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Physiology > Lecture 4-Sensory > Flashcards

Lecture 4-Sensory Flashcards

1
Q

Define Sensory Transduction

A

The conversion of a specific type of energy (stimulus) into an electrical signal (receptor potentials and nerve impulses)

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2
Q

Define Specificity

A

Each receptor is defined by a narrow range of stimuli.

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3
Q

What is the adequate stimulus?

A

The appropriate stimulus that activates a specific type of receptor at a low energy level.

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4
Q

What composes a sensory system?

A

Sensory receptors + Neural pathways + Target areas in the brain.

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5
Q

What is perception?

A

The internal representation of the outside world.

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6
Q

What are the 4 basic types of information coded by the sensory systems?

A

Modality
Intensity
Location
Timing

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7
Q

Modality

A

Vision, somatic sensation, taste and smell, hearing and balance.

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8
Q

Labeled Line Code

A

Excitation of a given sensory neuron gives rise to the same sensation whether natural or direct electrical stimulation.

It doesn’t matter the type of stimulation, excitation of a specific neuron will produce the same result.

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9
Q

Location

A

Representation of stimulus location is given by the sensory receptors which are arranged topographically.

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10
Q

Insensity

A

Amount of energy is given by the response amplitude of the receptor.
Represented by a change in action potential frequency or an increase in transmitter release.
The size of a receptor potential is related to stimulus intensity, meaning it is graded.

The more the input, the bigger the response.

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11
Q

Timing

A

Duration. Sensory receptor can respond to the stimulus for the duration of a stimulus, or just at the beginning and end of the stimulus.

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12
Q

What is the receptive field?

A

Area within a receptive structure where stimulation excites the cell. A receptor responds only to stimulation within this field.

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13
Q

What is a depolarizing receptor potential?

A

Inward current with positive ions moving into the cell. Will bring the membrane potential closer to the threshold for AP.

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14
Q

What is a hyperpolarizing receptor potential?

A

Outward current with positive ions moving out of the cell. Will move the membrane potential further away from threshold for AP.

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15
Q

What are mechanoreceptors?

A

Respond to mechanical deformation of the surrounding tissue and convert mechanical stimulus into electrical energy. They use stretch sensitive ion channels in the cell membrane that open and allow cations into the cell, which then lead to depolarization.

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16
Q

What do mechanoreceptors of the somatosensory system detect?

A

Touch, muscle stretch and joint position.

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17
Q

What do hair cells in the ear detect?

A

Fluid movement and give rise to sensations of hearing and balance.

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18
Q

What are the touch receptors in skin?

A

Meissner’s corpuscle, Merkel cells, Pacinian corpuscle and Ruffini endings.

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19
Q

What is the modality of touch receptors in skin?

A

Touch

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20
Q

How are intensity and duration coded in touch receptors in the skin?

A

Action potentials

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21
Q

Meissner’s and Pacinian corpuscles adapt ______ to a stimulus, whereas Ruffini’s endings and Merkel cells adapt _______.

A

Rapidly, slowly

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22
Q

What do chemoreceptors detect?

A

Pain, itch taste, smell, O2 and CO2.

Ex: Nasal chemoreceptors bind odorant molecules, a 2nd messenger system causes an increase in cAMP, leading to depolarization.

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23
Q

What do thermoreceptors respond to?

A

Hot, warm, cool or cold. Warm and cold receptors fire continuously (2-5 spikes per second) at 34 degrees C.

Extreme temperatures activate thermal nociceptors, signaling pain.

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24
Q

What do photoreceptors respond to?

A

Hyperpolarize in response to light.

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25
Q

What are Nociceptors?

A

Pain. Signal stimuli that cause tissue damage.

Most likely chemoreceptors responding indirectly to chemicals which are released by noxious stimuli.

TRP channels are involved

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26
Q

What do Mechanical Nociceptors give rise to?

A

A sharp pain, stimulated by strong signals. Pinch or sharp object.

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27
Q

Thermal nociceptors?

A

Activated by heat extremes and strong mechanical stimuli.

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28
Q

Polymodal nociceptors?

A

Slow burning sensation of pain in response to mechanical, thermal and chemical stimuli. Small unmyelinated fibers transmit info. Tooth pulp!

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29
Q

Define submodalities?

A

Receptor subtypes have specific response properties.

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30
Q

What is the submodalities of vision?

A

Different photoreceptors are sensitive to different light wavelengths.

