Transmission Of A Signal Across A Synapse PDF

Transmission of a Signal Across a Synapse BIO 30 – Unit A – Nervous & Endocrine Systems  Review of the Na-K Exchange Pump 1. Neuron is polarized – resting potential until a stimulus comes along (-70mV)  Resting potential is created by the Na-K exchange pump (a transport protein)....

Transmission of a Signal Across a Synapse BIO 30 – Unit A – Nervous & Endocrine Systems  Review of the Na-K Exchange Pump 1. Neuron is polarized – resting potential until a stimulus comes along (-70mV)  Resting potential is created by the Na-K exchange pump (a transport protein). This moves Na+ out and K+ in. 2. Action Potential – when a stimulus reaches the resting neuron, Na + ions move inside the membrane (neuron becomes depolarized)  if the threshold is reached, more Na+ channels open  “all or none response” – complete depolarization occurs  Impulse travels down the axon. If axon is myelinated, the impulse travels from node to node  Peak voltage causes Na+ channels to close and K+ channels to open 3. Repolarization – K+ move outside cell, Na+ stay inside the membrane  This is opposite of the initial polarized membrane that had Na+ on the outside and K+ on the inside 4. Neuron becomes hyperpolarized when more K+ ions are outside than Na+ inside.  This causes the cell’s potential to drop lower than resting 5. Refractory Period – returns K+ to the inside and Na+ to the outside 6. Na-K exchange pump goes back to work and keeps neuron at resting potential until there is another stimulus. Transmission of Nerve Impulses Nerve impulses have a domino effect – each neuron receives an impulse and passes it on to the next Through a chain of chemical events, the dendrites pick up an impulse that passes through the axon and is transmitted to the next neuron Synapse The simplest neural pathways have at least 2 neurons & 1 connection Synapse OR Synaptic Cleft – the connection between two neurons OR a neuron and an effector (the gap between the axon of one neuron and the dendrites of the next neuron). Neuromuscular Junction - synapse between a motor neuron and a muscle cell Synapse Impulses will travel from one end of neuron to the opposite end (synaptic terminal) Most terminals are not connected but have a gap (synaptic cleft) which will allow the chemicals (neurotransmitters) to move from one neuron to the next Neurotransmitters can also carry a signal from a neuron to an effector (gland or muscle) Here’s What Happens: Nerve impulses cause chemicals known as neurotransmitters to be released. The neurotransmitter binds with receptor proteins on the neuron membrane. Excitation or inhibition of the membrane occurs (coming up….) After the neurotransmitter produces its effect, the receptor releases it and enzymes in the cell will degrade it. Synapse What happens if a neuron receives multiple impulses? SUMMATION When impulses add together to reach threshold and cause a neuron to fire 5 4 3 1 Neurotransmitters Have either an excitatory or inhibitory effect Excitatory: stimulate the brain Receptor proteins trigger Na+ channels to open to allow sodium to enter the postsynaptic neuron This causes the postsynaptic neuron to be slightly depolarized (less than -70mV) If depolarization reaches the threshold (doesn’t always), then an action potential is generated. Neurotransmitters Inhibitory Receptor proteins trigger potassium ions to flow out This results in postsynaptic neuron to become hyperpolarized Inhibit the action of the target cell Neurotransmitters A neuron can be receiving various signals at the same time (inhibitory and excitatory) If the excitatory stimulus is strong enough, the depolarization will reach the point at which the axon is connected to the cell body and an impulse will be generated The postsynaptic neuron will then return to resting potential After neurotransmitters have their effect, enzymes break them down and they are reabsorbed. How Do Drugs Affect the Brain Types of Neurotransmitters Acetylcholine Crosses the neuromuscular junction (synapse between motor neuron and muscle cell) Excites the muscle cell membrane, causing depolarization and contraction of the muscle fiber If acetylcholine remains in synapse, muscle cell wouldn’t repolarize and would remain contracted (excited) Cholinesterase Enzyme Released into the synapse Breaks down acetylcholine so that it can be removed from the protein receptors The ion channel can then close and the membrane will repolarize in a fraction of a second. Norepinephrine Hormone Used by the brain and some autonomic neurons Compliments actions of epinephrine (adrenaline) – readies the body to respond in danger or other stressful situations Overproduction = increased blood pressure, anxiety, insomnia Dopamine Affects brain synapses in the control of body movements Linked to sensations of pleasure (i.e., eating) Excessive production = schizophrenia Not enough production = Parkinson’s disease Serotonin Regulates temperature and sensory perception Involved in mood control Inadequate amounts = depression GABA (Gamma-Aminobutyric Acid) Most common inhibitory neurotransmitter in the central nervous system. Lessens the ability of a neuron to receive, create, or send chemical messages to other nerve cells. Produces a calming effect on the body. Endorphins Act as natural pain relievers in synapses in the brain (also affects emotional areas of the brain) Deficiency linked to an increased risk of alcoholism A review… Inhibitory Excitatory  “off switches”  “on switches”  Regulate the activity of excitatory  Act as body’s natural stimulants neurotransmitters  Promote alertness, energy and activity  Slow things down  Dopamine  Body’s natural tranquilizers  Norepinephrine  Epinephrine  Induce sleep, promote calmness, lower  Acetylcholine aggression Enrichment Video For Review: Pg. 384, #3, 4, 5, 7