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NATS 1860 Note 12

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Natural Science
Course Code
NATS 1860
Keith Schneider

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NATS 1860 Note 12 Neurons, Spikes, Synapses: - Consider the following: o Brain Maps o Nerve cell components o Membrane structure o Ions and ion channels o Action potentials (spikes) o Spike propagation (how spikes get from one cell to another cell) o Synapses (Cajal discovered that the ends of one cell don’t form a junction on another cells, they meet at a “synapse” o Excitation and inhibition  There are two types  One excites and makes it fire  One turns it off, and prevents from firing o Mind altering drugs o Small Neural Networks Sensory and Motor Maps - Map of body surface is two dimensional: the retina is a very two dimensional sheet. o This is evidence as electrical brain stimulation o If you do motor control in dogs (stimulate electrically on different parts of the brain, different effects will play out)  Similar experiments were done on humans during epilepsy seizures surgeries - These maps are all distorted: they represent how much neural activity is coming or going from rather than the physical area of the body. o Based on the amount of information on muscles about how much information has to come in - Left half of the cortex receives information from the right half of our body, whereas the left motor cortex controls the right side of the body - Right half of the cortex senses the left half of the world and the right motor cortex controls left side of body - Corpus Callosum: axons connecting left and right cortex Neurons (Nerve cells) - A neuron is one nerve cell, and a nerve is typically around a million connection of nerve cells o A corpus callosum is a body of millions of nerve cells.  Axons are the main part of the nerve cell that are in nerve  Auditory nerves have 1.5 million axons  There are about 100 billion neurons in our brains and thousands of synapses from each neuron  We have about 100 trillion synapse - A nerve cell has a cell-body (soma) - It also has dendrites (dendritic tree/branches). They start at the soma and then go to different directions - The cell also has axons, another process that goes off. o Dendrites and axons have different functions from the nerve cells - The axons originates from a small thickening (protrusion) of the cell body called the (Axon hillock) - Finally, the axon terminates at all other axons in places called synapses Parts of Neuron - Dendrites and soma: they are site of synaptic contacts from other cells o This is where it receives information with other cells - Axon: o This is the input site; the site of stimulation of the cell. The axon is a long, thin cylinder that transmits electrical impulses from the cell to other parts of the brain  It is the output of the cell.  This is how the nerves talk to another - Synapse: contact between ends of an axon and dendrites of other neurons - Axon hillock: beginning of axon where nerves impulses are first triggered. Excitatory Neurons in Cortex: - These are cells in cortexes in which the soma uses its dendrites o The brain is very densely interconnected - The cortex of our brain is roughly 3mm thick. o If you take the entire surface area of our brain, it would be the size of a large, thin crust pizza. Neurons: Size and Time scale - In order to record electrical activity from nerve cells, you stick an electrode into the soma of a nerve cell, and you record the information o This has been done on humans since 1985. o From this discovery we know that we share the same cells with other species, the only difference is the way we use the cell - 1 micron = 1/1000 mm - The Soma is about 10 microns in diameter - Dendrites are about 3mm long. They’re much thinner - Axon diameter is about 1-2 microns o Axons can be as long as 1m. It’s still part of a single cell that is very thin, but very long. - 1 millisecond = 1/1000 second. - Electrical pulses that the brain produces pulses that are about 1ms long (spikes) o This is very slow compared to a computer running on GHz  However, the amount of information our brain processes is much greater Neuron Membrane - It consists of two layers of lipid molecules o The reason there are two is due to the structure of these molecules:
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