L4: Dermatomes and Myotomes and the Lumbar spine Flashcards
What day in embryology does the neural tube begin to develop?
Day 18
Under the influence of the notochord
Segmented –> neural level
How many somites does the neural tube split into?
34-35 somites by day 30
What do the somites differentiate into?
Ventral –> sclerotome –> vertebrae and ribs
Dorsal –> dermamyotome
–> dermatome –> dermis
–> myotome –> muslce tissue
Why does the skin and muscle have a common nerve supply?
Develop single dermamyotome –> association with a specific neural level
Take nerve supply with them –> spinal (segmental) nerve
Define dermatome?
Area of skin supplied by a single spinal nerve
What does the Foerster dermatome map show? What are some of the landmarks that help you learn the distribution?
Shows the neuronal supply to each area of skin on the body Anterior -Axilla level T2 -Nipples= T4/5 -Umbilicus= T10 -Groin= L1 -Knee= L3 -Small toe= S1
Posterior
- Back of head C2
- Back of neck C3
- Posterior shoulder C4
- S2 back of leg
- S5- bum hole!
Describe the structure of a typical neuron?
Cell body
Dendrites –> thin structures–> cell body
Axon–> axon hillock
What is the function of a neuron?
Receive, process and transmit information
Chemical and electrical signals
What is a myelin sheath?
Insulating layer–> speed up conduction
CNS–> Oligodendroctyres
PNS–> Schwann cells
What does a bundle of axons form in the CNS?
A tract
Describe the structure of a peripheral nerve?
Axon surrounded by Schwann cells Endoneurium--> connective tissue Axons--> bundled--> fascicles Perineurium--> connective tissue Fascicles grouped -->nerve Epineurium --> connective tissue
Describe the structure of the endoneurium? What does it contains?
- -> inner sleeve contains glycocalyx and mesh of collagen
- -> Endoneurial fluid
- -> Similar to BBB–> stops certain molecules crossing–> Analogous to CSF
- -> Nerve injury –> ↑ endoneurial fluid
What is contained within the epineurium?
High metabolic requirement
Blood vessels
Vasa Nervorum (small arteries)
What is a spinal nerve?
Short mixed nerve
Contains motor, sensory and autonomic fibres
Pass through intervertebral foramen
Compare the dorsal and ventral root?
Dorsal–> afferent–> sensory nerves
Ventral–> efferent –> motor neurones and autonomic fibres
How many pairs of spinal nerves are there? How are they named?
31 pairs of spinal nerves
Names according to level of VC that they emerge
Cervical spinal nerves–> named according inferior vertebrae e.g. C4 spinal nerve –> C3 vertebra superior, C4 vertebrae inferior
Thoracic/lumbar –> named according to superior vertebrae e.g. L3 spinal nerve–> L3 vertbrae superior, L4 vertebrae inferior
Where do the vertebra come from?
Sclerotome (ventral somite) –> + ribs thoracic region
Derived from two adjacent somites (half from each)
Where does the spinal cord pass?
Passes through vertebral foramen
Multiple form the spinal canal
Where do the spinal nerves leave?
Through intervertebral foramina
Where does the spinal cord run from?
Inferior margin of medulla oblongata (skull-- foramen magnum) Conus meduallris (L2) --> Cauda Equina
Why is the spinal cord shorter than the spinal canal?
Differential rates of growth
What do the sacral nerves exit through? What does S5 and coccygeal nerve exit through?
Sacral nerves–> sacral formaina
S5 and coccygeal –> sacral hiatus
What are rami?
The divisions of the spinal nerve after it has passed through the intervertebral foramen.
What are the division of the rami called? What do they supply?
Anterior or ventral rami–> muscles and skin of upper and lower limbs and lateral and ventral trunk
–> larger
Posterior or dorsal rami –> deep muscles and skin of the dorsal trunk
–> small
What nerve does each spinal nerve give off? What does this nerve do?
Meningeal branch
Re-enters spinal canal–> Intervertebral foramen
Supplies the vertebrae, ligaments of VC, blood vessels and meninges
Which part of the spinal cord gives out sympathetic fibres and which gives out parasympathetic fibres?
