‘fight Or Flight Response’ And Heart Rate

Question 1

What is the ‘fight or flight’ response

Answer 1

When an organism is being threatened and it responds by preparing the body for action

• nerve impulses from sensory neurones arrive at the hypothalamus, activating both the hormonal (endocrine) and the sympathetic nervous system

Question 2

Describe and explain the fight or flight response

Answer 2

• nerve impulse from sensory neurone arrives at hypothalamus, activating both eh endocrine system and the sympathetic nervous system
• the pituitary gland is stimulated to release the hormone ACTH.
  This causes the cortex of the adrenal gland to release steroidal hormones, to help respond to stress.
• the sympathetic nervous system is activated, triggering the release of adrenaline from the medulla region of the adrenal gland.
  The sympathetic nervous system and adrenaline produce a faster response than the hormones secreted by the cortex of the adrenal cortex

Effects:
- heart rate increases, and heart contracts with more force causing blood to be pumped around body faster
- muscles around the bronchioles relax, causing the airways to widen, so breathing is deeper
- the intercostal uncles and diaphragm also contract, increasing the rate and depth of breathing
- glycogen is converted into glucose via glycogenesis, so more glucose is available for muscles to respire
- muscles in the arterioles supplying the skin and gut constrict, and muscles in the arterioles supplying the heart, lungs and skeletal muscles dilate — so blood is diverted away from skin and gut to the heart, lungs and skeletal muscles.
This increases blood glow to skeletal muscles, making them ready for action
- erector pili muscles in the skin contract — this makes hair stand on end so animals looks bigger (to scare predator)

Question 3

Describe the control of heart rate via the nervous system

Answer 3

• the SAN generates electrical impulses that cause the cardiac muscles to contract
• the rate at which the SAN fires (i.e. the heart rate) is unconsciously controlled by the cardiovascular centre in the medulla oblongata

Question 4

What are the two centres within the medulla oblongata, linked to the SAN in the heart by motor neurones?

Answer 4

• one centre increases heart rate by sending impulses through the sympathetic nervous system, these impulses are transmitted by the accelerator nerve
• one centre decreases the heart rate by sending impulses through the parasympathetic nervous system, these impulses are transmitted by the vagus nerve

Question 5

What are the two types of receptors which provide information that affects the heart rate?

Answer 5

• baroreceptors (pressure receptors) — these receptors detect changes in the blood pressure. Present in the aorta, vena cava and carotid arteries
• chemoreceptors (chemical receptors) — these receptors detect changes in the level of particular chemical in the blood (e.g. carbon dioxide)
  They are present in the aorta, carotid artery (major artery i the neck that supplies the brain with blood, and the medulla

Question 6

What is the nervous response to high or low blood pressure?

Answer 6

1) high blood pressure-
Baroreceptors detect high blood pressure and send impulses along sensory neurones to the cardiovascular centre, which sends impulses along parasympathetic neurones. These secrete acetylcholine, which binds to receptors on the SAN, causing the heart rate to slow down to reduce blood pressure back to normal

2) low blood pressure
Baroreceptors detect the low blood pressure, and sends impulses along sensory neurones to the cardiovascular centre (in the medulla oblongata) which sends impulses along the sympathetic neurones. These secrete noradrenaline, which bind to receptors on the SAN, to increase the heart rate to increase the blood pressure back to normal

Question 7

What is the nervous response to high blood O2, and low blood O2?

Answer 7

1) high blood O2, low CO2, or high pH levels
Chemoreceptors detect chemical changes in the blood and sends impulses along sensory neurone to the cardiovascular system, which sends neurones along the parasympathetic neurones. These secrete acetylcholine which binds to receptors on the SAN, causing heart rate to decrease

2) low blood O2, high CO2 levels, low pH
Chemoreceptors detect chemical changes, ending impulse along sensory neurone to the cardiovascular system, which sends impulse to sympathetic neurones. These secrete noradrenaline which binds to receptors on the SAN, to increase the heart rate, increasing O2 levels back to normal.