Controlling Heart Rate

• what are smooth muscles?

  • found in airways, blood vessels, digestive tract, iris of eyes
  • autonomic NS
  • non-striated fibre
  • slow contraction speed
  • long time contracted
  • slower speed to fatigue
  • no regular arrangement - different cells can contract in different directions
  • fibres are spindle shaped and uninucleated
• what is cardiac muscle?

  • found in the heart
  • autonomic and somatic NS
  • specialised striated fibres
  • intermediate contraction speed
  • never fatigues
  • cells branch and interconnect resulting in simultaneous contraction
  • show striations, fibre are uninucleated
• what is skeletal muscle?

  • found in bodily muscle tissue
  • somatic NS
  • striated fibres
  • rapid contraction speed
  • short length of contraction
  • fatigues faster
  • regular arrangement so muscles contract in one direction
  • fibres are tubular and multinucleated
• what role does smooth muscle play in blood flow?

  • vasoconstriction and vasodilation - divert blood flow to vital organs
  • change diameter in arteriole walls to respond to needs of cells in terms of oxygen and glucose
• what does myogenic mean?

  • absent of cause by external neuronal stimulus
  • controls own stimulation/under own control
• what is the role of the sinoatrial node?

  • generates impulses for contractions of the heart and ensures coordination flow of blood through heart chambers
• what is the role of the atrioventricular node?

  • controls transmission of heart's electrical impulse from atria to ventricles
• what is the role of intercalated discs in cardiac muscle?

  membranes of adjacent myocytes that are fused together, freely permeable to ion to allow propagation of action potentials into next cell
• what is an antagonistic muscle pair?

  • two muscles working together to bring about coordinated movement
• what does a flexor muscle do?

  decrease angle between bones when they contract
• what does an extensor muscle do?

  • increases angle between two bones
• what is a myocyte?

  a muscle cell
• what is a sarcolemma?

  cell surface membrane of a muscle cell
• what is the sarcoplasmic reticulum?

  specialised endoplasmic reticulum containing calcium ions
• what is a t-tubule?

  deep clefts or infoldings in the sarcolemma
• what are myofibrils?

  • parallel structures
  • banded with regular stripes of dark and light staining bands
  • composed of actin and myosin
• why are there lots of mitochondria between myofibrils?

  supply ATP needed for contraction
• what is actin and myosin?

  • actin - thinner filament, consists of 2 strands twisted around each other
  • myosin - thicker/darker filament, consists of long rod-shaped fibres with bulbous heads that project to one side
• what is the I band?

  • lighter areas, where actin is not overlapped by myosin
• what is the A band?

  • darker areas - myosin is present
• what is the Z line?

  • line running down centre of the I band
• what is the M line?

  • line running down the centre of the A band
• what is the H zone?

  • area where myosin not overlapped by actin
• what is the sarcomere?

  • part of the fibril between 2 Z lines
• what is the response of a muscle to a single stimulus?

  • increasing the size of stimulus increases the muscle contractions up to a point
  • this is because more calcium ions are released from the sarcoplasmic reticulum, up to a point when all the calcium is released so the muscle contraction can't increase after this
• what is the response of a muscle cell to two stimuli?

  • two stimuli close together cause one larger contraction as when close together, calcium ions don't have time to get pumped back into sarcoplasmic reticulum before next stimulus causes more calcium ions to be released - more calcium released, bigger contraction
• what is the response of a muscle cell to a repeated stimulus?

  • multiple stimuli close together, one larger contraction, calcium ions don't have time to be pumped back into sarcoplasmic reticulum before next stimulus
  • contraction gets bigger to a point then decreases - all calcium is pumped out of sarcoplasmic reticulum, a lack of ATP or too high lactic acid levels
• what occurs if more myofibrils contract in unison?

  a stronger force of contraction