question: When your head grows, does the pressure in it change too?
comment: Yes (but causation has not been established). Surprisingly, we didn't know until 2015 - no one had thought to check. [A 2015 study]( URL_0 ) found that the pressure inside your skull decreases with age. However, two things are of note: * Adult intracranial pressure decreases at a rate of around 0.1 mmHg per year. This suggests that ICP is decreasing as a result of something *other* than skull size. * During childhood (when your head is growing a little bit), ICP changes at a much faster rate of 0.45 mmHg per year - but only when measured during the day. The nighttime pressure remains the same. This suggests that ICP is changing due to factors other than skull size. Currently, no studies have looked at a direct causal relationship between skull growth and ICP.
passages: In infants and small children, the effects of ICP differ because their cranial sutures have not closed. In infants, the fontanels, or soft spots on the head where the skull bones have not yet fused, bulge when ICP gets too high. ICP correlates with intraocular pressure (IOP) but seems to lack the accuracy necessary for close management of intracranial pressure in the acute posttraumatic period.
   In addition to the above, if mass effect is present with resulting displacement of brain tissue, additional signs may include pupillary dilatation, abducens palsies, and the Cushing's triad. Cushing's triad involves an increased systolic blood pressure, a widened pulse pressure, bradycardia, and an abnormal respiratory pattern. In children, a low heart rate is especially suggestive of high ICP.
   The pacinian corpuscle is one such structure. It has concentric layers like an onion, which form around the axon terminal. When pressure is applied and the corpuscle is deformed, mechanical stimulus is transferred to the axon, which fires. If the pressure is steady, stimulus ends; thus, typically these neurons respond with a transient depolarization during the initial deformation and again when the pressure is removed, which causes the corpuscle to change shape again. Other types of adaptation are important in extending the function of a number of other neurons.
  
  Section::::History.
   Craniotomies are holes drilled in the skull with the help of cranial drills to remove intracranial hematomas or relieve pressure from parts of the brain. As raised ICP's may be caused by the presence of a mass, removal of this via craniotomy will decrease raised ICP's.
   Section::::Vestibular system.
  
  In our vestibular system, neurons are undeveloped at neuronal birth and mature during the critical period of the first 2-3 postnatal weeks. Hence, disruption of maturation during this period can cause changes in normal balance and movement through space. Animals with abnormal vestibular development tend to have irregular motor skills.
   The spine of an infant at the time of birth differs from the adult spine. The "conus medullaris" (bottom of the spinal cord) terminates at the level of L1 in adults, but may range in term neonates (newly born babies) from L1-L3 levels. It is important to insert the spinal needle below the conus medullaris at the L3/L4 or L4/L5 interspinous levels. With growth of the spine, the conus typically reaches the adult level (L1) by 2 years of age.
   The Monro–Kellie hypothesis states that the cranial compartment is inelastic and that the volume inside the cranium is fixed. The cranium and its constituents (blood, CSF, and brain tissue) create a state of volume equilibrium, such that any increase in volume of one of the cranial constituents must be compensated by a decrease in volume of another.
   A compensatory mechanism involves the movement of cerebrospinal fluid from the cranial vault towards the spinal cord. The volume of blood in the cranial vault is auto-regulated by the brain, and will therefore not decrease that easily.
  
  Intracranial pressure will rise as a result of continued brain growth within the rigid skull. It appears that in children with craniosynostosis, the expected decrease of intracranial blood is probably not occurring as it should according to the Monro-Kellie hypothesis. This is shown when the brain expands in the fixed skull, which gives a faster rise in intracranial pressure than would be expected.
   Section::::Ultrasound time of the flight techniques.:Cranium diameter.
  
  Dimensions of the cranium or its structures are determined with the ultrasound “time-of-the-flight” technique that measures the transit time of an ultrasound wave and its (potentially multiple) echoes on their path through the cranium and calculates the corresponding distance(s) using known ultrasound propagation velocities in different tissues (e.g. bone, brain, or fluid). Unfortunately, a reproducible quantitative relationship between the diameter of the cranium and ICP could not be established because ICP-induced changes in the cranium diameter are very small compared to the inter-individual variability of skull sizes, shapes and thicknesses.
   "Physiosonics, Inc." used transcranial Doppler ultrasound to measure ICP indirectly by assessing the elasticity of the biological material in a defined part of the brain. However, the elasticity in the brain is highly dependent on many other variable individual factors apart from ICP, including arterial blood pressure, state of cerebral blood flow auto-regulation, and the level of edema. Therefore, this approach would require calibration and expert positioning.
  
  Section::::Skull bones.
   The range of intraoral pressure involved in various classes of ethnic wind instruments, such as Native American flutes, has been shown to be generally lower than Western classical wind instruments.
  
  Section::::Influencing factors.:Drugs.
  
