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Y1S2Anatomy > Sensory tract of spinal cord > Flashcards

Sensory tract of spinal cord Flashcards

1
Q

What are the components of the sensory system?

A

1) Receptors

2) Sensory (afferent) nerve fibers

3) Ascending tracts of the spinal cord

4) Sensory cortical areas in the brain (mostly contralateral)

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2
Q

What are the types of sensory information?

A

1) Exteroceptive sensations (from outside the body):
- Pain
- Temperature
- Touch (crude/fine)

2) Proprioceptive sensations (from inside the body)
- Pressure
- Sense of movement
- Sense of joint position

3) Visceral sensations
- Visceral pain from viscera

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3
Q

What are order neurons?

A

The neurons that carries sensation are usually 2 or 3, forming successive pathway from the receptor to the sensory area in the brain

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4
Q

What is meant by decussation?

A

It is the crossing of a pathway from one side to the other along their course

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5
Q

What is meant by somatotopy?

A

The order the nerves are arranged, like the sensory fibers of the upper part lies lateral to those carrying the sensation from the inferior parts

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6
Q

What are the different ascending tracts of the spinal cord?

A
  • There are 80 sensory tracts but we will only take 5, which are classified according to their location in the white matter

1) Posterior column tract
2) Dorsal & ventral spino-cerebellar tracts
3) Lateral spino-thalamic tract
4) Ventral spino-thalamic tract

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7
Q

Describe the scenario of the anterolateral system (spinothalamic tract)

A

1) 1st order neuron: unipolar cell body its cell body lies in the root ganglion, on arm goes to the organ while the other goes to the spinal cord

2) 2nd order neuron: Its cell body is found in the gray matter, its axon will cross the midline at the same level, rising in the lateral white matter of the spinal cord after crossing, the nerve crosses the spinal cord and brain stem and ends at the thalamus

3) 3rd order neuron from the thalamus to the sensory cortex in the brain

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8
Q

Where will we feel pain incase of an injury to the anterolateral system?

A

1) Lesions at the level of crossing have an ipsilateral effect

2) Lesions above the crossing have a contralateral effect

3) Injury to the spinal cord will have an effect on both sid

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9
Q

Describe the sensory scenario of the gracile and cuneate pathway

A

1) 1st order neuron enters the spinal cord from the same side without crossing to the medulla of the brain stem

2) 2nd order neuron, where the axons will cross the midline in the medulla, ascending in the opposite side and ending in the thalamus

3) 3rd order neuron from the thalamus to the sensory cortex in the brain

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10
Q

What is the effect of a lesion to the tract?

A
  • Affects the side experiencing it (ipsilateral) loss of proprioception and contralateral loss of pain and temperature
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11
Q

What is the effect of a lesion on the medulla?

A

It will affect all sensations

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12
Q

What is the effect of a lesion on the dorsal root ganglion?

A

Ipsilateral for both exteroceptive and proprioceptive sensations

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13
Q

What are the tracts of the posterior white column?

A

1) Gracile tract (fasciculus gracilis) medially from lower extremities

2) Cunate tract (fasciculus cuneatus) laterally from upper extremities

  • Gracile from lower + Cuneate from upper = posterior column tract for conscious proprioception
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14
Q

What is the function of the posterior column tract?

A

1) conscious proprioceptive sensations (sense of position, movement & vibration)

2) Fine (complex, discriminative)

3) Touch (tactile localization, tactile discrimination & stereognosis “Identify objects with your eyes closed”)

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15
Q

What are the tracts of the lateral white column?

A

1) Dorsal spinocerebellar tracts (unconscious proprioceptive sensation)

2) Ventral spinocerebellar tract (unconscious proprioceptive sensation)

3) Lateral spinothalamic tract (pain and temperature)

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16
Q

What are the tracts of the anterior white column?

A

Ventral spino-thalamic tract

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17
Q

What are the sensations felt by the ventral spinothalamic tract?

A

Pressure and crude touch

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18
Q

What are the three major sensory nuclei found in the grey matter?

A

1) Substantia gelatinosa (lamina II)

2) Nucleus proprius (lamina III & IV)

3) Dorsal nuclei (Clark’s nucleus/lamina VII)

  • The trace of the tracts is in the spinal cord but the crossing happens in the grey matter
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19
Q

What sensations are felt by the substantia gelatinosa nuclei?

