The Senses

The Senses



Sensory Receptors



General senses of touch

 Temperature  Pressure  Pain 

Special senses:

Equilibrium Taste, Sight, Hearing Smell,

Types of Receptors



Chemoreceptors



Pain receptors or nociceptors



Thermoreceptors



Mechanoreceptors



Photoreceptors

Somatic or Body Senses

 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



Warm receptors

  temperatures above 25 C (77 F) unresponsive to temperature above 45 C (113 F) 

Cold receptors

 temperature between 10 C (50 F) and 20 C (68 F) 

Pain receptors

  below 10 C above 45 C

Pain

 free nerve endings, widely distributed,stimulated by tissue damage,do not adapt 

Acute pain fibers:

impulses rapidly thin, myelinated, conduct 

Chronic pain fibers :

impulses more slowly thin, unmyelinated, conduct

Regulation of Pain

  

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

 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



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

 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



External Ear



Auricle



external auditory meatus



tympanic membrane-



Middle Ear



tympanic cavity



auditory ossicles-

malleus, incus, and stapes

Cont…….



oval window-

stapes vibrates against it to move fluids in inner ear



eustachian tube or Auditory-

ear to throat: connects middle 

Inner Ear



osseous labyrinth-

filled with perilymph bony canal in temporal bone 

membranous labyrinth-

tube within osseous labyrinth filled with endolymph

Cont…



3 Parts of Labyrinths



cochlea

  functions in hearing

semicircular canals

  functions in equilibrium

vestibule

 functions in equilibrium

Cochlea



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

 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

 Equilibrium has two functional parts  Static equilibrium   

Static Maculae

– receptors in the vestibule  Report on the position of the head  Dynamic equilibrium 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

 

Crista ampullaris

receptors in the semicircular canals –  Tuft of hair cells 

Action of angular head movements

 The cupula stimulates the hair cells 

Cupula

(gelatinous cap) covers the hair cells An impulse is sent via the vestibular nerve to the cerebellum

Eye Muscles



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



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 coat-

provides 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..



3. Inner retina

 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

How We See



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

 Jack Brown M.S. Biology  Shier,David, Jackie Butler, Ricki Lewis: Hole’s Human Anatomy and Physiology 10 th edition: 2004: McGraw-Hill  Marieb, Elaine: Essentials of Human Anatomy and Physiology 7 th edition. 2003: Pearson Education Inc: Benjamin Cummings pub.

 Microsoft Encarta Encyclopedia 2004