Physical Growth and Aging Across the Life Span

Sensory Development in Infancy

  • Infants' sensory abilities are surprisingly well-developed at birth or shortly after.

  • They can see depth and motion, distinguish colors and patterns, localize and discriminate sounds, and recognize the sound and smell of their mother.

  • Infants are sensitive to pain and largely use touch to explore their world.

    • Studies indicate newborns respond to even mild electric shock, showing increased heart rate, facial grimacing, and crying.

  • Touch is one of the most highly developed sensory systems in the newborn.

    • Reflexes such as the Babinski reflex (fanning out toes when the foot is stroked) illustrate the responsiveness to touch.

Motor Development in Infancy and Childhood

  • Infants are born with reflexes that help them adapt and protect themselves.

    • These reflexes include rooting, sucking, stepping, and grasping.

  • These reflexes may form the foundation for future, more complex behaviors.

    • For example, the stepping reflex may relate to later walking.

  • Brain growth is rapid during the preschool years, and lateralization (specialization of brain hemispheres) develops.

  • Infants show some ability to coordinate movements of their limbs by 3 months and make advances in fine motor skills.

  • By age 3, children show advances in their fine motor skills

    • They can copy figures, draw shapes, and manipulate small objects with increasing dexterity.

Reflexes in Infants

  • Reflexes are unlearned, organized, involuntary responses that occur automatically in the presence of certain stimuli.

  • Rooting Reflex: Present for 3 weeks. The neonate turns its head towards things that touch its cheek. Facilitates food intake.

    • An infant will turn its head and open its mouth to follow and "root" in the direction of a touch on the cheek or mouth.

  • Stepping Reflex: Present for 2 months. Movement of legs when held upright with feet touching the floor. Prepares infants for independent locomotion.

    • Though it disappears after a couple of months, it can be revived if the infant is put on a treadmill.

  • Swimming Reflex: Present for 4-6 months. Infant's tendency to paddle and kick in a swimming motion when lying facedown in water. Helps in avoidance of danger.

    • An infant placed face down in water will automatically start paddling and kicking, holding their breath.

  • Grasping Reflex: Present for 5-6 months. Infant's fingers close around an object placed in its hands. Provides support.

    • If an object is pressed into the palm of an infant, the fingers will reflexively curl around it.

  • Moro Reflex: Present for 6 months. Activated when support for the neck and head is suddenly removed. The arms thrust outward and then appear to grasp. It useful for monkey babies, who travel about by clinging to their mothers’ backs.

    • A sudden loud noise or lack of support will cause the infant to extend their arms and legs outward, arch their back, and then bring their arms back together as if grasping something.

  • Babinski Reflex: Present for 8-12 months. An infant fans out its toes in response to a stroke on the outside of its foot. Unknown function.

    • When the sole of the foot is stroked from heel to toe, the infant will spread their toes out.

  • Startle Reflex: Remains in different form. An infant, in response to a sudden noise, flings out its arms, arches its back, and spreads its fingers. It serves as protection.

    • A loud or sudden noise will cause the infant to throw back their head and extend their arms and legs.

  • Eye-blink Reflex: Remains. Rapid shutting and opening of eye on exposure to direct light. Protection of eye from direct light.

    • In response to bright light or a sudden puff of air, the infant will blink.

  • Sucking Reflex: Remains. Infants’ tendency to suck at things that touch its lips. Facilitates food intake.

    • Touching the roof of an infant’s mouth will trigger them to suck.

  • Gag Reflex: Remains. An infant’s reflex to clear its throat. Prevents choking.

    • A reflex to prevent the infant from choking.

Brain Development

  • Billions of connections form immediately after birth, and the brain shows plasticity (modifiability due to experience).

    • Early experiences can significantly influence brain structure and function.

  • Brain development enhances certain capabilities partly by pruning unnecessary neurons (synaptic pruning).

    • Synaptic pruning refines neural circuits, making the brain more efficient.

  • A baby’s brain triples its weight during their first 2 years of life, and it reaches more than three quarters of its adult weight and size by age 2.

  • Myelin, a fatty substance, insulates neurons and speeds nerve impulse transmission.

    • Myelination improves the efficiency of neural communication.

  • Myelination of the reticular formation (associated with attention and concentration) is completed by age 5.

    • This allows for better sustained attention spans in preschool children.

  • The corpus callosum, connecting the two brain hemispheres, thickens, developing as many as 800 million individual fibers.

    • Enhanced communication between hemispheres supports complex cognitive tasks.

  • Lateralization, where certain functions are located more in one hemisphere than the other, becomes pronounced during the preschool years.

    • Language processing is typically lateralized to the left hemisphere.

  • The left hemisphere processes data sequentially, while the right hemisphere processes it in a more global manner.

  • Sensitive periods exist during which environmental stimulation is crucial for development; deprivation can lead to lasting deficits.

    • These periods highlight the importance of early intervention for children at risk.

Neurons and Neural Connections

  • Infants are born with 100 to 200 billion neurons.

  • Neurons communicate via chemical messengers called neurotransmitters across synapses.

    • This electrochemical communication enables all brain functions.

  • Synaptic pruning eliminates unused neurons to allow established neurons to build more elaborate communication networks.

    • This process increases the efficiency of neural pathways.

  • In adulthood, a single neuron can have a minimum of 5,000 connections to other neurons.

Fine Motor Skills Development

  • 3 Months:

    • Opens hand

    • Holds on to rattle

  • 8 Months:

    • Grasps with finger and thumb

  • 11 Months:

    • Holds crayon

  • 16 Months:

    • Puts pegs in board

  • 24 Months:

    • Imitates lines on paper

  • 33 Months:

    • Copies figures such as a circle

Ages 3, 4, and 5 show additional fine motor development with skills increasing in intricacy.

