Download - E5 The human brain
E5 The human brain
489 - 498
Assessment StatementsE.5.1 Label, on a diagram of the brain, the medulla
oblongata, 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
cerebellum
hypothalamus
pituitary gland
medulla oblongataspinal
cord
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 glandthe 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 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 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 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
CENTRAL NERVOUS SYSTEM
(CNS)
PERIPHERALNERVOUS SYSTEM
(PNS)
NERVOUS SYSTEM
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)
PARASYMPATHETIC NERVOUS SYSTEM
(involuntary)
CONTROLS ORGANS IN TIMES OR STRESS
CONTROLS ORGANS WHEN BODY IS AT REST
The Organisation of the Nervous System
BRAIN AND SPINAL CORD
PERIPHERAL NS
Peripheral Nervous System (PNS)
PUPILS
SALIVARY GLANDS
HEART
BRONCHI
LIVER
STOMACH/ SMALL INTESTINE
ADRENAL GLAND / KIDNEYS
LARGE INTESTINE
BLADDER / GENITALS
The sympathetic nervous system (SNS)
Series of
ganglia
The cell bodies of its motor neurones lie in ganglia outside the spinal cord
It prepares the body for action
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
EYE
SALIVARY GLANDS
BRONCHI
HEART
STOMACH PYLORIC SPHINCTERPANCREAS
LARGE INTESTINE, ANAL SPHINCTER
GENITALS
BLADDER
The Parasympathetic Nervous System (PNS)
All nerve pathways begin in the brain, or at the top or bottom of the spinal cord
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 organHeart 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 Parasympathetic NSsecretes noradrenaline
or norepinephrineaccelerates heart ratecauses widening
(dilation) of the pupilsin gut, stomach,
pancreas, intestines & salivary glands inhibits activity by constricting blood flow to arterioles
relaxes (i.e. dilates) bronchi
inhibits emptying of bladder
secretes acetylcholine
slows down heart ratecauses narrowing
(constriction) of the pupilsin gut, stomach, pancreas,
intestines & salivary glands stimulates activity by maintaining normal blood flow to arterioles
constricts bronchipromotes emptying of
bladder
Sympathetic & Parasympathetic control of heart rate
heart muscles contract 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 nervous systems are part of the autonomic system
they have antagonistic actionsparasympathetic 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 pupilstimulation 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 parasympathetic nervous systems are part of the autonomic system
they have antagonistic actionssmooth 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 gutparasympathetic NS release
acetylcholinewhich dilates blood vessels
(arterioles) to the gut increasing blood flow to gut
Pupil reflex pupil reflex is rapid unconscious 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. 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
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 painkillersendorphins 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 parasympathetic control of blood flow to the gut.
Outline pupil reflexDiscuss 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.