A

Pain and temperature

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20
Q

What sensations are felt by the Nucleus proprius nuclei?

A

Pressure & crude touch

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21
Q

What sensations are felt by the Clarks/dorsal nuclei?

A

Spinocerebellar

22
Q

What is the origin of the tract fibers of the posterior column tract?

A
  • Central processes of the neurons in the dorsal root ganglia (1st order neuron) entering the spinal cord via the dorsal root of the spinal nerve
  • These fibers will then ascend on the same side without crossing in the spinal cord forming gracile and cuneate tracts (2nd order neuron)
  • They terminate in the gracile and cuneate nuclei found in the medulla oblongata
  • Once they reach the medulla they will cross-over (sensory decussation) forming the medial lemniscus (2nd order neuron)
  • The third order neuron will be in the thalamus (postero-lateral ventral nucleus of thalamus) PLVNT, their axons ascend through the internal capsule terminating in the sensory area of the cerebral cortex where conscious proprioceptive sensations are appreciated
  • Gracile the medial one (Sacral & lumbar) will carry sensations from the lower half of the body, while the cuneate the lateral one (trunk & cervical) will carry sensations from the upper half of the body
23
Q

What is the function of the dorsal and ventral spino-cerebellar tracts?

A

Carries unconscious proprioceptive sensations directly to the cerebellum, controlling muscle tone and maintaining the body posture

24
Q

What is the anatomical site of the dorsal & ventral spino-cerebellar tracts?

A

Lateral white column

25
Q

What is the origin of the dorsal & ventral spino-cerebellar tract fibers?

A

Nucleus dorsalis (Clark’s nucleus)

  • These cells lie in the dorsal grey horn of the spinal cord (2nd order neuron)
26
Q

Describe the route of the dorsal spinocerebellar tract

A

For the Dorsal spinocerebellar tract (Uncrossed)

The 1st order is in the dorsal ganglion cell then it ends in the gray matter where 2nd order starts (particularly Clark’s nucleus ) then it flexes back to the white matter (Note there is no crossing here) then it goes directly to the cerebellum (Without the need for a 3rd order)

  • Dorsal spino-cerebellar tract axons ascend on the same side till the medulla oblongata, entering the cerebellum on the same side via the inferior cerebellar peduncle (I.C.P)

Direct = (Dorsal) To remember that here there is no crossing

27
Q

Describe the pathway of the ventral spinocerebellar tract

A
  • Ventral spinocerebellar tract (Crossed)

Axons of second-order neurons cross the midline (ascend on the other side) and proceed to the other half of the cerebellum. Like the dorsal spinocerebellar tract, this tract sends impulses to both parts of the cerebellum and contains only two-order neurons

  • Ventral spino-cerebellar tracts axons cross the opposite side, then ascend to the midbrain, entering the cerebellum via the superior cerebellar peduncle
28
Q

Why do we have two paths for some tracts?

A

A type of protection that if one got hurt there will be another way

29
Q

What is tabes dorsalis?

A
  • Caused by syphilis “a STD causing microorganism”, which causes selective lesions to the nerve fibers of the dorsal root of the spinal nerve leading to:

1) Early irritation of the nerve fibers (severe pain)

2) Losing the sensation of pain in the affected segments

3) Loss of proprioceptive sensations (sensory ataxia “falling down when closing your eyes”, which is corrected by vision)

4) Hypotonia

5) Loss of tendon reflexes

30
Q

What is the function of the lateral spino-thalamic tract?

A

Carries pain and temperature sensations

31
Q

What is the anatomical site of the lateral spino-thalamic tract?

A

Lateral white column

32
Q

What is the origin of the lateral spino-thalamic tract fibers?

A

Substantia gelatinosa of Rolando (lamina III)

33
Q

Describe the pathway of the lateral spino-thalamic tract

A
  • The cells of (Substantia gelatinosa of Rolando (= Lamina II)) lie in the dorsal grey horn of the spinal cord (2nd order neuron), and their axons immediately cross the midline close to the central canal
  • On the contralateral side they ascend as the lateral spinothalamic tract
  • Once in the brain stem they are called the spinal lemniscus
  • They terminate in the thalamus (PLVNT) whose axons pass through the internal capsule and terminate in the sensory areas 1,2 & 3 in the cerebral cortex where pain and temp are sensed
34
Q

What is the function of the ventral spino-thalamic tract?

