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Human Physiology 2 - Unit 1 - Zach H. > Lecture 6: General Sensory Mechanisms III > Flashcards

Lecture 6: General Sensory Mechanisms III Flashcards

1
Q

How is a receptor potential created?

A

Potentials are created here by opening “modality” gated channels such as socium channels that are opened in response to membrane deformation caused by touch, pressure, or heat.

  • Note that receptors generate a type of local, decremental potential that is, essentially a local potential.
  • If the receptor potential is strong enough (through summation), it may generate an action potential at the first node of Ranvier on the primary sensory neuron.
  • Good example is the peripheral receptor - Pacinian corpuscle
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2
Q

Most sensory pathways are made up of which three neurons?

A
  • primary neurons (“first order neurons”)
  • secondary neurons (“second order neurons”)
  • tertiary neurons (“third order neurons”)
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3
Q

What type of receptors do primary neurons originate from?

A

Peripheral Receptors

*example: Merkel’s receptors*

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4
Q

How do primary neurons enter the spinal cord?

A

Via dorsal roots of spinal (cranial) nerves.

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5
Q

Where are the cell bodies of primary neurons located?

A

Dorsal Root Ganglia

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6
Q

Fill in the Blank:

Primary neurons synapse in the _____ with _____ neurons.

A

spinal cord; secondary neurons

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7
Q

Where do secondary neurons originate?

A

Gray matter of spinal cord.

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8
Q

Where do secondary neurons synapse with tertiary neurons?

A

Thalamus

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9
Q

True of False:

Secondary neurons travel through the spinal cord in one of the unmyelinated columns.

A

False - travel through spinal cord in myelinated columns.

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10
Q

Do secondary neurons decussate?

A

Yes

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11
Q

Where do tertiary neurons synapse?

A

Synapse in somatosensory cortex.

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12
Q

Where do tertiary neurons travel through on there way to synapse in the somatosensory cortex?

A
  • Travel through internal capsule.
    • myelinated pathway between thalamus and some of the basal nuclei
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13
Q

Where does the signals for two-point discrimination touch travel?

A

Dorsal column-medial lemniscal pathway.

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14
Q

What does two-point touch refer to?

A

“Two-point discrimination” touch refers to the ability to distinguish two separate points as close as 2 millimeters apart.

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15
Q

You know that lateral inhibition occurs at each synaptic level. What are these levels?

A
  • dorsal column nuclei
  • ventrobasal nuclei of thalamus
  • somatosensory cortex
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16
Q

What is lateral inhibition important in blocking in two-point discrimination touch?

A

Lateral inhibition is important in blocking the lateral spread of excitatory signals, thereby increasing the degree of contrast in the cerebral cortex.

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17
Q

What pathway carries two-point discrimination touch?

A

dorsal column-medial lemniscal pathway

  • REMEMBER: this pathway also carries pressure and vibration.
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18
Q

Trace the pathway through the CNS for the dorsal column-medial lemniscal pathway.

A
  • primary neurons are the “peripheral sensory neurons” that original from receptors in the periphery, travel through a spinal nerve and then through the dorsal root of the respective spinal nerve. Cell bodies of these neurons are found in the dorsal rot ganglia.
  • these primary neurons continue into the spinal cord and travel up the spinal cord through the dorsal columns (hence, the name of the pathway).
  • Primary neruons synapse with secondary neurons in the medulla.
  • Secondary neurons travel from the medulla and synapse with tertiary neurons in the ventrobasal complex of thalamus.
  • Tertiary neurons then travel through the internal capsule and synapse in the somatosensory cortex.
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19
Q

In the transmission of pinpoint stimulus signals to the cerebral cortex, at which synaptic levels do divergence occur?

A
  • dorsal column nuclei
  • thalamus
  • cortex
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20
Q

In the dorsal column-medial lemniscal pathway, where do axons from the lower limbs travel?

A

In the medial portions of the two dorsal columns.

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21
Q

In the dorsal column-medial lemniscal pathway, where do axons from the upper limbs travel?

A

In the lateral portions of the two dorsal columns.

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22
Q

What are the medial portions of the two dorsal columns in the dorsal column-medial lemniscal pathway called?

A

each of these areas of the dorsal columns (one per column) is called the fasciculus gracilis.

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23
Q

What are the lateral portions of the two dorsal columns in the dorsal column-medial lemniscal pathway called?

A

Each of these areas of the dorsal columns (one per column) is called the fasciculus cuneatus.

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24
Q

Where do the axons that are traveling in the fasciculus gracilis synapse?

A

Lower medulla in the Nucleus Gracilis.

