Transcript Chapter 15 - The Special Senses

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
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
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
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 noncolor 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 colorspecific 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:
– 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