Quiz 1 - Winter Quarter Flashcards
Rise of fore/hind limbs
cells of ectoderm, cells derived from dermatome, and hypaxial portion of the myotome mix with somatic component of lateral plate mesoderm
Mesenchyme core (undifferentiated tissue)
Lateral plate mesoderm: cartilage, bones, general CT
Paraxial mesoderm: somites, skeletal muscle
Ectoderm Cover (outer germ layer)
Out-pocketing of ventral body wall: Epidermis of skin, nails, hair
Spinal nerves that will form nervous plexuses
Hox genes determine…
…where limb buds will form & what limb will develop at a specific location
Early development of the limb goes from…
…The limb field to the limb bud
Limb bud
Promotion of outgrowth and patterning.
Originates as ridges in ventrolateral body wall
Limb field
Specific transcriptions factors act to induce an epithelium-to-mesenchyme transition that induces the formation of the limb bud
LImb bud axes
- Dorso-ventral
- Proximo-distal
- Cranial-caudal
Proximal-Distal Axis
the Apical Ectodermal Ridge (AER) directs pattern formation.
1. Terminal portion becomes flattened
2. Two constrictions divide the portion of each limb (stylopod, zeugopod, autopod)
Apical ectodermal ridge (AER)
thickened, specialized epithelium located at the dorsoventral border of the tip of the bud.
Has a feedback loop
Progress Zone (PZ)
the area of mesenchyme just proximal to the AER (encourages growth)
AER “grows” via a…
…feedback loop
Dorsal-Ventral Axis
Non-AER directs pattern formation.
Dorsal & Ventral aspects follow lateral folding of embryo.
Dorsal/Ventral signaling center resides…
…in the dorsal ectoderm
Zone of Polarizing Activity (ZPA)
Area of mesenchyme on caudal border.
Gives cranial-caudal identity to differentiating cells
ZPA cells express…?
Retinoic acid (RA) and sonic hedgehog (Shh)
ZPA (and Shh) requires input from…?
- Apical Ectodermal Ridge
- Dorsal Ectoderm
(they determine shape, proximal/distal, Cr/Ca; things like finger size)
Apoptosis
programed cell death
Accounts for lack of “webbing” between fingers
Necrosis
Traumatic cell death
Final limb morphology
Number of digits and limb segments
- AER breaks up and only covers the emerging digital rays
- Interdigital spaces no longer have AER and can now be sculpted by apoptosis
Homology
Existence of shared ancestry between a pair of structures, or genes, in different species
Pentadactyl limb
“ancestral” five digit condition
Horses–Post patterning changes
- Initial limb segments are all laid in cartilage (lay the pattern)
- Digits I & V are eliminated
- Digits II & IV reduction is the result of extensive apoptosis (splint bones)
Artiodactyls (Cattle & Swine) – Patterning changes
Digit loss and shift of central axis of foot between digits III & IV
Order of Digit Loss
Digit I
Digit V
Digit II
Digit IV
In some cases, bones fuse as well
Limb Rotation
- Forelimb rotates dorsally
- Hindlimb rotates ventrally
Shapes joint movement (stifle/elbow face opposite)
Shapes position of muscle compartments
Adduction
Toward the median plane
“ADD to the body”
Abduction
Away from median plane
“ABducting the limb”
Circumduction
Conical movement (combo of all other movements)
Inward rotation
Relative to long axis in toward the body
Outward rotation
Relative to long axis out away from the body
Flexion
movement that reduces the angle between bones
Extension
movement that increases angle between bones
Pronation
rotates forepaw caudally
“Pro” it on the floor
Supination
rotates forepaw cranially
“Soup”ination
Larger animals have…distal limb elements?
…Disproportionate…
They have relatively longer distal limb segments. They greatly elongate radius, ulna, tibia, metacarpal-tarsal elements, phalanges
Why extend distal limb elements out of proportion to proximal?
Moving distal elements, which have lower mass, requires much less force.
Additional muscle further from body requires greater torque and energy to move limbs
Elongating the limbs = energetic savings
Implications to extended distal limbs
Limb and joint disorders make up a substantial amount of equine medicine
Very long excursions of tendons distally
“Pulleys” for long tendons
Synovial sheaths and retinacula
These sheaths and flat tendons are locations of potential injury
Adaptations/Advantages of Elongated Tendons
Short muscles and especially elongated tendons provides elastic energy storage and savings
Limb and Back extensors…
…contract to maintain a standing quadrupedal posture
Smaller animals increase stride length via…
…vertebral column flexion/extension
Pelvic limbs are adapted for…
…propulsion. Accelerate the center of gravity forward and upward
Pelvic Limb Characteristics
- Longer and angular than thoracic limb
- Heavily muscled
- Connected directly to the vertebral column
Femur connects to acetabulum via:
Ligament of femoral head
Primary Abductors of the Hip
Superficial gluteal muscles (Lateral muscles of the pelvis)
- Primarily extend and abduct the hip
- Primarily innervated by Cranial gluteal n.
When one hindlimb is suspended (for urination, during stride etc.) the supporting limb hip abductors…
…contract to counteract adduction.
- Allows for balance
- Limb fixed distally so it moves the body trunk to restore balance
Primary Rotators of the Hip
Deep Gluteal Muscles
- primarily lateral rotators of the hip
- innervated by direct branches off lumbo- sacral trunk
Articularis coxae
Protects hip joint capsule from being nipped between the femoral and acetabular surfaces during movement
Primary Extensors of the Hip
Caudal Thigh Muscles
- Primarily extend hip (also stifle, hock)
- Innervated by sciatic n.
Caudofemoralis (felids only) =
Gluteofemoralis
- located proximally to the bicep femoris on the caudal aspect of the pelvic limb
Caudal crural abductor
Small muscle in carnivorans only
(Tenuissimus in cats)
Primary Adductors of the Hip
Medial Thigh Muscles
- Primary adduct hip
- Take origin from pelvis
- Primarily innervated by obturator nerve
Primary Flexors of the Hip
Sublumbar muscles
- innervated by direct branches of lumbrosacral plexus and femoral n.
Extensor muscles of the Stifle (Quad)
- group of 4 muscles
Lumbo-sacral plexus usually includes the ______ rami of ______?
Ventral; L4-S2
- There is an extra root in species with seven lumbar vertebrae
Femoral n. continues into the _____ and branches off of the _____?
Saphenous n.; L4-6
Obturator n. branches off…?
L4-6
Lumbosacral trunk comes from which ventral rami?
L6/7-S2
Lumbosacral trunk has 2 branches
- Cranial & Caudal Gluteal nn.
- Caudal cutaneous femoral n.
After branching, the lumbosacral trunk becomes…?
The Sciatic n.