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KINE3650 > Lec 5-Ascending Sensory Pathways > Flashcards

Lec 5-Ascending Sensory Pathways Flashcards

1
Q

What is the general pathway for ascending signals from the periphery to the cortex?

A

Ascending signals follow a three (and maybe a little more) neuron chain, involving first-order, second-order, and third-order neurons.

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2
Q

What does the sensory receptor do in the ascending pathway?

A

The sensory receptor sends an action potential down the peripheral process of a pseudo-unipolar neuron.

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3
Q

Where is the cell body of the first-order neuron located?

A

The first-order neuron has its cell body in a dorsal root ganglion.

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4
Q

What is the role of the second-order neuron in this pathway?.

A

The second-order neuron receives input from the first-order neuron and has its cell body in the dorsal horn of spinal grey matter

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5
Q

What is the final destination of the third-order neuron?

A

The third-order neuron has its cell body in the thalamus and serves as a relay for signals heading to the cortex.

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6
Q

What are first-order neurons responsible for in the sensory pathway?

A

First-order neurons transmit sensory information from the periphery to the central nervous system.

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7
Q

What are the characteristics of the fiber connected to the dorsal root in a first-order neuron?

A

The fiber is often myelinated and carries sensory information as action potentials

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8
Q

Which rootlets do first-order neurons typically project through?

A

First-order neurons usually project through the dorsal rootlets of the spinal cord.

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9
Q

How does the process of a first-order neuron enter the spinal cord?

A

The process of a first-order neuron enters the spinal cord through the dorsal root.

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10
Q

Where does a first-order neuron typically synapse?

A

First-order neurons typically synapse in the dorsal horn of the spinal cord.

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11
Q

In which region is the cell body of a second-order neuron located?

A

The cell body of a second-order neuron is typically located in the spinal cord or the brainstem.

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12
Q

Are there interneurons involved in the pathway of second-order neurons?

A

Yes, interneurons can be involved in the pathway of second-order neurons, especially in the spinal cord.

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13
Q

What do first, second and third-order neurons do?

A

First-order neurons transmit sensory information from the body to the spinal cord, second-order neurons relay this information from the spinal cord to the brain, and third-order neurons carry it from the thalamus to the sensory cortex for perception.

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14
Q

In which tract or column is the axon of a second-order neuron found?

A

The axon of a second-order neuron is found in specific tracts or columns depending on the sensory pathway it belongs to.

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15
Q

Where does the axon of a second-order neuron typically synapse?

A

The axon of a second-order neuron typically synapses in a specific region of the brain or thalamus, depending on the sensory pathway.

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16
Q

Where do third-order neurons synapse?

A

Third-order neurons synapse in the sensory cortex of the brain, including areas like the primary somatosensory cortex (SI) and secondary somatosensory cortex (SII).

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17
Q

What type of sensory information is processed by the region where third-order neurons synapse?

A

The region where third-order neurons synapse processes sensory information such as touch, pain, temperature, and pressure.

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18
Q

What sensations are carried by the Anterolateral System (ALS)?

A

Carries sensations such as nociception (pain), thermal sensations (temperature), itch, nondiscriminative touch, pressure, and some proprioception.

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19
Q

What are the components of the Dorsal Column–Medial Lemniscal System (DCMLS)?

A

The Dorsal Column–Medial Lemniscal System consists of the Fasciculus Gracilis, Fasciculus Cuneatus, and Medial Lemniscus.

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20
Q

Anterolateral System Steps

A

1) This sensory input enters the spinal cord via dorsal root ganglia.
2) In the dorsal horn, first-order neurons synapse with second-order neurons, which then decussate (cross to the opposite side) within the spinal cord.

Ascension: The decussated second-order neurons form the spinothalamic tract and ascend in the contralateral (opposite side) white matter of the spinal cord.

Thalamic Relay: As the spinothalamic tract ascends, it reaches the thalamus (specifically the ventral posterior lateral nucleus or VPL), where the second-order neurons synapse with third-order neurons.

Projection to Cortex: Third-order neurons project from the thalamus to the primary somatosensory cortex (S1) and secondary somatosensory cortex (S2) in the cerebral cortex.

