PSYC10003 Lecture Notes - Lecture 2: Multiple Sclerosis, Motor Neuron, Autoimmune Disease
2. Neurons, glia and mechanisms of communication within the
neuron
Multiple Sclerosis
• Multiple sclerosis: an acquired neurological disorder that attacks the insulating sheath (myelin)
that surrounds the axons of neurons
• Starts with visual impairment, problems eye movement, numbness, slurred speech, muscle
weakness (eventually leading to paraplegia)
• Characterised by occasional (on average, every couple of years), in which symptoms worsened,
punctuated by periods where symptoms disappear or are less severe
• More common in women, typically occurs in early adulthood (late 20's/30's)
• Autoimmune disorder
• Selectively attacks myelin surrounding axons of neurons
• Unknown cause
• Own immune system damages cells responsible for creating myelin sheath, leads to inability of
signals to be passed from neuron to neuron
• Some believe its caused by virus contracted around time of birth/early childhood
Withdrawal Reflex
• Occurs when we touch something that is very hot or otherwise painful
• The dendrites of a sensory neuron (in this example located in the skin of the hand) respond to a
noxious stimulus in the environment (a hot iron)
this signal is sent back along the axon to
the terminal buttons, which are located in the
spinal cord
here the terminal buttons release a
neurotransmitter into the synapse, and this
excites an interneuron, which resides within
the spinal cord itself
the interneuron then sends a message
down its axon, which in turn releases a
neurotransmitter to excite the motor neuron
the axon of the motor neuron joins a
nerve (a bundle of motor neurons) and
travels to a muscle in the arm, causing the
muscle to contract and pulling the hand away
from the hot surface.
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2
Role of Inhibition
In previous example, all synaptic connections had excitatory effects. What about inhibition?
• Eg. Carrying hot dish, ut you don’t want to reak it so you hold on and rush to the tale
• How was the withdrawal reflex overcome?
• As in previous slide, tendency to drop dish come from excitatory synapses on motor neurons in the
spinal cord
• Excitation can be counteracted by inhibition arising from another source: the brain
contains complex circuits
of neurons that represent
consequences of dropping dish (eg.
Embarrassment, expense, loss of
good meal)
These circuits send
information to spinal cord to
prevent from dropping dish
Relevant neuron in brain
sends message along axon to
spinal cord
Here it excites an
inhibitory interneuron which
releases an inhibitory
neurotransmitter, decreasing
activity of motor neuron, blocking
withdrawal reflex
• Excitatory and inhibitory effects compete to achieve desired result.
• Much more complex: involves hundreds or even thousands of sensory neurons, interneurons and
motor neurons, both in brain and spinal cord
• Purpose of example is to illustrate principles of neural connection
Neuronal Structure reflects the function
• Shape and size of neuron related to function
• Neurons of similar architecture tend to cluster in the CNS, reflecting functioning of particular region
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3
Neurons
• Neuron: the basic information-processing and information receiving unit of the nervous system
• Form complex networks within nervous system, but not directly connected
• Tiny gaps called synapses, across which chemicals called neurotransmitters are passed
1. Cell body: contains nucleus
(genetic material) and internal
organelles necessary for cell
maintenance.
2. Dendrites: tree-like branches
that allow neurons to communicate
with one another and receive
information from other neurons.
3. Axon: a long, slender fibre that
carries signals from the cell body.
The signal carried by an axon is an
action potential, which we shall see
later is a wave of electrical potential
that begins at the cell body and
travels down the axon to the
terminal buttons
4. Terminal buttons: small knobs at the ends of many branches of axons. Play critical role in
transmitting information from one neuron to another by secreting neurotransmitter. This chemical
passes across synaptic gap and can either excite or inhibit the next neuron in the chain.
• Neurons may receive info from terminal buttons of many other neurons and may send info to other
neurons via own terminal buttons
• Terminal buttons may form synapses with cell body or dendrites of other neurons
• Inside cell body are organelles needed for maintenance and proper functioning of cell
• Cytoplasm: jelly-like sustane inside ell. Inside this is…
o Mitochondria: use glucose to produce energy, produce adenosine and triphosphate (ATP)
which can be used throughout cell as energy source.
• Nucleus contains cell's chromosomes composed of deoxyribonucleic acid (DNA): genes that make
up chromosomes to provide recipes for making proteins. These proteins are needed to build the
cell, and also form enzymes that create and break down molecules
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Document Summary
Neurons, glia and mechanisms of communication within the neuron. In previous example, all synaptic connections had excitatory effects. These circuits send information to spinal cord to prevent from dropping dish sends message along axon to spinal cord inhibitory interneuron which releases an inhibitory neurotransmitter, decreasing activity of motor neuron, blocking withdrawal reflex. Neuronal structure reflects the function: shape and size of neuron related to function, neurons of similar architecture tend to cluster in the cns, reflecting functioning of particular region. Play critical role in transmitting information from one neuron to another by secreting neurotransmitter. Inside cell body are organelles needed for maintenance and proper functioning of cell: cytoplasm: jelly-like su(cid:271)stan(cid:272)e inside (cid:272)ell. These proteins are needed to build the cell, and also form enzymes that create and break down molecules. Smallest glial cells: act as phagocytes, like some astrocytes, also act as brain"s immune system, attack invading micro-organisms. Largely responsible for inflammation after brain damage: schwann cells.
