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General Senses
Sensations detected by simple
receptors
General Senses (cont’d)
Touch and Pressure
Temperature
Pain
Body position
Touch and Pressure
Cutaneous Sensations
Located within the skin
Meissner’s corpuscles – fine touch

Hairless skin

Fingers, palms, soles, lips, external
genitals
Krauses’s end bulbs

Like Meissner’s, but in mucous
membranes of mouth
Touch and Pressure (cont’d)
Merkel’s discs - less common
Epidermis
 Light touch receptors

Pacinian corpuscles – deep
pressure

Deep regions of skin, around joints
and tendons,in some visceral organs
Touch and Pressure (cont’d)
Ruffini’s corpuscles – deep &
continuous pressure

Deep in dermis, hypodermis, and
joint capsules
Temperature
Poorly understood
Free nerve ending in skin
Detects hot and cold
Can even cause pain
Pain
Informs brain of homeostatic
imbalances
Visceral pain

Visceral organs

Stomach or intestinal cramps, heartburn,
or headache
Pain (cont’d)
Referred pain
Major nerve impulses share
pathways
 Ex. Originates from the heart and
is felt in arm

Body Position
Proprioceptors
Skeletal muscle, joints, ligaments & CT
of bones & muscles
 Constantly advise brain of our own
movements
 Degree of muscle contraction, amount
of tension in tendons, position of a
joint, position of head relative to the
ground
 Enables you to control your body
movements

Body Position (cont’d)
Muscle spindles
Receptors between a tendon and
a skeletal muscle
 Detect when a muscle is
stretched and initiates a reflex
that resists that stretch
 Helps maintain muscular tone
and body posture

Special Senses
Smell
Taste
Sight
Hearing
Smell and Taste
Receptors are chemoreceptors

Respond to chemicals in solution
Smell
Olfaction
Thousands of olfactory
receptors in roof of nasal
cavity
Found high in nasal cavity
Smell (cont’d)
Sniffing helps to bring in more air
(containing odors) over the
olfactory mucosa
Olfactory pathways are closely
linked to the limbic (emotional
expression) system

Odors recall memories and arouse
emotional responses
Taste
Gustation
Gustatory (taste) cells are
located in the taste buds
Scattered throughout oral cavity
 Most of 10,000 on papillae on
surface of tongue
 Others found on roof of the
mouth & walls of pharynx

Taste (cont’d)
Gustatory cells
surrounded by
supporting cells –
gustatory hairs
(microvilli)
Protrude through
the taste pores
where they are
stimulated
Taste (cont’d)
Taste and appreciation of foods
is influenced by the sense of
smell and the temperature and
texture of foods.
Taste Sensations
Sweet
Sour
Bitter
Salty
Each concentrated in a region on
the tongue
Coffee, cinnamon, garlic, pepper –
combination
Sight
Depends on photoreceptors
 70% of all receptors
External/Accessory Structures
Extrinsic eye muscles

aim the eyes for following moving
object and convergence
External/Accessory Structures
(cont’d)
Lacrimal
apparatus
 Series of ducts
and glands
 Produce a saline
solution –
washes and
lubricates the
eye
External/Accessory Structures
(cont’d)
Eyelids – protect
 Eyelashes
 Ciliary glands –
modified sweat
glands between
eyelashes
 Meibomian
glands – produce
oily secretion
that lubricates
the eye
External/Accessory Structures
(cont’d)
Conjunctiva – delicate membrane
 Lines eyelids and covers part of
the outer surface of eye
 Secretes mucus – helps lubricate
 Conjunctivitis – inflammation
 Pinkeye - highly contagious
Structure of the Eye
Fibrous Tunic
Vascular Tunic
Sensory Tunic
Fibrous Tunic
Thick, outermost
layer

Sclera – “white of
the eye”
 Posterior
 Thick , tough
protective layer
 Provides shape to
eyeball
Fibrous Tunic (cont’d)

Cornea
 Anterior
 Transparent –
“window” of the
eye – allows
light in
 Bulges outward
slightly
Vascular Tunic
Middle Layer
Abundance of
blood vessels
Choroid –
provides
nutrition to
internal eye
structures

Prevents light’s
scattering
Vascular Tunic (cont’d)
Thick ciliary
body
 Help control
lens shape
Vascular Tunic (cont’d)
Colored iris
 Opening Pupil –
regulates
amount of
light entering
Vascular Tunic (cont’d)
Lens - behind the
pupil and iris



Cataract - when
transparency is lost
Held by suspensory
ligaments attached to
ciliary body
Separates eye into 2
main compartments –
anterior (aqueous)
and posterior
(vitreous) chambers
Fluid
Aqueous humor clear, watery fluid
circulated and
recycled through
the bloodstream


Helps maintain
intraocular pressure
Glaucoma –
drainage is blocked,
pressure increases

Possible blindness
Fluid (cont’d)
Vitreous humor thickened, gellike

Helps prevent
eyeball from
collapsing
Sensory Tunic
Inner layer of the eyeball
Contains the retina

Detection of light and transport
of impulse to optic nerve
Sensory Tunic (cont’d)

Millions of
photoreceptors
 Distributed over
entire retina,
except where
optic nerve
leaves the
eyeball
 Blind spot
(optic disc)
Sensory Tunic (cont’d)

Two types of photoreceptors
 Rods and cones
Sensory Tunic (cont’d)
 Rods
Black and white
 Sensitive to small levels
of light
 Most dense at periphery
of retina
 Night blindness – rod
function seriously
hampered

