Download Chapter 2, continued Basal ganglia Has three principal structures

Day 4
January-17-12
8:30 AM
Chapter 2, continued
Basal ganglia
A collection of nuclei just below the white matter of the cortex, controlling voluntary movement
- Has three principal structures: the caudate nucleus, putamen, and globus pallidus
- Destruction of these nuclei leads to disorders such as Parkinson's
Limbic system
A group of structures between the neocortex and brain stem - a fairly ancient structure
- Its principal structures are the amygdala (learning and remembering emotional memories),
hippocampus (motivation and emotion, as well as memory), and the cingulate cortex (also known
as the limbic cortex, right next to the corpus callosum)
- They work in concert to regulate emotional and sexual behaviours, memory, and spatial
navigation
Olfactory system
The olfactory system - handling smell - is the oldest sense humans have, and it connects directly to the
brain without passing through the thalamus
- Considered by some people to be part of the limbic system, as it has a strong connection to
emotion
- The olfactory bulbs passes information to the pyriform cortex, which handles perception of smell,
then passes the information on to the thalamus and on to the neocortex
- The fact that the olfactory system connects straight to the pyriform cortex, their neural
connections are a lot stronger
Chapter 2 - Peripheral nervous system
The somatic nervous system is monitored and controlled by the central nervous system - cranial nerves
are connected to the brain while the spinal nerves are connected to the spinal cord segments
*** Cranial nerves ***
The cranial nerves exit from the brain and travel through the body, and there are twelve of them, each
with a specific name and function
- Nerve 1 is the olfactory nerve, for smell
- Second is optic nerve for vision
- Three and Four, oculomotor and trochlear handle eye movement
- Fifth is trigeminal, handling masticatory movements and facial sensation (tends to transfer pain)
- Sixth is the adbucens, which also handles eye movement
- Seventh is facial nerve, for facial movement and sensation
- Eighth is the auditory vestibular, for hearing and balance
- Ninth is the glossopharyngeal, handling tongue and pharynx movement and sensation
- Tenth is the vagus, or vagal nerve, coming from the term vagrant - it travels quite far as it handles
the heart, blood vessels, viscera, and movement of larynx and pharynx
- Eleventh is the spinal accessory, handling neck muscles
- Twelfth is hypoglossal, handling tongue muscles
Spinal nerves
Law of Bell and Magendie: The general principle that sensory fibres are located dorsally and motor
fibres are located ventrally
PSYC 2200 Page 1
fibres are located ventrally
- Dorsal fibres are afferent, carrying information from the body's sensory receptors
- Ventral fibres are efferent, carrying information from the spinal cord to the muscles
There are 31 spinal nerves, with the top of the spine handling upper portions of the body and lower
portions handling lower parts of the body
- This is why breaks higher in the spine are more damaging, as they affect all the sections below
them - someone with a break low in the spine would only be paraplegic
Dermatome: An area of the skin supplied with afferent nerve fibers by a single spinal-cord dorsal root
- Only the highest spinal nerve, C1, is without an accompanying dermatome
From top to bottom, the spinal nerves are:
- Eight cervical nerves at the top of the spine, numbered C1-8, which are related to the head,
shoulders, and arms
- Twelve thoracic nerves, numbered T1-T12, are related to the torso
- Five lumbar nerves, numbered L1-L5, are attached to the waist and the front of the legs
- Finally, there are five sacral nerves, numbered S1-S5, handle the waist downwards and the backs
of the legs
Spinal cord segments are interconnected so adjacent segments can operate together to direct complex
coordinated movements
- For example, our fingers tend to move together, which is why some people have difficult moving
single isolated digits
Autonomic nervous system
Sympathetic nervous system: Arouses the body for action, and mediates the fight or flight response
Meanwhile, the parasympathetic system is the opposite of the sympathetic - prepares the body to rest
and digest, and reverses the fight or flight response
Ten basic principles of brain function
Principle 1: The brain's primary function is to produce behaviour, or movement, and to do so it must:
- Get and integrate information about the world
- Create a sensory reality - evolution has equipped each species with a view of the world that helps
it survive
Principle 2: The brain is plastic, as neural tissue has the capacity to adapt to the world by changing how
its functions are organized
- Neuroplasticity: The nervous system's potential for physical or chemical change that enhances its
adaptability to environmental change and its ability to compensate for injury
- While these are usually positive adaptive changes, consistently negative things can change the
brain for the worst (eg depression)
Principle 3: Many of the brain's circuits are crossed, with each hemisphere receiving sensory stimulation
from the opposite (contralateral) side of the body
- When information reaches the spinal cord, it crosses over to the opposite side of the body from
which it originated (this applies to afferent and efferent connections)
- It's only once they hit the spinal cord that the nerves cross over
- The somatic nervous system and olfactory system are exceptions, remaining ipsilateral (samesided)
Principle 4: The central nervous system functions on multiple levels, with sensory and motor functions
carried out in many places in the forebrain, spinal cord, and brainstem
- Each new addition to the central nervous system added a layer of behavioural complexity that
needed to be integrated into the existing system
- This is why information ascends through the nervous system - coming up the spinal cord and
through the thalamus and other areas before passing on to the neocortex
PSYC 2200 Page 2
through the thalamus and other areas before passing on to the neocortex
Principle 5: The brain is both symmetrical and asymmetrical - language and body control are
asymmetrical so that they can be synchronized and unified
Principle 6: Brain systems are organized both hierarchically and in parallel
- If there were a system that went in a straight line, from one level to another, the information
would be processed serially and organized hierarchically
- However, as the nervous system is organized in parallel, functions at the same level are integrated
together and always speaking to each other
- Vision is an example of hierarchical and parallel organization, with information proceeding
hierarchically from the eye's photoreceptors to the visual ganglia, then on to the thalamus and
