2: Development of limbs

syndactyly

skin webbing between fingers/toes. most frequently: 3rd and fourth fingers; 2 and 3rd toes . more common in foot

synostosis

fusion of phalanges

embryological basis of syndactyly

separate digital rays fail to form in 5th week or webbing of fingers fails to break down between 6th and 8th weeks. lack of differentiation between 2 or more digits. normally mesenchyme in periphery of hand and foot plate condenses to form the primordial of fingers and toes and thinner tissue between breaks down.

characteristic syndrome produced by thalidomide

amelia and meromelia. hands and feet attached to trunk by small, irregularly shaped bones, intestinal atresia and cardiac defects

Meromelia

gross defect of limb

amelia

complete absence of a limb

atresia

absence of a normal body opening; occlusion; closure

Polydactyly

supernumery of fingers and toes. often completely formed and lacks proper muscle fixation. . ulnar or radial side and foot on fibular side

cutaneous syndactyly

webbing of skin between fingers and toes due to failure of tissue to break down

osseous syndactyly

fusion of bones

structural defect underlying congenital dislocation of hip

socket doesnt fully cover ball

CHD is associated with breech presentation (i.e. buttocks rather than head delivered first). Speculate on why this might be so?

Breech presentation may place undue pressure on the developing hip joint: fails to complete normal development

mesenchyme

primitive undifferentiated connective tissue. derived from mesoderm. proliferation allows lengthening of limbs

talipes equinovarus

most common type of clubfoot. soles of feet turned medially and feet are sharply planter flexed. feet are fixed in tiptoe position

treatment for clubfoot

ponseti method. baby's foot being slowly manipulated in a better position and then being put in a cast. repeated weekly for 8 weeks. achilles tendon cut to release foot. special boots worn to keep in position until 4/5

The AER marks the boundary between the dorsal and ventral ectoderm. This forms an axial line. What does this mean in terms of sensory nerve supply to the limb?

s considerable overlap between adjacent dermatomes in terms of nerve supply so damage to one dorsal spinal root does not lead to anaesthesia to the entire dermatome as that area is innervated by other adjacent nerves. The line of junction between 2 dermatomes supplied from discontinuous spinal levels is known as the axial line. There is no overlap in nerve supply at the axial line as this marks the embryonic boundary between flexor and extensor compartments (C5 not near T1)

AER

ridge of thickened ectoderm at apex of developing limb bud. stimulates outgrowth of limb buds. maintains undifferentiated state in mesenchyme immediately underlying it. enables proliferation and lengthening of limb bud. limb growth is proximal to distal. induces development of digits and disappears when no longer needed

notochord clinical relevance

nucleus proposus in middle of IV. herniates and presses on spinal nerve (slipped disc) and commonly at l4-5 with l5 root nerve most affected causing radiating pain down the leg to big toe and weakness of extensor pollicis longus

c8 dermatome test

touch distal ventral aspect of little finger. ulnar nerve.

ulnar nerve roots

c8-t1

ulnar nerve type

mixed

t10 dermatome testing

touch umbillicus

Axillary nerve (C5-C6) test

regimental badge area

t4 surface anatomy marker

nipples

t6 surface anatomy marker

xiphistermun

t12 anatomy marker

pubis

Cervical nerves C5, C6 and C7 emerge above the corresponding numbered vertebra, while cervical nerve C8 emerges below vertebra C7. Explain why this is so

extra spinal nerve between 1st cervical vertebrae and skull so 7 cervical vertebrae and 8 cervical nerves. from t1 down, spinal nerves exit below corresponding vertebra

mytome

muscle/group of muscles recieve nerve supply from a single cord segment

dermatome map above shoulder

c2: above neck

c3: neck

c4: clavicle

c5: below clavicle

dermatome map trunk

t1: middle arm

-t12 pubis

dermatome map sub trunk

l1: below pubis but not genitals

brachial plexus

C5-T1

dermatome vs cutaneous distribution of peripheral nerve. clinical significance

dermatome strip of skin supplied by single spinal nerve whereas cutaneous distribution of peripheral nerve area of skin supplied by peripheral nerve. mostly arise from plexus which receives imput from many spinal root nerves. locate where damage has occured

pattern and outgrowth of limb bud starts to appear when

end of fourth week

epimysium

connective sheath covering entire muscle bundle

deep muscles of back supplied by which branch of spinal nerve

dorsal ramus

spinal cord

receives afferent fibres carry sensory nerve fibres through dorsal roots and sends efferent fibres which carry motor and autonomic nerve fibres through ventral roots

ectoderm tissues

mouth, nostril and nervous tissue, teeth, sweat glands. neurofibromatosis, sturge webber syndrome, tuberosis sclerosis

ventral side of thumb. dermatome and cutaneous nerve area

c6 and median nerve

describe epemere and hypomere

musculature into two regions. epemere goes dorsally to form erector spinae muscles and innervated by posterior ramus of spinal nerve roots. hypomere ventrally to form rest of musculature and innervated by anterior ramus of spinal nerve root

gross anatomy of spinal cord

has one enlargements from rostral to causal in cervical and lumbar regions. enlargements of spinal cord result from enlargement of grey matter that contains neural machinery to operate limbs

Hoxa genes

week 3 embryo development

3 germ layers. ecto, meso, endo

somites

rounded elevations of mesoderm which appear either side of neural tube on dorsal aspect of embryo from base of skull to tail region

ectoderm

forms epidermis and nervous system

fourth week of development

limb buds appear as small projections on lateral body wall

what core is limb bud

mesenchymal

how are digits formed

apoptosis of tissue between them