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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 Lewis’s world record for the 100 m sprint. But who was quickest?


On the starting blocks

Pressure sensors in the starting blocks record when a sprinter sets off.

This prevents the runner located furthest 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 starter’s gun is fired. The actual gun is normally silent – the ‘bang’ comes from speakers behind the starting blocks.


Pressure-time graph


Gaining the advantage


Scientists have found that it is physically impossible to react in less than 0.1 seconds. If a runner’s 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)

pre

ssu

re


Is there a correlation?


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 30 mph a car can travel 9 m 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 320 mph and take just0.02 seconds to reach the brain.


Interpreting signals

How can you find your reaction time?

1. Extend your arm over the edge of a table and have a partner hold a ruler between your fingers at the 0 cm mark.

2. The partner drops the ruler – catch it between 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 the central 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?

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 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 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.

nerve


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

cell body

dendrites


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 organ

nerve 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 of neurotransmitter molecules from synaptic vesicles.

synaptic vesicle

neurotransmitter molecules


Continuing the impulse

The neurotransmitters diffuse across the synaptic cleft and bind with receptors on the next neurone, triggering another impulse.

nerve impulse

receptor

synaptic cleft


The sequence of a reflex arc


True or false?


The iris reflex


Inside the eye

lensfocuses lighton retina

irisregulates amountof light entering eye

ciliary muscleschange shape of the lens

optic nervetransmits impulses to the brain

corneaprotects eye surface and focuses light rays

retinasenses lighthold lens in place

suspensory ligaments


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


What is monocular vision?

Animals with monocular vision have eyes spaced apart, providing a very wide field of view.

Animals like the horse have a combination of monocular and binocular vision.

Prey animals tend to have monocular vision because they need to see predators approaching from any direction. monocular

field of vision

binocularfield of vision

nofield of vision


Accommodation


Correcting sight


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 colour blind 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?


Parts of the eye


Glossary (1/2)

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

CNS – The central nervous system, consisting of the brain and spinal cord.

iris – The part of the eye that limits the amount of light entering 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 electrical impulses.


Glossary (2/2)

neurotransmitter – A chemical that diffuses across synapses 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 that carries electrical impulses from sense organs to the CNS.

synapse – The gap between two connecting neurones.


Anagrams


Multiple-choice quiz

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