A

Carries pressure, crude, light, and simple touches

35
Q

What is the anatomical site of the ventral spino-thalamic tract?

A

Anterior white column

36
Q

What is the origin of the ventral spino-thalamic tract fibers?

A
  • Nucleus proprius (Lamina II & IV)
  • These cells lie in the Dorsal Grey Horn of the S.C. (2nd. order neuron) Its axons immediately cross the midline (more anterior to the central canal).
  • On the contralateral side, they ⭡ as Ventral Spinothalamic T.
  • On the brain stem, the same fibers ⭡, are called Spinal Lemniscus
  • They terminate in Thalamus (in P.L.V.N.T.) [= 3rd. order neuron], whose axons pass through the Internal Capsule to terminate in the Sensory area (area 3,1& 2) of the cerebral cortex of the brain, where Pressure & crude (simple) touch are appreciated
37
Q

What is syringomyelia?

A
  • Formation of a cavity “fluid-filled cyst” in the central canal of the spinal cord affecting the thoracic segments mainly
  • It affects children and adults of all races and ethnicities
  • It can cause permanent nerve damage and paralysis
38
Q

What are the signs and symptoms associated with syringomyelia?

A

1) Loss of pain and temperature sensation on both sides of the thoracic region (jacket distribution)

2) Touch and pressure sensations are not affected (except very late)

3) Proprioceptive sensations are not affected

39
Q

What are some of the abnormalities regarding sensory perception?

A

1) Hypothesia: partial loss of sensitivity to sensory stimuli (diminished sensation)

2) Hyperesthesia: Increased sensitivity towards any stimuli

3) Paresthesia: An area of altered/abnormal sensation (like tingling or numbness)

4) Anesthesia: area of no sensation

5) Allodynia: Pain that results from a non-injurious stimulus to the skin

40
Q

What are the receptors that sense conscious proprioceptive sensations?

A

1) Meissner’s corpuscles

2) Pacinian corpuscles

3) Muscle spindles

41
Q

What are the receptors that sense Pain & temperature sensations?

A

Free nerve endings

42
Q

What are the receptors that sense Light touch & pressure sensations?

A

Free nerve endings

43
Q

What are the receptors that sense unconscious proprioceptive sensations?

A

1) Muscle spindles

2) Tendon organs

3) Joint receptors

44
Q

What are the 1st, 2nd & 3rd order neurons involved in the conscious proprioceptive sensations?

A
  • 1st is the dorsal root ganglion
  • 2nd order are the gracile and cuneate nuclei (in the medulla)
  • 3rd order neurons are the posterior lateral ventral nucleus of the thalamus (PLNT)
45
Q

What are the 1st, 2nd & 3rd order neurons involved in the pain & temperature sensations?

A
  • 1st is the dorsal root ganglion
  • 2nd order neuron is the substantial gelatinosa
  • 3rd order neurons are the posterior lateral ventral nucleus of the thalamus (PLNT)
46
Q

What are the 1st, 2nd & 3rd order neurons involved in the light touch & pressure sensations?

A
  • 1st is the dorsal root ganglion
  • 2nd order neuron is the substantial gelatinosa
  • 3rd order neurons are the posterior lateral ventral nucleus of the thalamus (PLNT)
47
Q

What are the 1st & 2nd order neurons involved in the unconscious proprioceptive sensations?

A
  • 1st is the dorsal root ganglion
  • 2nd order neuron is the Nucleus dorsalis (Clark’s nucleus)
48
Q

What are the pathways involved in the conscious proprioceptive sensation?

A

1) Gracile and cuneate tracts

2) Medial lemniscus

49
Q

What are the pathways involved in the pain & temp sensation?

A

1) Lateral spino-thalamic tract

2) Spinal lemniscus

50
Q

What are the pathways involved in the light touch & pressure sensation?

A

1) Ventral spino-thalamic tract

2) Spinal lemniscus

51
Q

What are the pathways involved in the unconscious proprioceptive sensation?

A

1) Dorsal spino-cerebellar tract

2) Ventral spino-cerebellar tract

52
Q

What are the different destinations regarding different sensations?

A

1) postcentral gyrus area (3, 1, 2)
- for conscious proprioception, pain, temp, light touch & pressure

2) Cerebellar cortex
- for unconscious proprioception

Y1S2Anatomy (18 decks)

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