Nervous and Endocrine Systems: Functions and Mechanisms

Posted on Jan 8, 2025 in Biology

The Nervous System: Structure and Function

The nervous system comprises the central nervous system (CNS) and peripheral nerves. It is composed of cells called neurons that can carry rapid electrical impulses.

Nerve Impulse Conduction

Nerve impulses are conducted from receptors to the CNS by sensory neurons, within the CNS by relay neurons, and from the CNS to effectors by motor neurons.

Resting and Action Potentials

  • Resting potential: The electrical potential across the plasma membrane of a cell that is not conducting an impulse.
  • Action potential: The reversal and restoration of the electrical potential across the plasma membrane of a cell, as an electrical impulse passes along it (depolarization and repolarization).

Nerve Impulse Transmission in Non-myelinated Neurons

  1. Resting potential rises above the threshold level.
  2. Voltage-gated sodium channels open.
  3. Sodium ions flow into the cell, and more sodium channels open.
  4. The inside of the cell develops a net positive charge compared to the outside, resulting in depolarization.
  5. Voltage-gated potassium channels open.
  6. Potassium ions flow out of the cell.
  7. The cell develops a net negative charge compared to the outside, resulting in repolarization.
  8. Concentration gradients are restored by sodium-potassium pumps.
  9. Resting potential is restored.

Principles of Synaptic Transmission

  1. An action potential reaches the end of a presynaptic neuron.
  2. Voltage-gated calcium channels open.
  3. Calcium ions flow into the presynaptic neuron.
  4. Vesicles with neurotransmitters inside the presynaptic neuron fuse with the plasma membrane.
  5. Neurotransmitters diffuse in the synaptic cleft and bind to receptors on the postsynaptic neuron.
  6. The receptors are channels that open and let sodium ions into the postsynaptic neuron.
  7. The sodium ions cause the postsynaptic membrane to depolarize.
  8. This causes an action potential that passes down the postsynaptic neuron.
  9. Neurotransmitters in the synaptic cleft are degraded, and the calcium ions are pumped back into the synaptic cleft.

The Endocrine System

The endocrine system consists of glands that release hormones that are transported in the blood.

Homeostasis: Maintaining Internal Balance

Homeostasis involves maintaining the internal environment between limits, including blood pH, carbon dioxide concentration, blood glucose concentration, body temperature, and water balance.

Homeostasis and Negative Feedback Mechanisms

  • Homeostasis maintains the internal environment between limits.
  • Negative feedback is used to do so. Any change from a set point results in an opposite change.

Body Temperature Control

Body temperature control involves the transfer of heat in the blood and the roles of the hypothalamus, sweat glands, skin arterioles, and shivering.

If blood temperature significantly increases above the set point

If blood temperature significantly drops below the set point

Skin arterioles increase in diameter so that more blood flows to the skin. By doing so, it transfers heat from the core of the body to the skin, and this heat is then lost to the external environment, cooling down the body in the process.

Skin arterioles decrease in diameter so that less blood flows to the skin. The diameter of the capillaries in the skin cannot change, but less blood flows through them. This prevents heat loss to the external environment as the temperature of the skin falls.

Skeletal muscle stays relaxed so that more heat is not generated.

Shivering occurs. This is when the skeletal muscle does many small, rapid contractions to generate heat.

Sweat glands secrete large amounts of sweat, which makes the surface of the skin moist. When water evaporates from the moist skin, it cools down the body.

Sweat glands do not secrete sweat, and so no water evaporation can occur as the skin stays dry.