1. Senses
Sensation: response to environment (i.e. stimulus) via generation of nerve impulse
-nerve impulses from the body are sent via ascending tracts in spinal cord to the brain
-from the special senses – in through the brain stem
-sensation occurs upon arrival of nerve impulse at cerebral cortex
-perception is the interpretation of these sensations after cortex processing

2. Senses can be classified in several ways based on:
1. what they respond to
1. Chemoreceptors
2. Mechanoreceptors
3. Nociceptors/pain receptors
4. Thermoreceptors
5. Photoreceptors
2. how they are structured
e.g. corpuscles, free nerve endings
3. their location
e.g. exteroceptors, interoceptors, proprioceptors, cutaneous receptors

3. General vs. Special Senses
Touch, pressure, itch, tickle, heat/cold = cutaneous receptors (touch)
Proprioception - proprioceptors
Special
Sight
Hearing
Vision
Smell

4. Proprioceptors
-located in muscles, joints and tendons (and the inner ear)
-provide position of limbs and degree of muscle relaxation
-proprioceptor types:
1. sensory neuron wrapped around a muscle fiber (i.e. muscle spindle
2. found embedded in a tendon
3. found in a joint
-stretching of muscle fiber, tendon or flexing of joint stimulates the receptor
Patellar reflex:
-muscle stretch, proprioceptor
fires impulse to spinal cord,
reflex arc results, muscle fiber
response

5. Cutaneous receptors – General Sensation of Touch
-located in skin
-receptors can be classified as cutaneous
-can also be classified as thermoreceptors,mechanoceptors, nociceptors etc….
-can also be classified as free nerve endings (exposed dendrites) or corpuscles (covered dendrites)
-impulses first sent to primary somatosensory area of brain – post-central gyrus of parietal lobe
-association areas of the parietal lobe continue the processing

6. Cutaneous receptors – General Sensation of Touch
-touch receptors: Meissner’s corpuscles(fingertips, lips, tongue, nipples, penis/clitoris)
Merkel disks (epidermis/dermis)
Root hair plexus (root of hair)
-pressure receptors: Pacinian corpuscles (lamellated corpuscle)
-temp receptors: free nerve endings that respond to cold OR warmth
-Krause end bulbs, Ruffini endings

7. Taste -taste requires dissolving of substances in saliva
-taste buds: salty, sweet, bitter and sour – more????
-accumulation of neurons called gustatory neurons
-10,000 taste buds found scattered over tongue, soft palate & larynx
-one taste bud responds to one kind of chemical called a tastant
-many taste buds are clustered at specific locations
– e.g. tip of tongue = sweet taste buds
bitter
salty
sour

8. Cranial Nerve I -taste buds are found on projections called papillae
-buds project gustatory “hairs” into canals found in between adjacent papillae
-canal opens onto the surface of the tongue
-saliva flows over surface of tongue, into the canals and over the gustatory “hairs”
Cranial
Nerve I

10. -four types of papillae
-only three types of papilla will bear taste buds
taste papillae:
foliate
fungiform
circumvallate
filiform (texture) – no taste buds

11. Anatomy of Taste Buds
An oval body consisting of 50 receptor cells (gustatory or taste cells) surrounded by supporting cells
each taste neuron projects a single gustatory hair projects upward through the taste pore
taste pore is exposed to saliva flowing over tongue
Basal cells develop into new receptor cells every 10 days.

12. Physiology of Taste Complete adaptation in 1 to 5 minutes
Thresholds for tastes vary among the 4 primary tastes
most sensitive to bitter (poisons)
least sensitive to salty and sweet
Mechanism
dissolved substance binds ligand-gated receptors on the gustatory hairs  action potential
action potential results in neurotransmitter release and stimulation of the 1st order neuron forming either cranial nerves, VII, IX and X

13. Gustatory Pathway gustatory fibers/axons found in three cranial nerves
VII (facial) serves anterior 2/3 of tongue
IX (glossopharyngeal) serves posterior 1/3 of tongue
X (vagus) serves palate & epiglottis
Signals travel to thalamus - extend from the thalamus to the primary gustatory area on parietal lobe of the cerebral cortex
provide conscious perception of taste
Taste fibers also extend to limbic system – association of taste with a memory

14. Smell -requires dissolving of chemicals in mucus
-neurons = olfactory cells - located within olfactory epithelium in the nasal cavity
-olfactory epithelium covers superior nasal conchae and cribriform plate
-contains neurons (olfactory cells) and supportive cells and basal cells

15. Olfactory epithelium Olfactory receptors Supporting cells
bipolar neurons with cilia or olfactory hairs
Supporting cells
columnar epithelium
Basal cells = stem cells
replace receptors monthly
Olfactory glands
produce mucus
Both epithelium & glands innervated by cranial nerve VII.

