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Lecture

PSYCH261 Lecture Notes - Axon Terminal, Mitochondrion, Myelin


Department
Psychology
Course Code
PSYCH261
Professor
Deltcho Valtchanov

Page:
of 5
Structure and Function of Neurons
Chapter 2
Cells of the Nervous System
*Neurons
*Soma – cell body (contains the nucleus).
*Dendrite – branched, treelike structure attached to soma; receives information from
other neurons.
*Synapse – junction between neurons.
*Axon – long, cylindrical structure conveys information from soma to terminal
buttons.
*Terminal Buttons – bud at the end of an axon branch.
Cells of the Nervous System
*Multipolar Neuron – one axon, many dendrites attached to soma.
*Bipolar Neuron – one axon and one dendrite attached to soma.
*Unipolar Neuron – one axon attached to soma;
*axon divides, one branch receiving sensory information and the other
sending information to central nervous system.
*Electrochemical Communication
*Electrical signal within the neuron
*Chemical signal between neurons
*Internal Structure
*Nucleus
*Contains the nucleolus and chromosomes involved in protein synthesis
and contain the cell’s DNA.
*Mitochondria
*Considered the power house of the cell because of their ability to extract
energy.
*Golgi Apparatus
*Acts as a packaging plant, where other molecules (e.g.,
neurotransmitters) are packaged in small containers
*Glia = “glue”: supporting cells that provide structural/nutritional support for the
nervous system.
*Astrocytes
*Provide structural support to neurons and clean up debris.
*Oligodendrocytes
*Support axons and produce the myelin sheath.
*Microglia
*Act as phagocytes and protect the brain from microorganisms.
Astrocytes
*“Star” cells
*Connect with multiple neurons and provide structural support
*Maintain the blood brain barrier
*Neurons receive nutrients from astrocytes
*(and some from capilliaries)
*Break down glucose into lactate
*(is metabolised faster than glucose)
*Phagocytic processes
Oligodendrocytes
*Produce myelin sheath for CNS
*Fatty covering of axons
*Aids efficient transmission of electrical signal along the axon
*Segmented – gaps in myelin sheath referred to as Nodes of Ranvier
Oligodendrocytes and Schwann cells
*Oligodendrocytes – CNS
*Myelinate multiple axons
*Schwann cell – PNS
*Myelinate a single axon
Blood-brain Barrier
*A semipermeable barrier between the CNS and circulatory system, which helps to
regulate the flow of nutrient rich fluid into the brain.
*Area Postrema
*A region of the medulla where the blood-brain barrier is weak. Toxins in the
blood stimulate this area, initiating vomiting
Communication Within a Neuron
*Components of a Simple Withdrawal Reflex
*Sensory Neuron
*Motor Neuron
*Interneuron
Communication Within a Neuron
*Inhibition in the Withdrawal Reflex
*Brain input prevents the withdrawal reflex by decreasing activity of the motor
neuron.
Measuring ‘Action’ Potentials
*Membrane Potential – electrical charge across a cell membrane; difference in
electrical potential inside and outside the cell.
*Resting Potential – membrane potential of a neuron when not being excited or
inhibited (~ -70 mV).
Measuring ‘Action’ Potentials
*Depolarization – reduction (toward zero) of membrane potential.
*Hyperpolarized – increase in the membrane potential of a cell.
*Action Potential – brief electrical impulse that provides the basis for conduction of
information along an axon.
*Threshold of Excitation – value of the membrane potential that must be reached to
produce an action potential.
Membrane Potential
*Intracellular Fluid Has Higher Levels of:
*Inside the cell we have more:
*Organic Anions (A-)
*Potassium Ions (K+)
*Extracellular Fluid
Has Higher Levels of:
*Chloride Ions (Cl-)
*Sodium Ions (Na+)
Membrane Potential
*Passive Forces Affect the Resting Potential
*Diffusion
*Natural movement of molecules from areas of high concentration to areas
of low concentration.
*Electrostatic Pressure
*Attraction of oppositely charged particles (ions) and repulsion of similarly
charged ions.
*Sodium-Potassium Pump
*Active mechanism in the membrane extrudes Na+ out and transports K+ in.
Action Potentials
*Occurs when the cell is depolarized to the threshold of excitation.
*Largely dependent upon the movement of Na+ and K+ ions across the membrane
via ion channels.