Sensory Function and Vision

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Sensory Function and Vision
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The General Senses

• Sensory receptors
• specialized cells that monitor the environment
  and relay information to the CNS.
• Free nerve endings are the simplest type they
  are the dendrites of sensory neurons
• Complex receptors (eyes) are housed in organs
• Some receptors respond to only one kind of
  stimulus

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All sensory receptors send info to the CNS via an
action potential

• At the CNS, info is routed according to the
  stimulus and its location
• The stronger the stimulus, the higher the
  frequency of action potentials
• Some receptors adapt, that is their sensitivity
  to a stimulus is reduced if the stimulus is
  continually applied (smell)
• The RAS can heighten or reduce awareness of
  sensory information

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General versus special senses

• General sense receptors included those for
  temperature, pain, pressure, touch, vibration
  proprioception (body position)
• These receptors are very simple in nature

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Special senses

• Special senses monitor vision, hearing,
  olfaction, gustation, and equilibrium through
  specialized sense organs
• These sense organs are highly specialized

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General sense receptors

• Are simple, found everywhere and are classified
  by their stimulus
• Nociceptors sensitive to pain
• Thermoreceptors respond to heat
• Mechanoreceptorsrespond to touch/pressure
• Chemoreceptors response to chemicals
• Only 1 of the info they provide ever reaches the
  cerebral cortex (our consciousness)

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Nociceptors/Pain receptors

• found in joints, periosteum of bone and skin
• do not adapt!
• 2 types of axons carry the painful sensations
• Fast pain sensations (localized, shooting pain)
  are carried by myelinated axons
• Slow pain sensations (generalized, aching pain)
  are carried by unmyelinated axons it is
  difficult to pinpoint the stimulus location
• Referred pain is the perception of pain coming
  from a body area that is NOT stimulated
• Pain originating in viscera is felt on body
  surfaces

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Referred pain

• For example, pain produced by a heart attack may
  feel as if it is coming from the arm because
  sensory information from the heart and the arm
  converge on the same nerve cells in the spinal
  cord.

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Thermoreceptors

• Free nerve endings in skin, muscle, liver, and
  hypothalamus
• they adapt quickly
• Cold receptors respond to temps lt50
• 4Xs as numerous as warm receptors
• Warm receptors respond to temps gt113
• Both are structurally identical

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Mechanoreceptors

• Membrane distortion opens mechanically regulated
  ion channels to create impulses. There are 3
  classes
• Tactile respond to touch
• Baroreceptors respond to pressure
• Proprioceptors respond to changes in body
  position

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Tactile receptors

• May be simple or complex, superficial or deep,
  fine (provide detailed information) or crude
  (provide little information)
• Merkels fine touch and pressure
• Pacinian deep pressure
• Meissners fine touch and pressure in select
  areas
• Ruffini pressure or distortion in deep dermal
  layers

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Baroreceptors are.

• stretch receptors that monitor changes in organ
  pressure in distensible organs
• rapidly adapting
• Generate an AP from their dendrites when organs
  are stretched or change position
• They monitor BP, respiration, digestion, and
  urinary control

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Chemoreceptors Only respond to dissolved
chemicals

• Rapidly adapting found in olfaction, taste the
  CNS at
• Medulla receptors are sensitive to pH/CO2
  changes in CSF trigger respiratory adjustments
• Aortic/Carotid bodies sensitive to changes in
  pH/CO2/O2 blood levels trigger adjustments in
  respiration and cardiovascular activity

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Proprioceptors.

• Monitor joint position muscle contraction
• DO NOT ADAPT
• Structurally complex are 2 types
• Tendon organs monitor tendon strain
• Muscle spindles monitor muscle length
• Most information from these receptors is
  monitored subconsciously
• Are vital for normal skeletal motor function

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Olfaction -The Sense of Smell

• Consists of paired olfactory organs made of
  epithelium containing olfactory receptors,
  supporting cells stem cells
• the receptor cells are highly modified neurons
  (chemoreceptors)
• Contains olfactory glands that produce a
  multifunctional mucus
• Sensory Pathway olf.epitheliumgtolf.bulbsgtolf.tra
  ctsgtcortex
• http//www.bbc.co.uk/science/humanbody/body/factfi
  les/smell/smell_ani_f5.swf

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The olfactory organs
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Gustation.taste

• http//www.bbc.co.uk/science/humanbody/body/factfi
  les/taste/taste_ani_f5.swf
• Taste buds are organs containing gustatory
  supporting cells that lie within papillae
• Chemicals contact taste hairs which change the MP
  of taste cells leads to an AP in the sensory
  neuron
• 4 primary taste sensations sweet, salt, sour,
  bitter
• Sensory Pathway sensory receptorsgtmedullagt
  thalamusgtprimary sensory cortex

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A complex sensory organ the eye.

