From the blogging activity part 2; we saw that neurotransmitters such as ATP and glutamate are released from the astroglia cells which may contact presynaptic nerons through gap junctions and by release of ATP. This allows for Ca2+ signals to release the transmitters to stimulate neuronal activity. The coupling of astrocytes and neurones results in very close communication between the cells. Neurone to astrocyte communication is promoted by glutamate which is released across the synaptic cleft. Released glutamate binds to glutamate receptors of the astrocyte which allows for the release of Ca2+. This is a form of paracrine cell signalling; whereby the astrocytes secrete chemicals to the neighbouring neurons.
The neurones then communicate with each other; action potentials are generated whereby ions are allowed to move into the membrane. Neurotransmission occurs as well whereby communication between the neurons are established as chemicals or electrical signals moves across a synapse.
These signals are passed on to the myocardial cells of the heart muscles which makes up part of the myocardium. Myocardial cells connects via intercalated discs which contains desmosomes and gap junctions which allows the passage of ions and small molecules from one to another through connexions. The Ca2+ being passed from the astrocytes to the neurones then to the myocardial cells then allows for contraction of the heart muscle.
Contributions: Stephfana Williams; Sheillina Mohammed and Naomi Ramnanan
COMMUNICATION BETWEEN ASTROCYTES AND MUSCLE CELLS:
Endocrine signaling is responsible for long distance communication between cells. Endocrine signaling are called hormones so therefore a hormone is responsible for taking messages long distances away to cells in other parts of the body. Astrocytes release a variety of signaling molecules including glutamate, D-serine and ATP. Glutamate released from the astrocyte signals to the neurons in a feedforward or what is known as a long-distance signal. The release of this glutamate is initiated by Ca2+ ions causing a neurone-astrocyte-endothelial cell signaling pathway which plays an important role in neuronal control and vascular tone. These neurotransmitters are released into the blood vessels which takes the message along to other cells in a neurone-astrocyte-blood vessel pathway which is involved in the regulation of cerebral blood flow. When an astrocyte releases ATP and prostranoids they may signal to microglia hence having effect on the activation of these cells also the products that are secreated. A brain trauma is then followed by this occurance. The release of these neurotransmitters upon reaching its target cell binds to specific receptors on the cells as a key would fit into a lock. When this transmitter is in place the interaction triggers a response from the target cell allowing the contraction of muscle or stimulation of enzyme activity. Acetylcholine (Ach) is a transmitter in the brain released by neurons, when reaching the target site on a muscle cell it binds to the receptors opening a sodium chennels and causing muscle contraction. Antibodies that block one type of Ach receptor may lead to myasthenia gravis which is a disease characterized by fatigue and muscle weakness.