CONTROL of the heart rate Flashcards
what does the SAN do
-acts as a pacemaker and initiates the heart beat
-a patch of modified muscle cells in the wall of the right atrium
-produces regular waves of electrical impulses
what happens to the impulses sent by the SAN
- spread rapidly through right and left atrium walls causing them to contract together
what happens once the impulse sent from the SAN causes the left and right atrium to contract
impulses dont pass directly to the ventricles but they reach the AVN
-between the artia and ventricles
where is the AVN located
between the artia and ventricles
what happens before the AVN reacts
there is a delay of 0,15 seconds before it reacts
why is there a delay before the AVN reacts
- to make sure that the ventricles are full of blood and contract after the atrium have
what happens to the impulses sent from the AVN after the ventricles have contracted
impulses rapidly travel through the bundle of his to all parts of the ventricles
what happens once the impulses have been sent to the bundle of his
-stimulates the contraction of the ventricles
-causing the blood to be pushed up and out of the arteries
label a heart
-vena cava
-san
-avn
-right atrium/ left
-bundle of his
-left, right ventricle
which part of the nervous system control,s the heart
-the automatic nervous system
which part of the body controls the automatic nervous system
the medula in the brain
what is the automatic nervous system divided into
-sympathetic nervous system =inc heart rate
-parasynthestic =slow down heart rate
how is the heart rate sped up during exercise
- the medulla
-sends more impulses along the sympathetic neurones to the SAN
-neurotransmitter NORADRENALINE is released
-stimulates the SAN
how is the heart rate slowed down
- the medulla
-sends more impulses along the parasympathetic neurones to the SAN
-neurotransmitter ACETYLCHOLINE is released.
-this inhibits the SAN
how does the heart rate increase ( more detail) during exercise
- heart race increases
-respiration increases and more co2 is removed
-this decreases blood ph
-chemoreceptors in the aortic and carotid bodies detect this and transmit MORE impulses to the medulla
-this increases heart rate by transmitting more impulses fro the medulla via the sympathetic neurones to the SAN
-the frequency of electrical impulses from the SAN increases , increasing heart rate - the heart rate returns to its resting state when exercise is completed .
-fewer impulses are transmitted from chemoreceptors to medulla
what other factor affects heart rate and how
-blood pressure
-increased blood flow to heat causes cardiac muscle to contract more strongly
-this pumps out an increased volume of blood
-this increase in blood pressure is detected by baroreceptors in the wall of the aorta and carotid artery
-if the blood pressure increases too much, these receptors send more impulses to medulla , stimulating cardio inhibitory centre and inhibiting the cardioacceletory centre
what is the refectory period
- the period after the formation of an action potential when a neurone cannot generate another action potential
-results in discrete impulses
-ensures that impulse travels in one direction along axon
- important in determining the maximum frequency of impulses along a neurone
how are action potentials transmitted
along a neurone as a nerve impulse or wave of depolarisation .
-increaes permebeality of the membrane to sodium ions in one area that stimulates a permeability in the next area of the axon and so on along the neurone
what is the all or nothing period
- a stimulus must be above a certain threshold for an impulse to be generated
-if below =no impulse
describe the structure of a synaptic knob
-between a neurones
-many vesicles containing acetylcholine
-mamy mitochondria , =atp for neurotransmitter to be made
- a presynaptic membrane
- synaptic gap
-post synaptic membrane containing SPECIFIC PROTEIN RECEPTORS.
-
what are neurones possessing acetylcholine known as
-cholinergic neurones
describe the mechanism of synaptic transmission
1) arrival of action potentials ( impulses) causes depolarisation of presynaptic membrane
2) stimulates CALCIUM channels to open in the pre synaptic membrane and calcium ions diffuse into synaptic knob
3) calcium ions cause synaptic vesicles to fuse with presynaptic membrane and break open
4) neurotransmitter acetylcholine is released and diffuses across synaptic cleft
5) acetylcholine attaches to specific protein receptor on the most synaptic membrane
6) this stimulates the entry of sodium ions .
-leading to depolarisation of post synaptic neurone and transmission of an impulse
7) acetylcholine is broken in post knob by enzyme ACETYLCHOLINESTERASE forming acetyl and choline
8) acetyl and choline are taken up into the synaptic knob by active transport and acetylcholine is re made
- at and re-synthesis require atp yielded from mitochondria
