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.
The sciatic nerve branches into the…?
- Common fibular (peroneal) n.
- Tibial n.
What does the cranial gluteal n. innervate?
- Tensor fasciae latae
- Gluteus medius
- Gluteus profundus
- Some species: contributes to gluteus superficialis
What does the caudal gluteal n. innervate?
- Gluteus superficialis
- Vertebral heads of origin of the hamstring muscles
What does the sciatic n. innervate?
- Deep gluteal mm.
- Caudal thigh mm.
What does the obturator n. innervate?
- Medial thigh mm (except sartorius)
- Obturator externus
What does the femoral n. innervate?
- Psoas major
- Sartorius (via saphenous)
- Quadriceps femoris
The femoral artery is a continuation of what artery?
The external iliac as it leaves the abdomen
What is the femoral triangle?
The blood vessels that make come together between the sartorius and pectineus. It creates a visible ridge for pulse taking
What are the branches of the femoral a.?
Deep femoral - goes caudally
Saphenous - branches caudally and then travels distally
What are the branches of the saphenous a.?
Cranial branch and the caudal branch of the saphenous a.
Branching happens caudally below the stifle
The popliteal a. comes from..?
The femoral a. as a continuation beginning around the popliteal muscle/lymph node/stifle.
What artery continues after the popliteal a.?
The cranial tibial a. continues down the leg and becomes the dorsal pedal a.
What arteries comes off the femoral a. to bring blood supply to the hip?
Medial circumflex a. comes off of the deep femoral.
Lateral circumflex femoral a. branches off the femoral.
The internal iliac a. is the parent for which arteries of the hip?
The caudal gluteal a. extends from the internal iliac and the cranial gluteal a. branches off the caudal.
3 joints of the stifle:
- Femoro-tibial joint
- Femoro-patellar joint
- Proximal tibio-fibular joint
What is the clinical relevance of all the stifle joints being contained in a single capsule?
Injection into any of the synovial compartments will therefore pass through to all joints of the stifle
What sesamoid bone grows within the tendon of the knee?
The patella
Extra stifle joint in dogs
Femoro-fabellar joint containg fabellae
What is the fabellae?
Sesamoid bone in proximal heads of gastrocnemius
Which muscle contains the connection between the tibia and sesamoid bone
Popliteus muscle
Name the 2 fibrocartilage discs within the stifle and describe their shape.
The medial meniscus and the lateral meniscus. they have semilunar shapes
What is the function of the menisci?
Stabilize the movement of the round femoral condyles on the flat tibial condyles
What is the purpose of the tendon of popliteus?
It pulls on the joint capsule
What is the purpose of the stifle ligaments?
They “de-limit movement”
they are more likely to be injured because of this
Describe the location/function of the patellar ligament (tendon).
It lays on the cranial aspect of the stifle distal to the patella
Describe the location/function of the medial collateral ligament.
On the medial aspect of the stifle connecting the femur and tibia.
Describe the location/function of the lateral collateral ligament.
On the lateral aspect of the stifle connecting the femur and the fibula.
Describe the location/function of the caudal cruciate ligament.
Prevents caudal slip of the tibia.
Criss crosses with the cranial cruciate.
Connects the caudal aspects of the femur and tibia.
Describe the location/function of the cranial cruciate ligament.
Prevents cranial slip of the tibia.
Criss crosses with the caudal cruciate.
Connects the caudal aspects of the femur and tibia
Describe the location/function of the meniscofemoral ligament.
Inserts on the caudal femur and tibia/fibula. It is one of several ligaments stabilizing the menisci.
What are the main movements of the stifle?
Flexion and Extension
Cats and dogs have some special mobility in the stifle. Describe them.
Translational: movement cranially - caudally
Rotation: along the long axis of the tibia
What happens when the stifle is flexed?
- Lateral collateral ligament loosens
- This allows internal rotation of the tibia and femur
- Cruciate ligaments “twist” on each other to limit the internal rotation (make it stronger)
What happens when the stifle is extended?
- Lateral collateral ligament tightens
- Tibia rotates externally
- Cruciate ligaments “untwist” and thus have no effect on limiting external rotation
What is a common ligament injury in dogs?
The CRANIAL cruciate ligament (more common)
- Usually from sudden rotation of the flexed stifle
- May be acute (sudden trauma) but more commonly chronic (degenerative changes)
How does the sartorius m. affect the stifle?