Sympathetic –> Thoracolumbar outflow –> T1-L2
Parasympathetic –> crainosacral outflow –> C1-8 and S1-5
What additional nerve is there in the thoracolumbar region? What is it contained within?
Preganglionic sympathetic nerve
White ramus (rami) communicans –> synapses
Exits via grey ramus (rami) communicans –> Post rami communicans
Why are they called the white and grey rami communicans?
White–> myelinated axons
Grey –> unmyelinated axons
What does the posterior (dorsal) rami divide into? What do they supply?
Divides into medial and lateral branches
- -> supply muscles and skin
- -> Inline with intervertebral foramen
Explain the anterior (ventral) rami distribution?
Skin and muscle of trunk–> segmented T2-L1
C1-C4 head, neck and shoulder
C5- T1–> upper limb (arm)
L1-S5 –> lower limb (leg)
What is the name of the plexus in the upper limb and the lower limb? What spinal nerves enter each?
Upper limb –> brachial plexus C5-T1
Lower limb –> Lumbosacral plexus L1-S5
What is significant about the anterior (ventral) rami in the limbs?
Supplies both the anterior (ventral) and posterior (dorsal) skin of the limbs
What do we mean by functional overlap?
Spinal nerve–> specific area –> does overlap a bit
Spinal nerve damage–> loss of sensation usually less extensive than expected
What is the axial line?
Junction between two dermatomes
Discontinuous spinal level
Midline of body in trunk
Limb–> anterior (ventral) and posterior (dorsal) axial lines –> mark the centre of the anterior and posterior compartments
In development which way do the limbs rotate?
Upper limb–> laterally 90 degrees
–> elbow and extensor muscles on posterior and lateral surface
Lower limb–> medially 90 degrees
–> knee and extensor muscles on anterior aspect
What is the pre-axial and post-axial borders?
Mark the border where flexors and extensors meet
Development
Pre-axial–> cephalic side
Post-axial–> caudual side
What marks the pre-axial and post-axial borders in a developed human?
Veins
Upper limb
–> Cephalic vein –> pre-axial border–> Lateral
–> Basilic vein–> post-axial border–> medial
Lower limb
–> Long (great) saphenous vein –> pre-axial border –> anteromedial aspect
–> Short (small) saphenous vein –> post-axial border –> posterior (posterolateral)
What happens to nerves in the brachial plexus?
Axons from single spinal nerves follow multiple different routes in plexus and emerge in several different peripheral nerves
What is unusual about peripheral nerves? What is the clinical consequence?
Contains fibres from more than one spinal nerve
Area of skin supplied–> doesn’t match dermatome map
Cutaneous innervation of that nerve
Sensory and motor nerves?
What is a myotome?
Group of muscle fibres supplied by a single spinal nerve
Usually muscle fibres in different muscles
How does a motor unit differ from a myotome?
Single motor neurone (single axon) and the muscle fibres it supplies
Myotome group of muscle fibres supplied by a single spinal nerve
What movements are associated with C5?
Shoulder abduction
External rotation
(Elbow flexion)
What movements are associated with C6?
Elbow flexion
Wrist extension
Supination
(Internal rotation of shoulder)
What movements are associated with C7?
Elbow extension
Wrist flexion
Pronation
(Finger flexion and extension)
What movements are associated with C8?
Finger flexion
Finger extension
(thumb extension, wrist ulnar deviation)
What movements are associated with T1?
Finger abduction and adduction
What movements are associated with L2?
Hip flexion
What movements are associated with L3?
Knee extension
hip adduction
What movements are associated with L4?
Ankle dorsiflexion
What movements are associated with L5?
Great toe extension
Ankle inversion, hip abduction
What movements are associated with S1?
Ankle plantar flexion
ankle eversion, hip extension
What movements are associated with S2?
Great toe flexion
knee flexion
What does Hilton’s law say?
Nerve supplying muscle also supplies joint capsule and skin overlaying the insertion point of a muscle
What is clinical significant about dermatomes and myotomes?
