6.01 - Spinal Cord Trauma

Front 1

Name the neurotransmitter released by preganglionic autonomic neurons. What receptor type does this transmitter activate?

Back 1

Acetycholine. Nicotinic receptors, which are ionotropic and fast-acting.

Front 2

At what spinal levels are sympathetic preganglion cell bodies located? In what part of the gray matter of the spinal of the cord are they located?

Back 2

Sympathetic cell bodies are found in the intermediolateral gray matter (also known as the lateral horn) of the spinal cord from T1 to L2.

Front 3

Where do the axons of preganglionic sympathetic neurons terminate?

Back 3

In the paravertebral ganglia or the prevertebral ganglia. (Exception: adrenal medulla)

Of the paravertebral ganglia, the thoracic 12 form the sympathetic trunk, while other paravertebral ganglia include the superior cervical ganglion, which provides sympathetic supply to the head and neck. The prevertebral ganglia include the coeliac ganglia (which supplies the digestive tract), as well as the superior and inferior mesenteric ganglia. An exception is the adrenal gland, located superior to the kidney, in which preganglionic fibres also terminate, onto chromaffin cells which secrete adrenaline (80%) and noradrenaline (20%) directly into the blood.

Front 4

What neurotransmitter is typically released by sympathetic postganglionic neurons? Name an exception to this rule.

Back 4

Noradrenaline. An exception is the sympathetic control of sweat glands, in which postganglionic fibres release acetylcholine, activating muscarinic receptors.

Front 5

Through which root (anterior or posterior) do preganglionic sympathetic fibres leave the spinal cord?

Back 5

The anterior root. The fibres of motoneurons also leave through this root.

Front 6

Which structure connects the mixed spinal nerve with the sympathetic trunk ganglion?

Back 6

The white ramus (so named as it is myelinated) connects the mixed spinal nerve (after the posterior and anterior roots have joined) to the sympathetic trunk.

Front 7

How many neurons are involved in an autonomic reflex arc?

Back 7

Three. Sympathetic preganglionic neurons receive excitatory or inhibitory impulses from spinal afferents via interneurons. They may also receive impulse from descending fibres (with or without interneurons).

Front 8

How does the typical location of a sympathetic ganglion differ from that of a parasympathetic one?

Back 8

Sympathetic ganglia are typically located paravertebrally or prevertebrally i.e. distant from their target organ. Parasympathetic ganglia are typically located on or near their target organ.

Front 9

What neurotransmitter is released by postganglionic parasympathetic fibres? On which type of receptor does this transmitter act?

Back 9

Acetylcholine, acting on muscarinic receptors, which are G-protein-coupled (metabotropic).

Front 10

Where are the cell bodies of sensory spinal neurons located?

Back 10

In the dorsal root ganglia.

Front 11

Define tetraplegia. In which spinal cord region must the lesion be at or above to cause tetraplegia?

Back 11

Tetraplegia is an injury to the spinal cord in the cervical region or above, with associated loss of muscle strength in all 4 extremities.

The term tetraplegia replaces 'quadraplegia' as both 'tetra' and 'plegia' have a Greek root.

Front 12

Injuries to which spinal cord regions cause paraplegia?

Back 12

Injury in the spinal cord in the thoracic, lumbar, or sacral segments, including the cauda equina and conus medullaris.

Front 13

What are the motor and sensory deficits in a lateral hemisection of the spinal cord? Which spinal tracts are responsible for these deficits?

Back 13

Interruption of the lateral corticospinal tract causes ipsilateral spastic paralysis below the level of the lesion, as well as an ipsilateral Babinski sign. Due to spinal shock, abnormal reflexes and the Babinski sign may not present in acute injury.
Interruption of the dorsal column-medial lemniscus pathway causes ipsilateral loss of tactile discrimination, vibration and proprioception below the level of the lesion.
Interruption of the lateral spinothalamic tracts causes contralateral loss of pain and temperature sensation usually 2-3 segments below the level of the lesion.

Front 14

Who were Brown and Séquard?

Back 14

One and the same. Charles Edward Brown-Séquard was a Mauritian physiologist and neurologist who, in 1850, became the first to describe what is now called Brown-Séquard syndrome. His unusual double-barrelled last name owes to his American father and French mother.

Front 15

What features of an neuronal injury can be used to distinguish between an upper motor neuron (UMN) lesion and a lower motor neuron (LMN) lesion?

