1. Lec 7-BIO Lab 1021 The Senses rev 6-11 Neurons communicate with our muscles or glands to produce a reaction within our body. They communicate through chemicals called neurotransmitters. However, in order to receive a stimulus from the environment, there is a specialized type of neuron called a receptor. Sensory input (called a stimulus) causes a change within or outside the body. The receptor accepts the stimulus (a form of energy such as heat, pressure, or sound). and converts the energy into a form that can be understood by the body.

2. Lec 7-BIO Lab 1022 The Senses Receptors are usually categorized by the kind of stimulus to which they respond. –Chemoreceptors are stimulated by chemicals that attach to receptors at the end of the sensory neuron. sense of taste and smell. –Pain Receptors –Mechanoreceptors are the largest class of receptors and include:

3. Lec 7-BIO Lab 1023 The Senses- mechanoreceptors stretch receptors proprioceptors tactile(touch and vibration) hair cells (ear) baroreceptors (sensitive to changes in blood pressure) –Thermoreceptors (temperature) –Photoreceptors (light) Receptor Adaptation when exposed to the same degree of stimulus, receptors stop sending impulses so you no longer respond to the stimulus.

4. Lec 7-BIO Lab 1024 The Senses The EYE composed of 3 tissue layers –outer layer is the sclera –middle layer is the choroid –inner layer is the retina The Sclera (or white of the eye) –is composed of tough, white connective tissue that is modified in the front eye muscles attach to the sclera

5. Lec 7-BIO Lab 1025 The Senses –this modified “spot” is called the cornea and is clear so that light can pass through cornea is the most exposed part of the eye and is vulnerable to damage from dust, dirt, etc. has high ability to regenerate and repair itself –can also be replaced surgically

6. Lec 7-BIO Lab 1026 The Senses Light passes through the cornea and a small fluid filled space called the aqueous humor –the aqueous humor is located between the cornea and the lens (the anterior chamber of the eye) –it nourishes and cushions the cornea and lens The vitreous body or vitreous humor is located behind the lens (in the posterior chamber of the eye) –this is a gel-like fluid –the fluid transports nutrients and wastes and maintains the shape of the eye

7. Lec 7-BIO Lab 1027 The Senses Choroid layer –middle layer which contains a large portion of the blood supply for the eye –is darkly pigmented to absorb light and prevent it from scattering and reflecting within the eye –Some red light is reflected back from the choroid however and causes the “red-eye effect” in photographs

8. Lec 7-BIO Lab 1028 The Senses The Choroid Layer –Contains the iris a ring of smooth muscles that regulates the opening of the pupil (the central opening of the iris which allows light to enter the eye) the iris gives the eye its color –and the ciliary body a ring of muscles that encircles the lens and can change the shape of the lens

9. Lec 7-BIO Lab 1029 The Senses The lens composed of transparent crystalline proteins focuses the visual image on the retina is held in the center of the ciliary body by suspensory ligaments precise focusing requires thickening or thinning of the lens the changing shape allows for focusing on near or distant objects

10. Lec 7-BIO Lab 10210 The Senses The Retina –innermost layer of tissue which contains 2 kinds of photoreceptors (light sensitive receptors) RODS sensitive to low levels of light (night time vision) –Allow us to see in black and white CONES require high levels of light –come in 3 varieties (red, green and blue) so we can see in color

11. Lec 7-BIO Lab 10211 The Senses –a dense collection of cones, the macula lutea, is found at the back of the eye near the fovea centralis, the center of focus –anything we wish to see in great detail is focused on the fovea centralis –the optic disc blind spot where nerve impulses that have been focused on the retina exit the eye via the optic nerve

12. Lec 7-BIO Lab 10212 The Senses Eye Protection –bony socket of the skull –layer of adipose tissue that cushions the socket –blinking –tears from the lacrimal gland cleanse, lubricate and protect the eye tears contain mucus, antibodies and lysozyme, a bacteria destroying enzyme the lacrimal ducts take excess tears from the eyes and drain them into the nose

13. Lec 7-BIO Lab 10213 EYE DISSECTION-SAFETY may get splashed as you open the eye Dissection –follow instructions on page 91 of text

14. Lec 7-BIO Lab 10214 The Ear Is an organ of both hearing and balance Outer Ear –consists of the pinna (visible portion of the ear) and the auditory or acoustic canal –sound waves arrive at the pinna and are directed into the auditory canal –the canal channels the sound to the eardrum or tympanic membrane which is a partition between the outer and middle ears The Senses

15. Lec 7-BIO Lab 10215 The Senses The Middle Ear is an air filled chamber within the temporal bone and contains 3 bones: the malleus (hammer), incus (anvil) and stapes (stirrup) –when soundwaves strike the eardrum, it causes the membrane to vibrate. The vibrations cause the malleus, incus and stapes to vibrate also. –The stapes touches another membrane, called the oval window (the beginning of the inner ear), and causes this membrane to vibrate. –The Eustachian tube is a connection between the middle ear and throat. It acts to equalize air pressure in the middle ear with that of the surrounding atmosphere

16. Lec 7-BIO Lab 10216 The Senses So, we have air conduction of sound via the outer ear and this is changed to bone conduction of sound in the middle ear Inner Ear –consists of the cochlea (where sound is converted into fluid movement), the vestibule and 3 semicircular canals –within the cochlea is the Organ of Corti which contains tactile receptors or hair cells

17. Lec 7-BIO Lab 10217 The Senses –the hair cells vibrate and bend which releases a neurotransmitter that generates impulses to nearby sensory neurons –different parts of the organ of Corti respond to different pitched tones so we can hear variations in sounds These impulses travel to the auditory nerve and we “hear” the sound

18. Lec 7-BIO Lab 10218 The Senses Balance and Equilibrium –the Vestibular Apparatus consists of the 3 semicircular canals for sensing rotational movement of the head and body (dynamic equilibrium). This tells us where we are in space. the vestibule which senses static (stationary) balance and linear acceleration of the head (static equilibrium)

19. Lec 7-BIO Lab 10219 The Senses The vestibule –contains hair cells, gel and otoliths (hard crystals of bone like material) –when the head tips forward, the otoliths slide toward the gravitational pull causing the hair cells to bend –this produces impulses in nearby sensory neurons which are transmitted to the brain for interpretation

20. Lec 7-BIO Lab 10220 REMINDER, Page 1 of 2 : 1. Long lab; you can work in groups of 3 if needed. 2. Perform the receptor tests on page 87 and 88. 3. Learn the parts of the eye on the eye models and the sheep eye. Use the bulleted list on page 91 for parts to identify on both. 4. Remember to follow safety procedures.

21. Lec 7-BIO Lab 10221 REMINDER, Page 2 of 2 : 5. When finished with the sheep eyes, discard them in the "discard" bucket. 6. Perform the eye tests on pages 90-92. You do not need to do the color blindness tests. 7. Learn the parts of the ear on the ear models. Use the bulleted list on page 94 to know what structures to locate. 8. Perform the ear tests on page 94. Do not perform the frequency test. 9. Strike the tuning fork on your palm, not on the table. Hold the fork by the bottom peg.