Determine which nerve is damages by assessing which muscles and skin area affected
Peripheral nerves–> multiple areas of damage more than one spinal nerve
When assessing a patient for a spinal cord injury what are you trying to determine?
Trying to determine the clinical neural level of injury
What do we mean by neural level?
The lowest level of fully intact sensation and motor function
What is the vertebral column made of?
Vertebrae, intervertebral discs and sacrum
What are the different divisions of the vertebral column?
Cervical (7), thoracic (12), lumbar (5), sacral (5 fused) and coccygeal (4 fused)
How are the intervertebral discs named?
Named relative to the vertebrae on each side of disc
Which parts of the spine are the most mobile?
The cervial and lumbar region
Which parts of the spine are the least mobile?
The thoracic–> attached to ribs
Sacrum 5 fused
Coccyx 4 fused
There are four curvatures in the spine, what are the called and when do they develop?
Thoracic and Sacral cruvatures –> primary –> kyphotic
–> primary –> during development
–> kyphotic anterior curvature
Cervial and lumbar curvatures –> secondary –> lordotic
–> secondary –> develop after birth –> holding head, sitting up –> IVD become wedge shaped
–> lordotic –> concave posteriorly
Balance each other out–> maintain centre of gravity in stable states
Great flexibility and resilience
How does the size of the vertebral bodies change as go inferiorly? Why?
Vertebral bodies increase in size
Compressive forces increase
Sacral vertebra–> fused, widened, anteriorly concave–> transmit forces through pelvis into legs
What are the functions of the vertebral column?
- ->Support weight of skull, pelvis, upper limbs and thoracic cage
- -> Protection
- -> Posture and locomotion
- -> Hematopoesis
Describe the anatomy of a lumba vertebra?
- -> kidney bean shaped vertebral body
- -> Vertebral arch (posterioly)–> (Pedicle, transverse process, lamina)
- -> Vertebral foramen (conus meduallris, cauda equina, meninges)
- -> Processes
- -> 2 transverse processes
- -> 2 superior articular processes
- -> 2 inferior articular process
- -> spinous process
Diagram page 68
What type of bone is the vertebral body? Why?
10% cortical bone
90% cancellous bone –> reduces weight and hematopoesis
What are the vertebrae end plates?
The superior and inferior surface of the vertebral body
Covered in hyaline cartilage
Articulate with IVD
What structures make up the vertebral arch/ posterior elements? What is its function?
Pedicle–> Between vertebral body and transverse processes
Transverse process –> attachment site
Lamina (laminae)–> between transverse processes and spinuous process
Spinous process –> attachment site
Protective tunnel
What is the function of the superior and inferior articular processes?
Create a mobile joint
Superior articular facet articulates with the inferior articular facet on an adjacent vertebral body
Zygapophyseal/ Facet joint–> synovial joint, hylaine cartilage
What is the intervertebral foramen? What passes though?
Space between the superior and inferior articular facets on adjacent vertebra
Created by the vertebral notch
Spinal nerves pass through
Label a diagram of the lumbar vertebrae?
Answer on page 68
What determines the amount of flexion and rotation permissable at the facet joints? Specific angles of the lumbar facets? What movement is permitted?
Angle of the articular facets Lumbar facet --> 90 degree in axial plane (perpendicular) --> 45 degree in coronal plane -->Superior facet--> posteriomedially -->Inferior facet --> anterolaterally Flexion and extension
What is the structure of the intervertebral disc?
Split into nucleus pulposus (central) and annulus fibrosus (peripheral)
70% water, 20% collagen and 10% proteoglycans
What is the main function of the annulus fibrosus? How is its structure linked to its function?
Shock absorber Highly resillient under compression Lamella of annular bands collagen in different orientations Outside--> Type 1 Inside--> fibrocartilagenous Avascular and aneural
What is the nucleus pulpous? What is its structure?
Remnant notochord Gelatinous Type 2 High oncotic pressure --> smaller at night --> water squeezed out Infant central --> adult more posterior
What are the ligaments in the vertebral column?
