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CNS Anatomy > Sheet 3 > Flashcards

Sheet 3 Flashcards

1
Q

What is sensation?

A

Converting one type of energy into a signal.

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2
Q

What are the types of mechanoreceptors?

A

1) Meissner’s corpuscle
2) Merkel’s disc (Tactile disc)
3) End organ of Ruffini
4) Pacinian corpuscle

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3
Q

What are Meissner’s corpuscles responsive to?

A

1) Touch
2) Pressure
3) Low frequency vibrations

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4
Q

Meissner’s corpuscles are ___(rapidly/slowly) adapting.

A

Rapidly

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5
Q

What are Merkel’s discs responsive to?

A

Discriminative touch

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6
Q

Merkel’s discs are ___(rapidly/slowly) adapting.

A

Slowly

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7
Q

What is the difference between rapidly and slowly adapting?

A

Signals fade away after the stimulus exposure in rapidly adapting receptor types; whereas, in slowly adapting receptors, the signal is transmitted as long as the stimulus is present.

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8
Q

What are end organs of Ruffini responsive to?

A

Skin stretch

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9
Q

End organs of Ruffini are ___(rapidly/slowly) adapting.

A

Slowly

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10
Q

What are Pacinian corpuscles responsive to?

A

High frequency vibrations

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11
Q

Pacinian corpuscles are ___(rapidly/slowly) adapting.

A

Rapidly adapting

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12
Q

What are thermoreceptors?

A

A type of free nerve endings (processes existing on bare skin) that detect changes in temperature.

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13
Q

What is an example of thermoreceptors?

A

TRP channels (TRPV1, TRPC, TRPM)

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14
Q

Why do we have many thermoreceptors?

A

Because each receptor is specific for a certain temperature. (Ex. TRPV2 is activated after 52, TRPV1 after 45.)

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15
Q

What are nociceptors?

A

A type of free nerve endings that detect damage (pain receptors).

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16
Q

Pain is considered as an:

A

Exaggeration of a certain type of energy (Ex. too much heat).

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17
Q

Why are nociceptors multimodal?

A

Because there’s no such thing as “pain” energy.

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18
Q

After the signal is received by receptors, where does it go?

A

It’s conducted through peripheral nerve fibers to the CNS.

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19
Q

When does adaptation of receptors happen?

A

When a receptor is continuously stimulated.

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20
Q

What is adaptation of receptors?

A

When receptors become less sensitive due to continued stimuli.

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21
Q

Which sensory fiber type is unmyelinated?

A

C

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22
Q

Which sensory fiber type is myelinated?

A

A

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23
Q

Which sensory fiber type has the largest diameter?

A

Aα

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24
Q

Which sensory fiber type has the smallest diameter?

A

C

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25
Q

Which sensory fiber type has the fastest conduction?

A

Aα

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26
Q

The greater the diameter, ___.

A

The greater the conduction velocity.

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27
Q

Order the sensory fibers in terms of decreasing velocity. (Start with fastest).

A

Aα > Aβ > Aδ > C

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28
Q

What do muscle spindle receptors detect?

A

Length of the muscle

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29
Q

What do golgi tendon organs detect?

A

Tension in the tendons

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30
Q

What is a receptive field?

A

An area of skin that receives sensation from a single nerve fiber (receptor).

31
Q

What is the importance of receptive fields?

A

The brain can discriminate a receptive field as an individual area; no matter how big or small the area is as long as it has its own fiber.

32
Q

The greater the density of receptors, the ____(greater/smaller) the receptive fields of individual afferent fibers.

A

Smaller

33
Q

The smaller the receptive field, the ___(greater/smaller) is the acuity or the discriminative touch.

A

Greater

34
Q

If many primary sensory neurons converge onto a single secondary neuron, this creates a very ___(small/large) receptive field. This means that:

A

Large; Two stimuli will be perceived as a single point because both stimuli fall within the same receptive field.

35
Q

If few primary sensory neurons converge, secondary receptive fields are ___(small/large). This means that:

A

Two stimuli activate separate pathways and are perceived as distinct stimuli.

36
Q

What does the labelled line theory state?

A

1) That individual primary afferent fibers carry information from a single type of receptor. (1 fiber has 1 type of receptor).
2) Individual receptors preferentially transduce information about an adequate stimulus (receptors are specific).

37
Q

What is an adequate stimulus?

A

The amount and type of energy required to stimulate a specific sensory organ

38
Q

What do we need to consider when talking about sensation?

A

1) Modality (type)
2) Locality
3) Intensity

39
Q

Where is The Posterior Column – Medial Lemniscal Pathway located?

A

In the posterior white column of the spinal cord

40
Q

The posterior white column is divided into two fasciculi on each side:

A

1) Medially: Fasciculus gracilis

2) Laterally: Fasciculus cuneatus

41
Q

What is discriminative touch sensation?

A

The ability to discriminate when touched in two different points

42
Q

What are the modalities of the The Posterior Column – Medial Lemniscal Pathway?

