CHAPTER 4: Neurodevelopment

BRAIN PLASTICITY

the brain's ability to reorganize itself by forming new neural connections

3 PERIODS OF PRENATAL DEVELOPMENT

Germinal, Embryonic, Fetal

Germinal

• zygote’s rapid cell division

• blastocyst formation

• implantation

Embryonic

organogenesis

Fetal

increased differentiation of body parts and greatly enlarged body size

CELLULAR DEVELOPMENT

1. Fertilization of the ovum and the sperm – zygote

2. Multiplication of the zygote

3. Cells differentiate to become muscle cells, some become multipolar neurons, some become glial cells, and so on.

4. Cells align themselves with the cells around them to form particular structures.

5. Cells establish appropriate functional relations with other cells.

5 PHASES OF NEURAL DEVELOPMENT

-         induction of the neural plate,

-         neural proliferation,

-         migration and aggregation

-         axon growth and synapse formation,

-         neuron death and synapse rearrangement.

neural plate

a small patch of ectodermal tissue on the dorsal surface of the developing embryo.

neural groove

forms when neural plate folds

neural tube

- forms when the lips of the neural groove fuses. The inside of the neural tube eventually becomes the cerebral ventricles and spinal canal

Neural proliferation

• Once the lips of the neural groove have fused to create the neural tube, the cells of the tube begin to proliferate (increase greatly in number).

• Most cell division in the neural tube occurs in the ventricular zone

Ventricular zone

the region adjacent to the ventricle (the fluid-filled center of the tube).

2 major factors govern migration in the developing neural tube

time and location

somal translocation

an extension grows from the developing cell in the general direction of the migration;

glia-mediated migration

Once the period of neural proliferation is well underway and the walls of the neural tube are thickening, radial glial cells appears in the developing neural tube.

Radial glial cells

a temporary network of glial cells

2 Kinds of Cell Migration

Radial migration

Tangential migration

Radial migration

proceeds from the ventricular zone in a straight line outward toward the outer wall of the tube;

Tangential migration

occurs at a right angle to radial migration that is, parallel to the tubes walls.

Aggregation

• Once developing neurons have migrated, they must align themselves with other developing neurons that have migrated to the same area to form the structures of the nervous system.

• Both migration and aggregation are thought to be mediated by cell-adhesion molecules (CAMs), which are located on the surfaces of neurons and other cells

Cell-adhesion molecules

have the ability to recognize molecules on other cells and adhere to them.

Axon Growth

• Once neurons have migrated to their appropriate positions and aggregated into neural structures, axons and dendrites begin to grow from them.For the nervous system to function, these projections must grow to appropriate targets.

Growth Cones

o    amoebalike structure at growing tip of an axon/ dentrite, which extends and retract filopodia.

Filopodia

- fingerlike cytoplasmic extensions as if searching for the correct route

Growth Cones

• The first growth cones to travel along a particular route in a developing nervous system are presumed to follow the correct trail by interacting with guidance molecules along the route.

• Then, subsequent growth cones embarking on the same journey follow the routes blazed by the pioneers.

fasciculation

- tendency of developing axons to grow along the paths established by preceding axons

Synapse Formation (Synaptogenesis)

• Once axons have reached their intended sites, they must establish an appropriate pattern of synapses.

passive process (necrosis)

developing neurons died when they failed to get adequate nutrition.

active (apoptosis)

cell death during development, genetic programs inside neurons are triggered and cause them to actively commit suicide.

Necrotic cells

break apart and spill their contents into extracellular fluid, and the consequence is potentially harmful inflammation usually leading to neurodegenerative disease

apoptotic cell death

DNA and other internal structures are cleaved apart and packaged in membranes before the cell breaks apart. These membranes contain molecules that attract scavenger microglia and other molecules that prevent inflammation

cancer

if apoptotic cell death are blocked, the consequence can be ?

Dopamine

involved in motor control, reward, and motivation

Serotonin

involved in mood regulation.

GABA

regulates neuronal excitability.

Glutamate

primary excitatory neurotransmitter

Acetylcholine

a role in muscle contractions and motor neuron function.

Biological Factors of Neurodevelopmental Disorders

(BEFORE BIRTH)

Genes (Down’s Syndrome, Fragile X Syndrome),

Infections (Toxoplasmosis, German Measles),

Teratogens (alcohol, tobacco, drugs)

Biological Factors of Neurodevelopmental Disorders (During Birth)

Hypoxia, Premature Birth, any birth complications

Biological Factors of Neurodevelopmental Disorders (After Birth)

Head injury, infections, brain tumors. Dysarthria (muscle)

Intellectual Disability

formerly called mental retardation,

•Deficits in intellectual functions, confirmed by both clinical assessment and intelligence testing. An IQ score of 65-75 (70 ± 5)

•Deficits in adaptive functioning that result in failure to meet developmental and sociocultural standards for personal independence and social responsibility. (Conceptual, Social, Practical)

frontal cortex and hippocampus.

brain regions implicated in ID

Communication Disorders

• Include deficits in language (form, function, and use of symbols), speech (articulation and production of sounds), and communication (verbal or nonverbal behavior

basal ganglia

responsible for motor control and the increase of dopamine levels for stuttering (CD)

4 Types of Communication Disorders

CD: Language Disorder

CD: Speech Sound Disorder

CD: Childhood-Onset Fluency Disorder

CD: Social (Pragmatic) Communication Disorder

CD: Language Disorder

• Difficulties in the acquisition and use of language due to deficits in the comprehension or production of vocabulary (aphasia), sentence structure, and discourse.

• Deficits are evident in spoken communication, written communication, or sign language.