Conscious Perception: The sensory information is processed in the cortex, leading to conscious perception of pain, temperature, and other sensations

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21
Q

What sensations are carried by the Dorsal column–medial lemniscal system (DCMLS)

A

Discriminative touch, flutter-vibratory sense, proprioception

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22
Q

What is a receptive field in sensory processing?

A

A receptive field is the area covered by a single sensory receptor.

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23
Q

How does having small receptive fields, like in the fingertips, affect sensory information?

A

Small receptive fields, such as those in the fingertips, provide high-resolution sensory information.

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24
Q

What kind of information do large receptive fields, like those in the back, provide?

A

Large receptive fields, like those in the back, provide low-resolution sensory information.

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25
Q

What are phasic receptors in sensory processing?

A

Phasic receptors are rapidly adapting receptors that respond to changes in a stimulus.

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26
Q

What distinguishes tonic receptors in sensory processing?

A

Tonic receptors are slowly adapting receptors that respond to ongoing, sustained stimuli.

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27
Q

What do interoceptors monitor in sensory processing?

A

Interoceptors monitor the state of the body’s internal environment, providing information about internal conditions.

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28
Q

What is the role of proprioceptors in sensory processing?

A

Proprioceptors are responsible for static position sense and kinesthetic sense, helping us perceive the body’s position and movement.

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29
Q

What do exteroceptors respond to in sensory processing?

A

Exteroceptors respond to touch, pressure, temperature, pain, and flutter-vibration.

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30
Q

What type of fibers are associated with mechanosensitive nociceptors, and what do they respond to?

A

Mechanosensitive nociceptors are associated with Aδ (III) fibers and respond to mechanical stimuli. They have nonencapsulated branching free nerve endings.

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31
Q

Which fibers are involved in temperature-sensitive nociceptors, and what stimuli do they respond to?

A

Temperature-sensitive nociceptors involve both Aδ (III) and C (IV) fibers, responding to temperature changes. They also have nonencapsulated branching free nerve endings.

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32
Q

What are polymodal nociceptors, and which type of fibers are associated with them?

A

Polymodal nociceptors are sensitive to multiple types of stimuli, and they are associated with C (IV) fibers. They have nonencapsulated branching free nerve endings

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33
Q

What are pruriceptors sensitive to, and which type of fibers are involved?

A

Pruriceptors are sensitive to histamine and are associated with C (IV) fibers. They have nonencapsulated branching free nerve endings

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34
Q

Nociceptors

A

These receptors detect pain and respond to harmful or potentially damaging stimuli.

35
Q

Thermoreceptors:

A

These receptors sense temperature and respond to changes in hot or cold stimuli.

36
Q

Mechanoreceptors:

A

These receptors respond to mechanical stimuli like pressure, touch, vibration, and stretching, allowing us to perceive sensations related to physical contact with objects or our environment.

37
Q

What type of receptors are cold receptors, and what type of nerve fibers are associated with them?

A

Cold receptors are associated with Aδ (III) nonencapsulated branching free nerve endings of lightly myelinated fibers.

38
Q

What type of receptors are warmth receptors, and what type of nerve fibers are associated with them?

A

Warmth receptors are associated with C (IV) nonencapsulated branching free nerve endings of unmyelinated fibers.

39
Q

What type of receptors are temperature-sensitive nociceptors, and what types of nerve fibers are associated with them?

A

Temperature-sensitive nociceptors are associated with both Aδ (III) and C (IV) nonencapsulated branching free nerve endings.

40
Q

What are nonencapsulated free nerve endings associated with, and what types of nerve fibers are involved?

A

Nonencapsulated free nerve endings are associated with both Aδ (III) and C (IV) fibers, which are often unmyelinated.

41
Q

What type of nerve fibers are associated with nonencapsulated peritrichial nerve endings, and where are they located?

A

Nonencapsulated peritrichial nerve endings are associated with Aβ fibers, which are myelinated and wrapped around the base of hair follicles. They are stimulated when the hair is bent.

42
Q

What do nonencapsulated tactile receptors do and what kind of nerve fibers are involved?

A

Nonencapsulated tactile receptors sense texture, shape, and edges, and they involve large, myelinated Aβ nerve fibers.

