Animal Responses

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The Brain

The Cerebrum

  • Largest part of brain - divided into two hemispheres connected by the corpus collosum
  • beneath surface is the cerebral cortex  - responsible for speech, emotions and decision making
  • cerebral cortex subdivided into sensory areas, association areas and motor areas 
  • impulses from ears, eyes and sense organs arrive at association areas 
  • in motor areas nerve impulses are sent to effectors

Cerebellum - Controls the coordiantion of movement and posture

  • Recieves impulses from ears, eyes and stretch receptors in muscles and other parts of the brain
  • Information is intergrated and used to coordinate the timing and pattern of skeletal muscle and contraction and relaxation. 

Medulla Oblongata - controls autonomic nervous system

  • Controls involuntary movements eg breathing and heartbeat 
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The Brain - 2

Hypothalamus - regulates the autonomic nervous system

  • also controls the secretion of hormones from the pituitary gland 
  • controls many homeostatic processes eg temperature regulation and water content of body fluids
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The Nervous System

Central Nervous System - 

  • brain and spinal cord 
  • made of grey matter (non-myelinated nerve cells) and white matter (myelinated nerve cells)
  • most cells are intermediate neurons  - short dendrites forming synapses with other cells
  • spinal cord extends from base of brain - cerebro-spinal fluid flows through the centre
  • meniges surround the brain and spinal cord - secrete cerebro-spinal fluid which absorbs mechanical shock and provides nutrients and oxygen to brain cells

Peripheral Nervous System 

  • Neurons that carry impulses in and out of the CNS - sensory neurons carry impulses from receptors and motor neurons carry impulses to effectors
  • sensory neuron cell bodies just outside spinal cord in dorsal root ganglia 
  • made of two systems - somatic and autonomic nervous system
  • somatic nervous system includes sensory neurons and motor neurons that take information to skeletal muscles
  • sensory neurones lie just outside in the spinal cord in dorsal root gsnglia
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The Nervous System - 2

Somatic Nervous System 

  • somatic nervous system includes sensory neurons and motor neurons that take information to skeletal muscles - under voluntary control

Autonomic Nervous System

  • carries action potentials to internal organs - viscera, and smooth muscle 
  • self governing  - operates independly of concious control - involunatry
  • controls cardiac muscle and activities of exocrine glands
  • motor neurons have cell bodies outside of CNS in autonomic ganglia - preganglionic neurone carries action potentials from CNS to autonomic ganglion
  • autonomic nervous system divivided into sympathetic and parasympathetic nervous system
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The Nervous System - 3

Sympathetic Nervous System 

  • From autonomic ganglia, axons pass to all organs in the body and form synapses with the muscle - transmitter substance is usually noradrenaline, which stimulates the tissue eg heart beats faster
  • Also stimulate the adrenal glands causing them to secrete adrenaline and noradrenaline
  • Brings about changes such as speeding up the heart rate, dialation of pupils, dialation of arteriolds

Parasympathetic Nervous System

  • All nerve pathways begin in the brain, top of spinal cord or bottom of spinal cord
  • Neurons go straight from there start location to the effector, and dont pass through an autonomic ganglia
  • many axons are in the vagus nerve - the neurotransmitter is acetylcholine, which has an inhibitor effect 
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Voluntary, Involuntary and Cardiac Muscle

Muscles are made of cells that are enlongated to form fibres 

Involuntary (Smooth Muscle)

  • under control of the autonomic nervous system
  • does not look stripy - said to be non-straited
  • made of individual cells with their own nucleus - cells are long and thin (400um by 5um wide)
  • found in walls of arteries/arteriolds, iris of the eye and walls of intestine
  • contraction caused by sliding of actin and myosin but are not arranged to form myofibrils or sarcomeres
  • contraction intiated by action potential along autonomic nervous system or by hormones such as adrenaline

Cardiac Muscle

  • only found in the heart 
  • straited, each cell containing fibrils made up or sarcomeres 
  • cells are smaller than skeletal muscle cells - each cell has one nucleus also
  • cells branch and form connections with adjacent cells
  • have more mitochondria 
  • have a contiunous supply of oxygen in order to perform continuous work
  • uses fatty acids rather than glucose as respiratory substrate
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Voluntary, Involuntary and Cardiac Muscle - 2

Skeletal Muscle (Voluntary)

  • Action leads to movement of skeleton 
  • cells contain several nuclei - syncitium
  • cells surrounded by cell surface membrane called sarcolemma - muscle cell cytoplasm known as sarcoplasm 
  • plasma membrane has infolds in the interior known as T tubules
  • sarcoplasm contains many mitochondria, sarcoplasmic reticullum (specialised endoplasmic reticulum) and myofibrils 
  • myofibrils are the contractile elements and consist of sarcomeres - two types of protein myofilaments - thin actin and think myosin
  • darker areas (A bands) are where the myosin is, lighter areas (I Bands) is where the actin is
  • Z line provides attachment of actin filaments whereas M lines provide attachment for myosin
  • between two Z lines is called a sarcomere
  • fatigues quickly
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Actin and Myosin


  • Myosin is a fibrous protein which has a tail attached to the M line and two heads
  • severall myosin molecules lie in a bindle, making a myosin filament


  • Actin is a globular protein but many together form a chain
  • two of these chains twist together to form an actin molecule
  • Tropomyosin twists around actin chains
  • Troponin attaches to the actin chain at regular intervals
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The Sliding Filament Model

The Power Stroke

  • Troponin and tropomysoin molecules change shape and move to different positions on actin exposing the binding site for myosin - myosin head binds to actin forming a cross-bridge
  • Myosin heads tilt pulling the actin filaments 
  • The heads then hydolyse ATP making them release the actin and moveback, and bind again
  • They tilt again pulling the actin further - this process can repeat aslong as the binding site is not blocked and if the muscle has enough ATP
  • The shortening of the sarcomere shortens the whole length of the muscle, known as contraction
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How Muscles Contract

  • Action potential arrives at end of motor neurone and acetylcholine diffuses across the synaptic cleft
  • Sarcolemma acts as post synaptic membrane and acetylcholine binds to the membrane, depolarising it and generating an action potential
  • the action potential travels down T tubules where its picked up by the sarcoplasmic reticullum - calcium ions are pumped in by active transport
  • action potential stops active transport and calcium ion channels open releasing calcium ions into the sarcoplasm
  • calcium binds to troponin molecules, causing troponin and tropomyosin to change shape and move, exposing the myosin heads binding site, ready for a cross bridge to be formed and muscle contraction to begin
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How Muscles Contract - 2

ATP Supply

  • Muscles have a small store of ATP but this is very minute
  • Creatine phosphate used after the small ATP reserves have been used
  • A phosphate is removed from creatine phosphate and used to regenerate ATP from ADP - enzyme creatine phosphotransferase is used
  • ATP can be supplied via respiration after this - either aerobically or anaerobically
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