Pg. 111 Synapses

What happens when the impulse reaches the end of the axon?

When an action potential reaches the terminals of an axon, it generally stops there. In most cases, action potentials are not transmitted from neurons to other cells. However, the information is transmitted. Transmission occurs at the synapses.

Synapses Key Point #1: Transmission of information between neurons occurs across synapses. Most are chemical synapses, involve the release of a neurotransmitter (chemical) Carried in a synaptic vesicle

Synaptic Process Key Point #2: Process Presynaptic neuron creates the neurotransmitter Neurotransmitter packaged into synaptic vesicles Stored in the synaptic terminal Neurotransmitter received by postsynaptic neuron

Cell Communication Example Cells communicate with each other through direct contact with other cells or from a distance via chemical signaling By neurotransmitters Here is another tool to add to your tool box of how cells communicate with one another. Today, it is neurotransmitters. Tomorrow, it is the endocrine system and hormones.

Calcium gated channels in the synaptic knob Note the structural features that allow the cell to cell communication to occur in the synaptic region: Calcium gated channels in the synaptic knob Sodium channels in the post-synaptic membrane Fluidity of the lipid bi-layer allows for exocytosis of the neurotransmitter The transfer of information that occurs at the synapse is a classic example of cell to cell communication. The membrane is specifically adapted for this task. The synaptic knob membrane contains voltage gated Ca2+ channels, the post synaptic membrane contains receptor-bearing sodium, Na+ channels, and the fluidity of the membrane allows for the fusion of vesicles.

Key Point #2: The process Action potentials depolarize the membrane of a presynapse, Opens gated calcium channels. Ca2+ enters the terminal Vesicles fuse the terminal membrane and release neurotransmitters by EXOCYTOSIS Neurotransmitters diffuses across the synaptic cleft to the postsynapse Neurotransmitters bind to the receptors embedded in the postsynaptic membrane.

Neurotransmitter Binds With A Receptor On The Postsynaptic Membrane The released neurotransmitter binds with the receptor on the postsynaptic membrane causing the channel to open allowing sodium ions to rush in. This influx of sodium can contribute to the development of an action potential in the receiving cell.

The neurotransmitter will then be released from the postsynaptic membrane and degraded.

Pg. 112 Neurotransmitters Share ONE good thing that happened to you today.

Neurotransmitters There are more than 100 neurotransmitters, belonging to five groups: acetylcholine, biogenic amines, amino acids, neuropeptides, and gases A single neurotransmitter may have more than a dozen different receptors

Neurotransmitters: Chemical Messengers In most animals, transmission across synapses involves chemical messengers called neurotransmitters such as: Acetylcholine Epinephrine Norepinephrine Dopamine Serotonin GABA These neurotransmitters are illustrative examples of the chemical messengers. Students should be familiar with all of these and become an expert on at least one of them.

There are a variety of neurotransmitters There are a variety of neurotransmitters. Some neurotransmitters inhibit impulse generation while others increase the likelihood an impulse will be generated.

Key Point #1:Acetylcholine The most common neurotransmitter in vertebrates and invertebrates. The response can be stimulatory or inhibitory For example: Acetylcholine excites skeletal muscles and inhibits cardiac muscle Involved in muscle stimulation, memory formation, and learning. Neurotransmitters are important in cell to cell communication. One cell (presynaptic) communicates with the second cell (postsynaptic) through the release and actions of the neurotransmitter. Acetylcholine stimulates the contraction of skeletal muscles. Interestingly, it acts as an inhibitor to cardiac muscle cell contraction. A metabotropic receptor is type of membrane receptor of eukaryotic cells that acts through a second messenger. It may be located at the surface of the cell or in vesicles.

Key Point #2: Biogenic Amines Derived from amino acids Examples: dopamine, serotonin, epinephrine, and norepinephrine Affect mod, sleep, attention, and learning

Key Point #3: Amino Acids and Peptides Example: endorphins Decrease pain perception

Key Point #4: Gases Key Point #4: Gases Some release gas Example Nitric oxide Causes vasodilation to areas Viagra

Ask students to practice talking through the events occurring at the chemical synapse with their partner. (Provide students with a copy of the diagram to label) Make students answer this question while keeping their arms to their sides and not moving at all.

Tell me what you know! Adding a poison that specifically disables the Na+/K+ pumps to a culture of neurons will cause: a. the resting membrane potential to drop to 0 mV. b. the inside of the neuron to become more negative relative to the outside. c. the inside of the neuron to become positively charged relative to the outside. d. sodium to diffuse out of the cell and potassium to diffuse into the cell. Answer: a

Work Time Directions: Complete the assignment using your textbook and notes. This is a valuable study tool for Friday’s quiz. Noise: with your cooperative partner Time: 15 minutes