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Western University
Physiology 3120
Tom Stavraky

1. -Brain is capable of incredible precision and in particular the cerebellum -An average neuron has 10000 synaptic connections on it; 10^15 synaptic connections in the human brain Anatomy of the Brain: -Central Nervous System: everything central and includes: the spinal cord and the brain -At the top of the spinal cord is a structure called the brain stem; structures of the brain stem are the midbrain, pons and the medulla -Above the region of the brain stem is the cerebellum, which consists of a cerebellar cortex and a cerebellar deep nuclei -At the top of the brain stem is a structure called the hypothalamus, which coordinates all sorts of neural and endocrine functions -Superimposed is this cerebral cortex, which is thrown into folds to increase the surface area; folds in valleys are called sulcus (ex. Central Sulcus) and hills are called gyrus (ex. Precentral Gyrus and Postcentral Gyrus, which are in front and behind the Central Sulcus respectively) -Within the central area are the basal ganglia and the thalamus There are 2 cell types in the brain: -Neurons: which fire action potentials and make synaptic connections -Glial cells: helper cells; contribute to the well being of the neurons; the energy supply for the brain is glucose and one function of glial cells is to provide glucose to neurons; neurons fire off action potentials and require energy to re-establish their gradients and they have metabolic activity to generate vesicles and other cell structures and the by-product of metabolism is ammonia (which can be toxic), so another function of glial cells is to remove ammonia; neurons fire action potentials where Na+ will rush in and K+ comes out, so if you fire a lot of action potentials you can have excess extracellular K+, which will change the membrane potentials, so another function of glial cells is to remove that K+; when neurons fire action potentials, at the end of the synapse they will release a transmitter, which should only function for a short period of time (excess transmitter will cause trouble), so glial cells will also suck up the excess transmitter; glial cells can also produce myelin sheeths around axons 2. -Diagram of a representative neuron -Can have axons that extend short distances (ex.1mm long) or in the motor cortex, you can have an axon that passes through the brain and travels all the way down the spinal cord Major elements of the neuron: -Cell soma: with the nucleus and where metabolic activity will take place -Dendrites: branches -Axon hillock: initial segment where the soma gives rise to the axon -Myelin Sheeths: the squares in the diagram; produced by the glial cells -In the terminal are vesicles of transmitter, which then can be released when an action potential travels down the axon -There are some incoming axons that will terminate on the axon terminal itself; the major one though is an incoming axon, which could be excitatory or inhibitory, synapsing on the dendrites and possibly the soma 3. -There are 2 types of synapses in the CNS: -Electrical Synapse: there is a gap junction (there is cytoplasmic continuity b/w the neurons); consequently if there are local currents associated with the action potential, they can travel down through the cytoplasm and the action potential can then move to the post-synaptic neuron without delay; electrical transmission is rapid b/c there is no delay aside from the normal conduction across a membrane; possibility of bidirectional transmission; low electrical resistance (low resistance to electrical current flow) pathway b/c it’s full of all the cytoplasm within the cell -Chemical Synapse: the most dominant synapse in the CNS (many more chemical synapses than electrical synapses in the CNS); synaptic gap or cleft has high electrical resistance (if you’ve got an action potential propogating down the presynaptic neuron, the local currents will travel into this region which has high electrical resistance and there will be decreased current flow and this current will not get to the other side); way to overcome this vesicles released by the local currents associated with the action potential and spill their transmitter into the synaptical cleft region and then diffuses across the synapse and then attaches to a receptor on the post synaptic surface; the mechanism that we know about for postsynaptic transmission is the NMJ (sort of a first step model) -Takes time (ex. Average of 1ms but can be seconds or minutes for some types of synaptic activi
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