Sensory Reception

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Sensory Reception

• Chapter 14

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Sensory Systems

• The means by which organisms receive signals from
  the external world and internal environment

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Sensation and Perception

• Sensation is conscious awareness of a stimulus
• Perception is understanding what a sensation
  means
• A perception of wetness arises from numerous
  sensations

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Types of Receptors

• Mechanoreceptors
• Thermoreceptors
• Pain receptors
• Chemoreceptors
• Osmoreceptors
• Photoreceptors

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Assessing a Stimulus

• Action potentials dont vary in amplitude
• Brain tells nature of stimulus by
• Particular pathway that carries the signal
• Frequency of action potentials along an axon
• Number of axons recruited

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Recordings of Action Potentials
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Sensory Adaptation

• A decrease in response to a stimulus being
  maintained at constant strength

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Somatic Sensations

• Touch
• Pressure
• Temperature
• Pain
• Motion
• Position

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Somatosensory Cortex
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Receptors in Skin

• Free nerve ending
• Ruffini ending
• Pacinian corpuscle
• Bulb of Krause
• Meissners corpuscle

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Referred Pain

• Sensations of pain from internal organs may be
  wrongly projected to part of the skin surface
• Heart attack can be felt as pain in skin above
  the heart and along the left shoulder and arm

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Properties of Sound

• Ear detects pressure waves
• Amplitude of waves corresponds to perceived
  loudness
• Frequency of waves (number per second)
  corresponds to perceived pitch

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Taste

• A special sense
• Chemoreceptors
• Five primary sensations
• sweet, sour, salty, bitter, and umami

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Smell

• A special sense
• Olfactory receptors
• Receptor axons lead to olfactory lobe

olfactory bulb
receptor cell
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Anatomy of Human Ear
stirrup
auditory nerve
anvil
hammer
auditory canal
eardrum
cochlea
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Sound Reception

• Sound waves make the eardrum vibrate
• Vibrations are transmitted to the bones of the
  middle ear
• The stirrup transmits force to the oval window of
  the fluid-filled cochlea

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Sound Reception

• Movement of oval window causes waves in the fluid
  inside cochlear ducts

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Sound Reception

• Organ of Corti senses fluid movement
• Hair cells are bent against overlying tectorial
  membrane, and they fire

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Balance and Equilibrium

• In humans, organs of equilibrium are located in
  the inner ear
• Vestibular apparatus

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Dynamic Equilibrium

• Rotating head movements cause pressure waves that
  bend a gelatinous cupula and stimulate hair cells
  inside it

cupula
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Acceleration-Deceleration

• Moving in response to gravity, otoliths bend
  projections of hair cells and stimulate the
  endings of sensory neurons

HEAD LEVEL
otolith
hair cell
HEAD TILTED
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Vision

• Sensitivity to light does not equal vision
• Vision requires two components
• Eyes
• Capacity for image formation in the brain

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Human Eye
sclera
retina
choroid
iris
fovea
optic disk
lens
pupil
cornea
part of optic nerve
aqueous humor
ciliary muscle
vitreous body
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Pattern of Stimulation

• Light rays pass through lens and converge on
  retina at back of eye
• The image that forms on the retina is upside down
  and reversed right to left compared with the
  stimulus
• Brain accounts for this during processing

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Pattern of Stimulation
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Visual Accommodation

• Adjustments of the lens
• Ciliary muscle encircles lens
• When this muscle relaxes, lens flattens, moves
  focal point farther back
• When it contracts, lens bulges, moves focal point
  toward front of eye

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The Photoreceptors

• Rods
• Contain the pigment rhodopsin
• Detect very dim light, changes in light intensity
• Cones
• Three kinds detect red, blue, or green
• Provide color sense and daytime vision

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Organization of Retina

• Photoreceptors lie at the back of the retina, in
  front of a pigmented epithelium
• For light to reach the photoreceptors, it must
  pass layers of neurons involved in visual
  processing

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To the Visual Cortex (1)

• Signals from photoreceptors are passed to bipolar
  sensory neurons, then to ganglion cells

bipolar cell
rod
ganglion cell
cone
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To the Visual Cortex (2)
Visual cortex
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Disorders of the Eye (1)

• Color blindness
• Focusing problems
• Nearsightedness and farsightedness
• Eye diseases
• Trachoma
• Histoplasmosis
• Herpes simplex infection

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Disorders of the Eye (2)

• Age-related problems
• Cataracts
• Macular degeneration
• Glaucoma
• Injuries
• Retinal detachment