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PSY318H5 (40)


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University of Toronto Mississauga
Ayesha Khan

Neurons • Basic unit of the nervous system • Communication • How do they differ from other cells? • Three main functions: Reception Conduction Transmission Anatomy of Neurons & Glia • Cajal: was the first to demonstrate that the individual cells comprising the nervous system remained separate He showed that they did not grow into each other as previously believed • Like other cells in the body, neurons contain the following structures: Membrane Nucleus Mitochondria Ribosomes Endoplasmic reticulum • All neurons have the following major components: Dendrites Soma/cell body Axon Presynaptic terminals • Dendrites are branching fibers with a surface lined with synaptic receptors responsible for bringing information into the neuron • Some dendrites also contain dendritic spines that further branch out and increase the surface area of the dendrite • The greater the surface area of the dendrite, the more information it can receive • Terms used to describe the neuron include the following: Afferent axon Efferent axon Interneurons or intrinsic neurons • Neurons vary in size, shape, and function • The shape of a neuron determines it connection with other neurons and contribution to the nervous system • The function is closely related to the shape of a neuron Example: Purkinje cells Selective permeability • Phospholipids bi-layer • Ion channels (passive diffusion) • Voltage-dependent channels (require electrical changes) • Ligand-gated channels (require a “ligand”) • Sodium-potassium pumps (require energy) • Calcium pumps (require energy) Alzheimer’s disease • Most common form of dementia • Dementia: loss of memory, judgment and reasoning, and changes in mood, behaviour, physical and communicative abilities. • Loss of neurons and synapses in the cerebral cortex • Cortical gyri shrink • Ventricles become enlarged • Plaques • Amyloid precursor protein  -amyloid protein Glial Cells • Glia (or neuroglia) are the other major components of the nervous system • Types of glia in the brain: Astrocytes help synchronize the activity of the axon by wrapping around the presynaptic terminal and taking up chemicals released by the axon Microglia remove waste material and other microorganisms that could prove harmful to the neuron • (Types of glia continued) Oligodendrocytes (in the brain and spinal cord) and Schwann cells (in the periphery of the body) build the myelin sheath that surrounds and insulates certain vertebrate axons Radial glia guide the migration of neurons and the growth of their axons and dendrites during embryonic development The Blood-Brain Barrier • The blood-brain barrier is a mechanism • The immune system destroys damaged or infected cells throughout the body • Because neurons in the brain generally do not regenerate, it is vitally important for the blood brain barrier to block incoming viruses, bacteria, or other harmful material from entering Nourishment in Vertebrate Neurons • Vertebrate neurons depend almost entirely on glucose: a sugar that is one of the few nutrients that can pass through the blood-brain barrier • Neurons need a steady supply of oxygen; 20% of all oxygen consumed by the body is used by the brain The Nerve Impulse • A nerve impulse is the electrical message that is transmitted down the axon of a neuron • The speed of nerve impulses ranges from less than 1 meter/second to 100 meters/second • A touch on the shoulder reaches the brain more quickly than a touch on the foot The Resting Potential of the Neuron • The membrane of a neuron maintains an electrical gradient A difference in the electrical charge inside and outside of the cell This is also known as polarization • At rest, the membrane maintains an electrical polarization or a difference in the electrical charge of two locations The inside of the membrane is slightly negative with respect to the outside (approximately -70 millivolts) The resting potential of a neuron refers to the state of the neuron prior to t
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