Week 8: Regional Anatomy: The Trunk

Question 1

What is regional Anatomy?

Answer 1

• Study by regions (as opposed to body systems) e.g. region of the head and neck, trunk, limbs
  
  • You will see parts of multiple body systems in a given region
  • Regional anatomy is important to understand the interactions of different systems in a given anatomical location
    Clinically it is important to differentially diagnose conditions when symptoms are localized to a particular region

Question 2

Region of the trunk:

Answer 2

• Can be divided into:
  
  • The back (posterior/dorsal) trunk
  • The anterior/ventral body cavities
  • Thoracic cavity
    Abdominopelvic cavity

Question 3

Main body systems of the posterior trunk:

Answer 3

• Integumentary: Protection and sensation, skin and subcutaneous tissue
  
  • Muscular: Stabilizes body position and produces movement, moving and maintaining the position of the axial skeleton, muscles of ventilation e.g. intercostals
  • Skeletal: Protection of organs, facilitates movement. Vertebral column, vertebrae, intervertebral discs and associated ligaments, sternum and ribs
    Nervous: Receives, interprets and elicits response to information, spinal cord and meninges, nerves

Question 4

The vertebral column:
Functions:

Answer 4

• Provides a framework for the body as part of the axial skeleton
  
  • Facilitates weight transfer
  • Protects the spinal cord and organs
  • Provides a location for muscle attachment
    General bone functions: Blood cell formation, calcium store

Question 5

Vertebral column structure:

Answer 5

• Made up of bone and connective tissue
  
  • Thirty-three vertebrae in a child and 26 in an adult
  • 7x cervical
  • 12 x thoracic
  • 5 x lumbar (fused in adults to form one)
  • 4x coccygeal (fused in adults to form one)
    Intravertebral discs made of fibrocartilage that are between vertebrae

Question 6

Components of typical vertebrae:

Answer 6

Vertebral body, vertebral arch, processes

Question 7

Vertebral body:

Answer 7

• Disc shaped anterior portion
  
  • Weight baring part of the vertebrae
    Superior and inferior surfaces attached to intravertebral discs

Question 8

Vertebral arch:

Answer 8

• The pedicles project posteriorly from the vertebral body and unite with the lamina to form the arch
  Houses the spinal cord and its protective tissues

Question 9

Processes:

Answer 9

• Transverse processes: Projects laterally from lamina- serve as muscle attachment sites
  
  • Spinous process: Projects posteriorly from lamina - serve as muscle attachment sites
    Superior and inferior articular processes (x2 of each) - serve as articulation sites of vertebrae above and below

Question 10

Structure of Cervical vertebrae:

Answer 10

Small, one vertebral two transverse foramina, often slender build C2-C6, no articular facet for ribs, articular facets are posterosuperior and anteroinferior, thick intervertebral discs relative to size of vertebral bodies

Question 11

Structure of thoracic vertebrae:

Answer 11

Larger, one vertebral foramina, long thick spinous processes, fairly large transverse process, articular faces for ribs present, articular facets are posterolateral, anteromedial, intervertebral discs are thin relative to the size of vertebral bodies,

Question 12

Structure of lumbar vertebrae:

Answer 12

Largest, one vertebral foramina, short blunt (posterior rather than inferior) spinous processes, large and blunt transverse process, articular facets for ribs are absent, direction of articular facets are medial and lateral, thickest size of intervertebral discs

Question 13

Vertebral column regions:

Answer 13

The neck region: Cervical vertebrae
- First two vertebrae (C1 and C2, known as the atlas and axis respectively) are specialised in structure to facilitate side-to-side movement of the head
The chest region: Thoracic vertebrae
- Articulate with the ribs
Lumbar region:
- Largest and strongest unfused vertebrae as the amount of body weight supported increases toward the inferior end of the vertebral column
Sacral and coccygeal region:
Serves as a strong foundation for the pelvic girdle

Question 14

Vertebral column curvatures

Answer 14

• When viewed in a sagittal plane, the four normal curves of the vertebral column are visible
  
  • Relative to the anterior (front) surface of the body
  • Cervical and lumbar curves are convex (bulge out)
    Thoracic and sacral curves are concave (cup inward)

Question 15

Functions of the vertebral curves:

Answer 15

• Increase vertebral column strength
  
  • Helps to maintain balance in an upright position
  • Shock absorption during walking
  • Protect vertebrae against fracture
    Cervical and lumbar curves may be progressively lost in old age

Question 16

Vertebral column joints:
There are 2 main types of joints in the vertebral column:

Answer 16

• Intervertebral discs and vertebral bodies form cartilagenous joints
  
  • These joints limit the range of intervertebral motion
  • Superior/inferior articular processes on adjoining vertebrae form facet/zygapophyseal joints
  • These are synovial joints
    The size, shape and positioning of the articulating surfaces and the resulting joint planes depend on the vertebral region. The orientation of the articular surfaces determine the type and range of movements possible at each region

Question 17

Vertebral column ligaments:

