OCR alevel biology animal responses

• How is the nervous system divided?

  1.The central nervous system which consists of the brain and spinal cord

  
  

  2.The peripheral nervous system which is split into somatic and autonomic nervous system .The autonomic system is then split into the sympathetic and parasympathetic nervous system.
• What is the function of the somatic and autonomic nervous system?

  Somatic nervous system- controls conscious activities such as running / playing video games

  
  

  Autonomic nervous system - controls unconscious activities e.g digestions split into the sympathetic system which gets the body ready for action fight/flight system releases the neurotransmitter noradrenaline and the parasympathetic nervous system which calms the body down releases the neurotransmitter acetylcholine
• Function of cerebellum

  Controls uncurious functions such as posture , balance and non-voluntary movement
• Function of cerebrum

  Vision , hearing , learning and thinking
• Function of hypothalamus

  Regulatory centre for temp and water balance controls complex patterns of behaviour such as sleeping and also produces hormones
• Function of medulla oblongata

  Automatically controls har rate and breathing rate , swallowing and coughing
• Function of pituitary gland

  Stores and releases hormones controlled by the hypothalamus
• Survival importance of reflexes

  -extremely fast

  -being involuntary responses

  -not having to be learnt
• Blinking reflex


  1.sensory nerve endings in the cornea are stimulated by touch

  
  

  2.nerve impulse is sent along the sensory neurone to a relay neurone in the central nervous system.

  
  

  3.the impulse is then passed from the relay neurone to motor neurones

  
  

  4.Motor neurones send impulses to effectors- the orbicularsis oculi muscles that move your eyelids

  
  

  5.These muscles contract causing your eyelids to close quickly and prevent your eye from being damaged
• Knee jerk reaction

  the reaction to a slight tap over the knee joint that causes the knee to jerk in response to assess the nervous system
• How does the knee jerk reflex work?

  Leg tapped just below the patella, stretches the patellar tendon, initiates the reflex arc, extensor muscle on top of the thigh contracts, relay neurone inhibits motor neurone of the flexor muscle so it relaxes, contraction of the extensor muscle causes the leg to kick
• Fight or flight response


  1.Nerve impulses from sensory neurones arrive at the hypothalamus activating both the hormonal system and the sympathetic nervous system.

  
  

  2.The pituitary gland is stimulated to release a hormone called ACTH this causes the cortex of the adrenal gland to release steroidal hormones.

  
  

  3.Sympathetic nervous system is activated triggering the release of adrenaline from the medulla region of the adrenal glands
• Effects of adrenaline and sympathetic nervous system

  1.Heart rate is increased

  
  

  2.Muscles around bronchioles relax - breathing is deeper

  
  

  3.glycogen is converted into glucose

  
  

  4.Muscles in the arteries supplying the skin and gut constrict
• Two types of receptors that provide information that affect heart rate

  Baroreceptors (pressure) - detect changes in blood pressure present the aorta , vena cava and carotid arteries

  
  

  chemoreceptors - detect changes in the level of chemicals in the blood such as carbon dioxide they are located in the aorta , carotid artery and medulla
• What happens if blood pressure is too high?

  1. Impulses are sent to the medulla oblongata centre which decreases heart rate

  
  

  2.The medulla oblongata sends impulses along parasympathetic neruons to the SAN which decreases the rate at which the heart beats .

  
  

  3. This reduces blood pressure back to normal
• What happens if blood pressure is too low?

  1. Impulses are sent to the medulla oblongta centre which increases heart rate.

  
  

  2. The medulla oblongata sends impulses along sympathetic neurons to the SAN which increases the rate at which the heart beats. This increases blood pressure back to normal
• Part of the brain responsible for controlling heart rate

  Medulla oblongata has two centres one for increasing heart rate - accelerator nerve and one for decreasing heart rate - vagus nerve
• What happens when carbon dioxide levels in the blood decreases?

  1. The pH of the blood rises this is detected by chemoreceptors in the wall of the carotid arteries.

  
  

  2. This results in a reduction in the frequency of the nerve impulses being sent to medulla oblongata

  
  

  3. In turn this reduces the frequency of the nerve impulses being sent to the SAN vis the SNS and thus heart rate decreases back to its normal level
• What happens when carbon dioxide levels in the blood increases?

  1. The pH of the blood decreases because carbonic acid is formed when the carbon dioxide interacts with water in the blood.

  
  

  2. If the chemoreceptors detect a decrease in blood pH a response is triggered to increase heart rate.

  
  

  3. Blood therefore flows more quickly to the lungs so carbon dioxide can be exhaled
• Adrenaline's function during fight/flight

  -triggers the liver cells to undergo glycogenolysis so that glucose is released into the blood stream.