Back 15

UMN Lesion:
Increased muscle tone (spastic paralysis)
Increased deep tendon reflexes
Upgoing plantar response

LMN:
Decreased muscle tone (flaccid paralysis)
Decreased or absent deep tendon reflexes
Downgoing plantar response
Fasciculations

Front 16

What is the difference between the neurologic level of injury and the skeletal level of injury?

Back 16

The neurologic level of injury is the most caudal level at which motor and sensory levels are intact, whereas the skeletal level of injury is the level of greatest vertebral damage on radiographic imaging.

Front 17

What is neurogenic shock? How can it be distinguished from hypovolemic shock?

Back 17

Neurogenic shock is manifested by the triad of hypotension, bradycardia, and hypothermia. Shock tends to occur more commonly in injuries above T6, secondary to the disruption of the sympathetic outflow from T1-L2 and to unopposed vagal tone, leading to a decrease in vascular resistance, and associated hypotension. Such a disruption also leads to a loss of cardiac sympathetic input, from T1-T5 spinal levels, leading to bradycardia.

In acute trauma it is important to differentiate neurogenic shock from hypovolemic shock. Unlike neurogenic shock, hypovolemic shock tends to associated with tachycardia.

Front 18

What is spinal shock?

Back 18

Spinal shock refers to a transient state of diminished or absent reflexes below the level of the lesion, with associated loss of all sensimotor functions. An initial increase in blood pressure due to the release of catecholamines, followed by hypotension, is noted. Flaccid paralysis, including of the bowel and bladder, is observed, and sometimes sustained priapism develops. These symptoms tend to last several hours to days until the reflex arcs below the level of the injury begin to function again (e.g., bulbocavernosus reflex, deep tendon reflexes)

Front 19

How does the location of the decussation of the spinothalamic tract and that of the lateral corticospinal tract differ?

Back 19

The spinothalamic tract decussates in the spinal cord at the anterior white comissure usually 1-2 segments above the spinal root entry. The lateral corticospinal tract decussates at the most caudal extent of the medulla in the brainstem in the pyramidal decussation, located ventrally.

Front 20

What sensation are Pacinian corpuscles responsible for? What sensation are Meissner's corpuscles responsible for?

Back 20

Pacinian (or lamellar) corpuscles are responsible for sensing vibration and pressure. The vibration sense is also used in determining texture, e.g. rough vs smooth. Meissner's (or tactile) corpuscles are responsible for light touch sensation.

Front 21

What is the function of the spinocerebellar tract? Where in the spinal cord is it located?

Back 21

The spinocerebellar tract is responsible for unconscious proprioceptive information, relayed to the cerebellum without decussation. It is located anterolaterally in the spinal cord, just outside o the spinothalamic tract.

Front 22

Describe the pathway of the neurons involved in the corticospinal tract between primary motor cortex and skeletal muscle.

Back 22

Two neurons are involved. The corticospinal tract is formed by neuronal fibres from the primary motor cortex (about 40%) as well as from M2, S1 and S2 in the cortex. These fibres then travel via the internal capsule to the cerebral peduncles and thence through the brainstem, decussating at the caudal extent of the medulla. From here the majority (about 80%) descend in the lateral corticospinal tract, eventually synapsing with lower motor neurons in the ventral horn. These second neurons send their fibres out via the ventral root and they via spinal nerves to their target muscles

Front 23

Which spinal roots are tested clinically by tapping the tendon of the following muscles?
(a) Biceps
(b) Brachioradialis
(c) Triceps
(d) Patellar
(e) Achilles

Back 23

(a) Biceps - C5 (C6)
(b) Brachioradialis - C6
(c) Triceps - C7
(d) Patellar - L4
(e) Achilles - S1

Front 24

A spinal cord injury above what level puts the patient at risk of autonomic dysreflexia (AD)?

Back 24

Patients are at risk of AD if their lesion is above the level of the splanchnic sympathetic outflow about T6. There have been documented cases with lesions as low as T10 though.

Front 25

Name five common signs and symptoms of autonomic dysreflexia.

Back 25

Sudden, significant rise in systolic and diastolic blood pressure. Note that normal systolic blood pressure for spinal cord injury patients above T6 is 90-100 mm Hg; blood pressure 20-40 mm Hg above the reference range for such patients may be a sign of AD.
Profuse sweating above the level of lesion, especially in the face, neck, and shoulders.
Flushing of the skin above the level of the lesion.
Nasal congestion
Blurred vision
Spots in the patient's visual field

Front 26

What is the commonest cause of traumatic spinal cord injuries (SCI)?

