reduces tension on suspensory ligaments and lens become more spherical shaped PATHWAY OF LIGHT light rays strike cornea – refracts and brings rays closer together aqueous humor pupil light rays pass through lens – further refracts rays vitreous humor focus point at back of retina – rods and cones rods and cones send electrical signal along the optic nerve occipital cortex of brain interprets vision signals CLINICAL VISION PROBLEMS • • • • • • • • Conjunctivitis (pink eye) – inflammation of conjunctiva usually from bacterial infection Trachoma – greatest single cause of blindness today, conjunctivitis causing scarring of cornea Myopia (nearsightedness) – can’t see distant objects, focal point too near the lens (in front of retina) Hyperopia (farsightedness) – can’t see close objects – focal point past retina Presybopia – decrease in ability of eye to accommodate near vision, occurs with age Astigmatism – defect where cornea or lens isn’t uniformly curved causing image to be out of focus Cataract – clouding of the lens as one ages, infection, trauma, UV Retinal detachment – separation of sensory retina from pigmented retina THE EAR • External ear - hearing - auricle, external auditory meatus and eardrum (tympanic membrane) • Middle ear - hearing - air-filled space containing auditory vesicles • Inner ear - hearing and balance - interconnected fluid-filled tunnels and chambers within the temperal lobe EXTERNAL EAR Auricle (pinna) • fleshy external part • elastic cartilage covered with skin External auditory meatus • passage leading to eardrum • lined with hairs and ceruminous glands (produce cerumen) Typmpanic membrane • separates external from middle ear • thin double layered membrane • vibrates with sound waves MIDDLE EAR • Air-filled cavity separated from internal ear by oval window and round window • Contains three auditory ossicles (bones) that transmit vibrations from the tympanic membrane to the oval window (1) malleus (hammer) - attaches to tympanic membrane (2) incus (anvil) - connects malleus to the stapes (3) stapes (stirrup) - base rests on oval window by annular ligament • Muscles: tensor tympani inserts on malleus, stapedius inserts on stapes INNER EAR Bony Labyrinth • Interconnecting tunnels and chambers continuous with the temporal bone • Divided into cochlea, vestibule, and semicircular canals Membranous Labyrinth • Fluid-filled tunnels and chambers inside the bony labyrinth Perilymph • Fluid found between bony and membranous labyrinths Endolymph • Fluid within membranous labyrinth INNER EAR CONT… Cochlea • Large snail shell shaped portion • Spiral lamina (bone) twists the cochlea into its shape • Extending from the spiral lamina is a Y-shaped membranous complex which divides the cochlea into 3 sections - the base of the Y is the spiral lamina - one branch is the vestibular membrane - the other branch is the basilar membrane - the space above is the scala vestibuli which extends from the oval window to the apex (helicotrema) - the space inbetween is the cochlear duct - the space below is the scala tympani which extends from the helicotrema to the round window - the scala vestibuli and tympani are both filled with perilymph fluid INNER EAR CONT… Organ of Corti (Spiral Organ) • Found in cochlear duct • Contains specialized sensory cells called hair cells extending from the basilar membrane - have 80-100 hairlike microvilli (stereocilia) on apical surface - hair tips are embedded within an acellular gelatinous shelf called the tectorial membrane - attached to the spiral lamina, remains stationary • Generates sound signals to sensory neurons through to the cochlear nerve INNER EAR CONT… • Hair cell arranged in rows - inner hair cells for hearing - outer hair cells regulate tension on basilar membrane • Hair bundle - stereocilia of one inner hair cell • Tip link (gating spring) - attaches to tip of each stereocilium in a hair bundle to the side of the longer one - as stereocilia bend the tip links open the K+ gates to generate action potential OPENING OF K+ GATES HEARING 1. 2. 3. 4. Sound waves from auricle and external auditory canal strike the tympanic membrane causing it to vibrate Vibration pushes the three bones of the middle ear - the foot plate of the stapes vibrates against the oval window Vibration of the oval window causes movement of the perilymph in the scala vestibuli Vibration of the perilymph produces waves in the endolymph – displacing the basilar membrane - short waves (high pitch) cause displacement near the oval window - long waves (low pitch) cause displacement near the helicotrema 5. • • Movement of the basilar membrane is detected in the hair cells of the Organ of Corti which are attached to its basilar membrane - as hair changes shape between basilar membrane and tectorial membrane K+ gates are opened and nerve impuse sent to temporal lobe to be interpreted Vibrations of the perilymph in the scala vestibuli and of the endolymph in the cochlear duct are transferred to the perilymph of the scala tympani Vibrations in the perilymph of the scala tympani are transferred to the round window where they are dampened BALANCE AND EQUILIBRIUM STATIC EQUILIBRIUM • associated with the vestibule and involved in evaluating the position of the head relative to gravity, detects linear acceleration and deceleration Vestibule • divided into utricle and saccule chambers • each chamber contains specialized patches of epithelium called maculae surrounded by endolymph • the maculae contain hair cells with microvilli (stereocilia) and one cilium (kinocilium) with their tips embedded in a gelatinous mass weighted down by otoliths (protein and calcium carbonate particles) • the gelatinous mass moves in response to gravity which bends the hair cells and initiates action potentials • changes in movement cause the otoliths to vary their pressure thus providing info regarding head position of acceleration KINETIC EQUILIBRIUM • associated with the semicircular canals • evaluates movement of the head in three dimensional space Semicircular Canals • semicircular canals contain endolymph and are positioned in the transverse, coronal and sagittal planes • The base of each expands into an ampulla • Within each ampulla is specialized epithelium forming a crista ampullaris - a ridge of epithelium with a curved gelatinous mass (cupula) • Displacement of the endolymph causes displacement of the cupula causing the stereocilia to bend and initiate an action potential to the hair cells