Newborns and reflexes

Question 1

Evolution of mammals

Answer 1

Depiction of mammal diversity at the Mesozoic/Cenozoic boundary (i.e., centred at 65 million years ago). The number of different basic types of mammals (orders) is clearly larger after the extinction event than before. Is an example of an adaptive radiation. Our order, Primates, is highlighted.

Most mammals 65 mill years ago were small.

Meteor hit the earth, blocking sunlight- extinction of dinosaurs.

Question 2

What is adaptive radiation?

Answer 2

Where organisms suddenly diversify while adapting to new or recently vacated ecological niches.

Question 3

Outline two key mammalian adaptions

Answer 3

1. Endothermy ‘warm-blooded’:
   - requires high-energy food
   - thermoregulatory adaptions (fur)
2. Live birth
   - mammary glands
   - adaptions for nursing
   - protection from predators
   - signalling behaviours (crying)

Question 4

Primates:
- what does parenting poses?
- what would humans related to primates be?

Answer 4

• parenting (or mothering) poses similar kinds of challenges to both humans and nonhumans.
• Humans related to primates would be logically and scientifically incorrect. We are primates- we have the same sort of needs. They elicit similar parenting behaviours.

Question 5

Primate Infants Considered in Relation to Other Mammals

Answer 5

Precocious (advanced):

• eyes and ears are not sealed shut
  (compare:carnivores, rodents)
• neural cell proliferation nearly complete at birth- have almost all neurons we will have at adulthood
  (compare: rats ~25%)
• moderately rapid locomotor development (compared to kangaroos in particular but not as advanced as horses)
  (not as fast as ungulates, faster than marsupials)

Altricial (slowly developing):

Dependent on mothers up to 4 years
Very extended juvenile life stage, hence very delayed adolescence.
Primates have extremely long juvenile epochs, relative to most other mammals, being dependent upon their mothers for years, in some cases.
The long juvenile stage entails a postponed reproductive maturity, relative to other mammals.

Question 6

A bar graph comparing the durations of different life history stages in five primate species: from lemurs to macaques to gibbons to chimpanzees and, finally, humans.

What does the comparison show?

Answer 6

Comparison shows very similar life history profiles between chimpanzees and humans, although humans seem unusual in having a significant post-reproductive lifespan (menopause); chimpanzees can reproduce throughout their lives.

(For most primates theres a relatively long gestation, followed by a period of infancy followed by a juvinille phase and an adult phase.

Similarity in history profile between humans and our nearest living relatives.)

Question 7

List sensory capabilities of newborn babies

Answer 7

• Touch (pain, pressure, proprioception, temperature)
• Balance (vestibular system)
• Smell
• Taste (salt, bitter, sweet, sour)
• Hearing (lower frequencies; ability to localise sounds improves over the first 7 years of life)
• Vision (about 20/400 at birth; improves to 20/20 at about 6 months)

Question 8

List some Neonatal Behavioural Repertoires

Answer 8

Orienting responses:
- visual tracking
- auditory tracking

Reflexes
- related to clinging: Palmar & plantar grasp, Moro
- related to nursing: Rooting, sucking
- related to locomotion: Crawling, stepping

Some reflexes are vestigial: they have partially or wholly lost their original function

Question 9

Vestigial

Answer 9

It is not obvious how, for example, a palmar grasp reflex or a Moro reflex is adaptive for modern humans, since they can’t cling to mother’s fur, unlike many other primates.

Some reflexes are vestigial: they have partially or wholly lost their original function

Question 10

Anenchephalic meaning

Answer 10

Absence of most of a brain. Reflexes therefore tend to be lower brainstem activities.

Question 11

List the neonatal reflexes

Answer 11

• The moro reflex
• Tonic neck reflex
• Palmer and plantar grasp reflex
• Step reflex
• Crawl reflex
• rooting reflex

Question 12

Neonatal Behavioural Assessment Scale (clinical assessment of neuromotor integrity in newborn babies)/ Brazelton scale:
What was demonstrated?

Answer 12

• Babinski reflex, a foot grasp, and assesses
  ankle clonus, a measure of muscle tone.
• pulling the baby up to a sitting position from
  supine, assessing how well the baby holds up his head in the process, and also demonstrates a hand grasp. Additionally, assessing tone and neck muscles.
• the walking reflex: if one holds a baby vertically
  over a substrate, the baby will display stepping motions with its legs. Also testing for muscle extremities in standing position.
• Moro reflex and then tests the baby’s
  behavourial regulation through its response to cuddling.
• a child visually tracking an object and also
  tracking an auditory stimulus.

Question 13

Can chimpanzees display neonatal reflexes?

Answer 13

Yes, they can display auditory tracking, the stepping reflex and a moro reflex.

Question 14

What is the difference in brain growth between Humans and Chimpanzees

Answer 14

A figure depicting the different patterns of postnatal brain growth in humans and chimpanzees over the first 20 years of life. Although, like most primates, both humans and chimpanzees have most of their neurons at birth, humans are born with much larger
brains and display much greater brain growth after parturition.

