Term
| What is the most abundant tissue type in the human body? |
|
Definition
|
|
Term
| What is the difference between parenchyma and stroma? |
|
Definition
| parenchyma tissue actually performs the function of the organ, the stroma is all the supporting structures |
|
|
Term
| Since epithelial tissue is avascular, how does it receive nourishment |
|
Definition
| from the well vascularized connective tissue underneath |
|
|
Term
| Name the 4 types of connective tissues. |
|
Definition
| CT proper, cartilage, bone, and specialized |
|
|
Term
| ligaments and tendons are made up of what type of connective tissue? |
|
Definition
|
|
Term
|
Definition
| flat expanded tendons (made of dense regular CT) |
|
|
Term
| What is a myotendinous junction? |
|
Definition
| connect muscle to bone and are continuous with muscles at myotendinous junctions |
|
|
Term
| Name 3 types of cartilage. Which type of cartilage is most often associated with synovial joints and functions to cushion and protect joint surfaces? |
|
Definition
| hyalin cartilage, elastic cartilage, and fibrocartilage. Hyalin is most associated with synovial joints and functions to protect joint surfaces |
|
|
Term
| Name the two types of mature bone tissue. Where are they located and what are their functions? |
|
Definition
compact bone, and trabecular bone. Compact bone consists of many vertical canals (osteons).
This vertical design functions to resist twisting and bending. Trabecular
bone is found at the ends of long bones and is composed of networks of
interconnecting bars and plates which offer resistance to compression and
lighten the weight of the bone itself. |
|
|
Term
|
Definition
| bone in a healthy person or animal will adapt to the loads under which it is placed.[1] If loading on a particular bone increases, the bone will remodel itself over time to become stronger to resist that sort of loading.[2] The internal architecture of the trabeculae undergoes adaptive changes |
|
|
Term
| What is the epiphyseal plate? |
|
Definition
| it is a hyaline cartilage plate in the metaphysis at each end of a long bone. |
|
|
Term
| Does the periosteum cover the joint surfaces of long bones? If not, what does? |
|
Definition
| no, joint surfaces are covered by hyalin cartilage. |
|
|
Term
| What are Sharpey's fibers? |
|
Definition
| Sharpey’s fibers are bundles of collagen that penetrate the outer layers of bone and serve to anchor Periosteum, tendons, ligaments and joint capsules to bone. |
|
|
Term
| Bone tissue is aneural. Why then does it hurt when you hit your shin? |
|
Definition
| the periosteum is highly innervated. |
|
|
Term
| do both spongy bone and compact bone adapt to the loads put on them? |
|
Definition
| the spongy bone is highly adapted to the forces acting on it, while the compact bone is not |
|
|
Term
| Describe the difference between intramembranous ossification and endochondral ossification. |
|
Definition
| Intramembranous Ossification = mesenchymal cell model --> osteoblasts --> bone, While endochondral ossification = mesenchymal cells --> chondroblasts --> hyalin cartilage model --> bone |
|
|
Term
| articular surfaces of bones that develop by endochondral ossification (all of the bones of the appendicular skeleton except the clavicle) are covered by what type of cartilage? |
|
Definition
|
|
Term
| Articular surfaces of bones that develop by intramembranous ossification are covered by what type of cartilage? |
|
Definition
|
|
Term
| A joint or articulation is also called an arthrosis. Describe the difference between a true joint (diarthrosis) and a false joint (synarthrosis). |
|
Definition
|
|
Term
| What tissue lines the articular surfaces of synovial joints? Are there any exceptions? |
|
Definition
| hyalin cartilage. ????????????? |
|
|
Term
| What are the two types of false joints? |
|
Definition
| fibrous joints and cartilagenous joints |
|
|
Term
| What is the function of synovial fluid? |
|
Definition
Synovial fluid is produced by the
internal synovial membrane and provides joint protection,
lubrication and nutrition |
|
|
Term
| What is a bursa? Articular disc? Meniscus? |
|
Definition
Bursa and synovial sheaths are fluid filled synovial sacs that
reduce friction where tendons pass over joint surfaces. Articular discs completely separate the
