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
AP1 Lab 11 – Ear and Eye, Dissection of Eye THE EAR – FOR HEARING AND BALANCE Figs. 15.24-15.31 The senses of both hearing and equilibrium are located in the ear. The ear is divided into three anatomical divisions. Identify the following on the models. 1) EXTERNAL EAR - consists of the auricle (a.k.a. pinna) which is the outwardly visible structure surrounding the entrance to the ear canal and the ear canal itself more properly called the external auditory canal (a.k.a. external acoustic meatus). At the end of the external acoustic meatus is the tympanic membrane (ear drum). The auricle or pinna collects sound waves and directs them into the external acoustic meatus (ear canal) in order to strike the tympanic membrane or tympanum (eardrum) and cause it to vibrate. Lining the walls of the external acoustic meatus are ceruminous glands secreting a waxy secretion known as cerumen (a.k.a. ear wax). What is the function of cerumen? 2) MIDDLE EAR The middle ear begins at the tympanum and is an air filled chamber located within the temporal bone. It contains the three small bones called auditory ossicles, which amplify and transmit the vibrations of the tympanum inward to the inner ear. Individually these 3 bones are malleus (hammer), incus (anvil), and stapes (stirrup) [pronounced “stay-peez”] There is also a flexible, pliable, mucous membrane lined tube that connects the middle ear cavity to the nasopharynx (upper throat) [pronounced “Nay-zo-fair-inks”]. This tube is known by several names: auditory tube, pharyngotympanic tube [“Far-in-jo-tim-panic”], and formerly the eustachian tube. Describe the function of this tube. Revised 1/11/2017 1 The normal position of this tube when an adult is upright is for it to run obliquely downward thus providing natural ‘drainage’ of any liquids that might enter the middle ear cavity. Can you see how an infection of the throat could travel to the middle ear? In small children this is even more likely to happen because this tube doesn’t yet tilt downward and liquids in the throat can easily travel toward the middle ear. Resulting middle ear infections are usually called “Otitis media”. This term translates literally as “inflamed middle ear.” Identify the tensor tympani muscle attached to the malleus. This muscle and a much smaller muscle called the stapedius muscle [not visible on our models] are involved in a reflex called the attenuation reflex. **Confirm all of above and previous page with your instructor.** OYO: Look up this attenuation reflex online and explain. Other online OYOs: What is an otoscope? What is a myringotomy and why is it done? What are ventilation tubes and why would they be installed? Revised 1/11/2017 2 3. INTERNAL OR INNER EAR This contains the sensory organs for both hearing and equilibrium. (Table 15.2) The inner ear can be described as a membranous labyrinth – a series of fluid filled tubes and sacs. This membranous labyrinth is suspended in a bony labyrinth (of nearly the same shape) by a fluid called perilymph. Imagine your hand fitting in a stiff glove filled with water. The glove is the bony labyrinth and your hand and fingers make up the membranous labyrinth. Your hand never really touches the glove because of the water. The perilymph fluid is very similar to CSF and is continuous with it. Leakage of this fluid from your patient’s ear canal is indicative of a basilar skull fracture. You would typically only see this in traumatic head injuries. The 2 parts of the membranous labyrinth are the snail shaped Cochlea (it contains the receptor structures for hearing) and the tubular vestibular complex (consisting of a chamber called the vestibule and 3 semicircular canals.) The vestibule and semicircular canals contain the sensory receptors for equilibrium. All parts of the membranous labyrinth are filled with a fluid called endolymph. When the 3 auditory ossicles vibrate in response to sound waves the endolymph vibrates in the cochlea stimulating receptors that send impulses that the brain interprets as sounds. Positions and movements of the head and body cause movements of the endolymph in the vestibule and the 3 semicircular canals. Sensors here send nerve impulses that your brain interprets as body position or movement so you know when you’re leaning forward or back or to the side or