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Neuroanatomy II > Spinal Cord Anatomy, Overview of Ascending and Descending Pathways > Flashcards

Spinal Cord Anatomy, Overview of Ascending and Descending Pathways Flashcards

1
Q

Where does the spinal cord begin and end?

A

Begins: Lower border of the foramen magnum (continuous with medulla oblongata).
Ends: Level of L1-L2 intervertebral disc (forms the conus medullaris).

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2
Q

What si the cauda equina?

A

Below the conus medullaris: Nerve fibers form the cauda equina

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3
Q

What are the meninges covering the spinal cord and their key features?

A

1️⃣ Dura Mater: Outer thick, fibrous layer (tough mother).
2️⃣ Arachnoid Mater: Middle delicate layer with cobweb-like structures.
3️⃣ Pia Mater: Inner layer tightly adhered to the spinal cord, extends as the filum terminale to anchor the spinal cord to the coccyx.
💧 Subarachnoid Space: Contains CSF (important for lumbar puncture).

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4
Q

Identify the major external landmarks of the spinal cord.

A

Cervical and lumbar enlargements: Supply upper and lower limbs.
Conus medullaris: Tapering end of the spinal cord.
Cauda equina: Bundle of nerve roots below the conus medullaris

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5
Q

Identify the major internal landmarks of the spinal cord.

A

Internal Landmarks:
Gray matter (central): Contains neuron cell bodies (processing).
White matter (peripheral): Contains myelinated axons (transmission).
Posterior horns: Sensory fibers.
Anterior horns: Motor fibers.

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6
Q

Describe the components and branches of a spinal nerve.

A

1️⃣ Dorsal Root: Carries sensory information to the spinal cord.
Contains the dorsal root ganglion (sensory neuron cell bodies).
2️⃣ Ventral Root: Carries motor information from the spinal cord.
3️⃣ Spinal Nerve: Union of dorsal and ventral roots; contains mixed fibers (sensory and motor).
4️⃣ Branches:
Dorsal Ramus: Innervates muscles and skin of the back.
Ventral Ramus: Innervates limbs and anterior trunk.
Autonomic branches in certain regions (sympathetic chain ganglia)

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7
Q

How are the meninges related to dorsal/ventral nerve roots and clinical procedures?

A

Dorsal and Ventral Roots: Pass through the meninges; CSF in the subarachnoid space surrounds them.

Root Compression: Can occur due to herniated discs or bone spurs, compressing nerves in intervertebral foramen.

Epidural Injection: Delivered into the epidural space (above dura mater).

Lumbar Puncture: Performed below L1-L2 (usually at L3-L4 or L4-L5) to avoid damaging the spinal cord.

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8
Q

What is a tract?

A

A tract is a collection of axons in the central nervous system (CNS).

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9
Q

What is a nerve?

A

A nerve is a collection of axons in the peripheral nervous system (PNS).

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10
Q

What is a nucleus?

A

A nucleus is a collection of neuronal bodies in the central nervous system (CNS).

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11
Q

What is a ganglion?

A

A ganglion is a collection of neuronal bodies in the peripheral nervous system (PNS).

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12
Q

Where is the spinal cord located and what are its boundaries?

A

The spinal cord extends from the base of the brain (medulla) to the lower border of the L1 vertebra in adults.

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13
Q

What are the segments of the spinal cord?

A

The spinal cord has 31 segments: C1-C8, T1-T12, L1-L5, S1-S5, Co-1.

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14
Q

What is the conus medullaris?

A

The conus medullaris is the terminal tapered portion of the spinal cord, located at the level of L1-L2.

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15
Q

What is the cauda equina?

A

The cauda equina is a collection of nerve roots distal to the conus medullaris, resembling a “horse’s tail.”

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16
Q

What is the filum terminale?

A

The filum terminale is the tapering end of the spinal cord beyond the conus medullaris, primarily composed of extensions of pia mater.

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17
Q

What is the function of the posterior funiculus in the spinal cord?

A

The posterior funiculus carries ascending sensory pathways, such as the dorsal column pathway (fine touch, proprioception, vibration).

