Axial skeleton Flashcards
What is the axial skeleton?
the portion of the skeletal system that is on the longitudinal axis of the body (runs down the center of gravity)
What are the 6 major components of the axial skeleton?
skull
notochord
hyoid (hyobranchial) apparatus
ribs
sternum
vertebral column
What are the major functions of the axial skeleton?
act as a framework to support and protect organs
provide a surface for muscle attachments including:
- neck, head, trunk
- respiration
- appendicular skeleton
involved in body movement (works with appendicular skeleton and muscles)
Joints of the axial skeleton are heavily reinforced with what to allow for restricted movement?
ligaments
T or F: axial bones are weak
false, they are very strong
what is the function of the notochord?
provided early vertebrates with non-bony support to allow swimming via lateral movement of spine
Describe the notochord
made of vacuolated cells covered by a fibrous and thick sheath
rigid, but also laterally flexible
Where is the notochord located within the body plan?
ventral and parallel to the dorsal hollow nerve cord
In what life stages is the notochord present?
larval urochordates: present in tail
cephalochordates and vertebrates: present in body and tail
embryo of all vertebrates but may be very reduced in adult
In vertebrates which lose or reduce the notochord in adulthood, what replaces it?
the vertebral column
What is the hyoid/hyobranchial apparatus?
group of visceral arches supporting the tongue and larynx in tetrapods
What are the functions of ribs and sternum in tetrapods?
protect the lungs and heart
Are ribs flexible or rigid? why?
flexible, in order to allow the lungs to expand for breathing
Describe the structure of ribs
thin
flexible
light
but strong enough to have chest muscles attached
Why must the ribs be thin and light?
in order to be flexible to allow lung expansion
What muscles attach to the ribs?
chest muslces
what do the chest muscles do?
support upper body and forelimbs
What do most of the ribs attach to at their medial (middle) ends?
the sternum via bridges of flexible cartilage
How is the sternum modified in amphibians?
except for frogs, the sternum is made of cartilage
frogs have cartilage and bone
it is attached to the pectoral girdle only - not to any ribs
What is the sternum attached to in amphibians?
the pectoral girdle, not ribs
How is the sternum modified in reptiles such as alligators and lizards?
sternum is cartilaginous
attached to ribs
What is the sternum attached to in alligators and lizards?
ribs
How is the sternum modified in reptiles such as snakes and turtles?
it is absent in both, but replaced by plastron in turtles
How is the sternum modified in flying birds?
one large body element articulating with the ribs
contains a strong central keel where flight muscles attach
what is the sternum attached to in flying birds?
multiple ribs and flight muscles
How is the sternum modified in mammals? what is it attached to?
it is composed of multiple bones
attached to ribs via costal cartilages
What are the individual units of the vertebral column?
vertebra
What are the basic units of an individual vertebra?
vertebral/neural arch
hemal arch
neural spine
centrum
transverse process
zygapophysis
intervertebral disks
What are the 5 regions of the vertebral column?
cervical (atlas and axis)
thoracic
lumbar
sacral
caudal
Where are the cervical vertebrae?
neck vertebrae (absent in fish), directly under the skull
atlas: the first cervical vertebra in terrestrial vertebrates
axis: the second cervical vertebra of mammals
What is the function of the atlas vertebra?
articulates with the skull and allows nodding movements of the head
What is the function of the axis vertebra?
allows rotation of the head
Which vertebrates lack the cervical vertebrae?
fish (think about how fish do not have a distinct head that can be moved around up and down and rotated)
which order, from the skull, do the cervical vertebrae arise? (if present)
atlas is the first vertebra - articulates with the skull
axis is the second vertebra
Where are the thoracic vertebrae?
in the chest region
these articulate with the ribs
What do the thoracic vertebrae articulate with?
the ribs
where are the lumbar vertebrae found?
the lower back
Where are the sacral vertebrae found?>
lower than the lower lumbar vertebrae
What is unique about the sacral vertebrae?
they are fused = called the sacrum
How many sacral vertebrae are fused in dogs and cats to create the sacrum? how about humans?
dogs and cats have 3 fused vertebrae making up the sacrum
humans have 5
Where are the caudal vertebrae?
the tail vertebrae
In birds, what forms the attachment for tail feathers to the caudal vertebrae?
the pygostyle
How many vertebral regions do fish have? what are they?