• Abilities are substantially and quantifiably below those expected for age

CD: Speech Sound Disorder

- Substituting one sound for another or omitting certain sounds completely

- Speech sound production requires both the phonological knowledge of speech sounds and the ability to coordinate the movements of the articulators (i.e., the jaw, tongue, and lips,) with breathing and vocalizing for speech

CD: Childhood-Onset Fluency Disorder

• Disturbances in the normal fluency and time patterning of speech (stuttering) that are inappropriate for the individual's age and language skills, persist over time

• The disturbance causes anxiety about speaking

CD: Social (Pragmatic) Communication Disorder

• Characterized by a primary difficulty with pragmatics, or the social use of language and communication, as manifested by deficits in understanding and following social rules of verbal and nonverbal communication

• SCD can occur by itself or with other diagnoses

AUTISM SPECTRUM DISORDER

A. persistent impairment in reciprocal social communication and social interaction

B. restricted, repetitive patterns of behavior, interests, or activities

ASD LEVEL 1: Requiring Support

-difficulty initiating social reactions
-organization and planning problems can hamper independence.

ASD LEVEL 2: Requiring Substantial Support

-social interaction limited to narrow special interests

-frequent restricted/repetitive behaviors

ASD LEVEL 3: Requiring Very Substantial Support

-severe deficits in verbal and nonverbal social communication skills

-great distress/difficulty changing action or focus

Structure of the Brain (ASD)

Prefrontal cortex

Orbitofrontal cortex

Amygdala

Temporoparietal cortex

Prefrontal cortex

essential for executive functions and social cognition, shows altered connectivity and activity

Orbitofrontal cortex

involved in decision making and emotional processing

Amygdala

responsible for processing emotions and social behavior, exhibits dysfunction and atypical connectivity,

Temporoparietal cortex

 responsible for social perception and theory of mind,

Autistic Savants

Savants are intellectually handicapped individuals who nevertheless display amazing and specific cognitive or artistic abilities.

Attention-deficit/ hyperactivity disorder

persistent pattern of inattention and/ or hyperactivity-impulsivity that interferes with functioning or development

Symptoms of Attention-deficit/ hyperactivity disorder

Inattention, Hyperactivity, and Impulsitivity

Inattention

as wandering off task, lacking persistence, having difficulty sustaining focus, and being disorganized and is not due to defiance or lack of comprehension.

Hyperactivity

refers to excessive motor activity when it is not appropriate, or excessive fidgeting, tapping, or talkativeness. In adults, hyperactivity may manifest as extreme restlessness or wearing others out with their activity.

Impulsivity

hasty actions that occur in the moment without forethought and that have high potential for harm to the individual

Structure of the Brain (ADHD)

Prefrontal cortex

Limbic System

Basal ganglia,

Prefrontal cortex

plays a crucial role in executive functions like attention, working memory, impulse control, and decision-making

Limbic System

responsible for regulating emotions, motivation, and reward processing,

Basal ganglia

situated deep within the brain, are involved in motor control, habit formation, and cognitive regulation.

3 Specific Learning Disorder

Dyslexia

Dysgraphia

Dyscalculia

Dyslexia

word-reading accuracy, reading rate or fluency, or reading comprehension.

Dysgraphia

spelling accuracy, grammar and punctuation accuracy, legible or fluent handwriting, or clarity and organization of written expression.

Dyscalculia

number sense, memorization of arithmetic facts, accurate or fluent calculations, or accurate math reasoning.

Structure of the Brain (SLD)

Corpus Callosum

Lateral Geniculate

Parietal lobe

Corpus Callosum

communication between the two hemispheres of the brain

Lateral Geniculate

the relay station between the eye and the visual cortex, responsible for visual processing

Parietal lobe

integration of senses

neurodevelopmental motor disorders

developmental coordination disorder,

stereotypic movement disorder, and

tic disorders.

Structure of the Brain (MD)

Primary Motor Cortex

Basal Ganglia

Cerebellum

Thalamus

Primary Motor Cortex

Initiates voluntary movements.

Basal Ganglia

Helps start and smooth out voluntary movements, suppress involuntary movements, and coordinate posture.

Cerebellum

Coordinates movements, maintains balance, and ensures smooth, accurate limb movements.

Thalamus

A relay station for motor and sensory information.

MD: Developmental Coordination Disorder

Difficulties are manifested as clumsiness as well as slowness and inaccuracy of performance of motor skills

• It is diagnosed only if the impairment in motor skills significantly interferes with the performance of, or participation in, daily activities

MD: Stereotypic Movement Disorder

The essential feature of stereotypic movement disorder is repetitive, seemingly driven, and apparently purposeless motor behavior

• Interfere with social, academic, or other activities and, in some children, may result in self-injury

MD: Tic Disorder

sudden, rapid, recurrent, nonrhythmic motor movements or vocalizations.

• An individual may have various tic symptoms over time, but at any point in time, the tic recurs in a characteristic fashion

Tourette’s Disorder

-1+ vocal tics and 2+ motor tics

-longer than 1 year

-no other medical conditions or substance use

Persistent (chronic) motor tic or vocal tic disorder

-motor or vocal tics, but not both

-longer than 1 year

-no other medical conditions or substance use; not TD

-must begin by age 18

-motor tics only or vocal tics only

Provisional Tic Disorder

-motor or vocal tics, or both, in any quantity

-less than 1 year

-no other medical conditions or substance use; not TD; not persistent (chronic) motor tic or vocal tic disorder

-must begin by age 18

4 Types of Tics

COPROPRAXIA

ECHOPRAXIA

PALILALIA

COPROLALIA

COPROPRAXIA

Sexual/obscene gestures

ECHOPRAXIA

Imitating other’s movements

PALILALIA

Repeating last heard word or phrase

COPROLALIA

Obscene, racial, or religious slurs