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18
Q

What is the function of the lateral funiculus?

A

The lateral funiculus contains both ascending sensory pathways (e.g., spinothalamic tract) and descending motor pathways (e.g., corticospinal tract).

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19
Q

What is the function of the anterior funiculus?

A

The anterior funiculus contains ascending sensory pathways and descending motor pathways, contributing to motor control and sensory processing.

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20
Q

What is the role of the dorsal grey horn?

A

The dorsal grey horn processes sensory information received from the body.

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21
Q

What is the function of the ventral grey horn?

A

The ventral grey horn contains motor neurons that send out signals to skeletal muscles.

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22
Q

What is the role of the lateral grey horn?

A

The lateral grey horn contains the cell bodies of autonomic motor neurons, influencing involuntary processes such as heart rate.

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23
Q

What is the central canal in the spinal cord?

A

The central canal is a narrow, fluid-filled space running through the center of the spinal cord, containing cerebrospinal fluid.

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24
Q

What are ascending tracts in the spinal cord?

A

Ascending tracts carry sensory information from the spinal cord to the cerebral cortex.

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25
Q

What are descending tracts in the spinal cord?

A

Descending tracts carry motor commands from the cerebral cortex to the spinal cord, controlling voluntary movement.

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26
Q

What sensory modalities does the dorsal column pathway convey?

A

The dorsal column pathway conveys fine touch, vibration, and proprioception.

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27
Q

What is the first order neuron in the dorsal column pathway?

A

The first order neuron is a sensory neuron that enters the spinal cord and ascends in the dorsal column without synapsing, carrying information from sensory receptors.

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28
Q

Where does the second order neuron of the dorsal column pathway decussate?

A

The second order neuron decussates at the medulla, forming the medial lemniscus, which then ascends to the thalamus.

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29
Q

Where is the third order neuron of the dorsal column pathway located?

A

The third order neuron is located in the thalamus and relays sensory information to the somatosensory cortex.

30
Q

How do you test the sensory modalities carried by the dorsal column pathway?

A

Sensory modalities can be tested using fine touch (cotton wisp), vibration (tuning fork), and proprioception (joint position sense).

31
Q

What are the modalities carried by the lateral spinothalamic tract?

A

The lateral spinothalamic tract carries pain and temperature sensations.

32
Q

What is the pathway of the lateral spinothalamic tract from receptor to the cortex?

A

Receptors: Free nerve endings (for pain and temperature)
First order: Dorsal root ganglia
Second order: Substantia gelatinosa (dorsal grey horn)
Third order: Thalamus
Decussation: At the same spinal segment or one segment above via the ventral white commissure

33
Q

How is the lateral spinothalamic tract tested clinically?

A

Pain is tested with sterile neurological examination pins, and temperature is tested with a volatile spray (e.g., ethyl chloride) which induces a cold sensation.

34
Q

What are the modalities carried by the anterior spinothalamic tract?

A

The anterior spinothalamic tract carries crude touch and pressure sensations.

35
Q

What is the pathway of the anterior spinothalamic tract?

A

Receptors: Free nerve endings
First order: Dorsal root ganglia
Second order: Substantia gelatinosa
Third order: Thalamus
Decussation: Some segments above the spinal level of entry

36
Q

What sensory modalities are conveyed by the dorsal column pathway?

A

The dorsal column pathway conveys fine touch, vibration, proprioception, two-point discrimination, and stereognosis.

37
Q

What is the pathway of the dorsal column tracts (Gracilis and Cuneatus)?

A
  • Receptors: Meissner’s corpuscles, Merkel’s discs, tendon organs, muscle spindles (mechanoreceptors and proprioceptors)
  • First order: Dorsal root ganglion
  • Second order: Nucleus gracilis and nucleus cuneatus (in the medulla)
  • Third order: Thalamus
  • Decussation: At the level of the sensory decussation in the medulla
38
Q

How are the fibers from the lower and upper body organized in the dorsal column?

A
  • Gracile fasciculus carries fibers from the lower body (below T6), located medially.
  • Cuneate fasciculus carries fibers from the upper body (above T6), located laterally.
39
Q

What happens to the dorsal column fibers after they reach the medulla?

