5.electricalsignals

7/27/2019 5.ElectricalSignals

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Reflexes and reaction times

Reaction times are how long it takes for the muscles to

respond from the start of a stimulus. In sprint races, reaction

times can determine who wins the race.

Why did Burrell

win the race?9.764

9.783

Carl Lewis

Leroy Burrell

Runner Sprint time (s)

In 1991, Leroy Burrell beat team mate Carl Lewiss world

record for the 100m sprint. But who was quickest?


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On the starting blocks

Pressure sensors are also put in

the starting blocks.

This prevents the runner locatedfurthest from the starter from

hearing the start signal last.

To understand you need to know the reaction time of each

runner. Sprint races are timed from the moment the starters

gun is fired. The actual gun is normally silentthe bang

comes from speakers behind the starting blocks.


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Pressure-time graph


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Gaining the advantage


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Scientists have found that it is physically impossible to reactin less than 0.1 seconds. If a runners reaction time is less

than 0.1 seconds then they must have deliberately started

before the signal was heard.

How can pressure-time graphs identify false-starts?

Fairer races

0.05 0.20.150.1

time (sec)

p

ressure


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Is there a correlation?


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The importance of fast reactions

What kind of factors slow down reaction times?

tiredness

alcohol

drugs

old age

!

Fast reactions can help you to avoid accidents. For example,

at 30mph a car can travel 9m before the driver is able to

respond to the hazard and start braking.



Detecting external stimuli



The brain can respond to touch, smell or taste stimuli in just

0.1 seconds, but sound and vision take longer.

How fast are electrical signals?

Nerve impulses

travel at up to

320mph and

take just

0.02 seconds

to reach the

brain.



Interpreting signals

How can you find your reaction time?

1. Extend your arm over the edge of a tableand have a partner hold a ruler between

your fingers at the 0cm mark.

2. The partner drops the ruler catch itbetween your fingers and thumb as

quickly as possible.

3. Repeat the test 10 times, recording the

results and calculate the mean (average)

distance. Then convert the distance into a

reaction time.



What types of reflexes do you know?

Common reflexes



Reflexes are fast, automatic protective

biological control systems that link a

stimulus to a response.

Many reflexes such as sneezing and focusing

your eyes occur naturally, but other reflexes

can be learned, i.e. conditioned responses.

Reflex reactions happen without you

having to think about them they are

involuntary. This is because thecentral nervous system (CNS) sends

electrical signals to the muscles before

the brain can pick up the message.

What are reflexes?



The central nervous system (CNS) is made up of the brain

and spinal cord.

What is the central nervous system?

cerebralcortex

cerebellum

brainstem

cerebral

hemisphere

spinal cordouter view cross-section



The cerebral cortex is the outer layer of the brain and

controls voluntary movements. Voluntary movements take

longer than reflex movements because more electrical

impulses have further to travel.

Trained sports people seem to move faster than the brain

can respond. They do this by anticipating what will happen

instead of waiting for a message from their senses.

The brain and movement

cerebral cortex initiates actions

cerebellum fine tunes muscle control

brainstem co-ordinates reflexes



What can go wrong?



What are neurones?

Neurones are specialized cells that conduct

electrical impulses through the body.

nerve

nerve fibre

A nerve is a bundle of many nerve

fibres enclosed within a protective

sheath. Nerve fibres are the long

axons of neurones together with

any associated tissues.



What do neurones look like?

The axons of most neurones are wrapped in an insulating

lipid layer called the myelin sheath. Why is this important?

Thin projections called dendrites extend from the cell body

and connect with other neurones, allowing electrical impulses

to pass from one to the other.

Neurones are elongated cells consisting of a cell body and

long, thin axon.

myelin

sheath

axon

dendrites

cell

body



What are sensory neurones?

Sensory neurones transmit messages from sense

receptors, such as the eye or nose, to the brain or spinal

cord.

cell body

nerve impulse

from sense organnerve impulse

to CNS



What are motor neurones?

Motor neurones transmit messages from the brain and

spinal cord to the muscles and glands.

cell body

muscle



A reflex arc



What is a synapse?

A synapse is a junction between two neurones across

which electrical signals pass. The human body contains up

to 500 trillion synapses.

presynaptic

cell

postsynaptic

cell



The release of neurotransmitters

When a nerve impulse arrives at the end of one neurone it

triggers the release ofneurotransmittermolecules from

synaptic vesicles.

synaptic

vesicle

neurotransmitter

molecules



synaptic

cleft

Continuing the impulse

The neurotransmitters diffuse across the synaptic cleft and

bind with receptors on the next neurone, triggering another

impulse.

nerveimpulse

receptor

Th f fl



The sequence of a reflex arc

T f l ?


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True or false?


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Th i i fl


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The iris reflex

I id th


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Inside the eye

lensfocuses light

on retina

iris

regulates amountof light entering eye

retinasenses light

optic nervetransmits impulses to

the brain

ciliary muscleschange shape of the lens

corneaprotects eye surface and

focuses light rays

suspensory ligamentshold lens in place

Wh t i bi l i i ?


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Animals with binocular vision have eyes close together.

This provides an overlapping field of view and enhanced

depth perception.

What is binocular vision?

monocular

field of

vision

binocular

field of

vision

Predators tend to have binocular vision because they need

to judge distances and anticipate the movement of prey.

no field

of vision

Wh t i l i i ?


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What is monocular vision?

Animals with monocular vision have eyes spaced apart,

providing a very wide field of view.

Animals like the

horse have acombination of

monocular and

binocular vision.

monocular

field of

vision

binocular

field of

vision

Prey animals tend to

have monocular vision

because they need to

see predatorsapproaching from any

direction.

no

field of

vision

A d ti


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Accommodation

Correcting sight


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Correcting sight

What is colour blindness?


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What is colour blindness?

Colour blindness (dichromatism) means that a person has

difficulty distinguishing between red and green.

If you have normal vision

you can see an eye in the

image. If you are colourblind you can only see

either red or orange

spots.

Colour blindness is caused by a lack of receptors in the retina

and affects about 7% of men and 1% of women.

What can you see in the circle?


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Glossary (1/2)


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Glossary (1/2)

accommodation The reflex reaction that keeps thelens the right shape to focus light on the retina.

CNS The central nervous system, consisting of the brainand spinal cord.

iris The part of the eye that limits the amount of lightentering the eye.

lens The part of the eye that focuses light on the retina.

motor neurone A neurone that carries electrical

impulses from the CNS to muscles and glands.

neurone A specialized cell that carries electricalimpulses.

Glossary (2/2)


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Glossary (2/2)

neurotransmitterA chemical that diffuses acrosssynapses to continue an impulse in a connecting neurone.

reaction time The time taken to respond to a stimulus.

reflex A fast, automatic protective response.

retina

The part of the eye that contains light receptors.

sensory neurone A neurone thatcarries electricalimpulses from sense organs to the CNS.

synapse The gap between two connecting neurones.

Anagrams


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Anagrams

Multiple choice quiz


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Multiple-choice quiz

5.electricalsignals

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