M5:S3 Animal responses

• Nervous system


  Clever system that allows many things to happen without conscious thought, e.g. digestion, breathing, blinking, yawning
• Responding to their environment helps animals survive
• Receptors

  • Detect stimuli
  • Communicate with effectors via nervous system or hormonal system
• Stimulus


  Any change in the internal or external environment
• Main structural systems of the nervous system

  • Central nervous system (brain and spinal cord)
  • Peripheral nervous system (neurones connecting CNS to body)
• Functional systems of the peripheral nervous system

  • Somatic nervous system (controls conscious activities)
  • Sympathetic nervous system (fight or flight system)
  • Parasympathetic nervous system (rest and digest system)
• Hypothalamus


  Controls body temperature
• Pituitary gland


  Controlled by hypothalamus, releases hormones and stimulates other glands
• Cerebrum


  • Largest part of brain, involved in vision, hearing, learning and thinking
• Medulla oblongata


  • Controls breathing rate and heart rate
• Cerebellum


  • Coordinates muscles, balance and posture
• Reflex

  Rapid, automatic response to a stimulus without conscious decision
• Blinking reflex


  1. Sensory nerve endings in cornea stimulated

  2. Nerve impulse to relay neurone in CNS

  3. Impulse to motor neurones

  4. Orbicularis oculi muscles contract to close eyelid
• Knee-jerk reflex


  1. Stretch receptors in quadriceps detect stretch

  2. Sensory neurone communicates directly with motor neurone in spinal cord

  3. Motor neurone carries impulse to quadriceps muscle to contract
• The autonomic nervous system controls unconscious activities
• Sympathetic nervous system


  The 'fight or flight' system, releases noradrenaline
• Parasympathetic nervous system


  The 'rest and digest' system, releases acetylcholine
• When an organism is threatened


  It responds with the fight or flight response
• Fight or flight response

  1. Nerve impulses activate hypothalamus

  2. Hypothalamus stimulates pituitary gland to release ACTH

  3. Adrenal gland cortex releases steroidal hormones

  4. Sympathetic nervous system activated, releases adrenaline

  5. Effects: increased heart rate, deeper breathing, glucose release, blood diverted to vital organs, hair stands on end
• Sinoatrial node (SAN)


  • Generates electrical impulses to make cardiac muscles contract
  • Heart rate controlled by medulla in brain
• Nervous system control of heart rate

  1. Baroreceptors detect blood pressure changes

  2. Chemoreceptors detect blood O2, CO2, pH changes

  3. Receptors send impulses to medulla

  4. Medulla sends impulses to SAN via vagus nerve (slows heart) or accelerator nerve (speeds heart)
• Hormonal system control of heart rate

  Adrenaline released binds to heart receptors, causing more frequent and forceful contractions, increasing heart rate
• Before you start, make sure you know how to measure your heart rate
• Measuring heart rate


  1. Find your pulse in your wrist by placing your index and middle finger where the base of your thumb meets your forearm

  2. Count the number of beats in 15 seconds

  3. Multiply by four to get the number of beats per minute
• Measuring heart rate before and after exercise

  1. Measure your heart rate at rest and record it in a table

  2. Do some gentle exercise, such as stepping on and off a step for about 5 minutes

  3. Immediately afterwards, measure your heart rate again

  4. Return to a resting position

  5. Measure your heart rate every minute until it returns to the starting rate

  6. Record how long it takes to return to normal
• Heart rate monitor


  • Contains sensors which measure your heart rate
• You could also measure other effects on heart rate in a similar way. For example, you could test the effect of a loud noise or the effect of anxiety (by doing something that makes you nervous)
• Analysing the effect of exercise on heart rate using Student's t-test

  1. Identify the null hypothesis

  2. Calculate the mean and standard deviation for each data set

  3. Use the formula to calculate t

  4. Calculate the degrees of freedom

  5. Look up the values for t in a table of critical values
• Null hypothesis


  There is no significant difference between the mean resting heart rate of people who received endurance training and those who did not
• If the result of your t-test is greater than the critical value at a P value of less than 2% (< 0.02), or even 1%, you can be even more confident that the difference is significant
• There is a different equation that you can use for paired data (data that includes two measurements for each person, eg before and after endurance training)
• My heart rate seems to be controlled by the boy next door...
• It's also rising rapidly at the sight of so much to learn. You've got to properly learn it though it's no good just having a rough idea. SANs, baroreceptors, chemoreceptors - get it learnt then try to reproduce the table from the previous page.
• Troponin molecules return to original shape

  1. Pulling attached tropomyosin molecules with them

  2. Tropomyosin molecules block actin-myosin binding sites again
• Muscles aren't contracted because no myosin heads are attached to actin filaments so there are no actin-myosin cross bridges
• Actin filaments slide back to relaxed position

  Lengthens the sarcomere
• Myofibrils


  Made up of two proteins
• What happens to sarcomeres as a muscle relaxes
• Bond formed when myosin head binds to actin filament


  Actin-myosin cross bridge
• ATP and CP provide the energy for muscle contraction