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The Senses
The Senses
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Sensory Receptors
General senses of touch
 Temperature
 Pressure
 Pain
Special senses: Taste, Sight, Hearing Smell,
Equilibrium
Types of Receptors
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Chemoreceptors
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Pain receptors or nociceptors
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Thermoreceptors
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Mechanoreceptors
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Photoreceptors
Somatic or Body Senses
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associated with skin, muscles, joints, and viscera
three groups
 exteroceptive senses – senses associated with body
surface; touch, pressure, temperature, pain
 proprioceptive senses – senses associated with
changes in muscles and tendons
 visceroceptive senses – senses associated with
changes in viscera
Touch and Pressure
Sensitivity to Temperature
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Warm receptors
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Cold receptors
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temperatures above 25 C (77 F)
unresponsive to temperature above 45 C (113 F)
temperature between 10 C (50 F) and 20 C (68 F)
Pain receptors
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below 10 C
above 45 C
Pain
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free nerve endings, widely distributed,stimulated
by tissue damage,do not adapt
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Acute pain fibers: thin, myelinated, conduct
impulses rapidly
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Chronic pain fibers: thin, unmyelinated, conduct
impulses more slowly
Regulation of Pain
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Thalamus
 aware of pain
Cerebral Cortex
 judges intensity of pain
 locates source or pain
 produces motor response to pain
 produces emotions to pain
Pain Inhibiting Substances
 enkephalins-Met-enkephalin is Tyr-Gly-Gly-Phe-Met.
Leu-enkephalin has Tyr-Gly-Gly-Phe-Leu.
 serotonin
 endorphins
Stretch Receptors
Found in
muscles and
tendons:
Can shut down
contraction if it
endangers the
body.
Can also be
turned off during
fight or flight
response
Smell
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Olfactory receptors are in the roof of the nasal cavity
 Neurons with long cilia
 Chemicals must be dissolved in mucus for detection
Impulses are transmitted via the olfactory nerve
Interpretation of smells is made in the cortex
Contain 1000 genes that code for the sense of smell,
but only a few hundred are active????
WHY
Olfaction
Taste
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Taste Buds: organs of taste, located on papillae of
tongue, roof of mouth, linings of cheeks and walls of
pharynx
The tongue is covered with projections called papillae
Taste buds are found on the sides of papillae
Gustatory cells are the receptors (Chemoreceptor)
 Have gustatory hairs (long microvilli)
 Hairs are stimulated by chemicals dissolved in saliva
Sensory impulses from taste receptors travel along cranial
nerves; facial nerve, glossopharyngeal nerve, and
vagus nerve, to medulla oblongata then to the thalamus
and to the gustatory cortex (for interpretation)
Taste
Hearing
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The ear houses 2 senses hearing and equilibrium.
mechanoreceptors
3 Sections
 External
 Middle
 Inner
Functions to collect and translate vibration in the
air
The Ear
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External Ear
Auricle
external auditory meatus
tympanic membraneMiddle Ear
tympanic cavity
auditory ossicles- malleus, incus, and stapes
Cont…….
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oval window- stapes vibrates against it to
move fluids in inner ear
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eustachian tube or Auditory- connects middle
ear to throat:
Inner Ear
osseous labyrinth- bony canal in temporal bone
filled with perilymph
membranous labyrinth- tube within osseous
labyrinth filled with endolymph
Cont…
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3 Parts of Labyrinths
 cochlea
 functions in hearing
 semicircular canals
 functions in equilibrium
 vestibule
 functions in equilibrium
Cochlea
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Scala vestibuli- upper compartment,
Scala tympani- lower compartment,
Cochlear duct- membranous labyrinth in
cochlea
Vestibular membrane- separates cochlear
duct from scala vestibuli
Basilar membrane- separates cochlear duct
from scala tympani
Organ of Corti
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group of hearing receptor cells (hair cells)
on upper surface of basilar membrane
different frequencies of vibration move different
parts of basilar membrane
particular sound frequencies cause hairs of
receptor cells to bend
nerve impulse generated
Overview of Hearing
Equilibrium
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Equilibrium has two functional parts
 Static equilibrium
 Dynamic equilibrium
Static
Maculae – receptors in the vestibule
 Report on the position of the head
 Send information via the vestibular nerve
Anatomy of the maculae
 Hair cells are embedded in the otolithic membrane
 Otoliths (tiny stones) float in a gel around the hair cells
 Movements cause otoliths to bend the hair cells
Dynamic Equilibrium
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Crista ampullaris –
receptors in the semicircular
canals
 Tuft of hair cells
 Cupula (gelatinous cap)
covers the hair cells
Action of angular head
movements
 The cupula stimulates the
hair cells
 An impulse is sent via the
vestibular nerve to the
cerebellum
Eye Muscles
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Superior rectus- rotates eye up and medially
Inferior rectus- rotates eye down and medially
Medial rectus- rotates eye medially
Lateral rectus- rotates eye laterally
Superior oblique- rotates eye down and laterally
Inferior oblique- rotates eye up and laterally
Eye Structure and Function
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3 layers- outer fibrous tunic, middle vascular tunic,
inner nervous tunic
1. Outer- Cornea- anterior portion transparent,
light transmission, light refraction Sclera- posterior
portion, opaque, protection
2. Middle- Iris- anterior, pigmented, controls light
intensity Ciliary body- anterior, pigmented, holds
lens, moves lens for focusing Choroid coatprovides blood supply, pigments absorb extra light
Anterior of eye filled with aqueous humor.
Lens-Transparent, lies behind iris, largely
composed of lens fibers, elastic, held in place by
suspensory ligaments of ciliary body
Cont..
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3. Inner- retina
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contains visual receptors
continuous with optic nerve
ends just behind margin of the ciliary body
composed of several layers
fovea centralis –produces sharpest vision
optic disc – blind spot
vitreous humor – thick gel that holds retina flat
against choroid coat
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How We See
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Photoreceptors:
Rods- long, thin projections, contain light
sensitive pigment called rhodopsin, hundred times
more sensitive to light than cones, provide vision in
dim light, produce colorless vision, produce
outlines of objects
Cones- short, blunt projections, contain light
sensitive pigments called erythrolabe(Red Light),
chlorolabe(Green Light), and cyanolabe(Blue
Light), provide vision in bright light, produce sharp
images, produce color vision
References
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Jack Brown M.S. Biology
Shier,David, Jackie Butler, Ricki Lewis:
Hole’s Human Anatomy and Physiology 10th
edition: 2004: McGraw-Hill
Marieb, Elaine: Essentials of Human
Anatomy and Physiology 7th edition. 2003:
Pearson Education Inc: Benjamin Cummings
pub.
Microsoft Encarta Encyclopedia 2004