1
Q
Mel/o
A
Limb/Part
2
Q
Pod/o
A
Limb/Foot
3
Q
Apic/o
A
Peak/Apex/Tip
4
Q
Derm/o
A
Skin
5
Q
Dactyl/o
A
Digit
6
Q
Embry/o
A
Embryo
7
Q
Chrondr/o
A
Cartilage
8
Q
Mer/o
A
Part of segment
9
Q
Zon/o
A
Belt/Region
10
Q
Proxim/o
A
Near/Close to
11
Q
Dist/o
A
Far/Away from
12
Q
Syn/o
A
Together/with
13
Q
Styl/o
A
Pillar/Column
14
Q
Zeug/o
A
Pair/Yoke
15
Q
A-
A
Without
16
Q
Auto-
A
Self/Automatic
17
Q
Epi-
A
Upon/Over/Above
18
Q
Brachy-
A
Short/Slow
19
Q
Endo-
A
Within/Inside
20
Q
Hypo-
A
Under/Below
21
Q
Inter-
A
Between/Among
22
Q
Poly-
A
Many/Much
23
Q
-is/-al/-ous/-ic
A
Pertaining to
24
Q
-y
A
Condition/State
25
Hypaxial Muscles
Muscles derived from the hypomere, including
subvertebral, lateral body wall, and ventral muscles.
26
Cartilaginous Stage
Phase of limb development where condensed
mesenchymal cells differentiate into chondrocytes, forming a cartilage model of future bones.
27
Joint Cavitation
Process of cell death and extracellular matrix remodeling that creates the joint cavity.
28
Mesenchymal Stage
Early stage of limb development consisting of a mesenchymal core covered by ectoderm.
29
Proximodistal Principle
Developmental pattern where growth occurs from central parts of the body outward toward the extremities.
30
Apical Epidermal Ridge (AER)
A thickened ridge of ectoderm at the distal tip of the developing limb bud that promotes limb outgrowth.
31
What is Musculoskeletal Development?
Limbs In this lecture, you will continue the study of musculoskeletal morphogenesis as we explore the emergence of limb anatomy.
32
Explain how the lateral mesoderm relates to limb development
Lateral Plate Mesoderm:
Provides connective tissue scaffolding, guiding muscle organization and attachments.
33
Describe the role of the myotome in the formation of limb muscles
34
Explain why the elbow bends in the opposite direction than the knee joint
To attain an adult anatomical position, the upper and lower limbs rotate in opposite directions and to different degrees, resulting in the adult elbow pointing posteriorly and the adult knee pointing anteriorly.
35
Describe the important difference between the upper limb and the lower limb developmentally.
36
What does Proximodistal Principle refers to?
the developmental pattern in which growth occurs from the central parts of the body (proximal) outward toward the extremities (distal).
While this principle primarily describes patterns of physical growth and motor development, its context can also extend to skeletal and limb formation during embryogenesis.
37
At how many weeks doing limb buds appear and grow out from the ventolateral body wall?
The end of 4th week
38
What is the Clinical Relevance of the AER disruption?
AER disruptions or signaling defects are linked to congenital limb abnormalities, such as amelia (absence of limbs) or meromelia (partial absence of limbs).
39
What do the limb buds consist of? What is the it derived from?
Mesenchyme core
Parietal mesoderm
40
What does the AER play a role in promoting and sustaining?
The outgrowth of the limb along the proximodistal axis
41
What is the primary role of the apical ectodermal ridge (AER) in limb development?
It promotes and sustains limb outgrowth along the proximodistal axis and maintains adjacent mesenchyme in an undifferentiated, proliferative state.
42
How does the AER prevent premature differentiation of mesenchyme?
It exerts an inhibiting influence on adjacent mesenchyme, keeping it in a state of rapid proliferation and preventing early differentiation.
43
What causes the proximal end of the limb to begin differentiating?
As the limb grows distally, the proximal end moves away from AER influence, allowing Growth and Differentiation Factors (GDFs) to become less inhibited, leading to differentiation.
44
Where do the myogenic progenitor cells originate? Where do the cells migrate to?
In the hypaxial portion of somites
migrate to the limb buds and form the future muscle tissue of the upper limb
45
What does the lateral plate mesoderm provide for the connective tissue?
Connective tissue scaffolding, guiding the muscle organization and attachments
46
What are the stages of upper limb skeletal development?
