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Lecture 5

BIOB33H3 Lecture Notes - Lecture 5: Fot, Cervical Vertebrae, Lumbar Vertebrae

Biological Sciences
Course Code
Connie Potroff

of 4
Lecture 5
The Skeletal System: Axial & Appendicular Divisions
(based on chapters 6, 7 and 8)
NEURULATION - process of nervous system formation from ectoderm
Neurulation starts with signals sent out by NOTOCHORD:
Notochord – extends down the midline from the mesoderm
-short rod of condensed mesoderm cells right underneath PS, induces (process of induction) cells of
the ectoderm to form a hollow nervous system tube - neurulation
-*releases bone hormones and other hormones that act on cells in the ectoderm which stimulates the
area of the ectoderm above the notochord to become the CNS
-during third week ectoderm forms thickened layer called NEURAL PLATE (cells proliferate and
become columnar and taller)
-by the end of the third week lateral edges elevate to form NEURAL GROOVE
-the folds neural groove folds approach each other gradually in the middle and fuse to form the
- eventually the NEURAL TUBE runs the length of the embryo
note: Spinabifida is the failure of the tube to close, skin doesn’t grow over the neural tube and it is
exposed to the environment
**Mesoderm subdivides into:
1. notochord - basis for central body axis and axial skeleton, induction of neural tube
2. paraxial mesoderm - one both sides of neural tube forms SOMITES, block-like masses responsible
for formation of most bone, muscle, cartilage, dermis and connective tissues
3. intermediate mesoderm - forms most of urinary and reproductive systems
4. lateral plate mesoderm - cardiovascular system, lining of body cavities and all connective tissue
components of limbs
5. head mesenchyme - connective tissue and musculature of face
Endoderm - inner-most tissue after embryonic folding
-forms lining of digestive, respiratory and urinary tracts, thyroid gland, parathyroid gland, thymus, liver,
gallbladder and pancreas
Skeletal System: Introduction
The skeleton is divided into 2 portions: the axial skeleton and the appendicular skeleton
It is a rigid framework of 206 bones , muscles and organs are attached by tendons and
oBones act as levers (with joints acting as pivots) when muscles contract and move body
The Axial Skeleton: - composed of bones along the central axis of the body – 80 bones
Divided into three regions:
Vertebral column
Thoracic cage
Functions of the axial skeleton:
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Framework that supports and protects organs in the dorsal and ventral body cavities
Protects special sense organs for taste, smell, hearing, balance, and vision
Attachment sites for muscles that:
Adjust the posture of the head, neck, and trunk
Move the thoracic cage for respiration
Stabilize the appendicular skeleton
The Skull and Associated Bones
Cranial and Facial Subdivisions of the Skull
The skull consists of
Face: 14 individual bones
Cranium: 8 individual bones
Associated bones: 7 individual bones (auditory ossicles – 3 per ear and hyoid bone)
Cranial bones – form cranium, encase and protect brain (8 bones)
Frontal bone – (1) forehead, roof of orbits
Parietal bones – (2) either side of the top of head
Temporal bones - (2) temples on either side of the head, protect sense organs of ear,
extensive area for attachment of muscles that close the jaw and move the head
Occipital bone – (1) back of head, foramen (opening) magnum connects cranial
cavity with spinal cavity
oSphenoid bone – (1) butterfly shaped, keystone of skull, unites cranial and facial bones
and base of cranium
oEthmoid bone – (1) between obits/walls, floor of cranium, part of nasal cavity and nasal
septum, part of nasal conchae involved with movement of air through sinouses
Facial bones – form bone framework of oral cavity and jaw (14 bones)
Nasal bones - (2) base of nose, cartilage forms the flexible portion
Lacrimal bones – (2) (lacrima =tear), encloses tear duct and drains tears into
nasal cavity
Vomer - (1) means plowshare (looks like part of a plow from the front), inferior part of
nasal septum
Maxilla – (2) the largest of the facial bones, together form the upper jaw,
articulate with all other facial bones except mandible, oral margins form the
alveolar processes that contain the upper teeth
Mandible – (1) forms the entire lower jaw, teeth are supported by the mandibular body,
articulates with the temporal bone (tempomandibular joint) for jaw movements when
talking or eating, high mobility but makes it easy to dislocate the jaw
Zygomatic bones – (2) cheek bones
**Inferior Nasal Conchae (2) one on each side of nasal septum, along with the nasal conchae
of the ethmoid bone, they create turbulence in inhaled air (slows air movement and provides
additional time for warming, humidification and dust removal before air reaches more
delicate portions of the respiratory tract)
Palatine bones (2) form inferior portions of the hard palate, part of nasal cavity and
eye orbit
Associated Bones
Auditory ossicles – 6 bones in middle ear (ear bones), smallest bones in the body,
transmit sound impulses; 2 malleus, 2 incus, 2 stapes
Hyoid Bone only bone that d oes not articulate w i th any other bone , above the larynx
(voice box) below mandible (jawbone) supports the tongue, aids in swallowing
The Vertebral Column
The adult vertebral column is made up of 26 bones:
24 vertebrae
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7 cervical vertebrae – cervical curve
12 thoracic vertebrae – thoracic curve
5 lumbar vertebrae – lumbar curve
1 sacrum (5 fused vertebrae) – sacral curve
1 coccyx (3-5 fused vertebrae)
These curves, along with muscle attachment to the various vertebral processes, help to maintain
Functions of the vertebral column
Encloses and protects the spinal cord
Supports the skull
Supports the weight of the head, neck, and trunk
Transfers weight to the lower limbs
Helps maintain the upright position of the body
Curves of the spine act like a spring to absorb muscle shock (without snapping)
Vertebral Processes of a Typical Vertebra
Vertebral body
Vertebral foramen
Spinous process
Transverse process (superior articular and inferior articular)
Transverse foramen
Intervertebral Joints
Function in shock absorbance
Inferior articular facet articulates with superior articular facet and they come together
in facet joints
Between bodies of vertebrae are intervertebral discs
Nucleus pulposis –gel-like pad in center of intervertebral disc (mostly water)
oAnulus fibrosis – surrounds nucleus pulposis, fibrocartilage with collagen fibers attach
to the vertebrae
Spinal nerves run through vertebral foramen and intervertebral foramen where the
spinal nerves emerge as they branch off the spinal cord
The Thoracic Cage
The thoracic cage has two functions:
It protects the heart, lungs, thymus, and other structures within the cavity
It serves as the attachment site for muscles involved in:
Positioning the vertebral column
Movements of the pectoral girdle and upper limb
The Thoracic Cage
The Thoracic Cage
Sternum (3 bones)
Xiphoid process
Ribs (24 ribs, 12 per side)
True ribs: 17
False ribs: 812
Vertebral ribs (floating ribs): 1112 (no anterior cartilage)
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