Introduction to the limbs Flashcards
What are the functions of bone? (x5)
• Support of the body shape. • System of levers for muscle action. • Protection of internal organs. • Site of blood cell formation. • Mineral storage pool.
What are the mechanical properties of bone? (x2) What gives them these properties?
• Has some cable-like flexibility and resistance to tension because framework is COLLAGEN and other bone proteins (collectively called osteoid). • Pillar-like stiffness and resistance to compression conferred by impregnation of collagen with crystalline mineral (hydroxyapatite – a complex calcium hydroxyphosphate).
What are the two bone structural arrangements? Where is each type found?
• WOVEN bone – immature. • LAMELLAR bone – mature. • In adults, woven bone is only found in repairing fractures.
What is the structure of a typical long bone?
- Head is called epiphysis.
- Shaft is called diaphysis.
- In the head, you will find SPONGY BONE; in the shaft, you will find denser COMPACT BONE which surrounds a MEDULLARY cavity containing bone marrow.
- Bones have articular cartilage on their reticular surface (where bone makes contact with another skeletal structure).
- Nutrient foramen are present where vessels can access the bone to deliver nutrients.
What is a reticular surface?
Where bone makes contact with another skeletal structure.
What are the different arrangements of lamellar bone called? (x2)
- Outer hard layer of compact lamellar bone is called CORTICAL BONE.
- Inner layer of interlacing struts (mesh) of lamellar bone is called CANCELLOUS, spongy or trabecular bone.
What are the functions of trabecular bone? (x4)
- Keep bone light. 2. They are still quite strong. 3. Trabeculae link together to distribute force across a large area. However, it cannot resist the same amount of compression as compact bone. 4. Contains space for marrow.
What is the structure of compact/cortical bone?
Compact bone is made up of OSTEON UNITS which are columns of bone with central canals containing vessels. The lamellar cells are concentric (circle around the canal). Osteocytes are osteoblasts that are embedded in the bone tissue i.e. the material it has secreted.
What is the cross-sectional structure of trabecular bone?
Osteocytes are embedded within the bone tissue, and osteoblasts are aligned along trabeculae of the new bone, and osteoclasts surround these structures too. The concentric nature of these cross-sections are less uniform than in compact bone.
What is the structure of osteon units? !!!
Osteons are units containing central canals surrounded by concentric circles of calcium deposits. In between these calcium deposits are OSTEOCYTES, which have many projections that embed into the deposits. Osteocytes are therefore able to form gap junctions with each other so they can share nutrients – nutrients can be passed from cells on the outside of bone to cell inside bone.
What is the vascular supply of long bones? (x2)
Major supply from nutrient arteries that pass in via nutrient foramen/canal and supply mostly the bone shaft. Epiphysial arteries supply the heads of bones.
What is the periosteum?
Outer surface of bone with a fibrous and cellular layer. It has a key role in bone growth and repair as it houses cells such as osteoblasts and has good vascular and sensory nerve supply – pain from damaged bone is usually felt here.
What is the process of differentiation of osteocytes?
Osteogenic cells are osteoblast precursors –> osteoblast –> osteocyte.
What differs in the functions of osteoblasts and osteocytes? !!!
• OSTEOBLASTS: located on the SURFACES of osteon units and make a protein mixture called OSTEOID which mineralizes to become bone. The osteoblast then DEPOSITS HYDROXIDE AND BICARBONATE IONS which hardens the bone. Osteoblasts become trapped inside this material and become osteocytes. • OSTEOCYTES: located WITHIN osteon units, maintain the bone matrix, and can activate/inactivate osteoblasts. The spaces they occupy are known as LACUNAE. They COMMUNICATE with osteoblasts and osteoclasts with projections.
From what are osteoclasts derived from?
Derived from the same cells which differentiate to form macrophages and monocytes.
What is the function of osteoclasts?
Bone resorption through breakdown of bone matrix.
What is the TIME-SCALE of bone development through life?
The skeleton starts to form at 6 weeks of fetal life and growth continues in some bones until 25 years of age.
What is ossification?
Laying down new bone material by cells called osteoblasts.
What are the two types of ossification? Where does each take place?
