Response to Stimuli (Chapter 9)

Created by: Tassillow
Created on: 28-05-16 20:21

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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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Response to Stimuli (Chapter 9)

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