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Download BIOL 4260 Human Evolu onary Anatomy Lecture 12: Limb
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BIOL 4260 Human Evolu3onary Anatomy Lecture 12: Limb Development Lecture 2: Fossil Record Outline • Limb Evolution • Limb Development • Limb Function A Few Definitions • Appendicular skeleton – girdles & limbs • Pectoral girdle – bony articulation of the upper limb with the axial skeleton • Pelvic girdle - bony articulation of the lower limb • Arm - upper aspect of upper limb (versus forearm) • Leg - lower portion of the lower limb (versus thigh) Pectoral Girdle Pelvic Girdle Forelimb & Hindlimb ... first there were fins.. First jawed and finned fishes > 400 mya Homologous upper limb structures derived from tetrapod Die Bauplan HOX genes regulate shape and type of bones Limbs Are Serial Homologues Proximal Distal Limb Girdles Development in tetrapods allowed head mobility, independent movement of limbs Much larger in terrestrial animals bear weight and provide attachment sites for muscles Limb Development • Limb buds • Patterning of limb elements • Patterning of limb musculature Limb Buds @ 4 weeks, C4 - T1/2 @ 5 weeks, L1/2 - S3 Embryological Origins • Outpocket of ectoderm and mesoderm • Dermomyotomes: skin and hypaxial muscles • Lateral plate mesoderm: bones • Similar “recipe” for upper and lower limbs Signaling molecules and gene expression 1. Upper limb outgrowth initiated by TBX5 & FGF10 2. Bone morphogenic proteins induce apical ectodermal ridge (AER), axes established 3. Fibroblast growth factors induce distal growth 4. More proximal areas slow division rates and differentiate Pinky vs.Thumb? ZPA - gene sonic hedgehog - regulates position of thumb- if misexpressed - creates mirror image Limb Development • Limb buds • Patterning of limb elements • Patterning of limb musculature Budding Muscles Note: Black dorsal Grey ventral Elevators Depressors Transformation into tetrapod forelimb Basic organization remains Some dorsal muscles migrate onto back Some ventral muscles migrate onto chest Transformation into mammalian forelimb Bring forelimb under body: 90 degree lateral rotation Dorsal muscles become caudal (posterior) Ventral muscles become cranial (anterior) Limb moves under the body to improve locomotion Quadrupeds pronate forearm to locomote Anatomical Position Forelimb: • Pollex is lateral • Developmentally ventral muscles typically anterior • Developmentally dorsal muscles typically posterior Innervation follows... Developmentally Ventral Shoulder & arm: Pectoralis major Pectoralis minor Coracobrachialis Biceps brachii Brachialis Superficial forearm: Pronator teres Flexor carpi radialis Palmaris longus Flexor digitorum superficialis Flexor carpi ulnaris Deep forearm: Flexor digitorum profundus Flexor pollicis longus Pronator quadratus Developmentally Dorsal Shoulder & arm: Supraspinatus Extensor carpi radialis longus Infraspinatus Extensor carpi radialis brevis Subscapularis Extensor digitorum Latissimus dorsi Extensor digiti minimi Teres major Extensor carpi ulnaris Teres minor Brachioradialis Deltoid Triceps brachii Anconeus Superficial forearm: Deep forearm: Abductor pollicis longus Extensor pollicis longus Extensor pollicis brevis Extensor indicis Supinator Lower Limb Transformation into mammalian hindlimb Bring hindlimb under body: 90 degree medial rotation - opposite direction of forelimb Most dorsal muscles become cranial (anterior) Most ventral muscles become caudal (posterior) Limb moves under the body to improve locomotion Quadruped foot is in correct position to locomote Anatomical Position Hindlimb: • Hallux is medial • Developmentally ventral muscles posterior and medial • Developmentally dorsal muscles anterior and lateral Developmentally Ventral Pelvis and thigh: Gracilis pectineus Adductors (longus, brevis, magnus) Obturator externus Obturator internus Gemellii ms. Quadratus femoris Biceps femoris (Long) Semitendinosus Semimembranosus Posterior leg: Gastrocnemius Soleus Plantaris Popliteus Flexor digitorum longus Tibialis posterior Flexor hallucis longus Developmentally Dorsal Pelvis & thigh: Psoas major Iliacus Tensor fasciae latae Gluteus minimus Gluteus medius Piriformis Gluteus maximus Sartorius Quadriceps femoris Biceps femoris (short) Anterior leg: Tibialis anterior Extensor hallucis longus Extensor digitorum longus Peroneus tertius Lateral leg: Peroneus longus Peroneus brevis Limb Functions Mammalian Limbs Limbs shifted from lateral position to below trunk reduced pectoral girdle helps suspend thorax Bipedalism Reinforcement of lower limb stability, strength Less demand on upper limb, reduction in weight, retained mobility Limb Functions • Mammals highly efficient - parasagittal movements • Locomotion: Quadrupeds: walking, running, climbing, jumping, leaping, crawling, swimming, flying, gliding Bipeds: obligate walking and running • Tool use: possible motivating force for human bipedalism - freeing of hands
