The sensory system

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The Sensory System
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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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The General Senses

• Sensory receptors specialized monitoring cells
• Free nerve endings simplest type, they are
  sensory neuron dendrites
• Adaptation reduction in sensitivity in the
  presence of constant stimulus
• RAS in the midbrain, it affects out state of
  consciousness

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• General senses temperature, pain, pressure,
  touch, vibration proprioception (body position)
• Special senses vision, hearing, smell
  (olfaction), taste (gustation), balance
  (equilibrium)

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General sense receptors

• Are simple, found everywhere and are classified
  by their stimulus
• Nociceptors sensitive to pain
• Thermoreceptors heat
• Mechanoreceptorstouch, pressure,
• Chemoreceptors chemicals
• Their info goes to the primary sensory cortex
  only 1 reaches the cortex

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Thermoreceptors

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

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Mechanoreceptors

• Membrane distortion opens ion channels to create
  impulses.3 classes
• Tactile touch
• Baroreceptors pressure
• Proprioceptors body position
• TACTILE receptors simple or complex,
  superficial or deep, fine (provide detailed info)
  or crude (provide little information)

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Baroreceptors.

• Stretch receptors (free nerve endings) that
  monitor changes in organ pressure (bladder,
  lungs, vessels, digestive tract)
• Rapidly adapting
• Generate AP from their dendrites when organs are
  stretched/change position
• They monitor blood pressure, respiration,
  digestion, 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 triggers resp. adjustments
• Aortic/Carotid bodies sensitive to changes in
  pH/CO2/O2 blood levels triggers 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 info from these receptors is monitored
  subconsciously

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Olfaction The sense of Smell

• Paired olfactory organs containing receptors,
  supporting cells stem cells
• olfactory glands produce mucus
• olfactory receptor cells are highly modified
  neurons (chemoreceptors)
• Pathway olf.epitheliumgtolf.bulbsgtolf.tractsgtcort
  ex

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Gustation.taste

• Taste buds individual organs containing
  gustatory supporting cells
• Chemicals contact taste hairs which change the MP
  of taste cell
• 4 primary taste sensations sweet, salt, sour,
  bitter
• Pathway sensory receptorsgtmedullagt
  thalamusgtprimary sensory cortex

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Vision

• Accessory structures palpebrae, eyelashes
  brows, exocrine glands, lacrimal glands,
  conjunctiva and 6 occulomotor muscles.
• The eye is hallow divided into anterior and
  posterior cavities
• Its walls are made of 3 tunics fibrous,
  vascular and neural

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Eye anatomy..

• Refer to your dissection lab.
• http//www.hhmi.org/senses/a/a110.htm
• Breaking the Code of Color
• How we see things that move

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Retinal organization

• Several cell layers
• Photoreceptor cells (rods cones)
• Bipolar cells
• Ganglion cells
• Optic Disc - blind spot

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Accommodation

• The process of focusing an image on the retina by
  changing lens shape
• Focusing (producing a clear image)
• light bends/refracts passing from 1 medium to
  another
• The lens changes shape to keep the image focused
  on the retina

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The Physiology of VisionHow is it that we see?

• Our photoreceptors respond to visible light
• Rods sensitive to photons (energy) but not
  their wavelength (color)
• Cones- 3 types, sensitive in bright light,
  responsive to wavelength they allow us to see
  color
• Lack of functional cones colorblindness

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Photoreception

• Light absorption requires rhodopsin a visual
  pigment found in the outer segments of the
  photoreceptor cells
• The process
• Light rhodopson opson activation
  enzyme activation NTmitter release
• Rhodopson regeneration follows

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The visual pathway.

• Photoreceptor stimulation
• Bipolar cell activation
• Stim. 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
• reflex centers of brain stem