Upper Limb Organization- Diogo

Question 1

The joint between the sternum (axial skeleton) and clavicle (shoulder girdle)

Answer 1

sterno-clavicular joint

Question 2

The joint between clavicle and scapula

Answer 2

acromio-clavicular joint

acromion is the bony process of the scapula

Question 3

Gleno-Humeral joint is what?

Answer 3

the joint between the scapula and the humerus

Glenoid cavity articulates with the head of the humerus. The glenoid cavity or glenoid fossa of scapula is a part of the shoulder.

Question 4

joint between the humerus and radius and ulna

Answer 4

elbow joint

radius is in the direction of thumb (lateral)
ulna is in the direction of the pinkey (more medial)

Question 5

joint between radius and carpals (hand)

Answer 5

wrist or radio-carpal joint

Question 6

joint between carpals and metacarpals

Answer 6

carpo-metacarpal joint

Question 7

What is the anatomical position?

Answer 7

hand is outward with thumbs facing outward or laterally

Question 8

What is the reference point in humans for determining what is axial or proximal?

Answer 8

the heart

Question 9

What is the direction of the fibula and tibia?

Answer 9

fibula is lateral and tibia is medial

Question 10

Why is the ventral rami an imperfection? What price do we have to pay for this imperfection?

Answer 10

The anterior or ventral muscles are innervated by the ventral rami. The posterior or dorsal muscles are innervated by the dorsal rami.

However, all muscles of the limbs, including those that are posterior are innervated by the ventral rami. This is an imperfection.

Imperfections are usually where diseases occur. One example of a ventral rami is the axillary nerve (anterior) that goes posteriorly to the axial side. It is very prone to damage and this is how we get disease. This is the price we pay for these imperfections.

Ventral rami is used to talk about anterior nerves.

Question 11

All the muscles come from what embryological structure and where do they migrate?

Answer 11

myotome

they migrate to form the skeletal muscle

Question 12

Myotomes are segmental in the fetus at what time?

Answer 12

6 weeks

At 8 weeks the myotomes diffuse and you lose the segmentation.

Question 13

The distal regions are more similar in terms of bone and muscles as opposed to the proximal regions. True or false?

Answer 13

True!!

The shoulder has nothing to do with the pelvis in the proximal region. In terms of muscles and bones, the distal regions are more similar.

Question 14

What are always different between the upper and lower limbs?

Answer 14

the nerves
the arteries

The upper and lower limbs converge to have similar shape, as they use similar genes, but only in the distal parts are they more similar in terms of bone and muscle than the proximal parts. All the parts of the limb are different in terms of nerves and arteries.

Question 15

What forms the distal epithelium on the day 30 of forelimb development in humans?

Answer 15

apical ectodermal ridge (AER)

Question 16

Which has more sonic hedgehog secretion, radius or ulna?

Answer 16

ulna

Question 17

What is between the radius and ulna on day 30 of forelimb development?

Answer 17

active polarizing zone where there are sonic hedgehog secretions

polarizing zone is to the ulna

Question 18

Tendons and muscles are together during embryogenesis. True or false?

Answer 18

FAAALLLSEEEE

Tendons and muscles are NOT together during embryogenesis. They come together later on.

Question 19

What directs the proximo-distal polarity?

Answer 19

apical ectoderm ridge

Question 20

What cells releases signals (what signals) to develop the latero-medial OR radio-ulnar OR cranio-caudal axis?

Answer 20

Zone of polarizing activity cells
at the ulnar/medial side of hand
release sonic hedgehog signals
That’s why the thumb has very low concentrations of sonic hedgehog.

Question 21

What is the factor being changed for a mirror hand image?

Answer 21

the zone of polarizing activity

there are two on the radial-lateral and ulna-medial side
instead of one on the ulna-medial side (normal)

Question 22

Zone of polarizing activity mediates _____________polarity and apical ectoderm ridge mediates _______________polarity.

Answer 22

latero-medial

proximo-distal

Question 23

What DEFINES the proximal/distal distance?

Answer 23

AER and Hox genes

Question 24

Forelimb (upperlimb) and hindlimb (lowerlimb) are regulated by which genes respectively?

Answer 24

upper limb is regulated by Tbx5 transcription factor

lower limb is regulated by TBx4, and Pitx1

Question 25

Without this, your fingers would be webbed AKA syndactyly.

Answer 25

apoptosis

Question 26

The discreptancy between the human standard anatomical position and the “true” anatomical position is with the LOWER LIMB rotated almost 180 degrees laterally. What is the position of the thumb in the anatomical position? What is the position of the hallux in the anatomical position? What is both of their positions in the “true” anatomical position?