A

The first-order neurons synapse in the gracile and cuneate nuclei in the medulla, and the second-order neurons decussate as internal arcuate fibers, forming the medial lemniscus, which ascends to the thalamus.

40
Q

What is the final destination of the dorsal column pathway in the cerebrum?

A

The medial lemniscus terminates in the ventral posterolateral (VPL) nucleus of the thalamus. Third-order neurons project from the VPL to the primary somatosensory cortex via the posterior limb of the internal capsule.

41
Q

How is the dorsal column pathway tested clinically?

A

Vibration: Tested using a 128Hz tuning fork on bony prominences.
Proprioception: Tested by moving a patient’s finger or toe and asking them to identify the position.
Fine touch: Tested using two-point discrimination and light touch.

42
Q

How is the spinothalamic tract tested clinically?

A

Pain: Tested using a pinprick (sterile neurological examination pins).
Temperature: Tested using a cold sensation from a volatile spray (e.g., ethyl chloride).

43
Q

How does the spinothalamic tract ascend through the brainstem?

A

The spinothalamic tract ascends through the medulla, pons, and midbrain to the thalamus, then relays sensory information to the postcentral gyrus in the primary somatosensory cortex.

44
Q

Where do the second-order neurons of the dorsal column pathway synapse in the brainstem?

A

The second-order neurons synapse in the gracile and cuneate nuclei of the medulla, then cross over to form the medial lemniscus.

45
Q

What is the corticospinal tract also referred to as?

A

The corticospinal tract is also known as the pyramidal tract, as it forms visible ridges, called pyramids, on the anterior surface of the medulla.

46
Q

What is the main function of the corticospinal tract?

A

The corticospinal tract controls voluntary movements of the contralateral (opposite) limbs and trunk, particularly the precision and speed of skilled movements.

47
Q

Where do the upper motor neurons (UMNs) of the corticospinal tract originate?

A

The UMNs of the corticospinal tract originate from the motor and premotor areas of the frontal lobe, specifically the pre-central gyrus (primary motor cortex).

48
Q

What is the pathway of corticospinal tract fibers in the cerebrum?

A

Corticospinal tract fibers travel from the motor cortex to the subcortical white matter, passing through the corona radiata before entering the posterior limb of the internal capsule.

49
Q

Through which structures in the brainstem does the corticospinal tract pass?

A

The corticospinal tract passes through the crus cerebri in the midbrain, the basilar pons, and the pyramids of the medulla.

50
Q

What happens to the corticospinal tract fibers at the medulla?

A

Approximately 90% of the fibers cross at the decussation of the pyramids in the caudal medulla, forming the lateral corticospinal tract. The remaining 10% form the ventral corticospinal tract, which decussates at the target spinal level.

51
Q

Where do the lateral and ventral corticospinal tracts travel in the spinal cord?

A
  • The lateral corticospinal tract travels in the lateral funiculus.
  • The ventral corticospinal tract travels in the anterior funiculus.
52
Q

Where do the corticospinal tracts synapse in the spinal cord?

A

The corticospinal tracts synapse with lower motor neurons (LMNs) in the anterior horn of the spinal cord at their respective levels.

53
Q

What are the signs and symptoms of a lower motor neuron (LMN) lesion?

A
  • Paralysis or paresis of specific muscles
  • Loss or reduction of tendon reflex activity
  • Reduced muscle tone
  • Fasciculations (muscle twitches)
  • Muscle atrophy
54
Q

What are the signs and symptoms of an upper motor neuron (UMN) lesion?

A
  • Paralysis or paresis of movements
  • Increased tendon reflex activity
  • Increased muscle tone (spasticity)
55
Q

How does a corticospinal tract lesion affect voluntary movement?

A

A lesion in the corticospinal tract can result in weakness or paralysis of voluntary movements, especially on the contralateral side of the body, depending on where the tract is damaged (e.g., in the brain or spinal cord).

56
Q

What clinical signs would you expect in a patient with a UMN lesion of the corticospinal tract?

