lab4 sensory
DESCRIPTION
physio lab sir bautista:)))TRANSCRIPT
SPECIAL SENSES
Last revised: 04/12/2023
The Senses
Sensory receptors transduce different forms of energy in the “real world” into nerve impulses.
Different sensory perceptions (sound, light, pressure) arise from differences in neural pathways. If the optic nerve delivers an impulse, the brain interprets it as
light.
Functional Categories of Sensory Receptors
Receptors can be classified according to the type of signal they transduce:
Chemoreceptors – sense chemicals in the environment Taste, smell, or blood
Photoreceptors – sense light Thermoreceptors – respond to cold or heat Mechanoreceptors – stimulated by mechanical deformation of the
receptor. Touch Hearing
Nociceptors – sense pain; damaged tissue release chemicals that excite sensory endings
Nociceptors
Pain receptors that depolarize when tissues are damaged. Stimuli can include heat, cold, pressure, or chemicals Glutamate and substance P are the main neurotransmitters. May be activated by chemicals released by damaged
tissues, such as ATP. Perception of pain can be enchanced by emotions and
expectations Pain reduction depends on endogenous opioids.
Nociceptors can be myelinated or unmyelinated Sudden, sharp pain is transmitted by myelinated
neurons. Dull, persistent pain in transmitted by unmyelinated
neurons.
Tonic and Phasic Receptors
Receptors can be categorized based on how they respond to a stimulus.
Phasic: respond with a burst of activity when a stimulus is first applied but quickly decrease their firing rate—adapt to the stimulus—if the stimulus is maintained. (fast-adapting)
Alerts us to changes in the environment Allow sensory adaptation Smell, touch, temperature
Tonic: maintain a high firing rate as long as the stimulus is applied. (slow-adapting)
Cutaneous Receptors Pain, cold, and heat receptors are naked
dendrites Cold receptors – located close to epidermis Warm receptors – located deeper in the dermis. Hot receptors – pain experienced by a hot stimulus is
sensed by a special nociceptor called a capsaicin receptor.
Touch and pressure receptors have special structures around their dendrites.
Meissner’s corpuscles Encapsulated dendrites in connective tissue Changes in texture and slow vibration
Pacinian corpuscles Encapsulated dendrites by concentric lamellae of
connective tissue structures Deep pressure and fast vibrations
Ruffini endings Sustained pressure Enlarged dendritic endings with open, elongated
capsule Merkel’s discs
Expanded dendritic endings Sustained touch and pressure Slow adapting
Two-Point Threshold Test
Measures the density of touch receptors The minimum distance at which two points of contact
can be felt.
High density of receptive fields = shorter minimum distance
Low density of receptive fields = longer minimum distance
HEARING AND EQUILIBRIUMThe Ears
Vestibular Apparatus
Provides a sense of equilibrium Located in the inner ear Consists of:
Otolith organs Linear acceleration
Utricle (horizontal) Saccule (vertical)
Semicircular canals Rotational acceleration
Both structures in the vestibular apparatus are: Filled with endolymph Contain sensory hair cells which
are activated by bending.
Sensory Hair Cells
Hair cells
Sensory nerve fiber Supporting cells
Otoliths
(a) Head upright (b) Head bent forward
Maculaof utricle
Hairs ofhair cells bend
Gelatinousmaterial sags
Gravitationalforce
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Hair cell
Supporting cells
Sensory (afferent) nerve fibers
Hairs
Cupula Cristaampullaris
(a) Head in still position
(b) Head rotating
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(c)
Crista ampullaris
Semicircular canal
Endolymph
Ampulla
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Semicircular Canals
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Clinical Applications
Nystagmus Involuntary oscillations of the eyes
when spinning is suddenly stopped.
Eyes continue to move in the direction of the spin, then jerk rapidly back to the midline.
When a person begins spinning, the cupula bends in the opposite direction.
If the movement suddenly stops, inertia of endolymph causes it to continue moving in the direction of the spin.
This is a normal phenomenon that helps maintain balance during spinning, however, nystagmus can also be a symptom of certain diseases, like Meniere’s disease.
Vertigo Loss of equilibrium with the illusion
of spinning May be caused by anything that alters
the firing rate of one of the vestibulocochlear nervers.
May be due to spinning or pathologically induced by by viral infections.
Tx: Antivert® (meclizine) Anticholinergic action Blocks conduction in the middle ear
vestibular-cerebellar pathways.
Anatomy of the Ear
Structures of the Middle Ear
Cavity between the tympanic membrane and the cochlea
Contains three bones called ossicles: Malleus Incus Stapes Vibrations are transmitted
and amplified along the bones.
The stapes is attached to the oval window, which transfers the vibrations into the inner ear.
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• Group of hearing receptor cells, called hair cells.
• On upper surface of basilar membrane
• Different frequencies of vibration move different parts of basilar membrane
• Particular sound frequencies cause hairs of receptor cells to bend
• Nerve impulse generated
Spiral organ (organ of Corti)
Hair cells
Basilar membrane
(a)
(b)
Scala vestibuli(contains perilymph)
Cochlear duct(contains endolymph)
Scala tympani(contains perilymph)
Branch ofcochlearnerve
Tectorialmembrane
Basilarmembrane
Supportingcells
Nervefibers
Branch ofcochlear nerve
Vestibular membrane
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Organ of Corti
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Figure 10-20 Sound transmission through the ear
Sound waves strikethe tympanicmembrane andbecome vibrations.
The sound waveenergy is transferredto the three bonesof the middle ear,which vibrate.
The stapes is attached tothe membrane of the ovalwindow. Vibrations of theoval window create fluidwaves within the cochlea.
The fluid waves push on theflexible membranes of thecochlear duct. Hair cells bendand ion channels open,creating an electrical signal thatalters neurotransmitter release.
Energy from the wavestransfers across thecochlear duct into thetympanic duct and isdissipated back intothe middle ear at theround window.
Neurotransmitter releaseonto sensory neuronscreates action potentialsthat travel through thecochlear nerve tothe brain.
Ear canal Malleus
Incus
Stapes
Cochlear nerve
Vestibular duct(perilymph)
Roundwindow
Tympanicmembrane
Cochlear duct(endolymph)
Tympanic duct(perilymph)
Ovalwindow
Clinical Applications
Conduction deafness Sound waves are not conducted
from the outer to inner ear. May be due to a buildup of
earwax, too much fluid in the middle ear, damage to eardrum, or overgrowth of bone in the middle ear.
Impairs hearing of all sound frequencies.
Can be helped by hearing aids.
Sensorineural deafness Nerve impulses are not conducted
from the cochlea to the auditory cortex. May be due to damaged hair cells. May only impair hearing of a
particular sound frequency. May be helped by cochlear
implants.
VISIONThe Eyes
Image is inverted on retina due to refraction of light.
Degree of refraction depends on: Refractive index (RI) of
media RI of air = 1.00 RI of cornea = 1.38
Curvature of the interface between the two media.
Functional Anatomy of the Eye
Functional Anatomy of the Eye
Rods: Provide black and white vision under low light intensities
Cones: Provide sharp color vision when light intensity is great Humans have trichromatic
vision due to the presence of three different types of cones: Blue, Green, and Red.
Photoreceptors
Visual Acuity
Sharpness of vision Depends upon resolving power
Ability of the visual system to resolve two closely spaced dots
Visual Abnormalities Myopia (nearsightedness)
Hyperopia (farsightedness)
Astigmatism uneven cornea or lens
Presbyopia hardening of the lens impedes accommodation