Synapses

Electrical and Chemical Synapses

Synapses are very very tiny spaces between cellsThe basic structural and functional units of life..  We’ve previous encountered synapses between a motor neuron and a skeletal muscle.  In the nervous systemThe organ system that controls body functions using electrical and chemical signals., there is so much more to talk about than acetylcholinealso know as ACh A neurotransmitter that stimulates muscle contraction.!  This diagram on the left ensures you know the exact location we are discussing with synapses.  We are going to consider the space between the axon terminalThe endpoint of an axon where neurotransmitters are stored and released into a synapse. of a sending cell. The pink one is here. And the dendrite of a receiving cell.  We have discussed the components and procedure involving a chemical synapseSynapses that transmit signals using neurotransmitters.. We will continue to explore these as examples in the nervous system.  However, be aware that in the heart, the cardiac muscle fibers of the myocardium are joined together by electrical synapsesSynapses where cells are directly connected by gap junctions; allow rapid signal transmission..  They have these channelsProtein passages in the cell membrane that allow specific molecules to pass through. that basically allow them to share cytoplasmThe gel-like substance within a cell that contains organelles and cytosol..  So, it one muscle fiber depolarizes, the other one depolarizes.  Have you ever played around with the electrical fence at a cattle farm?  No?  Well, let me tell you how it works. Before I do, you can never try this.  Ever.  I can’t stress enough how what I’m about to tell you is the misdirected actions of children. These unsupervised children acted at a family gathering in the early 1980s.  Never do this.  Ever.  Eyebrows fell off, taste buds changed for life, and some heard a pulsating sound for decades.

You and your cousin get some rope from the garage. Then, you both go down to the pond and get it wet.  You bring it back up to the fence. You stand on opposite sides of it. Each of you is holding the rope over your headRounded proximal end that fits into the acetabulum of the hip bone..  Other cousins are forming a chain of people, all with wet hands.  You and your cousin slowly lower the rope and POW! Everyone gets knocked back on their butts. 

Synapse Types by NXT

Later in this course we will consider the autonomic nervous systemThe part of the peripheral nervous system that controls involuntary functions such as heart rate, di, which is difficult to understand and visualize.  It works by controlling your rest and digest functions but also controlsVariables that remain constant to ensure a fair test. your fight or flight functions.  It does this by using a variety of neurotransmittersChemicals released by neurons to transmit signals across a synapse., sometimes the same one to excite one organ but inhibit another. 

But, when talking about resting and digesting, that takes excitation, right?  I mean you are digesting, that’s active glands and smooth muscle action.  So, you’re not dead when you are resting and digesting, you are just doing, like, housekeeping functions.  The fight or flight is for just that” situations of extreme and acute stress.  When we discuss the autonomic nervous system, we will talk about cholinergic synapses. These synapses all use acetylcholine. They are all excitatory.   They are usually exciting smooth muscle.  So, strangely, the rest and digest uses these almost exclusively. 

There are also adrenergic synapsesSynapses that use norepinephrine (or epinephrine) as their neurotransmitter., that we have yet to consider in this class.  Adrenergic synapses, as you can probably guess from the name are synapses that respond to epinephrineadrenaline): Fight-or-flight hormone from the adrenal medulla. and norepinephrineA neurotransmitter involved in attention, arousal, and the fight-or-flight response..  But whether these neurotransmitters excite or inhibit depends on the target organ.  For example, when running away from a startling sound, your trachea needs to relax and open. This allows more oxygen to enter your muscles.  At the same time, you need your cardiac muscle to be excited to pump either faster or with more force.  See?  Depends on the target organ. 

Let me blow. Your. Mind.  We are going to see the reality that many synapses have both vesicles and receptorsProteins located on the surface or inside cells that bind specific molecules (e.g., neurotransmitter for a variety of neurotransmitters.  So, trying to classify them by the type pf neurotransmitterChemicals that transmit signals across synapses. is not a good classification system.

Synapse Types by Effect

This isn’t a good classification system either. But it’s a step in the right direction. We are defining its function instead of its structure or neurotransmitters.  What I have here as a picture are the mechanisms of common migraine and seizure medications.  I’ve run through many of these in the big peach list from a condition called trigeminal neuralgia.  It hurts my face and these seizure drugs can be used for both migraines and pain conditions.  Check out gabapentin over here. It has the same effect as those other drugs. They all encourage more vesicles to be released.  Topiramate down here makes the neurotransmitter more likely to connect. 

On the diagram on the right, these same drugs have very different effects ats inhibitory synapses.  In factA statement based on direct observation that is repeatedly confirmed., they all seem to work on chloride channels in the receiving or the post synaptic neuron. 

Synapse Anatomy

I encourage you to go back to the previous chapter on muscle contractions and the events at the neuromuscular junctionThe connection between a motor neuron and a muscle fiber..  This picture is an adaptation of the events at the neuromuscular junction.  This picture is between two neuronsThe functional cells of the nervous system that transmit signals..  I encourage you to label more on this picture, label as much as you can.  Then, describe how one neuron alters the electrical charge of an action potentialA rapid, temporary electrical charge that travels along neurons, allowing signal transmission.. It transforms this into the chemical structure of neurotransmitters. These neurotransmitters connect with another neuron to initiate an action potential in it.  I mean, that’s what we are doing here, right?  We are taking electricity, turning into magical little moleculesGroups of atoms bonded together., and then using them to start electricity in another cell.  Draw this diagram in an effort to discover small details that you may not have uncovered in text.