  Intraocular pressure also varies with a number of other factors such as heart rate, respiration, fluid intake, systemic medication and topical drugs. Alcohol and marijuana consumption leads to a transient decrease in intraocular pressure and caffeine may increase intraocular pressure.
   Recent studies have examined the possibility of a critical period for thalamocortical connectivity in the auditory system. For example, Zhou and Merzenich (2008) studied the effects of noise on development in the primary auditory cortex in rats. In their study, rats were exposed to pulsed noise during the critical period and the effect on cortical processing was measured. Rats that were exposed to pulsed noise during the critical period had cortical neurons that were less able to respond to repeated stimuli; the early auditory environment interrupted normal structural organization during development.
   For example, if the original fluid was water and we replaced it with mercury at the same pressure, we would expect to see a rather different value for pressure head. In fact the specific weight of water is 9.8 kN/m and the specific weight of mercury is 133 kN/m. So, for any particular measurement of pressure head, the height of a column of water will be about [133/9.8 = 13.6] 13.6 times taller than a column of mercury would be. So if a water column meter reads "13.6 cm HO", then an equivalent measurement is "1.00 cm Hg".
   Many things will increase during development from embryo to adult. The main changes are blood pressure increase, an increase in the amount of blood one cardiac output (cycle) will produce, and an increase of stroke volume. There are not only increases seen during this time. Peripheral resistance (resistance to blood flow found in peripheral venous systems) will actually go down, allowing the circulation of the organism to become more facilitated. Development can be shown by "T. carnifex’"s response to hypoxia. This response will demonstrate the extent to which neurohormonal instruments are at work operating in the cardiovascular system. Blood pressure in response to hypoxia will go up in adults, but will not follow this pattern in younger organisms. In adulthood, this extent will be much larger in comparison to juveniles. The cellular (myocyte) membrane will alter its permeability as adulthood is reached, adrenergenic/cholinergic systems will develop, and the gas transport mechanisms in the formation and modification of ion channels will also develop. In early development, it is possible (but not proven) that cardiac receptors have an influence on the regulation of blood pressure.
   In a study of the head growth of 633 term-born children from the Avon Longitudinal Study of Parents and Children cohort, it was shown that prenatal growth and growth during infancy were associated with subsequent IQ. The study’s conclusion was that the brain volume a child achieves by the age of 1 year helps determine later intelligence. Growth in brain volume after infancy may not compensate for poorer earlier growth.
   Section::::Principles of maturation.
  
  He believed that a child’s growth & development are influenced by both their environment and genes, but he largely investigated the children's physiological development. He called this process maturation, that is, the process by which development is governed by intrinsic factors, principally the genes. 
  
  According to Gesell, the rate at which children develop primarily depends on the growth of their nervous system, consisting of the complicated web of nerve fibers, spinal cord, and brain. As the nervous system grows, their minds develop and their behaviors change accordingly.
  
  Section::::Principles of maturation.:The Concept of Maturation.
   During labour and birth, the infant's skull changes shape to fit through the birth canal, sometimes causing the child to be born with a misshapen or elongated head. It will usually return to normal on its own within a few days or weeks. Special exercises sometimes advised by physicians may assist the process.
  
  Section::::Physical characteristics of newborn.:Hair.
   Research is currently being done to test detection of hydrodynamic stimuli in manatees. While the anatomy of the follicle-sinus complexes of manatees have been well studied, there is much to learn about the neural circuits involved if such detection is possible and the way in which the hairs encode information about strength and location of a stimulus via timing differences in firing.
  
  Section::::Mammals.:Platypuses.
   The principal buffers for increased volumes include CSF and, to a lesser extent, blood volume. These buffers respond to increases in volume of the remaining intracranial constituents. For example, an increase in lesion volume (e.g., epidural hematoma) will be compensated by the downward displacement of CSF and venous blood.
  
  The Monro–Kellie hypothesis is named after Edinburgh doctors Alexander Monro and George Kellie.
  
  Section::::Diagnosis.
   This study investigated EEG Microstate variance across normal humans of varying age. It showed a "lawful, complex evolution with age" with spikes in mean microstate duration around ages 12, 16, 18, and 40–60 years, suggesting that there is significant cerebral evolution occurring at those ages. As for the cause of this, they hypothesized that it was due to the growth and restructure of neural pathways,
  
  Van De Ville, Britz, and Michel, 2010
   The blood pressure in the fetal aorta is approximately 30 mmHg at 20 weeks of gestation, and increases to ca 45 mmHg at 40 weeks of gestation. The fetal pulse pressure is ca 20 mmHg at 20 weeks of gestation, increasing to ca 30 mmHg at 40 weeks of gestation.
  
  The blood pressure decreases when passing through the placenta. In the arteria umbilicalis, it is ca 50 mmHg. It falls to 30 mmHg in the capillaries in the villi. Subsequently, the pressure is 20 mm Hg in the umbilical vein, returning to the heart.
  
  Section::::Physiology.:Flow.
   Nerve growth factor may contribute to increased longevity and mental capacity. Centenarian Rita Levi-Montalcini took a daily solution in the form of eye drops, and has stated that her brain is more active now than it was four decades ago. In 2014, Sundaravadivel Balasubramanian and coworkers at Medical University of South Carolina showed that NGF level is elevated in people who performed a single 20-minute yoga session involving "om-"chanting and "thirumoolar pranayama", when compared to a control group.
  
  Section::::Interactions.
  
  Nerve growth factor has been shown to interact with TrkA and p75NTR (LNGFR).
   In summary pressure head is a measurement of length, which can be converted to the units of pressure (force per unit area), as long as strict attention is paid to the density of the measurement fluid and the local value of g.
  
  Section::::Implications for gravitational anomalies on formula_12.
  
  We would normally use pressure head calculations in areas in which formula_6 is constant. However, if the gravitational field fluctuates, we can prove that pressure head fluctuates with it.
   For children with CP with limited movement and sensation, the risk of pressure sores increases. Pressure sores often occur on bony parts of the body. For example, pressure sores may occur when a child has limited feeling and movement of their lower body and uses a wheelchair; the tailbone bears weight when seated and can become vulnerable to pressure sores. The occupational therapist can educate the child, family, and caregivers about how to prevent pressure sores by monitoring the skin for areas of irritation, changing positions frequently, or using a tilt-in-space wheelchair.
  
  Section::::Occupational therapy.:Effect of cognitive and perceptual impairments.
   Other species also show similar tonotopic development during critical periods. Rat tonotopic develop is nearly identical to mouse, but the critical period is shifted slightly earlier, and barn owls show an analogous auditory development in Interaural Time Differences (ITD).
  
  Section::::Sensory mechanisms.:Central nervous system.:Plasticity of auditory critical period.
  