• is surrounded by accessory structures that act to
  protect, lubricate, and support it
• is a light, compact, durable, and highly
  specialized hollow organ that weighs about 8 oz
  and measures 1 inch in diameter.
• is divided into anterior (aqueous) posterior
  (vitreous) cavities.
• its walls are made of 3 tunics

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Accessory structures of the eye

• eyelids (palpebrae)
• eyelashes brows
• exocrine glands
• lacrimal apparatus
• Conjunctiva
• 6 extrinsic occulomotor muscles
• the inferior, superior, lateral and medial
  rectus muscles
• the superior and inferior oblique muscles

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Eye anatomy..

• http//www.macula.org/anatomy/eyeframe.html
• The hollow eye is divided into 2 cavities
• An anterior cavity which contains aqueous humor
• A posterior cavity which holds vitreous humor
• Humors act to stabilize eye shape and provide
  nutrients

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Eye anatomy tutorial

• http//www.wisc-online.com/objects/index_tj.asp?ob
  jidAP14304

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The Tunics of the eye

• Fibrous - the sclera anterior cornea
• Vascular contains blood vessels, lymphatics,
  choroid intrinsic muscles of the iris ciliary
  bodies (they support the lens)
• Neural the retina, it contains the rods and
  cones (photoreceptor cells), bipolar ganglion
  cells

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Retinal organization

• The retina is made of several cell layers
• Photoreceptor cells rods lie along the
  periphery cones lie at the back of the retina
• Bipolar cells synapse with the rods and cones
• Ganglion cells synapse with the bipolar cells
• The axons of the ganglion cells form the optic
  nerve
• http//www.macula.org/anatomy/retinaframe.html
  http//www.macula.org/anatomy/anatomy.html

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• Macula lutea area on the retina where the
  visual image forms, it contains only cones with
  the greatest numbers at the fovea centralis
• Optic Disc or blind spot is the area where the
  ganglion cell axons exit the eye to form the
  optic nerve

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Other structures of the eye

• Lens held in place by suspensory ligaments, it
  functions to focus the visual image onto the
  retina
• Cornea clear portion of the fibrous tunic it is
  contiguous with the sclera
• Iris part of the vascular tunic, it contains
  blood vessels, pigment, and 2 smooth muscle
  layers to control the width of the pupil.
• Ciliary body a thick region of the choroid that
  encircles the lens and supports the suspensory
  ligments of the lens

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Accommodation- focusing an image on the retina
by changing lens shape

• light bends/refracts as it passes from 1 medium
  to another. In the eye it goes through the
  cornea, a. humor, lens, v. humor. The
  refraction of light is constant through all but
  the lens
• The lens changes shape to keep the image focused
  on the retina for greatest visual acquity
• Accommodation occurs with response to light and
  to the distance of the object being viewed
• http//www.kscience.co.uk/animations/eye.swf

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The Physiology of VisionHow is it that we see?

• Photoreceptors respond to visible light
• Rods sensitive to photons (energy) but not
  their wavelength (color) allow for vision at
  night/dim light
• The 3 types of Cones (green, red, blue) need
  bright light are responsive to wavelength
  they allow us to see color
• Lack of functional cones colorblindness

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Photoreception

• Light absorption requires rhodopsin (opsin
  retinal) a visual pigment found in the outer
  segments of the photoreceptors
• The process
• Light rhodopson opson activation
  enzyme activation alteration of
  neurotransmitter release
• Rhodopson regeneration follows or the
  photoreceptor cells can not respond to further
  stimulation

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The visual pathway.

• Photoreceptor stimulation
• Bipolar cell activation
• Stimulation of ganglion cells whose axons form
  the
• Optic nerve that cross at the diencephalon and
  goes to the thalamus that routes info to the
  visual cortex of occipital lobe and the reflex
  centers of brain stem
• At the optic chiasm, a partial crossover of nerve
  fibers occurs
• http//www.sumanasinc.com/webcontent/anisamples/ne
  urobiology/visualpathways.html

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Your anatomy website

• http//wps.aw.com/bc_martini_eap_3/0,7016,454059-,
  00.html

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• http//www.hhmi.org/senses/a/a110.htm
• Its all in the Brain Illusions reveal the
  brains assumptions, sensing change in the
  environment, vision, hearing, and smell the
  best-known senses

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For use with Eye dissection

• http//www.1800contacts.com/StaticContent/vision10
  1/frames.html