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Neuroscience > N6 - Spinal cord and ascending tracts > Flashcards

N6 - Spinal cord and ascending tracts Flashcards

1
Q

what travels via the spinal cord?

A

With the exception of the face and part of the scalp, somatosensory afferents, and motor efferents to skeletal muscle

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2
Q

what are the functions of the spinal cord?

A
  • Receives primary afferent fibres from peripheral receptors in widespread somatic and visceral structures.
  • Sends motor axons to skeletal muscle.
  • Provides communications highway between brain and periphery.
  • Houses preganglionic neurons of sympathetic nervous system.
  • Houses some preganglionic neurons of parasympathetic nervous system
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3
Q

where is the transition of oligodendrosites to schwann cells?

A

when the roots leave the spinal cord, the axons are now myelinated by Schwann cells

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4
Q

What are the 2 enlargements of the spinal cord?

A
  • Cervical - related to upper limb

- Lumbar- related to lower limb

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5
Q

what occurs at each segment of the spinal cord to form roots?

A

A series of rootlets emerge from the dorsal and ventral aspects of each segment of the cord and coalesce to form a posterior (sensory) and anterior (motor) root respectively

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6
Q

where do the anterior and posterior roots pass through?

A

These roots pass through the subarachnoid space until they reach the appropriate intervertebral foramina

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7
Q

what happens to the posterior root as it passes through the foramina?

A

it is enlarged by the posterior (dorsal) root ganglion

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8
Q

What is formed when the two roots fuse?

A

produces posterior and anterior rami

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9
Q

what is the spinal cord continuous with?

A

medulla at a site just below the foramen magnum

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10
Q

where does the spinal cord terminate?

A

it terminates in a tapered cone-shape called the conus medularis

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11
Q

what does the conus medularis continue as?

A

thin connective tissue cord called the filum terminale which is anchored to the dorsum of the coccyx

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12
Q

Why is it important to differentiate the spinal segment from the vertebral level?

A

Note that the spinal cord ends at the L1 vertebral level (L2 at birth). For example, the L2 spinal segment is the segment that provides the L2 spinal nerve and innervates the L2 dermatome, BUT, it is actually found in the vertebral canal associated with the T11 vertebra

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13
Q

what lies in the dural spinal canal below L1?

A

the dorsal and ventral roots of the L2 and lower spinal nerves and the filum terminale

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14
Q

what is the collection of roots below L1 called?

A

cauda equina

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15
Q

Describe the spinal meninges.

A

The spinal meninges are continuous with the cranial meninges via the foramen magnum. And include all 3 layers, the dura mater, arachnoid mater and pia mater

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16
Q

what is the spinal cord suspended in the canal by?

A

a ribbon of tissue on the lateral aspects of the cord called the denticulate ligament

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17
Q

what is the denticulate ligament formed by?

A

pial and arachnoid tissue and attaches to the dura at points along the length of the cord

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18
Q

In the spinal cord, what is the subarachnoid space filled with?

A

CSF

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19
Q

What is the general internal anatomy of the spinal cord?

A

The cord is made up of an outer layer of white matter and an inner, ‘H’ shaped core of grey matter

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20
Q

what does the white matter consist of?

A

longitudinally oriented nerve fibres (axons), glial cells and blood vessels

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21
Q

what does the grey matter contain?

A

neuronal soma, cell processes, synapses, glia and blood vessels

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22
Q

what opens up into the 4th ventricle and extends the length of the spinal cord?

A

central canal

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23
Q

How does white matter vary as you descend the spinal cord?

A

White matter is greatest at cervical levels and is progressively less at more caudal levels

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24
Q

where is grey matter greatest in the spinal cord?

A

cervical and lumbar enlargements

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25
Q

what is white matter congenitally described as being made up of?

A

dorsal, lateral and ventral columns each containing a variety of fibre sizes from small unmyelinated to large myelinated

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26
Q

How can you tell from a photo what is the ventral and dorsal side?

A

Grey matter extends all the way to the surface on the dorsal side

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27
Q

How is grey matter divided?

A

divided into 4 parts, left and right dorsal and ventral horns, which together with the central grey matter form a rough ‘H’ shape

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28
Q

what does the horizontal part of the ‘H’ represent?

A

the dorsal and ventral grey commissures which surround the central canal

29
Q

What is the modality of the dorsal and ventral horns?

A

Dorsal- sensory

Ventral- motor

30
Q

what is special about spinal segments T1 to L2 in terms of grey matter?

A

there is also a smaller lateral horn which is also referred to at the intermediolateral cell group, which contains preganglionic sympathetic neurons (thoracic-lumbar outflow)

31
Q

Where is there a smaller group that contains preganglionic parasympathetic neurones?

A

S2-S4

32
Q

Grey matter of the spinal cord is divided into layers, what is this called and what synapses in these layers?

A
  • Rexed laminae
  • Pain sensations tends to synapse in more superficial layers of the dorsal horn, whereas innocuous stimuli (e.g. tactile afferents associated with hairs) tend to synapse more deeply
33
Q

what does the arterial supply of the spinal cord include?

A
  • Three major longitudinal arteries
  • Segmental arteries
  • Radicular arteries
34
Q

what are the 3 major longitudinal arteries?

A

one anterior and two posterior that originate from the vertebral arteries. These run the length of the cord

35
Q

Where are the segmental arteries derived from?

