Response to Stimuli Summary

Overview of Responses to Stimuli

-Sensory Control

-Nervous Control

-Control of Heart Rate

-Role of Receptors

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  • Response to Stimuli
    • Survival and Response
      • Nervous Control
        • Simple Reflex Arc
          • 1) Stimulus
          • 2) Receptor
          • 3) Sensory Neurone
          • 4) Intermediate Neurone
          • 5) Motor Neurone
          • 6) Effector
          • 7) Response
          • Important because...
            • Involuntary- Brain not overloaded
            • Protect from harmful stimuli
            • Fast- important for withdrawal reflexes
        • Nervous Organisation
          • Peripheral Nervous System
            • Sensory Nervous System
            • Motor Nervous System
              • Voluntary Nervous System (to body muscles; conscious)
              • Autonomic Nervous System (to glands, smooth muscle and cardiac muscle; unconscious)
          • Central Nervous System
            • Brain
            • Spinal Cord
      • Sensory Control
        • Taxes
          • Simple response directed by stimulus
          • Direct response to stimulus
          • Positive taxis = towards stimulus
          • Negative taxis = away from stimulus
        • Kinesis
          • Random movement in response to a stimulus
          • The more unpleasant the stimulus, the more rapid the movement
        • Tropisms
          • Growth movement in response to a stimulus
          • In plants
          • Positive = towards stimulus
          • Negative = Away from stimulus
          • Type of response named after stimulus (eg. light = phototropism)
    • Control of Heart Rate
      • Chemoreceptors
        • In wall of carotid arteries
        • Sensitive to changes in pH
        • Increase frequency of nerve impulses
        • Via sympathetic nervous system
      • Pressure Receptors
        • Blood pressure too high
          • Impulse via parasympathetic nervous system
          • SAN decreases heart rate
        • Blood pressure too low
          • Impulse via sympathetic nervous system
          • SAN increases heart rate
        • In wall of carotid arteries and aorta
      • Autonomic Nervous System
        • Controls involuntary activities of internal muscles and glands
        • Sympathetic- speeds up any activity
        • Parasympathetic- slows any activity
        • Antagnostic
      • Control Method
        • Changes in heart rate controlled by medulla oblongata
        • Medulla has 2 centres, one linked with sympathetic, one with parasympathetic
        • Centres linked to sinoatrial node
        • Stimulated by chemical and pressure changes in blood
    • Role of Receptors
      • Pacinian corpuscle
        • Only responds to mechanical pressure
        • Acts as a 'transducer' (converts information from stimulus to something that can be understood)
        • Produces a 'generator potential' (nerve impulse that stimuli information is converted to)
        • Stimulation of membranes produces deformation of stretch-mediated sodium channels
          • Leads to the establishment of a generator potential
      • Mammalian Eye
        • Rod cells
          • Rod shaped
          • Mostly around retina
          • Give poor visual acuity
          • Sensitivity to low light levels
        • Cone cells
          • Cone shaped
          • Mostly around fovea
          • Give good visual acuity
          • Not sensitive to low light levels

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