A

Discriminative touch sensation (including vibration and conscious proprioception)

43
Q

What is proprioception?

A

A muscle joint sense, by which the CNS knows how every muscle and joint of the body is positioned in space.

44
Q

What is proprioception important for?

A

Motor coordination

45
Q

Where does conscious proprioception reach?

A

The cortex

46
Q

Where does unconscious proprioception reach?

A

The cerebellum

47
Q

What does the posterior column specialize in?

A

High velocity and precise signals

48
Q

Which receptors are found in The Posterior Column – Medial Lemniscal Pathway

A

Most types of receptors (like

spindles and GTO) EXCEPT free nerve endings.

49
Q

Cell bodies of the 1st neurons are ___.

A

pseudo-unipolar

50
Q

What does pseudo-unipolar mean?

A

That they have a single stalk that divides into two processes: 1 peripheral and 1 central.

51
Q

What is the journey of the mechanoreceptors? (First order neuron until the second order neuron)

A

1) Mechanoreceptors enter the posterior white column
2) Their fibers ascend upwards ipsilaterally (on the same side they came from)
3) They go up until they reach the lower part of medulla oblongata
4) There, they synapse with the bodies of second order neurons.

52
Q

Second neuron bodies collect in two nuclei:

A

1) Medially: Nucleus gracilis

2) Laterally: Nucleus cuneatus

53
Q

Where do fasciculus gracilis fibers synapse?

A

In the nucleus gracilis

54
Q

Where do fasciculus cuneatus fibers synapse?

A

In the nucleus cuneatus

55
Q

What is a fasciculus?

A

A bundle of ascending white matter from the first order neuron.

56
Q

What is the journey of the second order neurons? (Until the third order neurons)

A

1) The processes of the second order neurons in the lower part of medulla oblongata cross over to the other side (primary sensory decussation) creating an arch. [Internal Arcuate Fiber]
2) Then they ascend contralaterally.
3) As they go up, these fibers gather and lie close to the midline, forming a lemniscus (an elongated shape) called medial lemniscus.
4) They keep ascending through the medulla oblongata, pons, and midbrain until they reach the thalamus where they synapse with the third order neurons.

57
Q

What are internal arcuate fibers?

A

Fibers consisting of axons traveling from the nucleus gracilis and nucleus cuneatus to the contralateral side of the medulla, where they will begin traveling up to the cortex as part of the medial lemniscus.

58
Q

What is the medial lemniscus?

A

Elongated bundle of white matter

59
Q

At the level of the second order neurons, the sensation is carried ___.

A

Contralaterally

60
Q

Give a summary of the journey of the second order neurons.

A

Dorsal Column Nuclei (Nucleus Gracilis and Cuneatus) -> Internal Arcuate
Fiber -> Lemniscal Decussation -> Medial Lemniscus

61
Q

Give a summary of the journey of the third order neurons.

A

Thalamus (VPL) (Internal Capsule —– Corona Radiata

62
Q

What is the journey of the third order neurons?

A

1) Ventral posterolateral nucleus (VPL) receives the medial lemniscus where the synapse between the
second and third order neurons takes place.
2) Third order neurons project from the thalamus towards the cortex (the outer aspect of the cerebrum (telencephalon)).
3) As the fibers head towards the cortex, they pass through the internal capsule.
4) As they approach the cortex, the fibers spread out forming corona radiata.
5) Here, they show localization as each
body part is represented by these fibers on a specific area.
6) They terminate into the primary somatosensory (Somesthetic) Area (SI) of the parietal lobe (of the cortex).

63
Q

What is the Ventral posterolateral nucleus (VPL)?

A

The thalamic nucleus related to the posterior white column.

64
Q

What is the internal capsule?

A 
A critical narrow area
between multiple nuclei:
1) Caudate nucleus
2) The thalamus medially
3) The lentiform nucleus laterally
65
Q

Why is the internal capsule called the projection center?

A

Because it connects the upper center with the lower center.

66
Q

What is the difference between fasciculus gracilis and cuneatus?

A

Same function, but:
Fasciculus gracilis transmits information coming from
areas inferior to T6 (lower parts of the body);
Fasciculus Cuneatus transmits above T6 (upper
part of the body).

67
Q

The lowest part of the body’s (foot) fibers would be most __(medial/lateral) to the column.

A

Medial

68
Q

What is the Somatotopic principle?

A

The correspondence of an area of the body to a specific point on the central nervous system. (Area of the body corresponds to a point on the primary somatosensory cortex (postcentral gyrus).)

69
Q

Where does the Somatotopic principle exist?

A

The cortex and the spinal cord.

70
Q

Modulation starts at __.

A

T6

71
Q

What is the thalamus?

A

Basically the secretary of the cortex.

72
Q

What is the thalamus made up of?

A

It’s made of two egg shaped

collections of gray matter.

73
Q

What does the thalamus consist of?

A

Multiple nuclei (VPL, VPM, etc).

74
Q

The body is represented as a ___ on the cortex which helps our CNS localize the body parts.

A

map/homunculus

CNS Anatomy (19 decks)

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