Download Somatic and Special Senses

Somatic and Special Senses
Categories
Somatic Senses
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Touch
Pressure
Temperature
Pain
Special Senses
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Smell
Taste
Hearing
Equilibrium
vision
Types of Receptors
Chemoreceptors – stimulated by changes
in the chemical concentration of
substances
Pain receptors - … by tissue damage
Thermoreceptors - … by changes in temp.
Mechanoreceptors - … by changes in
pressure or movement
Photoreceptors - … by light energy
Sensation
A feeling that occurs when the brain
interprets sensory impulses
Depends on which region of the brain
receives the impulse
Sensory adaptation – ability to ignore
unimportant stimuli
Somatic Senses
Senses of touch and pressure
– Free nerve endings (touch and pressure)
– Meissner’s corpuscles (light touch)
Abundant in hairless portions of body
– Pacinian corpuscles (heavy pressure)
Temperature senses
– Warm receptors
Sensitive to 77°F and above; become unresponsive at
temperatures above 113°F
At or above 113°F stimulates pain receptors, producing a
burning sensation
– Cold receptors
Sensitive 50°F to 68°F
Below 50°F stimulate pain receptors, producing a freezing
sensation
Sense of pain
– Widely distributed, except for brain
– Protect the body b/c tissue damage stimulates them
– Pain is perceived as unpleasant and it signals person
to act to remove the simulation
– Pain receptors adapt poorly
Visceral pain
– Localized damage to intestinal organs may
not elicit pain sensations
– More widespread stimulation, as when
intestinal walls are stretched, a strong pain
sensation may follow
– May feel as though it is coming from some
part of the body other than the part being
stimulated, a phenomenon known as referred
pain
Regulation of Pain Impulses
Awareness arises when impulses reach the
thalamus
Cerebral cortex determines pain intensity,
locates pain’s source, and mediates emotional
and motor responses to the pain
Graymatter in midbrain, pons, and medulla
oblongata regulate movement of pain impulses
from the spinal cord
Inhibiting substances released (enkephalins,
serotonin, endorphins)
Sense of Smell
Olfactory organs
contain the olfactory
receptors and are
yellowish-brown
masses of epithelium
about the size of
postage stamps that
cover the upper pars
of the nasal cavity
Olfactory receptors are bipolar neurons
surrounded by columnar epithelial cells
There are 400 types of olfactory receptor
proteins
Odorant molecules enter the nasal cavity
as gases, dissolve in watery fluids, and
then bind to the receptors in different
patterns
Stimulated olfactory receptors cells send
nerve impulses along their axons which
synapse with neurons located in
enlargements called olfactory bulbs
Within the olfactory
bulbs, the impulses
travel along the
olfactory tracts to the
limbic system within
the temporal lobe and
base of the frontal
lobes in the brain
Sense of smell adapts
rapidly but
adaptations to one
scent will not diminish
sensitivity to new
odors
Humans have about
12 million olfactory
receptor cells
Bloodhounds have 4
billion olfactory
receptor cells
Sense of Taste
Taste buds are special
organs of taste
Our 10,000 taste buds
are located primarily on
surface of the tongue and
are associated with tiny
elevations called papillae
About 1,000 taste buds
are scattered in the roof
of the mouth and walls of
the throat
Taste receptors
– Each taste bud includes a group of modified
epithelial cells, the gustatory cells, which
function as receptors cells
– Each taste bud has 50-150 receptor cells
– Entire structure is spherical with an opening
called the taste pore and projections called
taste hairs which are the sensitive parts
– Nerve fibers wrap around the taste cells
– Stimulation of taste cell triggers an impulse on
a nearby nerve fiber and the impulse travels
into the brain
The truth about cats and dogs…
– They can be satisfied with less varied diets
than humans
– Cats have 473 taste buds
– Dogs have 1,700 taste buds
Tasting
– Chemical must be dissolved in watery fluid
provided by salivary glands
– Food molecules bind to specific receptors
embedded in and projecting from taste hairs
on the taste cells
– Pattern of receptor types generate sensory
impulses on nearby nerve fibers in interpreted
as a particular taste sensation
Taste sensations
– Primary taste
sensations
Sweet
Sour
Salty
Bitter
– Others recognized
Alkaline
Metallic
Umami
Flavor
– Results from one or a combination of the
primary sensations
– Experiencing flavors involves tasting,
smelling, and feeling the texture and
temperature of foods
– Some foods, such as chili peppers and ginger,
trigger heat receptors
– Taste sensation undergoes adaptation rapidly
– Moving bits of food over the surface of the
tongue to stimulate different receptors at
different moments keeps us from losing taste
Sense of Hearing
Outer ear
– Auricle (funnel-like
structure)
– External auditory
meatus (ear canal)
– tympanic membrane
(ear drum)
Middle ear
– Air-filled space in the temporal bone
– Contains 3 small bones called auditory ossicles:
Malleus
Incus
Stapes
– Malleus attaches to eardrum and when the eardrum
