The human brain

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14 Νοε 2013 (πριν από 4 χρόνια και 1 μήνα)

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Option E.5


E.5.1 Label, on a diagram of the human brain, the
medulla oblongata, cerebellum, hypothalamus, pituitary
gland and cerebral hemispheres.


E.5.2 Outline the function of each of the parts of the
brain listed above.


E.5.3 Explain how animal experiments, lesion 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 the
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.

Cerebral hemispheres

act as
the integrating center for
high complex functions such
as learning, memory and
emotions.

Hypothalamus

maintains homeostasis,
coordinating the nervous and the
endocrine systems, secreting hormones
of the posterior pituitary, and releasing
factors regulating the anterior pituitary.

Pituitary gland

has two
lobes. The posterior lobe
stores and releases
hormones produced by
the hypothalamus and
the anterior lobe. It also
produces and secretes
hormones regulating
many body functions.

Medulla oblongata

controls automatic and
homeostatic activities, such as swallowing,
digestion, vomiting, breathing, and heart
activity.

Cerebellum

has two
hemispheres
and a highly
folded
surface. It
coordinates
unconscious
functions,
such as
movement
and balance.

area of tissue that has been damaged
through injury or disease


Brain divided into right and left hemispheres


Connected by a thick band of axons called the
corpus
callosum


Left hemisphere


Contains areas important for communication


If damaged, person may have difficulty speaking or
doing complicated movements


Right hemisphere


Specializes in receiving and analyzing information
which comes in through all of our senses


If damaged, person may have difficulty identifying
faces and locating an object correctly in space or
even identifying melodies



Mid 1800s: Neurologists observed that people
who had injuries on the
left

side had
speech and language
problems


People who had injuries in the same areas
but on the
right

side of the brain had no
language problems


Two areas of brain important for language
are named for those neurologists:


Injury to
Brocca’s

interferes with the ability to
volcalize

words


Injury to
Wernicke’s

area affects the ability to
put words into sentences


1960s: group of scientists interested in
patients who had undergone surgery to sever
their corpus callosum to relieve symptoms of
epilepsy (the optic chiasma remains intact)


The Split Brain Experiment

fMRI


fMRI uses radio waves and a strong magnetic
field, not X
-
rays


Enables scientists to see the blood flow in
the brain as it is occurring


Makes movies of what is going on in the brain
as the subject performs tasks or is exposed
to various stimuli


Can determine with some precision when
regions of the brain become active and how
long they remain active


fMRI used by doctors to determine:


A plan for surgery


Treatment for a stroke


Placement of radiation therapy for a brain tumor


Effects of degenerative brain disease such as
Alzheimer’s


Diagnosing how a diseased or injured brain is
working

Animal Experiments


Expose animals to addictive substances in
controlled situations


Respond similarly to human:


Want more and more of the substance


Spend lots of time and energy getting it


Keep taking it despite adverse conditions


Have withdrawal symptoms on withdrawal of
substance


Go back to the substance when stressed


Go back to the substance with another exposure
to that substance

Animal model for addiction?


Animal is trained to press a lever to get a
reward


Animal is given an injection of the addictive
substance as it pushes the lever


Two levers available: one gives substance,
one does not


If substance is reinforcing, animal will seek
to repeat the experience by pushing that
lever much more frequently and therefore,
support the hypothesis that substance is
addictive


Animal experiments can help us to determine
way in which drugs promote abuse


Animal experiments cannot replicate the
complete interaction of humans and drugs


Social factors can play a role


Addiction studies

Sympathetic and parasympathetic
control


Peripheral nervous system considered in two
parts,
somatic system

and
autonomic
system


Somatic system

takes sensory information
from sensory receptors to the CNS and then
sends back motor commands from the CNS to
the muscles


Autonomic system

is involuntary and
regulates activities of the glands, smooth
muscle, and the heart.