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31
Q

What are the submodalities of hearing?

A

Hair cells and auditory nerves are tuned to specific frequencies and activation of receptors occurs at very low energy levels.

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32
Q

What is the sensory threshold?

A

The lowest stimulus strength a subject can detect. In experiments this is defined as the amplitude detected in half of the trials. Changes in threshold can be a sign of disease, aging, adrenaline, etc.

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33
Q

What is log transformation?

A

Receptors that respond to a wide range of stimulus intensities perform a log transformation in converting the initial stimulus energy (S) into a receptor potential (R). R(alpha)logS

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34
Q

How do receptors which operate over a narrow range usually respond?

A

In a linear fashion. (Wide range=log)

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35
Q

How do receptors respond to a constant stimulus?

A

Adaption. Can be slow or rapid.

36
Q

Compare and contrast between a slowly adapting receptor and a rapidly adapting receptor.

A

A slowly adapting receptor will respond to a prolonged stimulus with a prolonged depolarization and action potential firing.

A rapidly adapting receptor will stop firing during a constant stimulus and is only active when stimulus intensity increases or decreases.

37
Q

Explain the traits of a pacinian corpuscle.

A

Rapidly adapting mechanoreceptor found in skin, joint capsules and the mesentery of the gut. Several layers of fluid-filled connective tissue lamella surround the nerve terminal. Think onion. Constant stimulus-fires at beginning and end. Vibrating stimulus-fires with each cycle

38
Q

What does the timing of AP’s depend upon?

A

The threshold and refractory period.

39
Q

Where the the ____________ neurons convey all _________ information from the limbs and trunk.

A

DRG, somatosensory

40
Q

The _________ nerve relays information from the cranial areas.

A

Trigeminal

41
Q

_____, ________, _______ and ________ sense have specialized sensory terminals and project to dorsal root ganglion neurons.

A

Touch, propioception, nocioception and temperature

42
Q

Do large or small diameter fibers have myelinated axons?

A

Large have myelinated. Small are unmyelinated.

43
Q

What type of fibers carry fast pain?

A

Group II and III.

44
Q

What type of pain do C fibers carry?

A

Slow or “dull” pain.

45
Q

What do rods detect?

A

Dim light, low acuity.

46
Q

Where do rods synapse?

A

Many rods synapse onto a bipolar cell.

47
Q

Where are cones concentrated and what do they detect?

A

The fovea, involved in color vision.

48
Q

How many cones synapse onto a bipolar cell?

A

Only a few synapse onto one bipolar cell.

49
Q

What are the layers of the retina?

A
  1. Pigment Epithelium
  2. Rods and cones
  3. Outer limiting membrane
  4. Muller cells
  5. Horizontal cells
  6. Bipolar cells
  7. Amacrine cells
  8. Ganglion cells
  9. Nerve fiber layer
  10. Inner limiting membrane
50
Q

What are the three regions of the Photoreceptor Structure?

A

Outer-segment, inner segment and synaptic terminal.

51
Q

What does the outer segment contain?

A

Photopigment (absorbs light) and rhodospin/cone pigment. Stacked membranous disks increase membrane surface area and allow concentration of light absorbing molecules.

52
Q

What does the inner segment of the photoreceptor structure contain?

A

Nucleus and biosynthetic machinery.

53
Q

What does the synaptic terminal of the photoreceptor structure contain?

A

Makes contact with the target cell.

54
Q

Describe the steps in phototransduction.

A
  1. cGMP in photoreceptors gates a cation channel. When the channel is open, it allows Na+ to flow into the cell. cGMP concentration is high in the dark, maintaining the channels in an open state and the cell is depolarized. RMP -40 mV.
  2. Light stimulates cGMP phosphodiesterase and cGMP concentration decreases.
  3. As cGMP concentration falls, channels close and the photoreceptor hyperpolarizes.
  4. Decreased release of either excitatory or inhibitory NT from synaptic terminals of the photoreceptor leads to either a depolarization or hyperpolarization of bipolar and horizontal cells.
55
Q

What is the dark current?

A

In phototransduction, it is the high cGMP concentration in the dark that maintainse open channels, allowing Na+ to flow into the cell.

56
Q

Give a brief summary of how a photoreceptor hyperpolarizes.

A
  1. Light leads to formation f Metahodopsin II
  2. Activation of the G protein transducin
  3. Activation of phosphodiesterase
  4. Decrease in cGMP
  5. Cation channels close (Na+ influx stops)
  6. PHOTORECEPTOR DEPOLARIZES
57
Q

How do Olfactory Receptor cells work?