16. Eustacian tube
With tubal tonsil

18. Olfaction: Sense of Smell
Odorants bind to receptors
Na+ channels open
Depolarization occurs
Nerve impulse is triggered
each olfactory neuron can respond to multiple odorants

19. Olfactory Pathway
Olfactory neurons pass through the foramina in the cribriform plate
Synapse with the neurons of the olfactory bulb
Axons of these neurons form the olfactory tract
bulb + tract = Cranial nerve I
CNI synapses on the primary olfactory area of temporal lobe
conscious awareness of smell begins
Other pathways lead to association areas in frontal lobe (e.g. Brodmann area 11) where identification of the odor occurs

20. Adaptation & Odor Thresholds
Adaptation = decreasing sensitivity of repeated stimuli over time
Olfactory adaptation is very rapid
50% in 1 second
complete in 1 minute
Low threshold
only a few molecules need to be present
e.g. methyl mercaptan added to natural gas as warning

21. Vision
-sight is generated by the bending and focusing of light onto the retina
Anterior cavity (anterior to lens)
filled with a liquid aqueous humor
produced by the ciliary body
continually drained
replaced every 90 minutes
2 chambers
anterior chamber between cornea and iris
posterior chamber between iris and lens
Posterior cavity (posterior to lens)
filled with vitreous body (jellylike)
formed once during embryonic life

22. Accessory Structures of Eye
Eyelids or palpebrae
protect & lubricate
epidermis, dermis, CT, orbicularis oculi m., tarsal plate, tarsal glands & conjunctiva
Tarsal glands
oily secretions keep lids from sticking together
Conjunctiva
palpebral & bulbar
stops at corneal edge
dilated BV--bloodshot

23. Extraocular Muscles
Six muscles that insert on the exterior surface of the eyeball
Innervated by CN III, IV or VI.
4 rectus muscles -- superior, inferior, lateral and medial
2 oblique muscles -- inferior and superior

24. Lacrimal Apparatus
about 1 ml of tears produced per day. Spread over eye by blinking. Contains bactericidal enzyme called lysozyme.

25. Tunics (Layers) of Eyeball
Fibrous Tunic (outer layer)
Sclera and Cornea
Vascular Tunic (middle layer)
Choroid layer
Iris
Ciliary body
Lens
Nervous Tunic (inner layer)
retina

26. Fibrous Tunic CORNEA Transparent & curved
Helps focus light by bending (refraction)
3 layers of epithelia, collagen fibers and fibroblasts
Shape has a “memory”
Nourished by tears & aqueous humor
SCLERA
“White” of the eye
Dense irregular connective tissue layer
Provides shape & support, attachment for eye muscles
Posteriorly pierced by Optic Nerve (CNII)

27. Vascular Tunic Choroid majority of vascular layer
found on top of the sclera and under the retina
pigmented epithelial cells that make melanin (melanocytes)
rich in blood vessels that provide nutrients to retina
melanin absorbs scattered light and ensures light passes through the choroid and into the retina

28. Vascular Tunic Lens: Avascular
Crystallin proteins arranged like layers in onion
Clear capsule & perfectly transparent
Lens held in place by suspensory ligaments which attach to the ciliary bodies
Focuses light on fovea (center of the retina)

29. Vascular Tunic Ciliary body
choroid extends to the front of the eye as ciliary muscles and ciliary processes
for controlling the shape of the lens
ciliary processes
folds from the ciliary body
secrete aqueous humor
ciliary muscle
smooth muscle that alters shape of lens
attach to the ciliary processes
Suspensory ligaments attach lens to ciliary process
Ciliary muscle controls tension on ligaments & lens

30. Vascular Tunic Aqueous Humor Continuously produced by ciliary body
Flows from posterior chamber into anterior through the pupil
Scleral venous sinus
canal of Schlemm
opening in white of eye at junction of cornea & sclera
drainage of aqueous humor from eye to bloodstream

