1. Afferents

2. The chemical senses

3. Sense of taste
Chemicals must dissolve in saliva, diffuse
into the taste pore, then contact gustatory
hairs.
Bitter receptors are the most sensitive,
followed by salty, and then sweet/sour
receptors.
Taste receptors adapt rapidly.

5. Transduction is the sensory mechanism by
which stimulus energy is converted into a
nerve impulse.

6. Sense of smell
To perceive a smell, the chemical must be
volatile, and it must dissolve in the fluid
coating of the olfactory epithelium.
The resulting action potential is conducted
to the olfactory bulbs.
G-proteins may be involved with
transduction in olfactory receptors.

9. Vision

10. Wavelength and color
Visible light is that portion of the electro-
magnetic spectrum with a wavelength range
of approximately 400nm-700nm.
Photons are small packets of light energy.
The visible spectrum is a band of colors
created when light passes through a prism.

12. Refraction and lenses
Reflection of light occurs when light waves
bounce off objects, and is responsible for
the stimulation of photoreceptors.
Refraction of light occurs when it contacts
the surface of a different medium at an
oblique angle.

13. When light waves are bent by a lens so that
they converge at a single point, it is called
the focal point.
A real image is the image formed by a
convex lens, and is upside down and
reversed.

15. Focusing of light on the retina
The far point of vision is that distance
beyond which no change in lens shape is
needed for focusing.
An emmetropic (normal) eye has a far point
of 6 meters.

18. Accommodation is the process that
increases the refractory power of the lends
so that diverging light rays are bent more
sharply.
The closest point on which we can focus
clearly is called the near point of vision.

19. Accommodation pupillary reflex occurs
when the circular muscles of the iris
enhance the effect of accommodation by
reducing the size of the pupil.
Convergence is the medial rotation of the
eyeballs by the medial rectus muscles so
that each is directed toward the object being
viewed.

20. Homeostatic imbalances
Myopia is a condition in which visual
images are focused in front of the retina.
Hyperopia is a condition in which visual
images are focused behind the retina.
Astigmatism is a condition in which
unequal curvature in different parts of the
lens leads to blurred vision.

21. Photoreception
Photoreception is the process by which the
eye detects light energy.
Photopigments exist in the outer segment of
photoreceptors, and are capable of changing
shape as they absorb light.

24. Retinal is a light absorbing molecule that
combines with proteins called opsins to
form four types of photopigments.
When bound to opsin, retinal has a bent
shape called the 11-cis isomer.
When the photopigment is struck by light,
retinal twists into a new configuration
called the all-trans isomer.

26. The visual pigment of rods is a deep purple
pigment called rhodopsin.
When rhodopsin absorbs light, retinal
changes to the its all-trans isomer, and the
retinal-opsin combination then breaks down
in a process known as the bleaching of the
pigment.

28. Light is transduced into an electrical event
when cyclic GMP, which normally holds
sodium channels open, is destroyed, thus
closing the sodium gates and causing
hyperpolarization of the membrane.
Transducin is a G protein subunit that binds
with free opsin, thus activating enzymes
that break down cGMP.

29. Light and dark adaptation
Light adaptation occurs when large amounts
of photopigment are broken down quickly
as a result of switching from darkness to
bright light.
Dark adaptation occurs when rhodopsin
accumulates after being bleached, as a
result of switching from bright light to
darkness.

30. Stereoscopic vision and depth
perception
Stereoscopic vision occurs due to an
overlap of the visual field, causing each eye
to see a different view.
Depth perception occurs as a result of
stereoscopic vision.

31. Visual processing
Ganglion cells with on-center receptive
fields are depolarized by light hitting the
field center, and are inhibited by light
hitting the periphery, while off-center fields
are depolarized by the reverse.
Unequal illumination of these fields caused
the ganglion cells to change their rate of
impulse conduction.

32. Hearing and equilibrium

34. Properties of sound
Sound is a pressure disturbance originating
from a vibrating object and propagated by
the molecules of the medium.
The distance between two consecutive
crests is called the wavelength.

37. Frequency is the number of waves that pass
a given point in a given time.
The term pitch refers to the perception of
different sound frequencies.

38. The intensity of a sound is related to the
pressure differences between its compressed
and rarefied areas.
The amplitude of a sound wave corresponds
to its height.

39. Loudness refers to the subjective
interpretation of sound intensity.
Sound intensity is measured in logarithmic
units called decibels (dB).

41. Excitation of hair cells in the
organ of Corti
One row of inner hair cells and three rows
of outer hair cells are sandwiched between
the tectorial and basilar membranes.
The hair cells protrude into the endolymph,
where the longest are enmeshed in the
tectorial membrane.

42. Homeostatic imbalances of
hearing
Deafness is any hearing loss.
Conduction deafness occurs when
something interferes with the conduction of
sound vibrations to the fluids of the inner
ear.

43. Otosclerosis (hardening of the ear) occurs
when overgrowth of bony tissue fuses the
stapes foot plate to the oval window or
fuses to ossicles to one another.
Sensorineural deafness results from damage
to neural structures at any point from the
cochlear hair cells to the auditory cortical
cells.

44. Tinnitus is a ringing or clicking sound in
the ears in the absence of auditory stimuli.
Meniere’s syndrome is a labyrinth disorder
that affects both the semicircular canals and
the cochlea, where the afflicted person has
repeated attacks of vertigo and nausea.

45. Mechanisms of equilibrium and
orientation
Equilibrium receptors of the inner ear can
be divided into two functional arms that
monitor static and dynamic equilibrium.

46. The maculae and static
equilibrium
The maculae are sensory receptors for static
equilibrium which monitor the position of
the head, and are located in the vestibule.

49. The crista ampullaris and
dynamic equilibrium
The crista ampullaris is an elevation in the
ampulla of each semicircular canal that
monitors dynamic equilibrium, which is
excited by acceleration and deceleration of
the head.
The cupula is a network of gelatinous
strands that contact each hair cell.

51. Vestibular nystagmus is a series of eye
movements that occurs during and
immediately after rotation of the body.

52. The equilibrium pathway to the
brain
Motion sickness is an equilibrium disorder
that is probably due to sensory input
mismatch.