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25
Q

Where do the axons that are traveling in the fasciculus cuneatus synapse?

A

Lower medulla in Nucleus Cuneatus.

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26
Q

True or False:

Secondary neurons travel through the brainstem as paired tracts referred to as the medial lemniscus.

A

True

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27
Q

In what portion of the thalamus do secondary neurons synapse with tertiary neurons?

A

basolateral nucleus of the thalamus

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28
Q

In the dorsal column-medial lemniscal pathway, which neuron (primary, secodary, or tertiary) is the one that decussates?

A

Secondary Neurons

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29
Q

What are the characteristics of fast pain?

A
  • it is felt within 0.1 seconds after stimulus is applied.
  • it is not felt in most deeper tissues.
  • it is generally elicited by mechanical and thermal stimuli.
  • it is typically carried by A-delta pain fibers (myelinated fibers)
  • these pain fibers typically terminate in lamina I (lamina marginalis) of the dorsal horns of the spinal cord.
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30
Q

True or False:

Pain receptors (nociceptors) are free nerve endings.

A

True

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31
Q

What are the characteristics of slow pain?

A
  • slow pain begins about 1 second after stimulus is applied and increases over several seconds.
  • it may be described as aching, slow burning, throbbing, nauseous, and chronic.
  • it can be elicited by mechanical, thermal, and chemical stimuli.
  • slow chronic pain is carried by C type fibers which mostly terminate in layers II and III (substantia gelatinosa) of the dorsal horns of the spinal cord.
32
Q

What are the only two sensations that are carried by both type A-gamma and type C fibers?

A
  • cold
  • warmth
33
Q

What pathway does pain travel through?

A

anterolateral pathways

34
Q

Where do primary pain fibers synapse, and with what?

A

In dorsal horns of the spinal cord (layers I, II, and III) with the secondary fibers.

35
Q

Once primary pain fibers synapse in the dorsal horns of the spinal cord with secondary fibers, what do secondary fibers immediately do?

A

Decussate and make up the anterolateral pathways.

36
Q

What tract do fast pain fibers make up?

A

neospinothalamic tracts

37
Q

You know that fast pain fibers make up the neospinothalamic tracts. Where do they synapse and terminate at in the thalamus?

A

Synapse and terminate in the ventrobasal nuclei of the thalamus.

38
Q

Which layers do C fibers synapse?

A

layers I and II

39
Q

Which layer do type A-dleta fibers synapse?

A

layer I

40
Q

What pathway does slow pain fibers make up?

A

paleospinothalamic pathway

41
Q

True or False:

Most of the paleospinothalamic secondary fibers terminate throughout the brainstem, although some pass all the way to the thalamus.

A

True

42
Q

What fiber type in the fast-pain pathway uses glutamate as its neurotransmitter?

A

Type A-delta fibers.

43
Q

What neurotransmitters do type C fibers of the slow, chronic-pain path release?

A

Both glutamate and substance P.

44
Q

Does glutamate act instantaneously?

A

Yes

45
Q

True or False:

Substance P is released more rapidly from type C fibers of the slow, chronic-pain pathway.

A

False - glutamate acts instantaneously, but substance P is releases more slowly.

46
Q

What causes Brown-Sequard syndrome?

A

Occurs when there is a hemisection of the spinal cord.

47
Q

You know that Brown-Sequard Syndrome occurs when there is a hemisetion of the spinal cord, but what motor functions are blocked with this syndrome?

A

ALL motor functions are blocked on the side of the transection in all segments below the level of the transcetion.

48
Q

Which sensations are lost on the opposite side of the body in patients with Brown-Sequard Syndrome?

A

Sensations of pain, heat, and cold (spinothalamic pathway) are lost on the OPPOSITE side of the body in dermatomes 2 - 6 segments below the level of the transection.

49
Q

Which sensations are lost on the same side of the body as the hemisection in patients with Brown-Sequard Syndrome?

A

Kinesthetic and position sensations, vibration sensation, discrete localization, and two-point discrimination are lost on the side of the transection in all dermatomes below the level of the transection.

  • Sensations lost:
    • kinesthetic and position
    • vibration
    • discrete localization
    • two-point discrimination
  • On the sode of the transection in ALL dermatomes below the level of the transection.
50
Q

Is crude touch lost in patients with Brown-Sequard Syndrome?

A

No, because it is poorly localized, thus it still persists because of partial transmission in the opposite spinothalamic tract.

51
Q

Why is “light touch” impaired on the side of the transection in patients with Brown-Sequard Syndrome?

A

Because the principal pathway for the transmission of light touch, the dorsal column, is transected. That is, the fibers in this column do not cross to the opposite side until they reach the medulla of the brain.

