Spinal cord, sensory and motor pathways

Question 1

Where does spinal cord end?

Answer 1

Ends at level of lower border of L1 vertebra (L1-L2 disc)

Question 2

What is the lowest part of the spinal cord? What is it’s shape?

Answer 2

The lowest part of the spinal cord is conical and is called the conus medullaris

Question 3

What is continuous with the conus medullaris? What is it composed of and where does it end?

Answer 3

fibrous cord called the filum terminale which is a strand of pia mater continue to the dorsal surface of the first coccygeal vertebra

Question 4

What are cervical and lumbar enlargements?

Answer 4

The enlargements contain increased numbers of motor neurons and interneurons. The cervical enlargement which supplies the upper limb is extended from C5 to T1 and the lumbosacral enlargement, which supplies the lower extremity, extends from L1 to S3.

Question 5

Describe the growth rate of the vertebral canal and the spinal cord

Answer 5

The spinal cord reaches its adult length before the vertebral canal does. Until the third month of fetal life, they both grow at the same rate, and the cord fills the canal. Thereafter, the vertebral column grows faster than the spinal cord does, so that at birth the spinal cord ends at L3 vertebra.

Question 6

What are the meninges of the spinal cord?

Answer 6

DAP
Dura mater
Arachnoid mater
Pia mater

Question 7

What are the spaces between the meninges?

Answer 7

The space between the dura mater and the wall of the vertebral canal is called the extradural (or epidural) space

The space between the dura and the arachnoid is called the subdural space.

The arachnoid and pia are separated by the subarachnoid space which contains the cerebrospinal fluid (CSF)

Question 8

What is the ligament that is a membranous continuation of the pia mater? What is it’s main purpose?

Answer 8

Denticulate ligament: attaches along a line between the dorsal and ventral roots of the spinal nerves intermittently. The lateral projection of the ligament tethers the spinal cord to the arachnoid, and through it to the dura mater, therefore stabilize the spinal cord within the vertebral column.

Question 9

Describe a lumbar puncture

Answer 9

The spinal cord terminates at vertebral level L1–L2 however, the arachnoid, dural sheaths and subarachnoid space continue caudally to S2. Therefore, needles can be safely inserted into the subarachnoid space (L3-L4)) in order to remove CSF for diagnostic purposes.

Question 10

Describe grey matter of spinal cord

Answer 10

H shaped, halves connected by grey commissure. Dorsal and ventral horns and in T1-L2 segments there is a lateral horn where preganglionic sympathetic neurons reside

Question 11

Describe white matter of spinal cord

Answer 11

Right and left halves via deep anterior median fissure and shallow posterior median sulcus. dorsal nerve roots are attached to the spinal cord along a shallow vertical groove, the posterolateral sulcus, which lies at a short distance anterior to the posterior median sulcus. The ventral nerve roots exit in the anterolateral sulcus

Question 12

Where are anterior and posterior funiculus? Where is lateral funiculus formed?

Answer 12

White matter medial to the posterolateral sulcus is called the posterior funiculus (posterior white column) and the anterior funiculus (anterior white column) lies medial to anterolateral sulcus

The lateral funiculus is formed between the anterolateral and posterolateral sulci. The white matter of the two halves of the spinal cord is connected the white commissures.

Question 13

Describe the thickness of spinal cord matters and why this is so

Answer 13

White matter is thickest in the cervical levels, where most ascending (sensory) fibers have already entered the cord and most descending (motor) fibers have not yet terminated on their targets. The gray matter is thicker at the cervical and lumbosacral levels than at the thoracic levels, particularly at the ventral horns, where lower motor neurons for the upper and lower limbs

Question 14

What is a tract and what are their directions and why?

Answer 14

A tract may be defined as a collection of nerve fibres having the same origin, course, and termination. Tracts may be ascending (sensory) or descending (motor). They are usually named after the masses of grey matter connected by them

Question 15

Name the main ascending (sensory) tracts

Answer 15

Dorsal Columns / Medial Lemniscal Pathway
Spinocerebellar tracts (ventral & dorsal)
Spinothalamic tract

Question 16

Name the main descending (motor) tracts

Answer 16

Corticospinal Tracts
Rubrospinal Tract
Tectospinal Tract
Vestibulospinal
Reticulospinal tract

Question 17

What is a spinal cord lesion? What are the main causes of this?

Answer 17

The Spinal cord lesions are a major source of disability because they affect motor, sensory, and autonomic pathways. The most common causes of spinal cord dysfunction are as follow:

Trauma or mechanical
Vascular
Nutritional deficiency (B12 or E Vitamins)
Cancer
Epidural abscess
Infection (such as HIV)
Inflammation such as MS or Lupus
Degenerative/ developmental

Question 18

Describe how paralysis occurs

Answer 18

Interruption of corticospinal pathways anywhere between the motor area of the cerebral cortex and the muscles themselves.