articular surfaces thus forming two separate cavities. A meniscus
is an incomplete disc that partially separates the joint surfaces |
|
|
Term
| Articular cartilage is aneural. Joints are innervated by nerves located within the joint capsule as well as structures surrounding the joint. What is Hilton's Law? |
|
Definition
| a nerve that innervates a joint also tends to innervate the muscles that move the joint and the skin that covers the distal attachments of those muscles. |
|
|
Term
| Articular cartilage is avascular. How is it nourished? What is an anastomosis? |
|
Definition
| It relies on diffusion of nutrients from synovial fluid as well as blood vessels in the adjacent bone. Articular arteries and veins arise from vessels around the joint forming networks (anastomoses) that pierce the capsule and ensure adequate joint vascularization |
|
|
Term
| describe the difference between an agonist and antagonist. |
|
Definition
| an agonist is the prime mover. An antagonist opposes the action of the prime mover |
|
|
Term
| What is a neurovascular bundle? |
|
Definition
| the nerve and arterial supply to a muscle usually enters the muscle's deep surface together as a bundle. |
|
|
Term
|
Definition
|
|
Term
| What is the difference between a isometric and an isotonic muscle contraction? |
|
Definition
| isometric contraction is where there is contraction over tonic levels, but no movement is produced. An isotonic musle contraction is contraction over tonic levels where there is movement. |
|
|
Term
| What is the difference between a concentric and an eccentric isotonic muscle contraction? |
|
Definition
| concentric shortening vs eccentric lengthening |
|
|
Term
| What are the three heads of the pectoral muscle? |
|
Definition
| sternal head, clavicular head, and ??????? Abdominal head???? |
|
|
Term
| are the clavicle and scapula part of the appendicular skeleton or the axial skeleton? |
|
Definition
|
|
Term
| Name the layer of loose CT which separates the breast from the deep pectoral fascia and allows for movement of underlying muscles. |
|
Definition
|
|
Term
| What is the significance of suspensory ligaments (coopers) in carcinoma of the breast? |
|
Definition
Carcinoma of the breast creates tension on these ligaments resulting in dimpling of the skin
superficial to the breast. |
|
|
Term
| Describe the primary arterial and venous supply to the mammary glands. |
|
Definition
| lateral thoracic artery, internal thoracic artery. |
|
|
Term
| Why do primary tumors of the breast often metastasize to axillary lymph nodes. |
|
Definition
| Cells that metastasize from primary tumors and enter lymphatic vessels often lodge and grow as secondary tumors in lymph nodes |
|
|
Term
| What type of fascia is the pectoral fascia? |
|
Definition
|
|
Term
| the cephalic vein is superficial. What is the other main superficial vein of the upper limb? |
|
Definition
|
|
Term
| What is the function of the lymphatic system? |
|
Definition
| The lymphatic system works in conjunction with the circulatory system to remove waste products from cells and tissues |
|
|
Term
| In general, recognize that lymph from the right side of the head and neck, right upper limb, right upper thorax, and right upper abdominal wall drain ultimately into large veins on the right side of the neck. Where does the lymph from the remaining parts of the body drain? |
|
Definition
| the large veins on the left side of the neck. |
|
|
Term
| Name the two largest lymphatic ducts which we will see in lab. |
|
Definition
| right lymphatic duct and the thoracic duct |
|
|
Term
| Name at least 4 types of lymphatic organs. |
|
Definition
| spleen, lymph node, thymus, tonsils |
|
|
Term
| What is the importance of lymph nodes during metastasis of primary tumors? |
|
Definition
| Cells that metastasize from primary tumors and enter lymphatic vessels often lodge and grow as secondary tumors in lymph nodes |
|
|
Term
| T or F. Lymph vessels have valves. |
|
Definition
|
|
Term
| T or F. Movement of lymph through lymphatic vessels is generated in a manner similar to veins. |
|
Definition
|
|
Term
| Why do large arteries contain a large amount of elastic tissue? |
|
Definition
| allows for great expansion and recoil during the cardiac cycle |
|
|
Term
| What is the function of smooth muscle within medium sized arteries within the periphery? |