eventually split into the dorsal and ventral streams, which operate in parallel
- The Binding problem is the way that we maintain an integrated, unified sense of a whole
experience despite our brain operating in parallel at times
Principle 7: Sensory and motor divisions exist throughout the nervous system
- For example, the somatic nervous system's spinal nerves are either sensory or motor in function,
while some cranial nerves are exclusively one or the other as well
- In the central nervous system, this division does exist to a certain extent - the hindbrain and
midbrain are extensions of the spinal cord, retaining dorsal (sensory information)/ventral (motor
information) organization
Principle 8: The sensory input to the brain is divided for object recognition and motor control
- One example is the dorsal and ventral processing steams in the visual system, with the dorsal
stream to process and aid in movement and the ventral stream (containing the fusiform facial
area) which identifies objects
Principle 9: Functions in the brain are both localized and distributed
- One example is the different areas of the brain that are involved in handling different parts of
language, such as Broca's area for speech production and Wernicke's area for speech
comprehension
- Some specific aspects are localized, but often they're distributed throughout the brain as well - to
a certain extent, this helps make the brain more resilient to failure
Principle 10: The nervous system works by juxtaposing excitation and inhibition - for example, flexing
the arm (tensing the muscles) is an excitation of the muscle while extending the arm (relaxing the
muscle) is an inhibition
- Brain injury can result in either the loss or release of behaviour by changing this delicate balance for example, people with Tourette's have a dysfunction in the system that inhibits inappropriate
language
Units of nervous system function
Neurons
The primary type of cell in the brain, forming the basis of information processing
Its dendrites gather information from other neurons, with more branched dendritic trees representing
more connections to other neurons
- As new connections are formed, new learning occurs
The cell body, or soma, which is the core region containing the nucleus and DNA
- This is where information is integrated - the axon hillock is where a neuron's electrical information
is summated
The axon is the output portion of the neuron, passing information on to other cells when action
potentials occur
Dendritic spines emerge from the branch, protrusions that increase a dendrite's surface area
This is the usual point of contact with axons of other cells
PSYC 2200 Page 3
- This is the usual point of contact with axons of other cells
Axon hillock is the juncture of soma and axon, where the action potential begins
The axon collaterals of a cell are the branches of an axon, similar to dendritic spines, leading to
connections with other neurons
The teleodendria are the end branches of an axon, containing the terminal buttons
- The terminal button is a knob at the tip of an axon's teleodendria that conveys information to
other neurons - also called an end foot
The synapse is where the magic happens - it's the gap between the terminal button of one neuron and
another
- They're usually axodendritic, meaning the axon connects to the dendrite of another neuron
- But they can also be axosomatic (the end foot of the axon and soma of the other nerve), as well as
occasionally axoaxonic (an axon connecting to another axon) - these two types of connections are
much stronger, as they're close to the axon hillock
- Anything that's close to the axon hillock (either axoaxonic connections near the bottom of the
axon hillock, or axosomatic connections near its top) has a larger influence on whether an action
potential occurs, while connections that are further away have a weaker influence
There are different types of neurons, as well, based on their structure or function - though generally
structure and function go together
- Sensory neurons bring information to the central nervous system
- Interneurons associate sensory and motor activity within the central nervous system
 They also form the connection at the spinal cord where information crosses from one side
to the other
 These neurons tend to have huge dendritic trees, as they're connected to a huge variety of
neurons
- Motor neurons send signals from the brain and spinal cord to the muscles
 They also tend to be multipolar, meaning they have multiple dendritic branches
Glial cells
There are five types of glial cells, which are actually much more numerous than neurons
Ependymal cells make and secrete cerebrospinal fluid, and are small, ovoid cells found in the walls of the
ventricles
Astrocyte are star shaped and symmetrical cells that provide structure support for neurons
- They transport substances between neurons and capillaries, transporting glucose and oxygen to
the cells
- It protects the brain through the blood-brain barrier, the portion of the brain's circulatory system
which inhibits the passage of many things from the blood stream to the brain
- The brain's capillaries are actually much more tightly bound than the capillaries in the rest of the
body, which is part of the formation of the blood-brain barrier
- Enhances brain activity by providing fuel to active brain regions
- Also involved in forming scar tissue
Microglia originate in the blood as an offshoot of the immune system, these cells are involved in
phagocytosis - they scavenge debris from the brain, such as dead cells
Oligodendroglia cells are the cells in the central nervous system that myelinate axons to aid in
information transfer
- Oligodendroglia are capable of myelinating multiple cells in the central nervous system
Schwann cells are similar to oligodendroglia, as they wrap around the other cells, but these are
responsible for myelinating the axons in the peripheral system
- Schwann cells wrap themselves around a single axon in the peripheral nervous system
PSYC 2200 Page 4
Schwann cells wrap themselves around a single axon in the peripheral nervous system
Disorders
Hydrocephalus is a build-up of pressure in the brain and swelling of the head caused if the flow of
cerebrospinal fluid is blocked due to stroke or injury
 Some babies are born with a dysfunction in their circulatory system - in order to deal with
this, they insert a shunt in order to drain the CSF in another way
 If the condition isn't treated, the excessive pressure can result in retardation
Multiple sclerosis (MS) is a nervous system disorder that results from the loss of myelin around axons this is a deterioration of Schwann cells
- Nobody knows what causes this, but at the moment it's considered an autoimmune disorder in
which the body sees its own Schwann cells as enemy cells to be attacked
PSYC 2200 Page 5