bio 7.7 - what makes our heart beat?

systole

• contraction of heat

diastole

• relaxation of heart

heartbeat/cardiac cycle

• average 70 beats per minute

• 0.15 secs: atria contracts, ventricle relaxes

• 0.30 secs: atria relaxes, atria contracts

• 0.40 secs: atria contracts, ventricle contracts

lub-dub sound/heartbeat

• due to closing of valves

• starts with atrioventricular and then semi-lunar

• heart beat is said to be intrinsic

• beats without any nervous system stimulation

• can be removed from body and still beat

• beat is controlled by nodal tissue which has both muscular and nervous tissue characteristics 

SA node (sinoatrial node)

• found in upper wall of right atrium

• initiates heartbeat and send out an impulse every 0.85 seconds

• impulse causes both atria to contract

AV Node ( atrioventricular node)

• found at bottom of right atrium near septum

• control heart rate

• serves as an electrical relay station

• slows the electrical current sent by SA Node to ensure atria fully contracts before signal is permitted to pass down through ventricles

bundle of His (the antrioventricular bundle)

• passes into ventricular septum and divides into two bundle branches, the left and right bundles

purkinje fibres

• bundles of His are called Purkyne or Purkinje fibers

• in walls of ventricles and septum

• stimulates both ventricles to contract from bottom upwards

P Curve on electrocardiogram

• records simultaneous contraction of atria as they drive the blood out into their ventricles

• first hump on gram

GRS on electrocardiogram

• contraction of ventricles as they drive blood out into their respective arteries

• Q: bottom of peak

• R: top of peak (due to longer and stronger contraction of ventricles pushing blood out of heart)

• S: bottom of peak

T curve on elctrocardiogram

• marks recovery of ventricles

• restoration of the normal electrical condition, preparing them for next contraction

heart rate controlled by nervous system

• heart rate center is located in medulla of brain

• SA node is connected to brain by vagus nerve (cranial nerve #10)

• pathway part of autonomic nervous system and has 2 systems that affect the heart rate: parasympathetic system and sympathetic system

parasympathetic system

• causes the heartbeat to slow

sympathetic system

• causes the heartbeat to increase during times of stress