Download E.5 Brain

E.5 The Brain
IB Assessment Statement
• E.5.1 Label, on a diagram of the brain, the
medulla oblongata, cerebellum,
hypothalamus, pituitary gland and cerebral
hemispheres.
Function of the Parts of the Human
Brain
• Medulla oblongata: controls automatic and homeostatic activities,
such as swallowing, digestion and vomiting, and breathing and
heart activity.
• Cerebellum: coordinates unconscious functions, such as movement
and balance.
• Hypothalamus: maintains homeostasis, coordinating the nervous
and endocrine systems, secreting hormones of the posterior
pituitary, and releasing factors regulating the anterior pituitary.
• 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.
IB Assessment Statement
• E.5.2 Outline the functions of each of the
parts of the brain listed in E.5.1.
IB ASSESSMENT STATEMENT
• 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.
Types of techniques that are used to find out
what the function of each part of the brain is:
1. Functional magnetic Resonance Imaging:
2. Lesions:
3. Animal Experiments:
E.5.3 Techniques used to discover the
function of the brain (fMRI)
FMRI (functional magnetic resonance imaging)
scanning
• Is a technique used to discover which part of
the brain are activated by a specific process.
• The experimental subject is placed in a
scanner and a high resolution scan of the
brain is taken.
E.5.3 Techniques used to discover the
function of the brain (fMRI)
FMRI (functional magnetic resonance imaging)
scanning
• The fMRI shows areas of the brain which have
increased blood flow.
• Increased blood flow is associated with increased
neuron activity.
• During experiments, when presented with a
stimulus the fMRI is taken and the region of the
brain with increased blood flow is linked to with
the processing of that stimulus information.
E.5.3 Lesions
• Lesions: Accidents, stokes, and tumors can be
damage specific parts of the brain.
– These damaged areas are called lesions.
– From these damaged areas function of these areas
can be deduced.
– For example, lesions in the Broca’s area of the left
hemisphere of the brain cause dysphasia (inability to
speak), but reading and writing is still possible…..thus
from this scientists know the Broca part of the brain is
important for processing speak.
E.5.3 Lesions case study
Lesion Studies:
• As is often the case in medicine improved understanding of normal
function often comes from the study of disease or injury.
• Study of when things go wrong often provides insight into normal
function.
• Lesions of brain result in a loss or alternation of behaviour linked to
the region of the brain affected by the lesion.
• Example: Phuneas Cage 1848
– Was working on a construction when an explosion sent a long metal
rod through his skull penetrating near the eye and exiting through the
roof of the skull. Phineas did not die, but the rod had passed through
the frontal lobes of the cerebral cortex. Whilst he survived the
accident his personality was altered and his ability to interact socially
was impaired. This is an extreme example
E.5.3 Animal Testing
• Many experiments have been performed of
animals, including primates.
• Often the procedures involve surgical procedures
– parts of the skull have to be removed to access
the brain.
• The animal must be keep alive so that the brain is
still functioning.
• Experimental procedures are carried out on the
brain and the effects of the animal are then
observed, either during the operation or
afterwards.
IB ASSESSMENT STATEMENT
E.5.3 Explain how
1. animal experiments,
2. lesions
3. and FMRI (functional magnetic resonance
imaging) scanning can be used in the
identification of the brain part involved in
specific functions.
IB Assessment Statement
• E.5.4 Explain sympathetic and
parasympathetic control of
– the heart rate,
– movements of the iris
– and flow of blood to the gut.
E.5.4 Sympathetic and
Parasympathetic Nervous system
Heart rate is controlled by the autonomic system
which is also divided into two parts,
1. the sympathetic
2. and parasympathetic nervous system.
Parasympathetic
"Rest and Digest" responses
Sympathetic
Fight or Flight" responses
E.5.4 Nervous Control Of the
Heart Beat
– Nerve control (extrinsic control):
• The cardiac center in the medulla oblongata
(located at the base of the brain) controls cardiac
output (both heart rate and stroke volume).
– stroke volume (SV) is the volume of blood
pumped from one ventricle of the heart with
each beat
• Opposing sympathetic (stimulatory) and
parasympathetic (inhibitory) impulses control
the pacemaker.
•
E.5.4 Slowing Down the Heart Rate
Vagus nerve is a cranial nerve that is part of the
parasympathetic division of the autonomic
(automatic) system.
» It arises from the medulla oblongata.
» Carries impulses to the heart continuously.
» Secretes a chemical called acetylcholine
on the heart.
» This chemical inhibits the pacemaker,
causing the heart rate to slow and the
contractile strength of the muscle to
weaken.
E.5.4 Speeding up the Heart Rate
• Accelerator nerve is part of the
sympathetic division of the autonomic
nervous system.
• It arises from the medulla oblongata
• The nerve secretes epinephrine (also called
adrenalin).
• Epinephrine stimulates the pacemaker, causing
the heart rate to increase, and contraction strength
to increase.
E.5.4 Blood Flow to the Gut
• Parasympathetic System: Blood vessels are
dilated, this increases blood flow to the gut.
• Sympathetic System: Blood vessels are
constricted, decreases blood flow to the gut.
E.5.4 Iris of the eye
• The iris reflex is under the control of the autonomic
system.
• If light is particularly bright the receptors cells of the
retina can be come over stimulated.
• To prevent over stimulation the iris is able to reduce
the amount of light entering through the constriction
of the pupil that as much light as possible reaches the
retina the pupil dilates.
• The mechanisms in the eye is based on two sets of
muscles, the circular and radial muscles.
• This antagonistic pair of muscles makes up the iris
E.5.4 Iris of the eye
• Parasympathetic System: causes circular
muscle fibres contract so the pupil constricts
to protect the pupil
• Sympathetic System: Causes Radial muscles
to contract, dilating the pupil to give it a
better image.
E.5.4 Iris of the eye
IB Assessment Statement
• E.5.5 Explain the pupil reflex.
IB Assessment Statement
• Discuss the concept of brain death and the
use of the pupil reflex in testing for this.
E.5.6 Death and the pupil reflex
• Descriptions of death at the biological level:
– Cardiac Death Criteria:
• No heart beat
• Ventilation has stopped
• Machines required to carry out basic life processes
– Brain Death
• Brain no longer responds to stimuli
• No purposeful movement or response
E.5.6 Death and the pupil reflex
• To determine if the brain is still functional
stimuli are presented such as shining light
into the eye and looking for the associated
pupil reflex. A reflex would indicate some
function at the basic brain level of the
medulla oblongata.
• Absence of the pupil reflex indicates no basic
brain function and allow surgeons to progress
towards harvesting organs.
• Much of this issue depends on ones definition
of 'living' and on local and national laws.
E.5.7 Pain perception and the role of
endorphins
• When a pain receptor in the skin is stimulated impulses are
transmitted to the central nervous system to the sensory areas of
the cerebral cortex.
• The pituitary secretes Endorphins into the blood stream and the
hypothalamus secretes them into the brain to block the receptor
molecules at synapses. In doing so the pain is reduced.
• An awareness of pain allows one to avoid acute injury being
aggravated into chronic injury.
• An awareness of pain allows one to avoid noxious substances.
• Perception of pain is also used in aspect of social organisation e.g
lion cubs mock fighting
• Having the perception of pain has a distinct survival benefit
however there comes a point at which the pain needs to be
blocked.