Week 4 - Dermatomes and Myotomes Flashcards
What is the adult nervous supply to the dermis and muscle of a dermamyotome?
A spinal segmental nerve
What is the spinal cord?
A cylindrical column of millions of nerve cell bodies and millions of neuronal axons
- Starts where the medulla of the brain ends
- It ends as the conus medullaris (where its membranes taper into a ligament; filum terminale)
- It runs through successive vertebral foramina of most, but not all, vertebrae of the vertebral column
- Shorter than the vertebral column
What is a vertebral segment?
Each vertebra of the vertebral column makes 1 vertebral segment (known as a neural level)
- There are vertebral foramen and intervertebral foramen
What are intervertebral foramen?
When successive vertebrae are joined and viewed from side-to-side there are successive side openings between them
What forms the spinal canal?
Successive foramina of vertebrae
Where does the spinal cord give off nerves?
Gives off a pair at each vertebral level (1 right and 1 left)
- These leave the spinal canal via intervertebral foramina
- Also known as segmental nerves or mixed spinal nerves
- In the cervical cord: spinal nerves emerge superior to their corresponding vertebral levels
- In the non-cervical cord: spinal nerves emerge inferior to their corresponding vertebral levels
What is the shape of the spinal cord?
2 enlargements at the cervical and lumbar levels
- Ends in a taper
What does each segmental nerve compromise of?
- Dorsal roots (sensory/afferent)
- Ventral roots (efferent, can be motor or autonomic)
What is the effect of overlap between adjacent dermatomes?
This is normal
- Some sections of skin are served by 2 successive spinal nerves
- A typical dermatome will be served by 3 successive sensory nerves
Where does the upper limb receive its nerve supply from?
It receives all of it from the spinal cord
- Most is derived from C5-T1 roots
- The rest comes from T2 roots
What nerves are found in the upper limb?
Brachial plexus nerves - Radial - Musculocutaneous - Ulnar - Axillary - Median Other nerves - Lateral pectoral - Upper subscapular - Lower subscapular - Dorsal scapular - Suprascapular - Long thoracic
Where does the lower limb receive its nerve supply from?
It receives all of it from the spinal cord
- Supplied from the lumbar and sacral spinal segments (L1-S4)
- The spinal nerves originate from 2 separate networks of nerves (Lumbar plexus (L1-L4), sacral plexus (L4-S4)
Describe the lumbar plexus
- Forms behind the psoas major muscle
- Nerves emerge either medially or laterally to the borders of the psoas major muscle
- Nerves emerging laterally = femoral (L2-L4), iliohypogastric, ilioinguinal, lateral cutaneous nerve of the thigh
- Nerves emerging medially = obturator nerve, lumbosacral trunk
Describe the sacral plexus
- Composed of lumbosacral trunk (half of L4, all of L5)
- Forms within the pelvic cavity
- Lies in relation to piriformis
- Sacral spinal segmental outflow
- Supplies: pelvic region, gluteal region, perineal region, lower limb via the sciatic nerve
What are the axial lines of limbs?
The line of junction of 2 dermatomes supplied from discontinuous spinal levels
- Limbs have posterior and anterior axial lines
- Can be said to mark boundaries between the flexor and extensor compartments of the limb (marked out by veins; cephalic and basilic, great saphenous and small saphenous)
What are nerve territories?
The area of skin that a nerve from the brachial plexus innervates
- Different to a dermatome
What muscles are there in the anterior forearm?
1st layer (lateral to medial): - Pronator teres - Flexor carpi radialis - Palmaris longus - Flexor carpi ulnaris 2nd layer: - Flexor digitorum superficialis 3rd layer: - Flexor pollicis longus - Flexor digitorum profundus 4th layer: - Pronator quadratus
What innervates the pronator teres?
Median nerve
What innervates the flexor carpi radialis?
Median nerve
What innervates the palmaris longus?
Median nerve
What innervates the flexor carpi ulnaris?
Ulnar nerve
What innervates the flexor digitorum superficialis?
Median nerve
What innervates the flexor pollicis longus?
Median nerve
What innervates the flexor digitorum profundum?
- Medial half = ulnar nerve
- Lateral half = median nerve
What innervates the pronator quadratus?
Median nerve
What is the action of the pronator teres?
Pronation of the forearm
What is the action of the flexor carpi radialis?
Flexion and adduction at the wrist
What is the action of the palmaris longus?
Flexion at the wrist
What is the action of the flexor carpi ulnaris?
Flexes and adducts at the wrist
What is the action of the flexor digitorum superficialis?
- Flexes the metacarpophalangeal joints at the fingers
- Flexes the proximal interphalangeal joints at the fingers
- Flexes at the wrist
What is the action of the flexor pollicis longus?
- Flexes the interphalangeal joint of the thumb
- Flexes the metacarpophalangeal joint of the thumb
What is the action of the flexor digitorum profundus?
- Flexes the distal interphalangeal joints of the fingers
- Flexes the metacarpophalangeal joints of the fingers
- Flexes the wrist
What is the action of the pronator quadratus?
Pronates the forearm
What are the common types of joint injury?
- Sprains
- Fractures
- Subluxations
- Dislocations
- Fracture dislocation/subluxation
What should you ask about to find out the history of the injury?
- Mechanism
- Time scale
- Ability to continue activity
- Swelling
- Weight bear
- Weakness
- Site of discomfort
- Mechanical symptoms
What should you look for when examining a joint injury?