Early Mesenchymal Stage
Late Mesenchymal Stage
Cartilaginous Stage
Endochondral Stage
47
What happens during Early Mesenchymal Stage?
This early limb development lays the groundwork for proximodistal growth, starting with the body’s core and projecting outward.
48
What is the early structure of a developing limb composed of?
It consists of a mesenchymal core derived from the lateral plate mesoderm, covered by ectoderm, and projects outward.
49
What happens during Late Mesenchymal Stage?
Mesenchymal cells (derived from the mesoderm) condense in the limb bud to form the precursors of skeletal structures.
50
What happens during Cartilaginous Stage?
The condensed mesenchymal cells differentiate into chondrocytes, forming a cartilaginous model of the future bones.
Proximodistal growth can be observed as the cartilage extends outward from the central axis of the body.
51
What happens during Endochondral Stage?
During this phase, the cartilaginous model is gradually replaced by bone through the process of endochondral ossification.
The growth continues outward, aligning with the proximodistal principle as bones elongate and mature.
52
What happens during embryogenesis?
Joint development is a highly orchestrated process
Ensuring the proper formation and function of skeletal articulations
53
What happens during mesenchymal condensation in limb development?
Mesenchymal cells aggregate in the limb bud to form skeletal precursors and differentiate into chondrocytes, creating a continuous cartilaginous model of developing bones.
54
What is the Interzone, and what is its role in limb development?
The Interzone is a distinct region at future joint sites, consisting of undifferentiated, flattened, densely packed mesenchymal cells, which contribute to joint formation.
55
How do synovial joints develop from the Interzone?
Central Interzone cells undergo apoptosis to form the joint cavity, while peripheral Interzone cells differentiate into articular cartilage, synovial membrane, and joint capsule, creating free-moving synovial joints.
56
How do cartilaginous joints develop from the Interzone?
Interzone cells differentiate into hyaline cartilage or fibrocartilage, forming joints such as synchondroses (e.g., intervertebral discs) and symphyses (e.g., costochondral joints).
57
How do fibrous joints develop from the Interzone?
Interzone cells differentiate into dense fibrous connective tissue, linking adjacent bones to form fibrous joints like syndesmoses (e.g., distal tibiofibular joint) and skull sutures.
58
What factors influence the differentiation of Interzone mesenchyme?
Growth and Differentiation Factors (GDFs), genetic factors, and fetal movements guide the differentiation of Interzone mesenchyme into specific joint types.
59
How is the joint cavity formed?
Within the Interzone, cell death (apoptosis) and extracellular matrix remodeling create a joint cavity, which is then filled with synovial fluid for lubrication.
60
How does articular cartilage develop?
It forms from mesenchymal cells at the joint surfaces, providing a smooth, durable surface for joint movement.
61
Where do the joint capsule and ligaments originate?
They arise from the surrounding mesenchyme, providing structural support and stability to the joint.
62
How does the synovial membrane develop?
It forms from the inner layer of the joint capsule and plays a crucial role in producing synovial fluid for joint lubrication.
63
What do the stylopod, zeugopod, and autopod differentiate into?
Stylopod (humerus and femur),
Zeugopod (radius/ulna and tibia/fibula)
Autopod (carpels, metacarpals, tarsals/metatarsals digits).
64
What is it called when the fingers and toes separates from the plates into five parts due to cell death?
Apoptosis
65
What are the schematic of human hand at 48 days? At 51 days?
At 48 days. Cell death in the plate creates a separate ridge for each digit
At 51 days. Cell death in the interdigital spaces produces separation of the digits
66
What is Amelia? What causes it? When does it normal occur?
1. Definition: Complete absence of one or both upper limbs.
2. Cause: Early failure in limb bud formation, often due to genetic mutations (e.g., TBX5 gene defects) or teratogenic exposures (e.g., thalidomide).
3. Timing: Occurs during the 4th week of embryogenesis.
67
What is Meromelia? What causes it? When does it normal occur?
1. Definition: Partial absence of a limb, where some structures (e.g., hand, forearm) are missing.
2. Cause: Disruption in proximodistal growth, often related to impaired function of the apical ectodermal ridge (AER) or FGF signaling pathways.
3. Timing: Develops later than amelia, typically during the 5th or 6th week
of gestation. 19
68
When do upper limb anomalies arise from?
