Neuronal Development Flashcards
What are the 3 stages of human development in utero?
- Pre-embryonic
- embryonic
- Fetal
Stage of development where cell division into two groups of cells are formed: inner cell mass (embryo) and outer cell mass (placenta)
Pre-embryonic
What are the two layers to first form in the inner cell mass? what is the third formed layer?
- Ectoderm
- Endoderm
- Mesoderm
What forms the skin and nervous system?
Ectoderm
What forms the musculoskeletal system?
mesoderm
What forms the deep internal organs?
endoderm
When does myelination of the nervous system begin?
During the fetal stage of development
What are the two phases of development of the nervous system that occur during the embryonic stage of development?
- Formation of the neural tube
2. Formation of the brain
Occurs day 18 after fertilization; Thickening of the ectoderm; forms in the middle; extends from head to tail region
Neural plate; A groove forms in center of neural plate, with folds on either side
What happens on day 22 after fertilization?
The folds of the neural groove grow up and toward each other and become connected, forming the neural tube; begins in the cervical region and “zips” up and down, leaving the ends open; after tube forms, neural crest cells breaks off
Open ends of the neural tube
Neuropores
Rostral neuropore closes by day 24; Caudal neuropore closes by day 26
If they do not close, there will be neurological problems
What happens if the caudal neuropore doesn’t close?
Spina bifida
- Vertebrae do not form normally
- Associated with inadequate folic acid intake by mother
What happens if the rostral neuropore doesn’t close
Anencephaly
- Failure of forebrain to develop correctly (Often brainstem is present)
- Skull does not form over incomplete brain
- Most fetuses die before birth
What aids in the closing of the neural tube?
Folic acid; pregnant women are recommended to take supplement
Neural tube layer that is inside of the tube and made up of cells (gray matter)
Mantle layer
Neural tube layer that is outside of the tube and made up of axons/processes of cells in mantle layer
Marginal layer
The inside space in the tube forms the
ventricular system
In the neural tube, the alar plate (association plate) is _____ and the basal plate (motor plate) is ____
Dorsal; ventral
Where do lower motor neurons develop?
Basal plate
Where do interneurons of sensory systems develop?
Alar plate
Line that divides the alar and basal plates of the neural tube
Sulcus limitans
Added onto neural tube from L5-S5
Secondary neurulation
Cells that separate during formation of neural tube, the cells migrate and form many different types of cells (Neurons, Glia, Non-neuronal cells)
Neural crest cells
What are the neuronal and glial derivatives of neural crest cells?
- Sensory neurons of somatic nervous system
- Sensory neurons of some cranial nerves
- Schwann cells of PNS
- Postganglionic neurons of autonomic nervous system
What are the three primary vesicles of the brain that develop during the 4th week?
- Prosencephalon (forebrain)
- Mesencephalon (midbrain)
- Rhombencephalon (hindbrain)
When do two of the primary vesicles split? which vesicles split? what do they split into?
5th week
- Prosencephalon - Telencephalon, diencephalon
- Rhombencephalon - Metenchephalon, myelencephalon
What are some of the brain structures to describe the adult brain?
- Telencephalon
- Diencephalon
- Mesencephalon
What does the telencephalon form in the brain?
- Cerebral hemispheres
2. Basal ganglia
What does the diencephalon form in the brain?
- Thalamus
2. Hypothalamus
What does the mesencephalon form in the brain?
Midbrain
Does not persist in adulthood; As flexure forms, the walls of neural tube split apart
Pontine flexure
What does the metencephalon form in the brain?
Cerebellum, most of the pons
What does the myelencephalon form in the brain?
Most medulla
What further development of the telencephalon occurs?
- The cerebral hemispheres expand so that they cover the diencephalon
- The hemispheres become C-shaped
- The insula region does not grow as fast, and it becomes covered by the frontal and temporal lobes
- Surface folds to produce gyri and sulci
Where are neurons that divide located?
Next to the ventricles
Where is the gray matter in the cerebral cortex?
outter surface of the brain
How do neurons migrate from next to the ventricles to the outter surface of the brain?
- Sending out processes, then following them
2. follow radial glia
When do neurons differentiate?
Once they reach their location (location can determine differentiation)
What acts as a “feeler” and tells the neuron where to go when neurons send out processes to migrate; samples environments (moves toward attractants, moves away from other chemicals)
Growth cone
When growth cone reaches its target vesicles are produced and synapse forms
What happens to neurons that do not make connections with other neurons or are not active?
They tend to die (esp motor neurons in the spinal cord)
During innervation of muscles; Initially more than one motor neuron innervates each muscle fiber; During development, axons retract so that only one motor neuron innervates each muscle fiber
Axonal retraction
What determines the muscle fiber type?
The nerve that innervates them
When does myelination begin? when is it complete?
4th fetal month; 3rd year of life
- Lower motor neurons – by 1 month
- Projections from motor cortex to spinal cord – 2 years (Babinski reflex)
There may be neurological problems that may not be immediately noticed; These impairments will become observed as the impaired systems become functional; For example, balance or lower extremity impairments may not be observed until a child begins to try to stand and walk
Growing into deficit
What causes the brain to increase in weight from 400 grams at birth to a 3fold increase at 3 years?
- Myelination
- Number of processes
Fully developed brains 1100-1700 grams
What age does brain weight begin to decline?
50’s - normal, brain knows how to work better so brain prunes back more
Times during development that are crucial for normal development and outcomes
Critical periods
When do critical periods occur?
- Neurons are dividing
- Neurons competing for connections
- i.e., vision, language
Herniation of cerebellar tonsils through the foramen magnum; Medulla and pons often small; Initially often have no symptoms but often begin in adolescence and early adulthood (Headache induced by coughing, sneezing, straining; Possible hydrocephalus (block CSF flow); Cranial nerve dysfunction)
Arnold-Chiara Type 1
- If deficits are stable, no treatment
- If deficits are progressing, the bone that is compressing the hind brain can be removed
Malformation of brainstem and cerebellum - extend through foramen magnum; Signs present in infancy; Usually associated with meningomyelocele
Arnold-Chiara Type 2
What are the symptoms of Arnold-Chiara type 2?
- Progressive hydrocephaly
- Paralysis of sternocleidomastoid muscles
- Deafness
- Weakness in lateral eye movements
- Weakness in facial muscles
Effect depends on stage of development; Disrupts neuronal proliferation; Interferes with neurodevelopment processes; Effects more subtle than those of alcohol
Fetal Cocaine Exposure
Non-progressive and permanent disorder; Injury to developing brain (Prenatal, postnatal, or at time of birth); Defined by motor and postural impairments, though may also have sensory and cognitive impairments; Growing into deficit is common
Cerebral palsy
Classification of CP based on tone: velocity–dependent resistance to stretch (faster the stretch, greater the resistance); Damaged neurons next to ventricles (Axons of neurons in cerebral cortex [corticospinal pathways]); Toe Walking; Scissor gait; Associated with premature birth
Spasticity
Classification of CP based on tone: involuntary movement; Damage in basal ganglia; Slow, writhing movements of extremities and/or trunk (athetosis); Poor control of proximal movement; Sustained, intermittent muscle contractions (dystonia)
Dyskinesia
Classification of CP based on tone: lack of coordination; Damage to cerebellum; Lack of coordination; Dysmetria (inability to move a body part the right distance); Weakness; Shaking movements (tremor) during movements
Ataxia
Classification of CP based on tone: reduced muscle tone
Hypotonia
Classification of CP based on tone: lead-pipe resistance to passive stretch (doesn’t matter how quickly you stretch, same resistance occurs)
Rigidity
