These notes are compiled using the textbook, lecture notes, and study outcomes. They are easy to understand and include diagrams. All of the visual material used in the textbook and in lectures are also included.
1. Nervous Tissue: The Basic Hardware
2. The Neural Impulse: Using Energy to Send Information
3. The Synapse: Where Neurons Meet
4. Neurotransmitters and Behaviour: Multi-talented Chemical Messengers
→ Behaviour depends on rapid information processing.
→ Nervous system = complex communication network in which signals are constantly being
transmitted, received, and integrated
1. Nervous Tissue: The Basic Hardware
→ Nervous system = living tissue composed of cells.
→ 2 major categories:
a. Neurons
b. Glia
a. Neurons:
→ Individual cells in the nervous system that receive, integrate, and Soma
transmit information.
→ Basic chains of communication within the nervous system.
→ Most neurons only communicate with other neurons.
→ Some neurons:
○ Receive signals from outside nervous system (form sensory
organs)
○ Carry messages from the nervous system to the muscles that
move the body.
Structure:
○ Soma / cell body:
Contains nucleus and most of the other structures
common to most cells
○ Dendrites: (individual branches of dendritic trees)
Parts specialised to receive information.
Information flows into the cell body and then travels away
from the soma along the axon
○ Axon (from Greek “Axle”):
Long thin fibre that transmits signals away from the soma
to other neurons, muscles, or glands
Vary in length
May communicate with several other cells.
Generally wrapped in myelin.
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b. Glia
→ Cells found throughout the nervous system – provide various types of support for neurons
→ Glia = literally means “glue”
→ Smaller than neurons and more abundant in the brain (account for 50% of the brain’s volume)
→ Serves multiple support functions;
○ Provision of certain nutrients for neurons
○ Insulation
○ Removal of waste products
→ Myelin sheaths that encase some axons = derived from special types of glial cells
→ Also plays complicated role in development of nervous system in the human embryo.
→ Recent research:
○ Glial cells may also play a role in sending and receiving chemical signals.
○ Some glia can detect neural impulses and send signals to other glial cells.
○ Glia cells may play an important role in memory formation
○ Gradual deterioration of glial tissue might contribute to Alzheimer’s disease
○ Glia cells play crucial role in the experience of chronic pain.
○ Impaired neural glial communication may contribute to psychological disorders, such as
schizophrenia.
2. The Neural Impulse: Using Energy to Send Information
→ The electrochemical properties of the neuron allow it to transmit signals.
→ The electric charge of a neuron can be measured with a pair of electrodes connected to an
oscilloscope, as Hodgkin and Huxley showed with a squid axon.
○ Because of its exceptionally thick axons, the squid has frequently been used by scientists
studying the neural impulse.
→ SEE PAGE 31 FOR MORE
A. At rest, the neuron’s voltage hovers around –70
millivolts.
B. When a neuron is stimulated, a brief jump occurs in its
voltage, resulting in a spike on the oscilloscope
recording of the neuron’s electrical activity. This change
in voltage, called an action potential, travels along the
axon like a spark travelling along a trail of gunpowder.
Neurons at Rest: A Tiny Battery
→ Neural impulse = complex electrochemical reaction.
→ Inside and outside neurons are fluids containing electrically charged atoms and molecules called ions.
→ Positively charged sodium and potassium ions + negatively charged chloride ions = flow back and
forth across cell membrane
○ Do not cross at the same rate.
→ Difference in flow rates leads to slightly higher concentration of negatively charged ions inside the cell
○ Creates negative charge within the neuron
→ Neuron at rest = a tiny battery – a store of potential energy
→ Resting potential of a neuron is its stable, negative charge when the cell is inactive.
○ Charge is about -70 millivolts (roughly one twentieth of the voltage of a torch)
The Action Potential: How Neurons Fire
→ If the voltage of a neuron remains constant = the cell is quiet + no messages are being sent.
→ When neuron is stimulated, channels in its cell membrane open = briefly allowing positively charged
sodium ions to rush in.
○ Neuron’s charge is less negative / or even positive
○ Creates action potential: a shift in a neuron’s electrical charge that travels along an axon.
After firing of action potential = channels in the cell membrane close (cannot fire until they
open again)
→ Absolute refractory period: minimum length of time after an action potential before another action
potential can begin.
○ Not very long -> about 1 or 2 milliseconds
○ Followed by a brief relative refractory period
Neuron can fire but threshold for firing is elevated
More intense stimulation is required to start an action potential.
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