Download 12 Unit 1

Somatic Senses & Special
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Senses
Unit 1
Chapter 12
special location
• Smell (olfaction)
• taste (gustation)
• vision
• balance
• hearing
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Special Senses
Somatic & Visceral
• Temperature
• Touch
• Pressure
• Vibration
• Proprioception
• Pain
• Internal organ conditions
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General Senses
Definition of Sensation
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Conscious or subconscious
awareness of change in external
or internal environment
Requires:
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Stimulus
Sensory receptor
Neural pathway
Brain region for integration
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Characteristics
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• Perception- conscious awareness
• Adaptation- decreased receptor
response with prolonged
stimulation
decreased perception
Adaptation speed varies with receptor
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Cerebral cortex function
Structural Types
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• Free nerve endingspain, thermal, tickle, itch & some touch
receptors
Touch pressure & vibration
• Specialized cells:
e.g. hair cells in inner ear
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• Encapsulated nerve endings
Receptor Mechanisms
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• Mechanoreceptors-
• Thermoreceptors- temperature
• Nociceptors – pain
• Photoreceptors- light
• Chemoreceptors- chemicals
Taste, smell, body fluid content
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cell deformation, stretching or bending
• Receptors- distributed unevenly
• In skin, mucous membranes,
muscles, tendons,& joints
• Dense receptors concentration in
fingertips, lips & tip of tongue
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Somatic Senses
• Touch, pressure, vibration, itch &
tickle
• Itch & tickle – free nerve
endings
• encapsulated mechanoreceptors
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Tactile sensations
Touch
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• Rapidly adapting receptors:
Meisner corpuscles
Hair root plexuses
Type I mechanoreceptors= Merkel discssurface receptors- stratum basale
Type II mechanoreceptors= Ruffini
corpuscles- deep in dermis & tendons
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• Slowly adapting receptors:
Pressure & Vibration
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• Sensation over large area
• Vibration = rapidly repetitive
stimuli
Corpuscles of touch- low frequency
Lamellated corpuscles- higher frequency
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Lamellated or Pacinian corpuscles
Rapid adapting & widely distributed
Figure 12.1
Itch & tickle
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• Itch- chemical stimulation of free
nerve endings
• Tickle- from free nerve endings
& lamellated corpuscles
Requires someone else- blocked by
signals from cerebellum
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Bradykinin from inflammation response
Thermal Sensations
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• Two kinds of thermoreceptors• Between 10o & 40o C - cold
Located in epidermis
• Between 32o & 48o C – warm
• Outside these ranges – nociceptors
• Both adapt rapidly but continue slow
signals during prolonged stimulus
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located in dermis
Pain Sensations
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Nociceptors- free nerve endings
Found in every tissue but brain
Very little adaptation
Fast pain= acute, sharp pain (0.1 sec)
not felt in deep tissues and well localized
Chronic, burning, aching or throbbing sensation
• Visceral pain location displaced to
surface = referred pain
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• Slow pain- slow starting & increases
Figure 12.2
Proprioception
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• Head and limb position & motion
• Kinesthesia= perception of movements
• Inner ear (hair ceils)- head position
• Tracts to primary sensory area of cerebral
cortex & cerebellum
• Slow & slight adaptation
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Located in muscles (muscle spindles), tendons (tendon
organs), in & around synovial joints (joint kinesthetic
receptors)
Figure 10.13
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Smell- Olfaction
• In upper surface of superior concha,
below cribiform plate
• Olfactory receptors-
• Supporting cellsepithelial cells – support & electrical insulation
• Basal cells- stem cells for receptors
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first order neurons of olfactory pathway
Connect to olfactory bulb
Have olfactory hairs containing chemoreceptors
Figure 12.3a
• Genetic evidence- 100’s of primary
odors
• Binding of chemical stimulates nerve
• Recognition of 10,000 odors from
combination of primary receptor
input
• Rapid adaptation by ~50% in 1 sec.
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Stimulation of Receptors
Olfactory Pathway
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• Olfactory receptor’s axons =
Olfactory nerves
through cribiform plate  olfactory bulbs
To primary olfactory area of temporal lobe
And limbic system - emotional response
to smells, e.g. nausea or arousal
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• Olfactory tract
Figure 12.3 b
• 5 primary tastes: salt, sweet, sour,
bitter & umami
• Perception of what we call taste
includes olfactory input
• Receptors in taste buds (~10,000)
• Located on tongue & pharynx &
epiglottis
• In structures called papillae
Vallate (back), fungiform (all over)
filiform- touch receptors only
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Taste- Gustatory Sensation
Figure 12.4a
Figure 12.4b
Structure of Taste Bud
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• Epithelial cells:
• Supporting cells surrounding
• Gustatory receptor cells
• Basal cells= stem cells
Produce supporting cells that develop
into receptor cells (10 day life span)
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Gustatory hair projects from receptor
through taste pore
Figure 12.4c
• Tastant- dissolved in saliva
• Receptors respond to more than
one tastant
• Release neural transmitter to
primary gustatory neuron
• Tastes arise from mix of input
form various areas
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Stimulation
Gustatory Pathway
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consciousness
• Also medulla  limbic system
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• Facial & glossopharyngeal-tongue
• vagus- pharynx & epiglottis
• to medulla oblongata
•  thalamus
•  primary gustatory area-
Vision- Eyes
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Superior Rectus, inferior rectus, lateral rectus, medial
rectus, superior oblique, inferior oblique
• Lacrimal apparatusGland lacrimal duct surface of upper eyelid 
lacrimal canal & nasolacrimal duct  nasal
cavity
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• Accessory structures• eye brows, eyelashes- protection
• eye lids- protection & lubrication
(blinking)
• extrinsic muscles- moving eyeball
Figure 12.5
Layers of Eyeball
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Fibrous tunic – Anterior clear cornea
Sclera- white of eye
Vascular tunic- contains:
Choroid- Lines most of internal surface
carries blood vessels
aqueous humor
• Iris- opens & closes pupilcontains pigment of eye color.
