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Neuroscience Exam 2 > Somatosensory System I - Introduction > Flashcards

Somatosensory System I - Introduction Flashcards

1
Q

Modalities

What are the 4 modalities mediated by the somatosensory system?

A

Discriminative Touch (and light touch)

Conscious Proprioception

Nociception

Temperature Sense

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2
Q

Modalities: Discriminative Touch

Definition

A

The ability to recognize the size, shape, and texture of objects and their movements across the skin.

Includes vibratory sense and pressure

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3
Q

Modalities: Conscious Proprioception

Definition

A

The sense of static position and movement of the limbs and body

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4
Q

Modalities: Conscious Proprioception

What is limb position sense?

A

The sense of the stationary position of the limbs

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5
Q

Modalities: Conscious Proprioception

What is kinesthesia

A

The sense of limb movement

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6
Q

Modalities: Unconscious Proprioception

What is unconscious proprioception?

A

Proprioceptive information that is conveyed from the spinal cord to the cerebellum via spinocerebellar tracts for the modulation of movements

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7
Q

Modalities: Nociception

Definition

A

The signaling of tissue damage or chemical irritation, typically perceived as pain or itch.

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8
Q

Modalities: Temperature Sense

Definition

A

The sense of warmth or cold

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9
Q

Modalities: Light touch

Definition; why is it rarely discussed?

A

Sense of cutaneous touch or light pressure.

Rarely discussed because absence produces little, if any, tactile sensibility disturbance if discriminative touch is maintained.

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10
Q

Modalities:

What is the common class of sensory neurons that all of these modalities share?

A

Dorsal root ganglion neurons

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11
Q

Dorsal Root Ganglion Neuron

What is the name given the the peripheral axons of the dorsal root ganglion neurons?

A

Primary afferent

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12
Q

Dorsal Root Ganglion Neuron:

How is somatosensory information from the cranial structures transmitted?

A

via cranial nerve sensory neurons on cranial nerves 5,7,9, and 10 that are functionally and morphologically homologous to dorsal root ganglion cells.

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13
Q

Dorsal Root Ganglion Neuron: Type

is the type of these neurons based on funcitonal role and on size and shape of neuronal processes?

A

Functional role: General somatic afferent

Processes: Pseudounipolar

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14
Q

Dorsal Root Ganglion Neuron: Receptors

What determines the sensory function of each dorsal root ganglion neuron?

A

The structure of the receptors

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15
Q

Dorsal Root Ganglion Neuron: Receptors

What is the function of the connective tissue capsules of the receptors? Do all receptors have them?

A

The capsules cary in complexity and surround the nerve terminal. What they are deformed in particular ways, they excite the dorsal root ganglion neuron.

Not all receptor have them - some (but few) receptors have free or bare nerve endings that are unencapsulated

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16
Q

Dorsal Root Ganglion Neuron: Mechanoreceptors

What is the function of mechanoreceptors in the skin?

A

They mediate touch

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17
Q

Dorsal Root Ganglion Neuron: Mechanoreceptors

What are the names of the somatosensory mechanoreceptors and where are they located (superficial vs. deep)

A 
Ruffini - deep
Pacinian - deep
Meissner Corpuscle - superficial
Merkel Disk - superficial
Free Nerve endings - superficial and deep
Hair Follicle - Deep
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18
Q

Dorsal Root Ganglion Neuron: Mechanoreceptors

What is the difference between the receptive fields of the receptors in the superficial and deep layers of the skin? What is the importance of this distinction?

A

Receptive fields are smaller in the superficial layer enabling the resolution of spatial differences, which is important for tactile discrimination and identifying ridges and specific details about objects.

Receptive fields are larger in the deep layer of the skin, enabling the resolution of coarse spatial differences, which is important for identifying the global properties of objects such as edges.

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19
Q

Dorsal Root Ganglion Neuron: Mechanoreceptors

What is the result of the varying density of mechanoreceptors throughout the body?

A

The spatial resolution of the stimuli on the skin varies as a result. This is why we have better 2 point discrimination in some areas than in others.

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20
Q

Dorsal Root Ganglion Neuron: Mechanoreceptors

What is sensed by rapidly adapting mechanoreceptors? Do they have high or low thresholds?

A

The motion of objects (speed and duration).

These receptors have LOWER THRESHOLDS and are therefore able to detect minute vibrations.

21
Q

Dorsal Root Ganglion Neuron: Mechanoreceptors

What is sensed by slowly adapting mechanoreceptors? Do they have high or low thresholds?

A

They signal the pressure and shape of objects.

They have HIGHER thresholds and therefore require more salient bumps or edges to be activated.

However, once these receptors are activated, they provide a clear image of contours.

22
Q

Dorsal Root Ganglion Neuron: Mechanoreceptors

How are the spatial characteristics of objects signaled?

A

By populations of mechanoreceptors, each populations sends info though its own pathway, and the pathways are parallel.

23
Q

Dorsal Root Ganglion Neuron: Mechanoreceptors

Where are the mechanoreceptors that mediate proprioception located?

A

In the muscles and joints (Muscle spindles, GTOs, Joint receptors)

24
Q

Dorsal Root Ganglion Neuron: Nociceptors

What is their function?

A

They mediate pain; in doing so, the serve an important protective function by warning of injuries that should be avoided or treated.

25
Q

Dorsal Root Ganglion Neuron: Nociceptors

What are the types of pain

A

Acute: pain that is short lived

Chronic: Pain that persists for an extended period of time.