turning, spinning, etc. Name and identify on the model the cranial nerve that is 100% sensory for hearing and balance ___________________________ **Confirm your identifications with your instructor. OYO: Go online to eHow.com and learn about motion sickness and explain several ways motion sickness (“antimotion”) drugs work? Revised 1/11/2017 3 OYO: Dysfunctions of Hearing and Balance 1. Otitis Media – Inflammation and infection of the middle ear. Typically, acute otitis media follows a cold: after a few days of a stuffy nose the ear becomes involved and can cause severe pain. The pain will usually settle within a day or two but can last over a week. Sometimes the ear drum ruptures discharging pus from the ear, but usually the ruptured drum will heal rapidly. At an anatomic level, the typical progression of acute otitis media occurs as follows: the tissues surrounding the Eustachian tube swell due to an upper respiratory infection, allergies, or dysfunction of the tubes. The Eustachian tube remains blocked most of the time. The air present in the middle ear is slowly absorbed into the surrounding tissues. A strong negative pressure creates a vacuum in the middle ear. The vacuum reaches a point where fluid from the surrounding tissues accumulates in the middle ear. 2. Hyperacusis – Extreme sensitivity to noise – can be caused by exposure to loud noise, or paralysis of an attenuating muscle, the stapedius. Paralysis of the stapedius allows wider oscillation of the stapes, resulting in heightened reaction of the auditory ossicles to sound vibration. 3. Presbycusis – age related hearing loss. Tends to start with higher frequencies, moving down into the voice range. Typical upper limit of hearing at age 50 is about 11,000 Hz. 4. NIHL – Noise induced hearing loss – There are two basic types of NIHL: NIHL caused by acoustic trauma and gradual developing NIHL. Acoustic trauma can be due to explosions, gunfire, etc. Gradual NIHL is repeated exposure to loud sounds over a period of time. This would include musical concerts, workplace noise, and IPod’s. Over 85 dB (A) of noise for 8 hours per day is the OSHA limit. NIHL usually occurs first at high frequencies (3000- 8000 Hz) and then spreads down to low frequencies. See the Web of Life website www.brazosport.edu/weboflife for a “virtual exhibit.” 5. Tinnitus – is the perception of sound in the human ear in the absence of corresponding external sound. Pulsatile tinnitus is usually objective in nature, resulting from altered blood flow or increased blood turbulence near the ear. Subjective tinnitus may be due to excessive exposure to loud noise, or ototoxic medications. 6. Meniere’s Syndrome - Disorder of all three parts of the labyrinth Symptoms - episodes of vertigo (sensation of a spinning motion), fluctuating hearing loss, tinnitus and sometimes feeling of fullness or pressure in ear and often accompanied by nausea. Normally affects one ear only Treated by antimotion drugs, low-salt diet and diuretics Creative uses of deafness: “The Mosquito” – high frequency sounds designed to prevent loitering of younger people “Teen Buzz” or “Mosquito ringtone” – A modulated 17 kHz sound that most people over 20 years of age cannot hear. Factoid: Human communication is in the range of 200 and 8,000 hertz. Teenagers can hear frequencies as high as 20,000 hertz. Therefore, teenagers are not human. Revised 1/11/2017 4 THE EYE Figs. 15.1-15.9 Identify these on diagrams, models, and your lab partner. SUPERFICIAL ANATOMY EXTRINSIC EYE MUSCLES: These muscles control directional movements of the eye. Name the 3 cranial nerves that innervate these muscles: __________________________, ______________________________, & ____________________________ LACRIMAL GLAND: (pronounced LAC-cri-mal) located in superior, lateral border of eye socket. The models with eyelids have this structure… other models without eyelids don’t. Secretes tears to lubricate surface of eye. Also secretes tears associated with crying. Tears contain an antibacterial enzyme called LYSOZYME. LACRIMAL PUNCTA: holes on the medial edges of all four eyelids for drainage of tears. View these on your lab partner. Tears are absorbed here, not produced here. Explain why your nose ‘runs’ when you cry. CONJUNCTIVA: (pronounced “kon-JUNK-ti-va”) the delicate, almost invisible, mucous membrane covering the visible parts of sclera and underside