52
Q

True or False:

Fast-sharp pain fibers continue up the spine in the lateral pain pathway and slow-chronic pain fibers continue in the anterolateral pain pathways.

A

True

53
Q

What are the 3 major components of the analgesia system?

A
  • Periaquaductal gray and periventricular regions of brainstem and third ventricle.
  • Raphe magnus nucleus and reticular nuclei in medulla.
  • Pain inhibitory complex in dorsal horns of spinal cord.
54
Q

What are the 3 types of receptors that discriminate thermal gradations?

A
  • Cold Receptors
  • Warmth Receptors
  • Pain Receptors
55
Q

What type of fibers (C or A-delta) are warmth sensations mainly transmitted over?

A

C-type fibers

56
Q

Which receptor is more numerous, cold or warmth receptors?

A

Cold receptors are 3-10 times as numerous as warm nerve receptors.

57
Q

Which type of fibers carry cold receptor sensations?

A

Small type A-delta myelinated endings.

58
Q

True or False:

Cold and warmth receptors are thought to be stimulated by changes in their metabolic rates.

A

True

59
Q

When does referred pain occur?

A

Occurs when visceral pain fibers are stimulated and stimulate some of the pain fibers that conduct pain signals from the skin.

60
Q

True or False:

Severe pain results when there is diffuse stimulation of pain nerve endings throughout the viscera (as opposed to highly localized types of damage to the viscera).

A

True

61
Q

Fill in the Blank:

All visceral pain from the thoracic and abdominal cavities is transmitted via _____ _____ pain fibers.

A

Type-C Fibers

62
Q

What are headaches a result of?

A

Headaches are the result of pain referred to the surface of the head from deep head structures.

63
Q

True or False:

The brain itself is almost completely insensitive to pain.

A

True

64
Q

What can cause intracranial headaches?

A
  • Headache of Meningitis
  • Headache caused by Low Cerebrospinal Fluid Pressure
  • Migraine Headache (result from abnormal vascular phenomena)
  • Alcoholic Headache
65
Q

What can cause extracranial types of headaches?

A
  • Headache resulting from Muscle Spasm
  • Headache caused by irritation of Nasal and Accessory Nasal Structures
  • Headache caused by Eye disorders
66
Q

Characterize headaches caused by meningitis, migraines, and removal of spinal fluid.

A
  • Meningitis
    • one of the most severe headaches
    • causes inflammation of all of the meninges
      • including sensitive areas of the dura and areas around the venous sinuses
    • damage can cause extreme headache pain referred over the entire head
  • Migraines
    • may result from abnormal vascular phenomena
    • begin with various prodromal sensations:
      • nausea
      • loss of vision in part of the field of vision
      • visual aura
      • other types of sensory hallucinations
    • Prodromal symptoms begin 30 min. to 1 hour before headache begins.
    • Occur twice as frequently in women as in men
  • Low Cerebrospinal Fluid Pressure
    • removing as little as 20 milliliters of fluid from the spinal canal, particularly if the person remains in an upright position, ofter causes intense intracranial headache
    • removing this fluid removes part of the flotation for the brain
    • weight of the brain stretches and otherwise distorts the various dural surfaces and thereby elicits the pain that causes the headache
67
Q

What is the definition of refraction?

A

Is the bending of light waves at an angulated surface of a transparent material.

68
Q

What is the definition of refractive index?

A

Is the ratio of the velocity of light in air to the velocity of light traveling in the substance. RI of air = 1.00

69
Q

What is the definition of refractive power?

A

Is a measure of how much a lens bends light waves. It is measured in diopters.

* 1 diopter = 1 meter divided by the focal length of a lens. *

70
Q

What is the definition of focal point?

A

The point through which all parallel rays of light will pass after passing through each part of the lens.

71
Q

What is the definition of focal length?

A

The distance from the center of the lens to the focal point.

72
Q

What is the definition of emmetropia?

A
  • Refers to the normal eye with regard to depth of focus.
  • Parallel light rays from distant objects are in sharp focus on the retina when the ciliary muscle is completely relaxed.
  • ALL distant objects can be seen clearly.
73
Q

What is the definition of hyperopia?

A
  • Farsightedness
  • Usually due to an eyeball that is too short or, occasionally a lens system that is too weak.
  • ALL distant objects can be seen clearly.
74
Q

What is the definition of myopia?

A
  • Nearsightedness
  • When ciliary muscle is completely relaxed, light rays coming from distant objects are focused in front of the retina.
  • Usually due to too long of an eyeball.
75
Q
A

Human Physiology 2 - Unit 1 - Zach H. (9 decks)

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