D’YOUVILLE COLLEGE
BIOLOGY 108/508 -HUMAN ANATOMY & PHYSIOLOGY II
LECTURE # 1
SENSORY ORGANS I
Chapter 13
1.
Introduction:
• homeostasis: maintenance of steady state; external & internal environments
monitored by sensory receptors
• receptors: environmental inputs to the afferent limb of the reflex arc
• single-celled (nerve ending) or complex organs containing receptors +
structures designed to facilitate reception of specific type of environmental condition
• receptors act as transducers to convert one form of energy (stimulus
modality) to another, e.g. light energy to electrical energy of nerve impulses
a. Perceptions (sensations): interpretation of inputs of electrical impulses
related to the destination in the brain; brain region produces a sensation (smell, sight,
touch, etc.) & “projects” perception to sensory field (accounts for “phantom limb”
phenomenon)
b. Sensory adaptation: reduced response to a sustained stimulus
2.
Types of Sensory Organs: (table 13 – 1)
According to Stimulus Modality:
a. chemoreceptors: chemicals dissolved in body fluids, e.g. olfactory and
gustatory organs, osmoreceptors, blood gas receptors, pH receptors
b. mechanoreceptors: physical distortion such as stretching, compression,
etc., e.g. baroreceptors, spindle organs, touch receptors of skin (Meissner’s
corpuscles), pressure receptors of skin (Pacinian corpuscles), organs of hearing and
equilibrium
c. thermoreceptors: temperature changes, e.g. cold receptors respond to
temperatures of 10º - 20º C.; heat receptors are sensitive to temperatures above body
temperature (up to 45 º C.)
d. photoreceptors: light energy, e.g. rods and cones of the retina.
• nociceptors: painful stimuli that may be triggered by extremes of any of
the other modalities or by noxious agents (e.g. prostaglandins) released at sites of
injury
• do not normally exhibit sensory adaptation
• neuropeptides (e.g. enkephalins or endorphins) may inhibit or diminish pain;
release may be triggered by serotonin & may provide the basis for placebo effects &
acupuncture.
• visceral pain (associated with internal organs) is experienced at sites
removed from the site of the pain stimulus, a phenomenon known as referred pain.
Alternative Classification:
Bio 108/508
lec. 1 - p. 2
a. exteroceptors: associated with the skin, e.g. Pacinian and Meissner’s
corpuscles, temperature receptors
b. proprioceptors: associated with muscles, tendons and joints, e.g. spindle
organs
c. visceroceptors: associated with internal organs, e.g. baroreceptors,
osmoreceptors
d. special sensory organs: more complex structures; include the senses of
taste (gustatory), smell (olfactory), sight (visual), hearing (auditory) and balance
(equilibrium)
Special Senses
Chapter 15
1.
Olfactory Organs: smell receptors are sensory hair cells in nasal epithelium
of roof of nasal cavity (fig
• variety of fragrances recognized including:
- floral, musky, pungent, putrid, peppermint, ether, camphor (formerly
construed to be the primary odorants); current consensus recognizes many more,
based upon identified anosmias and genes identified that code for olfactory receptors
• served by cranial nerve I (olfactory nerve): hair cells synapse within
olfactory bulb (table 13 – 2) with afferent neurons which transmit impulses, via areas
of limbic system, to regions of frontal and temporal lobes
2.
Gustatory Organs: taste buds are located mainly on sides of foliate,
fungiform and circumvallate papillae on tongue’s superior surface (fig. 15 – 23)
• taste buds are barrel-shaped clusters of cells, including hair cells &
supporting cells (fig 15 – 23c)
• five (formerly four) primary taste qualities are identified:
a. sweet: respond to sugars, alcohols, & certain amino acids
b. sour: sensitive to acids
c. salty: respond to metal ions, especially sodium
d. bitter: detect alkaloids (e.g., quinine & caffeine) and aspirin
e. umami: responsible ‘beef’ and ‘aged cheese’ tastes
• mainly cranial nerves VII, IX, & X (facial, glossopharyngeal, & vagus) (fig.
15 – 24)