Anterior and posterior longitudinal ligaments
Ligamentum Flavum
Interspinous ligaments
Supraspinous ligament
Where are the anterior and posterior longitudinal ligaments located?
Anterior and posterior to vertebral body
Anterior –> Anterior tubercule of C1 (atlas) to sacrum
–> attaches to periosteum of VB
–> loosely attached of IVD
Posterior –> Body of axis (C2) to sacral canal
–> continuous with tectorial membrane of atlanto-axis joint
What is the function of the anterior and posterior longitudinal ligaments?
Anterior –> stop hyperextension
Posterior–> stop hyperflexion
Where is the ligamentum flavum located? What is its function?
Between laminae of adjacent vertebrae
Streched during flexion–> return posture to normal
Where is the interspinous ligament found? Where is it the most developed? Composition?
Between the spinous process Lateral side can see it Fuse with supraspinous ligament Lumbar region Weak sheets--> fibrous tissue
What is the function of the interspinous ligament?
Prevent hyperflexion
Where is the supraspinous ligament located? Composition?
Tip of spinous process
Fuse with the interspinous ligament
Strong band of fibrous tissue
What is the function of the supraspinous ligament?
Prevents hyperflexion
Lax during extension
What is the anatomy (structure, articulations) of the sacrum and coccyx?
Sacrum --> 5 fused vertebrae Superiorly articulates with L5 Inferiorly articulates with coccyx Laterally --> ilium of pelvis Coccyx --> 4 fused vertebrae
What is the sacroilliac joint?
Joint between the sacrum and iliium bones
Where does the spinal cord run in the sacrum?
Sacral canal
Cauda equina
Terminates at sacral hiatus –> S4
How do the sacral and coccygeal nerve exit the sacral canal?
Pass through posterior sacral foramina
What attaches (provides longitudinal support) the spinal cord to the coccyx?
The filium terminale
Continuation of pia mater from conus medularis
20cm long
Why do people get smaller with age?
IVD compression
Annular fibrosis degeneration (wear and tear)
Nucleus pulposus–> thinner–> dehydration and degeneration
Vertebrae–> wedge shaped –> osteoporotic compression fractures
What is it called when the secondary curvatures start to disappear in old age? What changes occur?
Senile kyphosis Primary curvature re-established AF of IVD wear and tear NP looses turgor and becomes thinner Loss of height accompanied by osteoporotic fractures--> secondary curvatures disappear
Which vertebrae does the centre of gravity pass through?
C1/2 C7/T1 T12/L1 L5/S1 Weak points
Look at some X-rays, CT, MRI and isotope radiographs and identify the key features?
Page 75-78
What is mechanical back pain?
Pain when the spine is loaded
Worsens with exercise and is relieved by rest
How common is mechanical back pain? What are the risk factors?
Extremely common
50% of UK–> at least 24hrs in any one year
50% of those–> >4week
80% of population > 24hrs
Risk factors –> obesity, poor posture, sedentary lifestyle with deconditioning of paraspinal (core) muscles, poorly designed seating, incorrect manual handling
What are the degenerative changes associated with the vertebral column?
IVD dehydrates with age–> decreases height of disc–> bulging and ↑stress on joints
What are the names of the conditions associated with degenerative diseases?
Marginal osteophytosis–> bony spurs (syndesmophytes) develop adjacent to end plates of the disc
Osteoarthritic changes–> increased stress on the joints –> Facet joints innervated by meningeal nerve –> feels painful
Disc height↓ and arthritis = Small vertebral formanina –> compression of spinal nerve–> radicular or nerve pain
What is another name for a slipped disc? What are the different stages?
Herniation
- Disc degeneration: Chemical changes–> aging –> dehydration –> bulge
- Prolapse: protrusion of the nucleus pulposus–> slight impingement into spinal canal–> contained with Annulus fibrosis
- Extrusion: NP–> breaks though AF–> contained in disc space
- Sequestration: NP separates from main body of disc–> enters spinal canal
What is the most common site for a slipped disc? What age is it most common? How long does it take to resolve?
