3 - Development and Aging

When does development of the nervous system begin?

Day 18

When does the neural tube begin to develop?

Day 21

When should the neural tube be completely closed?

Day 24

When does neural tube begin to form the fore-, mid-, and hindbrains?

Day 28

What does the forebrain eventually become?

cerebral hemispheres, thalamus and the hypothalamus.

The midbrain does not change significantly after prenatal development.

True

What does the hindbrain eventually become?

pons, cerebellum, medulla and the spinal cord

Migration

Neurons move into their proper location

Differentiation

Cells acquire as specific function and structure

What neurological disorders are associated failure of cells to differentiate?

Fetal alcohol syndrome and Down syndrome 

Myelination

Occurs by oligodendroglia cells in CNS and Schwann cells in PNS

When does myelination begin and when is it MOSTLY complete?

Begins around 20 weeks gestation and is mostly complete at 2 years

What part of the brain is the last to myelinate and when does this occur?

The prefrontal cortex and around early adulthood (early to late twenties)

Synaptogenesis

The process of synapse formation that takes place throughout life

• Synapses are strengthened through firing (or use)

• Neural pathways that are not fired (or used) do not form synaptic pathway

• Early life is a critical period of where many synapses are created

At birth, cranial nerves for smell and taste are fully myelinated, but the optic nerves are not.

True

At birth, cranial nerves used for sucking and swallowing are myelinated, but other motor pathways are not.

True

How does aging affect the brain?

• Brain shrinks and myelin thins (synaptic function is less effective)

• Less synapses, postsynaptic receptors, and dendrites

• Substantia nigra secretes less dopamine (50%) between 20-60 yo

• Blood flow decreases (23%) between 33 and 61 yo

Anencephaly 

Results from incomplete closure of the cranial end of the neural tube

Spina bifida occulta

Occurs with the spinal cord and cauda equina develop normally and are covered by skin, but the neural arches are incomplete

Spina bifida cystica

Occurs when the vertebral arches fail to develop and a large sac of meninges protrudes from the back

Epilepsy

A brain disorder characterized by repeated seizures (generalized or partial)

• Brain becomes overexcited and fires random APs

• Causes: genetics brain disorder, head trauma, tumors, strokes, CP

Status Epilepticus

Toxic effects of overactivity and overheating

• Can result in death

• A generalized seizure that lasts over 30 mins or more

• This is a medical emergency

Periventricular leukomalacia 

Damage to the white matter next to the lateral ventricles that is caused by a lack of blood flow or decreased oxygen in the blood

• Can cause motor deficits that affect the lower extremities

Intraventricular hemorrhage

Bleeding into the ventricles of the brain

• Results in varying degrees of motor impairment depending on the extent of the bleeding

• Typically occurs before 30 weeks of gestation

Cerebral Palsy

Nonprogressive motor disorder that occurs prenatally, during the birth process, or shortly afterwards

• Causes: infection, lack of oxygen, intraventricular hemorrhage, premature birth, and brain injury

• Classified by the type of motor dysfunction despite presence of other impairments such as sensation, language and cognition

Spastic CP

• Lesion: UMN

• Motor S/S: Spastic paralysis

• Nonmotor problems: Impairments in sensory, vison, and hearing languages, problems, cognitive, and musculoskeletal 

Athetoid CP

• Lesion: Basal ganglia

• Motor S/S: Writhing movements

• Nonmotor problems: Impairments in sensory, vison, and hearing languages, problems, cognitive, and musculoskeletal 

Ataxic CP

• Lesion: Cerebellum

• Motor S/S: Ataxic

• Nonmotor problems: Impairments in sensory, vison, and hearing languages, problems, cognitive, and musculoskeletal 

Mixed CP

• Lesion: Mixture of motor areas

• Motor S/S: Spastic paralysis

• Nonmotor problems: Impairments in sensory, vison, and hearing languages, problems, cognitive, and musculoskeletal 

Down Syndrome

Genetic disorder that results from the presence of a 3rd copy of chromosome 21

• Includes: disability and hypotonia

• Smaller brains, fewer cortical neurons, and abnormally dendrites

• Cerebellum contains many undifferentiated cells

Autism

Pervasive development disorder

• Characterized by social interaction and communication

• Some people display stereotypical, repetitive behavior patterns and some cognitive impairments

• Brain produces less serotonin than normal

• Can have issue with movement (due to cerebellum)

Hydrocephalus 

•  Results from blockage of flow of CSF through the ventricles and subarachnoid space 

• Swelling of the brain ventricles causes compression and damage to neural tissues

• May occur in combination with spina bifida or Arnold-Chiari malformation

What is the relation between nutrition, exercise and cognitive function?

• Fitness is associated with better cognition, achievement and behavior, and fatness with worse scores

• Executive function, mathematics and reading achievement, and parent ratings of child behavior were related to fitness and fatness.

• The same is generally true for older adults (exercise can prevent or reduce age-related cognitive loss)