Transcript E5 - The human brain - IBDPBiology-Dnl

489 - 498
Assessment Statements
 E.5.1 Label, on a diagram of the brain, the medulla oblongata,
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cerebellum, hypothalamus, pituitary gland and cerebral
hemispheres.
E.5.2 Outline the functions of each of the parts of the brain
listed in E.5.1.
E.5.3 Explain how animal experiments, lesions and fMRI
(functional magnetic resonance imaging) scanning can be used
in the identification of the brain part involved in specific
functions.
E.5.4 Explain sympathetic and parasympathetic control of the
heart rate, movements of the iris and flow of blood to the gut.
E.5.5 Explain the pupil reflex.
E.5.6 Discuss the concept of brain death and the use of the
pupil reflex in testing for this.
E.5.7 Outline how pain is perceived and how endorphins can
act as painkillers.
On the diagram of the brain, label the following: medulla oblongata;
cerebellum; hypothalamus; pituitary gland & cerebral hemispheres
cerebral hemisphere
hypothalamus
cerebellum
pituitary gland
spinal cord
medulla oblongata
Functions of each of the parts of the brain
Part of the brain
Function(s)
medulla oblongata
controls autonomic functions of the body such as: heart
rate; blood pressure; ventilation; swallowing; vomiting;
digestion & cranial reflexes
Cerebellum
coordinates unconscious functions, such as movement and
balance
Hypothalamus
links nervous and endocrine systems; produces hormones
secreted by posterior pituitary; controls hormonal secretion
by pituitary; maintains homeostasis such as; control of body
temperature, hunger, thirst, fatigue, circadian cycles
pituitary gland
the posterior lobe stores and releases hormones produced
by the hypothalamus and the anterior lobe, and produces
and secretes hormones regulating many body functions
cerebral
hemispheres
act as the integrating centre for high complex functions
such as learning, memory and emotions
Use of animal experiments to identify the
brain part involved in specific functions
 experiments involves surgery to remove
part of the scull to access the brain
 animal must be alive during this
procedure
 different regions of the brain are
stimulated and the response of the
animal observed
 primates were often used but it raised
ethical issues due to their genetic
similarities to humans & the pain and
suffering the procedure caused
 example :- Pierre in 1820s showed that
removing thin slice of tissue from the
cerebellum of rabbits & birds resulted in
animals displaying lack of muscular
coordination & poor balance with no
other obvious effects
Lesions & their uses in identification of the brain
parts involved in specific functions
 lesions are any abnormalities in the
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brain tissue of an organism
lesions could be due to damage to
the brain tissue as a result of
accidents, stroke, tumour or
deliberate injury
lesions indicates effect of loss of a
brain tissue by comparing an
organism to a normal one
e.g. split brain patients led to
understanding different functional
roles of left and right hemispheres
of the brain
many actions of the body involve
different areas of the brain
damage may be to many parts of the
brain, thus making it difficult to
interpret due to complexity of
reactions
fMRI (functional magnetic resonance
imaging) scanning
 fMRI stands for functional
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magnetic resonance imaging
fMRI records changes in
blood flow to the brain
active parts of the brain have
increased blood flow
but not all brain activity is
detected by MRI
a subject is given a stimulus
which is designed to stimulate
brain activity
MRI links stimulus with
certain part of the brain
brain activity visualized by
coloured images
Use of fMRI scanning in identification of the brain
parts involved in specific functions
 fMRI gives a more specific
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knowledge of stimulated area of
the brain
e.g. it is used to study (diagnose)
ADHD, dyslexia, recovery from
strokes, music comprehension etc.
fMRI is non-invasive (no damage to
brain), can study healthy subjects
involves recording increased blood
flow & supply of oxygen to the
active parts of the brain
good spatial but poor temporal
resolution
it requires interpretation of
coloured images
there could be a problem of
statistical interpretations of models
The Organisation of the Nervous System
NERVOUS
SYSTEM
CENTRAL
NERVOUS
SYSTEM
(CNS)
BRAIN AND
SPINAL
CORD
PERIPHERAL
NERVOUS
SYSTEM
(PNS)
SOMATIC
NERVOUS
SYSTEM
(voluntary)
AUTONOMIC
NERVOUS
SYSTEM
(involuntary)
SENSORY AND MOTOR
NEURONES TO / FROM
SKELETAL MUSCLE
MOTOR NEURONES TO
INTERNAL ORGANS
SYMPATHETIC
NERVOUS
SYSTEM
(involuntary)
CONTROLS ORGANS IN
TIMES OR STRESS
PARASYMPATHETIC
NERVOUS SYSTEM
(involuntary)
CONTROLS ORGANS WHEN BODY IS
AT REST
PERIPHERAL
NS
Peripheral Nervous System (PNS)
The sympathetic nervous system (SNS)
PUPILS
SALIVARY GLANDS
The cell bodies of its motor
neurones lie in ganglia
outside the spinal cord
It prepares the body for
action
HEART
BRONCHI
LIVER
STOMACH/ SMALL
INTESTINE
ADRENAL GLAND /
KIDNEYS
LARGE INTESTINE
Series
of
ganglia
BLADDER /
GENITALS
The transmitter secreted
at these synapses is
usually nor adrenaline –
which stimulates organ
activity
The heart beats faster, eyes
get wider i.e. the pupil
dilates to improve vision,
“sinking” feeling in the
stomach due to decreased
blood supply to the gut.
SNS functions are FIGHT
OR FLIGHT
The Parasympathetic Nervous System (PNS)
EYE
All nerve pathways begin in
the brain, or at the top or
bottom of the spinal cord
SALIVARY GLANDS
BRONCHI
HEART
STOMACH PYLORIC
SPHINCTER
PANCREAS
LARGE INTESTINE, ANAL
SPHINCTER
BLADDER
GENITALS
The neurones keep going
‘till right inside the organ.
