Reflex Behaviors

The Brain and Reflex Behaviors The growth of the brain is a lifelong process fundamental to physical, cognitive, and emotional development.
Building of the brain The functions of the brain and the reflexes derive from the central nervous system. The central nervous system is located in the brain and the spinal cord, which is a bundle of nerves running through the backbone. The nervous cord in spine then branches out into a peripheral network of nerves extending to every part of the body. The brain then sends nerve signals or commands to specific parts of the body. The brain at birth is only about one-fourth to one third of its eventual adult size. The brain growth occurs in different stimulated moment called brain growth spurts.
At three weeks after conception the brain gradually develops from a long hollow tube into a spherical mass. The brain stem which is responsible for basic functions like breathing, bodily temperature, heart rate, sleep-wake cycle, has nearly finished growing. The Cerebellum which is the part that maintains balance and motor coordination grows fastest on during the first year of life. The cerebrum which is the largest part of the brain is separated into right and left hemispheres. Each hemisphere specializes in something. This specialization in hemispheres is called lateralization. The left hemisphere is mainly responsible for language and logical thinking. The right side is concerned with visually and spatial functions, like drawing or map reading. These two hemispheres are joined by a thick layer call the corpus callosum, allowing them to share information and coordinated commands. The brain is finally adult size at age 10. Each cerebral hemisphere has four lobes or sections, frontal, occipital, parietal, and temporal lobes, which control different functions that develop at different rates. The cerebral cortex which is the outer surface of the cerebrum oversees the functions of vision, hearing, and other sensory information; this section grows rapidly, and is mature at 6 months. * The frontal cortex is responsible for abstract thought, mental associations, remembering, and deliberate motor responses. * The temporal lobe is responsible to regulate emotion and receive sensory input. * The occipital lobe is the section of the brain that converts nerve impulses from the eyes into images. * The parietal lobe is associated with perception of stimuli such as pain and touch

The brain growth spurts that begins at about the third trimester of gestation (the period during which an embryo develops) and continues till the fourth year of life. It is important for the neurological functioning development. Smiling, babbling, crawling, walking, talking are ALL major sensory motor and cognitive milestones of infancy and toddlerhood.

Brain cells The brain is composed of two different types of cells, neurons and glials. Neurons, also known as nerve cells, send and receive information. Glial cells nourish and protect neurons. An estimated 250.000 immature neurons are produced through mitosis, at the beginning of the second month of gestation.
Neurons are composed of DNA. Most of the neurons in the cortex are in place by 20 weeks of gestation and its structure becomes fairly defined during the next 12 weeks. Once they are in a place neurons sprout dendrites and axons, which are narrow, branching fiber like extensions, axons sand signals to neurons and dendrites receive messages through the synapses (the nervous system’s communication links).A neuron can have from 5,000 to 100,000 synapse connections to and from the body sensory
receptors. The multiplication of dendrites and synaptic connections account for much of the growth of the brain in the first two and a-half years, and permits the emergence of new perceptual, cognitive, and motor abilities. When the neurons multiply, migrate to their assigned locations, and develop connections they undergo the complementary process of integration and differentiation. Integration is the process by which neurons coordinate the activities of muscle groups. Differentiation is the process by which cells take on certain specialized, structures and functions. In brain development cell death is the elimination of excess brain cells to achieve more efficient functioning. This is so there can be an efficient nervous system. Only about a half of neurons being produced survives and functions in adulthood. Neurons die, but other may continue to form during life.
Myelination
Myelination is a process where glial cells coat neural pathways with a fatty substance called myelin that enables faster and smoother communication between cells. This shows the achievement of mature functioning. Myeliantion begins about halfway through gestation in some parts of the brain and continue into adulthood in others. For example, the pathways related to the sense of touch are myelinated by birth, which is the first sense developed, because the baby must recognize when he feels a nipple or a bottle he/she’s reflex would be to start sucking, so they can eat. Another example would be that since myeliantion of visual pathways are slower to mature, it begins at birth and continues during the first five months of life. Hearing pathways may begin as early as five months, but the process is not complete until age 4. Myelination basically has to do with how signals are sent throughout the body, which make reflexes possible. Myelination helps senses develop at a right pace. Some myeliantions go on for just a few months after birth, but other like myelination of hippocampus, which has to do with memory stops at age 70. Myelination of sensory and motor pathway before birth in the spinal cord and after birth in the cerebral cortex may account for the appearance and disappearance of early reflexes.
Early reflexes Reflex behaviors are automatic involuntary, innate responses to stimulation. Human infants have an estimated 27 major reflexes, many of which are present at birth or soon after. Examples of types of reflexes are involuntary reflexes, also called reflex behavior which is controlled by the lower brain centers. Other examples are primitive reflexes, postural reflexes, and locomotors reflexes * Primitive reflex: sucking, rooting for the nipple. * Moro reflex: response to being startled * Postural reflex: reaction to changes in position or balance * Locomotor reflex: walking, swimming, do not appear until months after the reflexes have disappeared.

Involuntary reflexes disappear after six to twelve months. Protective reflexes such as blinking, yawning coughing sneezing, shivering and dilation of the pupils in the dark, remain. The unneeded reflexes that disappear have been partially myelinated, shifting to voluntary behavior.

Molding the Brain: The Role of
Experience

Even though the brains development may be genetically directed, it is continually modified by positive and negative environmental experiences. The term for this is malleability, or modifiability, of the brains plasticity.
Plasticity is the molding of the brain through experiences, as well as learning. Plasticity is an evolutionary mechanism to adapt to environmental change. Early experience can have lasting effects on the capacity of central nervous system to learn and store information. If the working connections of some section are not used from early, they can shut down forever. For example a monkey which was raise to 6 months old with one close eyelid was permanently blind in that eye. There apparently was loss of working connections between that eye and the visual cortex. Thus, if cortical connections are not made from early, these circuits may shut down forever. Ethical constrains prevent controlled experiments on the effects of environmental deprivation on human infants. Most of the 2-3 year old children in Romania did not walk or talk; whereas the older children played aimlessly. PET scans of their brains showed extreme inactivity in the temporal lobes, which regulate emotion and receive sensory input. It may also take early environmental simulation to fully overcome the effect of extreme deprivation.