L4/5 and L5/S1 due to mechanical loading
30-50yr olds
90% resolve in 3 months
With a slipped disc which nerves are most vulnerable?
1) Where cross the IVD (paracentrally) -traversing nerve
2) Where they exit the spinal canal in the intervertebral foramen (far laterally) -exiting nerve
What is the most common sort of herniation?
Paracentral prolapse –> 96% cases–> not reinforced by the posterior longitudinal ligament –> traversing nerve root most at risk
2% laterally –> Exiting nerve root at risk
2% centrally
What is the common name for radicular leg pain? Define it? Where is the pain experienced?
Sciatica
Pain caused by irritation or compression of one or more of the nerve roots that contributes to sciatic nerve (L4,5, S1,2,3)
Buttocs and back–> radiates to dermatome supplied by nerve
What is the typical distribution of pain in sciatica?
L4: Anterior thigh, knee and medial leg
L5: Lateral thigh, leg and dorsum of foot
S1: Posterior thigh, leg, heel and sole of foot
If compression causes paraesthesia –> tingling/pins and needles–> only experienced in affected dermatome
What is cauda equina syndrome?
Compression of the lumbar and sacral nerve roots
5% caused by disc prolapse
Other included –> tumour, spinal infection/abscess, spinal stenosis secondary to arthritis, vertebral fracture, spinal haemorrhage, late stage ankylosing spondylitis
What are the symptoms of cauda equina syndrome?
Bilateral sciatica Perianal numbness (saddle anaesthesia) Painless retention of urine Urinary/ feacal incontinence Erectile dysfunction
Why is caudia equina a medical emergancy?
Compression of the lumbar and sacral nerves
Decompression required with 48hr
>48hr prognosis is poor
Consequences serious–> chronic neuropathic pain, impotence, self catheterisation to pass urine, faecal incontinence or impaction, loss of sensation and lower limb weakness
What happens in spinal canal stenosis?
Abnormal narrowing of spinal canal
Compress spinal cord or nerve roots
Due to: Disc bulging, facet joint osteoarthritis, ligamentum flavum hypertrophy
Others–> fracture of VB, spondylolithesis, trauma
What are the symptoms of spinal canal stenosis?
Discomfort whilst standing (95% patients) Discomfort or pain in region affected Bilateral symptoms Numbness at or below level of stenosis Weakness at or below... Neurogenic claudication
What is neurogenic claudication?
Symptom
-Cramping pain or weakness in legs and therefore tends to limp
-Pain or pins and needles in legs on prolonged standing and walking, radiating in a sciatica distribution
-Due to compressions in spinal nerves –> emerge lumbrosacral spinal cord
Venous engorgement (exercise)–> reduced arterial flow and transient ischaemia–> pain or paraesthesia
-Relieved by flexion movements and rest
What is spondylolilthesis?
Displacement of the vertebrae above relative to the one below
Classified according to underlying cause
–> instability of facet joints, degenerative, fractures in neural arch, infection, defect in pars interarticularis (between superior and inferior articular facets)
What is the difference between spondylolysis and spondylolsthesis?
Spondylolysis–> fracture without displacement
Spondylolisthesis–> anterior displacement of upper vertebrae
What are some of the symptoms of spondylolisthesis? How is it treated?
Instability of VC
Some asymptomatic
Some discomfort–> lower back pain, incapacitating mechanical pain, sciatica, neurological claudication
Treatment–> screws and rods to hold in place
Why do you perform a lumbar puncture? Where does fluid come from?
Diagnostic test–> variety of CNS disorders including meningitis, MS etc
Withdrawal of fluid from the subarachnoid space of lumbar cistern
Between which lumbar vertebrae do you perform a lumbar puncture?
Between L3 and L4 or L4 and L5
At the level between the highest point of the iliac crests –> supracristal plane
What layers would the needle pass through?
Skin–> Subcutaneous fat –> supraspinous ligament–> interspinous ligament–> ligamentum flavum–> epidural fat and veins –> dura mater–> arachnoid mater into subarachnoid space
