K12 - Communication

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Embryology - 18 May 2024    Facebook link Pinterest link Twitter link  Expand to Translate  
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Biological communication occurs at many levels, from one cell communication with its neighbour in a tissue (paracrine), to signals released into the blood from one cell to signal to another cell or tissue (endocrine or hormone signaling). The signalling that occurs in the brain, spinal cord and other nervous tissues involves electrical (action potentials) signaling. All sensory information needs to be first converted into this form before the brain can interpret.

This page will introduce development of signaling in our special sensory nervous systems: the eyes for vision and the ears for hearing. Both systems convert signals in one medium (light or sound) into an electrical signal that our brain can understand.

Note that other animals may have additional sensory systems or sensory systems that allow highly specialised vision, hearing or touch.

For the Teacher
Mark Hill.jpg
  • This content is only as a brief introduction, designed for K12 students and does not cover all topics in the communication syllabus.
  • More detailed information can be found on the listed linked pages.
  • This website focusses on development issues rather that physiology and postnatal abnormalities.
K12 Links: Start Here | Week 1 | Week 2 | Week 3 | Week 4 | Week 5 to 8 | Arms and Legs | Heart | Fetus | Brain Growth | Eyes and Ears | Animal Development Times | Humans and Animal Embryology | Comparative Embryology | Thalidomide

Sound - Hearing

Hearing cartoon.jpg

This cartoon shows the adult "ear" with the 3 main divisions (outer, middle, inner).

Outer Ear
  • directs sound waves into the ear canal.
Middle Ear
  • converts sound waves in to mechanical movements or vibrations.
Inner Ear
  • converts mechanical movements into electrical signals.

Hearing Before Birth

Can a baby "hear" like we do before it is born?

Why can't the unborn baby hear?

Before birth the baby cannot "hear" like we do!

Instead during the third trimester vibrations of the mother's body, vibrate the fluid surrounding the baby, that then vibrate the baby's head and stimulate the hearing pathway. This can sometimes result in a "startle-like" response.

  1. The middle ear is filled with fluid instead of air so the middle ear bones (ossicles) cannot move freely.
  2. The pathway to the brain, and the part of the brain that interprets sounds, have not yet full developed.
Auditory neural pathway.jpg

The neural pathway from the ear to the brain.

External Ear Growth before Birth

What's so important about the outer ear?

Month 3 - Fetus Month 4 - Fetus Month 5 - Fetus
Streeter1922-plate04.jpg Streeter1922-plate05.jpg Streeter1922-plate06.jpg
About the Outer Ear shape and Position.
Fetal Alcohol Syndrome face.

The position and shape of the external ear can tell you about how the head grows before birth!

  • This can also be used as an indicator for some abnormalities in development.
    • For example, fetal alcohol syndrome "railroad track" ears curve at top part of outer ear is underdeveloped and folded over parallel to curve beneath.
  • Because the ear develops at the same time as some internal organs it can also indicate possible problems in other systems.
  • There are several genetic disorders that also result in abnormalities of the outer ear.

Testing a Baby's Hearing

Newborn hearing test

If a baby cannot hear you talk they cannot easily learn to speak!

Much of your first learning comes from being able to copy sounds that you hear. The parents or doctors would only know that a baby could not hear if they were not developing speech correctly or meeting other developmental milestones.

  • In the past - the tests were very simple, like turning their head to a bell or sound. They could also not be easily carried out on newborn infants.
  • Today - the tests are computer-based, requiring no infant response and can be easily carried out on newborn infants.
About Newborn Hearing Tests
  • The incidence of significant permanent hearing loss is approximately 1-3/1000 newborns.
  • It is thought that in NSW 86,000 births/year = 86-172 babies potentially born with significant permanent hearing loss.
  • Neonatal hearing screening is carried out in the USA, UK and in Australia.
  • In 2002, NSW introduced a Statewide Infant Screening Hearing Program (SWISH) using an automated auditory response technology (AABR).

Whats an Automated Auditory Brainstem Response?

(AABR) uses a computer generated stimulus (click) that is delivered through earphones and detected by scalp electrodes.

  • The test takes between 8 to 20 minutes and has a sensitivity 96-99%.
  • The basis of a neonatal hearing test that uses a trigger stimulus delivered through earphones and subsequent brain electrical activity then detected by scalp electrodes.
  • Then by computer analysis, averaging all the electrical activity following the trigger, peaks emerge reflecting signal passage activity through brain stem nuclei in the hearing central neural pathway.
  • Unlike other childhood auditory testing does not require a subject response.

Light - Vision

Eye and retina cartoon.jpg

This cartoon[1] shows the eyeball (left), a cartoon of the retinal cell organisation (middle) and an actual slice of the human retina.

The Eye
  • This is a cut through the eyeball showing the eye anatomy.
  • The retina forms the inner lining of the most of the back part of the eye.
  • The retina is the structure that converts light into electrical signals.
Retinal Cell Organization

These are the names of the cells and neurones required to convert light into electrical signals. (detect, process and carry)

  • Carry the signal to the brain - retinal ganglion cells (G, GCL) take the signals from the eye to the brain in the optic nerve.
  • Process the signals from the light detectors - Müller cell M, amacrine cell A, bipolar cell B, horizontal cell H process the signals from rods and cones.
  • Detect light - rod cells R and cone cells C, detect light and convert light into an electrical signal (action potential).
Notice that light has to pass through all the other retina cell layers to the detection cell layer. Then when an electrical signal, be transferred back up through these neurons to the ganglion cells, that carry the signal to the brain in the optic nerve.
  1. <pubmed>20855501</pubmed>| PMC3101587 | JCB

Glossary Links

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Cite this page: Hill, M.A. (2024, May 18) Embryology K12 - Communication. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/K12_-_Communication

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G