TOPIC 6

• Define Myogenic

  It will contract and relax on its own accord
• Cardiac Muscle is Myogenic
• What controls the rate of contraction?


  Wave of electrical activity/ Nervous system
• What 4 KEY areas of nervous system are involved in the rate of contraction?


  SAN (Sinoatrial Node)

  AVN (atrioventricular node)

  Bundle of His

  Purkyne Fibres
• Where is SAN located and what does it do?

  Located: in the right atrium

  Function: group of tissues/cells that act as pacemaker - SO set the pace of heartbeat
• Where is AVN located?


  located: near the border of right atrium and left ventricle
• What are bundle of his?


  Tissues running down the septum
• What are Purkyne Fibres?

  Specialised cardiac muscle fibres responsible for conducting electrical impulses in the heart.
• Where are purkyne fibres located?


  Walls of ventricles
• DRAW AND LABEL HEART?


  :

  
• Cardiac Cycle: Control of the heart process

  SAN initiates atrial contraction by releasing wave of depolarisation,

  when it reaches AVN, it triggers ventricular depolarisation via bundle of His and Purkyne fibres.

  A non-conductive layer between atria and ventricles stop WOD travelling directly to ventricles

  AVN delay ensures atrial blood fills the ventricles before repolarisation and cardiac muscle relaxation.
• How is heart rate controlled?

  The medulla oblongata in the brain controls the heart rate, via the autonomic nervous system

  1. a centre linked to SAN to increase heart rate by releasing WOD more frequently via the sympathetic nervous system
  2. Another to decrease heart rate by decreased WOD release via the parasympathetic nervous system
• The heart rate changes in response to which 2 stimuli?


  pH and Blood pressure
• What receptor is changes in pH detected by?


  Chemoreceptors
• What receptor is changes in blood pressure detected by?


  Pressure receptors
• Where are both chemoreceptors and pressure receptors found?

  Walls of Aorta and Carotid artery (blood vessel that attches to aorta)
• How does pH of blood decrease?

  pH of blood will decrease during times of high respiratory rate, due to production of CO2 and lactic acid

  XS acid must be removed from blood to rapidly prevent enzymes denaturing
• What happens to bring pH levels back to normal?


  Increasing the heart rate (more impulses via sympathetic nervous system)

  SO CO2 can issue out into alveoli more rapidly

  and be exhaled
• What happens when blood pressure is too high?


  this can cause damage to walls of arteries

  TO PREVENT:

  more impulses sent via parasympathetic nervous system to decrease heart rate
• What happens if blood pressure too low?


  Insufficient supply of oxygenated blood to respiring cells and removal of waste

  TO PREVENT:

  More impulses via sympathetic nervous system to increase the heart rate
• Draw a myelinated motor neurone?


  :

  
• Myelinated neurone structure: cell body?

  Cell Body: contains all the organelles found in an animal cell. proteins and neurotransmitter chemicals made here
• Myelinated neurone structure: dendrites?

  Dendrites: carry action potentials to surrounding cells
• Myelinated neurone structure: axon?

  conductive, long fibre that carries nervous impulses along motor neurone
• Myelinated neurone structure: Schwann cells?


  Wrap around axon and form myelin sheath, which is a lipid, it insulates and does not allow charged ions to pass through
• What are the gaps where no insulation between myelin sheath called?

  nodes of ranvier
• What is the resting potential?


  When a neurone is not conducting an impulse/ when there is no stimulus

  • the difference between electrical charge inside and outside neurone
  • There are more positive ions, Na+ and K+ outside compared to inside of axon
  • so therefore inside is more negative at -70mV (resting potential)
• How is resting potential established + maintained when no stimulus?

  Maintained through sodium-potassium pump (involves active transport and ATP)

  • In this pump 2K+ IONS in and 3NA+ out of axon so
  • creates an electrochemical gradient causing K+ to diffuse out and Na+ to diffuse in
  • Membrane more permeable to K+ so more moved out resulting in -70mV (more +ions outside of cell/axon)
• When is an action potential generated?


  when there is a stimulus/ large enough stimulus
• What is an action potential?


  when neurone voltage increases beyond a set point from resting potential - this generates a nervous impulse
• How does depolarisation occur?


  when neurone membrane is more permeable to Na+
• What happens once an action potential is generated?


  Moves along axon like Mexican wave
• Where do action potentials generate in the neurone?

  Nodes of ranvier
• If unmyelinated axon would it be quicker or longer for this process to occur?


  longer as would happen at every position and would take longer to reach end
• What is the ALL-or-nothing principle?


  NOTHING: If depolarisation does not hit threshold (-55mV) an action potential and impulse are not produced

  ALL: any stimulus that does trigger depolarisation to -55mV will always peak at same max voltage (-40mV)

  • BUT bigger stimulus leads to increased frequency of action potentials

  This Ensures that animals only respond to stimulus' large enough rather than every change in environment
• What is the refractory period?

  Recovery phase after an action potential has been generated, the membrane can not be stimulated as sodium channels are recovering.
• 3 REASONS WHY REFRACTORY PERIOD IS IMPORTANT?

  ensures that discrete impulses are produced, so each is separate (helps identify source of particular stimulus)

  ensures that action potentials travel in one direction, stops spreading out in two directions (which would prevent a response)

  limits number of impulse transmission, prevents over reaction to a stimulus
• 3 factors that affect speed of conduction?

  Myelination + saltatory conduction, axon diameter, temperature.
• Explain how myelination affects speed of conduction?

  action potential jumps from node to node (saltatory conduction)

  as myelin sheath insulated so ions cannot diffuse in and out so jump node to node

  which means the action potential travels along axon faster
• Explain how axon diameter affects speed of conduction?


  Wide diameter increases speed of conductance

  Wider diameter means less leakage of ions and so action potentials travel faster