Response to Stimuli (Chapter 9)

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  • Response to Stimuli
    • Sensory Reception
      • Stimulus and Response
        • Stimulus = detectable change in external/ internal environment of an organism that  causes a response
        • Selection pressure
          • those that survive reproduce and pass alleles onto next generation
            • Natural Selection
          • faster response = more survival
          • e.g.
            • Move towards a food source
            • Move away from harm
              • predators
              • extreme temperatures
        • Stimulus detected by receptors
        • Response carried out by effectors
          • Muscles
          • Glands
        • Communication between receptors and effectors
          • Hormones
            • Slow
            • Plants and animals
          • Nervous system
            • animals
            • Rapid
            • Stimulus > receptor > coordinator > effector > response
      • Taxes
        • Directional response to a stimulus
          • postive = towards
          • negative = away from
        • Environmental
        • movement
          • Whole organism
          • Part of organism
        • e.g.
          • single celled algae
            • positive phototaxis
            • inreases photosynthesis
          • Bacteria
            • positive chemotaxis
            • high concentration of glucose (food source)
          • Earthworms
            • negative phototaxis
            • into soil
              • conserve water
              • find food
              • avoid predators
      • Kineses
        • non-directional response to a stimulus
        • unpleasant conditions
          • more rapid movement
          • more rapid change or direction
        • e.g. temperature and humidity
        • e.g. woodlice
          • preder moist conditions
      • Tropisms
        • plants
        • growth response to a directional stimulus
          • postive = towards
          • negative = away from
        • e.g.
          • shoots
            • positive phototropism
            • more light for photosynthesis
          • roots
            • negative phototropism
              • roots into soil for water and mineral ions
            • positive geotropism
              • roots into soil for water and mineral ions
            • positive hydrotropism
              • Take in most water
    • Nervous Control
      • Nervous organisation
        • CNS
          • brain
          • spinal cord
        • PNS
          • pairs of nerves from brain or spinal cord
          • Types
            • Sensory neurones
              • receptors > CNS
            • Motor neurones
              • CNS > effectors
              • Voluntary
                • to muscles
                • conscious contol
              • Autonomic
                • to
                  • glands
                  • smooth muscle
                  • cardiac muscle
                • subconscious
      • The Spinal Cord
        • Column of nervous tissue
        • runs along back
        • Inside vertebral column for protection
        • pairs of nerves emerging at intervals
      • Reflex Arc
        • involuntary
        • spinal reflex
        • 3 neurons
        • Stages
          • 1.stimulus
          • 2.Receptor
          • 3.Sensory neurone
          • 4.Relay/ Intermediate neurone
          • 5.Motor neurone
          • 6.Effector
          • 7.Response
        • Importance
          • Involuntary
            • brain free to carry out more complex actions
            • brain not overloaded
            • sometimes sent to brain to override if necessary
          • Protect body
            • from birth
            • do not have to be learned
          • Fast
            • pathway short
            • 1 or 2 synapses
    • Control of Heart Rate
      • The Autonomic Nervous System
        • 'self-governing' / involuntary
        • control of internal muscles and glands
        • Sympathetic
          • speeds up
          • occurs when
            • exercise strenuously
            • Powerful emotions
          • Fight or flight
            • heightens awareness
            • prepares for activity
          • Stimulates effectors
        • Parasympathetic
          • inhibits effectors
          • slows down
          • normal resting conditions
          • Concerned with
            • conserving energy
            • Replenishing reserves
        • antagonistic
          • opposite of each other
          • balance of two systems needed
      • Control of Heart Rate
        • Control by chemoreceptors
          • in wall of carotid arteries
          • change in pH results from [CO2]
            • CO2 acid in solution
            • more CO2 lowers pH
          • Process
            • 1.pH lower
              • higher [CO2]
            • 2.detect
              • in aorta and carotid arteries
              • increase frequency of impulses to centre that inreases heart rate
            • 3.Inreases heart rate
              • frequency of impulses from centre increases
              • down sypathetic system
              • to sinoatrial node
            • 4.CO2 level return to normal
              • increased blood flow
              • more CO2 removed by lungs
            • 5.frerquency of impulases to medulla oblongata decreased
              • pH back to normal
            • 6.heart rate decreases to normal
              • frequency of impulses to SAN decreased
        • Control by pressure receptors
          • Blood pressure below norm
            • impulse to centre that increases heart rate
            • sympathetic
            • heart rate increased
          • Blood pressure above norm
            • impulse to centre that decreases heart rate
            • parasympathetic
            • heart rate decreased
          • in walls of aorta and carotid arteries
        • Resting = 70bpm
        • altered for varying oxygen demands
        • Medulla Oblongata
          • controls changes to heart rate
          • region of brain
          • 2 centres
            • Increases
              • linked to sinoatrial node
              • sympathetic
            • Decreases
              • linked to sinoatrial node
              • Parasympathetic
    • Role of Receptors
      • Receptors working together in the eye
        • Rod Cells
          • black and white
          • 120 million in each eye
          • many share single sensory neurone
            • repond to very low light intensity
            • retinal onvergence
            • summation
              • spatial
              • high probability threshold reached
            • Low visual acuity
          • pigment broken down
            • to produce generator potential
            • rhodopsin
            • can occur at low light intensities
        • Cone cells
          • 3 types
            • each respond to different wavelength
            • proportion allows full colour vision
          • 6 million in each eye
          • each has own bipolar cell/sensory neurone
            • only respond to hugh light intensity
            • high visual acuity
          • pigment broken down
            • iodopsin
            • occurs at high light intensities
            • to produce generator potential
            • cannot see colour in dark
        • distinguish between different light intensities
        • range of receptors needed
        • in Mammalian eye
          • on Retina
        • Distibution
          • fovea
            • Light focused here
            • Cone cells only
            • less cone cells futher away
              • Only rod cells at peripheries
              • As lower light intensity further away
          • optic nerve
            • blind spot
            • No rods or cones
      • Structure and Function of Pacinian corpuscle
        • pressure receptor
        • found in
          • fingers
          • feet
          • external genitalia
          • joints
          • ligaments
          • tendons
        • nerone surrounded by layers of tissue seperated by gel
        • function
          • 1.Resting
            • stretch mediated sodium channels closed
            • resting potential
          • 2.Pressure applied
            • changes shape
            • membrane around neurone stretched
          • 3.sodium channels open
            • sodium ions diffuse in
          • 4.depolarised
            • generator potential produced
          • 5.action potential produced
      • Features of Sensory Recption
        • Specific to specific type of stimulus
          • pressure
          • heat
          • light
          • sound
        • Produces generator potential
          • acts as transducer
          • converts stimulus energy to impulse energy
          • convert to generator potential

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