- Swelling
- Bruising
- Obvious deformity
- Puncture/skin wounds
- Joint fluid
- Painful anatomical sites
- Laxity (loose ligaments)
- Crepitus (pops/snaps when bending joints)
- Range of movement
- Pulses difficult to feel
What are some classic nerve associations with joint injuries?
- Axillary nerve injury and shoulder dislocation
- Sciatic nerve injury and hip dislocation
- Median nerve and colles fracture
- Arterial injury/common perennial nerve and knee dislocation
What should you do when assessing a joint injury?
- Can use gas and air, sedate, use local anaesthetic or put fully asleep to relieve pain/discomfort
- Check for neuromuscular damage
What investigations can you do for joint injuries?
- X-rays
- Stress views (type of x-ray, demonstrate the amount of joint cartilage left)
- Arthography (radioluscent dye is injected into the bloodstream which will eventually absorb into the joint, or injected directly into the joint)
- MRI
- CT scan
- Aspiration (drain fluid from joint; if fat is present then there is a fracture, fat from bone marrow)
What treatments can you do for joint injuries?
Determined by the type of injury and individual patient circumstances Take photographs if possible Open injuries require: - Ιmmediate cleaning - Irrigation and reduction - Tetanus status - Coverage of wound Subsequently need surgical debridement/washout and fixation as an emergency
Describe a sprain
Damage to a ligament
- Can be complete (may require surgery) or partial
- They have damaged fibres with continuity intact
- Mechanisms: forces which stress the ligaments
What are the common sites for sprains?
- Ankle
- Knee
- Joints of the hand (usually thumb)
Describe a dislocation
Complete loss of continuity of the articulating surface of the joint
What are the common sites for dislocations?
- Fingers
- Shoulder (anterior or posterior)
Describe a subluxation
A partial loss of continuity of the articulating surfaces of the joint
What are the common sites for subluxations?
Shoulder joint
Describe a fracture
A break in the continuity of bone
- Causes = stress, trauma, deficiency, pathological
When assessing a fracture, what do you look for?
- Position
- Open or closed?
- Displacement
- Depression
- Comminution (small fragments)
- Quality of bone
What are the aims of fracture treatment?
- Pain relief
- Prevent infection
- Restoration of normal joint anatomy as far as possible
- Maintenance of position
- Monitor healing process
- Rehabilitate
What are the different methods of treatments for joint injuries?
- Conservation and support
- Manipulate and hold with cash
- Manipulate and insert wires
- Open reduction internal fixation (screws, plates, wires, combinations)
- External fixation
- Arthroplasty
- Excision
- Osteotomy (re-align)
- Amputation
- Arthrodesis
What are some characteristics of hip fractures?
- Very common
- High associated mortality (since often seen in the elderly)
- Usually managed operatively
- Consequences of injury: pain, stiffness, deformity, loss of function, cosmetically poor
What are the different types of hip fractures?
- Intracapsular
- Extracapsular
What happens if a fracture/dislocation tears the capsule and ligament in the hip joint?
Blood supply to the femur head is very important
- If this happens, then blood supply is lost
- It causes necrosis
What is a Colles’ fracture?
Common wrist fracture
- Common in elderly people with low bone density
- A transverse fracture of the distal radius with dorsal displacement and shortening of the wrist
- Often accompanied by a fracture of the ulnar styloid
What is a Smith’s fracture?
Common wrist fracture
- Distal radius fracture
- Palmar displacement and angulation
- Shortened radius
- Causes soft tissue swelling
- Distal fragment is placed anteriorly
- Opposite of colles’
What is the course of the ulnar nerve?
Travels down the medial side of the anterior arm
- Passes posterior to the medial epicondyle
- Pierces the 2 heads of the flexor carpi ulnaris
- Continues down the medial side of the anterior forearm
What is the course of the median nerve?
Travels down the medial side of the anterior arm, but lateral to the ulnar nerve
- Enters into the anterior compartment of the forearm via the cubital fossa
- Crosses over the brachial artery to become situated in the middle of the anterior arm
- Travels between the flexor digitorum profundus and the flexor digitorum superficialis muscles
- Enters the hand via the carpal tunnel
What is the course of the radial nerve?
Travels down the posterior arm (mainly)
- Travels in the radial groove of the humerus
- Accompanied by the brachial artery
- Moves anteriorly over the lateral epicondyle, through the cubital fossa
- Splits into a superficial branch and a deep branch once it enters the forearm
What happens to the brachial artery in the distal region of the cubital fossa?
It bifurcates into the radial and ulnar artery
Where does the radial artery run?
From the distal region of the cubital fossa
- Between the brachioradialis and flexor pollicis
Where does the ulnar artery run?
From the distal region of the cubital fossa
- Between the flexor carpi ulnas and flexor digitorum profundus
What deep veins are found in the anterior forearm?
- Radial veins
- Interosseous veins
- Ulnar veins
- Deep venous arcade
- Accompanying veins of the superficial palmar arch
What superficial veins are found in the anterior forearm?
- Cephalic vein (from the dorsal venous network of the hand)
- Basilic vein (from the dorsal venous network of the hand)
- Median cubital vein (connects the cephalic and basilic veins in the cubital fossa)
List the myotomes
- C5 = Elbow flexion
- C6 = Wrist extension
- C7 = Elbow extension
- C8 = Finger flexion
- T1 = Finger abduction
- L2 = Hip flexion
- L3 = Knee extension
- L4 = Ankle dorsiflexion
- L5 = Great toe extension
- S1 = Ankle plantarflexion