Cranial head- extends stifle
Caudal head - flexes stifle
Medial compartment
How does the gracilis m. affect the stifle?
Flexes stifle
medial compartment
How does the adductor/pectineus affect the stifle?
They don’t do much to move the stifle but are located on it.
Medial compartment
How does the biceps femoris affect the stifle?
Extends stifle; except caudal portion whcih flexes the stifle
Lateral compartment
How does the semitendinosis affect the stifle?
Flexes it
Lateral compartment
How does the semimembranosus affect the stifle?
Attachement to femur extends stifle
Attachement to tibia flexes or extends, depending on position of the limb
Lateral compartment
How does the quadriceps femoris affect the stifle?
Extends stifle. Has 4 parts
- Rectus femoris (comes down from hip)
- Vastus medialis
- Vastus lateralis
- Vastus intermedius
Cranial compartment
How does the iliopsoas affect the stifle?
Flex hip
cranial compartment
The quadriceps femoris inserts where?
Onto the tibial tuberosity via the patellar ligaments
The specialization of the horse stifle allows them to…?
Lock the stifle when the hindlimb is extended which allows the horse to save energy because the muscles don’t need to flex.
How is the horse able to “lock” their stifle?
The distal femur has an enlarged medial epicondylar ridge. This is palpable.
- Two surfaces of the trochlea: gliding and resting surface
Describe a horse’s patella?
- Diamond shaped
- Extends medially via patellar fibrocartilage
- Caudally facing surface of patella = larger; engages gliding surface of trochlea
- Distally directed surface = narrow; engages resting surface when in full extension
Name the 3 ligaments for the patella in horses.
Intermediate, Lateral, and Medial patellar ligs.
Stifle innervation
- Sciatic
- Obturatior
- Cranial and caudal gluteal nn.
- Femoral n. : originates L4-6 nn. and innervates Iliopsoas, sartorius, quad. femoris
Implications of femoral nerve lesions
Catastrophic!!
- Paralyzes the quads, resulting in collapse of stifle and disabling the entire limb.
- No compensation available
- Skin of medial surface of limb is deprived of sensation
3 tiers of the Hock and Tarsus
- Proximal tier
- Middle tier
- Distal tier
Bones in the Proximal tier
Talus/Astragalus lays medial
Calcaneus lays lateral (sticks out)
Middle tier bone and variations among species
Central tarsus bone
- Carnivora: about 1/2 width; slight curve proximally
- Equine: 3/4 of width; flat
- Bovine: fuses w/ tarsal 4
Distal tier bones and variations among species
Tarsals 1-4 #ed in mediolateral sequence.
4th bone is constantly present, deeper, and intrudes into middle tier
- Carnivora: all 4 seperate
- Equine: small 1 & 2 fused, wider 3
- Bovine: 2 & 3 fused, 4 fused with central
Talus/Astragalus characteristics
- Trochlea: proximal surface; articulates w/ tibia and fibula
- Head: distal articular surface; articulates w/ central tarsus
Calcaneus Characteristics
Located mostly lateral to talus
- Sustentaculum tali (talar shelf): supports plantar surface of talus and tendon of flexor digitalis superficailis
- Tuber calcanei: proximal end (heel); attachment for calcaneal tendon (achilles); free lever arm for movement at hock
- Head (distal end): articulates with fourth tarsal
Metatarsal Characteristics
- Longer (about 20%) than the metacarpals and more rounded
- MT I is rudimentary (dewclaw)
Phalanges characteristics
Proximal, intermediate, and distal bones
-Also have banana-shaped proximal/distal sesamoid bones
Base, body, head of MT and Ph
Base - proximal
Body - middle
Head - Distal
Horse talus characteristics
- Trochlea of talus conforms with cochlea of tibia providing free extension/flexion
- Fibula and tibia fuse distally to form cochlea
- Head is small and flattened providing greater stability
Talus in artiodactyls
The talar head expands to form a “double-pulley astragalus” where the talus articulates with central and fourth tarsal
Hock Joints
- Tarso-crural or Talo-crural
- Proximal intertarsal
- Distal intertarsal
- Tarsometatarsal
Movement of hock occurs at which joint?
Talocrural joint.
