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Chapter 49.2 - Notes
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Specific brain structures arise during embryonic development
Cerebrum, the part of the brain that lies just beneath the skull, it divided into the right
and left cerebral hemispheres. It is responsible for many activities such as calculation,
contemplation, learning, emotions and memory
A thick band of axons known as corpus callosum enables the right and left cerebral
cortices to communicate
The cerebellum coordinates movement and balance and helps in learning and
remembering motor skills, as well as receiving sensory information about the
positions of the joints and the lengths of the muscle and input from the auditory and
visual systems, such as hand eye coordination
The diencephalon gives rise to the thalamus, hypothalamus and epithalamus
The thalamus is the main input center for sensory information, all senses are sorted in
the thalamus and sent to the appropriate cerebral centers
The hypothalamus contains the body’s thermostat and the central biological clock; it
also controls the pituitary gland. The hypothalamus also regulates hunger and thirst,
as well as sexual behavior and the fight or flight response
The brainstem consists of the midbrain, pons and the medulla oblongata
The midbrain receives and integrates several types of sensory information and sends
it to specific regions of the forebrain
A major function of the pons and medulla is to transfer information between the PNS
and the midbrain and forebrain, as well as coordinating the large scale body
movements, such as running and climbing
The medulla also controls several automatic homeostasis functions such as breathing,
heart and blood vessel activity, swallowing, vomiting and digestion
As a human embryo develops, the neural tube forms three anterior bulges – forebrain,
midbrain and hindbrain
The midbrain and parts of the hindbrain develop into the brainstem, a stalk that joins
with the spinal cord
The rest of the hindbrain forms the cerebellum
The forebrain develops into the diencephalon, including the neuroendocrine tissue of
the brain and the telencephalon, which becomes the cerebrum
The brainstem and cerebrum control arousal and sleep
Arousal is a state of awareness of the external world
Sleep is a state in which external stimuli are received but not consciously perceived
Sleep is also an active state
Although sleep is essential for survival, we still know very little about its function, one
hypothesis is that sleep and dreams are involved in consolidating learning and
memory
The core of the brainstem has a diffuse network of neurons called the reticular
formation, which partially controls arousal and sleep
Acting as a sensory filter the reticular formation determines which incoming
information reaches the cerebrum. The more information the cerebrum receives the
more alert the person is, although the brain often ignores certain stimuli while
actively processing other inputs
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The hormone melatonin is produced by the pineal gland and plays a role in bird and
mammal sleep cycles, because peak melatonin secretion occurs at night
(This system of neurons distributed throughout the core of the brainstem filters
sensor input (blue arrows), blocking familiar and repetitive information that
constantly enters the nervous system. It sends the filtered input to the cerebral cortex
(green arrows).)
Dolphins sleep with one brain hemisphere at a time and are therefore able to swim
while being “asleep”
(EEG recordings were made separately for the two sides of a dolphin‘s brain. Low
frequency activity was recorded in one hemisphere while higher frequency activity
typical of being awake was recorded in the other hemisphere.)
Cycles of sleep and wakefulness are examples of circadian rhythms, a daily cycles of
biological activity
Mammalian circadian rhythms rely on a biological clock, a molecular mechanism that
directs periodic gene expression
Biological clocks are typically synchronized to light and dark cycles, they can maintain
a roughly 24 hour cycle even in the absence of environmental cues
Circadian rhythms are coordinated by a group of neurons in the hypothalamus called
the Suprachiasmatic nucleus (SCN)
In response to transmission of sensory information by the eyes, the SCN acts as a
pacemaker, synchronizing the biological clock in cells throughout the body to the
natural cycles of day lengths
SCN also determines the circadian rhythm of the whole animal
(Wild type hamster – 24 hours, T hamster – 20 hours, absence of external cues, to
determine if the SCN controls the circadian rhythm, surgically removed the SCN from
wild type and T hamsters, transplant of an SCN from a hamster of the opposite
genotype)
Generation and experience of emotions involve many brain structures including the
amygdala, hippocampus, and parts of the thalamus
These structures are grouped as the limbic system
The limbic system also functions in motivation, olfaction, behavior and memory
Generation and experience of emotion also require interaction between the limbic
system and sensory areas of the cerebrum
The structure most important to the storage of emotion in the memory is the
amygdala
Emotional experiences are often stored as memories that can be recalled by similar
circumstances. In the case of fear, emotional memory is stored separately from the
memory system that supports explicit recall of events
Damage to the amygdala results in reduced capacity for emotional memory
(Functional brain imaging I is aiding the investigation of recovery from stroke and
other brain traumas, as well as helping map abnormalities in migraine headaches,
dyslexia and many psychiatric disorders)