SME
Grade 9 Science · Problem type
How fast a nerve impulse travels
Use this for “An impulse travels 1 m from the toe to the spinal cord at 50 m/s. How long does it take?”
Diagram
The
impulse
runs
1
m
at
50
m/s:
1,000
×
1
50
=
20
ms.
The axon is myelinated, so the impulse jumps from node to node.
This is an example. Type your own values to start a new problem.
t (ms)
=
d (m)
÷
v (m/s)
Formulas
t
=
d
v
0.02
=
1
50
Formulas are worked in s. The step-by-step shows the conversions.
Assumptions
•
The impulse moves along the axon at a steady speed.
•
Axons wrapped in myelin carry impulses fastest, up to about 120 m/s; thin axons without it, about 1 m/s.
•
The time is in milliseconds: 1,000 ms is 1 s.
Step-by-step
WE KNOW
d = 1 m, v = 50 m/s
FIND
time to travel (t)
Step 1 · Find time to travel (t)
Use t = d ÷ v
Distance
speed
is
the
time.
t
=
1
50
t
=
0.02
s
Step 2 · Convert the answers
Change each answer back to the unit you chose.
t = 0.02 s = 20 ms (1 s = 1000 ms)
Check
Put the numbers back in. Both sides should match.
0.02
=
1
50
✓
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