vibrates, the malleus vibrates in unison
– The malleus causes the incus to vibrate, and the
incus passes the movement on to the stapes
– Vibration of the stapes at the oval window moves a
fluid within the inner ear, which stimulates the hearing
receptors
– Auditory ossicles also help increase (amplify)
the force of vibrations
– The pressure that the stapes applies on the
oval window is many times greater than the
pressure that sound waves exert on the
eardrum
Auditory tube (eustachian tube)
– Connects each middle ear to the throat
– Conducts air between the tympanic cavity and
the outside of the body by way of the throat
– Auditory tube helps maintain equal air
pressure on both sides of the eardrum, which
is necessary for normal hearing
– Ex. Rapid changes in altitude may push
eardrum inward as air pressure on the outside
of the eardrum incerases
Steps in the generation of sensory impulses
from the ear
– Sound waves enter external acoustic meatus
1. Waves of changing pressure cause eardrum to
reproduce vibrations coming from sound wave
source
2. Auditory ossicles amplify and transmit vibrations to
end of stapes
3. Movement of stapes at oval window transmits
vibrations to perilymph in scala vestibuli
4. Vibrations pass through vestibular membrane and
enter endolymph of cochlear duct
6. Different frequencies of vibration in
endolymph stimulate different sets of
receptor cells
7. As a receptor cell depolarizes, its membrane
becomes more permeable to calcium ions
8. Inward diffusion of calcium ions causes
vesicles at the base of the receptor cell to
release neurotransmitter
9. Neurotransmitter stimulates ends of nearby
sensory neurons
10. Sensory impulses are triggered on fibers of
the cochlear branch of vestibulocochlear
nerve
11. Auditory cortex of temporal lobe interprets
sensory impulses
Factors of hearing loss
– Conductive deafness
Interference with the transmission of vibrations to
the inner ear
May be due to plugging of the external acoustic
meatus or to changes in the eardrum or auditory
ossicles
Eardrum may harden as a result of disease and
thus be less responsive to sound waves
Disease or injury may tear or perforate the
eardrum
– Sensorineural deafness
Damage to the cochlea, auditory nerve, or auditory
nerve pathways
Causes by loud sounds, tumors in the CNS, brain
damage as a result of vascular accidents, or use of
certain drugs
Sense of Equilibrium
Static equilibrium
– Sense the position of the head, maintaining
stability and posture when the head and body
are still
– Organs located with the vestibule, a bony
chamber between the semicircular canals and
the cochlea
– A tiny structure called a macula contains
numerous hair cells which serve as sensory
receptors
– When the head is upright, the hairs of the hair cells
project upward into a mass of gelatinous material,
which has grains of calcium carbonate embedded in it
– Head bending tilt the gelatinous mass and they sag in
response to gravity
– Hairs within the mass bends and they signal nerve
fibers
– Nerve impulses travel into the CNS and informs brain
of head’s new position
– Brain responds by sending motor impulses to skeletal
muscles, which contract or relax to maintain balance
Dynamic equilibrium
– Aid in maintaining balance when the head and
body suddenly move or rotate
– Organs are the three semicircular canals
– Each responds to a different anatomical plane
– Each canal ends in a swelling called an
ampulla which contains the sensory organs
crista ampullaris
– Each of the crista ampullaris contains a
number of sensory hairs cells which extend
upward in a gelatinous mass
– Rapid turns of the head or body simulate
these hair cells
– Other sensory structures that aid in
maintaining equilibrium
Mechanoreceptors associated with joins
Eyes detect changes in posture
Motion sickness
– Nausea, vomiting, and
headache
– Arise from senses that
don’t make sense
– Eyes of person reading in a
moving car, for example,
signal the brain that the
person is stationary,
because the print doesn’t
move
– Skin and inner ear,
however, detects
movement
– To lessen the misery, focus
on the horizon or an object
in the distance ahead or
take dramamine
Sense of Sight
Visual accessory organs
– Eyelid
Skin
– Thinnest skin in the body
– Covers the lid’s outer surface and fuses with its inner
lining near the margin of the lid
Muscle
– Eyelids moved by orbicularis oculi and levator palpebrae
superioris
Conjuctivia
– Mucous membrane that lines the inner surfaces of the
eyelids and fols back to cover the anterior sruface of the
eyeball, except for its central portion (cornea)
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Cornea
Lens
Fornix
Marginal conjuctiva
Lacrimal glands
Tarsus, a fibrous
connective tissue
– Lacrimal glands
Secretes tears
Moistens and lubricates
the surface of the eye and
the lining of the lids
Contain lysozyme that is
an anti-bacterial agent,
reducing the risk of eye
infections
– Extrinsic muscles
Arise from the bones of the orbit and insert by broad tendons
on the eye’s tough outer surface
Six muscles move the eye in various directions
Structure of the eye
