Download 5.4.1 The Flight and Fight Reflex

OCR A2 F215 THE FLIGHT AND FIGHT REFLEX
Specification:
a) Explain how, in mammals, the ‘fight or flight’ response to environmental
stimuli is coordinated by the nervous and endocrine systems
Coordination involving the Nervous and Endocrine Systems
 Coordination refers to the mechanisms by which all the organs of the
body work together, to bring about a response to the environment, in
order to bring about the survival of the organism

In animals, coordination involves both the nervous and endocrine
systems
Coordination in Mammals

The nervous and endocrine systems of mammals are complex

With both systems, stimuli in the external and internal environments are
detected by receptors

The responses to these stimuli are coordinated to ensure survival

Responses to external stimuli usually involve the brain. The brain controls
these responses by involving other parts of the nervous system and/or the
endocrine system, via the hypothalamus that controls the pituitary gland
Fight and Flight Stimuli
The stimuli are dangerous sights and/or dangerous sounds
Fight and Flight Response (see diagrams on page 239 in your textbook)

The fight and flight response refers to the range of coordinated responses
in animals, to dangerous stimuli

The nervous and endocrine systems allow the animal to be ready for the
actions of confronting the danger (fighting) or escaping from it (running
away)
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
These actions require impulses in somatic motor neurones that cause
skeletal muscle contraction and in autonomic motor neurones that control
cardiac and smooth muscle contraction

The cerebrum receives sensory impulses from eye and ear receptors
when dangerous stimuli are detected

The cerebrum activates the hypothalamus

The hypothalamus stimulates the sympathetic nervous system in the
autonomic nervous system control centre in the medulla oblongata and
also stimulates the pituitary gland

Many of the responses involve the adrenal gland. The sympathetic
nervous system stimulates the adrenal medulla to secrete more
adrenaline into blood plasma

In addition, the pituitary gland secretes ACTH, a hormone that stimulates
the adrenal cortex to secrete cortisol and other hormones. Cortisol helps
to control the metabolism of glucose and proteins in the liver. Some other
adrenal cortex hormones help the body to resist stressors (stimuli that
cause the stress response)
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PHYSIOLOGICAL RESPONSES IN
THE FIGHT AND FLIGHT REFLEX
COORDINATION PROCESSES
Pupils dilate
Hypothalamus stimulates sympathetic
motor control of iris muscles. Also
stimulated by adrenaline
Hypothalamus stimulates sympathetic
motor control of cardiac muscle, SAN
and AVN via acceleratory nerve. Also
stimulated by adrenaline
Heart rate and stroke volume increase
Breathing rate and depth increases
Hypothalamus stimulates sympathetic
motor control of intercostal muscles
and diaphragm.
Smooth muscles in the bronchioles
and trachea relax to widen the airways
Stimulated by adrenaline and
sympathetic motor control of airway
smooth muscle fibres
Arterioles to the digestive system, the
skin and the kidneys are constricted.
Arterioles to the skeletal muscles and
liver are dilated
Hypothalamus stimulates sympathetic
motor control of smooth muscle fibres
in arteriole walls bringing about
vasoconstriction. Also stimulated by
adrenaline
Hypothalamus stimulates sympathetic
motor control of the adrenal medulla
to increase adrenaline secretion.
Adrenaline stimulates glycogenolysis
in liver and muscles
Sympathetic motor control and
adrenaline effect
Blood glucose levels increase
Blood pressure increases because
stroke volume increases and
vasoconstriction increases
Metabolic rate increases
Contraction of erector pili muscles in
the skin causes hairs to stand up
Effect of adrenaline on the liver and
muscles
Effect of adrenaline and sympathetic
motor control
Endorphins (natural painkillers) are
released in the brain
Sweat production increases
Effect of sympathetic motor control
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ADVANTAGE TO
PREPARE FOR FIGHT
AND FLIGHT
More light enters eye so
that the stimulus can be
seen more clearly
Increases blood flow to
vital organs such as the
skeletal muscles in
preparation for fighting
/flight from danger
Increases rate of gas
exchange. More O2
required for increased
respiration rate in
muscles and liver.
Increased CO2 product
from inc. respiration rate
Widens airways to
accommodate increased
air flow into and out of the
lungs
Allows increased blood
flow to skeletal muscles
and liver so that muscles
can contract at a faster
rate
To supply more glucose
to skeletal muscles for
increased rate of muscle
contraction
Same as described above
for increased heart
rate/stroke volume
Allows increased muscle
contraction in skeletal
muscles for fight/flight
In many animals, this
makes the animal
attacked look bigger and
more fierce
Painkillers may be
necessary if the victim is
injured during the fight
To remove the increased
heat produced from
increased respiration rate
in liver and skeletal
muscles
Complete the table below to describe how internal organs function differently in a calm and
frightened mammal
ORGAN
CALM ANIMAL
Heart
Lungs
Skeletal muscles
Liver
Digestive system
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FRIGHTENED ANIMAL
Answers to table on previous page
ORGAN**
CALM ANIMAL
FRIGHTENED ANIMAL
Heart
Slower heart rate/lower stroke
volume/lower cardiac output*
Faster heart rate/greater stroke
volume/higher cardiac output
Lungs
Slower breathing rate/lower
tidal volume/shallower
breathing*
Faster breathing rate/greater
tidal volume/deeper breathing
Skeletal muscles
Arterioles constricted therefore
less blood flow to muscles
Arterioles dilated therefore
more blood flow to muscles
Less muscle contraction
More muscle contraction
More glucose taken up from
blood
More glucose released into
blood
More glycogenesis/ glucose 
glycogen
More glycogenolysis/glycogen
 glucose
More peristalsis
Less peristalsis
More blood flow to gut
(arterioles vasodilate)
Less blood flow to gut
(arterioles vasoconstrict)
More secretion of digestive
enzymes
Less secretion of digestive
enzymes
More digestion
Less digestion
Liver
Digestive system
organs/intestines and
stomach
*Note that for a calm animal, it is unacceptable to write ‘normal/steady/regular’. You have to
indicate slower/lower
** It is important to name organs as examples not structures such as bronchioles
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