2
trunk and caudal
How many vertebral regions do amphibians have? what are they?
4
cervical, trunk, sacral, caudal
except anurans (tailless), which lack the caudal
Compare the vertebral regions of frogs and salamanders
both have cervical, trunk and sacral vertebrae regions
frogs do not have caudal
How many vertebral regions do non-bird reptiles have? what are they?
5
cervical, thoracic, lumbar, sacral, caudal
How many vertebral regions do birds have? what are they?
5
cervical, thoracic, lumbar, sacral, caudal
How many vertebral regions do mammals have? what are they?
5
cervical, thoracic, lumbar, sacral, caudal (or coccyx in mammals without tails)
Which vertebrate group(s) have trunk vertebrae?
fish and amphibians
Which vertebrate group is the only one that lacks cervical vertebrae?
fish
What are the major functions of the vertebral column?
enclose and protect spinal cord
structural support
allows for movement of head
points of attachment for ribs and muscles
Similarities and differences between axial skeleton of fish and amphibians?
similarities:
- both have trunk and caudal (anurans do not though) vertebrae
differences:
fish only have 2 vertebral regions (trunk and caudal)
amphibians have 3-4 (cervical, trunk, sacral, and some have caudal)
Differences between axial skeleton of fish and reptiles?
similarities:
- both have caudal vertebrae
differences:
fish have 2 vertebral regions (trunk, caudal)
reptiles have 5 vertebral regions (cervical, thoracic, lumbar, sacral, caudal)
fish do not have neck vertebrae
reptiles have more diversity in their axial skeleton
Differences between axial skeleton of fish and birds?
birds have 5 vertebral regions, fish have 2
birds have a lot of fused vertebrae = rigid vertebral column, fish have much more flexible vertebral column for lateral movement
Differences between axial skeleton of fish and mammals?
mammals have 5 vertebral regions, fish have 2
Differences between axial skeleton of amphibians and non-bird reptiles?
amphibians have 4 vertebral columns, reptiles have 5
both have: cervical, sacral, and caudal
amphibians also have trunk
reptiles lack trunk, but also have lumbar and thoracic
Differences between axial skeleton of amphibians and birds?
amphibians have 4 vertebral columns, birds have 5
both have: cervical, sacral, and caudal
amphibians also have trunk
birds lack trunk, but also have lumbar and thoracic
birds also have pygostyle in caudal region
Differences between axial skeleton of amphibians and mammals?
amphibians have 4 vertebral columns, mammals have 5
both have: cervical, sacral, and caudal
amphibians also have trunk
mammals lack trunk, but also have lumbar and thoracic
mammals have a fused sacrum
Differences between axial skeleton of non-bird reptiles and birds?
they have the same 5 regions (cervical, thoracic, lumbar, sacral, caudal)
birds have pygostyles to attach tail feathers to caudal vertebrae, whereas nonbird reptiles do not
birds have very rigid vertebral column, many vertebrae are fused
Differences between axial skeleton of non-bird reptiles and mammals?
reptiles do not have spinal curves
mammals have thoracic and sacral curves during fetal development
after birth, mammals have lumbar and cervical curves (these allow for upright positions)
Differences between axial skeleton of birds and mammals?
birds have 5 thoracic vertebrae, 4 of which are fused
all thoracic vertebrae in mammals are attached to a pair of ribs
What allows the upright position in mammals?
the appearance of secondary curves (lumbar and cervical curves) after birth allows the shift of body weight
What are the primary spinal curves in mammals?
thoracic and sacral because they are present during fetal development and accommodate internal organs
What is the function of primary spinal curves in mammals?
to support and protect the internal organs during fetal development
thoracic and sacral
what is the function of secondary spinal curves in mammals?
to compensate for shifting body weight to allow for an upright posture
cervical and lumbar