- INTRAMEMBRANOUS: where vascular connective tissue is already present, bone matrix (osteoid) is deposited around collagen and mineralises. Because bone is formed according to the arrangement of the vascular network it arose from, the newly formed bone is WOVEN. It therefore later undergoes remodelling to lamellar bone (see photo). THIS OCCURS IN: the flat bones of the skull and mandible in foetus and in fractures.
- ENDOCHONDRAL: where a bone is to be formed, a cartilage model of the bone is formed. Cartilage calcifies and chondrocytes die. This promotes periosteal osteoclasts to cut channels for sprouting vessels into the bone. Osteoblasts enter with the vessels and build the bone around them. Because channels for vessels are already cut, bone formed is LAMELLAR and does not require remodelling. THIS OCCURS IN: the long bones of foetus and continues until adulthood.
How does endochondral growth of bones continue into adulthood?
- [Numbers correspond to picture.] Imagine your cartilaginous bone model.
- Cartilage calcifies first at the shaft.
- Cartilaginous calcification promotes recruitment of blood vessels to the shaft – this becomes the PRIMARY OSSIFICATION CENTER.
- Ossification occurs in the shaft, but epiphysis remain cartilaginous and uncalcified.
- Epiphysis begin to calcify, and vessels are finally recruited to this area. A SECONDARY ossification centre is formed.
- THE RESULT: a small epiphyseal plate is left between the head and shaft of the developed bone. This remains cartilaginous until adulthood. Therefore, growth of the SHAFT continues at this cartilaginous plate. Growth cessation only occurs when cartilage growth ceases and plate is over-run by ossification.
How can you distinguish between child and adult bone in x-ray?
Epiphyseal plates are present in children’s x-ray – shown by arrows.
How is bone adaptable? (x4)
• Can grow without compromising its support functions. • Increases or decreases bulk and density in response to pattern of use e.g. people who come back from space have lower bone density because of lowered mechanical use. • Can alter its external and internal shape in response to pattern of use – remodelling. • Can repair when fractured.
How do bones grow in diameter?
• Called APPOSITIONAL GROWTH – addition to exterior at the periosteum.
- Osteoblasts and osteoclasts create ridges and grooves in the bone surface.
- Blood vessels align in these grooves.
- Osteoblasts build new osteon units round these vessels.
- Osteoclasts remove bone from the endosteal surface (thin layer of connective tissue that lines the inner surface of vesicular canals or the medullary cavity in long bones).
What is the process of fracture healing?
- HAEMATOMA is formed where the fracture occurs.
- The haematoma becomes infiltrated with NEW BLOOD VESSELS.
- WOVEN BONE begins to form as this newly vascularised area is invade by fibrous matrix and cartilage/bone progenitors (intramembranous ossification – I think).
- Bone is remodelled to LAMELLAR BONE and the fracture is healed.
Where is the safe area for intramuscular injections?
Buttock.
Describe the neurological and orientational development of the limbs?
- Upper limbs arise from the nervous supply of C5-T1.
- Lower limbs arise from the nervous supply of L2-S3.
- In the anatomical position, upper limb flexors face anteriorly while extensors face posteriorly.
- In the anatomical position, lower limb flexors face posteriorly while extensors face posteriorly. This is because in early development, the lower limbs rotate internally – there is a permanent pronation during foetal growth = twisting of the dermatome fields as seen in the photo.
What are the compartments of the upper limb? (x7) !!!
- Pectoral girdle muscles (chest) – anterior and posterior.
- Intrinsic shoulder muscles.
- Anterior arm muscles – flexors (in medicine, arm refers to the UPPER arm i.e. between shoulder and elbow).
- Posterior arm muscles – extensors.
- Anterior forearm muscles – flexors (in medicine, forearm refers to the LOWER arm).
- Posterior forearm muscles – extensors.
- Intrinsic hand muscles.
- Don’t know how much of the picture we need to remember, but I guess we will have to learn them all at some point in Year 2, so might as well learn them now!
What is included in the pectoral girdle compartments?
Involves chest, back and neck muscles, pectoralis major, deltoid, serratus anterior, trapezius, latissimus dorsi (though this is innervated by a different nerve to the rest – CN supply instead) and rotator cuff muscle of the shoulder.