|
Definition
|
|
Term
| Why is more blood contained within the venous versus arterial system? |
|
Definition
| Veins are more numerous and variable than arteries. Veins have a larger outermost CT layer or tunica externa (adventitia) and a smaller middle smooth muscle layer than arteries of the same diameter. Thus, veins have a higher capacitance than arteries |
|
|
Term
| Describe the location of deep vs superfiscial veins? |
|
Definition
| Deep veins are located deep to the investing (deep) fascia and accompany arteries of the same name. These venae comitantes are usually double or multiple in number and enclosed with their companion artery in a sheath. Superficial veins are located in the superficial fascia and do not accompany an artery |
|
|
Term
| is the cephalic vein a superficial or deep vein? Why? |
|
Definition
| superficial. It doesn’t accompany an artery, and it is near the surface. |
|
|
Term
| What are venae comitantes? |
|
Definition
| deep veins that accompany an artery. |
|
|
Term
| what are the mechanisms that achieve venous return to the heart? |
|
Definition
Valves are often present in veins, particularly those located in the periphery
inferior to the level of the heart. These are usually paired cusps that are
particularly important in venous return to the heart. As surrounding muscles
contract, blood within veins is “milked” toward the heart. Deep venous return
is further assisted by arterial pulses which compress their accompanying veins
within the CT sheath. |
|
|
Term
| Describe the pathology behind varicose veins. |
|
Definition
| failure of the perforating veins causes an increase in volume and pressure of superficial veins. |
|
|
Term
| Describe the pathology of deep vein thrombosis. |
|
Definition
| A deep vein thrombosis (DVT) originates in the deep veins of the legs. Predisposing factors include smoking, hospitalization and air travel. The clot may dislodge and pass into the venous system. Normal blood flow can be disrupted causing swelling of the legs. |
|
|
Term
| What is the difference between a thrombus and an embolis? |
|
Definition
| a thrombus is a solid mass of platelets and/or fibrin (and other components of blood) that forms locally in a vessel. An embolus is most often a piece of a thrombus that has broken free and is carried toward the brain by the bloodstream |
|
|
Term
| What are the three tunics surrounding an artery or vein? |
|
Definition
| tunica adventitia, tunica media, tunica intima |
|
|
Term
| Collections of nerve cell bodies within the CNS are called _______ and located in ______ matter. |
|
Definition
|
|
Term
| Collections of nerve cell bodies within the PNS are called ________. |
|
Definition
|
|
Term
| Bundles of nerve processes within the CNS are called _______ and located in _______ matter. |
|
Definition
|
|
Term
| Bundles of nerve processes within the PNS are called _______. |
|
Definition
|
|
Term
| Functionally, neurons and their processes in the PNS are generally classified as sensory or motor. The cell bodes of the sensory neurons in the PNS are locted in the _______ _________ ganglia while the cell bodies of the motor neurons are located in the _______ ________ of the spinal cord. |
|
Definition
| dorsal root; ventral horn |
|
|
Term
| sensory fibers are also called ________. Motor fibers are also called ______. Describe how motor and sensory neurons look. |
|
Definition
| afferent; efferent. Afferent have a cell body in the middle, pseudounipolar, efferents bipolar. |
|
|
Term
| Sensory fibers exit on the ______ surface of the spinal cord while motor fibers exit the _______ surface of the spinal cord. Sensory rootlets join within the intervertebral foramen to form a _______ nerve. |
|
Definition
|
|
Term
| Spinal nerves quickly divide into branches called _______. Describe the course of these branches to the dorsal and ventral surfaces of the body. |
|
Definition
| rami. ??????????????????? |
|
|
Term
| Motor and sensory neurons can be further classified as somatic or visceral (autonomic). To what does the word somatic and visceral refer? This is key to remembering their function |
|
Definition
| somatic = body; visceral = organ |
|
|
Term
| What is the difference between general and speciAL fiber types? |
|
Definition
| special are cranial nerves |
|
|
Term
