Anatomy of the Spinal Cord and Autonomic Nervous System Flashcards
How many pairs of spinal nerves are there?
31 pairs 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal nerve
What level does the spinal cord taper off to form the conus medullaris?
L2
Explain why the spinal cord enlarges in the cervical and lumbosacral region
To accommodate for the extra spinal nerve rooms for the upper and lower limb respectively
Where is the cauda equina located?
L2-S5
What nerves does the cauda equina contain?
Motor nerves, sensory nerves, (parasympathetic) sacral plexus
Between which vertebral levels is the cervical enlargement located?
C5-T1
Between which vertebral levels is the lumbosacral enlargement located?
T11-L2
What is the filum terminale?
Prolongation of pia mater that extends from the conus medullaris to the coccyx. This anchors the cord to the coccyx and provides ‘longitudinal support’ to the cord.
What bones and ligaments form the anterior wall of the vertebral canal?
Anterior longitudinal ligament
Vertebral bodies
Posterior longitudinal ligament
What bones and ligaments form the posterior wall of the vertebral canal?
Ligamentum flavum
Spinous processes
Supraspinatous ligament
What bones and ligaments form the lateral wall of the vertebral canal?
Interspinal ligament
Where does the ligaments flavum run?
The ligamentum flavum are paired ligaments that runs between adjacent laminae of the vertebral bodies
Where does the interspinous ligament run?
It runs laterally to the vertebral canal connecting adjacent spinous processes. Found in between the supraspinous and ligamentum flavum.
Describe the path of the spinal cord
Extends from the medulla oblongata through the foramen magnum and terminates at the lower border of L1 vertebra or the upper border of L2 vertebra.
Where are the anterior and posterior spinal arteries located? What can form if these rupture?
In the subdural space.
A subdural haematoma
What ligaments suspend the spinal cord in the dural sheath?
Denticulate ligaments (also separate dorsal and ventral spinal nerve roots)
Name two risk factors for a spinal extradural haematoma
1) Spinal spondylosis- most commonly cervical canal stenosis
2) Anticoagulation
What clinical features accompany spinal extradural haematomas?
Neurological deficit and pain
What is a spondylosis ?
“Spinal arthritis”- degenerative and osteoarthritic changes in the spinal vertebral column
What are the most likely spinal levels for a spinal EDH to develop?
Cervicothoracic region
What is the name for the expanded subarachnoid space located below the level of L2? What is its clinical relevance?
Below L2, the subarachnoid space expands to form the lumbar cistern. This space is used to collect CSF fluid during lumbar punctures and during spinal anaesthesia LPs are normally introduced at L3/L4 level which is the highest point of the iliac crest
Are traumatic EDH normally anterior or posterior?
Anterior because
1) Ossification of the posterior longitudinal ligament
2) Burst or compression fractures of the vertebral bodies
Why are spinal EDH an emergency?
The EDH can spread across the entire spinal cord which can lead to a compressive myelopathy.
What is caudal equine syndrome? How does it present?
Injury to the lumbosacral nerve roots
Areflexic bowel and/or bladder so patients can present with dysfunctioning bowel/bladder e.g. perianal anaesthesia
Variable motor and sensory loss in the lower limbs- usually asymmetrical
List some common cause of caudal equina?
Disc herniation in the lumbar region
Narrowing of the spinal canal (stenosis)
A spinal lesion or tumour
Spinal infection/inflammation/haemorrhage/fracture
Complication of severe lumbar spine injury e.g. car crash/fall/gunshot
Is cauda equina an upper or lower motor lesion?
LMN as it’s the nerve roots that are affected. If signs of UMN exist e.g. increased reflexes, suspect spinal cord involvement.
State the key sensory points when testing the C6,C7 & C8 dermatomes?
C6- Dorsum of the hand , proximal phalanx of the thumb
C7- Dorsum of the hand, proximal phalanx of the middle finger
C8- Dorsum of the hand, proximal phalanx of the little finger
Which key sensory points are located on the
1) radial and b) ulnar side of the antecubital fossa?
Radial side of ACF- C5
Medial side - T1
Which key sensory point is located in the axilla?
T2
What key sensory point is located in the mid-clavicular line, 4th intercostal space?
T4- just under nipples
Which plane are T3-T12 key sensory points tested?
Mid clavicular line
What key sensory point is located over the medial femoral condyle?
L3
What key sensory point is located over the medial malleolus ?
L4
What key sensory point is on the third metatarsal phalangeal joint?
L5
Where would you test the sensory function of S1?
