Development Of The Nervous System Flashcards
(28 cards)
What is Gastrulation?
Gastrulation aka Distinction (cell fate)
- Begins as the local invagination of a subset of cells in the early embryo
- Divides embryo into three distinct germ layers (ectoderm,mesodermal,endoderm)
- Defines the midline to create the basic body axes
-> Formation of the notochord:determines direction (like a compass,nautical) (mesodermal cells; transient structure)
-> Neuroectoderm: Origin of the entire nervous system
What are the three germ layers and what do they form?
Ectoderm: skin and nervous system (neuroectoderm)
Mesoderm: muscle, connective tissue, and the cardiovascular system (and skeleton but not skull)
Endoderm: majority of internal organs
What is neurulation?
- Process defined by the development of the neural plate and ultimately the neural tube
- Notochord tells ectoderm to turn into neuroectoderm (origin of nervous system)
- Neuroectoderm thickens and becomes the neural plate
- Neural plate folds around the edges (neural folds)
- Folds form a tube (neural tube)
-> Adjacent mesoderm subdivides into somites (precursor for the axial musculature and skeleton)
-> NEURAL TUBE, adjacent to somites, DEVELOPS INTO SPINAL CORD
-> Neural crest cells give rise to the sensory and autonomic (sympathetic) ganglia (PNS)
-> Anterior neural fold will develop into the BRAIN
What do somites give rise to ?
Dermatomes and Myotomes
Dermatomes: area of skin derived by a somite and innervated from a single spinal nerve
Myotomes: group of muscles derived from a single somite and innervated by one spinal nerve
C5 Myotome: Action Tested and Muscle
Action to be tested
- Shoulder abduction and shoulder flexion
Muscle
- Deltoid
C5, C6 Myotome: Action Tested and Muscle
Action to be tested
- elbow flexion
Muscle
- Biceps
Action to be tested
- wrist extension
Muscle
- extensor carpi radialis longus
- extensor carpi radialis brevis
C7 Myotome: Action Tested and Muscle
Action to be tested
- elbow extension
Muscle
- triceps
Action to be tested
- wrist flexion
Muscle
- flexor carpi radialis
- flexor carpi ulnaris
C8 Myotome: Action Tested and Muscle
Action to be tested
- Ulnar deviation
Muscle
- flexor carpi ulnaris
- extensor carpi ulnaris
T1 Myotome: Action Tested and Muscle
Action to be tested
- digit abduction/adduction
Muscle
- Interossei
L2 L3 Myotome: Action Tested and Muscle
Action to be tested
- hip flexion
Muscle
- Iliopsoas
L2 L3 L4 Myotome: Action Tested and Muscle
Action to be tested
- Knee extension
Muscle
- Quadriceps
L4 Myotome: Action Tested and Muscle
Action to be Tested
- ankle dorsiflexion
Muscle
- tibialis anterior
L5 Myotome: Action Tested and Muscle
Action to be tested
- great toe extension
Muscle
- extensor hallucis longus
S1 Myotome: Action Tested and Muscle
Action to be tested
- Plantarflexion
Muscle
- Gastrocnemius
Action to be tested
- ankle eversion
Muscle
- fibularis longus
- fibularis brevis
What are the Neural Tube defects on the cranial (rostral end)?
Anencephaly
- Absence of all or most of the brain without closure of the skull
Hydraencephaly
- Absence of cerebral hemispheres or cerebral cortex (replaced with CSF)
- Skull and meninges may or may not be intact
Encephalocele
- Skull defect with partial protrusion of the brain (frontal or occipital)
What are the Neural Tube defects on the Spinal (caudal end)?
Spina Bifida
- Defect in the closure of the spinous process or processes
What is spina bifida occulta?
Spina Bifida occulta
- Absence of laminate or spinous process
- Spinal cord, meninges, and CSF CONTAINED in spinal canal
- Mildest form; high incidence of tethered spinal cord
- Typically, does not cause neurological impairments
What is spina bifida meningocele?
- No lamina or spinous process/processes
- Spinal cord contained within the spinal canal
- Protrusion of the meninges and CSF OUTSIDE of the spinal canal
What is spina bifida myelomeningocele?
- No lamina or spinous process/processes
- Protrusion of the spinal cord, meninges, and CSF OUTSIDE of the spinal canal
- Most common form
What co-morbidities are associated with Myelomeningocele?
Hydrocephalus
- Accumulation of CSF in the ventricles leading to increased intracranial pressure
- Congenital or acquired
Arnold-Chiari Malformation
- Displacement of the brainstem and cerebellar tonsils beyond the foramen magnum
- Resultant disruption of CSF (cerebral aqueduct/4th ventricle); “obstructive hydrocephalus”
What is neuronal migration in the PNS?
- Neural crest cell differentiation guided by signaling molecules along the migratory path or target destination
Neural crest cells
- ANS, enteric and sensory neurons
Non-neuronal cells of the neural crest
- Melanocytes (pigment cells)
- Chromaffin (adrenal gland cells)
Where does Neurogenesis occur?
Occurs in the ventricular zone
- Innermost cell layer surrounding the lumen of the neural tube
- Contains precursor cells
Precursor Cell Division
- Produce new stem cells OR
- Neuroblasts (immature nerve cells)
Precursor cells disappear in most brain regions following birth
What is neuronal migration in the CNS?
- Guided predominantly by glial cells
Ex: Cortical projection neurons (pyramidal cells) - Neuroblast migrate from ventricular zone to cortical plate via radial glia
- Radial glial guide neurons to their final destination (“inside out migration”)
Describe Neuroblast Development
- Outgrowth of processes occurs shortly after Neurogenesis
- Cellular polarization distinguishes the dendrites (transduction) from the axons (secretion)
- Neurites initially form -> axon defined over time with remaining processes developing into dendrites
-> Axonal growth will lead to target tissue
