Help with Neurotransmitter and Receptor Physiology - Anatomy

Once an action potential has reached the end of the presynaptic neuron, voltage-gated calcium channels are stimulated, allowing calcium to enter the neuron. This influx of calcium stimulates the release of neurotransmitters into the synaptic cleft.

The neurotransmitters then bind to receptors on the surface of the postsynaptic neuron to generate small electrical stimuli. The sum of these stimuli must reach threshold in order for an action potential to be generated.

GABA and acetylcholine are two common neurotransmitters. GABA generally inhibits the postsynaptic neuron, while acetylcholine generally excites/stimulates the postsynaptic neuron.

Neurotransmitters will never enter the postsynaptic neuron. They will attach to receptors on the membrane of the postsynaptic neuron, release, and then be dealt with while in the synaptic cleft. In some instances, the neurotransmitter simply diffuses away from the synapse, but in most cases synaptic proteins help to recycle the molecules. Some enzymes will break the neurotransmitter into parts, which then reenter the presynaptic neuron and are reassembled. Acetylcholinesterase is a common example of this type of enzyme. Other neurons use membrane pumps to retrieve neurotransmitter from the synaptic cleft.

Acetylcholine activates muscarinic receptors in postganglioinic parasympathetic nervous tissue and nicotinic receptors in skeletal muscle fibers, and preganglionic sympathetic and parasympathetic nervous tissue.

Neurotransmitters are packaged in vesicles, traveling through the synaptic cleft (space between neurons) from the pre-synaptic membrane to the post-synaptic membrane, where they bind to their receptors and influence the post-synaptic membrane potential.

Muscarinic acetylcholine receptors (mAChRs) are found in the G protein-receptor complexes in the cell membrane of certain neurons. The suffix -ergic means exhibiting or stimulating the activity of. For example, dopaminergic receptors bind to dopamine.

Renshaw cells are interneurons in the spinal cord that release the inhibitory neurotransmitter glycine.

Competitive inhibitors directly compete with ligands for the same binding sites (active sites). Irreversible inhibitors are molecules that bind irreversible to the active site. Covalent modulators are molecules that bind covalently to proteins and changes their activity. pH and temperature may alter the 3D shape of the protein and can be irreversible, while ligand binding, and competitive inhibition is a reversible process that involves the formation of weak, not covalent, bonds.

The depolarization of the presynaptic membrane causes voltage-gated calcium channels to enter from the extracellular space. This causes the synaptic vessels which are docked on the presynaptic terminal to fuse with the presynaptic membrane and release the neurotransmitter into the synaptic cleft.

Acetylcholine is the neurotransmitter found at the neuromuscular junction and many other synapses found in the nervous system. It binds to receptors on the postsynaptic membrane to induce muscular contraction.

GABA is the most common inhibitory neurotransmitter in the brain. Glutamate is the most common excitatory neurotransmitter in the brain. Dopamine is a monoamine which can sometimes be inhibitory, but is not the most common.

Cholinergic neurons, whether in the sympathetic or parasympathetic nervous system, release acetylcholine as the neurotransmitter. Nonadrenergic, noncholinergic neurons include some postganglionic parasympathetic neurons of the gastrointestinal tract, which release substance P and nitric oxide. Adrenergic neurons release norepinephrine.

Norepinephrine is released by adrenergic neurons.

Cholinergic neurons release acetylcholine as their neurotransmitter (in the sympathetic or parasympathetic nervous system).

Nonadrenergic, noncholinergic neurons (which include postganglionic parasympathetic neurons of the gastrointestinal tract) release substance P and nitric oxide.

Nociceptors are pain receptors that. Mechanoreceptors respond when tissue is deformed by mechanical forces. Photoreceptors respond to light. Chemoreceptors respond to chemicals. Thermoreceptors respond to changes in temperature.

Pacinian corpuscles are found in deeper in the dermis rather than in the dermal papillae. Merkel cells are found in the epidermal-dermal border and are responsible for perception of light and touch. Carcinoma is a type of tumor. Meissner's corpuscles are the mechanoreceptors that are found in the dermal papillae, and are very sensitive to light touches.

When there is tissue damage, substance P plays a very important role in the sensation of pain through stimulating primary afferent neurons in pain perception pathways. Enkephalin is a neurotransmitter that inhibits the neurons that transmit pain impulses to the brain. Serotonin is a monoamine neurotransmitter and dopamine is a catecholamine/phenethylamine neurotransmitter.

Glutamic acid is an excitatory neurotransmitter. During a cerebrovascular accident, cells that have died due to oxygen deprivation release large quantities of glutamic acid. This causes surrounding cells to become overexcited and eventually die. This process is called excitotoxicity.

Opioid neuroactive peptides include enkephalins, endorphins, and dynorphin. These bind to opiate receptors in the brain, which also bind opiate drugs such as heroin and morphine. These are known to play a role in response to injury stress and pain perception and are released during exercise. Non-opioid neuroactive peptides do not bind opiates and their function is not well understood. Amino acids include glutamic acid and GABA. Biogenic amines include monoamines and catecholamines, which include norepinephrine, epinephrine, dopamine, and serotonin.

The substantia nigra is composed of primarily dopamine. When the substantia nigra is effected by a disease, a patient can present with Parkinson-like symptoms. Most common symptom is resting tremors.

Acetylcholine utilizes both muscarinic and nicotinic receptors. The nicotinic receptors are ionotropic and are primarily excitatory. Whereas, the muscarinic receptors are metabotropic and can be either excitatory or inhibitory. All receptors that bind acetylcholine are referred to as cholinergic.

Physiologically, when the PAG is stimulated serotonin is produced. Serotonin will increase the pain threshold (ascending tract) and inhibit pain receptors (descending tract).