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Lecture 5

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Biological Sciences
Connie Potroff

1 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 NEURAL TUBE - 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 ligaments o Bones 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: Skull Vertebral column Thoracic cage Functions of the axial skeleton: © 2012 Pearson Education, Inc. 2 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 o Sphenoid bone – (1) butterfly shaped, keystone of skull, unites cranial and facial bones and base of cranium o Ethmoid 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 sou
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