Answer 17

• Ligaments are dense fibrous connective tissue
  
  • They attach bone to bone
  • Serve to limit joint movement
  • Anterior longitudinal ligament (most anterior element) - limits extension
  • Posterior longitudinal ligament - limits flexion
  • Intertransverse ligament - limits lateral flexion
    Supraspinous (on top of spinous) ligaments - limit flexion

Question 18

Recall: Muscles and movement

Answer 18

• Muscles must cross a joint to make movement
  
  • Muscle attachment sites are:
  • Origin: muscle beginning, does not move during contraction, usually proximal end of bone/joint
  • Insertion: Muscle end - is pulled towards the origin during contraction. Usually distal end of bone/joint

Question 19

Flexion of the vertebral column:

Answer 19

• Flexion occurs in the sagittal plane
  
  • Muscles involved in flexion are positioned anterior ro intervertebral joints
    Rectus abdominus

Question 20

Extension of the vertebral column:

Answer 20

• Extension occurs in the sagittal plane
  
  • Muscles involved in extension are positioned posterior to the intervertebral joints
    Erector spinae muscle group

Question 21

Rotation of the vertebral column:

Answer 21

• Rotation occurs in the transverse/horizontal plane
  
  • Muscles involved in rotation are positioned in an oblique direction
  • Sternocleidomastoid, internal and external obliques

Question 22

Lateral flexion of the vertebral column:

Answer 22

• Lateral flexion occurs in the coronal/frontal plane
  
  • Muscles involved in lateral flexion are positioned lateral to the intervertebral joint
  • Erector spinae muscle group
  • Internal and external obliques

Question 23

Development of the vertebral column:
Embryonic development:

Answer 23

• During the third week of embryonic development, three distinct germ layers develop and form different structures of the body
  
  • Endoderm: Gives rise to epithelial linings and glands of digestive and respiratory systems, abdominal organs and urinary bladder
  • Mesoderm: Gives rise to all connective tissue, muscular tissue, the dermis, the vascular system and the urogenital system (except the urinary bladder)
  • Ectoderm: Gives rise to epidermis, nails, hair and nervous tissue

Question 24

Differentiation of the Mesoderm:

Answer 24

• Recall that the mesoderm gives rise to all connective tissue, muscular tissue, the dermis and the vascular system and the urogenital system (except the urinary bladder)
  
  • During embryonic development, there are modifications that occur to the mesoderm on either side of the notochord
    These modifications are called somite’s (number of somite pairs increases as embryo develops/lengthens

Question 25

Differentiation of Somite's: Differentiate into three possible structures:

Answer 25

1. Sclerotome: Forms the vertebrae and ribs 2. Dermatome: Forms dermis of the skin 3. Myotome: Forms skeletal muscle of the neck, trunk and limbs) that further differentiates into - Epimere: Muscles on the posterior/dorsal surface - Hypomere: Muscles on the anterior/ventral surface

Question 26

Innervation and blood supply of the trunk Recall: Structure of spinal nerves:

Answer 26

- Anterior/ventral roots contain motor neurons (motor info out) and posterior/dorsal roots contain sensory neurons (sensory info in) - Spinal nerves form where the anterior and posterior root comes together as they exit the spinal cord through the intervertebral foramina - Spinal nerves branch into anterior and posterior rami Trunk region supplied by rami from spinal nerves T1-T12

Question 27

Anterior and posterior rami:

Answer 27

- Posterior ramus supplies the structures of the back - Anterior ramus supplies the entire anterior surface of the body and the limbs (hence large diameter) - Any given ramus may have the following branches - Muscular branch: Innervating muscle - Cutaneous branch: Innervating skin - Articular branch: Innervating the joint Vascular branch: Innervating blood vessels

Question 28

Arterial supply of the trunk: - The major artery supplying the trunk (thoracic and abdominopelvic regions) is the aorta The aorta has 4 distinct regions:

Answer 28

1. Ascending aorta 2. Aortic arch 3. Thoracic (descending aorta) - Spans from approx T4-T12 vertebral level - Has many branches to supply structures of the thoracic region - Passes through the diaphragm (aortic hiatus) 4. Abdominal aorta - Continuation of thoracic aorta and spans from approx. T12-L4 vertebral level Has many branches to supply structures of the abdominopelvic region - Descending thoracic aorta: Aorta that rises from the heart, ascending aorta and then it will continue down as the descending aorta. Branches of the descending thoracic aorta will supply the tissues of the thoracic part of the trunk. Descending thoracic aorta will Peirce the diaphragm and continue to the abdominal region and will be called the abdominal aorta Abdominal aorta: Branches will supply abdominal and pelvic part of the trunk

Question 29

Venous drainage of the trunk:

Answer 29

- Recall: Wherever there is an artery, you will find a vein The major veins that drain the trunk (thoracic and abdominopelvic regions) are the superior and inferior vena cava - Inferior vena cava: drain lower part - Superior vena cava: Drain upper half of the body - Nerves arteries, veins and lymphatics will travel together and form neurovascular bundles