This pathway comprises a two-neuron pathway that is responsible for movement, upper and lower motor neurons

Question 19

Describe upper and lower motor neurones

Answer 19

The upper motor neuron is located in the cerebral cortex and its axon terminates in the spinal cord. The second neuron is located in the ventral horn of the spinal cord and sends out an axon that travels through a peripheral nerve to innervate muscle. This neuron is referred to as the lower motor neuron.

Question 20

Contrast upper and lower motor neurone symptoms regarding lesions

Answer 20

Upper motor neuron

-Spastic paralysis of the affected muscles (increase muscle tone)
-Exaggerated tendon reflexes
-Sign of Babinski – upturning and spreading of the toes on stroking sole of foot (extensor plantar response) instead of normal babinski reflex

Lower motor neuron

-Flaccid paralysis of affected muscles (decrease muscle tone)
-Diminished or absent tendon reflexes
-Progressive atrophy of deprived muscles

Question 21

Compare complete (transverse) lesions to incomplete lesions

Answer 21

Complete (transverse) spinal cord injury has no motor or sensory functions below the level of injury.

Incomplete spinal cord injury has some preservation of sensory and/or motor function below the level of injury. There are a number of different patterns of incomplete cord injury such as:
-Brown Sequard Syndrome (hemicord section)
-Posterior Cord Lesion

Question 22

What is Brown Sequard Syndrome?

Answer 22

One side of the spinal cord is damaged with dorsal column interruption resulting in ipsilateral paralysis and loss of proprioception with contralateral loss of temperature and pain sensation. Relatively normal pain and temperature sensation remain on the ipsilateral side

Question 23

Describe a posterior cord lesion

Answer 23

Preserves motor function, pain and temperature pathways but with loss of light touch, proprioception and vibration due to damage to the posterior column pathway (blue color)

Question 24

Describe ALS and how it occurs

Answer 24

Progressive degenerative disease in which the corticospinal tracts (upper motor neuron) and ventral horn cells (lower motor neuron) degenerate, often beginning with the lower limbs and later involving the upper limbs.
Degeneration of the ventral horn cells in the cervical spinal cord results in weakness and, ultimately, in loss of control in muscles of the hand, trunk, and lower limbs. Bladder and bowel functions are also impaired due to the loss of descending autonomic pathways.

Question 25

A 24-year-old man was admitted to a hospital due to a stab injury in his spinal cord during a violent fight with his friend. In the emergency room, exam was notable for the following symptoms:
- Flaccid paralysis in the right leg
- T6 loss of proprioception and touch sensations in the right leg
- T6 loss of loss of pain and temperature in the left leg

(a) On the basis of the mentioned symptoms, where is the lesion in the spinal cord segment & the vertebral level?
(b) What kind of lesion of spinal cord can cause these symptoms?
(C) Explain how the patient lost pain sensation in the left side and proprioception sensation in the right side

Answer 25

a) T6 spinal cord level, T4 vertebral level
b) Brown-Sequard syndrome
c) pain and temp are carried from contralateral side and cross over in the spinal cord whereas proprioception crosses over in the medulla and is ipsilateral

Question 26

A 58-year-old woman woke up one morning with fever and a painful, blistering rash on his right back. He visited his family doctor; on examination he had unilateral vesicular eruption in the distribution
(week 1 workshop Q3). There was decreased pinprick sensation in the same distribution as the rash, however muscle movements were normal.

On the basis of the aforementioned symptoms and signs,
a) what is the most likely diagnosis?
b) what part of the spinal nerve might be affected? Root/nerve/ramus (ventral or lateral) /dorsal root ganglion

Answer 26

a) shingles
b) Dorsal root ganglion as it is sensory syndrome and appears as single stripe of blisters within a dermatome. T3 to L3 dermatome lesions are frequent

Question 27

A 61-year-old man complained to his local physician that his legs had begun to feel weak over the past few months and that the weakness was progressive over time involving his arms as well. Eventually, he
couldn’t move his limbs at all, and he began to lose bladder control (Sensation seemed to be relatively intact).
Based on the symptoms, explain what is the most likely diagnosis?

Answer 27

Motor neurons involved, progressive. Begins from lower limbs and spreads upwards. Both upper and lower motor neurons affected. Therefore ALS

Question 28

Two patients were presented to Brisbane Royal hospital emergency due to a car accident. On the clinical examinations, both patients showed signs of paralysis in their right leg. The clinician believes
patient 1 shows signs of upper motor lesion and patient 2 has lower motor lesion symptoms. Explain the difference between lower motor neuron (LMN) and upper motor neuron (UMN) lesions (be sure to include type of paralysis, tendon reflex, contralateral or ipsilateral).

Answer 28

Lower motor neurons terminates in muscle, muscle directly affected. Flaccid paralysis. Upper motor neuron paralysis still has resistance therefore spastic paralysis