Key Concepts in Neurotransmission and Hormonal Regulation

Neurotransmitters and Synaptic Receptors

Receptor proteins act on the membrane of the next neuron to excite, inhibit, or alter its sensitivity in various ways.

Differences Between Synapses and Endplates

• Synapse: A terminal junction between a nerve and the soma or dendrites of another neuron. Synapses can be both excitatory and inhibitory.
• Endplate: A junction between a nerve and a muscle fiber. Synaptic buttons at the endplate always secrete acetylcholine.

Electrical Phenomena in Neural Excitation

Before excitation, the neuron presents a potential of -65mV. Protein phosphate ions do not diffuse through the membrane. Internally, there is K+, while Na+ and Cl- are external.

Upon excitation, sodium channels open, making the membrane permeable. The influx of Na+ ions increases positive charges internally, raising the voltage to -45mV.

The Role of the Thalamus in Sensation

In the thalamus, signals begin to penetrate the field of consciousness. It determines sensations such as heat, touch, or cold.

Functions of Thyroid Hormones

Triiodothyronine (T3) and Thyroxine (T4) increase the speed of energy release and oxidation processes in body cells, elevating the metabolic rate and heat generation.

The Essential Role of Iodine

Elementary iodine reacts with thyroglobulin, a part of the amino acid tyrosine, converting the thyroglobulin molecule into thyroxine.

Effects of Growth Hormone

Growth hormone exerts effects on almost all tissues. It enhances amino acid absorption and protein synthesis by cells, while redistributing protein degradation.

After adolescence, it stimulates the liver to secrete Somatomedin C, which acts on the stimulation of cartilage and bone growth.

Physiological Effects of Insulin

Insulin promotes glucose transport into the interior of almost all cells, primarily muscle, fat, and liver cells.

• Glucokinase: Allows glucose to react with phosphate ions.
• Glycogen Synthase: Allows glucose to react together to form glycogen.