Download Axial Skeleton

Lab 5, BIO 105
Axial Skeleton
• Consists of 80 bones
• Forms longitudinal axis of body
• Three major regions
– Skull
– Vertebral column
– Thoracic cage
• Supports head, neck and trunk
• Protects brain, spinal cord, and thoracic
organs
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The Skull
Cranial bones
• Enclose the brain in the cranial cavity
• Provide sites of attachment for head and neck
muscles
2. Facial bones
• Framework of face and the sense organs
• Openings for air and food passage
• Sites of attachment for teeth and muscles of
facial expression
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Temporal Bones
• Major markings: zygomatic process, mandibular
fossa external auditory (or acoustic) meatus,
mastoid process, mastoid sinus, styloid process
Occipital Bone
Most of skull’s posterior wall and base
Articulates with 1st vertebra
Sites of attachment for the ligaments which attach the
neck to the skull and the neck and back muscles
Major markings: foramen magnum, occipital condyles,
external occipital protuberance and crest
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Figure 7.8
Zygomatic Bones:
Cheekbones and lateral and inferior margins of
orbits
Ethmoid Bone• Deepest skull bone; lies between the sphenoid and
nasal bones
• Forms most of the bony area between the nasal
cavity and the orbits
• Contributes to medial wall of orbits
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Sphenoid Bone--Butterfly or bat-shaped bone that
spreads across the middle of the skull
• Articulates with all other cranial bones-holds other
bones of the skull together
• Made up of the following areas:
– Body
--Lesser wings
– Greater wings
--Pterygoid processes
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Sutural or Wormian Bones
Tiny irregularly shaped bones that appear within
sutures
Irregular shape due to different ossification rates of the
flat, skull bones
Maxilla Bones
• Medially fused to form upper jaw and central portion
of facial bones
• Keystone bonearticulates with all other facial
bones except mandible
• Major markings: palantine process, alveoli,
infraorbital fissure, maxillary sinus
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Sinuses: Mucosa-lined, air-filled spaces found in frontal,
sphenoid, ethmoid, and maxillary bones
Air enters from the nasal cavity and mucus drains into the
nasal cavity from the sinuses
Lighten the skull , Enhance resonance of voice
• Nasal bones —thin, medially fused bones that
form bridge of nose
• Lacrimal bones —contribute to the medial
walls of orbits and has a deep groove called
the lacrimal fossa that houses the lacrimal sac
• Vomer--plow shaped bone that forms part of
nasal septum
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Mandible or lower jaw
• Largest, strongest bone of face
• Temporomandibular joint: only freely movable joint
in skull
• Major markings: coronoid process, mandibular
condyle (also called condyloid process), body, mental
foramina (nerves for tooth sensation travel through
these), ramus, and alveoli
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Nasal Cavity
• Constructed of bone and hyaline cartilage
• Roof formed by ethmoid
• Lateral walls formed by part of ethmoid and palantine bones, and inferior
nasal conchae
• Floor formed by palantine process of the maxilla and palantine bone
Orbits
• Bony cavities in which eyes are enclosed (and cushioned by adipose tissue)
and also contains the lacrimal glands
• Sites of attachment for eye muscles
• Formed by parts of seven bones: frontal, sphenoid, zygomatic, maxilla,
palantine, lacrimal and ethmoid
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Hyoid Bone: Not actually bone of the skull; lies inferior to the
mandible in the anterior neck
• Only bone in the body that does not articulate directly with
another bone;
• Is a movable base for the tongue, attachment point for the
muscles of swallowing and speech which raise and lower the
larynx while swallowing and talking
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Vertebral Column
• Flexible, curved structure containing 26 irregular
bones (vertebrae)
• Transmits weight of trunk to lower limbs
• Surrounds and protects spinal cord
• Vertebrae get larger (moving from cervical to lumbar)
because they have to support more weight
– Cervical vertebrae (7)—vertebrae of the neck
– Thoracic vertebrae (12)—vertebrae of thoracic
cavity
– Lumbar vertebrae (5)—vertebra of lower back
– Sacrum—bone inferior to lumbar vertebrae and
articulates with hip bones
– Coccyx—end of vertebral column
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Curves of the Vertebral Column
• Increase resilience and flexibility of spine
