Ch. 15 Sensory System
Ch. 15 Sensory System
Ch. 15 Sensory System
2/4/15 6:06 PM
Senses: Classification
Sensory Process
1. Sensation refers to the activation of sensory receptors & generation/transmission
of an AP by those sensory receptors to the brain
2. Perception refers to
Classification
1. General Senses
o senses wide spread throughout the body & are simple senses
a. ex: sense of touch &/or pain
2. Special Senses
o utilized senses that are localized in a particular region of the body
a. ex: smell &/or taste
o there are 5 special senses:
1. Olfactory sense smell, nasal
utilizes the olfactory receptors localized in the nose
2. Gustatory sense taste, mouth
utilizes the gustatory receptors localized within the taste buds
of the tongue
3. Visual sense sight, eyes
utilizes photoreceptors localized within the eyeball
4. Auditory sense hearing, ear
utilizes hair cells localized within the inner ear
5. Vestibular sense balance & equilibrium, ear
utilizes hair cells localized within the inner ear
Sensory Receptors: Classification
According to their structure, sensory receptors can be classified as:
1. Simple composed of unipolar, sensory neurons
** refers to both simple & complex receptors the unipolar, sensory neurons have a
simple process that splits into 2 branches close to the cell body of the neuron
a. 1 of the branches is the receptor of the neuron
b. the other/outer branch synapses with the secondary sensory neuron
o Structure:
a. generally lack myelin sheaths, unmyelinated
b. have free nerve endings
dendrites are free
o ex: nociceptors (pain receptors; sensation of pain) & thermoreceptors (allows
to perceive various temperatures) that are in the skin.
o utilized by general senses
2. Complex composed of unipolar, sensory neurons
o Structure:
a. axons are myelinated
causing transmission of AP to be faster
b. nerve endings are closed
dendrites are enclosed within several layers of CT forming a
capsule
o ex: tactile receptors (allows to perceive sensation of touch) in the skin
o utilized by general senses
3. Special composed of non neuronal cells
o highly complex & highly modified epithelial cells
o utilized by all special senses except for the olfactory sense
Senses 1
Senses 2
2. Interoceptors
o located deep within the body; typically within visceral organs
o best suited for detecting internal stimuli (stimuli that arises from the body)
o examples include:
Senses 4
Senses 6
Senses 2
Oblique:
divided into 2 oblique muscles:
Superior oblique
Inferior oblique
both oblique muscles are responsible for rotating the eyes lightly on its
axis
normally the actions/movements of the eyes are coordinated, so that the eyes move
in parallel a process known as conjugated case
the corneas transparent structure allows light to enter the eye through
the pupil
i. corneal transparency is attributed to 3 things:
smaller collagen & elastic fibers (& more proteoglycans)
cells & fibers are arranged in a regular pattern which allows for
light rays to pass in between them
low water content prevents the scattering of the light rays
the avascularity of the cornea allows for few complications with corneal
transplants
i. the cornea does not have a direct blood supply
ii. so White Blood Cells do not have access to the newly transplanted
cornea
iii. without access, WBCs cannot recognize the new cornea as foreign &
therefore, cannot initiate a new response to destroy the tissue
2. Vascular coat/tunic middle layer
o contains a large amount of blood vessels
o composed of the Choroid:
a. contains pigment producing melanocytes
melanocytes produce melanin (brown black pigment)
i. melanin absorbs refracted & reflected light to minimize the glare within
the eye
b. the choroid gives rise to 2 structures:
Ciliary body
i. consists of the ciliary process that produces the aqueous humor
the aqueous humor is the fluid that fills the anterior cavity
the anterior cavity is the space that extends from the lens to
the cornea
ii. the ciliary process & associated ciliary muscle (both make up the
ciliary body) are attached to the chrystalline lens via fibers/strings
called suspensory ligaments
iii. it is responsible for regulating the shape of the lens through the
contraction of the smooth muscle, a process known as Lens
Accommodation
the lens system is involved on focusing the image on the back of
the retina
Distant Vision when a person looks at an object at some
distance from them:
ciliary muscles automatically relax
suspensory ligaments become taut
this then causes the chrystalline lens to assume a flattened
shape
this then allows for the object at some distance to be
precisely focused on the back of the retina
Near Vision when a person switches their gaze to a nearby
object:
the ciliary muscles automatically contract
suspensory ligaments relax
causing the chrystalline lens to assume a spherical shape
allowing the light rays to be precisely focused on the back of
the retina resulting in a clear image
Iris (the colored part of the eye)
Senses 4
i.