A

Odorant molecules bind to receptors on cilia in the mucus layer. Receptors are coupled to G-proteins which when bound to a odorant molecule activates adenyl cyclase. Adenyl cyclase enhances the conversion of ATP to cAMP, leading to the activation of a cation channel and Na+ influx. AP’s travel down the axon of olfactory receptor cells towards the olfactory bulb. (Other pathways involve PLC and IP3)

58
Q

What are the 5 tastes that taste receptor respond to?

A

Salt, sour, bitter, sweet and umami.

59
Q

Where are taste receptors found?

A

In taste buds on the tongue surface and are constantly replaced.

60
Q

How do taste receptors work?

A

Molecules gate ion channels directly or through second messenger pathways, causing depolarization.

61
Q

What was recently identified as a taste NT?

A

ATP

62
Q

What type of transducers are hair cells?

A

Mechanotransducers.

63
Q

What are tip links?

A

Ion channels are gated by tip links which connect adjacent sterocilia in the hair bundle.

64
Q

At rest, what percentage of the cation channels are open?

A

Approximately 10%.

65
Q

How do you depolarize a hair cell?

A

Pushing the hair bundle in the excitatory direction, towards the tallest cilia, opens more channels and K+ from the endolymph enters and depolarizes the hair cell.

66
Q

How do you hyperpolarize a hair cell?

A

Pushing the bundle away from the tallest cilia closes the cation channels and hyperpolarizes the hair cell.

67
Q

Do hair cells fire AP’s?

A

No. The receptor potential is graded.

68
Q

Where do the sound waves enter the fluid-filled scala vestibuli?

A

At the oval window.

69
Q

Along what membrane does the wave travel along, stimulate hair cells?

A

Basilar membrane.

70
Q

How are inner hair cells stimulated?

A

Inner hair cells are sensory. They are stimulated by the basilar membrane vibrating, and a shearing motion between the stereocilia and tectorial membrane.

71
Q

The _______ hair cells are motile and can change basilar membrane motion.

A

Outer hair cells.

72
Q

How are the cochlea hair cells organized?

A

Tonotopically. High frequencies are at the base, while low frequencies are at the apex.

73
Q

What are the steps in the auditory process?

A
  1. Sound causes hair cells to release the NT glutamate onto afferent nerves.
  2. Cochlear nerves synapse on neurons of dorsal and ventral cochlear nuclei in the medulla.
  3. Axons ascend into the inferior colliculus then the the medial geniculate nucleus of the thalamus.
  4. Fibers then project from the thalamus to he auditory cortex. Tonotopy is preserved at all levels.
74
Q

What does the vestibular system provide?

A

A sense of equilibrium/balance.

75
Q

Where is the vestibular system located?

A

Fluid filled sacs located in the petrous portion of the temporal bone.

76
Q

What to the hair cells of the ampullae do?

A

Hair cells of the ampullae in the semicircular canals respond to head rotation.

77
Q

What do hair cells in the otolith organs do?

A

Respond to linear accelerations of the head.

78
Q

What are the otolith organs?

A

Utricle and Saccule

79
Q

How do the semicircular canals work?

A

Endolymph within the canals stimulates hair cells in the crista ampullaris during head rotation by moving the cupula. Vestibular nerve then carries the signals to the brain.

Even at rest, the vestibular nerve fires action potentials. During a rotation, the firing rate will increase and then adapt.

80
Q

What senses the rotational movement and what senses the linear or horizontal movement?

A

Semicircular canals=rotational

The otolith organs (utricle and saccule)=linear or horizonatal

81
Q

What does each macula contain?

A

A gelatinous membrane and otoconia overlying the hair cells.

82
Q

What are otoconia?

A

Calcium carbonate crystals.

83
Q

What does a hair bundle contain?

A

Several stereocilia and at one side a single kinocilium.

84
Q

What does the kinocilium give the haircell?

A

Directional sensitivite.

85
Q

How does the organization of the utricle and saccule cells provide the brain information on head orientation?

A

They are oriented in different directions

86
Q

What is the Vestibular Ocular Reflex, or VOR?

A

During a head rotation, the vestibular system signals how fast the head is moving and the oculomotor system responds to keep visual field stable. A head movement to the left will result in slow eye movements to the right.

Physiology (2 decks)

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