Answer 26

-human standard anatomical position
thumb: lateral
big toe : medial

-“true” anatomical position
thumb: lateral
hallux (big toe): lateral

Question 27

The brachial artery (branch of the brachial plexus) supplies the blood for what?

Answer 27

the muscles of the upper limb on the posterior side

Question 28

Tool use is NOT exclusive of humans due to what evolutionary implication?

Answer 28

bipedalism opposition
this movement is exceptionally refined in the human species where the more mobile thumb is exchanged for the other digits moving badly

Question 29

What grips are primates/animals and humans able to perform due to bipedalism opposition?

Answer 29

primates/animals mainly use power grip

humans are the only ones who can do precision grip

Question 30

The specialization of voice leads to what trade-off/price we have to pay?

Answer 30

humans are the most susceptible to choking because

there’s a big space between the tongue and larynx and food could get into the larynx instead of the oesophagus

Other animals have a small space so there’s hardly any choking for them

Question 31

An abnormal configuration is considered what?

Answer 31

a birth defect

Question 32

1-2% of this are found in the NORMAL human population.

Answer 32

human variation

Question 33

These are found in more than 3% of the normal human population. Palmaris longus is an example.

Answer 33

polymorphisms

Question 34

Limb defections are present in the normal human population. True or false?

Answer 34

FALLLSEE

limb defects are birth defects which are NOT present in the normal human population

Question 35

There is no normal in a population. There’s a continuum. Normal is just a simplification.

Answer 35

He’s trying to explain that we ought to understand that “normal” has just been our way of simplifying things.

Question 36

What is the sensitive period of limb development?

Answer 36

4th to 8th week

Question 37

This limb malformation describes the absence of one or more complete limbs.

Answer 37

Amelia, ectromelia

Question 38

This limb malformation describes short, ill-formed upper or lower limbs–named for their resemblance to the flippers of a seal.

Answer 38

phocomelia

Question 39

What is ectrodactyly? Polydactyly? Syndactyly? Adactyly?

Answer 39

ectrodactyly: complete absence of one or more digits
polydactyly: presence of extra digits or parts of digits
syndactyly: fusion of digits
adactyly: absence of all the digits on a limb

Question 40

We can predict the number of surgeries a patient with polydactyly and syndactyly can have. True or false?

Answer 40

TRUE!!!

• no thumb: muscles that go to thumb are still there but will go to digit 2
• 2 thumbs: muscles that go to the lateral thumb will now go to the MOST lateral digit (in anatomical position)

Question 41

Thalidomide teratogen taken by pregnant women to alleviate morning sickness caused what type of limb malformation?

Answer 41

amelia, phocomelia

Question 42

When does limb formation occur for the human embryo?

This is also known as the phylotypic stage.

Answer 42

Week 6

During the phylotypic stage around Week 6 of embryogenesis, genes like Tbx form the limbs, head, gut, etc.. If you mess up the phylotypic stage then you have a lot of different defects. That’s why 1-8 weeks is a very sensitive stage!!

lower limbs are formed after the phylotypic stage

Question 43

Limb anomalies are usually due to teratogenesis, however some limb anomalies are inherited. What is an example?

Answer 43

Lobster claw hand or foot is inherited as autosomal dominant trait. It is inherited genetically.

Achondroplasia: a form of short-limbed dwarfism

Question 44

This is a hereditary condition in which the growth of long bones by ossification of cartilage is retarded, resulting in very short limbs relative to the trunk, and sometimes a face that is small in relation to the (normal-sized) skull.

Answer 44

Achondroplasia which affects the limbs (lower and sometimes both lower and upper limb).

Question 45

Motor innervation of all limb muscles is by ___________which are derived from the neural tube. Sensory innervation receives contribution from neural crest cells.

Answer 45

ventral rami

Question 46

Why are there different models of extensor digitorum communis tendons (EDC tendons)?

Answer 46

It allows for more flexibility. You can still have some functionality with less or more than 5 digits.

Question 47

How is the brachial plexus of the ventral rami an imperfection?

Answer 47

The brachial plexus of the ventral rami innervates the upper limb muscles. Brachial plexus are anterior to the clavicle and shoulder. The shoulder muscles are on the posterior side. So you have brachial plexus nerves coming from the anterior side to innervate shoulders on the posterior side.

You pay the price for the imperfections (nerves are more susceptible to damage).

The pectoral nerves on the anterior side innervate the pectoralis muscles on the anterior side so these are less prone to damage.