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LABORATORY NINE Special Senses

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1 LABORATORY NINE Special Senses
Lab Practicum II is next week…125pt + EC…Muscle anatomy & physiology, endocrine system, nervous system, and special senses…dissections are guaranteed to be on the exam

2 Cow Eye Dissection (Google, Image, Cow Eye Dissection)
Identify the assigned superficial structures Make a coronal section With the scalpel make an incision 1cm (the width of the scalpel's blade) below the junction of cornea & sclera With scissors cut around the cornea keeping the 1cm distance from the junction all around To remove the jellylike transparent substance, hold down the lens by left thumb and scoop out the jellylike substance by right thumb Detach the lens from the iris Scoop out the jellylike substance from the posterior cavity very gently not to disturb the retina (immerse the posterior part of the cow eye in the water to reshape the retina) Identify the assigned structures Use the human eye model to study the muscles responsible for eye movement Lens looks like a bath bead and in a live animal is transparent Cornea is also transparent in a live animal Iris is the smooth flat colored part of the eye, and ciliary body is the more textured mushroom like structure behind it (more lateral to iris) Both iris & lens are able to change shape by the contracting muscles surrounding them Anterior cavity is the space between iris and cornea, in front of the lens, and the posterior cavity is the cavity behind the lens…Lens divides the eye to the anterior and posterior cavities… Retina is where all the sensory receptors for the eye are located Choroid is a continuous pigmented layer behind the retina (more dorsal)…the black color absorbs light, so it does not reflect inside the eye To find the optic disc, swirl the retina around to find the place the retina is attached to the floor of the eye…This is where all the sensory neurons are merging to form the optic nerve II…There is no photoreceptor in this spot, that is why it’s called the blind spot Fovea centralis has the highest number of photoreceptors and it is your focal point…Macula is the tissue around the fovea centralis and when it’s degenerated, the person can not focus sharply

3 Sensory Nerve Endings in the Skin

4 Cutaneous Sensation (Exercise 9A, P151)
#2 & #3, p152: Two-point discrimination test #4, p152: Duration of sensation Subjects eyes should be closed Record your observations in the related section in your lab report Subject’s eyes should be closed not to interpret what’s going on by vision sense When sensation disappears, the receptors are not firing (adaptation to touch)…Constant unchanging stimuli are not important, so adaptation to them is hugely energy conserving for body…imagine wearing a tight jeans, you’ll get used to it very soon…Otherwise, it would drive you crazy throughout the day…While driving, you could not focus to another important stimuli that needed your immediate reaction…

5 Muscles of the Eye To identify the medial/lateral ends of the eye:
To determine the medial rectus muscles from lateral rectus muscle, you need to know where the medial part of the eye is…to determine that, look for the superior and inferior oblique muscles… To identify the medial/lateral ends of the eye: For superior/inferior oblique muscles, their attached part to the sclera is the more lateral side Optic nerve II is located more medially

6 Sagittal Section of the Eye

7 Vision (Exercise 9B, p153) #4, p153: Blind spot test
#5, p154: Visual acuity #6, p154: Astigmatism #7, p155: Color blindness Record your results in the related section in your lab report

8 External, Middle, and Inner Ear
ear models are often disassembled on the lab practicum (e.g. the inner ear structures may be at one station, the tympanic membrane shown separately, & the rest of the model at a separate station

9 Organ of Corti (Observe the model & demonstration microscope)
If you unroll the cochlea and make a cross section of it, you’ll be able to see the organ of corti The middle ear, where the ear ossicles are, is filled with air The inner ear, inside the cochlea, vestibule, and semicircular canal is filled with liquid When the sound waves travel through external auditory canal, they make the tympanic membrane to vibrate, which in turn vibrates the ear ossicles, which then vibrates the fluid inside the cochlea, which then results in the movement of tectorial membrane of organ of corti, causing the hair cells to bend and an action potential is then generated. Vestibule and semicircular canals have a function in maintaining the individual’s balance and detecting movements in essentially any direction…

10 Hearing and Equilibrium (Exercise 9C, p155)
#3, p156: Hearing acuity test #4, p157: Ability to locate the source of a sound #5, p157: The Rinne test #6, p157: Evaluation of balance Subjects eyes should be closed Record your observations in the related section in your lab report We use tympanic membrane to hear sounds, snake uses his bones to hear sounds…Rinne test is to determine if you’re using your bones to hear, or you hear the normal way

11 The Tongue (a) Dorsal Surface
(b) Papilla (enlargements on the surface of the tongue) (c) Taste bud (view the microscopic slide)

12 Taste and Olfaction (Exercise 9D, p158)
Test your sense of taste using a taste paper Record your results in the related section in your lab report Being able to taste this bitter taste is genetically pre-determined


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