What are the compartments of the lower limb? (x10) Don’t need to remember all these – just introducing us to what we will be studying later in the year.
- Hip abductors (gluteal).
- Hip extensors (gluteal).
- Hip flexors.
- Anterior thigh muscles – extensors.
- Medial thigh muscles – adductors.
- Posterior thigh muscles – flexors.
- Anterior leg muscles – extensors (dorsiflexors). Leg refers to the lower leg in medicine i.e. between knee and ankle.
- Lateral leg muscles – foot evertors.
- Posterior leg muscles – flexors (plantarflexors).
- Intrinsic foot muscles – variety of functions.
What is the arterial blood supply of the upper limb?
Aorta –> subclavian artery –> axillary artery –> brachial artery (branches to deep brachial artery) –> ulnar and radial arteries –> deep and superficial hand palmar arches –> metacarpal and digital arteries.
What are vena comitans?
A pair of veins, (occasionally more) that closely accompany an artery in such a manner that the pulsations of the artery aid venous return and involved in heating blood travelling back to the heart. These are more present in the distal regions of the limb where there’s e.g. not just one radial vein, but a pair of radial veins – see photo.
What is the venous drainage of the upper limb?
- Deep and superficial veins mirror the arterial supply.
- Dorsal venous arch (superficial, hand), radial and ulnar veins, cephalic and basilic veins, axillary vein, subclavian vein, superior vena cava.
- All deep veins are paired to an artery.
What is the clinical importance of superficial veins in the upper limb?
Superficial veins in the region of the Cubital Fossa are commonly used for phlebotomy. In particular, the MEDIAN CUBITAL VEIN, linking the basilic and cephalic veins. The dorsal venous arch may also be used.
What is the arterial blood supply of the lower limb?
- Aorta –> common iliac arteries –> internal and external iliac arteries.
- External iliac artery –> Femoral artery and deep femoral artery.
- Femoral artery –> popliteal artery –> posterior tibial artery, anterior tibial artery, peroneal (or fibular) artery –> dorsalis pedis.
What is the venous drainage of the lower limb?
- Deep and superficial veins mirror the arterial supply.
- DEEP SYSTEM: anterior and posterior tibial venae comitantes, popliteal vein, femoral vein, external iliac vein.
- SUPERFICIAL SYSTEM: venous arches, long saphenous vein and short saphenous vein.
What is the femoral triangle? Clinical importance?
Marked superiorly by the inguinal ligament, medially by the medial border of the adductor longus muscle and laterally by the medial border of the sartorius muscle. The region of the groin where the femoral artery is accessed e.g. access to cardiac vessels to carry out angiograms (x-ray to examine blood vessels using special dye) and angioplasty. A pulse can be felt in this area.
What are varicose veins?
Perforating veins (labelled) connecting superficial and deep veins contain a valve that will allow flow only from superficial to deep veins. If such valve is compromised, blood is pushed from deep to superficial veins leading to varicose veins.
What is segmental innervation?
Describes the dermatomes/myotomes innervated by individual spinal nerves. Note that the dermatomes in the leg twist so that anterior becomes posterior and vice versa – this is because of the permanent pronation in foetal development.
What are the principles of organisation of segmental nerve supplies for MYOTOMES? (x5)
- The anterior rami of spinal nerves in the brachial and lumbosacral plexuses have anterior and posterior divisions – the anterior division of the anterior rami innervates the flexor muscles; the posterior division of the anterior rami innervates the extensor muscles.
- Muscles are supplied by two adjacent spinal segments.
- Any muscles that have the same action on a joint have the same nerve supply.
- Opposing muscles are innervated by nerves found 1-2 segments above or below e.g. biceps may be innervated by one spinal segment, but triceps are innervated by a spinal segment 1-2 segments above or below the biceps’ segment.
- The more distal in the limb, the more caudal (lower down) the spinal segment innervating it.
What is the difference between peripheral and segmental innervation? !!! Help!?
A segment is an area supplied by fibres from a single nerve root. Each peripheral nerve is made up of fibres deriving from different nerve roots (remember, plexuses mean that nerves get all mixed up). A skin region supplied by a peripheral nerve is called the CUTANEOUS INNERVATION of that nerve.