Question 30

Superior vena cava:

Answer 30

- Located in the thoracic region Has many branches that allow it to drain deoxygenated from the upper half of the body (head, neck, upper limbs and upper thoracic) back to the heart

Question 31

Inferior vena cava

Answer 31

- Located in the abdominopelvic region Has many branched that allow it to drain deoxygenated from the lower half of the body (lower thoracic, abdominopelvic and lower limbs) back to the heart

Question 32

Muscle placement and movement:

Answer 32

- Application of knowledge: A muscle must cross a joint to act on that joint, the position of a muscle relative to a joint determines the plane and direction of movement it can produce - Flexion: Muscle to lie anterior to the joint at which the movement occurs e.g. intervertebral joints. Muscle would need to lie anterior to the intervertebral joints - Extension: Muscle would need to lie posterior to intervertebral joints, support extension of VC - Rotation: Direction of muscle fibers. For rotation, direction would need to be oblique, primary muscles are internal and external obliques - Lateral flexion: Position of muscle needs to be lateral to intervertebral joints. Erectus spinae, internal and external obliques

Question 33

Innervation of the trunk:

Answer 33

- Ventral ramus = front - Dorsal ramus = back - Supplies muscles along the surface and will also have a dorsal ramus towards the dorsal aspect of the trunk - Supplies muscle along dorsal surface of the trunk Spinal nerves: Thoracic spinal nerves - Other tissues around the wall that need to be innervated - Tissue innervation: The nerve that supplies the muscle acting a joint also supplies tissues of that joint and the skin over the muscles and/or the joint - e.g. dorsal ramus will supply joint and skin over the muscle The ventral ramus supplies anterior/lateral abdominal wall

Question 34

Structures innervated by branches (dorsal/ventral rami) of spinal nerves

Answer 34

- Muscular branches: Innervating muscle - Cutaneous branches: Innervating skin - Articular branches: Innervating the joint - Vascular branches: Innervating blood vessels

Question 35

Spine and structure of segments:

Answer 35

- Most vertebrae share a similar shape with the following features: - Body: The major part of the bone e.g. vertebral body - Protuberances (bumps) for attachment sites for muscles or ligaments e.g. transverse processes - Articular surfaces for articulation (joint) with another bone e.g. superior and inferior facets Depression/holes for passage of other structures e.g. foramen

Question 36

What are the functions of these features of a vertebra: The vertebral body Transverse processes Intervertebral foramen Superior portion of the foramen

Answer 36

The vertebral body is a weight bearing surface, allowing the transmission of load through the spine. It is also part of the cartilaginous joint formed with the intervertebral disc and the adjacent vertebral body. Transverse processes provide a site for muscle and ligament attachment. The vertebral foramen provides a passage for the spinal cord and cauda equina. The intervertebral foramen provides a passage for the spinal nerves. The superior portion of the foramen is formed by the inferior notch of the superior vertebra and the inferior portion in formed by the superior notch of the inferior vertebra

Question 37

Vertebral column curvatures

Answer 37

- Primary curvatures concave anteriorly and develop before birth in all regions - Secondary curvatures are concave posteriorly and develop during childhood as a result of changes in shape of vertebrae and intervertebral discs - Secondary curvatures facilitate upright postures

Question 38

Joints of the vertebral column

Answer 38

- There are 2 main types of joints - Intervertebral discs and vertebral bodies form cartilaginous joints. These joints limit the range of intervertebral motion Facet joints (zygapophyseal joints) are synovial joints which limit the direction of intervertebral motion based on the orientation of the articular facets

Question 39

Ligaments of the spinal joints:

Answer 39

- Ligaments are made up of dense fibrous connective tissue, the major fiber type is collage with is inelastic - Ligament attaches bone to bone - The role of a ligament is to limit joint movements Ligaments of the spinal joints can be continuous across the whole spine rather than specific to a specific joint at a particular level of the spine

Question 40

Spinal nerves:

Answer 40

- In the cervical region a spinal nerve leaves the vertebral canal through the intervertebral foramen immediately proximal to the vertebra for which it is named - e.g. C5 spinal nerve leaves through the intervertebral foramen between C5 and C4 In the thoracic and lumbar region, the spinal nerve leaves the vertebral canal through the intervertebral foramen immediately distal to the vertebra for which it is named. Therefore the T8 spinal nerve leaves through the intervertebral foramen between T8 and T9

Question 41

Patient A wants to know what the major difference is in function of the vertebrae of the thoracic region compared to the vertebrae of the other regions.

Answer 41

They anchor the rib cage

Question 42

Patient A wants to know which of the normal vertebral curvatures are primary curvatures.

Answer 42

Thoracic and Sacral

Question 43

Patient A wants to know about movements permitted by the vertebral column. Which of the following statements matches (A) The spinal movement, and (B) the plane in which the movement occurs in.

Answer 43

(A) Rotation (B) Transverse/Horizontal plane

Question 44

Which of the following muscles would NOT be innervated by branches of the posterior ramus

Answer 44

Rectus abdominus