Upper limb developmental anomalies arise from disruptions in the normal processes of limb development. These anomalies vary in severity and may occur in isolation or as part of syndromes affecting multiple systems.
69
What is Brachydactyly? What causes it? When does is clinical features?
Definition: Shortening of fingers or toes due to underdeveloped or missing phalanges.
Cause: Genetic mutations, often involving genes like BMPs or HOX genes.
Clinical Features: Affects hand function and appearance; varies in severity.
70
What is Syndactyly? What causes it? When does is clinical features?
Definition: Fusion of two or more fingers or toes resulting from failure of interdigital apoptosis during development.
Cause: Genetic factors (e.g., mutations in the FGFR1 or HOXD13 genes); may be isolated or part of syndromes (e.g., Apert syndrome).
Clinical Features: Can be simple (soft tissue fusion) or complex (bone fusion).
71
What is Polydactyly? What causes it? When does is clinical features?
Definition: Presence of extra fingers or toes.
Cause: Genetic mutations affecting anterior-posterior axis patterning, often linked to defects in Sonic Hedgehog (SHH) signaling.
Clinical Features: May be preaxial (thumb side), postaxial (pinky side), or central.
These anomalies can occur in isolation or as part of syndromic conditions and may impact both function and aesthetics.
72
Where does the sclerotomal portion of the somite migrate around?
Migrated around the notochord for axial skeletal development
73
Where does the dermatonal portion of the somite migrate around?
Migrated posteriorly to differentiate into the skin of the dorsal surface of the developing embryo.
74
What are the condensation of myotomal cells differentiates into?
1. Dorsomedial muscle cells = Epimere
2. Ventrolateral muscle cells = Hypomere
75
What does the hypomere develop into?
The hypomere migrates to form hypaxial (ventral) muscles, including subvertebral muscles, lateral body wall muscles, and ventral muscles.
76
What are subvertebral muscles, and where are they located?
Subvertebral muscles develop from the hypomere and are located on the ventral side of the vertebral column.
77
What are the four layers of lateral body wall muscles?
1. Supracostal muscles (outermost)
2. External muscles
3. Middle muscles
4. Innermost muscles
78
What role do ventral muscles play in the body?
Ventral muscles, derived from the hypomere, contribute to the muscles of the anterior body wall, aiding in movement and structural support.
79
When does migration of the upper limb happen?
4th-5th week
80
When does aggregation and compartmentalization of the upper limb happen?
5th - 6th week
81
How do myoblasts migrate into the developing upper limb?
Myoblasts migrate from cervical and upper thoracic somites (C5–T1) into the upper limb bud, guided by molecular growth and differentiation factors (GDFs).
82
When does differentiation of the upper limb happen?
6th=8th week
83
When does patterning and innervation of the upper limb happen?
7th-8th week
84
When does maturation of the upper limb happen?
Fetal period
85
How do migrating myoblasts organize in the developing upper limb?
Myoblasts aggregate into two primary muscle masses:
• Dorsal Mass → Extensors and supinators (e.g., triceps brachii, forearm extensors).
• Ventral Mass → Flexors and pronators (e.g., biceps brachii, forearm flexors).
86
How do myoblasts mature into skeletal muscle fibers?
Myoblasts differentiate into myotubes, which eventually develop into skeletal muscle fibers, driven by myogenic regulatory GDFs.
87
What directs muscle patterning and innervation?
• Patterning → Directed by surrounding connective tissue from the lateral plate mesoderm.
• Innervation → Guided by the brachial plexus (C5–T1), which helps organize functional muscle groups.
88
What happens during muscle maturation in the fetal period?
Muscle fibers grow, attach to bones via tendons, refine their innervation, and establish a vascular supply, completing functional units.
89
What do the dorsal mass derivatives?
- Shoulder muscles: Deltoid, supraspinatus, infraspinatus.
- Posterior arm: Triceps brachii.
- Posterior forearm: Extensors.
90
What do the ventral mass derivatives?
- Anterior arm: Biceps brachii, brachialis.
- Anterior forearm: Flexors, pronators.
- Intrinsic hand muscles.
91
What are the primitive vertebrate?
Elevator (dorsal) muscles
Depressor (ventral) muscles
Muscle–nerve relationship
92
What are the premammalian limb?