• Allow us to stay in upright position
• Shock absorber—prevents lower extremity shock from
easily reaching brain
– Cervical and lumbar areas are concave curves
(posteriorly)
• Thoracic and sacral areas are convex curves
(posteriorly)
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Intervertebral Discs
•
Cushionlike pad composed of two parts
1. Nucleus pulposus
• Inner gelatinous nucleus that gives disc
elasticity and compressibility
2. Anulus fibrosus
• Surrounds nucleus pulposus; composed of
collagen and fibrocartilage
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General Structure of Vertebrae
• Body or centrum: anterior weight-bearing region
• Vertebral arch: posterior: composed of pedicles and
laminae that, along with centrum, enclose vertebral
foramen
• Vertebral foramina: compose vertebral canal
through which spinal cord runs
• Pedicles (little feet):project posteriorly from
vertebral body, form sides of arch
• Laminae: flat plates, complete arch posteriorly
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• Spinous process —projects posteriorly
• Transverse processes —project laterally
• Both of these are attachment sites for muscles
and ligaments that move and stabilize vertebrae
• Superior articular processes —protrude superiorly
• Inferior articular processes —protrude inferiorly
• Intervertebral foramina
– Lateral openings formed by notched areas on
superior and inferior borders of adjacent
vertebrae for spinal nerves
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Cervical Vertebrae
• C1 to C7: smallest, lightest vertebrae
• C3 to C7 have an oval body, short spinous processes
which are often bifurcated, and large, triangular
shaped vertebral foramen
• C1 (atlas) and C2 (axis) have unique features
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Atlas (C1)---No body or spinous process (doesn’t
need a body because it supports the weight of
the head vs the entire body)
• “Yes” vertebra
• Superior surfaces of lateral masses articulate with
the occipital condyles
• c1 and c2 are differ from the rest of the
vertebrae in that there is no intervertebral
disc between them
Axis (C2)---Dens (a pivot area for the rotation of the
atlas) projects superiorly into the anterior arch of
the atlas; “No” bone
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• Thoracic Vertebrae--T1 to T12.
**All
articulate with ribs
• **Location of articular facets prevent flexion and
extension but allow rotation of this area of spine;
have facets for articulation with head of ribs
• **Have long spinous process, a heart shaped body,
circular vertebral foramen
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Lumbar Vertebrae: L1 to L5, located in the small
of the back
• Flat hatchet-shaped spinous processes
• Orientation of articular facets locks lumbar
vertebrae together to prevent rotation and
provide added stability; Body is thick and
massive to support the weight of the body
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Sacrum
– 5 fused vertebrae (S1–S5) which make the
posterior wall of pelvis
– Articulates with L5 superiorly, and with auricular
surfaces of the hip bones laterally
– Markings: Sacral foramina, sacral canal
Coccyx
– Tailbone
– 3–5 fused vertebrae
– Articulates superiorly with sacrum
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Thoracic or Rib Cage
• Composed of thoracic vertebrae, sternum, ribs and
costal cartilage (cartilage which attach ribs to sternum)
• Functions
– Forms protective cage around heart, lungs, and great
blood vessels
– Supports shoulder girdle and upper limbs
– Provides attachment sites for many neck, back, chest
and shoulder muscles
– Intercostal muscles used during breathing lift and
lower the thorax
– some flexibility in rib cage due to cartilage so we can
breathe
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Ribs and Their Attachments
• 12 pairs make up the sides of the thoracic cavity
• All attach posteriorly to body and transverse
processes of the thoracic vertebrae
• Pairs 1 through 7
– True ribs because attach directly to sternum by costal
cartilages
• Pairs 8 through12 : False ribs—
– Pairs 8–10; attach indirectly to sternum by joining
costal cartilage of rib above
– Pairs 11–12--floating ribs; no attachment to sternum
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Developmental Aspects: Fetal Skull
• Infant skull has more bones than adult skull because skull
bones are unfused and are connected by fontanelles
– Fontanelles: Unossified remnants of fibrous
membranes between fetal skull bones
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LABWORK
1. Identify and describe the bones and bone markings
listed in the handout.
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