Download BIOL 4260 Human Evolu.onary Anatomy Lecture 5: Bone

BIOL  4260   Human  Evolu3onary  Anatomy   Lecture  5:  Bone  Development  &  Trunk  Anatomy  

Lecture 2: Fossil Record

Segmentation

•  Cyclic genescreate segme ntation clock for somite production Final #s

4 occipital 8 cervical 12 thoracic 5 lumbar 5 sacral 4 coccygeal

Paraxial mesoderm somite dermomyotome and sclerotome

Fate of the dermomyotome: dermatome - dermis myotome - muscles

Dermatome Map: Cutaneous innervation of skin follows developmental patterning

Myotome Fate

Epaxial and hypaxial muscles

Limb Buds

@ 4 weeks, C4-T1/2 @ 5 weeks, L1/2 -S3

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

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)

BONES

Bone Markings

Q.  Why  would  a  bone  have  trochanter,  tuberosi3es,  etc.    

Microscopic Structure of Compact Bones

Spongy  bone  possess  lamellae  

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  

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  

Fetal Intramembranous and Endochondral Ossification

10 week old human fetus

16 week old human fetus

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    

Intramembranous (Dermal) Ossification

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

Stages in Endochondral Ossification

Fracture Repair

Organization of Cartilage within Epiphyseal Plate of Growing Long Bone

Epiphyseal Plates and Lines

Juvenile

Adult

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    

Appositional Bone Growth - increases diameter of bone

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        

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    

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

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

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

The Vertebral Column regions and Normal curvatures

Vertebral  column  is  divided  into   five  major  regions  

Four  dis1nct  curvatures  give   vertebral  column  an  S-­‐shape  

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

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  

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  

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

General Structure of Vertebrae

PLAY  

Spine  (horizontal)  

Cervical Vertebrae •  Seven cervical vertebrae (C1 – C7) – smallest and lightest vertebrae •  Atlas has no body or spinous process •  Axis has unique odontoid process •  C3 – C7 are typical cervical vertebrae •  •  •  •  • 

Body  is  wider  laterally,  but  small   Spinous  processes  are  short  and  bifid  (except  C7)   Vertebral  foramina  are  large  and  triangular   Transverse  processes  contain  transverse  foramina   Superior  ar3cular  facets  face  superoposteriorly  

Cervical Vertebrae

Cervical Vertebrae

The Atlas •  C1 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”    

The Atlas