Nervous & Sensory System Changes Flashcards
Neurulation
formation of the neural tube
Neurulation depends on
presence of the notochord (porition of mesoderm under what will become the neuroectoderm)
Neurulation Steps
- Notochord becomes neuroectoderm/neural plate
- Neural tube forms (lateral edges of neural plate fold up toward eachother)
- Neural tube detaches from ectoderm layer, leaving neural crest
Neural crest is precursor to
PNS, sensory ganglia & autonomic ganglia
Autonomic Ganglia is precursor to
spinal cord & brain
- vesicle formation
- ventricles & spinal cord
sulcas limitans
as the walls of the neural tube thicken, sulcas limitans develops and divides neural tube into ventral and drorsal portions (spinal cord-midbarin)
Dorsal region (after division of sulcus limitans)
=alar plate; mediates sensory (afferent) information
Ventral region (after division of sulcus limitans)
= basal plate; mediates motor (efferent) information
Defects of neuralization are charaterized by:
failure of the neural tube to close at either end (anterior/cephallic or posteriorly/caudal)
Posterior neuropore does not close =
spina bifida
Anterior neuropore does not close =
Ancephaly
3 zones of cell proliferation
- Germinal matrix zone
- Intermediate zone
- Marginal zone
Germinal matrix zone
a. lines the lateral ventricles and central canal
b. site of cell proliferation (MITOSIS) - neuroblasts & glioblasts
c. eventually form epithelium (ventricles) and chroid plexus (CSF)
Intermediate zone (mantle)
a. cells from GMZ migrate to intermediate zone (post-mitotic)
b. eventually form functional layers in spinal cord, brain stem, cerebellum, cortex
c. eventually becomes grey matter
Marginal zone
Eventually will become white mater - made up of axons from the intermediate zone
Cell migration, aggregation, and differentiation
Neurons migrate to a specific location based on the functions they will perform
What helps guide early migration
Thyroxin & glial cells
In what zone do axons with similar functions bundle to form tracts
marginal zone
Disorders of migration/differentiation
Dyslexia, seizure disorder, agenesis of corpus collosum
When axons migrate toward a target, they must make a ___ to survive
synaptic connection
- axons that dont make connections die off
- axons that make synpases but are not needed also die off
Survival of the fittest concept (synpases)
several axons synapse on a single muscle cell, but only one can innervate, others retract; this improves the quality of movement
Competition concept (synpases)
Axons of neurons supporting function of target site are ones to survive even if several axons synapse at target
when do dendrites form
after axon nears target
Myelination =
insulation of long axons; improves conduction velocity
-begins in 4th gestational month and continues after birth
Gyri and sulci
- form by 8 fetal months
- increase SA without increasing the volume needed
Throughout gestation the brain undergoes a
rapid increase in size and weight
Anterior portion of the forebrain growth
- eventually becomes the cerebral hemisphere
- expands so much that it enevelopes the diencephalon; this is why the thalamus and hypothalamus are located deep in the cortex
Brain expands ventro-laterally to form
-temporal lobe curving into a “C” shape
Increase in brain size esp. prevalent in
first 2 years
3-10 months
associated with functional skill development and gross motor skills (walking)
15-24 months
associated with development of language
dendritic branching/formation is impacted by
experience
High levels of ___ reflect growth, capillary network formation, synpatic formation
glucose metabolism
-high in infancy and remains high through childhood (3-9 years)
By age __, size and relationship of parts resemble adult brain
2
MRI studies 7-16 year olds
- increase white matter decrease grey mater in parietal lobes
- increase white mater in occipital lobe
- decrease grey mater in temporal lobe
- associate with cognitive tasks: verbal learning, organization, attention, concentration
Studies for 12-30 year olds
Maturation in frontal lobe and striatal structures (internal capsule, arcuate fibers)
Organization critical periods continue until
shortly after birth
Rapid growth of dendrites and synapses in:
first 2 yeaars
When do synaptic and dendritic density reach adult density
late adolescence
synapse and dendtritic development continue into adulthood in response to:
experience/practice - LEARNING
Myelination is most active from
prenatal –> first year of life
myleination continues to:
about 40 years of age with last intracortical connections becoming myelinated
Anatomical brain changes in older adult
- Decrease in brain weight and volume: primary in frontal and temporal lobes (amygdala - emotions and hippocampus- working memory)
- atrophy of neurons
- Neuronal loss associated with Parkinson’s and Alzheimers
- Enlargement in ventricles
-accelerated in 70s-80s
Cellular changes in older adult brain
- Loss of white matter: related to axon and myelin degeneration- may lead to reaction time changes
- Dendrite degeneration- impacts neural plasticity
- Senile plaques - occurs to a greater extent with Alzheimers
- Neurofibrillary tangles - bundles more pronounced in Alzheimers
- decreased neurotransmission - decreased receptor sites, decreased sensitivity of receptors, decreased amount of neurotransmitter
- free radicals - cause breakdown of cellular structure
- brain generates more free radicals than other tissue in the body
Infant development: meylination of the corticospinal tract primarily occurs from
8mons gestation through the 1st year of life
How does myelination affect the types and quality of movement observed in an infant
during the time of myelination of the corticospinal tract we see the greatest development in gross & fine motor skills
ex: walking, crawling
How does diet and nutrition contribute to the development of Nervous system during infancy
glucose, fats, and lipids important for the development of the nervous system
Brain growth spurt times
6-8
10-12
18
Corticopsinal tract becomes morphologically mature at
10
Corticospinal tract becomes electrophysically mature at
13
*although the structure of the tract is adult like in its connections and anatomical configurations, it does not yet exhibit adult levels of neurotransmission
Effects of feedbaack on motor performance in kids vs adults
Adults show higher error scores with 100% feedback compared to 62% feedback
Children show lower error scores with 100% feedback versus 62% feedback
Specific changes in older adulthood/aging
atrophy of both white and grey matter; these structural changes have been associated with an increase in reaction time for the initiation of complex motor tasks
How would age related changes affect the performance and safety of the older adult?