of eyelids. Lubricates and reduces friction between eyelid and cornea when blinking. Have your lab partner pull down their lower eyelids to see this pinkish membrane. SCLERA: The tough, white, outermost layer of the eyeball wall. Maintains shape of the globe. Look at your lab partner’s eyes. The ‘whites’ of the eyes are the sclera. “Don’t shoot till you see the scleras of their eyes.” CORNEA: The clear, “bubble” on the front of the eye... Is actually an extension of the sclera. Performs the initial refraction (bending) of light as it enters the eye. The lens makes final adjustments in refraction for focusing. Is the most easily transplanted body part because there is no direct blood flow to the cornea so rejection is less likely. Look at your lab partner’s eyes from the side to see the cornea. OPTIC NERVE: Function? ______________________________________________________ And it is cranial nerve #? ___ INTERNAL ANATOMY IRIS: the “colored” part of your eye. Consists of pigments and two layers of muscle that adjust the diameter of the pupil to control the amount of light entering the eye. Constricts pupils in bright light. Dilates pupils in dim light to allow in more light. These are smooth muscles under involuntary control of the ANS. Which division of the ANS would dilate the eye? _______________ which would constrict? ______________ PUPIL: the hole at the center of the iris that allows light to enter and strike the retina. The diameter of the pupil is controlled by contraction & relaxation of the iris. LENS: a bi-convex disc directly behind the pupil. Performs accommodation (focusing). Its curvature is adjusted by ciliary muscle contraction to refract (bend) light for focusing of the image on the retina. **Confirm identifications with instructor Revised 1/11/2017 5 CILIARY MUSCLE/BODY: The ring of muscle around the lens adjusting its shape for focusing. It attaches to the edges of the lens. [On the models, it appears as white stripes on the inside of the anterior portion of the globe.] RETINA: innermost layer of the eye wall containing photoreceptors and axons leading out to optic nerve. (Appears light brown or reddish-tan on models.) Covers only the posterior 2/3 to ¾ of globe of eye. Is where the energy of light is converted into electrical nerve impulses by PHOTORECEPTORS called RODS and CONES. CHOROID LAYER: middle of the 3 layers of the eye wall. (On models: appears very dark brown to black.) Is highly vascular and darkly pigmented. Nourishes the retina and assists with absorption of light to prevent its scattering within the eye. ANTERIOR SEGMENT (CAVITY): space between the lens and cornea filled with AQUEOUS HUMOR. “Humors” is an old, generic name for body fluids. Subdivided into anterior and posterior chambers by the iris. AQUEOUS HUMOR: a thin, watery fluid in the anterior segment. Is continuously replenished as older fluid drains out through CANALS OF SCHLEMM. POSTERIOR SEGMENT (CAVITY): space between the lens and retina filled with vitreous humor. VITREOUS HUMOR: a thick, viscous fluid which helps hold the delicate retina against the choroid. Is not replaced. If you lose it, it’s gone. On the models it is represented by the clear plastic globe. The eyes contain 99% of all the sensory receptors in the body. They are called photoreceptors. What are the two types of photoreceptors found in the retina? __________ & __________ Which is the more abundant type of photoreceptor? ______________ Which type is more sensitive to light? They only need a little bit of light to work?_________ Cones use a chemical photopigment called photopsins. Rods use a chemical photopigment called rhodopsin. Both receptor types are activated when their photopigment is “broken down” by light. Online OYO: 1) The last time you stepped into a dark theater it took several minutes before you could see well. Explain. 