Reflex Arcs Reflex Arcs

SNAB Topic 8 Grey MatterSNAB Topic 8 Grey Matter

Lesson 3Lesson 3

Learning ObjectivesLearning Objectives

Describe the path of nerve impulses in Describe the path of nerve impulses in reflex arcsreflex arcs

Describe the pupil reflexDescribe the pupil reflexExplain the process by which the pupil Explain the process by which the pupil

reflex is controlledreflex is controlled

Key Notes Interesting Facts Questions

Reflex ActionsReflex Actions

Many of the actions we carry out every Many of the actions we carry out every day are done without conscious thoughtday are done without conscious thought

These are call These are call Reflex ActionsReflex ActionsThe nerve impulses in reflex actions do The nerve impulses in reflex actions do

not follow the same path as those in not follow the same path as those in conscious actionsconscious actions

The path they follow is called the The path they follow is called the Reflex Reflex ArcArc

GCSE Review QuestionGCSE Review Question

What neuron is unique to the Reflex Arc?What neuron is unique to the Reflex Arc?A. Effector

B. Motor

C. Relay

D. Sensory

Examples of Reflex ArcsExamples of Reflex Arcs

Knee Jerk Reaction – Involved in keeping Knee Jerk Reaction – Involved in keeping standingstanding

Pupil Dilation – Protect eyes from lightPupil Dilation – Protect eyes from lightVomit ReflexVomit ReflexCough ReflexCough ReflexSneeze ReflexSneeze ReflexEye tracking ReflexEye tracking Reflex

Nervous Im

pulse Pathw

ay N

ervous Impulse P

athway

in a Reflex A

rcin a R

eflex Arc

Interlink/Relay NeuronsInterlink/Relay Neurons

These neurons are These neurons are the vital part of the the vital part of the reflex arcreflex arc

They connect the They connect the Sensory neuron to the Sensory neuron to the Motor/Effector neuronMotor/Effector neuron

They can be found in They can be found in the grey matter of the the grey matter of the spinal cord and in the spinal cord and in the midbrainmidbrain

Advantage of ReflexesAdvantage of Reflexes

The reflex arc allows The reflex arc allows a much quicker a much quicker response to stimuliresponse to stimuli

This is especially This is especially important where the important where the stimuli is a source of stimuli is a source of potential damage e.g. potential damage e.g. a hot object, a sharp a hot object, a sharp pinpin

Inhibition of the Reflex ResponseInhibition of the Reflex Response

The reflex response is considerably The reflex response is considerably inhibited in several situations:inhibited in several situations:

Exposure to Noradrenalin Exposure to Noradrenalin (Parasympathetic nervous system)(Parasympathetic nervous system)

TirednessTirednessHigh Blood AlcoholHigh Blood AlcoholEffect from Sedative Drugs (e.g. Effect from Sedative Drugs (e.g.

Cannabis)Cannabis)

Stimulation of the Reflex ResponseStimulation of the Reflex Response

The speed of the reflex response can be The speed of the reflex response can be increase by several factors:increase by several factors:

Exposure to adrenaline (Sympathetic Exposure to adrenaline (Sympathetic Nervous System)Nervous System)

Exposure to stimulant drugs (Caffeine, Exposure to stimulant drugs (Caffeine, Beta Amphetamines/Speed)Beta Amphetamines/Speed)

The Pupil Reflex ResponseThe Pupil Reflex Response

The pupil response allows the iris to The pupil response allows the iris to contract and dilatecontract and dilate

This changes the size of the pupilThis changes the size of the pupil In the eye the pupil acts like an apertureIn the eye the pupil acts like an aperture It controls the amount of light which enters It controls the amount of light which enters

the eye..the eye..… … and protect the retina from and protect the retina from

“overexposure”“overexposure”

Bright Light, Bright LightBright Light, Bright Light

When light levels are When light levels are high high CircularCircular muscles in the iris muscles in the iris contractcontract

This causes the pupil This causes the pupil to become smallerto become smaller

This is controlled by This is controlled by the parasympathetic the parasympathetic nervous systemnervous system

In the Dark…In the Dark…

When light levels are When light levels are low low Radial Radial muscles muscles contractcontract

This causes the pupil This causes the pupil to increase in sizeto increase in size

This is caused by the This is caused by the sympathetic nervous sympathetic nervous systemsystem

Diagram of Pupil ResponseDiagram of Pupil Response

Control of the Pupil Reflex: In DetailControl of the Pupil Reflex: In Detail

When high levels of light strike When high levels of light strike photoreceptorsphotoreceptors in the retina they cause in the retina they cause nervous impulses to be sent along the nervous impulses to be sent along the SensorySensory neuron ( neuron (Optic NerveOptic Nerve))

These impulses are co-ordinated by relay These impulses are co-ordinated by relay neurons in the neurons in the MidbrainMidbrain

Signals are then sent along the Signals are then sent along the parasympathetic nervous system parasympathetic nervous system

Diagram

of the Pupil

Diagram

of the Pupil

Reflex A

rcR

eflex Arc

Eye Dilation VideosEye Dilation Videos

http://video.google.co.uk/videoplay?docid=-4513396283977692296&q=pupil

http://video.google.co.uk/videoplay?http://video.google.co.uk/videoplay?docid=-2586168005397990196&q=pupildocid=-2586168005397990196&q=pupil

http://video.google.co.uk/videoplay?http://video.google.co.uk/videoplay?docid=-docid=-6096473483443032157&q=pupil+reflex6096473483443032157&q=pupil+reflex

AtropineAtropine

Atropine is a sedative drug made from the Atropine is a sedative drug made from the deadly nightshade plant (deadly nightshade plant (Atropa Atropa belladonna)belladonna)

It was apparently used in the middles ages It was apparently used in the middles ages by women to dilate there pupilsby women to dilate there pupils

This is the source of the word belladonna This is the source of the word belladonna in Latin and Belle in French in Latin and Belle in French

Check PointCheck Point

What muscle contracts when the pupil What muscle contracts when the pupil dilates?dilates?

A.A. OpticOptic

B.B. RadialRadial

C.C. Ocular MotorOcular Motor

D.D. CircularCircular

Check PointCheck Point

What nervous system is involved in pupil What nervous system is involved in pupil contraction?contraction?

A.A. SomaticSomatic

B.B. SympatheticSympathetic

C.C. CentralCentral

D.D. ParasympatheticParasympathetic

Correct!Correct!

Try Again!Try Again!