  
  

  -This allows respiration to increase so more energy is available for muscle contraction .
• Skeletal muscle (voluntary muscle)

  -controlled consciously made up of many muscle fibres ( many nuclei)

  
  

  - responsible for movement e.g biceps and triceps

  
  

  - fibres appear striated

  
  

  -contraction speed = rapid

  
  

  -length of contraction is short

  
  

  -fibres are tubular and multinucleated
• Involuntary muscle (smooth muscle)

  - non-striated

  -involuntary

  -contraction speed = slow

  -length of contraction = relatively long time

  -fibres are spindled shaped and uninucleated

  -Gut smooth muscles contract to move food along
• Cardiac muscle

  -found only in the heart

  -myogenic meaning they contract without the need for a nervous stimulus - causes heart to beat in a regular rhythm

  -involuntary

  -cell branch and interconnect resulting in simultaneous contraction

  -contraction speed = intermediate

  -fibres branched and uninucleated
• Describe the structure of skeletal muscles

  1. Made up of large bundles of long cells = muscle fibres

  
  

  2.Cell membrane of the muscle fibres = sarcolema .

  
  

  3.The sarcolemma has many deep tube-like projections that fold in from its outer surface = transverse (T) tubules - help spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre.

  
  

  4.Sacroplasmic reticulum - stores and releases calcium ions needed for contraction.

  
  

  5.Muscle fibres have lots of mitochondria - ATP for muscle contraction
• What are myofibrils?

  -Myofibrils are located in the sarcoplasm

  -Each myofibril is made up of two types of protein filament

  Thick filaments-myosin. Thin filaments-actin
• What do dark bands and light bands contain?

  1. Dark bands contain thick myosin filaments and some overlapping thin actin filaments - A bands

  
  

  2.Light bands contain thin actin filaments - I bands
• H band


  thick myosin filaments only
• M line and Z line

  M line - attachment for myosin filaments

  Z line - attachment for actin filaments
• What is a sarcomere?

  Section of myofibril between two z lines
• Sliding filament theory

  1.Myosin and actin filaments slide over one another to make the sarcomeres contract

  
  

  2.Simultaneous contraction of lots of sacromeres means the myofibrils and muscle fibres contract

  
  

  3.Sarcomeres return to original length as muscle relaxes
• Myosin filaments structure


  1.Globular heads that are hinged so they can move back and forth.

  
  

  2.Each myosin head has a binding site for actin and a binding site for ATP
• Actin filaments structure


  1. Binding sites for myosin heads called actin - myosin binding sites

  
  

  2.Proteins tropomyosin and troponin found between actin filaments attached to each other and help myofilaments move past each other.
• Muscle contraction triggered by action potential stage 1

  1.Action potential triggers influx of calcium ions

  .when an action potential from motor neurone stimulates a muscle cell it depolarises the sacrolema depolarisation spreads down T tubules to the sarcoplasmic reticulum

  
  

  .This causes the sarcoplasmic reticulum to release Ca 2+ into sarcoplasm

  
  

  .it binds to troponin causing shape change this pulls attached tropomyyosin out of action - myosin binding site on actin filament this exposes the binding site which allows myosin head to bind
• Muscle contraction triggered by action potential stage 2

  2. ATP provides energy to move myosin head

  
  

  .Ca2+ activate enzyme ATpase this breaks down ATP (Into ADP + Pi). This provides energy for muscle contraction

  
  

  .Energy releases from ATP moves myosin head which pulls actin filament into a rowing action
• Muscle contraction triggered by action potential stage 3


  3. Break cross bridge

  
  

  .ATP provides energy to break actin myosin cross bridge so myosin head detached

  
  

  .It reattaches to different binding sites further along the actin filament

  
  

  .A new actin myosin cross bridge is formed and cycle is completed

  
  

  .Cross bridges form and break rapidly pulling actin filament along this shortens the sacromere making the muscle contract.
• What happens when excitation stops?

  1.when muscle stops being stimulated calcium ions leave binding sites on troponin molecules and are moved by AT into the sarcoplasmic reticulum

  
  

  2.Troponin molecules return to original shape pulling attached tropomyosin molecules with them tropomyosin blocks actin-myosin binding sites

  
  

  3.Muscles arent contracted because no myosin heads are attached to actin filaments - slide back to relaxed positions which lengthens sarcomere
• How is ATP generated by aerobic respiration

  -ATP generated via oxidative phosphorylation in the cell's mitochondria

  
  

  -Only works when there's oxygen

  
  

  -good for low intensity exercise such as walking or jogging
• How is ATP generated by anaerobic respiration?

  -ATP made rapidly by glycolysis

  -end product is pyruvate which is converted to lactate by lactate fermentation

  -Lacatate builds up quickly in the muscle and cases muscle fatigue

  -Good for short periods of hard exercise
• Fast muscle fibres


  -contract rapidly

  -rely on anaerobic respiration for ATP supply

  -fewer capillaries

  -They are suited to short bursts of high-intensity activity as they fatigue quicklydue to the lactate produced from anaerobic respiration
• Why do fast muscle fibres look paler in colour than slow muslce fibres?


  Low amounts of myoglobin are present in fast muscle fibres.

  
  

  .Myoglobin is a red pigment molecule that is similar to haemoglobin

  
  

  .myoglobin functions as a store of oxygen in muscles and increases the rate of oxygen absorption from the capillaries

  
  

  Due to this fast muscle fibres appear paler in colour