Senses
Read chapter 18 – senses and using your class notes answer: 1. Define a sensory receptor
A structre specialized to receive information from the environment and to generate nerve impulses a. List the five distinct kinds of sensory receptors and explain the nature of each with an example Sensory Receptor | Nature | Chemoreceptor | Respong to chemical substances in immediate vicinity. Taste, smell, chemoreceptors in blood vessels monitoring O2, CO2, and pH | Pain receptors (type of chemoreceptors) | Type of chemoreceptor. Naked dendrites that respond to chemicals released by damaged tissues give warning ie. appendicitis | Mechanoreceptors | Stimulated by mechanical forces (usually pressure). Sense of touch, stretch in lungs, hearing and pressure waves | Thermoreceptors | Stimulated by changes in temperature. Warm/cold receptors. In skin and hypothalamus | Photoreceptors | Respond to light energy. Eyes. Rod cell stimulation gives black/white vision, cone cells give colour vision |

2. For the sense of taste state: i. Location of receptors: taste buds (cells) on tongue (tip, upper front, margins and back ii. Type of stimulation:chemical iii. Flavours which can be tastedsweet, sour, salty, bitter

3. For the sense of smell state: iv. Location of receptors:olfactory cells high in the roof of the nasal cavity. Cells are modified neurons. Connected to olfactory bulb an extension of the brain v. Type of stimulation:chemical

4. On the following diagram of the eye, label the following parts: vi. vii. Sclera viii. Cornea ix. Choroid x. Pupil xi. Iris xii. Lens xiii. Ciliary body xiv. Aqueous humour xv. Vitreous humour xvi. Retina xvii. Fovea centralis xviii. Rentinal blood vessels xix. Optic nerve

b. State the main function for each part of the eye listed see page 350 Structure | Function | Sclera | Protects and supports eyeball (becomes cornea) | Cornea | Refracts light rays | Choroid | Absorbs stray light (becomes iris) | Retina | Contains receptors for sight (photoreceptors) | Rods (in retina) | Black/white vision | Cones | Colour vision | Fovea centralis (contains cones) | Acute vision | Lens | Refects and focuses light rays to retina | Ciliary body | Holds lens in place/accomodation | Iris | Regulates light entrance; regulates size of pupil | Pupil | Admits light | Humours | Transmit light rays and support eyeball | Optic nerve | Transmit impulse to brain |

c. Describe the difference between rods and cones
Rods: more numerous, dim-light and peripheral receptors, more sensitive to light than cones, but do not provide sharp images or colour
Cones: operate in bright light and provide high-acuity colour vision, have one of three different pigments to give colourk 5. Explain the process of visioning (focusing)
When we look at an object light rays pass through the pupil and are “focused” on the retina. Focusing starts with the cornea and continues as light rays pass through the lens and the humours. The image produced is much smaller than the object due to refraction and is upside down (inverted) and laterally reversed (left to right). The lens provides additional focusing power as visual accommodation occurs for close vision controlled by the ciliary muscle within the ciliary body. When focusing on a distance object the lens is flat because ciliary muscle is relaxed. When focusing on a near object, the lens accommodates and becomes rounded because the ciliary muscle contracts. The optic nerve transmits the nerve impulse to the brain.

6. Since there are only three types of cones, how can you explain the fact that we see many more colours?
The three types of cones are B(blue), G (green), and R (red). Each pigment is made of rental and opsin but there is a slight difference in the structure of opsin in each. To see any color, the brain must compare the input from different kinds of cone cells and then make many other comparisons as well.
The lightning-fast work of judging a color begins in the retina, which has three layers of cells. * Signals from the red and green cones in the first layer are compared by specialized red-green "opponent" cells in the second layer. * Other opponent cells then compare signals from blue cones with the combined signals from red and green cones.

7. Explain why you often have to blow your nose after crying.
Because the lacriminal gland that produces tears empties through the excretory laciminal duct into the nasal cavity. 8. Describe the process of hearing
The process of hearing begins when sound waves enter the auditory canal. Sufficient sound wave motion causes the tympanic membrane to vibrate slightly. The malleus then takes the pressure from the inner surface of the tympanic membrane and passes it by means of incus to the stapes where the pressure has become about 20x greater (sound amplified). The stapes strikes the membrane of the oval window, cuasing it to vibrate, and in this way the pressure is passed to the fluid in the cochlea. Within the cochlea the pressure is transmitted to the round window which bulges. In addition, other membranes in the cochlea vibrate and collectively cause a nerve impulse to begin in the cochlear nerve which travels to the brain stem eventually reaching the auditory area of the cerebral cortex where the impulses are interpreted as sound

NOTE: * Cochlear nerve (auditory nerve) originates from a structure in the cochlear canal called the spiral organ (organ of Corti) * The cochlea itself is made up of three canals – the cochlear canal, vestibular canal, and the tympanic canal * In the cochlea are two membranes – basilar membrane (the lower wall of the cochlear canal) and the tectorial membrane in which hairs are embedded (like the hairs on the spiral organ) are involved in sound transmission to the auditory nerve. Through vibration hair cells with cilia respond to mechanical stimulation – called mechano receptors which are sensitive to pressure. * Structures called saccule,otolith and utricle are receptors in the semicircular canals where balance is maintained. 9. Explain how we maintain our sense of equilibrium
Equilibrium has two functional parts d. Static equilibrium- in the vestibule
Maculae – receptors in the vestibule: utricle and saccule which are membranous sacs containing stereocilia (hair cells) which are covered in an otolithic membrane. Otoliths made of calcium carbonate (CaCO3) rest on the membrane. When head bends the otoliths are displaced and move the otolithic membrane over the stereocilia. The stereocilia then:
-Report on the position of the head
-Send information via the vestibular nerve

e. Dynamic equilibrium- in the semicircular canals called ampulla. Inside the ampulla is the cristae ampullaris which the receptor which is tiny tufts of hair cells. The cupula goes over the hair (called stereocilia) and can be pushed by endolymph which pulls the hairs. An impulse is sent via the vestibular nerve to the cerebellum. Continuous movement of the fluid in the semi-circular canals can be one form of motion sickness.

10. On the following diagram of the ear, label the following parts:

f. g. Auditory canal h. Tympanic membrane i. Malleus j. Incus k. Stapes l. Oval window m. Cochlea n. Semicircular canals o. Round window p. Vestibule q. Vestibular nerve r. Cochlear never (auditory nerve) s. Pinna t. Auditory tube