What happens at the synapse between two neurones

A. Kimberely McAllister/ Scott Cameron If you were to take a human brain and toss it in a blender — not that you should — the resulting slurry of cells wouldn’t be special in the way that the human brain is. No thoughts, no worries, no wonder or awe. That’s because it’s the connections between those cells that make the brain so amazing. By sending electrical signals from nerve cell to nerve cell within a great network of connections, the brain creates thoughts as mundane as “Where are my keys?” or as profound as “I think, therefore I am.” James Provost (CC BY-ND) Kimberley McAllister has been fascinated by the human brain since college. As a graduate student in the 1990s studying developmental neurobiology, she was drawn to the question of how the brain is built: how individual brain cells in a growing fetus somehow organize themselves into an organ capable one day of pondering the mysteries of life. Now director of the Center for Neuroscience at the University of California, Davis, McAllister continues to investigate how the brain’s nerve cells — called neurons — find each other, connect and disengage. She spoke with Knowable Magazine about key discoveries in the study of brain networks, and new work revealing their importance in disease. This conversation has been edited for length and clarity. The links between neurons are called synapses. What exactly is a synapse, and what happens there? It’s basically a connection: one cell talking to another. A brain cell, or a neur...

• Describe the basis of the resting membrane potential • Explain the stages of an action potential and how action potentials are propagated • Explain the similarities and differences between chemical and electrical synapses • Describe long-term potentiation and long-term depression All functions performed by the nervous system—from a simple motor reflex to more advanced functions like making a memory or a decision—require neurons to communicate with one another. While humans use words and body language to communicate, neurons use electrical and chemical signals. Just like a person in a committee, one neuron usually receives and synthesizes messages from multiple other neurons before “making the decision” to send the message on to other neurons. Nerve Impulse Transmission within a Neuron For the nervous system to function, neurons must be able to send and receive signals. These signals are possible because each neuron has a charged cellular membrane (a voltage difference between the inside and the outside), and the charge of this membrane can change in response to neurotransmitter molecules released from other neurons and environmental stimuli. To understand how neurons communicate, one must first understand the basis of the baseline or ‘resting’ membrane charge. Neuronal Charged Membranes The lipid bilayer membrane that surrounds a neuron is impermeable to charged molecules or ions. To enter or exit the neuron, ions must pass through special proteins called ion channels th...

When we're kids, our brains are amazing at learning. We absorb information from the outside world with ease, and we can adapt to anything. But as we age, our brains become a little more fixed. Our brain circuits become a little less flexible. You may have heard of a concept called neuroplasticity, our brain's ability to change or rewire itself. This is of course central to learning and memory, but it's also important for understanding a surprisingly wide array of medical conditions, including things like epilepsy, depression, even Alzheimer's disease. Today's guest, So I was excited to talk to Shatz about our brain's capacity for change, and I started off by asking about this sort of simple question, why exactly do we have this learning superpower as kids to do things like pick up languages and why does it go away? Shatz is Sapp Family Provostial Professor of Biology and of Neurobiology, the Catherine Holman Johnson director of Stanford Bio-X, and a member of the Wu Tsai Neurosciences Institute at Stanford. Learn More • • • • • Episode Credits This episode was produced by producer Michael Osborne, with production assistance by Morgan Honaker, and hosted by Nicholas Weiler. Art by Aimee Garza. Episode Transcript Nicholas Weiler: This is From Our Neurons to Yours, a podcast from the Wu Tsai Neurosciences Institute at Stanford University. On this show, we crisscross scientific disciplines to bring you to the frontiers of brain science. I'm your host, Nicholas Weiler. Here's t...

• • • For the nervous system to function, neurons must be able to communicate with each other, and they do this through structures called synapses. At the synapse, the terminal of a presynaptic cell comes into close contact with the cell membrane of a postsynaptic neuron. Figure 8.1. The terminal of a presynaptic neuron comes into close contact with a postsynaptic cell at the synapse. ‘Synapse’ by Synapse Types There are two types of synapses: electrical and chemical. Electrical Electrical synapses outnumber chemical synapses in the developing nervous system Electrical synapses are a physical connection between two neurons. Cell membrane proteins called connexons form gap junctions between the neurons. The gap junctions form pores that allow ions to flow between neurons, so as an action potential propagates in the presynaptic neuron, the influx of sodium can move directly into the postsynaptic neuron and depolarize the cell. The response in the postsynaptic cell is almost immediate, with little to no delay between signaling in the pre- and postsynaptic neurons. Electrical synapses play an important role in the development of the nervous system but are also present throughout the developed nervous system, although in much smaller numbers that chemical synapses. Animation 8.1. Membrane-bound proteins called connexons form gap junctions between presynaptic and postsynaptic neurons. This allows for direct exchange of ions between neurons. An action potential in the presynaptic...

The synapse along with its neurotransmitters acts as a physiological valve, directing the conduction of nerve impulse in regular circuits and preventing random and chaotic stimulation of nerves. The arrival of a nerve impulse at the pre synaptic terminal causes a movement towards the synaptic vesicles. These fuse with the membrane and release neurotransmitters. A single neurotransmitter may elicit different responses from different receptors. The neurotransmitter transmits the nerve impulse to the post synaptic fibre , by diffusing across the synaptic cleft and binding to receptor molecules on the post synaptic membrane. This results in a series of reactions that open ' channel shaped ' protein molecules. Electrically charged ions then flow through the channels in or out of the neurons. If the net flow of positively charged ions is large enough, it leads to the generation of a new nerve impulse called as action potential. Later the neurotransmitter molecules are deactivated by enzymes in the synaptic cleft.

