BIO 265 Human Anatomy and Physiology II Introduction BIO 265 Human Anatomy and Physiology II

The Prophet’s View of Education “You are all in school. Do not waste your time. This is a time of great opportunity that you will never have again as long as you live. Make the most of it right now…. “…you can’t afford to waste your time. There is so much to learn. Give it the very best that you have.” – Gordon B. Hinckley

Syllabus Syllabus What does it take to succeed in Bro. Wray’s class? First Reading Assignment – Due Wednesday in Class

Chapter 15 – The Special Senses BIO 265 - Human A&P II Chapter 15 – The Special Senses

Introduction What are the special senses? The special senses vs. the general senses Location Receptors Chemoreceptors – taste and smell Mechanoreceptors – hearing and equilibrium Photoreceptors - vision

Taste The senses of taste and smell are similar chemoreceptors are stimulated by chemicals that bind to them and generate action potentials There are about 10,000 taste buds on the tongue Each taste bud has about 50 gustatory cells that are responsible for taste The gustatory cells have several microvilli called gustatory hairs Figure 15.1

Taste Buds Figure 15.1

Taste The sensation of taste: molecules become dissolved in the saliva The molecules can then bind to chemoreceptors This causes depolarization of the cell This results in an action potential that is conducted to the cerebral cortex Figure 15.2

Taste Buds Figure 15.1

Gustatory Pathway Figure 15.2

Taste The sensation of taste is derived from a small number of primary tastes Sour, salty, bitter, sweet, and umami Hot or spicy foods actually stimulate pain receptors

Taste CD animation The wide variety of tastes also come from the sense of smell Smell actually accounts for about 80% of our sensation of taste

Olfaction Olfaction or smell occurs by stimulation of receptors located in the nasal cavity in the olfactory recess Figure 15.3

Sense of Smell Figure 15.3

Olfaction There are 10 million olfactory neurons within the olfactory epithelium These connect with the left or right olfactory bulbs Figure 15.3 and from other text

Sense of Smell Figure 15.3

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Olfaction The olfactory neurons have a tuft of cilia that lie at the end of the dendrite (olfactory hairs) surrounded by a layer of mucus When chemicals become dissolved in the mucus they can bind to chemoreceptors on the cilia This depolarizes the cilia and leads to an action potential in the olfactory neuron

Olfaction The action potential is conducted into the cerebrum where the smell is perceived Figures from other text

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Olfaction CD animation It is believed that the 4000 (or more) different smells perceived by humans actually come from a combination of 7 to 50 primary odors Olfactory adaptation occurs in response to continual exposure to a certain odor Barn yard, paper mill, cookies, etc. Actual receptor function – Figure 15.4

Visual System The visual system includes the eyes, accessory structures, and the optic nerves. What are some of the accessory structures? Eye brows Eye lids blink every 3-7 seconds blinking reflex from eyelashes Figure 15.5 and from other text

Visual System Conjunctiva Pink eye or conjunctivitis Figure from other text

Visual System Lacrimal apparatus Watery eyes and one of the mysteries of life Figure 15.6

Visual System Extrinsic eye muscles – Figure 15.7

Visual System Anatomy of the eye The eye contains three layers or tunics Fibrous tunic Sclera – whites of the eye, made of dense connective tissue with elastic fibers Cornea – transparent structure covering the anterior surface of the eye Very sensitive to touch Figure 15.8

Visual System Vascular tunic – contains most of the blood vessels of the eye Choroid – dark brown, thin membrane associated with the sclera Ciliary body – contains ciliary muscles that attach to the lens by suspensory ligaments These muscles change the shape of the lens for focusing Iris – the colored portion of the eye, contains smooth muscle to control the size of the pupil Eye color details Figures 15.8 and 15.9 and from other text

Visual System Nervous tunic – also called the retina Pigmented retina Sensory retina – contains photoreceptor cells called rods and cones Figures 15.8 and 15.10

Visual System Optic disk and the blind spot Figure 15.10b

Visual System There are about 250,000,000 rods and cones in the retina!!! Rods are very sensitive to light, but cannot detect colors Cones require more light, but they are sensitive to color and allow us to distinguish fine detail Retina organization and the fovea centralis

Visual System Viewing the retina – Figure 15.11

Visual System Compartments of the eye: Anterior segment – filled with aqueous humor that provides nutrients for the cornea Glaucoma and blindness Posterior segment – filled with vitreous humor Figure 15.12

Visual System Lens – transparent, flexible structure Allows focusing of light on the retina Figures 15.12 and 15.17

Visual Systems Focusing problems Myopia – nearsightedness Hyperopia – farsightedness Figure 15.18

Visual Systems So, how do we see things?