43
Q

What are Meissner’s corpuscles, and what type of nerve fibers are associated with them?

A

Meissner’s corpuscles are encapsulated nerve endings associated with Aβ fibers. They are rapidly adapting and critical for two-point discrimination

44
Q

What are Pacinian corpuscles, and what type of nerve fibers are associated with them?

A

Pacinian corpuscles are the largest mechanoreceptors, and they have Aβ-fiber terminals encapsulated by layers of modified fibroblasts in connective tissue capsules. They exhibit rapid adaptation, likely in response to pressure and vibratory stimuli.

45
Q

What are Ruffini’s end organs?

A

Ruffini’s end organs are encapsulated nerve endings.

46
Q

What type of nerve fibers are associated with Ruffini’s end organs?

A

They are associated with unmyelinated peripheral terminals of Aβ myelinated fibers.

47
Q

What is their adaptation characteristic? (Ruffini end)

A

Ruffini’s end organs are slowly adapting.

48
Q

What type of stimuli do they (Ruffini end) respond to?

A

They respond to stretching of collagen bundles in the skin or joint capsules.

49
Q

What role do Ruffini’s end organs play in sensory perception?

A

They play an important role in kinesthesia (sense of movement) and proprioception (sense of body position).

50
Q

What are Golgi tendon organs (GTOs)?

A

Golgi tendon organs (GTOs) are sensory receptors located in tendons.

51
Q

What type of nerve fibers are associated with Golgi tendon organs (GTOs)?

A

Golgi tendon organs are associated with large-diameter, type Aα (group Ib) sensory fibers.

52
Q

What is the structure of the nerve fibers associated with GTOs?

A

The sensory fibers connected to GTOs have myelinated axon branches that terminate in numerous unmyelinated terminals.

53
Q

Where are the axon branches of GTO-associated sensory fibers located?

A

The axon branches of GTO-associated sensory fibers are located within intrafusal tendon fibers.

54
Q

What is the primary function of Golgi tendon organs (GTOs)?

A

The primary function of GTOs is to respond to the overall tension of tendons.

55
Q

What are the two main pathways within the anterolateral tracts?

A

The anterolateral tracts consist of the direct pathway known as the spinothalamic tract and the indirect pathway known as the spinoreticular tract.

56
Q

What distinguishes the indirect pathway (spinoreticular tract) within the anterolateral tracts?

A

The indirect pathway synapses in the reticular formation before reaching the thalamus, making it “indirect” compared to the direct spinothalamic tract.

57
Q

What types of nerve fibers are associated with first-order neurons in anterolateral nociception?

A

First-order neurons in anterolateral nociception include fast Aδ fibers and slow C fibers.

58
Q

Which type of nerve fibers are most commonly found in the direct pathway of the Spinothalamic pathway?

A

The direct pathway consists of mostly Aδ fibers.

59
Q

What are A-fibers, and what types of information do they transmit?

A

A-fibers are myelinated nerve fibers that transmit nerve impulses at relatively high speeds

60
Q

What are C-fibers, and what types of information do they transmit?

A

C-fibers are unmyelinated nerve fibers that transmit nerve impulses at slower speeds.

61
Q

What is the role of Aα-fibers in the nervous system?

A

Aα-fibers are the largest and fastest-conducting A-fibers. They are responsible for transmitting proprioceptive information related to muscle and joint position, playing a crucial role in motor control.

62
Q

What is the function of Aβ-fibers?

A

Aβ-fibers are myelinated fibers that conduct nerve impulses at a moderate speed. They transmit information related to touch, pressure, and vibration sensations.

63
Q

What types of sensations are transmitted by Aδ-fibers?

A

Aδ-fibers, which are relatively small myelinated fibers, transmit sensations of sharp, localized pain and temperature changes

64
Q

Do most fibers in the direct pathway ascend contralaterally or ipsilaterally?

A

Most fibers in the direct pathway ascend contralaterally, meaning they cross to the opposite side of the spinal cord.

65
Q

Where do most projections of the direct pathway in the Spinothalamic pathway terminate in the thalamus?

A

Most projections of the direct pathway terminate in the Ventral Posterior Lateral nucleus (VPL) in the thalamus.

