PS101 Lecture Notes - Lecture 5: Reticular Formation, Quantitative Trait Locus, Muscle Tone
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1. Read Chapter 3: The Biological Bases of Behaviour (pp. 105-135)
•In order to understand what parts of the brain control various functions/ behaviours we examine the brain using various
methods. Electrical recordings help to understand sleep patterns; Lesioning (used primarily on animals) works on the
premise that if we destroy a piece of the brain and see what behaviour is affected, then we know how the brain controls
that behaviour; Electrical stimulation (if we stimulate a part of the brain, then we can tell which function is affected) and
finally, brain imaging, where we can see the brain react to various stimuli.
•The cerebral cortex is the newest part of the brain, from an evolutionary perspective. It is largest in humans, getting
progressively smaller in animals such as the chimp, cat and rat. It is divided into "lobes": frontal, parietal, occipital and
temporal. Check out the learning activity, "The Portable Brain" for a handy way to learn these lobes, and remember
them in testing situations and beyond.
•Check out the discussion question on music/brain to help you learn the parts of the brain and their functions.
•Both neurotransmitters and hormones are chemical messages but neurotransmitters are part of the nervous system,
travel through axons to the receptors and travel short distances, higher speeds at through specific neural networks. In
contrast, hormones are part of the endocrine system, diffuse through the bloodstream to get to receptors and travel far
distances at slower speeds and target less specific areas (e.g., sex hormones affect a wide variety of body parts-
organs, body shape, hair growth etc.)
•The fight-flight response is affected by both the nervous system and endocrine system. The hypothalamus (in the
central nervous system) controls the pituitary gland (endocrine system), which controls hormone release. Thus, there
are two paths traveled to create the fight/flight response: 1) via the nervous system and either the sympathetic or
parasympathetic system responds depending on the message and 2) the pituitary gland notifies the adrenal glands to
release stress hormones so that the body can prepare
•The endocrine system has an effective negative feedback system (like a thermostat) that regulates hormone release.
For example, when too many stress hormones are released in the body a signal is sent back to the hypothalamus to
stop requesting them. Similarly, when we eat sugar, the body needs to digest it, so insulin is released. When digestion
is sufficient the body sends a message to the hypothalamus saying ‘no more is needed’ and insulin production stops.
•One of the important tools to critically evaluate claims that genetics causes behaviour is to understand how the
research is conducted. Perhaps the strongest test of whether genetics causes behaviour is identical twin tests, where
those twins are raised apart. The rationale is that if twins raised apart still show the same behaviour (e.g., depression)
then it can't be environment because they were raised apart and therefore had different environments. The only thing
that is the same across them is their genetics (identical twins have 100% of their genetics in common.
•However, we have to ask ourselves whether it is really the case that twins reared apart will have completely different
environments. First, studies show that identical twins often get adopted into similar socio-economic groups and even
locations. Second, imagine a set of twins who are 6'8" tall. This is of course a unique characteristic; someone this tall
will likely be asked whether they play basketball, they may indeed play basketball, be on a team, and get a sense of
self-esteem from sports. That is, if one twin has all these experiences and is treated in a particular way by everyone
because he/she is so tall, it is likely that the other twin has a similar experience. So, by virtue of looking similar, they
provoke similar reactions by others and likely experience similar things (i.e., similar environmental factors). Similarly,
people argue that personality differences in siblings must be genetic given they grew up in the same house and
therefore have the same environment. Do they really? In fact, parents parent very differently across child 1 and child 2.
They are not the same; they're older, and /or they may live in a different place/location.
The brain can be divided into 3 major regions: the hindbrain, the midbrain, and the forebrain.
Brainstem: appears to be a stem from which the rest of the brain “flowers”, like the head of a
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The hindbrain includes the cerebellum and two structures found in the lower part of the
brainstem: the medulla and the pods. The medulla, which attaches to the spinal cord, is in charge
of largely unconscious but vital functions, including circulating blood, breathing, maintaining
muscle tone, and regulating reflexes such as sneezing, coughing, and salivating. The pons,
(bridge) includes a bridge of fibres that connects the brainstem with the cerebellum. The pons
also contains several clusters of cell bodies involved with sleep and arousal. The cerebellum
(literally “little brain”) is a relatively large and deeply folded structure located adjacent to the
back surface of the brainstem. It is critical to the coordination of movement and to the sense of
equilibrium. The cerebellum plays a key role in organizing the sensory information that guides
these movements. It is your cerebellum that allows you to hold your hand out to the side and then
smoothly bring your finger to a stop on your nose. (test for drunk driving=cerebellum is one of
the first structures depressed by alcohol). Damage to the cerebellum disrupts fine motor skills
(writing, typing, and playing an instrument).
The midbrain is the segment of the brainstem that lies between the hindbrain and the forebrain.
The midbrain contains an area that is concerned with integrating sensory processes, such as
vision and hearing. Running through the hindbrain and the midbrain is the reticular formation.
Lying at the central core of the brainstem, the reticular formation contributes to the modulation
of muscle reflexes, breathing, and pain perception. It is best known for its role in the regulation
of sleep and arousal. Activity in the ascending fibres of the reticular formation contributes to
The forebrain is the largest and most complex region of the brain, encompassing a variety of
structures, including the thalamus, hypothalamus, limbic system, and cerebrum. The thalamus,
hypothalamus, and the limbic system form the core of the forebrain and are located near the top
of the brainstem. Above them is the cerebrum (the seat of complex thought). The thalamus is a
structure in the forebrain through which all sensory information (except smell) must pass to get
to the cerebral cortex. This way station is made up of clusters of cell bodies (somas). It appears
to play an active role in integrating information from various senses. The hypothalamus (under
the thalamus) is a structure found near the base of the forebrain that is involved in the regulation
of basic biological needs. Many key functions: control the autonomic nervous system, serves as a
vital link between the brain and the endocrine system, plays a major role in the regulation of
basic biological drives (four fs: fighting, fleeing, feeding, and mating). The hypothalamus clearly
contributes to the control of hunger and other basic biological processes, including thirst and
temperature regulation. The limbic system is a loosely connected network of structures located
roughly along the border between the cerebral cortex and deeper subcortical areas. It is not a
well-defined anatomical system with clear boundaries. Broadly defined, it includes: part of the
thalamus and hypothalamus, the hippocampus, the amygdala and other structures. The limbic
system is involved in the regulation of emotion, memory, and motivation (even the tendency to
be optimistic). The hippocampus and adjacent structures play a role in memory processes and a
role in prediction and imagination. Evidence links the limbic system to the experience of
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