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Somatic and Special Senses

Chapter 10

Mackenzie Dwyer

on 4 October 2012

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Transcript of Somatic and Special Senses

Chapter 10 Touch and Pressure: Somatic Senses Temperature Pain Somatic and
Special Senses 2 types of senses Somatic Senses Special Senses touch, pressure, temperature, pain
widely distributed through skin and deeper tissue
structurally simple smell, taste, hearing, equilibrium, vision
complex, specialized organs 5 Types of receptors Chemoreceptors Pain Receptors Thermoreceptors Mechanoreceptors Photoreceptors changes in chemical concentration of substances tissue damage changes in temperature changes in pressure or movement light energy Free nerve endings
epithelial tissues
Meissner's corpuscles
hairless portions of skin, such as lips, fingertips, palms, soles, nipples, and external genital organs
sensation of light touch
Pacinian corpuscles
deeper subcutaneous tissues and in muscle tendons and joint ligaments
sensation of deep pressure Warm Receptors
most sensitive to temperatures above 25 C ( 77 F)
unresponsive above 45 C (113 F)
temperatures near and above 45 C stimulate pain receptors
Cold Receptors
most sensitive to temperatures between 10 C (50 F) and 20 C (68 F)
temperatures below 10 C stimulate pain receptors
Both warm and cold receptors adapt rapidly Receptors are free nerve endings, widely distributed throughout skin and internal tissues except for the brain
Protects body by creating an unpleasant sensation so the person acts to remove the stimulus
Adapt poorly, so pain may persist even when the stimulus is gone
Phenomenon of Referred Pain:
pain felt in a place other than the place being stimulated
Ex: pain felt in left shoulder or left upper limb from pain stimulation in the heart
pain from the heart travels along the same nerve pathways as those from the skin of the left shoulder, so the brain may attribute the location of the stimulus incorrectly Pain nerve fibers Conduct impulses away from pain receptors
relatively thin, myelinated
conduct impulses rapidly, associated with sharp pain
thin, unmyelinated
conduct more slowly, creating a dull, aching sensation Inhibiting Pain Naturally 1. Biochemicals that can block pain signals by inhibiting presynaptic nerve fibers in the posterior horn of the spinal cord
enkaphalins and serotonin
2. Endorphins in pituitary gland and hypothalamus Special Senses Sense of Smell: Olfactory Chemoreceptors: chemicals dissolved in liquids stimulate
Works closely with taste to aid in
food selection
Olfactory organs consist of
receptors and supporting cells
in the nasal cavity
Receptors are bipolar neurons
with cilia containing 400 types
of receptor proteins
Combine with odorant molecules that enter as gases but dissolve in the watery fluids
Adapts rapidly, but does not diminish sensitivity to new odors

Pathway: receptor-> receptor axon -> neurons in olfactory bulbs ->olfactory tracts -> limbic system -> olfactory cortex Sense of Taste Chemoreceptors, similar to olfactory, located in taste buds
There are approx. 10,000 taste buds
Mostly on tongue surface, with about 1,000 scattered on the roof of mouth and walls of throat
Within a taste bud:
50-150 taste cells functioning as receptors
supporting cells
a spherical opening (taste pore) at the top with taste hairs protruding as the sensitive part of the receptor cells
a network of nerve fibers ready for stimulation from the receptor cells to send an impulse to the brain
Taste Sensations
Flavor may result from one or a combination of the primary sensations Area most sensitive
tip of tongue
margins of tongue
all of tongue
back of tongue Pathway: taste receptors -> fibers of the facial, glossopharyngeal, and vagus nerves ->medulla oblongata -> thalamus ->gustatory cortex in the parietal lobe Sense of Hearing The organ of hearing: the ear
Outer Ear
auricle, acoustic meatus, and eardrum
collects sound waves of vibrating objects
Middle Ear (tympanic cavity)
air-filled space in temporal bone
auditory ossicles
malleus, incus, stapes
transmits vibrations from eardrum to inner ear
oval window leads to inner ear
Inner Ear
complex system of chambers and tubes called a labyrinth
osseous labyrinth
membranous labyrinth
labyrinth includes 3 semicircular canals (for equilibrium sense) and a cochlea for hearing
Organ of Corti contains the hearing receptors
hair cells within the organ of Corti are stimulated when they are deformed by the sound waves (mechanoreceptors)
different hair cells have different sensitivities
hair cells act like neurons (polarized and release neurotransmitters), which stimulate nearby sensory nerve fibers to the cochlear branch of the vestibulocochlear nerve to the auditory cortex of the temporal lobe Sense of Equilibrium Static:
sense the position of the head, maintaining stability and posture when the head and body are still Dynamic:
detect motion and aid in maintaining balance and stability In the vestibule, a bony chamber between the semicircular canals and the cochlea In the three semicircular canals Hair cells (acting as mechanoreceptors) in a gelatinous mass receive stimulation when the gel makes them shift from the head or body moving Sense of Sight The eye: a hollow, spherical structure about 2.5 cm in diameter with 3 layers
Outer layer:
Middle layer:
choroid coat
ciliary body
Inner layer:
receptor cells
fovea centralis
optic disc
Posterior cavity within the retina
filled with vitreous humor Visual Receptors
2 types of modified neurons:
long, thin projections
black and white vision
1 type
general outlines of objects
short, blunt projections
color vision
3 types
sharp images
Nerves from the retina form the optic nerve, travel through the optic chiasm where some cross over, mixing visuals from each eye, to the thalamus and then to optic radiations pathways to the visual cortex of the occipital lobes Questions? Mechanoreceptors: Thermoreceptors
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