Neuroscience

Neurotransmitters (The Neuron) Part 1

Chemical transmission is the major mechanism of synaptic communication in the brain. To understand how neurotransmitters function, several issues must be addressed. These issues include how neurotransmitters are synthesized, released, removed from the synaptic cleft, and metabolized. In addition, it is important to identify the characteristics, anatomical loci, and functional properties of the receptors that […]

Neurotransmitters (The Neuron) Part 2

Individual Small Molecule Neurotransmitters In the following sections, important information regarding the synthesis, removal, distribution, and physiological and clinical significance is discussed for selected small molecule neurotransmitters. Acetylcholine Synthesis The following steps are involved in the synthesis and release of acetylcholine (Ach [Fig. 8-5]). 1. Glucose enters the nerve terminal by passive transport (facilitated diffusion). […]

Neurotransmitters (The Neuron) Part 3

Gamma Aminobutyric Acid Synthesis and Removal. The following steps are involved in the synthesis of gamma aminobutyric acid (GABA) and its removal from the synaptic cleft (Fig. 8-8). 1. Glutamine is converted into glutamate by an enzyme, glutaminase. 2. GABA is formed by a-decarboxylation of glutamate. This reaction is catalyzed by a cytosolic enzyme, L-glutamic […]

Neurotransmitters (The Neuron) Part 4

Physiological and Clinical Considerations Parkinson’s Disease. This disease is characterized by an expressionless face (clinicians sometimes refer to it as "mask-like face"), slowness of movement (bradykinesia or hypokinetic syndrome), rigidity of the extremities and the neck, and tremors in the hands. Patients with Parkinson’s disease have a gait that is characterized by short wide-based steps […]

Neurotransmitters (The Neuron) Part 5

Imidazole amines Imidazole amines consist of an imidazole ring with an attached amino group. Imidazole consists of a five-membered ring containing two nitrogen atoms with a hydrogen atom located on either of the two nitrogen atoms. Histamine consists of an imidazole ring and an amino group connected by two methylene groups. Histamine Synthesis and Removal. […]

Neurotransmitters (The Neuron) Part 6

Receptors Receptors are proteins located on neuronal membranes with which neurotransmitters bind; the result is the opening or closing of specific ion channels. There are two families of receptors: (1) ionotropic or ligand-gated receptors, and (2) metabotropic or G-protein-coupled receptors. Ionotropic Receptors Ionotropic receptors usually consist of multimeric proteins (different proteins, usually five). Each subunit […]

Neurotransmitters (The Neuron) Part 7

Cholinergic Muscarinic Receptors The steps involved in the binding of ACh to the cholinergic muscarinic receptor and the events that follow are shown in Figure 8-21 A. ACh binds with muscarinic receptor; a G-protein (Go) is activated; the enzyme phos-pholipase-C is stimulated; and two second messengers (inositol triphosphate [IP3] and diacylglycerol [DAG]) are produced. IP3 […]

The Spinal Cord (Organization of the Central Nervous System) Part 1

The spinal cord is a critical component for the transmission of sensory information to the brain as well as for the regulation of motor and autonomic functions. It receives sensory information from somatic and visceral receptors through dorsal roots, transmits this information to higher centers in the brain through ascending tracts, receives signals from higher […]

The Spinal Cord (Organization of the Central Nervous System) Part 2

Spinal Segments The spinal cord consists of 31 segments (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal) based on the existence of 31 pairs of spinal nerves. Each segment (except the first cervical and coccygeal segments) receives dorsal and ventral root filaments on each side. A schematic representation of different spinal segments […]

The Spinal Cord (Organization of the Central Nervous System) Part 3

Cuneocerebellar Tract The course of this tract is shown in Figure 9-8B. It should be recalled that the nucleus dorsalis of Clarke is not present in the spinal segments rostral to C8. Therefore, afferent fibers entering the spinal cord rostral to this level ascend ipsilaterally in the fasciculus cuneatus and project to neurons located in […]

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