Thursday, July 31, 2008

Diving-Surfacing: Parallel Convergence

The blue whale's nose resembles the human nose and sea otter nose during backfloating.

Backfloating & Swimming: Infant 15 months old: Breathe on back, Swim on stomach

The Aquaphotic Respiratory Cycle (ARC)


The Aquaphotic Respiratory Cycle (ARC) contains two components, relying upon the trigeminal cranial nerve:

1) submergence - Mammalian Divers Reflex (MDR) (stifled inhale)
2) emergence - Photic Sneeze (PS) (explosive exhale)

The MDR (from air surface to ~2m+ water depth) occurs when the face is
suddenly pressured, chilled and darkened which results in a inhale
reflex BUT since the face is submerged underwater, the inhaling reflex
is stifled and converted into O2 conservation or Mammalian Divers Reflex.

Human Physiology, Klinke, Silbernagel et al., 2006,
MDR: trigeminal cranial afferent nerve (V) relays the information that the
nasal and mouth cavities are submerged, which triggers the autonomus
nervous system to

* bradicardia, meaning a reduction of heart rate to about 4/5 of
normal rate
* blood "shift"(?) to the thorax to support the lung when under
pressure to keep it from collapsing (which would be bad for numerous
* vasoconstriction, first in the limbs to protect vital organs,
and later of everything except the heart and the brain, which creates
a heart-brain circuit

The PS (from ~2m+ water depth to air surface) occurs when the face is
suddenly well lit after dark adaptation (accomodation for improved vision), (pressure and thermal changes
increase neural stimulus) -> fast forced CO2 exhale reflex and
"instant" oxygenation of tissues.

DDeden [AAT, Deeper Blue, The ARC blog]

The Ear-Popper is a handheld, battery-powered device that delivers a
constant, controlled stream of air pressure and flow into the nasal
cavity, diverting air up the Eustachian tube when the patient
swallows. This "pops" the ear so the fluid can drain, unblocking the
ear and restoring hearing.

Chapter five, appropriately called "Getting Ahead", begins with Shubin
studying cranial nerves several days before an anatomy test. Most
cranial are easy because they have only one function and attach to one
muscle or organ. Four, however, are a bit more difficult to trace.
Shubin focuses on two of the four - the trigeminal and the facial.
Each breaks up into a number of smaller branches that take a complex
path through the head. The trigeminal nerves controls some of the
muscles we use for chewing, innervate teeth, control some muscles in
the inner ear, and is responsible for facial sensation. The facial
nerve controls the muscles used in making facial expressions and like
the trigeminal, it also controls some muscles in the inner ear. The
question is why? As Shubin puts it:

Nothing about them seems to make any sense. For example, both the
trigeminal and the facial nerves send tiny branches to muscles inside
our ears. Why do two different nerves, which innervate entirely
different parts of the face and jaw, send branches to ear muscles that
lie adjacent to one another? Even more confusing, the trigeminal and
facial almost crisscross as they send branches to our face and jaw. Why? To answer that we need to look at the developing embryo. Part of the answer lies in the four arches that for roughly 3-4 weeks after
conception. The first arch tissues, ultimately, form the upper and
lower jaws, the malleus and incus, and all the muscles that supply
them. The second arch forms the stapes, the hyoid and the muscles that
control facial expression. The trigeminal comes from the first arch,
while the facial nerve comes from the second. But there is more. In
sharks, the first arch forms the jaws, which are enervated by the
trigeminal. The second arch, in sharks, forms a cartilage rod that
eventually breaks up to form to bones that support the jaws. The first
bone is the equivalent to the hyoid in humans and supports the lower
jaw. The second bone, which supports the upper jaw is equivalent to
the stapes in humans. oing a step further, if we look at Amphioxus we
can see a notochord. Humans have one too, but ours breaks up early in
embryology and, according to Shubin, becime part of the intervertebral
disks. Like humans, Amphioxus also has arches. In this case, the
arches form cartilage that support the gill slits. Going back in time,
say 500 million years, we can see the notochord preserved in some of
the earliest worm fossils.

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