Elevator/extensor (dorsal) muscles
Depressor/Flexor (ventral) muscles
Muscle–nerve relationship
93
What does the annexation of body wall and head muscles by the superior limb refer to?
It describes the evolutionary and developmental process where limb musculature integrates contributions from axial and cranial structures.
94
How did limb muscles evolve in vertebrates?
Limb muscles evolved from fins in ancestral vertebrates, incorporating musculature originally associated with the body wall and head.
95
Why was the integration of head and body wall muscles into the limbs important?
This integration enabled complex limb movements necessary for terrestrial locomotion and manipulation.
96
Where are limb muscles primarily derived?
Limb muscles are primarily derived from somites, with additional contributions from nearby body wall and cranial musculature.
97
What is the functional significance of the annexation of body wall and cranial musculature in the upper limb?
The annexation allows for a wide range of upper limb movements, integrating axial stability with appendicular dexterity.
98
How do axial muscles and limb muscles work together in coordinated movements?
Axial muscles (e.g., trapezius) and limb muscles (e.g., deltoid) enable coordinated movements like lifting, pushing, and pulling.
99
What does the annexation of the outermost body wall and head muscles into the superior limb reflect?
It reflects an evolutionary adaptation, enabling the complexity and functionality of the human upper limb.
100
Where are hypaxial muscles located and what is their primary function?
Hypaxial muscles are located on the ventral (front) side of the body or below the axis of the vertebral column. They are primarily involved in movements of the trunk and limbs, as well as supporting respiration.
101
What are sub vertebral (ventral) muscles and their function?
Sub vertebral (ventral) muscles are located along the front of the spine and are involved in the flexion and rotation of the vertebral column. Examples include the psoas and longus colli.
102
What muscles make up the four-layered lateral wall muscles and what is their function?
The four-layered lateral wall muscles comprise the external oblique, internal oblique, and transversus abdominis. They are involved in trunk movements and support respiration.
103
What are supracostal muscles and what is their role?
Supracostal muscles are accessory respiratory muscles that aid in rib elevation and support the mechanics of breathing.
104
How do the external, middle, and internal intercostal muscles function?
These muscles are organized into three layers and control the expansion and contraction of the rib cage during breathing.
105
What is the function of the rectus abdominis?
The rectus abdominis is key for trunk flexion and core stability, supporting trunk movement, posture, and respiration.
106
What do the outermost body wall muscles, particularly those associated with the hypaxial portion of somites, do in the developing upper limb?
These muscles extend into the developing upper limb.
107
What happens to the muscles that were initially part of the thoracic body wall?
They become specialized for upper limb movement and stabilization.
108
Which muscles are annexed from the body wall by the upper limb for scapular stabilization?
• Levator scapulae
• Rhomboid major
• Rhomboideus minor
• Serratus anterior
• Pectoralis minor
• Subclavius
109
What are the head muscle contributions to the upper limb, specifically in the shoulder region?
Muscles originally associated with branchial (pharyngeal) arches are annexed for limb function, especially in the shoulder region.
110
Which muscle is derived from the branchial mesoderm and innervated by the accessory nerve, stabilizing and moving the scapula?
Trapezius
111
What is the origin and innervation of the Sternocleidomastoid?
It originates from the same mesoderm as the trapezius and shares innervation with the trapezius through the spinal accessory nerve (cranial nerve XI).
112
What is the significance of the second pharyngeal arch mesoderm in upper limb development?
It gives rise to muscles that are innervated by the spinal accessory nerve (cranial nerve XI) and are involved in shoulder stabilization and movement.
113
How did head muscles contribute to upper limb development?
Originally associated with cranial and neck functions like respiration, feeding, and facial expression, these muscles were annexed for locomotor and manipulative functions in the shoulder region, aiding in upper limb activities such as lifting, pulling, and stabilizing.
114
How are head muscles integrated into the shoulder girdle during embryogenesis?
Through the migration and differentiation of mesodermal cells, head muscles are integrated into the shoulder girdle.
115
What distinguishes the innervation of head muscles in upper limb development?
These muscles are innervated by cranial nerves (rather than spinal nerves), reflecting their pharyngeal arch origin.
116
What is “retrogrowth” in limb development?
Retrogrowth refers to the process where muscles originating from the limb bud mesenchyme extend and “grow back” to anchor themselves to the axial skeleton, helping establish their role as proximal stabilizers and movers.