| What are the four general classifications of nerves found in the nervous system. What are the locations of their cell bodies and their function? |
|
Definition
| GSA's and GVA's which are lcoated in the dorsal root ganglia and function. |
|
|
Term
|
Definition
| A single somatic motor neuron and all of the muscle fibers it innervates is called a motor unit |
|
|
Term
| In the somatic nervous system, how many neurons are required to complete the pathway between a GSA receptor in the skin and the CNS? How many GSE neurons are required to complete the pathway from the spinal cord to a skeletal muscle? |
|
Definition
|
|
Term
| In the autonomic nervous system, how many neurons are required to complete the pathway between a GVA receptor on an organ and the CNS? How many GVE neurons are required to complete the pathway from the spinal cord to a smooth muscle? |
|
Definition
|
|
Term
| the cell bodies of both GSA and GVA sensory neurons are located in dorsal root ganglia. Describe how these fiber types differ. |
|
Definition
GSA's Conveys cutaneous sensation (pain, temperature, vibration, pressure) from skin
and proprioception from joints and muscles in body wall and limbs. GVA's Conveys reflex sensations, pain, distension and chemical change, from viscera, glands and blood vessels |
|
|
Term
| What is the difference in the distribution of sympathetic and parasympathetic nerve fibers in the body? Are there parasympathetic nfibers in the extremeties? If no, why? |
|
Definition
| sympathetics are distributed throughout the body as they help regulate blood flow. Parasympathetics are mostly located in the gut. They are to help you return to baseline and are not located in the extremeties. |
|
|
Term
| What is the function of dendrites? Axons? |
|
Definition
| Dendrites are specialized for reception of stimuli while axons for conduction of an action potential to other cells |
|
|
Term
|
Definition
| Myelin insulates the axons and speeds transmission |
|
|
Term
|
Definition
| neurons communicate at synapses, junction of two neurons. |
|
|
Term
| What are the 3 connective tissues layers associated with the CNS and PNS? Name the spaces formed by these tissues. What space is not a real space but an interface? Which space contains CSF? Which space contains a large vertebral venous plexus? |
|
Definition
| pia mater, arachnoid mater, and dura mater. Between the vertebrae and the dura mater is the epidural space, which contains the large vertebral venous plexus. Between the dura mater and the arachnoid mater is called the subdural space, and it is not a real space, but an interface. Between the arachnoid mater and the pia mater is the subarachnoid space and this is where the CSF is. |
|
|
Term
| What is the conus medullaris and at what is its approximate location (what vertebral level?)? What is the cauda equina? Why are there cervical and lumbar enlargements within the spinal cord? What are the names of the tooth like extensions of pia mater that uspend the spinal cord within the dural sac? |
|
Definition
| the conus medullaris is the termination of the spinal cord at approximately L1/L2 |
|
|
Term
| describe the difference between the filum terminale internus and externus? |
|
Definition
| filum terimale internus is a slender thread of pia extending from the termination of the spinal cord to the bottom of the dural sac. Once it exits the dural sac, it becomes the filum terminale externus and is continuous with the coxyggeal ligament |
|
|
Term
| what is the lumbar cistern and why is it the acceptable location for performing a spinal tap to remove CSF? |
|
Definition
| it is an enlargement of the subarachnoid space between L2 and S2. the spinal cord has ended, and we have some extra space so this is the safest place to take a spinal tap. |
|
|
Term
| Why are lumbar and sacral spinal nerves so much longer in appearance than those of the cervical and thoracic regions? |
|
Definition
| the spinal cord ends at L1/L2, but the spinal nerves have to keep going to exit at the intervertebral foramen of their respective vertebrae, so their rootlets are much longer. |
|
|
Term
| Rib #1 articulates with the sternum at the ___________ |
|
Definition
|
|
Term
| Why are ribs 1-7 called true ribs and 8-10 called false ribs? |
|
Definition