-what to do as the PT
poor reaction times = driving dangers, increased falls
- As the PT: think MAINTAIN & ACCOMODATE; you cannot necesarily change the neuroplasticity of an older patient
Prenatal development: TOUCH
- mouth
- body
- top of head
Mouth: 7-8 weeks
Body: 17 weeks
Top/back of head: does not develop as soon - decreased sensitivity necessary during birthing process
Vestibular development
semicircular canals; 9-10weeks - can react in change in position
Special senses development
Sight - light perception: 6 months gestation
Hearing: 24 weeks gestation - consistent response to sound at 28 weeks gestation
Goals of postural orientation in prenatal development
- head vertical
2. eyes horizontal
Focal distance of a new born
7-10 inches
Newborns can detect temp changes up to
5-6 degrees
Touch development infancy-toddler
- can localize 7-9mons
- specific location: 12-16 months
Auditory development infant-toddler
- myelination occurs 1mon after birth
- turns to sounds at approx 3 months
Vision development infant-toddler
- colors at 2 months (red and yellow); 4 months (all colors)
- tracking develops from 2mons - 6 mons
- binoccular vision begins at 3 months - takes 2 yeas to develop
Kinesthesia develops from
5-12
Accuity develops at
8 yo
Memory develops at
12 yo
Vestibular development in childhood-adolescence
Maturation complete 10-14
Sensitivity decreases at 2.5 yo through puberty
children and adolesence main take away
need stability before mobility
-think of graph: use of vestibular input to minimize postural sway
Child and adolesence vision
- 5-10 refining ability to track moving object
- figure/ground perception at 8yo
- adult level depth perception at 12
3-4 years spatial awareness
can perceive dichotomous relationships (top/bottom, over/under)
5 years old spatial awareness
develop laterally (right vs left)
6-12 year old spatial awareness
develops directionality (laterality and spatial awareness)
6 yo spatial awareness
mirrors/intimidates movements
7 years old spatial awareness
body is point of reference to objects (ball is in front of me)
10 years old spatial awareness
can determine right and left of a person facing them
12 year old spatial awareness
orientation within the environment (sun sets in west)
touch, temp, pain, vibration senses in older adult
function deceases - related to decreased number of receptors (Pacinian corpscles and meissners corpuscles)
begin to lose vibration sense at:
50 y.o
- related to # of pacinian corpuscles
- nerve conduction velocity
- seen in LEs
temp & thermoregulation older adult
temp receptors decrease - less sensitive
hypothalamus changes - difficulty with regulation
vestibular changes older adult
A. > 75 y.o = 40% decrease in myelination of vestibular nerve fibers
B. loss of hair cells
C. Results in loss of dynamic balance
Hearing changes older adult
A. Presbycusus- decreased acuity (esp for high frequency tones)
- can begin at 30 yo
- changes in both ear and cortical processing
Taste and smell changes in older adult
-decline with age: impacts nutrition
Vision changes older adult
- vision acuity increases - age 40, begins to decrease by 60; by 85 = 80% loss
- cataracts form > 30 y.o ; 33% of all 80 y.o have fully developed cataraacts
- color discrimination decreases (esp. green-blue)
- glare more of a problem
- difficulty with low levels of light (pupil size decreases - less light into eye)
- difficulty with bright lights/sudden changes of light - due to retinal sensitivity
- decreased depth perception - decreased contrast sensitivtiy
- dark adaptation takes longer
- presbyopia - diminished ability to focus on reading distance
- thickening of lens; changes in cilary mm activity
