CONTROL of the heart rate

Question 1

what does the SAN do

Answer 1

-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

Question 2

what happens to the impulses sent by the SAN

Answer 2

• spread rapidly through right and left atrium walls causing them to contract together

Question 3

what happens once the impulse sent from the SAN causes the left and right atrium to contract

Answer 3

impulses dont pass directly to the ventricles but they reach the AVN
-between the artia and ventricles

Question 4

where is the AVN located

Answer 4

between the artia and ventricles

Question 5

what happens before the AVN reacts

Answer 5

there is a delay of 0,15 seconds before it reacts

Question 6

why is there a delay before the AVN reacts

Answer 6

• to make sure that the ventricles are full of blood and contract after the atrium have

Question 7

what happens to the impulses sent from the AVN after the ventricles have contracted

Answer 7

impulses rapidly travel through the bundle of his to all parts of the ventricles

Question 8

what happens once the impulses have been sent to the bundle of his

Answer 8

-stimulates the contraction of the ventricles
-causing the blood to be pushed up and out of the arteries

Question 9

label a heart

Answer 9

-vena cava
-san
-avn
-right atrium/ left
-bundle of his
-left, right ventricle

Question 10

which part of the nervous system control,s the heart

Answer 10

-the automatic nervous system

Question 11

which part of the body controls the automatic nervous system

Answer 11

the medula in the brain

Question 12

what is the automatic nervous system divided into

Answer 12

-sympathetic nervous system =inc heart rate
-parasynthestic =slow down heart rate

Question 13

how is the heart rate sped up during exercise

Answer 13

• the medulla
  -sends more impulses along the sympathetic neurones to the SAN
  -neurotransmitter NORADRENALINE is released
  -stimulates the SAN

Question 14

how is the heart rate slowed down

Answer 14

• the medulla
  -sends more impulses along the parasympathetic neurones to the SAN
  -neurotransmitter ACETYLCHOLINE is released.
  -this inhibits the SAN

Question 15

how does the heart rate increase ( more detail) during exercise

Answer 15

• 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

Question 16

what other factor affects heart rate and how

Answer 16

-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

Question 17

what is the refectory period

Answer 17

• 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

Question 18

how are action potentials transmitted

Answer 18

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

Question 19

what is the all or nothing period

Answer 19

• a stimulus must be above a certain threshold for an impulse to be generated
  -if below =no impulse

Question 20

describe the structure of a synaptic knob

Answer 20

-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.

-

Question 21

what are neurones possessing acetylcholine known as

Answer 21

-cholinergic neurones

Question 22

describe the mechanism of synaptic transmission

Answer 22

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