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Lecture 12: Sensory Receptors and Special Senses
I. General Terms
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sensation - awareness of external/internal conditions
perception - conscious registration of conditions
stimulus - change that can initiate nerve impulse
receptor (sense organ) - converts stimulus to impulse
transduction - changing stimulus signal into nerve signal
generator potential - electrical impulse in receptor
receptor potential - receptor releases neurotransmitter
adaptation - decreased sensitivity with repeat stimuli
a. rapidly adapting - pressure, touch, smell
b. slowly adapting - pain, position, blood chemicals
I. afterimage - sensation even after stimulus is gone
J. modality - distinct property of each sensation
II. General Classification of Receptors
A. Location
1. exteroreceptors - respond to external environment
2. enteroreceptors - respond to internal environment
3. proprioreceptors - respond to body position/motion
B. Type of Stimulus Detected
1. mechanoreceptors - any mechanical deviation
a. touch, pressure, vibration, proprioception etc.
2. thermoreceptors - changes in temperature
3. nocireceptors - pain; physical or chemical damage
4. photoreceptors - light; rods & cones of the eye
5. chemoreceptors - shapes of different molecules
a. taste, smell, chemicals of blood
C. Simplicity or Complexity of the Receptor Structure
1. simple receptors - associated with general senses
a. touch, pressure, temperature, vibration, pain
2. complex receptors - associated with SPECIAL senses
a. smell, taste, sight, hearing, equilibrium
III. Classification of General Senses
A. Cutaneous (Skin) Senses
1. tactile (touch)
a. light touch - location not perceived
b. discriminative touch - location perceived
c. Merkel's discs - discriminative touch
d. Meissner's corpuscle - discriminative touch
e. organs of Ruffini - deep, continuous touch
2. pressure
a. felt over a large area than touch, deeper
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b. Pacinian corpuscle - lower layer of dermis
3. vibration
a. detect high and low frequency vibrations
4. thermosensation
a. respond to hot/cold; may be free nerve endings
5. pain
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b.
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(nociception)
acute pain - very quick, not felt in deep areas
chronic pain - longer lasting, gradual increase
somatic pain - skin, muscles, joints
i. superficial -skin
ii. deep - muscle, joint, tendon, fascia
d. visceral pain - from receptors in organs
e. referred pain - projected to skin above organ
B. Proprioceptive (kinesthetic) Sense
1. function - position of limbs/body and equilibrium
2. muscle spindles
a. intrafusal fibers - inner muscle fibers
i. type Ia sensory fiber - in center
ii. type II sensory fiber - at ends
iii. gamma motor neurons - from ventral horn
b. extrafusal fibers - outer muscle fibers
i. alpha motor neurons - form ventral horn
3. Golgi (tendon) organs
a. at junction of tendon and muscle
4. Joint Kinesthetic receptors
a. within/around synovial joints
IV. Classification of Special Senses
A. Olfaction (smell)
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olfactory
olfactory
olfactory
olfactory
olfactory
cells - bipolar neurons in epithelium
glands - secrete mucus to clean epithelium
nerve (I) - axons of olfactory cells
bulbs - brain region where (I) synapses
tract - axons from bulbs to cortex
B. Gustation (taste)
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gustatory cells - neuron with hairlike extension
taste buds - location of gustatory cells
facial nerve (VII) - anterior 2/3 of tongue
glossopharyngeal nerve (IX) - posterior 1/3
vagus nerve (X) - throat and epiglottis
-> medulla -> thalamus -> cortex
C. Vision
1. Accessory Structures of the Eye
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a. eyebrows
b. eyelids (palpebrae)
i. levator palpebrae superioris muscle
ii. palpebral fissure
iii. lateral commissure
iv. medial commissure
v. lacrimal caruncle (lacrimal gland) crying
c. tarsal plate - inner wall of eyelid
d. tarsal glands - secrete oil
e. conjunctiva - mucous membrane of eyelid
f. eyelashes
g. lacrimal gland - for tear secretion
i. lacrimal ducts
ii. lacrimal puncta
iii. lacrimal sac
iv. nasolacrimal duct
2. The Structure of the Eyeball
a. fibrous tunic - outer coat of the eyeball
i. sclera - posterior portion
ii. cornea - anterior portion
b. vascular tunic (uvea) - middle layer
i. choroid - posterior, pigment/vasculature
ii. ciliary body - muscle shapes lens
iii. iris - colored part, with pupil (hole)
c. nervous tunic (retina) - posterior surface
i. photoreceptors (rods & cones)
ii. bipolar cells
iii. ganglion cells
d. lens - just behind pupil and iris
3. Pathway of Light to the Brain
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photoreceptors pick up the light
ganglion cells converge signals -> optic nerve
optic nerve -> lateral geniculate of thalamus
lateral geniculate -> occipital cortex
D. Hearing & Equilibrium
1. external ear
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pinna (auricle) - Ross Perot
helix - rim of the pinna
lobule - your mate's favorite part
external auditory canal
ceruminous glands - love that earwax!
tympanic membrane (eardrum)
2. middle ear
a. tympanic antrum - chamber to air cells
b. auditory (Eustachian) tube - to nasopharynx
c. auditory ossicles - bones of middle ear
i. malleus - attached to tympanic membrane
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ii. incus - intermediate bone
iii. stapes - stirrup
d. tensor tympani muscles - to malleus (protect)
e. stapedius muscle - to stapes (protect)
f. oval and round windows - to inner ear
3. inner ear (labyrinth)
a. bony labyrinth - has fluid called perilymph
i. vestibule
ii. cochlea
iii. semicircular canals
b. membranous labyrinth - has endolymph
c. vestibule - oval central portion body labyr.
i. utricle & saccule - two sacs
d. cochlea - sound organ, sounds are sensed here
e. semicircular canals - equilibrium in 3-D
4. Neural Pathway for Sound/Equilibrium Sensation
a. cochlea/vestibular -> vestibulocochlear (VIII)
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