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First year semester 2 > Development of the head > Flashcards

Development of the head Flashcards

1
Q

Describe the difference between segmental development in the trunk versus the head

A

Explain the different embryological tissues and what structures they give rise to

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2
Q

How many cranial nerves are there?
How are these numbered
How are these named?

A

12 PAIRS

  1. Numbered using roman numerals I to XII in a rostro-caudal direction
  2. Names according to either Function, Anatomical Characteristics OR Distribution
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3
Q

Why is it important to understand the development of the head?

A

Clinically very important (clinical tests) to know the functional anatomy of these nerves but in the adult they don’t appear to follow any sort of logic. Understanding dev = some form of logic restored

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4
Q

What are the first 4 cranial nerves. Numbers, roman numerals and names

A 
1 = I = Olfactory
2 = II = Optic
3 = III = Occulomotor
4 = IV = Trochlear
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5
Q

What are the numbers, roman numerals and names of the cranial nerves 5 to 8

A 
5 = V = Trigeminal
6 = VI = Abducent
7 = VII = Facial
8 = VIII = Vestibulo-cochlear
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6
Q

What are the numbers, roman numerals and names of the last 4 cranial nerves

A 
9 = IX = Glosso - pharyngeal
10 = X = Vagus
11 = XI = Accessory
12 = XII = Hypo - glossal
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7
Q

What are the three types of embryological tissue?

A
  1. Ectoderm which gives rise to stuff on the outside (skin)
  2. Endoderm = stuff on inside = usually epithelium of some sort
  3. Mesoderm = inside = usually muscle
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8
Q

Development of Coelomic Cavity in the trunk

A
  1. There is a belt of mesoderm on LHS and RHS with a gap in the middle
  2. Gap = CAVITATION = which goes on to form the body cavity of that part of the animal.
  3. Summary: in trunk, cavitation of mesoderm results in splanchnic and somatic lateral plate mesoderm enclosing a coelomic cavity
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9
Q

Development of mesoderm in the Head. diff between this and in trunk

A
  1. Cavitation does NOT occur like it does in trunk
  2. Lateral plate mesoderm remains as solid belt of tissue surrounding first part of gut tube (mouth)
  3. Intermediate mesoderm fails to develop whereas in trunk = forms various other structures
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10
Q

How segmental is the trunk and the head?

A
  1. Adult trunk is clearly segmental

2. Head appears not to be but embryonically it once was

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11
Q

How many segments are there?

A
  1. seven
  2. Each segment has each different embryological tissue and therefore each diff nerve needed to supply
  3. There are some exceptions as the head develops
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12
Q

What does each segment consist of? and what do these form?

A
  1. Ectoderm - outside (skin)
  2. Somites (S1-7) -skeletal muscle under voluntary control
  3. Endoderm (gut tube) - lining
  4. Lateral plate mesoderm (A1-6) - exception = also skeletal muscle under voluntary control but not origionated from somite
  5. Segmental arteries
  6. Neuraxis
  7. Nerves (next lecture)
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13
Q

When get a structure what do you initially need to determine?

A
  1. whether it is under conscious (somatic) control or unconscious (autonomic) control
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14
Q

What are afferent and what is efferent signals

A 
Afferent = back towards brain = sensory info. Aff adn S = interchangable
Efferent = motor
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15
Q

What does ectoderm form.
What is ectoderms function and innervation.
What is between each segment? and names

A

It forms outer epithelial covering (skin)
Function = somatic sensation
Innervation = somatic Afferents
1. GAPS
2. Outside gaps = clefts (think between donut)
3. inside = pouches (think within donut)
4. Side of each donut = pharyngeal arch

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16
Q

What is interesting about the ectoderm at the front of the head?

A
  1. It invaginates inwards into segments 1 & 2
  2. Forming Stomodeum (oral opening)
  3. Means that segments 1 and 2 don’t have endoderm
17
Q

What is stomodeal ectoderm

A
  1. An oral plate of tissue where stomodeal ectoderm meets pharyngeal endoderm 2. 2. Location: boundary between segments 2 and 3. This perforates
18
Q

What does endoderm form?

Where is sensation supplied from?

A
  1. Forms inner epithelial covering
  2. Sensation supplied via autonomic afferents - unconscious
  3. Motor function (sym and para) is supplied via autonomic efferents
19
Q

What is lateral Plate mesoderm

A
  1. gives rise to muscle structures (not from somites!) called special visceral muscle
  2. Under conscious control
  3. Innervated by special visceral efferents - only head
20
Q

What are three other componetns of the head

A
  1. Somites
  2. Segmental Arteries
  3. Neuraxis
21
Q

What do somites form in the head?

A
  1. Each segment has a pair of somites
  2. which form striated muscle of the eyeball and tongue
  3. innervated by somatic efferents
22
Q

Why sometimes we go looking for a nerve by there sin’t one?

