anatomy

Nervous System 101 Study Guide Notes: Neurotransmitter Anatomy, Glutamate vs Acetylcholine vs Histamine vs Norepinephrine vs Dopamine vs Serotonin, Selective Serotonin Reuptake Inhibitors [MCAT, USMLE, Biology, Medicine]

In this lesson, we explore the nervous system and share notes as part of the study guide series. We will explore the awesome brain and nerves! Topics include neurotransmitter anatomy, glutamate, acetylcholine, histamine, norepinephrine, dopamine, serotonin, selective serotonin reuptake inhibitors.

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Neurotransmitter Anatomy

  • Recall, neurotransmitters are molecules that communicate between neurons and their target cells at chemical synapses.
  • Some neurotransmitters are released by neurons that are distributed throughout the nervous system.
  • Ex: glutamate (most common excitatory neurotransmitter), GABA (inhibitory, in the brain), and glycine (inhibitory, in spinal cord)
  • Other neurotransmitters are more specific to certain areas.
  • Areas of the brain that have collections of neurons send axons diffusely to release specific neurotransmitters into the cerebral cortex. (Also other areas, but mostly that)
  • These widespread projections coming up towards the cerebral cortex dump lots of a specific neurotransmitter all over certain areas of the cerebral cortex; and they’re very important for functions of the higher nervous system (i.e. cognition, emotion, and consciousness).

Glutamate

  • Glutamate — Some particular areas in the reticular formation of the brain stem and parts of the thalamus that project axons diffusely to cerebral cortex and release glutamate all over cerebral cortex.
  • Reticular activating system = collection of neurons that have diffuse projection of glutamate
  • Without this system, there is no consciousness

Acetylcholine

  • Acetylcholine — The basalis and septal nuclei send diffuse projections of acetylcholine all over the cerebral cortex. [affects peripheral nervous system.]
  • Lower motor neurons that come out of CNS and have axons that synapse on skeletal muscle cells release acetylcholine
  • Most neurons of the autonomic nervous system also release acetylcholine, a smaller number release norepinephrine as their neurotransmitter.

Histamine

  • Histamine — There are a number of neurons in the hypothalamus that send projections to release histamine all over the cerebral cortex.

Norepinephrine

  • Norepinephrine — The local ceuruleus is an area in the pons section of the brainstem that sends neurons releasing norepinephrine all over the cerebral cortex. [affects peripheral nervous system]
  • Most neurons of the autonomic nervous system also release acetylcholine, a smaller number release norepinephrine as their neurotransmitter.

Serotonin

  • Serotonin — A number of raphe nuclei are present at all levels of the brain stem (midbrain, pons and medulla) that release serotonin up to cortex and other parts of the immune system.

Dopamine

  • Dopamine —The ventral tegmental area is in the midbrain, and it diffusely projects dopamine onto the cortex. [affects central nervous system]
  • There are also a couple of projection systems of dopamine that aren’t into the cerebral cortex but that are important for functions of the central nervous system, and can become problems for medications that affect dopamine neurotransmission.
  • One such collection of neurons in the midbrain is called the substantia nigra, and it’s projecting dopamine to another part of the basal ganglia (specifically to a couple of nuclei deep in the cerebral hemisphere) called the striatum.
  • Problems with this system of dopamine getting from substantia nigra to the striatum appear to be a big part of what happens in Parkinsons’ disease.
  • There are also dopaminergic neurons in the hypothalamus that send dopamine down to the pituitary gland to control the release of prolactin.
  • All these diffuse projection systems are very important to the higher functions of the nervous system.
  • Many psychiatric disorders appear to involve dysfunction of these neurotransmitter systems and thus, many psychiatric drugs influence these systems.
  • Dopamine is released from the ventral tegmentum (also known as the ventral tegmental area) to the limbic system through the nucleus accumbens. Dopamine is released from the substantia nigra to the striatum. Dopamine is released from the hypothalamus to the pituitary gland.

Selective Serotonin Reuptake Inhibitors SSRIs

One specific type of antidepressant medication works by blocking the removal of neurotransmitters. Which of the following neurotransmitters is most likely the target of the antidepressant medication?

  • The neurotransmitter must be classified as one of the types that is associated with attention, cognition, and emotion.
  • The medication works by blocking the removal of the neurotransmitter; acetylcholine is not removed from the receptor, but is broken down by enzymes.
  • Selective Serotonin Reuptake Inhibitors (SSRI’s) function by blocking the reuptake of serotonin, which allows more serotonin to be present.

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