Sensory Physiology

1
Chapter 10

• Sensory Physiology

2

• What is reality?!

3
Web sites for images used

• www.macula.org/anatomy/retinaframe.html (check
  it out!)
• www.trueorigin.org/retina.asp
• thalamus.wustl.edu/course/eyeret.html
• faculty.washington.edu/chudler/retina.html
• www.optobionics.com/artificialretina.htm

4

• SENSES

5
Sensory Receptors

• Perceptions of the world are created by the brain
  (CNS) from info derived from the sensory
  receptors (neurons) of the PNS.
• Receptors transduce (change) different forms of
  sensation to nerve impulses.

6
Note Receptor
7
Functional Categories of Sensory Receptors

• Photoreceptors light
• Chemoreceptors chemicals
• Thermoreceptors temperature.
• Mechanoreceptors touch and pressure
• Nociceptors pain
• Proprioceptors body position

8
Categories of Sensory Receptors

• Note
• Sensation of chemicals can be
• Airborne -smell
• Dissolved- taste
• Internal- pain!

9
Sensory Adaptation

• Tonic receptors
• Produce constant rate of firing as long as
  stimulus is applied.
• Pain.
• Phasic receptors
• Burst of activity but quickly reduce firing rate
  (adapt) if stimulus maintained.
• Sensory adaptation
• Temperature

10
Sensory Adaptation
11
Senses

• Adequate stimulus
• least amount to activate a receptor.

12
Senses

• Regardless of how a sensory neuron is stimulated,
  only one type of sensation will be perceived.
• e.g. bonk on head-gt see stars!

13
Receptor Potentials

• In response to stimulus, sensory nerve endings
  produce a local graded change in membrane
  potential called receptor potential.
• Analogous to EPSPs.

14
Senses

• General senses tactile sensation (touch,
  pressure, stretch, vibration), temperature, pain,
  proprioception, itch
• Special senses vision, hearing, smell, taste,
  and equilibrium

15

• TOUCH

16
Cutaneous Sensations

• Temperature
• - relative changes in temperature
• - free nerve endings
• cold-more of them, less warm
• heat-deeper in skin
• - sense 20-40o C (rest is sensed as pain)

17
Cutaneous Sensations

• Hair follicle receptors
• - free nerve endings wrapped around hair
  follicle
• - detect light touch (from bending of hair)
• Itch receptors
• - chemoreceptors (histamine or bradykinin)

18
Cutaneous Sensations

• Merkel discs
• - expanded dendritic ending free nerve ending
  surrounded by disc shaped epidermal cells
• - detect light touch (and steady pressure)

19
Cutaneous Sensations

• Encapsulated dendritic endings
• - sensory neurons inside connective tissue
  capsule
• Meissners corpuscles
• - nerve ending plus Schwann cell plus connective
  tissue
• - light touch (and stroking), especially in
  hairless skin
• Pacinian corpuscles
• - nerve ending plus many layers of collagen and
  flat cells
• - vibration
• - deep in dermis

20
Cutaneous Sensations
21
Receptive Fields

• Receptive field
• a sensory receptor only responds to stimuli
  located inside their receptive field.
• Think of it as the territory for which each
  neuron is responsible!

22
Receptive Fields

• Back and legs have few sensory endings.
• Receptive field of each is large.
• Fingertips have large of cutaneous receptors.
• Receptive field of each is small.

23
Two-Point Touch Threshold

• Two-point thouch threshold
• minimum distance at which 2 points of touch can
  be perceived as separate.
• It is a way to determine the size of the
  receptive fields

24
Two-Point Touch Threshold
25
Proprioreceptors

• Proprioreceptors
• Detect stretch
• Tell you location of body parts!
• Protect against overstretching.

26
Proprioreceptors

• Muscle spindles
• - in muscles
• - initiate reflex to counteract stretch
• Golgi tendon organs
• - in tendons
• - initiate reflex to counteract stretch
• Joint kinesthetic receptors
• - location of joint in space, angle of bending of
  joint
• - include Pacini, Ruffinis corpuscles, free
  nerve endings

27

• PAIN

28
Pain

• Nociceptors (pain)
• Use substance P or glutamate as NT.
• Respond to chemicals from injured cells (ATP,
  bradykinin).
• Both myelinated and unmyelinated.
• Signals trouble, pay attention!
• Mysterious!

