Anatomy Practical 3 Flashcards
Define neurulation
Formation and closure of the neural tube
How does neurulation occur?
- notochord induces above ectroderm to thicken and differentiate into the neuroectoderm = neural plate
- neural plate dorsally folds = neural tube
- neuroectoderm converging edges = neural crest cells which line up in 2 columns down the tube
What are the neuropores?
- anterior and posterior on neural tube connecting lumen of neural tube and amniotic cavity
- anterior neuropore forms adult brain
- posterior neuropore forms adult spinal cord
What does the lumen of the neural tube develop into?
Brain ventricles and central canal of the spinal cord
When do the neuropores close?
- anterior closes at 25-26 days
- posterior closes at 27-28 days
What do the neural crest cells become?
Peripheral nerves, endocrine glands, CT and specialized tissue
What do cranial neural crest cells differentiate into?
- neurocranium
- meninges
- CT
- cranial nerves
(enter pharyngeal arches and pouches = thymic cells)
What do the trunk neural crest cells differentiate into?
1) Melanocytes (produce pigment, travel through dermis in ectoderm colonising skin and hair follicles)
2) Migrate to sclerotome = DRG, Sympathetic neurons, PS nerves, adrenomedullary cells, Schwann cells (of gut/abdomen/pelvis)
What is spina bifida?
- most common neural tube defect
- if posterior neuropore does not close
- neurogenetic
- disability extent depends on where spina bifida is and ammout of nerve tissue involved
What does spina bifida include?
- spina bifida cystica (myelomeningocele and meningocele)
- spina bifida occulta (mild, most common, 1 or more vertebrae malformed, small tuft of hair/dimple/birth mark)
What is myelomeningocele?
- most serious form of spina bifida
- sac contains CSF and nerves and spinal cord parts
What is meningocele?
- sac containing CSF and meninges
- less common and less severe
What defects do you get if the anterior neuropore fails to close?
- encephalocele
- anencephaly
What is anencephaly?
- born without parts of brain and skull
- cerebrum fails to develop without skull
- face and neck abnormalities
- 11-14 weeks detected during gestation via US or maternal serum alpha fetoprotein as if high levels of alpha fetoprotein crosses placenta to mother indicates open neural tube defect
- majority stillborn or die with few hours
What is encephalocele?
- herniation of meninges and brain tissue outside cranium
- usually midline
- cranial meningocele = only meninges
- encephalocele = brain tissue
- ventriculocele = ventricle within herniated brain part
How do the brain vesicles form?
- 3 primary at week 4
- 5 secondary at week 5
What are the primary vesicles?
- prosencephalon (forebrain)
- mesencephalon (midbrain)
- rhombencephalon (hindbrain)
What are the secondary vesicles?
- telencephalon
- diencephalon
- mesencephalon
- metencephalon
- myelencephalon
What brain structures come from which secondary vesicles?
- telencephalon (cerebral hemispheres - white matter/cortex/basal nuclei)
- diencephalon (thalamus, hypothalamus, epithalamus, retina)
- mesencephalon (midbrain)
- metencephalon (pons, cerebellum)
- myelncephalon (medulla oblangata)
Which ventricles come from which secondary vesicles?
- telencephalon (lateral)
- diencephalon (third)
- mesencephalon (cerebral aqueduct)
- metencephalon (4th ventricle)
- myelencephalon (4th ventricle)
What is hydrocephalus?
- dilatation of cerebral ventricles
- CSF drained into bloodstream via arachnoid villi
- ventricle dilatation due to blockage of CSF or over-production of CSF
- increased pressure in ventricle
- congenital or acquired later in life via stroke/TBI/tumours/meningitis
- manage: reduce brain pressure and restore normal CSF flow via shunts OR endoscopic third ventriculostomy
What is cerebral palsy?
- group of non-progressive neuromuscular disorders caused by brain damage
- classified by severity, topographical distribution or motor function
- damage to immature brain = vascular, hypoxic-ischaemic, teratogenic, genetic, infection, toxins, metabolic problems, trauma
What makes up the pharyngeal apparatus?
- pharyngeal arches
- pouches
- grooves
- membranes
(develop in week 4, arch and pouch 5 regress)
What are the pharyngeal arches?
- 1-4 and 6 contain mesoderm and neural crest cells
- mesoderm = muscles and arteries
- neural crest cells = bone and CT
- CN associated with each arch
What are the pharyngeal pouches?
- evaginations of endoderm lining the foregut
- oral cavity and oesophagus
- internal
What are the pharyngeal grooves?
- clefts
- invaginations of ectoderm
- between each pharyngeal arch
- external
What are the pharyngeal membranes?
- consist of ecto, meso and endoderm and neural ncrest cells
- between each arch
What CN and structures are derived from arch 1?
CN V
mesoderm = muscles of mastication, mylohyoid
neural crest cells = maxilla, mandible, zygomatic bone, squamous temporal bone, palatine bone, vomer
What CN and structures are derived from arch 2?
