Thursday September 27, 2012
Chapter 3: The Brain
1) The Nervous System
- The master control centre of the body
- 3 major neurons
o Sensory neurons inputs messages from sensory organs to brain and spinal
o Motor neurons transmit output messages from brain and spinal cord to the
o Interneurons perform connective functions within the nervous system
- Divided into the central nervous system which consists of the brain and the spinal
cord, and the peripheral nervous system which consists of the muscles, glands
and sensory receptors
a) Peripheral Nervous System
- Contains the structures outside the brain and spinal cord
- 2 major divisions:
o Somatic Nervous System
Voluntary muscle activation
Consists of sensory neurons and motor neurons
o Autonomic Nervous System
Controls involuntary muscles such as respiration, smooth muscles,
cardiac muscles, circulation digestion, etc.
Contains 2 subdivisions that help maintain homeostasis, the body’s way
of adjusting itself to external factors:
Sympathetic nervous system activates. For example, in a flight-
or-fight response, the sympathetic nervous system pump more
blood to the muscle and dilates the pupil to allow more light into the
Parasympathetic nervous system deactivates and slows down
the body processes, or maintains it back to its natural state
b) Central Nervous System
- Contains the spinal cords, which connects to peripheral nervous system, and the
o The Spinal Cord
Nerves leave and enter the CNS by the spinal cord
Its neurons are protected by the vertebrae
H-Shaped and consists of grey matter bodies and their interconnections
White myelinated axons surround the grey matter and connect to each
other and the higher centres of the brain Sensory nerves enter the back side of the spine, while the motor nerves
leave the by the front
Spinal reflexes allow a stimulus-response without the involvement of the
brain. For example, if you put your finger over fire, sensory receptors will
trigger nerve impulses into the spinal cord and synapse with interneurons.
The interneurons will then excite the motor neurons that will cause the
hand to pull away.
Transmitting messages to and from the brain takes slightly longer than it
does with the spine; therefore, spinal reflexes reduce reaction time and
any potential damage
o The Brain
The most active energy consumer within the body, taking up the 20% of
the oxygen in rating state
Brain is never at rest.
Scientists have developed four methods to study brain-behaviour methods
Neuropsychological tests measures verbal and non-verbal behaviours
that have been affected by brain damage, usually from people who have
suffered from accidents or diseases
Destruction and stimulation techniques. This method involves
destroying specific nerve tissues with electricity, cold/heat or chemicals.
Afterwards, the consequences are studied. Stimulation is an alternative
method in which electric current or chemicals are applied to a certain
region of the brain.
Electrical recording measures the electrical activity of the neurons. EEG
(electroencephalogram) measures large groups of neurons. It then
produces patterns that correspond to certain states of consciousness,
such as wakefulness and sleep. The patterns can also indicate certain
Brain imaging is the latest method that allows neuroscientists to peer into
Computerized Axial Tomography (CT) scans uses narrow X-ray
beams to construct a picture of brain structures.
Positron emission tomography (PET) scans measures brain
activity by radioactive substance injected into the brain. Active
areas accumulate radioactive glucose.
Magnetic resonance imaging (MRI) combines the features of CT
and PET scans, thus allowing both brain structures and activity to
be measured. MRI images are produced based on the response of
atoms to the magnetic impulse delivered by the device. A computer
analyzes the voltage emitted by the tissues. MRI also displays the
active neurotransmitters in the brain regions.
2) THE HIERARCHICAL BRAIN: STRUCTURES AND BEHAVIOURAL FUNCTIONS - Structures of the brain govern the basic physiological functions such as breathing
and heart rate.
- Divided into 3 major divisions: the hindbrain, the lowest and most primitive (as in
least evolved); the midbrain, which lies above the hindbrain; and the forebrain.
a) The Hindbrain
- As the spinal cord enters the brain, it enlarges into a stalk-like structure called the
brain stem. Another major portion of the hindbrain, the cerebellum, is attached to
- The first structure that lies in the brain stem is the medulla. This structure has vital
functions, such as breathing and circulation. Damage of the medulla causes death or
at best, life support.
- The medulla also acts as a leeway for the sensory and motor nerve tracts coming
from the spinal cord on the left and descending from the brain on the right.
- The pons lies above the medulla and contains many neurons that regulate sleep
- The cerebellum regulates muscular movement and balance. It also plays a role in
learning and memory. Motor control functions of the cerebellum can be disrupted by
alcohol; physical damages can result in motor disturbances, such as inability to walk.
b) The Midbrain
- Lies just above the hindbrain, the midbrain contains groups of sensory and motor
neurons, and also sensory and motor fibre tracts that connect to the higher and
lower portions of the nervous system
- The sensory region is the relay centre for auditory and visual systems
- Reticular formation is located right above the hindbrain into the midbrain. It acts as
a filter to alert both higher and lower regions of the brain.