29
Pain

• TRPV1
• - Heat is felt as pain!
• - responds to heat, chili peppers, garlic!
• - aka vanilloid receptor, capsaicin receptor
• - part of TRP family of channels which respond
  to
• both temperature and chemicals
• - Ca for Na
• - Non heat sensitive analogue in spleen,
• lung,intestine
• - Naturopathic (i.e. unexplained) pain?
• brain.phgy.queensu.ca/pare/assets/520Somatic20Se
  nses20Slides.pdf
• http//www.eurekalert.org/pub_releases/2005-05/cp-
  aot051805.php

30

• TASTE

31
Human Taste Receptors
The Human Tongue
Microvilli
Papillae withTaste Buds
Taste Pore
ReceptorCells
SupportingCells
A Taste Bud
32
Taste

• Gustation
• Taste cells epithelial cells
• Are clustered in barrel-shaped taste buds.
• Taste cells are not neurons, but act like them.

33
Taste

• Salty, sour, sweet, bitter,unami.
• Current thinking each taste bud contains taste
  cells responsive to each of the above (so all
  parts of the tongue can taste everything).
• Mixed info is relayed by the connecting fibers
  resulting in a complex medley of tastes.

34
Taste

• Salty
• Na channels.
• Anions such as Cl modify perceived saltiness.
• Sour
• H channels
• Sweet and bitter
• receptors coupled to G-proteins (or IP3)
• Unami
• glutamate (msg)

35

• SMELL

36
Smell (olfaction)

• Olfactory receptor cells bipolar neurons, in
  nose.
• Supporting cells (epithelial) make certain
  odorants less lipid soluble
• basal cells stem cells!!!
• Axons of sensory neurons project directly up into
  olfactory bulb of cerebrum.
• Neurons in olfactory bulb then project to
  amygdala, etc.

37
Smell
38
Smell

• Olfactory receptor cells
• Thousands of different receptors!
• Amplified by second messengers (G proteins).
• Medley of info leads to 10,000 smells.

39

• HEARING

40
Sound

• Sound waves
• Frequency
• Measured in hertz (cycles per second).
• Greater the frequency the higher the pitch.
• Intensity (loudness)
• Amplitude of sound waves.
• Measured in decibels (db).

41
Ear
42
Ear

• Outer ear tympanic membrane (eardrum) amplifies
  sound waves
• Middle ear small bones vibrate
• Inner ear cochlea (winds around, fluid-filled)
  contains organ of Corti (aka spiral organ).

43
Ear

• Organ of Corti contains hair cells (epithelial)
  with stereocilia.

44
Hair cells
45
Ear

• Sound waves travel into ear -gt stereocilia on
  hair cells in organ of Corti bend -gt neurons -gt
  brain

46
Ear

• Frequency (pitch) sorted in cochlea by location
• Intensity more NT, more frequent AP.

47
Hearing Impairments

• Conduction deafness
• - Impaired outer or middle ear.
• - Hearing aids.
• Sensorineural (perception) deafness
• - Impaired cochlea or auditory cortex.
• - Cochlear implants plasticity of auditory
  cortex.

48
Vestibular Apparatus

• Vestibular apparatus
• - Inner ear (semicircular canals)
• - Equilibrium, vertigo
• - also by bending of stereocilia of hair cells.

49
Vestibular Apparatus
50

• VISION

51
Vision

• Wavelengths 400 700 nm constitute visible light
  for humans.

52
TheHumanEye
VitreousHumor
Retina
Lens Muscle
Sclera
Ligaments
Choroid
Iris
Fovea
Lens
Pupil
Cornea
AqueousHumor
Optic Nerve
eyelid
Blind Spot
53
EYE

• Sclera white, connective tissue
• Cornea transparent, good at self-repair
• Pupil central opening
• Iris colored muscle
• Aqueous and vitreous humor
• Retina

54
EYE
55
IRIS

• Iris
• Bright light parasympathetic circularly
  arranged smooth muscles contract -gt smaller pupil
• Dim light sympathetic radially arranged smooth
  muscles contract -gt larger pupil

56
(No Transcript)
57
Refraction

• Refraction bending of light when it passes from
  a medium of one density into a medium of another
  density.
• Result image is inverted on retina.

58
Refraction
59
Visual Acuity

• Visual Acuity
• Sharpness of vision.
• Depends upon resolving power
• Ability of the visual system to resolve 2 closely
  spaced dots.
• Myopia (nearsightedness)
• Image brought to focus in front of retina.
• Hyperopia (farsightedness)
• Image brought to focus behind the retina.
• Astigmatism
• Asymmetry of the cornea and/or lens.
• Images of lines of circle appear blurred.