31. Constriction of the Pupil
Vascular Tunic -- The Iris
is a colored extension off the ciliary processes
Constrictor pupillae muscles (circular muscles)
Contraction results in pupil constriction
are innervated by parasympathetic fibers while
Dilator pupillae muscles (radial muscles)
are innervated by sympathetic fibers
Contraction results in pupil dilation
Response varies with different levels of light
Constriction of the Pupil
Sharpens vision by preventing blurry edges
Protects retina very excessively bright light

32. Nervous Tunic = Retina posterior 3/4 of eyeball
anterior edge = ora serrata
central depression in retina is the fovea centralis (inside the macula lutea)
accumulation of color-sensitive photoceptors (cones)
View with Ophthalmoscope

33. Nervous Tunic = Retina Optic disc
attachment of retina to the optic nerve
also known as the blind spot (no photoreceptors)

34. Layers of Retina Pigmented epithelium Retina: 3 layers of neurons
nonvisual portion
absorbs stray light & helps keep image clear
Retina:
3 layers of neurons
photoreceptor layer
bipolar neuron layer
ganglion neuron layer
2 other cell types (modify the signal)
horizontal cells
amacrine cells
CHOROID
Posterior cavity

35. Photoreceptors -rod and cones
-rod cells: black and white, bright and dark
-cone cells: color vision
-visual pigment is rhodopsin: opsin and retinal
-visual pigment of a photoreceptor is found in “discs” in the outer segment of the photoreceptor
-inner segment is the cell body
-synaptic endings for neurotransmitter release

36. Photoreceptors Rods----rod shaped outer segment
low light photoreceptor
images in dim light
90 to 120 million rod cells at the edge of the retina
peripheral & night vision
Cones----cone shaped outer segment
4.5 to 6 million cones concentrated in the fovea centralis
sharp, color vision
less sensitive to light than cones but they operate faster (detect changes in shape, give fine details)
three types – red, blue and green

37. Physiology of Vision In darkness In light
Na+ channels are held open and photoreceptor is always partially depolarized - continuous release of an inhibitory neurotransmitter onto bipolar cells
The bipolar cells are prevented from creating their action potential
No nerve impulse leaves the retina = NO IMAGE
In light
Light is absorbed by the rhodopsin pigment - activates enzymes in the photoreceptor
These enzymes cause the closing of Na+ channels – hyperpolarizing the photoreceptor – no action potential!!
release of inhibitory neurotransmitter is stopped
bipolar cells can now spontaneously generate their action potential
this creates an action potential in the ganglion cells – via an electrical synapse
a nerve impulse will travel towards the brain = IMAGE

38. Major Processes of Image Formation
Refraction of light
light rays must fall upon the retina – so they must be bent
refraction = bending of light as it passes from one substance (air) into a 2nd substance with a different density (cornea)
in the eye, light is refracted by the cornea and the lens
Accommodation of the lens
changing shape of lens so that light is focused
Constriction of the pupil
less light enters the eye

39. Refraction by the Cornea & Lens
image focused on retina is inverted & reversed from left to right
brain learns to work with that information – switches it back in the occipital lobe
For objects far away - 75% of refraction is done by cornea -- rest is done by the lens
light rays from more than 20’ are nearly parallel and only need to be bent enough to focus on retina – mainly by the cornea
For objects close up - light rays from less than 6’ are more divergent & need more refraction – cornea and lens
Corneal refraction
Corneal
& lens
refraction

40. Accommodation & the Lens
View a distant object
lens is nearly flat by pulling of suspensory ligaments on the lens
this requires relaxation of the ciliary muscles!!!!!
View a close object
ciliary muscle contracts & decreases the pull on the lens by the suspensory ligaments
elastic lens thickens as the tension is removed from it
this causes a rounding of the lens – more refraction
Accommodation – rounding of the lens to bend light rays for close up vision

41. Emmetropic eye (normal)
can refract light from 20 ft away
Myopia (nearsighted)
eyeball is too long from front to back
glasses concave
Hypermetropic (farsighted)
eyeball is too short
glasses convex (coke-bottle)
Astigmatism
corneal surface wavy
parts of image out of focus

42. Hearing & Equilibrium -outer ear: pinna - cartilage and skin
-for collection of sound waves
-middle ear: tympanic membrane and 3 ossicles (malleus, incus, stapes)
-transmission of sound waves to inner ear
-inner ear: cochlea (hearing), saccule, utricle & three semicircular canals (balance)