66
Q

Where does the direct pathway primarily synapse in the spinal cord?

A

Mainly in lamina I of the spinal cord.

67
Q

What kind of sensory quality does the direct pathway provide?

A

Provides precise location and type of pain (e.g., sharp, localized pain).

68
Q

What types of fibers are found in the indirect pathways (e.g., spinoreticular, spinomesencephalic)?

A

Mix of Aδ and C fibers.

69
Q

How is the route of the indirect pathways different from the direct pathway?

A

[Answer] It follows complex pathways with brainstem synapses.

70
Q

What is the primary contribution of the indirect pathways to pain perception?

A

Contributes to overall pain experience, including emotional and autonomic responses.

71
Q

Where do the indirect pathways, such as the spinoreticular and spinomesencephalic tracts, synapse?

A

They synapse at multiple levels of the reticular formation in the brainstem

72
Q

How do most fibers in the indirect pathways ascend?
.

A

Most fibers in the indirect pathways ascend ipsilaterally

73
Q

What are some of the peripheral receptors that can initiate the peripheral process of DCMLS first-order neurons?

A

Meissner’s corpuscles, Pacinian corpuscles, muscle stretch receptors, Golgi tendon organs (GTOs), Ruffini end organs.

74
Q

How do DCMLS first-order neurons project into the spinal cord?

A

They project via the medial division of the dorsal root.

75
Q

Where do DCMLS first-order neurons ascend in the spinal cord?

A

They ascend ipsilaterally via long ascending fibers in the fasciculus gracilis (below T6) and fasciculus cuneatus (above T6) to the nucleus gracilis or nucleus cuneatus in the medulla.

76
Q

Where are second-order neurons of the DCMLS located in the brainstem?

A

Second-order neurons of the DCMLS are located in nuclei gracilis (NG) or nuclei cuneatus (NC) in the posterior medulla.

77
Q

Dorsal (posterior) spinocerebellar tract.

A

Sensory pathway responsible for proprioceptive input from the ipsilateral lower limb and trunk to the cerebellum

78
Q

What type of proprioceptive information does the cuneocerebellar tract transmit, and from which body regions?

A

The cuneocerebellar tract carries proprioceptive information from the neck, upper limb, and upper half of the trunk.

79
Q

What type of proprioceptive input does the ventral spinocerebellar tract transmit, and from which body regions?

A

The ventral spinocerebellar tract carries proprioceptive input from the lower limb and trunk.

80
Q

What is the primary function of the ventral spinocerebellar tract?

A

It is primarily involved in the maintenance of posture and the coordination of limb movements.

81
Q

What type of proprioceptive information does the rostral spinocerebellar tract carry, and from which body regions?

A

The rostral spinocerebellar tract transmits proprioceptive information from the head and upper limb.

82
Q

What is the role of the Dorsal Column-Medial Lemniscal System (DCMLS) in sensory transmission?

A

The DCMLS transmits discriminative touch, proprioception, and vibratory sensations via two main tracts: fasciculus gracilis (lower body) and fasciculus cuneatus (upper body), with minimal processing.

83
Q

DCLM Steps:

A

1) First-order neurons carrying sensory input from mechanoreceptors synapse in specific nuclei, namely the nucleus gracilis and nucleus cuneatus,

2) Second-order neurons project sensory information as the medial lemniscus, crossing the midline in the brainstem (pons), and ascend to the thalamus, primarily to the ventral posterior lateral nucleus (VPL).

3)Third-order neurons relay precise sensory information to the somatosensory cortex for conscious perception.

84
Q

Indirect Pathway Steps

A

1) Detecting stimulu
2) Slow C fibers carry sensory information to the spinal cord’s dorsal horn.
3) First-order neurons enter the spinal cord via dorsal roots and synapse in the dorsal horn.
4) Unlike the direct pathway, the indirect pathway involves multiple synapses in the dorsal horn, leading to signal spread.
5) Some neurons project to the brainstem’s reticular formation.
6) Signals are further relayed to the thalamus, then diffuse to different brain regions, including the cortex and limbic system.
7) This diffuse signaling contributes to the emotional and autonomic aspects of pain perception.

KINE3650 (17 decks)

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