| true ribs articulate with both the sternum and the vertebrae. The false ribs 8-10 articulate with the vertebrae and the rib superior to them. Ribs 11 and 12 are floating ribs as they only articulate with the vertebrae |
|
|
Term
| How are intercostal spaces named? |
|
Definition
| The spaces are named according to the rib forming the superior border of the space. Thus, there are 11 intercostal spaces. A subcostal space lies below the twelfth rib. |
|
|
Term
| Typical ribs #3-9 feature heads with two facets. Why? |
|
Definition
| they articulate with two vertebrae. |
|
|
Term
| With what structures do the tubercles of ribs articulate? |
|
Definition
| the transverse process of the corresponding vertebrae. |
|
|
Term
| describe the thoracic outlet? i.e. what are its boundaries and why is it important? |
|
Definition
| it is bordered Posteriorly by the T1 vertebra, Laterally by the first pair of ribs, Anteriorly by the superior border of the manubrium. It is the space for the passage of the nerves and vessels which supply the upper limb |
|
|
Term
| What is the difference between these joints of the ribcage: costovertebral, costotransverse, sternocostal |
|
Definition
|
|
Term
| describe an intervertebral disc. |
|
Definition
Intervertebral discs are located between adjacent vertebral bodies (C2-S1) and provide additional stability and shock absorption. Intervertebral discs are composed of an annulus fibrosus and a
nucleus pulposus. The annulus is a ring of concentric lamellae of fibrocartilage which surrounds and contains the spread of the softer nuclear core. |
|
|
Term
| Review using a picture all ligaments of the vertebral column. What is the significance of ligamentum nuchae? |
|
Definition
| certain muscles of the back like the trap and splenius have attachments here. |
|
|
Term
| How is the vertebral column innervated? |
|
Definition
| Most other parts of the vertebral column are innervated by (recurrent) meningeal branches of the spinal nerves themselves |
|
|
Term
| Describe primary and secondary curvatures as well as abnormal curvatures of the spine. How would one describe a left scoliosis in the thoracic region. |
|
Definition
| The primary curvature of the vertebral column reflects the shape of the embryo (concave on ventral surface). Secondary curves, (concave on dorsal surface) form in the cervical and lumbar regions during normal development. |
|
|
Term
| Uncovertebral joints are located in what region? Mammilary bodies are located in what region? |
|
Definition
| The concave superior surfaces of the (C3-C6) bodies are significant for uncinate processes. Uncovertebral “joints” (of Luska) are frequent sites of bone spur (osteophyte) formation. Mammillary processes are located at each superior articular process of lumbar vertebrae. These processes are important sites for muscle attachments. |
|
|
Term
| describe the anatomical position of the scapula on the rib cage in relation to thoracic spinous processes. |
|
Definition
| Usually between T2 and T7 |
|
|
Term
| Describe the supracristal plane. |
|
Definition
| If you place your hands on your waist at the superior aspect of the iliac crest (i.e. supracristal plane) you are at the approximate level of the interspace between L4 and L5 |
|
|
Term
| Are sensory cutaneous superficial fibers from dorsla or ventral rami? |
|
Definition
| it has to be ventral because the dorsals only go to the deep muscles of the back! |
|
|
Term
| Define dermatome and myotome |
|
Definition
Each somite block differentiates into a sclerotome, myotome, and dermatome. The myotome differentiates into primitive skeletal muscle cells (myoblasts). These myotome cells separate and migrate toward the dorsal or ventral embryonic surfaces to form:
•Epimere (epaxial) – intrinsic (deep) back muscles
•Hypomere (hypaxial) – anterolateral muscles of trunk
forming outer, intermediate and inner muscular layers. The DERMATOME forms mesenchyme
that develops into the dermis and subcutaneous tissue of the skin. |
|
|
Term
| Why is the dermatome pattern easier to visualize in the trunk vs the upper limbs? |
|
Definition
| The dorsal and ventral rami of thoracic spinal nerves maintain their segmental distribution as they supply the ventral and dorsal surfaces of the trunk because they are close to their origin. This is not the case for limbs. Dermatome patterns in the limbs become increasingly variable as one moves further from the axis of the trunk |
