PSYA01H3 Chapter Notes - Chapter 3: Neuroglia, Sensory Neuron, Multiple Sclerosis
Chapter 3 Notes
neurons: cells in the nervous system that communicate with one another to perform
information-processing tasks
!The electrical and chemical activities of the neurons are the starting point of all
behaviour, thought and emotion. There are about 100 billion cells in the brain
performing different tasks that allow us to function.
Discovery of Neuron Function
- Late 1880’s: Spanish physician Santiago Ramon y Calaj learned about a new
technique for staining neurons in the brain
-the stain highlighted entire cells’ appearance-->different shapes and sizes
-neurons had threads extending outwards towards other neurons, but did not actually
touch--> he figured that they process information, and that they had to communicate
somehow --> discover dendrites and axon!
Cajal also discovered:
-three basic parts of neurons: cell body, dendrites, and axon
Cell body/soma: largest component of neuron, coordinates information-processing
tasks and keeps cell alive, protein synthesis, energy production and metabolism
functions take place here, surrounded by porous cell membrane allowing molecules in
and out of cell, such as ions: small electrically charged molecules
!Nucleus: (located in cell body): houses chromosomes containing DNA
Axon: transmits information to other neurons, muscles or glands, each neuron has one
of these. The axon can be up to a meter long!
Dendrites: (Greek word for tree) Receive information from other neurons and transmit it
to the cell
Myelin Sheath: insulating layer of fatty material on many neurons
!-->composed of Glial cells: support cells found in nervous system. There are 10
to 50 times as many glial cells as there are neurons
!Demyelinating diseases such as multiple sclerosis: less “insulation” causes loss
of feeling in limbs, partial blindness, movement and cognition problems
Synapse: gap between the axon of one neuron and dendrites of the other
Major Neuron Types
Sensory neurons: receieve information from external world and convey it to the brain
through spinal cord. In our eyes, these cells’ endings are sensitive to light e.g. bipolar
Motor neurons: carry signals from spinal cord to muscles to produce movement (a lot
of these have long axons)
Interneurons: compose most of the nervous system; connect sensory neurons, motor
neurons or other interneurons e.g. Purkinje and pyramidal
Neurons Specialized by Location
Purkinje cells: interneuron carrying information from cerebellum to rest of brain and
spinal cord-->dense, elaborate dendrites resembling bushes
Pyramidal cells: interneuron found in cerebral cortex, triangular cell body and single
long dendrite with smaller ones
Bipolar cells: sensory neuron in retina, single axon and single dendrite.
Electrochemical Actions of Neurons: Information Processing
-Electrochemical action of neurons: information processing between neurons
proceeds in conduction (conduction of electric signal over relatively long distances
within neurons, from dendrites, to cell body, to axon) and transmission (transmission of
chemical signals between neurons over synapse)
resting potential: difference in electric charge between the inside and outside of a
neuron’s cell membrane; arises from the difference in concentrations of ions inside and
outside the neuron’s cell membrane-->negative because matching K+ concentration
outside the neuron to match K+ concentration inside neuron causes resting potential to
disappear. In resting state, channels allowing K+ molecules to flow freely are open,
while channels allowing Na+ and other ions are generally closed. Because there is a
naturally higher concentration of K+ inside the neuron, some move outside through
open channels, leaving the inside with a charge of about -70 millivolts relative to outside
action potential: an electric signal that is conducted along a neuron’s axon to a
synapse. Biologists working with squid giant axon discovered: brief electric shock
conducted large electric impulse down the length of axon; electric impulse is the action
potential, which only occurred when the electric shock reached a certain threshold.
All-or-nothing event: Electric stimulation below threshold fails to cause action potential,
at or above always does--> +40 millivolts, because K+ channels shut down and Na+
and other positively charged ion channels open up, Na+ ions flow from outside to inside.
After action potential reaches maximum, membrane channels go back to normal and
axon returns to resting potential.
refractory period: time following an action potential during which a new action potential
cannot be initiated--> as membrane channels return to resting potential, many Na+ are
left inside axon and K+ outside, which is an imbalance of ions.
Nodes of Ranvier: breakpoints between myelin, electric current seems to jump over
these, and this process is called saltatory conduction
terminal buttons: knoblike structures that branch out from an axon, filled with tiny
“bags” that contain neurotransmitters: chemicals that transmit information across the
synapse to a receiving neuron’s dendrites
Document Summary
Neurons: cells in the nervous system that communicate with one another to perform information-processing tasks. The electrical and chemical activities of the neurons are the starting point of all behaviour, thought and emotion. There are about 100 billion cells in the brain performing different tasks that allow us to function. Late 1880"s: spanish physician santiago ramon y calaj learned about a new technique for staining neurons in the brain. The stain highlighted entire cells" appearance-->different shapes and sizes. Neurons had threads extending outwards towards other neurons, but did not actually touch--> he gured that they process information, and that they had to communicate somehow --> discover dendrites and axon! Nucleus: (located in cell body): houses chromosomes containing dna. Three basic parts of neurons: cell body, dendrites, and axon. Axon: transmits information to other neurons, muscles or glands, each neuron has one of these. The axon can be up to a meter long!