Here they synapse with a
motor neurone
The transmitter secreted
at these synapses is
acetylcholine and this has
an inhibitory effect on the
organ
Heart rate decreases,
increased blood flow to the
gut, constricts pupil to
protect retina
PNS functions are REST
AND DIGEST
Effects of Sympathetic & Parasympathetic NS
Sympathetic NS
 secretes noradrenaline or
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norepinephrine
accelerates heart rate
causes widening (dilation) of
the pupils
in gut, stomach, pancreas,
intestines & salivary glands
inhibits activity by
constricting blood flow to
arterioles
relaxes (i.e. dilates) bronchi
inhibits emptying of bladder
Parasympathetic NS
 secretes acetylcholine
 slows down heart rate
 causes narrowing
(constriction) of the pupils
 in gut, stomach, pancreas,
intestines & salivary glands
stimulates activity by
maintaining normal blood
flow to arterioles
 constricts bronchi
 promotes emptying of bladder
Sympathetic & Parasympathetic control of
heart rate
 heart muscles contract
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without nervous stimulation
i.e. myogenic contractions
SA node is the pacemaker, it
generates heart beat (i.e.
initiates each cardiac cycle)
epinephrine (adrenalin)
speeds up the heart rate
sympathetic &
parasympathetic nervous
system control the heart rate
sympathetic NS speeds up
heart rate while
Parasympathetic NS slows
heart rate (back to normal
rate)
Sympathetic & parasympathetic control of
movements of the iris
 sympathetic and parasympathetic
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nervous systems are part of the
autonomic system
they have antagonistic actions
parasympathetic neurons control
the circular muscle of the iris
while sympathetic neurons control
the radial muscle of iris
stimulation of radial muscles of
the iris by sympathetic NS causes
the muscles to contract
dilating (widening) the pupil
stimulation of circular muscles of
the iris by parasympathetic NS
causes the muscles to contract
constricting (narrowing) the pupil
Sympathetic & Parasympathetic control of
blood flow to the gut
 sympathetic and
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parasympathetic nervous
systems are part of the
autonomic system
they have antagonistic actions
smooth muscle in blood vessels
(arterioles) are controlled by
sympathetic & parasympathetic
nerves
sympathetic NS release
norepinephrine (noradrenaline)
which constricts blood vessels
(arterioles) to the gut
decreasing blood flow to gut
parasympathetic NS release
acetylcholine
which dilates blood vessels
(arterioles) to the gut
increasing blood flow to gut
Pupil reflex
 pupil reflex is rapid unconscious
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response to change in light intensity
it controls amount of light entering
eye to prevent damage to retina
it allows sufficient light in for vision
impulses from retina are monitored
for intensity by brain stem (part of
the brain that include the medulla
oblongata)
in bright light, circular muscles in
iris contract causing pupil to
constrict
in dim, light longitudinal (radial)
muscles in iris contract causing pupil
dilation
constriction is caused by
parasympathetic NS while dilation is
caused by action of sympathetic NS
Concept of brain death
 brain death is a legal medical definition of death
 some cases of coma are irreversible while other
cases may recover
 damage in the medulla oblongata is generally
permanent
 doctors have to diagnose damage to the medulla
oblongata to decide treatment
 they use tests of brain stem (part of the brain
that include the medulla oblongata) function to
decide whether to preserve patient’s life, without
brain stem function life cannot continue
 they test pupil reflex by shining light into the eye
 if pupils do not constrict with light, this suggests
brain death
 more than one test used to diagnose brain death
including lack of response to pain or cranial
reflexes
 legal & ethical definition needed for organ
donation & long term use of life-support
machines may be inappropriate
Use of the pupil reflex in testing of brain
death
 pupil reflex is a brain stem reflex i.e.
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shows activity in the medulla oblongata
pupil reflex must be absent if the brain is
death
pupil reflex is possible in coma victims
where motor function is absent
pupil reflex alone is not enough to
diagnose brain death
other criteria of testing brain death
include coma, absence of response to
pain in all extremities, absence of brain
stem reflexes, lack of respiratory
movements
some cases of coma are irreversible while
some cases may recover
doctors need to diagnose damage to
decide treatment, long-term life support
or organ donation
How pain is perceived
 impulses passed from pain
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receptors to sensory areas of
the cerebral cortex
where pain is perceived (i.e.
feelings of pain in the areas of
the cerebral cortex)
awareness of pain allows one
to avoid acute injury &
noxious substances
the pituitary secretes
endorphins into the blood
stream and the hypothalamus
secretes them into the brain
to block the receptor
molecules at synapses
in so doing, the pain is
reduced
How endorphins act as painkillers
 endorphins released by
pituitary gland during
stress, injury or exercise
 endorphins block
transmission of impulses
at synapses involved in
pain perception
 they bind to receptors in
the membrane of
neurons involved in
sending pain signal
 by blocking the release
of neurotransmitters
Self Assessment Questions (SAQs)
 Outline the functions of each
of the following parts of the
brain: medulla oblongata;
cerebellum; hypothalamus;
pituitary gland & cerebral
hemispheres.
 Explain how lesions & fMRI
scanning can be used in the
identifying brain part & their
functions.
 Explain sympathetic and
parasympathetic control of
the heart rate.
 Explain sympathetic and
parasympathetic control of
movements of the iris .
 Explain sympathetic and
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parasympathetic control of
blood flow to the gut.
Outline pupil reflex
Discuss the concept of brain
death.
Outline the use of the pupil
reflex in testing brain death.
Outline how pain is
perceived.
Explain how endorphins act
as painkillers.