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animal responses (muscle contraction (neuromuscular junctions (= a synapse…

- - - - when an action potential from a motor neurone stimulates a muscle cell, it depolarises the sarcolemma . depolarisation spreads down the t tubules to the sarcoplasmic reticulum
      - this causes SR to release store of Ca2+ ions into sarcoplasm
      - calcium ions bind to troponin causing it to change shape , this pulls attached tropomyosin out of actin-myosin binding site on actin filament
      - this exposes binding site which allows myosin head to bind
      - actin-myosin cross bridge is formed
    - - Ca2+ ions activate ATPase which breaks down ATP into ADP and Pi to provide envy for muscle contraction
      - the energy released from ATP moves the myosin head which pulls the actin filament
    - - ATP provide energy for break actin-myosin cross bridge so myosin head attached from actin filament after its moved
      - myosin head then reattaches to a different binding site further along actin filament forming anew actin-myosin cross bridge and the cycle is repeated
      - many cross bridges break and form rapidly pulling the actin filament along which shortens the sarcomere , causing muscle to contract
      - cycle will continue as long as calcium ions are bound to troponin
  - - - most ATP is generated via oxidative phosphorylation in mitochondria
      - only occurs when oxygen is present
    - - ATP is made rapidly by glycolysis
      - end product of glycolysis is pyruvate which is converted to lactate by lactate fermentation
      - lactate can build up in muscles causing fatigue
    - - ATP is made by phosphorylating ADP by adding a phosphate group from creatine phosphate
      - CP is stored inside cells and the ATP-CP system generates ATP quickly
      - ATP-CP system is anaerobic
      - CP runs out very quickly
  - - - controlled consciously
      - it is striated
      - many muscle fibres have multiple nuclei
      - muscle cells form fibres and is surrounded by sarcolemma
      - contains actin and myosin
    - - controlled unconsciously
      - contract slowly and don't fatigue
      - each muscle fibre has one nuclei
      - 500ym long cells
      - contains myofibrils which are divided into a chain of sub units called sarcomeres
    - - myogenic (but contraction is controlled by autonomic nervous system)
      - made of fibres connected via intercalated discs which have low electrical resistance so nerve impulses pass easily through cells
      - muscles fibres are branched and form cross bridges to allow nerve impulses to spread through whole muscle
      - each muscle fibre has one nucleus
      - don't fatigue
      - striated
- - - - heart rate is increased- so blood is pumped around body faster
      - the muscles around the bronchioles relax- breathing is deeper
      - glycogen is converted into glucose- so more glucose is available for muscles for respiration
      - muscles in the arterioles applying blood to skin/ gut constrict, muscles in arterioles supplying blood to heart, lungs and skeletal muscle dilate
      - erector pili muscles in skin contract- hairs stand on end so animal looks bigger
  - - - pressure receptors (baroreceptors) in the aorta and vena cava - stimulated by high and low blood pressure
      - chemical receptors (chemoreceptors) in he aorta the carotid artery and the medulla - monitor O2 and CO2 level in blood and blood pH
- - - - motor system= conducts action potentials from CNS to effectors
        
        autonomic nervous system= controls unconscious activities e.g. digestion, consists of motor neurones that conduct action potentials under involuntary control, most are non myelinated, at least 2 neurones between CNS and effector, connected to ganglia
        
        sympathetic nervous system= increases activity (fight or flight), release noradrenaline neurotransmitter, ganglia outside CNS, consists of lots of nerves leading out of CNS each leading to separate effector, short preganglionic neurones, long post ganglionic neurones
        
        parasympathetic nervous system= decreases activity, release acetylcholine neurotransmitter, ganglia is in effector tissue, consists of a few nerves leading out of CNS which divide and lead to different effectors, long preganglionic neurones, short post ganglionic neurones
        
        somatic nervous system= controls conscious activities e.g. running, consists of motor neurones that conduct action potentials to effectors under voluntary control, most are myelinated so response is rapid, one single neurone connecting CNS to effector
      - sensory nervous system= dendrons of sensory neurones enter CNS, conduct action potentials from CNS to sensory receptors, neurones have cell body in dorsal root leading to spinal chord and a short axon
  - - - located beneath middle part of brain
      - maintains body temp- action potentials from receptors in skin and core body temp mediated by H and N systems, osmoregulation-mediated by H system
      - produces hormones which control the pituitary gland
    - - found beneath hypothalamus
      - releases hormones and stimulates other glands
      - anterior lobe produces its own hormones in response to hormones produced by hypothalamus e.g. lactation, stress, growth
    - - at the base of brain at the top of the spinal chord
      - it automatically controls heart and breathing rate and blood pressure
      - sends action potentials via autonomic nervous system
    - - cerebellum is beneath cerebrum and also has a highly folded cortex
      - it is important for muscle contraction and relaxation, posture and coordination of balance
      - can be learnt/ practised e.g. learning to ride a bike
      - connected to cerebrum by pons
    - - controls= conscious thought, conscious actions, factual memory, emotional responses, decision making
      - splits into 2 hemispheres connected by corpus callosum
      - outermost layer= cerebral cortex - sensory areas receive action potentials indirectly from sensory neurones, association areas compare sensory input with previous experiences to decide appropriate response, motor areas send action potentials to effectors (size of region are related to complexity of movements in parts of body)
  - - - sensory nerve endings in cornea are stimulated by touch
      - a nerve impulse is sent along the sensory neurone to a relay neurone in the CNS
      - the impulse is then passed from the relay neurones to the motor neurones
      - the motor neurones send impulses to the effectors- the orbiculares oculi muscles that move eyelids. these muscles contract causing the eyelid to close quickly and prevent eye being damaged
      - stimulated by= object touching eye, loud sound, sudden movements, bright light
      - corneal reflex
        
        controlled by sensory neurone in cornea which enters pons, synapse connects sensory neurone to relay neurone which passes action potential to motor neurone which passes out of brain to facial muscles causing eyelid to blink
        
        pathway is short and direct so reflex is rapid, effects both eyes
        
        sensory neurone also passes action potential to myelinated neurones in pons which is carried to sensory region of cerebral cortex to inform that stimulus has occured allowing reflex to be overriden by conscious control, cerebral cortex can send inhibitory signals to motor centre in pons which prevents formation of action potential to motor neurone
      - optical reflex
        
        protects light sensitive cells in retina from damage
        
        mediated by optical centre of cerebral cortex
        
        slower than corneal reflex
    - - stretch receptors (muscle spindles) in the quadriceps muscle detect that the muscle is being stretched
      - a nerve impulse is passed along a sensory neurone which communicates directly with a motor neurone in the spinal chord
      - the motor neurone carries the nerve impulse to the effector causing it to contract so the lower leg moves forward quickly
      - sensory neurone--> motor neurone
      - brain cannot inhibit reflex as there is no relay neurone (not enough delay to trigger inhibition)
      - during walking/running muscle spindles are stimulated , as an action potential is sent to muscles in thigh stimulating contraction, inhibitory action potentials are sent to synapses in reflex arc to prevent reflex contraction of opposing muscle