A

vertebral, deep cervical, intercostal and lumbar arteries

36
Q

where do the radicular arteries travel?

A

along the dorsal and ventral roots

37
Q

what supplies 2/3 of the cross-sectional area of the spinal cord?

A

anterior spinal artery

38
Q

Describe the venous drainage of the spinal cord.

A

The venous drainage of the cord follows a similar pattern to the supply, with both longitudinal and segmental veins

39
Q

Where do the longitudinal veins drain?

A

cerebellar veins and cranial sinuses

40
Q

Where do segmental veins drain?

A

into local vertebral plexuses, and then into thoracic, abdominal or intercostal veins

41
Q

What is different about the dura in the spinal canal compared to the cranial cavity?

A

In the spinal canal the dura is not attached to the periosteum, there is a space between the dura and the bone

42
Q

what is the space between the dura and the bone called?

A

epidural space

43
Q

what does the epidural space contain?

A

adipose tissue and the anterior and posterior epidural venus plexuses

44
Q

what is the epidural space utilized in?

A

epidural anaesethesia

45
Q

what does the dorsal column/medial lemniscus system carry?

A

Fine touch, vibration sense and conscious proprioception (with the exception of some proprioception from the lower limb)

46
Q

what is the site of decussation (crossing over) in the Dorsal Column/Medial Lemniscus System?

A

In the medulla

47
Q

How many neurones are in the Dorsal Column/Medial Lemniscus System?

A

3

48
Q

What are the 3 neurones in the Dorsal Column/Medial Lemniscus System?

A
  • The gracile fasciculus contains first order neurones from the leg fibres and the cuneate fasciculus contains the first order of the arm fibres (ipsilateral information)
  • these fibres ascend to the medulla where they synapse and terminate on second order neurones located in the gracile nucleus and cuneate nucleus
  • the axons of the second order neurones will decussate in the medulla and ascend as the medial lemniscus
  • the second order neurones will synapse in the ventral posterior nucleus of the thalamus
  • the third order neurones will project to the somatosensory cortex, located in the post central gyrus of the parietal lobe
49
Q

what nucleus does the sensory fibres from the leg go to?

A

gracile nucleus

50
Q

what nucleus does the sensory fibres from the arm go to?

A

cuneate nucleus

51
Q

Describe proprioception from the lower limb.

A

Some information travels via the DC/ML system. Some ascends in the dorsal column to thoracic/upper lumbar regions, synapses in Clarke’s column, and then projects to the medulla in the dorsal spinocerebellar tract. Then rejoins medial lemniscal system to reach thalamus and cortex

52
Q

where does clarke’s column extend?

A

T1-L2

53
Q

what does the spinothalamic tract carry?

A

Carries pain, temperature, deep pressure

54
Q

what is the site of decussation (crossing over) in the spinothalamic tract?

A

fibres cross segmentally

55
Q

how many neurone are there in the spinothalamic tract?

A

3

56
Q

How is information carried to the cortex in the spinothalamic tract?

A
  • primary afferent , first order neurones enter the spinal cord
  • these will terminate in the contralateral dorsal horn and enter spinothalmic tract
  • the spinothalamic axons of the second order neurones will decussate by passing through the dental white commissure and entering the contralateral spinothalamic tract
  • axons carrying pain and temperature will decussate promptly within one segment of their origin while those carrying touch and pressure may ascend for several segments before crossing
  • the second order neurones will run directly through the brainstem in the spinal leminscus
  • these fibres will synapse in the ventral posterior nucleus of the thalamus where the third order neurones will project to the somatosensory cortex.
57
Q

Describe gate theory in its methods to modulate pain.

A

Dorsal root ganglion carrying pain via action potentials activates tract cell which cause pain to be carried to the thalamus.
Rubbing applied near damaged area comes in the same segment of the spinal cord and stimulates interneuron which is inhibitory on the tract cell that sends pain and therefor modulates the pain

58
Q

What are other ways of modulating pain and describe them?

A

Descending control of pain from brain stem to spinal cord pathways.
-Pain up through brain stem- activates a descending system which inhibits pain from the same synpases

59
Q

What are the 2 types of pain?

A
  • discrimitive

- affective

60
Q

What is the target nucleus in the thalamus of the spinothalamic (discriminative pain) tract?

A

VPL nucleus

61
Q

What is the corical projection of the spinothalamic (discriminative pain) tract?

A

post central gyrus

62
Q

what type of pain is discriminative and what fibres are involved?

A

Localising pain- well localised and brief

via A delta fibres (small myelinated fibres)

63
Q

What is the target nucleus in the thalamus of the spinoreticular (affective pain) tract?

A

Intralamnar nucleus

64
Q

What is the corical projection of the spinoreticular (affective pain) tract?

A

-cingulate gyrus
- Also connect to Hypothalamus and
Amygdala (deep in temporal lobe)

65
Q

what type of pain is affective and what fibres are involved?

A

Suffering pain- less localised and longer lasting

via unmyelinated C fibres

66
Q

What is the cingulate gyrus connected to?

A

-connected to limbic system (emotion)

67
Q

What is the somatotopic organisation of the neurones?

A

The body is mapped onto the cortex

68
Q

What is caused by sensory fibres crossing the midline?

A

the left side of the body is represented on the right cortex and vice versa

69
Q

where is the primary somatosensory cortex located?

A

postcentral gyrus

Neuroscience (21 decks)

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