Presentation on theme: "Limbs Evolution, Development And Organisation 212 – 2004 – Week 13 Avinash Bharadwaj."— Presentation transcript:
Limbs Evolution, Development And Organisation 212 – 2004 – Week 13 Avinash Bharadwaj
Origins Extensions (appendages) of the body wall Hypaxial structures Supplied by ventral rami of spinal nerves! Two pairs Pectoral and pelvic fins Forelimbs and hindlimbs (quadrupeds) Upper and lower limbs (humans)
General Plan Fins Pectoral and Pelvic The Axis Borders Preaxial Postaxial Surfaces & Muscles Dorsal and ventral All limb musculature is hypaxial! “Dorsal” and “Ventral” refer to arrangements within the limb.
The Tetrapod Limb Limb girdles – pectoral and pelvic Anchor to the trunk (vertebral column) Limb “Segments” (Not to be confused with developmental segments!) Arm / Thigh (1 bone) Forearm / Leg (2 bones) Carpus (Wrist) / Tarsus – 8 bones Metacarpus / Metatarsus – 5 bones Digits – 2, 3, 3, 3, 3. Basic pentadactyl structure Modifications
Human Limbs - Comparison Stabililty and movement – a compromise Lower limbs Support Locomotion Upper limbs Reaching out Grasping Fine movements Greater mobility
Terminology of Movements Flexion / Extension Bending and straightening Flexion : approximation of ventral surfaces Special terms for ankle and foot Abduction / Adduction Abduction : Movement away from midline Special reference line for fingers and toes Rotation : Medial and Lateral Other movements Pronation / supination (forearm and hand) Inversion and eversion (Foot) All joints do not exhibit all movements.
The Tetrapod Limb Dorsal and ventral surfaces Limb girdles (not shown here)
Muscles Groups In general… Flexors and adductors are ventral muscles. Extensors and abductors are dorsal muscles. There are notable exceptions!
Girdles – Upper Limb Clavicle…? Complex history Membrane bone Variable Scapula – dorsal Coracoid – ventral (Fused to scapula) Most shoulder muscles are dorsal
The Mammalian Upper Limb Elevation of the trunk The pectoral muscle sling Girdle components Clavicle…
Limb Rotation Recognise ventral and dorsal surfaces Nature of skin in human limbs Arm, forearm and palm – ventral surfaces Thigh and leg – Dorsal surfaces are anterior! Foot – “dorsum” faces up Sole faces the ground Normal angulation Terminology “Flexion” – plantarflexion “Extension” - dorsiflexion
Limb Axes Embryonic positions Thumb and great toe face cranially Final position Thumb lateral, great toe medial! Radius – preaxial, ulna postaxial Tibia – preaxial, fibula postaxial
Limb – Body Wall Segments Upper Limb : C5 to T1 Lower Limb : L2 to S3 Both hypaxial, supplied by ventral rami Nerve Plexuses Upper Limb Brachial Plexus : Ventral rami of C5 – T1 Lower Limb Lumbar and sacral plaxuses (Lumbosacral plexus) L 2,3,4 + S 1,2,3
Nerve Plexuses and Muscles Ventral rami – ventral and dorsal divisions For ventral and dorsal muscles Pattern simpler in lower limb Brachial plexus : more stages
Muscle Groups - Shoulder Deltoid Pectoralis major and minor Pectorals (front) : The only ventral muscles of shoulder!
Arm Ventral and dorsal groups Ventral – flexors of elbow Dorsal – extensors of elbow
Forearm Flexors : Wrist and fingers + Hand muscles : Ventral! Extensors Ext. Wrist + fingers Abductors of thumb
Brachial Plexus Roots : Ventral rami, C 5 to T 1 Trunks: Three - Upper, Middle, Lower Divisions : Two from each trunk Cords: Three
Functional Considerations In mammals : Locomotion Mobility The variable clavicle Primates incl. Humans Prehension Mobility and grasping – range Brachiation The Human Hand – power and precision
Lower Limb – Thigh Muscle Groups Anterior : Flexors of hip, extensors of knee Medial – adductors Posterior : Extensors of hip, flexors of knee
Leg – Muscle Groups Anterior Extensor Lateral Peroneal Posterior Flexor
The Limbs Compared – 1 Ilium, Ischium, Pubis Sacrum Hip joint Deep acetabulum More stable Scapula (+ coracoid), clavicle No vertebral anchor Shoulder joint Shallow glenoid Highly movable Upper Lower
Flexor compartments anterior Forearm movements Pronation and supination Preaxial bone (radius) lateral Postaxial bone (ulna) medial (Also true for digits) Versatile hand The Limbs Compared – 2 Upper Lower Flexor compartments posterior Fixed leg bones Socket for ankle Preaxial bone (tibia) medial Postaxial bone (fibula) lateral Stable, supporting foot
Core Concepts Hypaxial structures Common plan Identify bones Preaxial and postaxial structures Rotation of limbs Functional considerations
Conducting this unit has been a great pleasure. Thank you and best wishes.