The human brain

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14 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

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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

(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


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


has two
and a highly
surface. It
such as
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

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

side had
speech and language

People who had injuries in the same areas
but on the

side of the brain had no
language problems

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

Injury to

interferes with the ability to


Injury to

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 uses radio waves and a strong magnetic
field, not X

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

Diagnosing how a diseased or injured brain is

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

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

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

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

Peripheral nervous system considered in two
somatic 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

Response is “fight or

Response is to relax

Neurotransmitter is

Neurotransmitter is



Antagonistic systems

Sympathetic system associated with fight or

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

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


stops the action of acetylcholine

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

Optic nerve connects with the

nucleus of the brain stem

From the

nucleus, a message is
sent to the

nucleus whose
axons run along the

nerves back
to the eye


nerves synapses on the


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

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
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

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

Further tests:

Electroencephalogram (EEG)

Cerebral blood flow (CBF)

Measures brain activity in

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

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


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


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

Can direct other brain cells to release pain
suppressing endorphins

First discovered by scientists studying opium

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
relieving properties

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