60
Visual Acuity
61
Accommodation

• Accomodation
• - Ability of the eyes to keep the image focused
  on the retina as the distance between the eyes
  and object varies.
• - Due to ciliary muscle and flexibility of lens.
• Presbyopia less accomodation, usually with age.

62
Accommodation
63
Accomodation
64

• RETINA

65
Retina

• Photoreceptors rods and cones!
• Other neurons bipolar, amacrine, horizontal,
  ganglion cells.
• Retinal pigmented epithelium
• One cell thick
• Phagocytosis
• Protective pigments

66
Retina
Light
67
Human Retina

• Inverted
• Light passes through neurons or wires before
  hitting the photoreceptors.

68
Retina
69
Photoreceptors Rods Cones
Optic Nerve
light
Signal-ProcessingNeurons
GanglionCell
Membrane discs bearingrhodopsin
70
Retina
71
Retina
72
Retina
73
Blind spot

• Optic disc ganglion nerve fibers gather as optic
  disc, and exit as OPTIC NERVE
• This results in a BLIND SPOT.
• Blood vessels also enter and exit at the blind
  spot.

74
Blind spot
75
Photoreceptors

• Rods
• - Light leads to bleaching reaction.
• . Rhodopsin dissociates into retinal and
  opsin.
• . Dark current stops.
• . Inhibition of bipolar neurons stops, and
  AP fire!
• Cones similar.
• Dark current is perhaps like braking a car at a
  stoplight its faster to just release brakes
  than to entirely start the car!

76
Photoreceptors

• Dark current Na channels open all the time and
  inhibitory NT are being released
• Until free opsins are present (due to light!).
• How? Each opsin associates with hundreds of
  G-proteins called transducins (which amplify the
  signal).
• Light induced change in opsin causes dissociation
  of G-proteins and
• Na channels close.

77
Photoreceptors
Na channels close, inhibitory NT isnt
released Bipolar cell releases excitatory NT
This stimulates ganglion cell to fire an AP down
the optic nerve!
78
retina
79
Rods vs. Cones

• Rods best for night vision, low light
• Rods absorb blue-green (not red)
• Cones less sensitive than rods to light.
• Cones provide color vision and greater visual
  acuity.
• Humans (trichromats) blue, red, green cones (by
  what absorb).

80
Cones

• Each type of cone contains retinal plus a special
  pigment/opsin.
• Gene for green and red opsins are on X
  chromosome men are more likely to be missing one
  and therefore colorblind.

81
Cones
M
L
S
82
Convergence

• Convergence
• 120 million rods, 6 million cones, yet only 1.2
  million axons enter the optic nerve

83
Convergence
84
Fovea

• Fovea contains only cones.
• Each cone converges with just one bipolar neuron.
• Best visual acuity.
• (2 u vs. 1 mm2 at periphery of retina!)

85
Fovea
86
Fovea
87
Fovea
88
Vision

• Saccadic eye movements
• Small, quick movements to move focus.
• Eyes appear still.
• Keeps words focused at fovea as read!
• Prevents too much bleaching.

89
Neural Pathways from Retina

• RIGHT half of visual field projects to LEFT half
  of retina of both eyes.
• In brain LEFT LGN (lateral geniculate nucleus)
  receives input from both eyes from the RIGHT half
  of the visual field.
• And viceversa!
• Each retina projects both ipsilaterally and
  contralaterally!

90
Neural Pathways from Retina
91
Vision

• LGN (in thalamus, in diencephalon, forebrain)
• Projects to ocular dominance columns in visual
  cortex (occipital lobe, cerebrum/telecephalon,
  forebrain)

http//neuro.med.harvard.edu/site/Shatzweb
92
Vision

• Binocular vision (both eyes at once!)
• - Activity-dependant wiring
• neurons which fire together, wire together
• Critical period
• use it or lose it
• true of other brain (and body) functions!

93
Vision

• Brain breaks down the info from your eyes, then
  reconstructs it into one image.

94
Vision

• Cortex neurons specific to..
• Rapid left to right movements
• Slow left to right movements
• Faces
• Edges
• Etc.

95

• Furthermore

96
Synestaesia

• Synestaesia
• Humans with unusual, linked senses.
• Some artists!
• e.g. colored hearing, noisy smells, smelly
  touch, etc.!!!

97
Other senses

• Animals have sensory abilities we dont have.
• - They see, hear, taste, touch differently.
• - They sense other forms of info (magnets,
  electrical fields, etc.).
• Cats vomeronasal?!
• Birds magnetic fields of the earth
• Electric fish
• http//faculty.washington.edu/chudler/amaze.html

98
Electrolocation