Synapses Where two neurons meet there is a small gap called a synapse . An electrical impulse cannot directly cross the gap so a different mechanism has to be used. • An electrical nerve impulse travels along the first axon. • When the nerve impulse reaches the dendrites at the end of the axon, chemical messengers called neurotransmitters are released. • These chemicals diffuse across the synapse (the gap between the two neurons). The chemicals bind with receptor molecules on the membrane of the second neuron. • The receptor molecules on the second neuron can only bind to the specific neurotransmitters released from the first neuron. • The binding of neurotransmitter to the receptors stimulates the second neuron to transmit an electrical impulse along its axon . The signal therefore has been carried from one neuron to the next.

Synapse: • Synapse is defined as the point of contact between the terminal branches of the axon of one neuron with the dendrite of another neuron. • Two neurons communicate through this junction. • This communication occurs through the production of neurotransmitters. • In a synapse, two neurons are involved. • One neuron that transmits the neurotransmitters is called a presynaptic neuron and the other neuron that acts like a receptor is called the postsynaptic neuron. Mechanism of synapse: • When an electric impulse is generated, chemicals called neurotransmitters are generated at the end of the axons. • These substances are covered with vesicles called synaptic vesicles. • A small space between these two terminals is a gap called the synaptic cleft. • These synaptic vesicles dissolve in that space and the chemicals within them pass through the space between the two neurons and reach the dendrites of the postsynaptic neuron. • The chemoreceptors located on the membranes of the postsynaptic neuron, get stimulated. • This stimulation causes voltage-gated Ca 2+ ion channels to open and the influx of these ions takes place. • As neurotransmitter reaches the postsynaptic neuron, depolarization or hyperpolarization takes place, which is according to the nature of the ions involved.

• • At the junction between two neurons ( • The • In an intact brain, the balance of hundreds of excitatory and inhibitory inputs to a neuron determines whether an action potential will result. Neurons are essentially electrical devices. There are many channels sitting in the cell membrane (the boundary between a cell’s inside and outside) that allow positive or negative ions to flow into and out of the cell. Normally, the inside of the cell is more negative than the outside; neuroscientists say that the inside is around -70 mV with respect to the outside, or that the cell’s resting membrane potential is -70 mV. This membrane potential isn’t static. It’s constantly going up and down, depending mostly on the inputs coming from the These are respectively termed excitatory and inhibitory inputs, as they promote or inhibit the generation of action potentials (the reason some inputs are excitatory and others inhibitory is that different types of neuron release different Action potentials are the fundamental units of communication between neurons and occur when the sum total of all of the excitatory and inhibitory inputs makes the neuron’s membrane potential reach around -50 mV (see diagram), a value called the action potential threshold. Neuroscientists often refer to action potentials as ‘spikes’, or say a neuron has ‘fired a spike’ or ‘spiked’. The term is a reference to the shape of an action potential as recorded using sensitive electrical equipment. A neuron spikes when a ...

• Describe the basis of the resting membrane potential • Explain the stages of an action potential and how action potentials are propagated • Explain the similarities and differences between chemical and electrical synapses • Describe long-term potentiation and long-term depression All functions performed by the nervous system—from a simple motor reflex to more advanced functions like making a memory or a decision—require neurons to communicate with one another. While humans use words and body language to communicate, neurons use electrical and chemical signals. Just like a person in a committee, one neuron usually receives and synthesizes messages from multiple other neurons before “making the decision” to send the message on to other neurons. Nerve Impulse Transmission within a Neuron For the nervous system to function, neurons must be able to send and receive signals. These signals are possible because each neuron has a charged cellular membrane (a voltage difference between the inside and the outside), and the charge of this membrane can change in response to neurotransmitter molecules released from other neurons and environmental stimuli. To understand how neurons communicate, one must first understand the basis of the baseline or ‘resting’ membrane charge. Neuronal Charged Membranes The lipid bilayer membrane that surrounds a neuron is impermeable to charged molecules or ions. To enter or exit the neuron, ions must pass through special proteins called ion channels th...

• • At the junction between two neurons ( • The • In an intact brain, the balance of hundreds of excitatory and inhibitory inputs to a neuron determines whether an action potential will result. Neurons are essentially electrical devices. There are many channels sitting in the cell membrane (the boundary between a cell’s inside and outside) that allow positive or negative ions to flow into and out of the cell. Normally, the inside of the cell is more negative than the outside; neuroscientists say that the inside is around -70 mV with respect to the outside, or that the cell’s resting membrane potential is -70 mV. This membrane potential isn’t static. It’s constantly going up and down, depending mostly on the inputs coming from the These are respectively termed excitatory and inhibitory inputs, as they promote or inhibit the generation of action potentials (the reason some inputs are excitatory and others inhibitory is that different types of neuron release different Action potentials are the fundamental units of communication between neurons and occur when the sum total of all of the excitatory and inhibitory inputs makes the neuron’s membrane potential reach around -50 mV (see diagram), a value called the action potential threshold. Neuroscientists often refer to action potentials as ‘spikes’, or say a neuron has ‘fired a spike’ or ‘spiked’. The term is a reference to the shape of an action potential as recorded using sensitive electrical equipment. A neuron spikes when a ...