Transcript The Motor System

A quick who’s who and what’s what
What Do We Need
In Order To Move?
• Muscles and Bones:
– To produce the actions that allow us to interact
with our environment
• Neurons
– To tell the muscles what to do
But how do they communicate to let us move?
Brain
Messages can be sent from our Brain down
through our spinal cord….
Spinal Cord
…when they leave the spinal cord they connect with
other neurons…
Peripheral nerves
…these neurons then connect with muscles allowing us
to perform actions like kicking a soccer ball.
Types of Muscle Control
Voluntary control
• This is how we produce movements that we think about
• Goes through many connections in the nervous system
• Example: Kicking a soccer ball
Reflexes
• Movements we don’t need to think about
• Many of these movements do not even need the brain
• Example: Pulling your hand away when you accidentally touch something sharp
Reflex Movements
These involve a simple connection, with only a
few neurons talking to each other directly
Sensory neuron
picks up a signal,
such as pain
Motor neuron tells a muscle
to move
Voluntary Movements
These involve a longer process, this time bringing the brain into the picture.
It can begin in the brain with wanting to act on something, combining that
with information from the environment
Example: Kicking a soccer ball.
Brain
Considers all information and
makes a decision…
Input
Let’s Be BrainReach Investigators!
Visual Grasp Reflex
• Everything you see with your eyes open is your visual field.
• If something moves or changes in our visual field, even on
the edges – for example, a light quickly turns on and off –
our eyes immediately move to look at it without needing to
think about it.
• This is the “visual grasp reflex”. When a signal (the light) is
provided, our eyes move to put that signal in the middle of
our visual field
So let’s now try out some reflexes and see what
happens when we introduce our voluntary system
into the mix…
What You Will Need
• 2 flashlights
• 2 pieces of regular white paper
• 2 elastic bands
• A partner
Note: if you don’t have flashlights or elastic bands, you can try it using your fingers. Just replace turning the light on and
off with snapping your fingers (just make sure your partner is close enough to see them).
Experiment 1: Visual Grasp Reflex
Instructions
Step 1: Pair up! One person is the experimenter and the other is the subject
Step 2:
Experimenter: Hold one flashlight (turned off) in each hand somewhere your
partner can see the light
Subject: Look straight forward at the experimenter’s eyes.
Step 3:
Subject: When you see a flashing light, look at it without moving your head.
Experimenter: Without giving any clues about which flashlight you’ll use, quickly
turn one of the flashlights on and off.
Did you notice what happened to your partner’s eyes? If not, try
again!
Let’s Bring In Voluntary Control…
We are going to test the difference
between your voluntary and reflex
systems by comparing reaction time
Reaction time = the time from when you
give the signal – in our case, light – and
when the subject responds to the
movement
Experiment 2
Instructions
Subject:
Look at the opposite flashlight when you see the other one flash –
look at the one that stayed off
Experimenter:
Turn one flashlight on and off, like last time.
Do it a few times, switching which flashlight you use randomly.
(Don’t just go back and forth, or the subject will know what’s
coming!)
Let’s Bring In Voluntary Control…
– Did you notice the subject’s eyes move faster when
they were looking at the flashing light or when
they were looking at the opposite light?
– If it’s hard for you to see, ask your subject how he
or she felt
• They probably felt like they took longer to look away
from the light (voluntary) than at it (reflex)
Experiment 3
Hold your index finger in front of your partner’s face.
1. Starting with your finger in front of your partner’s nose, ask
him or her to follow your fingertip with his or her eyes as you
move it slowly up and down, left to right, and in circles.
2. Now, ask your partner move their eyes the same way, but
don’t use your finger – just watch their eyes. He or she will
have to move his or her eyes smoothly up and down, left to
right, and in circles, just like they did before, but without
following anything they can see.
Notice a difference?
Probably, your partner moved their eyes
smoothly the first time (following your finger),
but in the second, his or her eye movements
were choppy, not smooth.
How the brain controls our eyes to track objects
(reflexes, in the first version) is different from the
system it uses to move our eyes voluntarily
(second version).
Why Have Both?
Good:
Bad:
Voluntary
Control
Reflex
Control
Flexible
Fast
Slow
Predictable
(not flexible)
Let’s Review What We’ve Learned…
Our motor activity can be broken up into movements that we control through our voluntary
system and our reflexes.
Voluntary movements usually take more time to perform because they need to be processed by
the brain, and they can do more complicated things.
Reflexes let neurons talk to each other directly without going through the brain, making
response time much faster between seeing (or feeling!) something and reacting
We need both kinds of motor responses in different situations!