Human brains weigh about 1200 grams
Chimpanzee brains weigh about 200 grams

Question 15

Explain:
- Glia
- Myelination
- Synaptogenesis

Answer 15

Glia: (non-neuron cells in the CNS)
Most neurons present at birth, but glia continue to multiply. Glia provide structural support, maintenance and insulate neuronal axons and myelin

Myelination: Formation of fatty sheathes around axons:
Unmyelinated: ~1 metre/second
Myelinated: ~10-100 metres/second

Synaptogenesis: Formation of new connections between neurons

Question 16

True or false: unmyelinated neurons transmit electrochemical waves slower than myelinated?

Answer 16

True

Question 17

What are the structures of a neuron?

Answer 17

• dendrites
• cell body
• axon
• axon terminals

An inset depicts synaptic connections between dendritic and axonal terminals. Axon terminals connect to neighbouring neurons.

Question 18

In the CNS, where do oligodendrocytes lay down?

Answer 18

In the CNS, oligodendrocytes lay down myelin sheaths

Question 19

In the peripheral nervous system, what is myelination done by?

Answer 19

In the peripheral nervous system, myelination is down by Schwann cells.

Question 20

Myelination:
1) what brain areas myelinate after birth?
2) when large areas of the brain aren’t myelinated yet, what is the implication of this?

Answer 20

1) Lighter cortical areas myelinate after birth
2) large areas of the cortical surface of the brain are not yet myelinated, which has implications for the speed of neural processing in these areas.

Question 21

Synaptogenesis:
At what ages does growth peak for the visual, auditory and prefrontal cortex areas?

Answer 21

There are rapid increases in synaptogenesis from brith. They peak at different times then start to fall.

Visual Cortex: 1 year
Auditory Cortex: 3 years
Prefrontal Cortex: 3 years

Question 22

Stimpson et al. (2010) showing pattern of synaptogenesis in chimpanzees- results

Answer 22

Synaptic Density in the developing Neocortex of chimpanzees.

Peaks at:
Primary somatosensory cortex: 12-24 months
Primary motor cortex: 12-24 months
Rostral prefrontal cortex: 60-72 months
Prestriate visual cortex: 12-24 months

Question 23

What can you conclude from synaptogenesis at birth, 1 month, 3 months, 6 months, 15 months ad 24 months.

Answer 23

Although the number of cell bodies stays constant, there is an ever-increasing density of dendritic spines over this time period.

In early development brains are dynamically changing organs (i terms of their interconnectivity)

Dendritic Growth in Broca’s area

Question 24

Evidence for Critical and Sensitive Periods in Brain development

Answer 24

Sensory deprivation studies

Eg. Hubel and Wiesel, monocular and binocular deprivation studies. Clinical effects of congenital sensory deprivation (eg. cataracts)

Effects of extreme social deprivation on brain development.

Eg. physiology and growth of brain in cases of extreme social neglect.

Question 25

Monocular Deprivation Cats:

Figure depicting a population of neurons in the visual cortex of unoperated cats. These neurons are categorized in terms of the degree of binocular dominance they display.

Answer 25

On the left, I Category 1, are neurons that respond to stimulation from the ipsilateral eye (that is, the eye on the same side of the body as the visual cortex, here, the left side). On the far right, in Category 7, are neurons that respond to stimulation from the eye on the contralateral side (i.e., the eye on the opposite side of the body, so if these neurons are sampled from the left visual cortex, then they respond to visual input to the right eye).
Most neurons respond to input from both eyes, to varying degrees, categorized here as 2 (mostly respond to ipsilateral input) to 6 (mostly respond to contralateral input).

about 80% of neurons were activated from both eyes. In cats, some cells in the left cortex responded to the left eye only. Then the opposite (7) responded mostly to the input in the right eye. Vast majority were binocular.

Question 26

Monocular Deprivation Cats:
Here, cats have had their ipsilateral eye sutured shut, so that they do not receive any visual input into that eye.

Answer 26

After some time, even when the ipsilateral eye is allowed to receive input, the visual cortex is now almost completely populated by cells that only respond to input from the contralateral eye (Category 7). Thus, even though the eye, itself is working properly, the brain can no longer process visual input from the ipsilateral eye, and the cats are effectively blind in that eye for life.

When they sampled on the LH, most of the cells they sampled responded only to input in the right eye- the eye that had access to visual field throughout the infancy and juvinille phase.\These show that its not the case that individual neurons in our visual cortex are preordained by genetics. It actually depends on environmental input.

Plasticity disappears over a relatively short period of time.

Question 27

Congenital Cataracts

Answer 27

The research with animals led to effective treatment of this condition in humans.

Causes are largely unknown but it is associated with a variety of chromosomal disnormities.

Long term successes decreases with the age of the child

Humans need certain kinds of stimulation

Question 28

CT scan of a healthy 3 year old and a 3 year old child suffering from severe sensory-deprivation neglect.
What is the difference in images?

Answer 28

Healthy: average sized head size

Extreme neglect: smaller brain and cerebral ventricles (hollow areas in the middle of the brain through which cerebrospinal fluid flows) are much larger

Question 29

Difference in image of 9 year olds PET scans between a typically developing child and a Romanian orphan.

What is the difference?

Answer 29

The Romanian orphan shows reduced glucose activity in prefrontal and temporal regions.

However, not every child comes out in these environments with developmental pathologies.(less affected by these environmental deprivations.