A
  1. If a certain strucutre disappears completely
  2. Structures that form from these won’t form
  3. no need for a nerve to go to that absence structure
23
Q

What 3 things could happen to a structure?

A
  1. Obliteration
  2. Fail to develop further
  3. Migration (somite 6 and 7)
24
Q

What structures disappear?

A
  1. somites 4 &5
  2. Pharyngeal arch 5 and associated endo, ecto, lateral plate mesoderm, nerves and arterial arches
  3. Arterial arches 1 and 2
  4. Pharyngeal clefts/ pouches 5 and 6
  5. Ectoderm of segments 6 and 7
25
Q

Which structures fail to develop further

A
  1. Ectoderm of arch 2

2. Ectoderm of segments 3-5

26
Q

How does the tongue develop?

A
  1. Invagination of arch 1 = front of tongue is covered by ectoderm
  2. middle tongue derived from endoderm of arch 2 to develop = separation in tongue
  3. Back of T = lined by endoderm = arch 3
    Muscle = migration of somites 6 and 7
27
Q

What do the extrinsic and intrinsic muscles of the tongue do

A
  1. Intrinsic = within tongue

2. Extrinsic attach tongue to head

28
Q

How does the tongue develop?

A
  1. Invagination of arch 1 = front of tongue is covered by ectoderm
  2. middle tongue derived from endoderm of arch 2 to develop = separation in tongue
  3. Back of T = lined by endoderm = arch 3
    Muscle = migration of somites 6 and 7. Conscious control: somatic efferents
29
Q

Where does the Pituitary gland form from

A
  1. Pouch in arch 1
  2. invagination = ectoderm, forms anterior and intermediate pituitary
  3. Posterior pituitary develops fromm brain step
30
Q

Where deo the THyroid gladn develop from?

A
  1. Arch 2 endoderm
  2. Thyroid moved down
  3. Thyroglossal duct = foetal remnant of migration of T gladn from top of arch 2
31
Q

Where do Larynx, Trachea and lungs form from?

A
  1. Depression in floor of arches 4 and 6

2. Lined by endoderm as within mouth

32
Q

What forms from the clefts adn pouches

A
  1. Cleft (outsdie)1 = external ear, boundary = ear drum
  2. Pouch (inside) 1 = middle ear cavity / eustachian tube
  3. Clefts 2-4 disappear
  4. Pouch 2 = palatine tonsil
  5. Pouch 3 = parathyroid & thymus
  6. Pouch 4 = parathyroid, thymus ultimobranchial body
33
Q

How does the ear drum develop

A
  1. Cleft 1 and pouch 1 = no perforation between the 2 = bit of tissue between these two = ear drum
34
Q

What deos the Ectoderm in each segment form?

A
  1. ectoderm 1 = skin top of head
  2. Ecto 2 = rest of skin of head
    - —-> split by eyes
  3. Ecto 3, 4, 5 = small area of skin in external ear
  4. Ecto 6 adn 7 fails to develop
35
Q

What do somites form

A
  1. Skeletal msucle under conscious control
  2. Somites 1-2 = extrinsic muscles of eye
  3. 4 and 5 disappear
    6-7 = muscles of tongue
36
Q

What do somites 1 2 and 3 develop

A 
S1 = all rectus muscles (except lateral rectus) & ventral oblique
S2 = dorsal oblique
S3 = lateral rectus & retractor oculi
37
Q

What forms from the diff arches from the lateral plate mesoderm?

A
  1. Arch 1 (seg 2) = chewing muscles / malleus & incus
  2. Arch 2 (seg 3) = facial muscles / stapes & hyoid
  3. Arch 3 (seg 4) = stylopharyngeus muscle / hyoid
  4. Arch 4 (seg 5) = pharyngeal muscles & cricothyroid muscle / laryngeal cartilages
  5. Arch 5 (seg 6) disappears
  6. Arch 6 (seg 7) = laryngeal muscles / laryngeal cartilages
38
Q

What forms from the diff arches from the lateral plate mesoderm?

A

INNERVATED BY SPECIAL VISCERAL EFFERENT!!

  1. Arch 1 (seg 2) = chewing muscles / malleus & incus
  2. Arch 2 (seg 3) = facial muscles / stapes & hyoid
  3. Arch 3 (seg 4) = stylopharyngeus muscle / hyoid
  4. Arch 4 (seg 5) = pharyngeal muscles & cricothyroid muscle / laryngeal cartilages
  5. Arch 5 (seg 6) disappears
  6. Arch 6 (seg 7) = laryngeal muscles / laryngeal cartilages
39
Q

What are the different nerve fibres in the trunk and head

A
  1. Conscious/ somatic then sensory or motor, afferent or efferent
  2. ## unconscious/ autonomic sensory or motor, afferent or efferentHEAD this PLUS 5th component = special visceral efferent, innervate muscle derived from lateral plate mesoderm

First year semester 2 (50 decks)

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