2) When you come out of the theater into bright sunlight your eyes hurt for a minute or two. Explain. OPTIC DISC: that point on the retina where all the nerve fibers (axons) from the photoreceptors converge and exit to become the optic nerve. Is sometimes called the "BLIND SPOT" because there are no photoreceptors here. FOVEA CENTRALIS: an area lateral to each optic disc. Cones are concentrated here providing you the sharpest visual acuity. **Confirm identifications with instructor. Revised 1/11/2017 6 OYO: Disorders of the Eye DETACHED RETINA: It’s usually not the retina separating from the choroid. Instead there are actually two layers of the retina. When they separate it leads to death of photoreceptors and neurons because of separation from blood flow from the underlying choroid layer. GLAUCOMA: excess pressure in the anterior segment created when aqueous humor does not drain properly. Pressure is transmitted through the vitreous humor to the retina where blood flow can be cut off causing permanent damage to the optic nerve. CONJUNCTIVITIS: inflammation of the conjunctiva… many “PINK EYE” is conjunctivitis due to bacterial infection STY: possible causes. and is very contagious. inflammation of a sebaceous gland at the base of an eyelash. CATARACT: a gradual “clouding” of the lens likely due to excess UV exposure. When it interferes significantly with vision the lens is replaced with an artificial one. ASTIGMATISM: a defect or abnormal curvature in the cornea. Parts of an image are distorted. MYOPIA (NEAR SIGHTEDNESS): Close images are seen clearly but distant images are focused in front of the retina and therefore out of focus. Is the result of the globe of the eye being too elongated or the cornea being curved too sharply. Usually correctable with glasses, contacts, or laser surgery. HYPEROPIA (FAR SIGHTEDNESS): opposite of above. COLOR BLINDNESS: lack of ability to distinguish colors accurately. Due to absence of certain cones or lack of the appropriate photopigment. More common in men. MACULAR DEGENERATION: Breakdown of cells in the central portion of the retina resulting in loss of central vision but not peripheral. Cause is usually unknown and there is no known way to prevent or correct the problem. Most often appears in persons over age 50. Revised 1/11/2017 7 DISSECTION OF THE EYE Images from Cat Dissection Manual p. 165 and the “Photographs” manual p. 95 will be helpful. ID the following superficial structures: Cornea - is not clear on these specimens because the Na+ pumps are no longer working (after death) and water has accumulated and light rays are scattered rather than passing straight through. Conjunctiva – appears a dull tan / gray color Extrinsic Eye Muscles – remnants may or may not be present on your specimen amongst a lot of connective tissue Optic Nerve – you will find the stump of the nerve attached to the back side of the eyeball. Now bisect the eyeball along the coronal/frontal plane separating it into anterior and posterior halves. This will be difficult as the sclera is amazingly tough. Please be careful with the sharp tools. Pierce it with the point of a knife and then use long smooth strokes to complete the cut. Cut all the way through the eye separating it completely into anterior and posterior halves. ON THE ANTERIOR PROTION: Lens and vitreous humor. Often these will fall out and may resemble raw egg white with a hard, whitish yolk. If they are still in place use your finger to scoop the lens and jelly-like vitreous humor away from where the lens is attached to the ciliary muscle. Use small scissors to cut around the perimeter of the cornea (not the white sclera) to completely remove it. Identify: Iris - will not be clearly visible through the cloudy cornea but is recognizable once the cornea is removed. Try to see fibers that radiate outward from the pupil as well as fibers that run in a circular around the pupil. Pupil - duh Ciliary Muscle – Look from the posterior side of the anterior half of the eye and see the dark muscle fibers radiating from where the lens was. Bits of this muscle are likely still attached to the edges of the lens. ON THE POSTERIOR PORTION: Sclera Choroid Layer (black and blue in color) Notice that part of the choroid layer is a shiny blue color. This reflects light rather than absorbs it enabling this animal to see better at night than you and I. The retina actually gets stimulated by light passing in and on its way back out. The choroid layer in humans is solid black so light is not reflected back out. Therefore we see poorly at night. Retina If this very delicate layer hasn’t already detached it will be tan in color. Use your probe to move it around and discover it is attached at only one spot… the ____________________. Optic Disc – the retina will appear to converge and be attached here. **Confirm identifications with instructor. Revised 1/11/2017 8