Visual Systems

Visual Systems CD Demo – preview of sight

Visual Systems Function of the Retina There are about 120 million rods and 6-7 million cones in each retina Rods are bipolar photoreceptor cells involved in non- color vision They are especially important in low light conditions Rods contain a special light-sensitive molecule called rhodopsin composed of: Opsin – protein portion (membrane protein) Retinal – light absorbing pigment (derived from Vit. A) Figure 15.19

Visual Systems When light strikes the rhodopsin, the retinal changes shape This activates a messenger system that leads to hyperpolarization of the cell Figure 15.21

Visual Systems This hyperpolarization is strange A photoreceptor cell not exposed to light has open Na+ ion channels The movement of Na+ into the cell causes depolarization This depolarization causes the cell to release an inhibitory neurotransmitter (glutamate) Glutamate blocks action potential generation in the neighboring association neurons Figure 15.22

Visual Systems When photoreceptor cells are exposed to light, the Na+ channels are closed This causes hyperpolarization of the cell Hyperpolarization blocks the release of glutamate Therefore the association neuron generates an action potential which is conducted to the brain Figure from other text

Visual Systems

Visual Systems CD-animation Light and dark adaptation? involves rhodopsin as well as pupil size Bright light lowers the amount of rhodopsin in the rods Figure 15.21

Visual Systems Cones function in color vision and visual acuity Differences between rods and cones (sensitivity and color) Cool Marker Example Cones function much like rods, but they contain iodopsin instead of rhodopsin Iodopsin is a combination of retinal and a color-specific opsin protein

Visual Systems The opsin in cones can respond to either blue, green, or red light Color blindness comes from not having one type of cone The color of an object results from the combination of blue, green, and red cones that respond Orange color – 99% of red cones, 42% of green cones, 0% of blue cones Yellow would lead to more green cones, etc. Figure from other text

Visual Systems Distribution of rods and cones ~35,000 cones in the fovea centralis, no rods Neuronal pathways for vision Figure 15.23 and from other text

Visual Systems

Visual Systems Summary of Vision

Hearing Hearing involves three parts of the ear: Figure 15.25 The external ear – the auricle (or pinna) and external auditory meatus (this ends at the tympanic membrane) The middle ear – air-filled space containing the ossicles (the malleus, incus, and stapes) The inner ear – fluid-filled cavities containing the sensory organs of hearing and balance Figure 15.25

Hearing Steps involved in hearing: Sound waves are collected by the auricle The waves move through the external auditory meatus to the tympanic membrane This causes vibration of the membrane The vibration of the tympanic membrane is conducted to the inner ear by the ossicles Figure 15.25

Hearing The stapes is connected to a flexible membrane covering the oval window on the cochlea As the stapes vibrates, the sound waves are conducted into the inner ear This causes waves in the fluid of the cochlea Figure from other text

Hearing As the waves pass through the inner ear, microvilli on hair cells are bent The bending of the microvilli results in action potentials The action potentials are then conducted through the vestibulocochlear nerve to the brain Figures 15.28

Hearing CD Demo of Hearing

Balance The organs of balance: Vestibule – gives position of the head relative to gravity Semi-circular canals – evaluates movements of the head

Balance Head position – there are 2 patches of sensory cells in the vestibule These are covered by a gelatinous fluid containing otoliths The gelatinous mass moves in response to gravity and bends microvilli on the sensory cells The brain interprets the pattern of action potentials as head position Figures 15.35 and 15.36

Balance Detection of Motion – semicircular canals The base of each semicircular canal is enlarged to form the ampulla Within the ampulla is the cupula Figure from other text

Balance When the fluid moves past the cupula it bends and generates action potentials This is perceived as motion of the head Figure 15.37 and from other text

Balance CD animations