– Hollow, spherical structure about 2.5 cm in
diameter
– Wall has 3 distinct layers
Outer fibrous layer
Middle vascular layer
Inner nervous layer
– Spaces within the eye are filled with fluids that
support its wall and internal parts and help
maintain its shape
Outer layer
– Outermost layer (1/6 of layer) is transparent
cornea, which is the window of the eye and
helps focus entering light rays
– Composed largely of connective tissue
– Very few cells and no blood vessels
– Along its circumference, the cornea is
continuous with the sclera, the white portion
of the eye (5/6 of layer)
– Opaque due to many large collagenous and
elastic fibers
– Sclera protects the eye and is an attachment
for the extrinsic muscles
– The optic nerve and blood vessels pierce the
sclera in the back of the eye
Most common cause of blindness is loss of
transparency of the cornea
A corneal transplant can replace the central 2/3
of the defective cornea with a similar-sized
portion of cornea from a donor eye
Middle layer
– Choroid coat
Posterior 5/6 of the globe of the eye
Contains blood vessels which nourish surrounding
tissue
Contains melanocytes
Melanin absorbs excess light and keeps the inside
of the eye dark
– Ciliary body
Extends forward from the choroid coat and forms
and internal ring around the front of the eye
Contains ciliary muscles
– Lens
Transparent and held in place by suspensory
ligaments
Adjusts shape to facilitate focusing, called
accommodation
– Cataracts
Lens or its capsule slowly becomes cloudy and
opaque
Without treatment, they cause blindness
Causes by breakdown of protein within lens after
age 45
– Iris
Thin diaphragm composed mostly of connective
tissue and smooth muscle fibers
Colored portion of the eye
Lies between the cornea and the lens
– Aqueous humor
Watery fluid secreted by the ciliary body
Circulates through the pupil (circular opening in the
center of the iris) and into the anterior chamber
helps nourish cornea and lens and aids in
maintaining the shape of the front of the eye
Smooth muscle fibers of iris are organized into two
groups, a circular set and a radial set
When circular set contracts, pupil gets smaller and
less light enters
When the radial set contracts, the pupil’s diameter
increases and more light enters
Glaucoma
– Disorder in which rate of
aqueous humor formation
exceeds rate of its removal
– Fluid pressure squeezes
shut blood vessels that
supply the receptor cells of
the retina
– Cells that are robbed of
nutrients and oxygen may
die and permanent
blindness can result
– Treated with drugs, laser
therapy, or surgery
Inner layer
– Retina
Contains the visual receptor cells (photoreceptors)
Continuous with the optic nerve and extends
forward as the inner lining of the eyeball
Central region is a yellowish spot called the
maculla lutea
Depression in its center is called the fovea
centralis which is where the sharpest vision occurs
Optic disc is just medial to the fovea centralis and
contains a central artery and vein which are
continuous with the capillary networks
Space bounded by the lens, ciliary body, and retina
is the largest compartment and is filled with a
transparent, jellylike fluid called vitreous humor
Vitreous humor helps eye maintain shape
Light refraction
– When a person sees something, either the object is
giving off light or light waves are reflected from it
– These light waves enter the eye and an image of the
object is focused on the retina
– Focusing bends the light waves, a phenomenon
called refraction
– Convex surface of the cornea refracts light waves
from outside objects
– Convex surface of lens then refracts the light again
– If eye shape is normal, light waves focus sharply on
the retina
– Image that forms is upside down and reversed from
left to right
– Visual cortex interprets the image in its proper
position
interaction
Visual receptors
– Modified neurons
– Rods
Have long, thin projections at their ends
Provide black and white vision
Provide general outline of objects
100 times more sensitive to light than cones
Humans have 125 million of them
– Cones
Short, blunt projections
Provide color vision
Provide sharp images
Humans have 7 million of them
– Stimulated only when light reaches them
– Visual pigments
Both rods and cones contain light-sensitive pigments that
decompose when they absorb light energy
Within rods, pigment is called rhodopsin
– In presence of light, these molecules breakdown into a
colorless protein called opsin and a yellowish substance called
retinal that is synthesized from vitamin A
Poor vision in dim light, called night blindness results from
vitamin A deficiency
– Decomposition of rhodopsin activates an enzyme that initiates
a series of reactions altering the permeability of the rod cell
membrane
– As a result, a complex pattern of nerve impulses originates in
the retina along the optic nerve to the brain, where they are
interpreted as vision
Within cones
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Erythrolabe: most sensitive to red light waves
Chlorolabe: most sensitive to green light waves
Cyanolabe: most sensitive to blue light waves
All 3 stimulated: white; none: black
Visual nerve pathway