CNVII
mesoderm = muscles of facial expression, stylohyoid
neural crest cells = stapes, styloid process, lesser horn of hyoid
What CN and structures are derived from arch 3?
CN IX
mesoderm = stylopharyngeus
neural crest cells = greater horn of hyoid
What CN and structures are derived from arch 4?
CN X
mesoderm = soft palate muscles, pharynx muscles expect stylopharyngeus, cricothyroid
What CN and structures are derived from arch 6?
CN X - recurrent laryngeal
mesoderm = larynx intrinsic muscles except cricothyroid, upper oesophageal muscles, laryngeal cartilages
Where does the digastric muscle originate from?
- anterior belly from the 1st pharyngeal arch
- posterior belly from the 2nd pharyngeal arch
What is microtia?
- congenital deformity
- underdeveloped/absent pinna (external ear)
- conduction deafness
- defect of 1st pharyngeal arch
How does the thyroid gland develop?
- midline of tongue endoderm forms thyroid diverticulum
- migrates caudally anterior to laryngeal cartilages and hyoid bone
- attached to tongue via thyroglossal duct which obliterates = foramen cecum
What is the anterior 2/3 of the tongue derived from?
- pharyngeal arch 1
What is the innervation of the tongue?
- anterior 2/3 (chorda tympani - branch of facial - for special taste sensation and lingual - branch of trigeminal V3 - for general sensation)
- posterior 1/3 (glossopharyngeal for general and special sensation)
What is the posterior 1/3 of the tongue derived from?
pharyngeal arches 2,3,4
What forms the face?
3 swellings
- frontonasal prominence
- maxillary prominence
- mandibular prominence
How does the face develop?
- nasal placodes develop on ventrolateral frontonasal prominence
- invaginate into mesoderm = nasal pits = medial and lateral nasal prominences
- nasolacrimal groove between maxillary prominence and lateral nasal prominence = nasolacrimal duct and lacrimal sac
- intermaxillary segment forms when maxillary prominence pushes 2 medial nasal prominences together at midline
What does the medial nasal prominence become?
- forehead/upper lip/nasal septum/philtrum
Which pharyngeal arch do the maxillary and mandibular prominences emerge from?
- pharyngeal arch 1
What does the intermaxillary segment form?
- philtrum of lip
- 4 incisors
- primary palate
How does the secondary palate develop?
- from palatine shelves of maxillary prominences
- project down then horizontally fusing along palatine raphe
- primary and secondary palates fuse at incisive foramen
- bones develop in primary and anterior part of secondary palate
What is cleft lip?
- failure of maxillary prominence to fuse with medial nasal prominence
- underlying mesoderm fails to expand = persistent labial groove
What is cleft palate?
- palatine shelves fail to fuse with primary palate/each other and nasal septum/both
What are the 5 dilatations along the primitive heart tube?
- truncus arteriosus
- bulbus cordis
- primitive ventricle
- primitive atrium
- sinus venosus
What do the 5 dilatations of the primitive heart tube become?
- truncus arteriosus = pulmonary artery and aorta
- bulbus cordis = smooth part of ventricles
- primitive ventricle = trabeculated ventricles
- primitive atria = trabeculated atria
- sinus venosus = smooth part of right atria, coronary sinus, oblique vein of left atrium
What is dextrocardia?
- when the heart loops to the left rather than to the right
What is situs invertus?
- all organs are mirror imaged
How does the foramen ovale close?
- before birth higher pressure in RA than LA
- neonates take first breath in so lungs expand
- decreased pressure in pulmonary circuit
- LA pressure > RA
- forces septum primum against septum secundum closing foramen ovale
What does the umbilical vein become after birth?
Ligamentum teres
What organs make up the foregut?
pharynx, oesophagus, stomach, proximal duodenum
liver, gall bladder, bile duct, pancreas
How does oesophageal atresia iccur?
- tracheoesophageal septum deviates dorsally favouring the trachea so oesophagus ends as closed tube
What is omphalocele?
extra abdominal herniation with peritoneum
What is gastroschisis?
- extra abdominal herniation without peritoneum covering
- related to Hirschprung’s disease
What is Meckel’s diverticulum?
- remains of embryonic vitello-intestinal duct
- pancreatic and gastric ectopic tissue contains
- 2 inches
- 2 feet from ileocaexcal junction
What is a rectovesical fistula?
- abnormal connection between rectum and bladder
What is a rectourethral fistula?
- abnormal connection between rectum and urethra
What is a rectovaginal fistula?
- abnormal connection between rectum and vagina
What does the nephrogenic cord develop into?
- pronephros
- mesonephros
- metanephros
What is a pelvic kidney?
- kidney fails to migrate cranially
What is a horseshoe kidney?
- 2 metanephric masses fuse
- stuck when ascend at IMA