loss of its ability to change shape or loss in the shape of the eye would cause
the light rays to be focused either in front or back of the retina resulting in
blurred vision
Vitreous humor contribute to the refraction of light
Photoreceptors
act as tranducers 2 types include:
o Rods involved with monochromatic (black/white) vision
activated by low intensity light
allow us to see in darkness (night vision)
o Cones
activated by high intensity light
involved with visual acuity
the ability to see objects in fine detail
ex: reading a book
rich in fovea centralis & macula lutea (surrounds the fovea centralis)
as you move away to the periphery of the retina, the rods become more exclusive
both rods & cones contain lectin membranes known as discs
o discs are made up of a phospholipid bilayer
o photopigments are embedded in the membrane
Photopigment
o made up of 2 proteins:
opsin
retinal (derived from vitamin A)
o when light hits the photopigments in the rods/cones, it bleaches the opsin & retinal
separate
the separation causes the photoreceptors to become hyperpolarized
hyperpolarization removes the inhibition on bipolar cells to allow them to
generate APs that are propogated via ganglions & optic nerve towards
the brain
Optic disk blind spot
o contains no photoreceptors
no image can be formed in this area
o area where axons of the ganglion cells leave the eye to form the optic nerve which
carries the AP from the photoreceptors to the thalamus & then to the primary visual
cortex of the occipital lobe where all the APs are integrated to from an image
Macular degeneration loss of photoreceptors in the fovea centralis & macula lutea
o results in central blindness where individual cannot see or perceive an image in the
central area of the retina
o peripheral vision remains in tact
Cones & Color
electromagnetic spectrum consists of waves of different wavelengths & frequencies
o UV light wavelengths <400nm
incapable of activating photoreceptors as they lack UV receptors
invisible to the human eye
o Visible light wavelengths of 400 700 nm
only portion of the electromagnetic spectrum that can activate photoreceptors
activate rods & cones
cones are intimately involved in color vision; 3 types of cones:
Cupula
Extraocular skeletal muscle movement of the eyes
cerebellum coordinates with the contraction of the
extraocular skeletal muscle to track the visual field during
rotational movement
iii. part of the membranous labyrinth (contains perilymph)
iv. as you rotate, the endolymph circulates in the direction of the rotation
(left/right) within the semicircular canals & the cupula (as well as
stereocilia) becomes bent; the cell membrane deforms, activating the
hair cells to generate greater frequencies of APs reaching the
cerebellum of the brain this allows the brain to determine which way
the body is rotating
such sensory information & information from propioreceptors are
integrated within the cerebellum to maintain the appriopriate
muscle tone & to shift the position of the lymphs to shift the weight
in order to maintain balance
Cochlea attached to the vestibule
i. houses hair cells
ii. involved in the sense of hearing sending nerve impulses to the
primary auditory cortex of the temporal lobe of the cerebrum
iii. made up of 3 chambers
Scala vestibuli (upper) part of the bony labyrinth & contains
perilymph
Cochlear duct (middle) separated from the scala vestibuli (via the
vestibular membrane) & the scala tympani (via basilar membrane)
represents the membranous labyrinth containing endolymph
Scala tympani (inner) part of the bony labyrinth, containing
perilymph
iv. includes the spiral organ (organocorti)
lies on top of the basilar membrane
separates the cochlear duct from the scala tympani
consists of 2 types of cells:
Hair cells considered the functional units of hearing
tectorial membrane (gelatinous cavity) hovers over the hair
cells
stereocilia are projections of the hair cells partially
embedded within the tectorial membrane
hair cells synapses with dendrites of the sensory neurons,
where the axons form the cochlear nerve leading to the
brain
hair cells are mechanoreceptors & transducers
Sustentacular cells provide physical & metabolic support to
the hair cells
Senses 1
o
o
Sustentaculr cells: provides physical & metabolic support to the olfactory cells
Basal cells: stem cell that differentiates, generating new olfactory &
sustentacular cells
both cells are often replaced by basal cells on an average of 7 days
Olfactory glands: exocrine lands that deliver mucus onto the apical surface of the
olfactory epithelium
the mucus allows for the incoming odor molecules from the air to dissolve
within the mucus, enabling them to interact with the olfactory receptors of the
olfactory hairs
various tastes binds to the hairs to depolarize the cell resulting in APS
towards the brain,
on the basal surface, it synapses with primary sensory neurons where the
axons project into the relay center of the brain (thalamus) & then synapse with
secondary sensory neurons & project into the primary gustatory cortex of the
insular lobe
Senses 2
o
o
sustentacular cells (support cells) give physical & metabolic support to gustatory
cells
basal cells regenerate gustatory & sustenatcular cells every ~7 days.