Lateral aspect of calcaneus
Where would you test the sensory function of S2?
Middle of popliteal fossa
Where would you test the sensory function of S4/5?
Less than one cm away from anal sphincter
What is a complete spinal injury?
An injury is complete if it causes loss of sensory and motor function in the anus area (sacral segments S4,S5)
This is ASIA A classification
What is an incomplete spinal injury?
A spinal injury is classified as incomplete if there is evidence of ANY motor or sensory function in the area around the anus (S4,S5). ASIA classifications B-D.
B= Sensory incomplete- Sensory function intact, motor function not intact below neurological level, including no motor function of the S4,S5 region.
C= Motor incomplete- Sensory intact, motor affected. Half of key muscles below neurological level have a muscle grade less than 3
D= Motor incomplete- Sensory intact, motor affected. At least half of muscles below neurological level have a muscle grade greater than 3
E= normal
What scale defines the extent of spinal injury?
ASIA impairment scale
What is a myotome?
Group of muscles innervated by a single spinal nerve root
Most muscles are innervated by multiple nerve roots. Which nerve roots are most strongly associated with the movement elbow flexion?
C5
The biceps brachii flex the elbow and they are innervated by the musculocutaneous nerve derived from brachial plexus, nerve roots C5,C6 & C7. C5 is the most strongly associated.
What nerve root is most strongly associated with wrist extension?
C6
What nerve root is most strongly associated with elbow extension?
C7
What nerve root is most strongly associated with finger flexion?
C8
What nerve root is most strongly associated with finger abduction?
T1
What movement is L2 responsible for?
Hip flexion
What movement is L3 responsible for?
Knee extension
What movement is L4 responsible for?
Ankle dorsiflexion
What movement is L5 responsible for?
Great toe extension
What movement is S1 responsible for?
Ankle plantarflexion
Which spinal levels are tested when testing the biceps tendon reflex?
C5,C6
Which spinal levels are tested when testing the triceps tendon?
C7,C8
Which spinal levels are tested when testing the patella tendon?
L3,L4
Which spinal levels are tested when testing the achillies tendon?
S1, S2
Which spinal levels are tested when testing the anal reflex
S2, S3 & S4
What is the blood supply of the spinal cord?
Two posterior spinal arteries (PSAs) and a single larger anterior spinal artery (ASA)
Where do the anterior spinal arteries arise from?
The vertebral arteries just before they anastomose to form the basilar.
What two arteries may the posterior spinal arteries arise from?
In the majority of individuals, the PSA arises from the PICA (Posterior inferior cerebellar artery) but in the minority can arise directly from the vertebral artery.
What general parts of the spinal cord does the ASA supply?
Anterior 2/3rds of the spinal cord. Approximately the whole cord anterior to the posterior columns.
What functional regions does the PSA supply?
Dorsal columns
How could a haemorrhage in the medulla lead to sensory deficit in proprioception, fine touch and vibration?
Haemorrhage in medulla could damage the PICA which gives off the PSA artery. The PSA artery supplies the dorsal columns in the spinal cord responsible for these sensory functions
In addition to the anterior and posterior spinal arteries, what other arteries reinforce the blood supply of the spinal cord?
Segmental medullary arteries reinforce the spinal cord’s blood supply. Radicular arteries supply the nerve roots
Where do the radicular arteries arise from?
Ascending cervical arteries, deep cervical arteries, posterior intercostal arteries, lumbar arteries and lateral sacral arteries.
Which foramina do the radicular arteries pass through to supply the spinal cord?
Intervertebral foramina
Which spinal artery does the great radicular artery of Adamkiewicz anastomose with?
Anterior spinal artery
Where does the great radicular artery of Adamkiewicz arise from? What spinal cord levels does it generally supply?
(Left) posterior intercostal artery
Lumbar and sacral regions of the spinal cord
What syndrome can occur if the great radicular artery of Adamkiewicz is damaged? How does this present?
Anterior spinal artery syndrome
Urinary and/or faecal incontinence, lower leg weakness
Sensory function is often preserved to some degree (dorsal columns not affected)
Why should a vascular surgeon be cautious when repairing a thoracic or thoraco-abdominal aortic aneurysm ?
Needs to be cautious to identify and avoid the great radicular artery of Adamkiewicz as if disrupted, this could cause anterior cord syndrome
What is the great radicular artery of Adamkiewicz also referred to as?
Anterior segmental medullary artery
If the blood supply from aorta is disrupted, what vessels can help maintain collateral blood supply to the spinal cord?