Sympathetic system


Parasympathetic system

Comparison chart

Sympathetic system

Parasympathetic system

Important in emergency

Important in returning to
normal

Response is “fight or
flight”

Response is to relax

Neurotransmitter is
noradrenaline

Neurotransmitter is
acetylcholine

Excitatory

inhibitory

Antagonistic systems


Sympathetic system associated with fight or
flight


You need quick energy


System increases heart rate, stroke volume to
supply more glucose and oxygen


Dilates bronchi to give more oxygen


Dilates pupil by contracting radial muscles
surrounding iris


Blood to gut is restricted by contraction smooth
muscle of blood vessels carrying blood there


Parasympathetic takes over in a relaxed state


Nerves return the system to normal


Pupil of eye constricts


Heart rate slows, stroke volume is reduced


Blood returns to the digestive system


Smooth muscle of the blood vessels relax

Pupil reflex


Close your eyes and then suddenly open
them


Pupil will close in response to the sudden
input of light as the eyes open


Cranial reflex


Iris contains two sets of smooth muscle to
open and close the pupil


Response caused by acetylcholine


Atropine

stops the action of acetylcholine


Optic nerve receives the messages from the
retina in the back of the eye


Optic nerve connects with the
pretectal

nucleus of the brain stem


From the
pretectal

nucleus, a message is
sent to the
Edinger
-
Westphal

nucleus whose
axons run along the
oculomotor

nerves back
to the eye


Oculomotor

nerves synapses on the
ciliary

ganglion


Axons of the ganglion stimulate the circular
muscle of the iris so it contracts



Def: that time when a physician has
determined that the brain and brain stem
have irreversibly lost all neurological
function


Patients in a coma have neurological signs
that can be measured


Movement of extremities



if arms and legs are raised and
let fall, there must be no other movement or hesitation in
the fall


Eye movement



eyes must remain fixed showing lack of
brain
-
to
-
motor
-
nerve reflex (as the head is turned there is
no rolling motion of the eyes)


Corneal reflex



this must be absent (when a cotton swab
is dragged over the cornea, the eye does not blink)


Pupil reflex



this must be absent (pupils do not constrict
in response to a very bright light shone into both eyes)


Gag reflex



this must be absent (insertion of a small tube
into the throat of a comatose patient will cause a gag
reflex)


Respiration(breathing) response



this must be absent (if
the patient is removed from a ventilator, the dead brain
gives no response)


Can still have spinal reflexes such as the
knee jerk reflex


Spinal reflexes do not involve the brain


A short reflex motion can still be exhibited if
the hand or foot is touched in a certain
manner


Further tests:


Electroencephalogram (EEG)


Cerebral blood flow (CBF)





Measures brain activity in
microvolts


Very sensitive test


Some electrical activity is shown on the EEG
if a patient is in a deep coma


Life after death


Radioactive isotope is injected into the
bloodstream


Radioactive counter is then placed over the
head for about 30 minutes


If no activity is detected, this is conclusive
evidence of brain death


Pain signals are carried by peripheral nerve
fibers from all over the body to the spinal cord
and relayed to the sensory area of the brain


Peripheral fibers connect with pain receptors
called
nocioreceptors


Nocioreceptors

are capable of sensing excess
heat, pressure or chemicals from injured tissues


Nocioreceptors

are located in the skin and also
in the muscle, bones, joints and membranes
around your organs


Nerve impulses of pain travel to the spinal cord


Ascending tracts in the spinal cord send the
messages up to the brain


Can tell the muscles to stop the action which
is causing the pain stimulus


Can alert the autonomic nervous system if
the pain requires change in heart rate or
breathing


Can direct other brain cells to release pain
-
suppressing endorphins


First discovered by scientists studying opium
addiction


Found receptors for the opiates, morphine
and heroin in brain cells


Scientists found that the molecules made by
plants were mimicking endorphins


Endorphins are CNS neurotransmitters with
pain
-
relieving properties


Small peptides which bind to opiate
receptors and block the transmission of
impulses at synapses involved in
pain
perception