The musculoskeletal system: Axial Flashcards
What is the musculoskeletal system? Origin?
- bones and muscles that move body around
- mesodermal origin
What is the axial skeleton composed of?
vertebrae; sternum/ribs; skull
Functions of the axial skeleton?
- protection of CNS (spinal chord/brain) and viscera (thoracic and abdominal)
- breathing movements (ribs and sternum)
- support and movement
Name + number vertebrae in humans
- 7 cervical (neck)
- 12 thoracic
- 5 lumbar
- 5 sacral (large, fused into single mass, support weight/pelvis)
- 3-5 coccygeal (tail - tiny, fused)
What is the atlas joint?
- atlas = C1 (has transverse ligament)
- axis = C2 (has dens = odontoid process)
- flexion-extension + pivot joint
Why is the lumbar spine vulnerable?
-lies between wide thorax and wide pelvis
-heavily loaded
(region that often collapses in elderly due to osteoporosis)
What is osteoporosis?
- eating away of bone in spine
- bone lost faster than can be repaired
- sponge-like vertebrae = collapse of spine (particularly in elderly)
What is the most variable part of the vertebral column? What is its function?
- the coccyx = what’s left of the tail
- pelvic floor muscles attach to coccyx (important for strengthening after childbirth)
What are the axial muscles? What movements do they allow?
-epaxial muscles
-deep back muscles (dorsal to ribs/vertebrae)
-extend spine
-hypaxial muscles
-intercostal + abdominal wall muscles (ventral to
ribs/vertebrae)
-flex spine
What is the difference between vertebrates and invertebrates?
-invertebrates: lack vertebral column
(insects, jellyfish, flatworms, starfish…)
-vertebrates: animals with vertebrae
Describe earliest vertebrate ancestors + their evolution
-earliest vertebrate ancestors had no vertebrae
-body stiffened by flexible mesodermal rod - notochord
(lies immediately below nerve cord)
-nerve chord and notochord then became enclosed in vertebrae = stronger, allow more complex muscles + movements
How does vertebral formation occur?
sclerotome from somites
-forms vertebral (neural arches)
-forms vertebral body (notochord in middle)
(=around neural tube)
What are intervertebral discs?
- in between vertebral bodies
- contribution from sclerotome + notochord
- tough fibrous outer ring
- soft central nucleus pulposus = remnant of notochord
What is a disc herniation?
- outer fiber can tear = part of nucleus pulposus comes out; pushes against spinal nerves-“slipped disc”
- often in lumbar region (vulnerable)
How does resegmentation keep muscle-verterba relationships?
- each vertebra formed by portions of 2 adjacent somites
- means that vertebra joined up by muscle (myotome from 1 somite attached to 2 parts of dif. vertebrae it will form)
What is metameric segmentation?
- repetition of segments
- found in invertebrates: worms, centipedes (each segment has same structure)
- also obvious in long-bodied vertebrates: snakes
Give signs of segmentation in human development
- somites
- muscle blocks (myotome) innervated by segmentally arranged spinal nerves
- dermatomes - segmental sensory pattern to the skin (each dermatome receives sensory nerve supply from 1 segmental spinal nerve)
-most obvious in thorax: intercostal muscles of chest, segmental pattern of blood vessels, of nerves to muscle and skin, ribs/vertebrae and sternum
What is vertebral regionalisation?
-Bony fish:
similar vertebrae, undifferentiated muscle flex body
-Early tetrapod to primitive amniote
-vertebral regionalisation: muscles differentiate for
simple limb movements (move onto land, need
support)
- Therapsid
- distinct neck = head mobility
- muscles differentiate for limbs/breathing mvts
- loss of ribs = lumbar region
(throughout process: more differentiation in vertebral column = more dif types of vertebrae)
What variation is there in the cervical + lumbar region in mammals?
-all mammals have 7 cervical vertebrae, but in dif sizes (ex: giraffes)
(=evolutionary constraint, while reptiles and bird show great variation)
-differences in length of lumbar region in mammals
=different locomotor strategies
(ex: giraffes: few lumbar vertebrae
but cats: longer lumbar region: flexibility, speed, agility)
What bones do somites give rise to?
-occipital bone + vertebrae
When does specification of segmental identity take place?
-identity (cervical or thoracic or lumbar…) determined before somite formation
-transplanting “thoracic” presomitic paraxial mesoderm into “cervical” mesoderm
=vertebrae with ribs in cervical region
=transplant does not change cell fate
What is homeosis?
- anatomical change where one segment/body part replaced by another
- William Bateson FRS - observed in insects
What are homeotic mutations?
-homeotic mutations
=mutations caused by homeosis
-Calvin Bridges
-2 recessive mutations:
bithorax (bx)=anterior haltere into wing
bithoraxoid (bxd)=posterior haltere into posterior
wing
What are antennapedia mutations in drosophila?
- transformation of antennae (sex organs) into legs (normally expressed in thorax)
- gain of function mutation
How many homeotic genes and complexes in drosophila melanogaster?
Drosophila -8 homeotic genes -found close to each other on Xsome B -in 2 complexes: antennapedia complex (5) + bithorax complex (3)
How many homeotic genes and complexes in tribolium (flower beetle)?
Tribolium (flower beetle):
- 9 homeotic genes
- only 1 complex (typical in insects)