Internal thoracic artery and lateral thoracic arteries can anastomose with the posterior intercostals.
What are the radiculospinal arteries?
Small arteries that arise from the body wall and supply JUST the ventral and dorsal nerve root (Radiculo=root, spinal=spine). These arteries do not anastomose with the anterior and posterior spinal arteries
What is the arterial vasocorona?
Anastomoses between the anterior and posterior spinal arteries which supply the peripheral lateral aspect of the spinal cord
What symptoms would a patient present with if the anterior spinal artery is blocked?
Bilateral motor paralysis, bilateral loss of pain and temp, bilateral spastic parasis (muscle weakness), bilateral ataxia
What is found in white matter?
Ascending and descending tracts
What does the grey matter contain?
Cell bodies, dendrites, axon terminals
Name the three principal ascending and 1 descending tract
Ascending:
1) Dorsal columns/posterior column-medial lemniscal pathway
2) Spinothalamic/Anterolateral
3) Spinocerebellar
Descending:
1) Corticospinal
What are the two bundles of axons called that make up the dorsal columns?
Gracile and cuneate fasciculus
What information do the dorsal columns contain? Where do the tracts decussate ?
Conscious proprioception, discriminative touch, vibration
Medulla oblongata
What information do the anterolateral tracts contain? Where do the tracts decussate?
Antero- crude touch and pressure
Lateral- pain and temperature
Decussate in the spinal cord 1-2 vertebral levels above where they entered. After synapsing with first order neurons in the substantia gelatinosa, these neurons decussate and travel in two distinct tracts up to the thalamus
What information is carried with the spinocerebellar tract? Where do these axons decussate ?
Unconscious proprioception
These fibres do not decussate
What information is carried in the corticospinal tract? Where do these axons decussate?
Voluntary movement
Decussation in the medulla
Why does the ratio between the grey and white matter change at the lower levels of the spinal cord?
Ratio of grey:white matter increases at the lower levels of the spinal cord to accommodate for the cell bodies involved in the lumbosacral plexus (not thoracic plexus)
The thoracic lateral horn contains cell bodies for which part of the nervous system?
Sympathetic chain
The sacral lateral horn contains cell bodies for which part of the autonomic nervous system?
Parasympathetic
Which cranial nerves contain parasympathetic fibres?
3,7,9,10
In which tract are the autonomic descending fibres? What is the approximate location of this tract?
Hypothalamospinal tract located adjacent to lateral horns.
Give three examples of conditions that are caused by INCOMPLETE spinal injury
Central cord syndrome, Brown-Sequard and anterior cord syndrome
Describe the classical presentation of central cord syndrome
Motor weakness which is more pronounced in the upper limbs than the lower limbs.
Preservation of sensory function varies
What is the most common MOI for central cord syndrome?
Hyperextension of the neck and inward buckling of ligamentum flavum (connects laminae). Subsequent compression, oedema and haemorrhage
What age group is most commonly affected in central cord syndrome?
Older generation as can often occur secondary to cervical spondylosis (spinal arthritis)
Also more at risk of falls leading to neck hyperextension when head hits floor.
In central cord syndrome, why are the hands and arms more affected than the lower limbs? What tracts are involved?
Corticospinal tract has the arm fibres more medially than the leg fibres (similar to motor homunculus therefore hands most medial then arms, trunk, legs, foot)
Describe the clinical features of anterior cord syndrome
Motor paralysis of the lower limbs due to affected corticospinal tracts
Autonomic dysfunction e.g. orthostatic hypotension due to disruption of thoracic and lateral horns (contains SNS/PNS cell bodies).
Pain and temperature loss due to spinothalamic damage
What sensory modality would be intact following anterior cord syndrome
2-point discrimination, vibration, conscious proprioception (dorsal columns not affected)
State the two most common causes of anterior cord syndrome
1) Thromboembolic disease- occlusion of the anterior spinal artery and ischaemia of affected area
2) Retropulsion of bony fragments in trauma
What main tracts are affected in anterior cord syndrome
Spinothalamic, corticospinal
What sort of conditions tend to cause Brown Sequard Syndrome?
Chronic conditions such as an intraspinal tumour or gradual degeneration
Describe the clinical features of brown sequard
Ipsilateral loss of fine touch, vibration, proprioception and contralateral loss of pain and temperature
Describe sympathetic innervation from the hypothalamus to the eye
Hypothalamus-> Medulla-> Sympathetic descending tract-> Sympathetic descending tract ( in the eye, T1 ventral root)-> pre ganglionic neuron-> superior cervical ganglion->post ganglionic neutrons follow blood vessels to innervate relevant muscles e.g. dilator muscles e.g. superior tarsal muscle, sphinctor pupillae.