|
|
Term
| Name the areas within the upper limb which are used clinically to assess spinal nerve integrity via dermatomes. Aka, areas of skin with no overlap between adjacent spinal segments. |
|
Definition
C3 – base of neck like a “collar”
C4 – over the shoulder like a “shawl”
C5 – anterolateral arm just lateral to
deltopectoral groove
C6 – lateral side of the thumb
C7 – middle finger
C8 – medial side of little finger
T1 – distal medial arm
T2 – axilla |
|
|
Term
| Describe the difference between extrinsic and intrinsic back muscles. Which group is innervated by dorsal rami? |
|
Definition
Muscles of the deep back are called intrinsic muscles because their embryonic origin is in the back. They are innervated by dorsal rami of spinal nerves. Muscles in the superficial and intermediate group are called extrinsic muscles because of their embryonic origin.
They are innervated by ventral rami of spinal nerves |
|
|
Term
| What are the attachments for the splenius capitis and splenius cervicis? Actions? |
|
Definition
| Splenius capitis: Lower ½ lig. nuchae; Spinous processes C7-T4; Lateral 1/3 superior nuchal line; mastoid process; Bilaterally extend head; unilaterally laterally flex and rotate head to same side splenius cervicis: Spinous processes T3-T6; Transverse processes C1-C3;Bilaterally extend neck; unilaterally laterally flex and rotate neck to same side. |
|
|
Term
| Describe the thoracolumbar fascia. |
|
Definition
Thoracolumbar fascia provides a medial attachment for the latissimus dorsi and the serratus posterior inferior. In the lumbar region, the thoracolumbar fascia extends as three layers to invest
the muscles of the deep back and one muscle of the posterior abdominal wall. It attaches medially to spinous and transverse processes and laterally to the ribs (thoracic region) and the iliac crest |
|
|
Term
| Name the three bands of the erector spinae, and in general, what are their attachments and actions? |
|
Definition
| spinalis (interconnect the spinous processes of adjacent vertebrae), longissimus (iliac crest to mastoid process), illiocostalis (iliac crest to angles of ribs 6-12). All tend to bilaterally extend spine/head; unilaterally laterally flex and rotate spine/head to same side |
|
|
Term
| Describe in general the formation of the three germ layers. |
|
Definition
| Cells of the blastocyst that will become the embryo differentiate into a bilaminar disc consisting of an: outer epiblast and inner hypoblast. During gastrulation (week 3), a primitive streak appears in the caudal midline of the epiblast. Cells of the epiblast invaginate into the streak to form a third layer between the epiblast and hypoblast, the embryonic mesoderm. |
|
|
Term
| the epithelium of the skin is derived from which germ layer? The lining of the digestive tract is derived from which germ layer? |
|
Definition
| epithelium is from ectoderm, the digestive tract is from endoderm. |
|
|
Term
| the dermis of the skin is derived from which germ layer? |
|
Definition
|
|
Term
| the tissues that make up the musculoskeletal system is derived from which germ layer? |
|
Definition
|
|
Term
| The CNS/PNS is derived from which layer? |
|
Definition
|
|
Term
| The cardiovascular system is derived from which layer? |
|
Definition
|
|
Term
| what is the notochord and how is it formed? |
|
Definition
A primitive node lies on the cranial end of the primitive streak. Cells arising from the primitive node invaginate between the ectoderm and endoderm to form a narrow rod of cells. This
primitive rod or notochord forms the axis of the embryo around which the axial skeleton develops |
|
|
Term
| describe the formation of the neural tube and neural crest cells from the ectoderm? What do these structures form in the embryo? |
|
Definition
Ectoderm is induced by cells within the notochord to form a thickened plate. This neural plate invaginates to form the neural tube (precursor to CNS). Neural crest cells pinch off during this
process and migrate laterally to later form: spinal (DRG), cranial and sympathetic ganglia associated with the PNS |
|
|
Term
| name the three paired structures derived from mesoderm which lie adjacent to the neural tube? |
|
Definition
Mesoderm differentiates into three paired
regions on either side of the neural tube:
1. Paraxial mesoderm forms somites.
2. Intermediate mesoderm contributes
to the urogenital system.
3. Lateral plate mesoderm |
|
|
Term
| understand in general the development of the body cavity? How does lateral plate parietal and visceral mesoderm contribute? Draw this out. |
|
Definition
Lateral plate mesoderm further divides into:
a. Parietal (somatic) mesoderm combines with surface ectoderm to form the lateral and
ventral body wall. Parietal mesoderm also forms CT of muscle/viscera.
b. Visceral (splanchnic) mesoderm combines with endoderm to form the walls of the gut,
vessels and heart. Visceral mesoderm also forms most smooth and cardiac muscle.
c. A primitive body cavity (coelom) forms between the parietal and visceral mesoderm |
|
|
Term
| what is a somite? Describe in general the migration of sclerotome, myotome and dermatome cells into the trunk and what structures they form. Make sure you understand the difference between the terms epaxial and hyaxial |
|
Definition
| Somites are paired blocks of paraxial mesoderm that form on either side of the neural tube. Sclerotome forms vertebral column and ribs. Myotome forms primitive skeletal muscles. Dermatome forms dermis and subcutaneous tissue of the skin. |
|
|
Term
| define sclerotome, myotome, and dermatome in regards to a single spinal segment. What is a dermatome map? |
|
Definition
Sclerotome = portion of bone and joints
supplied by a single spinal segment.
Myotome = group of skeletal muscles
supplied by a single spinal segment.
Dermatome = cutaneous area of skin
supplied by a single spinal segment. |
|
|
Term
| the limb buds are outgrowths of the body wall. Describe in general how cells from the lateral plate (somatic mesoderm) form the limb bud. What structures of the limb do they form. |
|
Definition
Each primitive limb bud consists of a mass of mesenchyme derived from the lateral plate of somatic mesoderm covered by a layer of epithelium derived from ectoderm. These lateral plate mesenchymal cells will undergo endochondral ossification: mesenchymal cells → chondroblasts → hyaline cartilage model → bone. (Exception within limbs: clavicle) 2. Limb buds begin as flat paddles projecting from the body wall. The paddles have defined ventral and dorsal surfaces as well as cranial (preaxial) and caudal (postaxial) borders. The thumb/big toe lie on the cranial border and the pinky/little toe on the caudal border. 3. Skeletal muscle cells derived from the somatic hypomere migrate into the limb buds. Epiblast → mesoderm → paraxial mesoderm → somites → myotome → hypomere. Somitic dermatome cells which form the dermis and subcutaneous tissues of the skin similarly migrate. 4. Remember each somite has a close relationship with a single spinal nerve. Ventral rami migrate into the mesenchyme of the developing limb buds around week 5 allowing each spinal segment to innervate structures associated with their corresponding somite. 5. Deep fascia within the limb buds contain and separate the developing muscles into well-defined groups or compartments. Each limb muscle will receive innervation from multiple spinal segments and will retain this relationship no matter how far it migrates from its original somatic segment. Muscles that lie on the ventral surface of the embryo become flexors; those on the dorsal surface of the embryo, extensors |
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|