43. External Ear Function = collect sounds Structures
auricle or pinna
elastic cartilage covered with
skin
external auditory canal
curved 1” tube of cartilage & bone
leading into temporal bone
ceruminous glands produce cerumen
= ear wax
tympanic membrane or eardrum
epidermis, collagen & elastic fibers, simple cuboidal epith.
Perforated eardrum (hole is present)
at time of injury (pain, ringing, hearing loss, dizziness)
caused by explosion, scuba diving, or ear infection

44. Middle Ear Cavity Air filled cavity in the temporal bone
Separated from the external ear by the tympanic membrane
Contains 3 ear ossicles connected by synovial joints
malleus attached to tympanic membrane, incus &
stapes attached to the membrane of oval window
stapedius and tensor tympani muscles attach to these ossicles – prevent large vibrations that would damage the inner ear

45. Middle Ear Cavity
Oval window
Round
window
Separated from external ear by eardrum and from internal ear by oval & round windows
These windows have membranes similar to the tympanic membrane
Will vibrate with the same frequency as the tympanic membrane
As the oval window pushes in the round window must bulge outwards to keep the pressure within the ear in a safe zone

46. Middle Ear Cavity Eustacian tube leads to nasopharynx
helps to equalize pressure on both sides of eardrum – better vibration and better sound

47. Inner Ear---Bony & Membranous Labyrinth
Bony labyrinth = set of tube-like chambers carved into the petrous part of temporal bone
surrounds & protects Membranous Labyrinth
filled with a fluid called perilymph
Membranous labyrinth = set of fluid-filled tubes within the bony labyrinth
filled with a fluid called endolymph
contains sensory receptors for hearing & balance
comprised of: utricle, saccule, ampulla, 3 semicircular ducts & cochlea

48. Inner ear in the temporal bone

49. Cochlear Anatomy Cochlea is made of 3 fluid-filled channels
scala vestibuli, scala tympani and scala media (cochlear duct)
Partitions that separate the channels are Y shaped
vestibular membrane above & basilar membrane below form a central fluid filled chamber = scala media (cochlear duct)

50. Cochlear Physiology
Vibration of the stapes upon the oval window pushes it in  sends vibrations into the fluid of the scala vestibuli and scala tympani
The movement of the fluid within these scala stimulates the neurons of the scala media  HEARING
Fluid pressure is dissipated at round window - which bulges out as the oval window pushes in

51. within the cochlear duct is the organ of hearing = Organ of Corti
Organ of Corti made up of a top Tectorial membrane and a bottom Basilar membrane “sandwiching” a collection of sensory neurons
Sensory neurons are called hair cells –bear large cilia called stereocilia
Stereocilia embed themselves in the tectorial membrane
Fluid vibrations moving through the scala vestibuli and tympani push in on the fluid in the cochlear duct
This shifts the basilar membrane back and forth and bends the hair cells that are “stuck” in the tectorial membrane
Results in an action potential – stimulates the sensory neurons of the 8th cranial nerve (acoustic or vestibulocochlear nerve)  processing in temporal lobe

52. Scala tympani
Scala vestibuli
Vestibular membrane
Tectorial membrane
Basilar membrane

53. Equilibrium (Balance)
Static equilibrium
maintain the position of the body (head) relative to the force of gravity
macula receptors within saccule & utricle
Dynamic equilibrium
maintain body position (head) during
sudden movement of any type--rotation,
deceleration or acceleration
crista receptors within ampulla
of semicircular ducts

54. Saccule & Utricle
Located between the semicircular canals and the cochlea = area known as vestibule
Oval window positioned over utricle
Round window positioned over saccule
Both contain receptors known as the macula

55. Static equilibrium: Saccule & Utricle
Thickened regions called macula within the saccule & utricle
macula made up of:
hair cells (neurons with stereocilia)
supporting cells that secrete gelatinous otolithic membrane
otolithic membrane contains calcium carbonate crystals called otoliths that move when you tip your head
head movement and otolith movement bends the hair cells and results in action potentials

56. 3 SC canals: anterior, posterior & horizontal/lateral
detect different movements
small elevation within each of three semicircular ducts = ampulla

57. Dynamic equilibrium: Semicircular Ducts
Hair cells in the ampulla are covered with cupula of gelatinous material
When you move, fluid in the canal bends cupula stimulating hair cells to produce an action potential
The AP stimulates the neurons of the vestibulocochlear nerve (CNVIII)
Signals run from CNVIII to the temporal lobe, motor cortex, cerebellum and to the medulla