Describe the sympathetic innervation of the heart
Hypothalamus-> Sympathetic descending tract-> Leave spinal corn by thoracic lateral horn-> short pre ganglionic neutrons travel down ventral horn-> enter sympathetic chain at T1-T4 level-> ascend to cervical ganglia* and synapse with post ganglionic neurons-> post ganglionic fibres combine to form the cardiac plexus which innervates the atria, ventricles and conduction system of heart.
*sympathetic cardiac nerves also originate from T1 (non-ascending)
Where are the sympathetic ganglia located?
Sympathetic trunk
Collateral sympathetic ganglia that innervated the lower abdominal organs and pelvis are located in the coeliac (foregut), superior mesenteric (midgut) and inferior mesenteric (handgun) ganglia which are located in the abdominal cavity close to their effector organs.
Where it the sympathetic trunk located?
TRICK QUESTION! Sympathetic trunks extend the entire length of the spinal cord whereas sympathetic NERVES leave the spinal cord between levels T1-L2.
Which receptors and neurotransmitters are involved in the sympathetic innervation of the heart?
Preganglionic neurons release acetylcholine which binds to nicotinic receptors on post ganglionic neurons. These neurons release norepinephrine which binds to beta 1&2 adrenergic receptors in cardiac tissue
What structures received sympathetic innervation in the periphery ?
Sympathetic chain supplies
1) SOMATIC SYMPATHETIC NERVES which supply skin and body wall.
2) Visceral sympathetic nerves-> Organs
3 functions of SOMATIC SYMPATHETIC NERVES
1) vasomotor- blood vessel vasodilation
2) pilomotor- arrector pili muscles
3) sudomotor- sweat glands
What is the most common cause of hypovolaemia in trauma?
Haemorrhage
What type of shock should be suspected in patients with spinal cord injury?
Neurogenic shock
Following a spinal cord injury, why would a patient be hypotensive, bradycardic and warm to touch?
Damage to the spinal cord can cause damage to the sympathetic nervous system can result in unopposed parasympathetic stimulation of the heart.
Lack of sympathetic innervation to arteries and VEINS leads to vasodilation. Vasodilation reduces the systemic vessel resistance and blood pools in the periphery which reduces perfusion and venous return. This is why the skin is warm to touch. Reduce preload results in a reduced end diastolic volume resulting in a reduced stroke volume and cardiac output. This results in a reduced blood pressure.
Reduced sympathetic innervation of the heart results in a reduced heart rate which further reduces blood pressure.
What are the clinical features of neurogenic shock?
Bradycardia** (heart rate increases in other forms of shock), warm skin, organ dysfunction (organs become starved of oxygen due to reduced perfusion)
How would you manage neurogenic shock?
Pressors- vasoconstriction
IV fluids- crystalloid
Atropine- increase heart rate
Neurogenic shock indicates a lesion above which level
T5- Sympathetic nerves which innervate the heart leave spinal cord at levels T1-T4
Why do patients with acute spinal cord injury sometimes present with priapism?
Abrupt loss of sympathetic input to the pelvic vasculature leads to increased parasympathetic input and uncontrolled arterial inflow directly into the penile sinusoidal spaces.
What injury level would you expect if a spinal cord injury patient presented with priapism ?
TRICK QUESTION- any level of the spinal cord because the sympathetic nerves that supply the penile vasculature arise from the conus medullaris of the cord
Describe the parasympathetic innervation of the bladder
Splanchnic nerve arises from S2-S4 synapses in pelvic ganglion with the pelvic nerve. Pelvic nerve innervates the detrusor muscle causing contraction and micturition
Explain the reflex bladder in spinal cord injury above T12
Afferent signals from the bladder wall are unable to reach the brain, and the patient will have no awareness of bladder filling. There is also no descending control over the external urethral sphincter (somatic, pudendal), and it is constantly relaxed.
There is a functioning spinal reflex, where the parasympathetic system initiates detrusor contraction in response to bladder wall stretch. Thus, the bladder automatically empties as it fills – known as the reflex bladder.
Which cranial nerves carry parasympathetic fibres?
3, 7, 9, 10
Name the parasympathetic ganglia
Ciliary ganglion
Otic ganglion
Pterygopalatine ganglion
Sub Mandibular ganglion