- Atypical hinge joint: helps pelvic limb be external to thoracic limb when they overlap during high-speed running
Medial/Lateral collateral ligaments of the hock characteristics
- Extend from tibia/fibula to base of metatarsus
- Help prevent lateral/medial movement
- Each has a long superficial part (full length) and shorter deeper part (restricted to proximal level of articulation
Long plantar ligament characteristics
- Caudal aspect
- Supports foot
- Extends from plantar surface of calcaneus, over 4th tarsal bone to MT
3 Synovial compartments of hock
A. Includes tarocrural and proximal intertarsal joints
- Laterodorsal, mediodorsal, medioplantar, lateral planter pouches (weaker parts where swelling may occur)
B. Distal intertarsal join
C. Tarsometatarsal joint
Caudal muscles of the leg
- Gastrocnemius
- Flexor digitorum superficialis: goes to digits
- Flexor digitorum profundus (Flx dig lateralis-goes to 1st digit, flx dig medialis, tibialis caudalis)
- Popliteus: very proximal
Craniolateral Muscles of the leg
- Tibialis cranialis
- Extensor digitorum longus
- Peroneus longus
- Peroneus brevis
- Peroneus tertius
**All 5 are never found simultaneously in any one of our species of study
Peroneus (fibularis) tertius
- Not present in carnivores
- Almost completely tendinous in Equine
- More fleshy in bovine
Innervation of the Leg and Tarsus
Sciatic Nerve splits into 2 in the thigh:
- Tibial nerve: enters between 2 heads of gastrocnemius. Can be seen between common calcaneal tendon and caudal crural muscles before splitting to innervate the pes
- Fibular nerve: enters lateral to gastrocnemius. Continues into the dorsum of the pes
Blood supply of the leg
Saphenous a branches into:
- Cranial branch of the saphenous a –> dorsal metatarsal aa.
- Caudal branch of the saphenous a. –> medial and lateral plantar and metatarsal aa.
Popliteal a branches into:
- Cranial tibial a.
- Dorsal pedal a.
Blood supply of the leg in horses
The saphenous a. loops and gives off branches:
- Medial/Lateral plantar & metatarsal aa.
- Medial/lateral digital aa.
Veins of the Leg
Deep veins accompany arteries and have same name.
*Superficial veins:
- Lateral saphenous v.: larger, on lateral aspect of leg; drains into popliteal v.
- Medial saphenous v.: on medial aspect, will travel into thigh before draining into femoral v.
What is the hoof?
- Cornified covering of the distal end of the digit of ungulates.
- Modification of skin: insensitive/sensitive layers
Perissodactyl
Odd-toed ungulates
Ex: horse
Artiodactyl
Even-toed ungulates
Ex: cattle, goat, sheep, pig
What is the hoof capsule made up of?
Epidermis (germinative, proliferative & keratinized layers.
- Consists of strati corneum (keratinized), granulosum, spinsosum (differentiating), basale (stem cells)
Corium (innervated and vascularized)
- Consists of papillary dermis (AVN) and reticular dermis
What is the periople?
Zone of transition from the skin to the hoof.
What are the main regions of the hoof?
Wall, sole, and frog
Where does the wall of the hoof go?
It extends distally, medially, and laterally from the periople
Perioplic and coronary grooves run where?
At the proximal border of the hoof wall
What and where are the bars of the hoof?
They are portions of the wall on the palmar region that bend dorsally.
What is the frog?
The triangular and irregular region of the undersurface. Helps support weight. The point of the frog is the cleft
What is the sole?
The smooth part of the undersurface of the hoof. Does not touch frog
What is the portion of the palmar region where the sole and frog meet?
The bulbs in the paracuneal grooves
What is the corium?
A single layer that is continuous with skin of the limbs. It has different zones but one continuous layer
What are the different zone of the corium?
Perioplic, coronary, and laminar regions at the wall.
The frog and sole, the corium have their own respective regions
What are the strata of the hoof wall in order from outer to inner?
- Stratum externum
- Outer stratum medium
- inner stratum medium
- stratum internum
What stratum layer corresponds with the perioplic corium? And what does it do?
Stratum externum: contains stem cells that give rise to the proliferative cells that eventually get keratinized and constitue the stratum sternum of the wall
What stratum layer corresponds with the coronary corium? And what does it do?
Outer & inner strati medium: stem cells form the outer and inner strati medium
What stratum layer corresponds with the laminar corium? And what does it do?
Stratum internum: stem cells are quiescent
Explain how the hoof grows.
The wall strata extend distally, the hoof does NOT grow from the inner to the outer regions
