6.1 stimulus and response

• How does the ability to respond to a stimulus increase chance of survival?

  Move away from threat

  Move towards resources
• Two systems of communciations are...

  Endocrine and nervous
• Stimulus


  A detectable change in the internal or external environment which brings about a resposne
• Kinesis


  Random movement response, rate of movement determined by strength of stimulus
• Taxis


  Directional movement response
• Tropism


  Directional growth response
• IAA


  Indolecetic acid - plant growth factor
• IAA in the shoot

  -Produced at tip

  -Stimulates growth

  -Diffuses to shaded side

  -shoot bends towards light
• Benefit of shoot bending to light

  More light energy for light-dependent reaction
• IAA in the root

  -produced at tip

  -inhibits growth

  -diffuses to lower side

  -root bends downwards
• Benefits of root bending downwards

  Provides greater anchorage

  Increases uptake of water and mineral ions
• Motor pathways


  From CNS to effector
• Sensory pathways


  To CNS from receptor
• Sympathetic system


  fight or flight
• parasympathetic system


  rest and digest
• What is the reflex arc?

  Unconscious, involuntary response to a stimulus
• How does the simple reflex give a survival advantage?

  Quick (bypasses brain), innate, fewer synapses

  Protects cells/tissues from danger

  protect from predators
• Reflex Arc Sequence


  Receptor -> sensory neurone -> relay neurone -> motor neurone -> effector
• Sensory Neurone


  Carries impulse from receptor to spinal cord
• Motor Neurone


  Carries impulse from spinal cord to muscle or gland
• Relay Neurone


  In spinal cord, relays signal from sensory to motor neurone
• receptor specif


  each stimulus has specific receptor
• What is the receptor for changes in pressure?

  Panician Corpuscle
• How do receptors create a generator potential?

  Acting as a transducer (changing one form of energy to another)
• Structure of Panincian Corpuscle

  Capsule of connective tissue (contains collagen)

  Gel in between layers of tissue

  Stretched, mediated sodium ion channels in membrane of neurone
• How does a panician corpuscle work?

  -Pressure distorts the layers of tissues

  -Neurone membrane is streched

  -Stretched-mediated sodium ion channels open

  -sodium ions diffuse into neurone

  -generator potential established
• Which receptors are specific for change in light intensity?

  Rods and Cones
• Rods

  -sensitive to low light

  -poor visual acuity

  -periphery of retina

  -1 type

  -lots
• Cones

  -not sensitive to low light

  -high visual acuity

  -flovea (few at retina)

  -3 types

  -fewer
• How do rods/cones work?


  contain optical pigments which are broken down when they absorb light which changes permeability of membrane
• Optical pigment in rods

  Rhodopsin which is broken down easily in low intensity
• Optical pigment in cones

  3 types of iodopsin to enable distinction between colours
• summation in rods

  multiple rod cells connect to 1 neurone so have lower visual acuity because if multiple adjacent rod cells are stimulated, retinal convergence will happen and only one impulse will transmitted.
• Ratio between cone cells and neurones

  1:1

  Higher visual acuity because if adjacent cones are stimulated, 2 seperate impulses are transmitted.
• Cardiac tissue


  myogenic, connected tissues so electrical impulses can pass through, more mitochondria
• Myogenic tissue


  tissue which can contract without nervous stimulation
• Sino Atrial Node


  Natural pacemaker in wall of right atrium, sends out wave of depolarisation across both atria
• Atrioventricular Node


  Wall of atria, picks up depolarisation and transmits it down the bundle of his to the apex of the heart after a delay to allow the atria to empty
• Purkyne fibres


  Branched from bundle of his, transmit impulse to the ventricles which are sitmulated to contract
• Where are the Chemoreceptors and pressure receptors located?

  Wall of carotid artery and aorta