Sensory Tunic (cont’d)
 Cones
Color
 Require more light
 Provides sharper image
 Densest in center of retina
 Fovea centralis – lateral to
each blind spot – only cones
– greatest visual acuity
 Color blindness – due to a
congenital lack of one or
more of the cone types

Pathway of Light Through
the Eye
Light rays bend when they
pass from air to the fluids and
solids of the eyeball

Refraction
The lens changes shape

Accommodation
Errors of Refraction
Myopia - nearsightedness
Hyperopia - farsightedness
Astigmatism – unequal
curvatures in different parts of
the cornea.
All are correctable with lenses
Errors of Refraction (cont’d)
Presbyopia
“Old person’s vision”
 Many people over 50 – lens is
non-accommodating due to loss
of elasticity of lens
 Difficult to focus close up

Pathway of Light
Cornea  aqueous humor 
(through pupil)  aqueous
humor  lens  vitreous
humor  retina
Physiology of Vision
Image formed on retina
Rods and cones convert light
waves to a series of signals
Result in generation of action
potential in ganglion cells
Physiology of Vision (cont’d)
Rods and cones contain pigments
that decompose when exposed to
light
Pigment decomposition leads to
nerve impulse generation
Visual Pathways
Electrical signals pass from
photoreceptors to bipolar
neurons to ganglion cells
Action potential is generated
Leave retina via optic nerve as
nerve impulses transmitted to
optic cortex.
Result is vision
Binocular Vision
Overlap of
visual fields and
inputs from
both eyes
(binocular
vision) to each
optic cortex
provide for
depth
perception (3D
vision)
Eye Reflexes
Convergence

Movement of eyes medially when
we view close objects
Photopupillary

Exposure to bright light causes
pupils to constrict
Accommodation pupillary

Pupils constrict when we view
close objects
Hearing and Equilibrium
Audation
Detected by mechanoreceptors

Deep within the ear
The Ear
Outer ear
Middle ear
Inner Ear
Outer Ear
Auricle (pinna)outer
appendage
External
auditory canal
Outer Ear (cont’d)
Together direct
sound waves to
the eardrum
(tympanic
membrane)

Separates outer
from middle ear
Sound
transmission only
Middle Ear
Tympanic cavity
Air-filled cavity
within temporal
bone
Middle Ear (cont’d)
Ossicles and
auditory tube

Ossicles
transmit
vibratory motion
from the
eardrum to the
oval window
Middle Ear (cont’d)
Ossicles and
auditory tube
(cont’d)

Auditory tube
links middle ear
with the throat
 Allows
pressure to be
equalized on
both sides of
eardrum
Middle Ear (cont’d)
Ossicles and
auditory tube
(cont’d)

Otitis media –
inflammation of
the middle ear
 Common
result of sore
throat
Middle Ear (cont’d)
Sound transmission
only
Tympanic
membrane (ear
drum)
3 auditory ossicles
(smallest bones in
body)



Malleus (hammer)
Incus (anvil)
Stapes (stirrup)
Middle Ear (cont’d)
Ossicles convert
sound waves into
vibrations and
transmit to the oval
window


Opening in tympanic
cavity -opens to
cochlea
Vibrations from
stapes cause fluids
to move,
stimulating hearing
receptors
Inner Ear
Bony labyrinth
Winding, complicated series of
passageways
Inner Ear (cont’d)
Bony chambers in
temporal bone

Semicircular canals


Vestibule


3 loops that lie at right
angles to one another
Chamber between
canals and cochlea
Within both canals and
vestibule - equilibrium
receptors
Inner Ear (cont’d)
Bony chambers in
temporal bone
(cont’d)
 Cochlea
 Looks like snail
shell
 Hearing
receptors
Inner Ear (cont’d)

Bony labyrinth filled with plasmalike
fluid called perilymph
 Suspended in perilymph membranous labyrinth
 Contains a thicker fluid called
endolymph
Inner Ear (cont’d)
 Organ
of Corti
 Located in the cochlea
 Contains receptors that
respond to waves
Auditory Nerve Pathway
Hair cells in organ of Corti convert
motion of endolymph to release
neurotransmitters
Initiates a nerve impulse

Carried to the medulla  midbrain 
thalamus  terminates in temporal lobe
of cerebral cortex
Deafness
Conduction deafness

Something interferes with
conduction of sound vibrations to
the fluids of the inner ear
 Build up of ear wax
 Fusion of ossicles
 Ruptured ear drum
 Otitis media
Deafness (cont’d)
Sensorineural deafness
Degeneration or damage to
receptor cells in Organ of Corti, to
cochlear nerve, or to neurons of
auditory cortex.
 Often results from extended
listening to loud sounds

Deafness (cont’d)
Sensorineural deafness
(cont’d)

Presbycussis
 Type of sensorineural deafness
 By age of 60
 Loss in ability to hear high
tones and speech sounds
 Becoming more common in
younger people
Deafness (cont’d)
Hearing aids more helpful with
sensorineural
Also cochlear implants with
sensorineural
The Sense of Equilibrium
Detected by receptor cells in inner
ear
Static

Sensation of body position detected by
vestibules
The Sense of Equilibrium
(cont’d)
Dynamic
Sensations of rapid movement detected
by semicircular canal
 Receptor region – crista ampularis

The Sense of Equilibrium
(cont’d)
Sight and proprioceptors (muscles
and tendons) also important in
providing info used to control
balance