Chapter 4:Adaptive Reflexes, Brain Development, and Motor Skills
What motor skills are regulated by adaptive reflexes?
1. The palmar reflex occurs when something is placed in the palm of an infant’s hand and the infant
quickly wraps their fingers around the object that touched their palm. Their grip is typically quite
strong (infants can typically hold their own body weight); however, they may release their
fingers/grip quite suddenly. On average, this reflex disappears when an infant is approximately 4-6
- Can’t control, reflex
2. The sucking reflex occurs when something touches the roof of an infant’s mouth. There are two
aspects to the sucking reflex: (1) expression - to express milk from a nipple an infant instinctively
presses the nipple between the roof of their mouth and their tongue, and (2) milking –the infant
instinctively moves their tongue from the areola to the nipple to coax milk from the breast. On
average, this reflex disappears when an infant is approximately 4 months.
3. The rooting reflex occurs when anything strokes an infant’s cheek or corner of their mouth. The
infant will automatically turn their head towards the side that was touched. On average, this reflex
disappears when an infant is approximately 3-4 months.
4. The stepping reflex occurs when the soles of an infant’s feet touch a flat surface. When infants are
held upright with their feet placed on a flat surface, they will lift their legs as if they are marching or
stepping. On average, this reflex disappears when an infant is approximately 8-12 months.
5. The plantar reflex is an infant’s tendency to curl their toes down or away from their shin. On
average, this reflex disappears when an infant is approximately 12 months. How are adaptive reflexes related to brain development and motor skills?
It is widely believed that infants are equipped with adaptive reflexes at birth to enable them to perform
crucial motor skills, which they would otherwise be incapable of performing due to insufficient brain
development. What aspects of brain development are well developed and poorly developed at birth?
Abrief summary of brain development in infancy…
(Relates to IQs for Chapter 3: 4a-c & Chapter 4: 2a-e, 3a)
The human brain has 100-200 billion neurons. As stated in chapter 3, the production of neurons jumps
into high gear between the 10 to 18 weeks of prenatal development (this process is referred to as
neuronal proliferation.As a result of this ‘rapid neuron manufacturing’period, most fetuses have
already produced virtually all of the neurons they will ever produce, by the 28 week of prenatal
development. So if nearly all the neurons are present at birth, why are some sensory skills poorly
developed and why can’t infants perform so many motor skills?
Neurons (unlike other cells in our body) are not tightly packed together.As a result, neurons have tiny
gaps or synapses between each other. These gaps or synapses are necessary to allow neurons to
maximize their ability to connect to and communicate with 100s or 1000s of other neurons. However, in
order for neurons to effectively connect across these gaps, the neuron structure must further develop.
What additional neuron structures must develop to enable neurons to receive information from multiple
neurons and to send information to multiple neurons?
As stated in chapter 3, when neurons travel from the neuron-manufacturing site (in the embryo’s neural
tube) to their final positions in the brain, neurons consist of cell bodies only. However, once neurons are
in their designated place, they begin to differentiate, establishing their unique functions by building
connections with certain neighboring neurons. Two neuronal structures or projections enable neurons to
form connections with other neurons: dendrites and axons. Dendrites bring information (from other
neurons) to the cell body; axons take information away from the cell body (to other neurons).
Consequently, these two projections allow neurons to send and receive messages to one another across
the gaps or spaces between neurons.Although some neurons have already formed synapses between
each other, the production of synaptic connections (or synaptogenesis) dramatically increases during
infancy and toddlerhood. And synaptogenesis or the increase in synaptic connections is due to dendrite
and axon growth.
As neurons form connections with each other, stimulation becomes vital to their survival (that is,
synapses are activity-dependent).