4 mistakes learners make with the nervous system, each one named and explained.
A signal travels one way through a fixed sequence, and the gaps between the neurones are crossed by chemicals, not by electricity.
You describe pulling away from a pin as the brain deciding to move the hand.
You are awake and you notice it happening, so it feels like a decision you made.
Question. In a reflex arc, where does the signal go after the sensory neurone?
A common answer. to the conscious part of the brain, which decides what to do
The answer. to a relay neurone in the spinal cord, and straight back out
Why. Going through the spinal cord is what makes it fast, and you feel the pain afterwards.
If it has to be fast, it does not go to the brain first.
You say the lens does the focusing and the cornea is just a clear window.
The lens is the part that changes shape, and changing shape is what focusing looks like.
Question. Which part of the eye bends light the most?
A common answer. the lens
The answer. the cornea
Why. The cornea does most of the bending; the lens makes the fine adjustment for distance.
Most of the bending is fixed. Only the last part of it is adjustable.
You call the hot pan the receptor, or the hand the effector and also the stimulus.
All three words arrive in the same sentence and all three are part of the same event.
Question. You touch something hot and pull your hand away. What is the receptor?
A common answer. the hot object
The answer. the temperature receptor in the skin
Why. The stimulus is the heat, the receptor detects it, and the muscle that moves the arm is the effector.
Put the three in order before you name any of them.
You describe the impulse jumping the synapse as a spark or a current.
The impulse really is electrical along the neurone, and the gap is drawn as a tiny space you could imagine it crossing.
Question. How does a signal cross the gap between two neurones?
A common answer. it jumps across as an electrical spark
The answer. a chemical is released, which diffuses across and starts a new impulse
Why. The neurones do not touch, so the message is carried by a neurotransmitter across the gap.
At every gap, say the word chemical. There is no spark anywhere in the body.
WAJD spots these patterns in your child's answers and names the one behind their wrong answers, instead of just marking them wrong.