PBL 4 - Spinal Shock Flashcards
Describe the corticobulbar pathway.
- Upper motor neuron fibres converge in the cerebral cortex and pass through the internal capsule
a. They then enter the brainstem - In the brainstem, upper motor neurons terminate on the motor nuclei of the cranial nerves (the LMN)
- Most upper motor neurons innervate the cranial nerves bilaterally
a. e.g. fibres from the left primary motor cortex innervate the left and right trochlear nerves - There are 2 exceptions, where upper motor neurons innervate the cranial nerves contralaterally
a. Facial nerve (CN7)
b. Hypoglossal nerve (CN12)
Describe the corticospinal pathway.
- Motor input comes from 4 areas:
a. Primary motor cortex
b. Premotor cortex
c. Supplementary motor area
d. Somatosensory area - UMN crosses internal capsule and descends into the medulla.
- In the medulla, the UMN splits into 2:
a. LATERAL CORTICOSPINAL TRACT (85%)
- –Fibres decussate in the medulla
- –Fibres descend to terminate in the ventral horn of all spinal levels
- –They then synapse onto LMN
b. ANTERIOR CORTICOSPINAL TRACT (15%)
- –Fibres remain ipsilateral
- –Fibres descend into the cervical and upper thoracic spinal segments
- –Fibres then decussate and synapse onto the LMN
Describe the functions of the 4 areas which create motor input.
Primary motor cortex
-Excitation of a single neuron makes a specific movement, rather than exciting a specific muscle
Premotor cortex
- More specific movements
- Mirror neurons activated when observing/copying other people
Supplementary motor area
-Bilateral movements
Somatosensory area
-Input from ascending sensory tracts
List the extrapyramidal descending motor tracts.
Reticulospinal tract
Vestibulospinal tract
Rubrospinal tract
Tectospinal tract
Which extrapyramidal tracts decussate to provide contralateral innervation, and which ones stay ipsilateral?
IPSILATERAL:
Reticulospinal
Vestibulospinal
CONTRALATERAL:
Tectospinal
Rubrospinal
Describe the function of each extrapyramidal tract.
RETICULOSPINAL
- Medial: aids voluntary movements, increases muscle tone
- Lateral: inhibits voluntary movements, decreases muscle tone
VESTIBULOSPINAL
1. Controls balance and posture (receives input from balance organs)
RUBROSPINAL
1. Fine control of hand movements
TECTOSPINAL
1. Head movements following visual stimuli
Describe the dorsal column-medial lemniscus pathway.
- Non-pain stimuli are carried from receptors to the spinal cord via primary neurons; these give off 2 branches:
a. Minor branch: into deep dorsal horn
b. Major branch: into dorsal column - The dorsal column branch then ascends into the medulla
- In the medulla, the primary neuron synapses with the secondary neuron, which then decussates (i.e. crosses over) onto the other side of the medulla via the internal arcuate fibres
a. This then ascends into the thalamus via the medial lemniscus (of the medulla) - In the thalamus, the secondary neuron synapses with the tertiary neuron
- This cross the internal capsule of the brain and enters the sensory cortex
Describe the ASIA impairment scale.
A – Complete
-No motor/sensory function below S4-S5
B – Incomplete
- Sensory function below neurological level and in S4-S5
- No motor function below neurological level
C – Incomplete:
- Motor function preserved below neurological level
- More than half of the key muscle groups below neurological level have a muscle grade of less than 3
D – Incomplete
-At least half of the key muscle groups below neurological level of a muscle grade of 3
E – Normal:
-Sensory/motor function is normal
Briefly describe the effects of spinal injury at different levels.
Cervical region:
- Quadriplegia
- Compromised sympathetic nervous system:
a. Autonomic dysreflexia
b. Hypotension
c. Bradycardia - Inability to breathe if injury is C3 or above
Thoracic region:
- Paraplegic
a. Full use of upper limb; varying use of chest/back muscles - Compromised sympathetic nervous system if spinal injury is above T4 (normal below that)
Lumbar/sacral region:
- Paraplegic
a. Some lower limb movement may be possible
At what point will spinal injuries cause:
a) Respiratory failure?
b) Respiratory distress?
c) Loss of sympathetic innervation?
Respiratory failure - C1-C3
Respiratory distress - C4
Loss of sympathetic innervation - T6
List consequences of spinal injury.
- Respiratory failure
- Respiratory distress
- Loss of sympathetic innervation
- Spinal shock
- Bladder/bowel dysfunction
- Sexual dysfunction in males
- Loss of sensation
- Other consequences:
a. DVT
b. Pulmonary embolism
c. Acute/chronic neuropathic pain
d. Autonomic dysreflexia
What is autonomic dysreflexia?
When noxious stimuli below the level of injury cause sympathetic overactivity due to the loss of parasympathetic activity from the brain and sacral spine
NOTE: this is permanent, as opposed to the loss of sympathetic innervation due to injury
List some clinical features of autonomic dysreflexia.
- Tachycardia
- Extreme hypertension
- Headaches
- Sweating
- Loss of bladder/bowel control
- Increased risk of stroke
Define spinal shock.
Temporary suppression of all reflex activity in the spine below the level of injury
Describe the pathogenesis of spinal shock.
Trauma causes K+ to move into the extracellular fluid
Tissue destruction occurs:
- Traumatic incident (instant)
- Post-traumatic infarction (minutes-days)
a. Microscopic haemorrhages in grey matter/pia mater
b. White matter becomes oedematous
c. This results in ischaemia and neuron death
- –White matter regains circulation within 24 hours
- –Grey matter does not
d. Bleeding and swelling may spread to adjacent spinal segments
e. Inflammatory infiltration of the lesion
- –This causes release of free radicals etc. which causes further tissue damage
f. Apoptosis of oligodendrocytes causes demyelination
- –This leads to further neuron death
g. Collagenous scar formation (3-4 weeks)