Back 26

Motor vehicle accidents are the commonest cause of traumatic SCI, accounting for approximately 50% of such cases.

Front 27

What motor and sensory deficits are noted the anterior cord syndrome? Which artery supplies this region of the cord?

Back 27

The anterior cord syndrome can result from occlusion of the anterior spinal artery which supplies this region of the cord.

Patients typically display: Complete motor paralysis below the level of the lesion due to interruption of the corticospinal tract
Loss of pain and temperature sensation at and below the level of the lesion due to interruption of the spinothalamic tract
Retained proprioception and vibratory sensation due to intact dorsal column-medial leminscus pathway.

Front 28

Where in the spinal cord are the cell bodies of lower motor neurons located? What is the commonest degenerative disease affecting these neurons?

Back 28

The ventral horn of the spinal gray matter. Amyotrophic lateral sclerosis (ALS) is the most common degenerative disease of the motor neuron system. It affects lower motor neurons that reside in the anterior horn of the spinal cord and in the brain stem; corticospinal upper motor neurons that reside in the precentral gyrus; and, frequently, prefrontal motor neurons that are involved in planning or orchestrating the work of the upper and lower motor neurons. If only lower motor neurons are involved, the disease is called progressive muscular atrophy (PMA).

Front 29

How is a complete spinal cord lesion defined?

Back 29

In a complete lesion, no voluntary motor or sensory function is preserved more than 3 segments below the level of the injury and in particular the lowest sacral segments; this includes impairment of autonomic function with loss of bladder and bowel control. Conversely, if there is some preservation of voluntary motor and/or sensory function, including sacral sensory sparing, the injury is defined as incomplete.

Front 30

Descending tracts may be categorised into those associated with basic movements and skilled movements. Which tracts are in each category and what are the functions of each group of tracts?

Back 30

Basic movements - reticulospinal, vestibulospinal - these tracts maintain posture and regulate autonomics.

Skilled - rubrospinal, corticospinal - these tracts are involved in the skilled distal movements of limbs.

Front 31

Name the four parasympathetic ganglia that innervate structures in the head and neck, their cranial nerve supply and the major structures they innervate.

Back 31

Cillary - III - sphincter pupillae
Pterygopalantine - VII - lacrimal gland and nasal septum
Submandibular - VII - sublingual and submandibular glands
Otic - IX - parotid gland

Front 32

What receptor type is found at the neuromuscular junction? Which autoimmune condition specifically affects these receptors?

Back 32

Nicotinic cholinergic receptors. Myasthenia Gravis typically involves autoantibodies acting against these receptors. The clinical hallmark of this disorder is muscle fatigue.

Front 33

Name the commonest cause of traumatic epidural haemorrhage.

Back 33

Rupture of the middle meningeal artery (or vein) caused by trauma to the temporal bone.

The middle meningeal artery is a branch of the maxillary artery which is itself a terminal branch of the external carotid artery. The artery runs intracranially under the pterion, the meeting point of four cranial bones and the weakest point in the skull.

Front 34

Does hypotension following acute injury to the cervical or high thoracic spinal cord indicate the need for active fluid resuscitation?

Back 34

No, hypotension does not necessarily indicate volume loss and may instead be due to interruption of descending inputs to preganglionic sympathetic neurons or interruption of sympathetic outflow. Overinfusion in patients with uncomplicated spinal shock may cause pulmonary oedema.

Front 35

Which of the following factors is/are associated with a complete spinal cord lesion in the lower cervical region?

a) Diaphragmatic breathing.
b) Long-term dependence on mechanical ventilator.
c) Sputum retention and atelectasis.
d) Ventilation-perfusion mismatch.

Back 35

A,C, D are TRUE
B is False

A- A complete injury in the lower cervical cord causes paralysis of all intercostal muscles and therefore reliance on diaphragmatic function for breathing.
B - Pressure support or full mechanical ventilation may sometimes be necessary initially after injury, if ascending post-traumatic cord oedema or pneumonia develops. However, longer term artificial ventilation is not required when innervation to the diaphragm from C3-5 cord segments through the phrenic nerves remains intact.

C- Loss of intercostal muscle function results in impairment of coughing and effective clearance of secretions which commonly leads to atelectasis. Regular chest physiotherapy with postural drainage, assisted coughing and breathing exercises are essential to prevent chest complications.

D- Alterations in ventilation and perfusion after cervical and high thoracic spinal cord injury result in 1) underventilation of perfused alveoli, leading to shunting of venous blood through the lungs and 2) underperfusion of ventilated alveoli, which increases the dead space.