• Pupil = hole for light passage
Adjusted by iris to control amount of light through the lens
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• Ciliary body- focuses the lens and secretes
Figure 12.6
Figure 12.7
Layers of Eyeball (Cont.)
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• Retina- two layers
• neural layer- outgrowth of brain
• pigmented layer- helps absorb
stray light
between choroid & neural layer
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Photoreceptor layer
Bipolar cell layer
Ganglion cell layer
Photoreceptors
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• Rods very sensitive, black & white
• Cones- color sensitive,
• 3 types-blue, green & red
Color vision results from combined input
Area of highest visual resolution
• Information  bipolar layer
ganglion cells axons = optic
nerve
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• Cones mostly in central fovea in
center of macula lutea
Figure 12.8
Interior of Eyeball
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• Two cavities- Anterior cavity &
Vitreous Chamber divided by lens
• Anterior filled with aqueous humor
• Vitreous chamber- filled with vitreous
body
Gel-like - holds retina against choroid
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Drains into canal of schlemm.- replaced ~90 min.
Maintains eye shape & nourishes lens & cornea
Responsible for intraocular pressure
Refraction of Light
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• 75% occurs at cornea
• Lens- focuses light on the retina
• Image is inverted but brain adjusts &
interprets distance and size
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• Light rays bend on passing from
medium of one density to another of
different density = refraction
Figure 12.9a
Figure 12.9b
Figure 12.9c
Accommodation
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• Lens adjusts for distance to keep image
focused on retina
• Myopia= can’t accommodate distant
objects- Eyeball is too long
• Hyperopia = can’t accommodate far
objects- Eyeball is too short
• Astigmatism= irregular curvature of
cornea or lens
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With distant objects ciliary muscle is relaxed
Contracts as the object becomes closer
Figure 12.10
Other visual controls
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• Constriction of pupilautonomic reflex to center light on lens
as object nears it is necessary to maintain focus
on single object for binocular vision
• Photoreceptors: light  neural signal
light is absorbed by a photopigment (rhodpsin)
which splits into opsin & retinal
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• Convergence- eyes rotate toward
midline
• Optic nerve through optic chiasm
• About 1/2 cross over into optic tract
•  hypothalamus occipital lobes
• Right brain sees left side of object
• Left brain sees right side of object
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Visual Pathway
Figure 12.11
Structures
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• Outer ear- Auricle, external auditory
canal & tympanic membrane (ear drum)
Canal contains hairs & ceruminous glands
• Middle ear- auditory tube (eustachian
tube) & ossicles
• Inner ear- Bony labyrinth & membranous
labyrinth filled with endolymph
Cochlea- sense organ of hearing ,
vestibule & semicircular canals- organs of balance
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Ossicles = Malleus, incus, & stapes-attached to oval
window
Figure 12.12
Details of inner structure
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• Vestibule includes
Two sacs: utricle & saccule
• Semicircular canals- orthogonal
End in swelling called ampulla
Semiscisular ducts connect to utricle
Cochlear duct- membranous & has endolymph
Above: Scala vestibuli - ends at oval window
Below: Scala tympani - ends at round window
In cochlear duct- spiral organ = organ of Corti
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• Cochlea- 3 channels
Spiral Organ
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• Sits on basilar membrane
• Contains supporting cells & hair cells
• Hair cells =receptors for auditory
sensations
• Synapse with sensory & motor
neurons in cochlear branch of
vestibulocochlear nerve
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between scala tympani & cochlear duct
Figure 12.13a
Figure 12.13b
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Waves in air auditory canal
tympanic membrane & ossicle movement
 pressure waves in perilymph
scala vestibuli scala tympani
pressure waves in endolymph
 basilar membrane bending hair cells
 neural transmitter to sensory neurons
Pitch (wavelength)  location in cochlea
Volume (loudness) intensity of waves
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Physiology of Hearing
Figure 12.14
• Cochlear neurons end on same
side in medulla
• Through midbrain to thalamus
• Auditory Cortex on Temporal
lobe
Receives input from both ears
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Auditory Pathway
Physiology of Equilibrium
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• Static equilibrium- position
relative to gravity
• Dynamic equilibrium- position
in response to head movement
• Sensed in maculae of Utricle &
Saccule
• gravity pulls on otoliths in otolithic
membrane
• bends hair cells
• Triggers nerve impulses in vestibular
branch of vestibulochochlear nerve
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Static equilibrium
Figure 12.15a
Figure 12.15b
Dynamic Equilibrium
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• Semicircular canals- at right angles to
each other
• Cristae in each ampulla have hair
cells and supporting cells
• When head turns hair cells move
• Endolymph lags and bends hair cells
• Bend triggers nerve impulse in
vestibular branch
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Figure 12.16a
Figure 12.16b
• Axons from vestibular branch
• medulla or cerebellum
• Medulla motor for eye & head
& neck
•  spinal cord tracts for
adjusting muscle tone & postural
muscles
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Equilibrium Pathways