BIOL 4260 Human Evolu3onary Anatomy Lecture 5: Bone Development & Trunk Anatomy. Lecture 2: Fossil Record

Transcription

1 BIOL 4260 Human Evolu3onary Anatomy Lecture 5: Bone Development & Trunk Anatomy Lecture 2: Fossil Record

2 Segmentation Cyclic genescreate segme ntation clock for somite production Final #s 4 occipital 8 cervical 12 thoracic 5 lumbar 5 sacral 4 coccygeal

3 Paraxial mesoderm somite dermomyotome and sclerotome

4 Fate of the dermomyotome: dermatome - dermis myotome - muscles

5 Dermatome Map: Cutaneous innervation of skin follows developmental patterning

6 Myotome Fate Epaxial and hypaxial muscles

7 Limb 4 weeks, 5 weeks, L1/2 -S3

8 Brains Cranial end of neural tube More on this in 2 months

9 Summary & KeyPoints Understand main stages of first few months of life Trace development of embryo during first week, second week, third week Understand gastrulation, neurulation, segmental body organization Trace fates of 3 germ layers & somites (more on this next week)

10 BONES

11 Bone Markings Q. Why would a bone have trochanter, tuberosi3es, etc.

12 Microscopic Structure of Compact Bones Spongy bone possess lamellae

13 Chemical Composition of Bone Bone consists of cells separated by an extracellular matrix 35% organic components Cells (osteoblast, osteoclasts, osteocytes) Osteoid - collagen fibers in ground substance composed of proteoglycans and glycoproteins Collagen abundant in the ground substance and provides tensile strength 65% inorganic mineral salts invade the bone matrix Primarily calcium phosphate Resists compression by making bone hard

14 Osteogenesis: Bone (osteo) formation (genesis) At six weeks of in-utero development, the skeleton is composed of cartilage tissue or mesenchymal tissue After six weeks bone begins to form by Mesenchymal cells will be replaced by bone cells Car3lage cells will be replaced by bone cells This process of replacing other 3ssues with bone is called ossifica1on Calcification The deposi3on of calcium ions into any 3ssue Though any 3ssue can be calcified, only ossifica3on results in bone forma3on

15 Fetal Intramembranous and Endochondral Ossification 10 week old human fetus 16 week old human fetus

16 Bone Development Ossification (osteogenesis) bone-tissue formation Intramembranous ossifica1on Membranous bones formed directly from (and within) mesenchyme. Mesenchyme is embryonic CT Bones of the roof of the skull (examples: frontal and parietal bones) and clavicles Begins about 8 weeks of fetal life Endochondral ossifica1on Bones develop from preexis1ng hyaline car1lage Involved in forma3on of all bones from base of the skull and many bones inferior to it such as limb bones, vertebrae, and hips

17 Intramembranous (Dermal) Ossification

18 Endochondral Ossification All bones except some bones of the skull and clavicles Bones are modeled in hyaline cartilage Begins forming late in the second month of embryonic development Continues forming until early adulthood

19 Stages in Endochondral Ossification

20 Fracture Repair

21 Organization of Cartilage within Epiphyseal Plate of Growing Long Bone

22 Epiphyseal Plates and Lines Juvenile Adult

23 Postnatal Growth of Endochondral Bones During childhood and adolescence Bones lengthen en3rely by growth of the epiphyseal plates Growing bones widen as they lengthen. Widening is achieved by addi3on of bone matrix by differen3a3on of the cells of the inner layer of periosteum into osteoblasts..this is called apposi1onal growth Most bones stop growing in early childhood

24 Appositional Bone Growth - increases diameter of bone

25 Bone Remodeling Bone is dynamic living tissue 500 mg of calcium may enter or leave the adult skeleton each day. Cancellous bone of the skeleton is replaced every 3 4 years Compact bone is replaced every 10 years Other real life examples: Realignment of teeth by orthodon3st Shrinking of bone following disuse Hardening of bone with exercise

26 Bone Remodeling Bone deposit and removal Occurs at periosteal and endosteal surfaces Bone remodeling Bone deposi1on accomplished by osteoblasts (blast=greek germinate) Bone reabsorp1on accomplished by osteoclasts (clast=greek to break). Summary: Bone remodeling is coordinated by a fine mix of osteoblast, osteocyte ac1vity Control: Indirectly via Calcium regula1on Directly arising from stresses

27 Vertebral Column Dual pillar system for weight bearing: anterior/ventral pillar (bodies) & posterior/dorsal pillar (arch) Monotonic increase in size of body

28 The Axial Skeleton 80 named bones Consists of: skull- 22 bones associated bones Hyoid+6 auditory bones vertebral column bony thorax Support for head, neck, trunk Protection

29 The Vertebral Column Formed from 26 bones in the adult Supports and transmits weight of head, neck and trunk to the appendicular skeleton of lower limbs Surrounds and protects the spinal cord Serves as attachment sites for the ribs and muscles of the neck and back Held in place by ligaments Anterior and posterior longitudinal ligaments Ligamentum flavum Others

30 The Vertebral Column regions and Normal curvatures Vertebral column is divided into five major regions Four dis1nct curvatures give vertebral column an S- shape

31 Normal Curvatures Four distinct curvatures give vertebral column an S-shape Primary: Thoracic and sacral curvatures Are convex posteriorly Secondary: Cervical and lumbar curvature Are concave posteriorly Curvatures increase the resilience of the spine Note: In fetus, only the primary curves present. Column therefore C shaped

32 Abnormal curvatures Abnormal spinal curvatures Scoliosis an abnormal lateral curvature Kyphosis an exaggerated thoracic curvature Lordosis an accentuated lumbar curvature swayback Stenosis of the lumbar spine A narrowing of the vertebral canal

33 Regions Vertebral Characteristics Specific regions of the spine perform specific functions Types of movement that occur between vertebrae Flexion and extension Lateral flexion Rota3on in the long axis

34 General features of vertebrae A. Centrum-aka body: weight bearing Separated by IV discs B. Pedicle paired: Encloses posteriolateral C. Lamina paired D. Spinous process E. Transverse process paired F. Neural arch b+c. Some people say A contributes to arch. Not entirely accurate G. Intervertebral disc H. Articular facets

35 General Structure of Vertebrae PLAY Spine (horizontal)

36 Cervical Vertebrae Seven cervical vertebrae (C 1 C 7 ) smallest and lightest vertebrae Atlas has no body or spinous process Axis has unique odontoid process C 3 C 7 are typical cervical vertebrae Body is wider laterally, but small Spinous processes are short and bifid (except C 7 ) Vertebral foramina are large and triangular Transverse processes contain transverse foramina Superior ar3cular facets face superoposteriorly

37 Cervical Vertebrae

38 Cervical Vertebrae

39 The Atlas C 1 is termed the atlas Lacks a body and spinous process Supports the skull Superior ar3cular facets are oval and receive the occipital condyles Inferior ar3cular facets are round Allows flexion and extension of neck Nodding the head yes

40 The Atlas