Handedness

  • Most children show a clear preference for the use of one hand over the other (handedness).

    • This preference is typically established by age 3 or 4.

  • The word sinister is derived from a Latin word meaning “on the left.”

Toilet Training

  • Children have no bladder or bowel control until the age of 12 months and only slight control for 6 months after that.

    • Physiological readiness is essential for successful toilet training.

  • Some children show signs of readiness for toilet training between 18 and 24 months, some are not ready until 30 months or older

    • Readiness signs include staying dry for longer periods, showing interest in the toilet, and being able to follow simple instructions.

Gross Motor Skills

  • By age 3, children have mastered jumping, hopping on one foot, skipping, and running.

  • By ages 4 and 5, their skills have become more refined as they have gained greater control over their muscles.

    • Four year olds can climb stairs alternating feet, and 5-year-olds can often skip and hop with ease.

  • By age 4 they can throw a ball with enough accuracy that a friend can catch it

    • They can also typically catch a bounced ball.

  • by age 5 they can toss a ring and have it land on a peg 5 feet away.

  • Boys can typically throw a ball better and jump higher

  • Girls and boys differ in several aspects of gross motor coordination. In part, this difference is produced by variations in muscle strength, which is somewhat greater in boys than in girls

    • Cultural expectations and opportunities for practice also contribute to these differences.

Physical Growth in Preschool and Middle Childhood

  • By age 2, the average child weighs 25 to 30 pounds and is close to 36 inches tall.

  • By the time children are 6 years old, they weigh about 46 pounds and stand 46 inches tall.

  • The eustachian tube in the ear changes its orientation, which may cause earaches.

    • This change can make children more susceptible to ear infections.

Physical Changes in Adolescence (Puberty)

  • Puberty begins when the pituitary gland in the brain signals other glands to produce sex hormones (androgens or estrogens).

  • Girls' growth spurt begins around age 10, and boys' starts around age 12.

  • The Changes of Sexual Maturation During Adolescence

Sexual Development

  • Menarche: the onset of menstruation

  • Spermarche: A male’s first ejaculation

  • Primary sex characteristics are associated with the development of the organs and body structures related directly to reproduction

    • This includes the growth of the testes and ovaries.

  • Secondary sex characteristics are the visible signs of sexual maturity that do not involve the sex organs directly.

    • Examples include the development of breasts in females and facial hair in males.

Physical Changes in Adulthood

  • Early adulthood is often the first time people have to deal seriously with negative developmental changes.

    • This can include changes in metabolism, skin elasticity, and sensory acuity.

  • Western cultures there is a double standard for appearance by which women are judged more harshly than men

  • Osteoporosis, which affects 25 percent of women over 60, is a primary cause of broken bones among people in late adulthood.

    • Bone density decreases, making bones more brittle and prone to fracture.

Aging

  • The brain becomes smaller and lighter with age, and blood flow is reduced.

    • This can affect cognitive functions such as memory and processing speed.

  • Physical fitness is related to better performance on mental tests and may prevent brain tissue loss.

    • Exercise and cognitive stimulation can help maintain brain health.

  • The young old are 65 to 74 years old. The old old are between 75 and 84, and the oldest old are 85 and older.

  • The number of people over 85 is projected to increase from 4 million to 18 million by 2050

  • Two explanations generated to explain the slowing down in old age are the nervous-system-oriented peripheral slowing hypothesis and the whole-body-oriented generalized slowing hypothesis.

  • The peripheral slowing hypothesis, suggests that the peripheral nervous system, which encompasses the nerves that branch from the spinal cord and brain to the extremities of the body, becomes less efficient with age.

    • This slowing affects reaction time and motor skills.

  • The generalized slowing hypothesis, by contrast, processing in all parts of the nervous system, including the brain, is less efficient.

    • Cognitive processing and decision-making are affected.

Sensory Changes in Aging

  • Old age brings many changes in sensory perception that can cause social and psychological difficulties.

    • Sensory decline can lead to isolation and depression.

  • Taste and smell sensitivity can decline, leading to malnutrition.

    • Decreased appetite and poor food choices can result.

  • Hearing impairments can hamper one's social life.

    • Difficulty communicating can lead to withdrawal from social activities.

  • In midlife, most people notice changes in the sensitivity of their eyes and other sense organs.

  • All the organs seem to shift at about the same rate, but the changes are particularly marked in vision and hearing.

  • A nearly universal change in midlife is the loss of near vision, called presbyopia.

  • Cataracts bring blurred vision and glare in bright light.

  • Glaucoma occurs when pressure in the fluid of the eye increases, either because the fluid cannot drain properly or too much fluid is produced.

  • The ability to hear high-pitched, high-frequency sounds usually degrades first, a problem called presbycusis.

  • Alterations in taste and smell have been associated with major depression

    • These sensory changes can exacerbate or contribute to mood disorders.

Premature Births

  • Preterm infants, or premature infants, are born prior to 38 weeks after conception

  • Around 1 out of 10 infants are born earlier than normal

  • infants weigh less than 2,500 grams (around 5 1/2 pounds)

  • Women who have delivered preterm in an earlier pregnancy or who have experienced preterm labor, Being pregnant with twins are Birthweight Risk Factors for Low-Birthweight Preterm Infants

  • A baby born earlier than 25 weeks has less than a 50–50 chance of survival

    • Advances in neonatal care have improved survival rates for very preterm infants.

  • The overall rate of infant mortality in the United States (defined as death within the first year of life) is 5.7 deaths per 1,000 live births.