117
Which muscles arise from the somitic mesoderm near the intertubercular groove, and where do they attach?
• Pectoralis major: Anchors to the clavicle, sternum, and costal cartilages.
• Latissimus dorsi: Anchors to the spinous processes of lower thoracic and lumbar vertebrae, as well as the iliac crest.
• Teres major: Attaches to the scapula (appendicular skeleton).
118
How does the connective tissue from the lateral plate mesoderm influence muscle development?
It guides the elongation and extension of muscles proximally during retrogrowth, ensuring that they attach properly to the axial skeleton.
119
What is the clinical significance of nerve injuries, particularly to the Spinal Accessory Nerve (SAN)?
Damage to the SAN can affect muscles like the trapezius. SAN injury can occur due to surgery (neck surgeries, lymph node biopsies), trauma (blunt or penetrating), or conditions like whiplash.
120
What congenital defects may arise from aberrations in muscle development or migration?
Conditions like Poland syndrome (missing pectoralis muscle) or accessory muscles in the limb may occur due to issues with muscle development or migration.
121
What is Poland syndrome?
Poland syndrome is a congenital condition characterized by the absence or underdevelopment of the pectoralis muscle on one side of the body. This condition may result in asymmetry of the chest and shoulder, with varying degrees of functional limitation in arm movement.
122
What causes Poland syndrome?
Poland syndrome is thought to result from disruptions during embryonic development, particularly in the migration of mesodermal cells that form the pectoralis muscle. It is typically unilateral and may be associated with other congenital anomalies, such as missing or underdeveloped fingers.
123
How do congenital defects like Poland syndrome affect limb function?
Poland syndrome can result in limited shoulder mobility and asymmetry, particularly affecting activities that require the use of the upper limbs, such as lifting or pushing. The absence of the pectoralis muscle can lead to weak chest and shoulder muscles, reducing overall strength in the affected arm.
124
What are the types of polydactyly based on location?
• Preaxial: Extra digits on the thumb side of the hand or foot
• Postaxial: Extra digits on the pinky side
• Central: Extra digits occurring in the middle of the hand or foot
125
What is the orientation of the limb buds before rotation (around 7 weeks)?
Prior to limb rotation, the upper limb buds project laterally with the flexor (ventral) surfaces facing anteriorly and the extensor (dorsal) surfaces facing posteriorly.
126
How does the upper limb rotate around the 7th-8th week?
Around the 7th to 8th week, the upper limb undergoes a 90-degree lateral rotation:
• The extensor muscles (previously dorsal) shift to the lateral and posterior sides.
• The flexor muscles (previously ventral) shift to the medial and anterior sides.
127
How do nerves adapt to the new muscle orientation after limb rotation?
After rotation, the nerves adapt to the new muscle orientation:
• The radial nerve, which innervates extensor muscles, moves to a posterior position.
• The median and ulnar nerves, which innervate flexor muscles, shift to an anterior and medial position.
128
What are dermatomes, and what is their role?
Dermatomes are distinct regions of the skin that are innervated by sensory fibers from a single spinal nerve. They are critical for understanding sensory innervation and are used in clinical diagnostics to identify specific nerve involvement.
129
How do dermatomes relate to limb segments?
Dermatomes correspond to specific regions in the limbs, with each spinal nerve providing sensory innervation to designated areas of the arms, hands, legs, and feet. This segmentation is integral to understanding limb function and pathology.
130
Why is dermatomal mapping clinically significant?
Dermatomal mapping is essential for diagnosing sensory deficits and neurological disorders. Loss of sensation in a particular dermatome can indicate nerve compression, injury, or disease affecting specific spinal segments.
131
How does the segmentation of the nervous system relate to dermatomal distribution?
During embryonic development, the neural tube forms spinal cord segments, each associated with a somite, leading to the formation of spinal nerves that correspond to specific dermatomal areas.
132
What role does dermatomal mapping play in neurological diagnosis?
Dermatomal mapping helps identify nerve function issues and sensory perception abnormalities by pinpointing affected spinal nerves, aiding in diagnosis and treatment planning.
133
How is dermatomal mapping clinically significant?
Dermatomal mapping is useful for diagnosing sensory deficits and neurological disorders. A loss of sensation in a specific dermatome can indicate nerve compression or damage in a particular spinal segment.