A

You would observe spasticity, hyperreflexia (increased reflexes), and possible clonus (involuntary muscle contractions). There may also be a positive Babinski sign (upward toe movement).

57
Q

What are the extrapyramidal tracts?

A

The extrapyramidal tracts include the vestibulospinal, reticulospinal, rubrospinal, and tectospinal tracts, which are responsible for the regulation of posture, balance, and involuntary movements. These tracts do not pass through the pyramids of the medulla.

58
Q

How do extrapyramidal tracts differ from the corticospinal tract?

A

Unlike the corticospinal tract (which controls voluntary, skilled movements), the extrapyramidal tracts are involved in involuntary movements, posture regulation, and muscle tone adjustments

59
Q

What is the function of the vestibulospinal tract?

A

The vestibulospinal tract is involved in maintaining balance and posture by controlling the extensor muscles of the trunk and limbs in response to vestibular input from the inner ear.

60
Q

Where does the vestibulospinal tract originate and decussate?

A

The vestibulospinal tract originates in the vestibular nuclei in the brainstem and does not decussate (cross over). It descends ipsilaterally (on the same side).

61
Q

What is the role of the reticulospinal tract?

A

The reticulospinal tract helps regulate muscle tone and posture and is involved in controlling the reflex activity of the spinal cord, especially in response to stimuli from the brainstem.

62
Q

Where does the reticulospinal tract originate and decussate?

A

The reticulospinal tract originates in the reticular formation of the brainstem. Some fibers decussate, but many remain ipsilateral (on the same side).

63
Q

What is the function of the rubrospinal tract?

A

The rubrospinal tract is involved in controlling fine motor movements, particularly those related to the upper limbs, and assists in voluntary movement coordination.

64
Q

Where does the rubrospinal tract originate and decussate?

A

The rubrospinal tract originates in the red nucleus of the midbrain and decussates immediately (crosses over) to the opposite side.

65
Q

What is the function of the tectospinal tract?

A

The tectospinal tract is involved in coordinating head and neck movements in response to visual and auditory stimuli, helping to orient the body toward stimuli.

66
Q

Where does the tectospinal tract originate and decussate?

A

The tectospinal tract originates in the superior colliculus of the midbrain and decussates immediately at the level of the midbrain, before descending to the cervical spinal cord.

67
Q

How can lesions in the extrapyramidal tracts manifest clinically?

A

Lesions in the extrapyramidal tracts can result in motor disturbances such as rigidity, tremors, postural instability, and dyskinesias (involuntary movements). These symptoms are often seen in conditions like Parkinson’s disease.

68
Q

What is the most common cause of spinal cord syndromes?

A

Spinal cord syndromes are commonly caused by trauma, compression, ischemia, or infections affecting the spinal cord, leading to various deficits depending on the location and extent of injury.

69
Q

What is Brown-Séquard Syndrome?

A

Brown-Séquard Syndrome is a condition resulting from hemisection (damage to one side) of the spinal cord. It causes:

  • Ipsilateral (same side) motor loss and proprioception loss.
  • Contralateral (opposite side) pain and temperature sensation loss.
70
Q

What is Anterior Cord Syndrome?

A

Anterior Cord Syndrome results from damage to the anterior part of the spinal cord, affecting the corticospinal and spinothalamic tracts. It leads to:

Bilateral motor paralysis (due to corticospinal tract damage).
Loss of pain and temperature sensation (due to spinothalamic tract damage).
Preserved proprioception and vibration (due to the intact posterior column).

71
Q

What is Central Cord Syndrome?

A

Central Cord Syndrome is typically caused by trauma that affects the central portion of the spinal cord. It results in:

Greater motor weakness in the upper limbs than in the lower limbs.
Loss of pain and temperature sensation in a “cape-like” distribution across the upper body.

72
Q

What is the clinical presentation of a Posterior Cord Syndrome?

A

A: Posterior Cord Syndrome involves damage to the dorsal columns, leading to:

Loss of proprioception, vibration, and fine touch sensation.
Preservation of motor function and pain/temperature sensation

Neuroanatomy II (1 decks)

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