Assessment Statements Obj

E11 Define the terms stimulus response and reflex 1

E12 Explain the role of receptors sensory neurons relay neurons motor neurons synapses and effectors in the response of animals to stimuli 3

E13Draw and label a diagram of a reflex arc for a pain withdrawal reflex including the spinal cord and its spinal nerves the receptor cell sensory neuron relay neuron motor neuron and effector Include white and grey matter dorsal and ventral roots

1

E14Explain how animal responses can be affected by natural selection using two examples

bull Sylvia atricapilla (blackcap bird) migration changes bull Heliconius cydno butterflies and changes in mate preference

3

Assessment statements from Online IB Biology Subject GuideCommand terms httpi-biologynetibdpbiocommand-terms

What connections can you make with other topics

Stimulus amp Response

nerves hormones homeostasis

evolution

The Pain ReflexThe pain withdrawal reflex is a rapid unconscious response to danger or injury It is mediated by the spinersquos grey matter

Reflex animation from httpwwwbbccoukschoolsgcsebitesizescienceadd_ocr_pre_2011brain_mindreflexactionsrev1shtml

A very basic overview from the BBC

Spine-mediated pain reflex arc from httpenwikibooksorgwikiAnatomy_and_Physiology_of_AnimalsNervous_System

The Pain ReflexThe pain withdrawal reflex is a rapid unconscious response to danger or injury It is mediated by the spinersquos grey matter

(nociceptors)

Spine-mediated pain reflex arc from httpenwikibooksorgwikiAnatomy_and_Physiology_of_AnimalsNervous_System

The Pain ReflexThe pain withdrawal reflex is a rapid unconscious response to danger or injury It is mediated by the spinersquos grey matter

Injury stimulates pain receptors (nociceptors) causing Ca2+ ions to rush in This depolarises the sensory neuron and starts an action potential

httpwwwvetedacukanimalpainPagesanimation2htm

(nociceptors)

Spine-mediated pain reflex arc from httpenwikibooksorgwikiAnatomy_and_Physiology_of_AnimalsNervous_System

The Pain ReflexThe pain withdrawal reflex is a rapid unconscious response to danger or injury It is mediated by the spinersquos grey matter

Injury stimulates pain receptors (nociceptors) causing Ca2+ ions to rush in This depolarises the sensory neuron and starts an action potential

httpwwwvetedacukanimalpainPagesanimation2htm

(nociceptors)

propagates the AP along theaxon (review action and resting potentials)

Spine-mediated pain reflex arc from httpenwikibooksorgwikiAnatomy_and_Physiology_of_AnimalsNervous_System

The Pain ReflexThe pain withdrawal reflex is a rapid unconscious response to danger or injury It is mediated by the spinersquos grey matter

Relay neurons (interneurons in the animation above) are in the grey matter of the spine They receive the signal from the sensory neuron through synaptic transmission (review it) and coordinate the response to pain

bull An excitatory neurotransmitter (eg ACh) is sent across the next synapse to the motor neuron for muscles to contract

bull An inhibitory NT is used to send a signal to antagonistic (opposite) muscles to relax

httpbcswhfreemancomthelifewirecontentchp464601sswf

Spine-mediated pain reflex arc from httpenwikibooksorgwikiAnatomy_and_Physiology_of_AnimalsNervous_System

The Pain ReflexThe pain withdrawal reflex is a rapid unconscious response to danger or injury It is mediated by the spinersquos grey matter

(nociceptors)

Finally the motor neurons conduct the AP from the relay neuron to the effector (muscle) bull Muscles that need to contract

receive and excitatory signal bull Muscles that need to relax

receive an inhibitory signal

The response is rapid movement away from the source of pain

A

Dorsal root ganglion (passage for neurons)

Ventral root ganglion (passage for neurons)

BC

D

EF

G

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