Nervous System Anatomy and Neuron Function Explained

Central Nervous System: Information Analysis, Storage, and Coordinating Actions

Spinal Cord: In the center of the spinal reflexes, the spinal cord processes information through sensory nerves that carry impulses from the body to the brain. Motor nerves and nerves from the spinal cord spread to the brain and the effectors.

Brainstem:

Medulla Oblongata: Contains the cardiovascular center (controls heart rate and strength, and the diameter of blood vessels) and the respiratory center.

Pons: Its nuclei are the pneumotaxic center (shortens inspiration and facilitates expiration) and the apneustic center (prolongs inspiration, inhibiting expiration).

Midbrain: Contains reflex centers for eye movement, head and neck.

Diencephalon: Contains the thalamus and hypothalamus, the main coordinator of the cerebrum.

Thalamus: Receives sensory information and transmits sensations such as pain, temperature and pressure, sending the information to the cerebral cortex.

Hypothalamus: Regulates homeostasis. It forms part of the regulation of smooth muscle contraction and heart function, and of the glands. It regulates body temperature and is responsible for the sensation of hunger and thirst.

Cerebellum: Controls skeletal muscle contractions, coordination, balance, position and the execution of precise movements.

Cerebrum: Interprets sensory impulses. It controls voluntary motor movements, and its association complexes participate in memory, emotions, reasoning and intellectual functions.

Primary Sensory Functions: Receives information from sensory receptors and conducts impulses to where they are interpreted and associated.

Memory, Learning and Language: Learning and memory depend on the cerebrum. Learning is a process by which the individual acquires dynamic knowledge, allowing adaptation to the context. Memory is the retention of knowledge and its use to recall it in a given context.

The Neuron

Cell Body (Soma): Contains the nucleus and cytoplasm with organelles such as lysosomes, mitochondria, and the Golgi apparatus. Also contains Nissl bodies, which are rough endoplasmic reticulum, and neurofibrils, which are filaments that form the cytoskeleton.

Dendrites: Short branched extensions that extend from the soma.

Axon: A long cylindrical projection from the soma. It contains cytoplasm (axoplasm) with mitochondria and neurofibrils. In the vertebrate nervous system, axons are covered by a myelin sheath, a lipid-protein layer produced by Schwann cells.

Axon Terminals (Synaptic Knobs): The axon divides into branches, each ending in several synaptic knobs.

Function: The neuron has the ability to communicate with other cells and transmit electrochemical signals rapidly. Nervous impulses travel through its three main components: sensory, integrative and motor.

Types of Neurons

Sensory or Afferent Neurons: Conduct nervous impulses from receptors toward the central integrating center (the brain and spinal cord).

Association Neurons: Found in integrating centers, they connect sensory and motor neurons.

Motor or Efferent Neurons: Conduct nervous impulses from the center to an effector (muscle or gland).

Unipolar Neurons: Have a single process (axon) with general branches. This type is predominant in invertebrates.

Bipolar Neurons: Have two extensions on opposite poles of the neuron.

Multipolar Neurons: Have one axon and several dendrites emerging from different parts of the soma. This type is predominant in the vertebrate nervous system.

Membrane Potential and Nerve Impulses

Membrane Potential: The plasma membrane has an electrical charge difference between the inside and outside. The extracellular fluid is positively charged relative to the intracellular fluid, which is negatively charged. This potential is called the membrane potential.

Electrical Potential: The difference in the amount of electrical charge between a region of positive charge and a region of negative charge.

Resting Potential: The differential distribution of charges across the membrane determines that the neuron is electrically polarized.

Action Potential: A change in polarity occurs in the membrane when a stimulus is generated.

Nerve Impulse: The action potential travels along the membrane. If the intensity of the stimulus reaches or exceeds the excitation threshold, the neuron generates a nerve impulse. This follows the all-or-nothing law.

Repolarization: Restoration of the neuron to its normal state through the movement of potassium and sodium ions.

Depolarization: The resting potential can be changed by stimuli captured by sensory receptors.

Threshold Intensity: A stimulus of sufficient magnitude to trigger an action potential.