Nociceptive: occurs in 2 phases -

1) First pain is sharp and localized
2) Second pain is dull, burning, or diffuse

Neuropathic: this is neural pain cased by injury to a neural structure.

26
Q

Dorsal Root Ganglion Neuron: Nociceptors

What is their receptor type?

A

Unencapsulated free nerve endings

27
Q

Dorsal Root Ganglion Neuron: Nociceptors

What stimuli activate the mechanical nociceptors?

A

Intensive pressure applied to the skin. Evokes sensations of sharp or pricking pain.

28
Q

Dorsal Root Ganglion Neuron: Nociceptors

What stimuli activate the thermal nociceptors?

A

extreme temperatures

29
Q

Dorsal Root Ganglion Neuron: Nociceptors

What stimuli activate the Polymodal nociceptors?

A

High intensity mechanical, thermal, or chemical stimuli. Evokes a sense of slow, burning pain.

30
Q

Dorsal Root Ganglion Neuron: Nociceptors

What is one hypothesis for how noxious stimuli depolarize free sensory nerve endings and generate action potentials?

A

It is likely that nociceptors are really chemoreceptors that are sensitive to the concentration of irritant chemicals released in the surrounding tissue by noxious mechanical or thermal stimuli, or exogenous chemicals that penetrate the skin and these chemicals initiate the pain pathway

31
Q

Dorsal Root Ganglion Neuron: Thermoreceptors

What do they do?

A

Mediate Temperature

32
Q

Dorsal Root Ganglion Neuron: Thermoreceptors

What are the 4 types of thermal sensation?

A

Cold
Cool
Warm
Hot

33
Q

Dorsal Root Ganglion Neuron: Thermoreceptors

How do thermoreceptors differentiate the types of thermal sensation?

A

By detecting the differences between the external temperature of the air or objects contacting he body and the normal skin temperature of 34 degrees celsius

34
Q

Dorsal Root Ganglion Neuron: Thermoreceptors

What type of receptors are they?

A

Un-encapsulated free nerve endings

35
Q

Dorsal Root Ganglion Neuron: Thermoreceptors

What stimuli activate the warmth thermoreceptors?

A

Temperatures of 29 to 45 degrees celsius. They are most active at 45 degrees C

36
Q

Dorsal Root Ganglion Neuron: Thermoreceptors

What stimuli activate the cold thermoreceptors?

A

Temperatures of 5 to 40 degrees celsius. Most active at25 degrees C

37
Q

Dorsal Root Ganglion Neuron: Thermoreceptors

When do thermoreceptors fire?

A

They are tonically active at constant temperatures and the signals that they are transmitting are governed by the temperature they sense.

When temperature changes, they show a graded response.

Coding for skin temperature involves comparing the relative activity of the different populations of thermal receptors.

38
Q

Dorsal Root Ganglion Neuron: Fibers

How are they classified?

A

Based on conduction velocity and fiber diameter.

39
Q

Dorsal Root Ganglion Neuron: Fibers

What are the types of fibers in cutaneous nerves and what receptors are they associated with?

A

Ia and Ib - Primary muscle spindles and GTOs
II - Secondary muscle spindles and skin mechanoreceptors
III - skin mechanoreceptors and nociceptors
IV - thermoreceptors and polymodal receptors

40
Q

Dorsal Root Ganglion Neuron: Fibers

What is the ranking of the fiber diameters for the 4 fiber types of cutaneous nerves?

A

Ia and Ib - largest, fastest transmission; followed by II then III then IV which are the slowest

41
Q

Dorsal Root Ganglion Neuron: Fibers

Which dorsal root ganglion receptors are innervated by fibers with fast conduction velocities? What are the characteristics of these fibers?

A

Proprioceptors and mechenoreceptors

These fibers are myelinated and large in diameter

42
Q

Dorsal Root Ganglion Neuron: Fibers

Which dorsal root ganglion receptors are innervated by fibers with slow conduction velocities? What are the characteristics of these fibers?

A

Nociceptors and thermoreceptors

These fibers are small in diameter and can be either myelinated or unmyelinated

43
Q

General Organization of Pathways

What makes us the neural pathways from the periphery to the highest level of the CNS in the somatosensory system?

A

The pathway is comprised for 3 neurons (excluding interneurons)

These neurons communicate at the level of the spinal cord, then then thalamus, then the cortex.

44
Q

General Organization of Pathways

What are the first neurons in the pathway to be activated? where do their cell bodies lie?

A

Once an adequate stimulus evokes a receptor potential in a receptor, an action potential is initiated in the peripheral process of the FIRST ORDER neuron, whose cell body is in the dorsal root ganglion

45
Q

General Organization of Pathways

With what structure to the central processes of the dorsal root ganglion neurons synapse once they receive the signal from the peripheral axon?

A

They synapse with the dendrites of the second order neurons, whose cell bodies lie either in the spinal cord or in the brainstem.

46
Q

General Organization of Pathways

What is the pathway of the axons of the second order neurons? Where do they synapse?

A

The axons of the second order neurons CROSS THE MIDLINE, and ascend to synapse with the dendrites of the third order neurons, whose cell bodies lie in the thalamus.

47
Q

General Organization of Pathways

Where do the axons of the third order neurons synapse? What is their path on the way there?

A

The axons of the third order neurons pass through the posterior limb of the internal capsule to the post-central gyrus and posterior para-central gyrus of the cerebral cortex (the primary somatosensory cortex)

48
Q

General Organization of Pathways

Where is inhibition happening throughout this pathway?

A

At all of the synapses.

Neuroscience Exam 2 (8 decks)

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