WEEK 6

Question 1

Structure and Function of the Pericardium

Answer 1

• fibrous bag around heart
  • prevents heart from overfilling
  • secures heart in place
  • protection
• fluid secreting membrane on inside
  • allows heart to not adhere to surfaces

Question 2

Location of Heart

Answer 2

• in mediastinum between second rib and fifth intercostal space
• on superior surface of diaphragm
• two-thirds of heart to left of midsternal line
• anterior to vertebral column, posterior to sternum

Question 3

External heart anatomy

Answer 3

• approx. size of fist
• oblique orientation
• base (posterior surface) leans toward right shoulder
• apex points towards left hip
• apical impulse palpated between fifth and sixth ribs, just below left nipple

Question 4

Coronary arteries

Answer 4

• supply myocardium and epicardium
• originate at base of ascending aorta

Question 5

Heart conduction summary

Answer 5

1. Sinoatrial (SA) node fires (~ 70 times/min)
2. Cardiac muscle of right atrium conducts and contracts
3. Impulse reaches AV node down the IV septum via AV bundles
4. AV bundles branch to Purkinje fibres that supply papillary muscles and walls of ventricles

Question 6

Sympathetic stimulation

Answer 6

↑heart rate, ↑force of contractions, indirectly dilates coronary arteries by inhibiting their constriction
- supplies more oxygen and nutrients to myocardium during increased activity

Question 7

Parasympathetic stimulation

Answer 7

↓heart rate,↓force of contractions, constricts coronary arteries
- saves energy between periods of increased demand

Question 8

Aorta branches (12)

Answer 8

• right common carotid
• right subclavian
• brachiocephalic
• left subclavian
• left common carotid
• right and left coronary
• celiac trunk
• superior mesenteric
• renal
• gonadal
• inferior mesenteric
• common iliac

Question 9

Lymphatic system’s contribution

Answer 9

It returns interstitial fluid, which has leaked from veins, back into the cardiovascular system

Question 10

Ca2+ regulation of contraction

Answer 10

• Ca2+ injection causes contraction
• Ca2+ deprivation prevents contraction

Question 11

Neuromuscular junction (NMJ)

Answer 11

1. AKA the motor end plate - a cholinergic synapse
2. Motor neurons secrete acetylcholine (ACh) when
   stimulated
3. Nicotinic ACh receptors (nAChR) are ligand-gated Na+
   channels
   
   • Nicotinic (nAChR)
     • Ionotropic - ligand-gated Nai channel
     • Always excitatory

Question 12

Wave summation

Answer 12

Progressively increases Ca2+ conc. which increases tension (actin + myosin)

Question 13

Maximum tension (tetanus)

Answer 13

Is reached when all actin + myosin are forming cross bridges

Question 14

Process of Excitation-Contraction coupling

Answer 14

1) Action potential (AP) reaches end plate and causes release of acetylcholine
2) Binds to nicotine receptors, generating EPP and Na+ floods in
3) AP generated and moves along sarcolemma down T-tubules
4) DHPR activated and opens RyR
5) Ca2+ floods into mycoplasma
6) Binds to Tn-C and pulls TM, exposing myosin binding sites
7) Power stroke