Quinto teórico: Neurona y sinapsis.

Neuronal Structure and Function

Introduction to Neurons

• The video begins with an overview of the evolution of cells, focusing on how certain cells differentiated to form neurons in the central nervous system.

• Neurons can vary significantly in size and shape, typically measuring from micrometers to a few centimeters.

Anatomy of a Neuron

• Key components include the soma (cell body), dendrites (extensions that receive signals), and axon (long projection that transmits signals).

• The axon is often covered by a myelin sheath, produced by Schwann cells or oligodendrocytes, which enhances signal transmission efficiency.

Types of Cells in Nervous Tissue

• Besides neurons, there are supporting cells known as glial cells that provide protection, nourishment, and waste removal for neuronal tissue.

• Myelinated areas are referred to as white matter due to their appearance under microscopy; gray matter consists of neuron cell bodies.

Brain Structure Insights

• A small section of the cerebral cortex reveals numerous neuronal bodies; axons generally extend inward towards other brain regions.

• The cerebral cortex is organized into layers with distinct functions; active processes require significant energy from these regions.

Historical Context and Importance of Neurons

• Ramón y Cajal's discoveries in the 1850s established that the nervous system is primarily composed of neurons and supportive glial cells.

• Neurons are crucial for responding to stimuli; estimates suggest there are around 100 billion neurons in the human brain, facilitating complex interactions.

Detailed Neuronal Functionality

• Each neuron has a nucleus containing DNA (deoxyribonucleic acid); they receive information through dendrites and transmit it via axons.

Classification of Neurons

Types of Neurons

• Neurons can be classified based on their shape and the number of polarizations: unipolar, bipolar, and multipolar.

• Specific neuron types are named after their discoverers, such as De Gaulle neurons and pyramidal neurons.

Functional Classification

• Neurons can also be categorized by function: sensory (afferent), motor (efferent), and interneurons.

• Sensory neurons transmit stimuli from the periphery to the brain for interpretation, while motor neurons carry responses from the brain to muscles.

Structure of Neurons

• The neuron body functions similarly to other cells in the body, performing metabolic processes like energy production and protein synthesis.

• Terminal action involves vesicles containing neurotransmitters that facilitate communication between neurons.

Neuronal Communication

Synaptic Transmission

• When a neuronal cell transmits information, it interacts with other cells through synapses where axons connect with dendrites.

• Myelin sheaths surround axons; their absence leads to demyelination disorders affecting cognitive functions and causing paralysis.

Electrical Activity

• Neurons respond to stimuli by generating small electrical discharges across their membranes, crucial for transmitting signals throughout the nervous system.

Sensory Reception

Specialized Receptors

• Different types of sensory receptors are specialized for various stimuli such as touch, vision, taste, and smell.

• Areas of high sensitivity include lips and fingertips due to a higher concentration of sensory receptors compared to less sensitive areas like legs.

Olfactory and Visual Systems

• The olfactory system is highly developed but less utilized in modern humans; however, it remains one of our most extraordinary senses.

Understanding Sensory Systems and Neural Communication

Overview of Sensory Systems

• The occipital lobe is crucial for awareness of form and color, but it is not the only sensory system; others include the vestibular and proprioceptive systems.

• The vestibular system, located in the inner ear, consists of small stones in a liquid that stimulate nerve endings as we move, providing information about balance and orientation.

Interoceptors and Emotional Responses

• Interceptors are responsible for internal sensations such as hunger or emotional distress, indicating how our body reacts to various stimuli.

• Miscommunication between proprioceptive signals and visual input can lead to dizziness when spinning while focusing on an object.

Neural Transmission Mechanisms

• Synaptic transmission involves action potentials traveling through neurons to create synapses where neurotransmitters facilitate communication between cells.

• Chemical synapses involve neurotransmitter release from vesicles, which can generate electrical responses in adjacent neurons.

Action Potentials and Membrane Dynamics

• Neurons transmit signals via action potentials that travel along axons to dendrites of other neurons, illustrating how sensory information is processed.

• The process of depolarization involves changes in ion distribution across the neuron's membrane, critical for generating action potentials.

Membrane Structure and Ion Movement

• Neuronal membranes consist of a phospholipid bilayer with embedded proteins acting as channels for ion movement essential for neuronal function.

Understanding Neuronal Action Potentials

The Basics of Electrical Charges in Neurons

• Neurons typically exhibit a positive charge outside and a negative charge inside, creating a voltage difference essential for their function.

• Early researchers like Hodgkin and Huxley were pivotal in measuring these voltages, which are crucial for the nervous system's functionality, using amplification devices to detect small voltages (around millivolts).

Resting Potential and Stimulus Response

• At rest, neurons maintain a voltage of approximately -70 millivolts. This resting state is critical before any stimulation occurs.

• When an adequate stimulus is applied, it can lead to depolarization—a rapid change in membrane potential that initiates an action potential if the threshold is reached.

Mechanism of Action Potential

• Upon reaching the threshold, there’s a significant influx of positive charges as sodium channels open, causing a swift rise in voltage from -70 mV to +40 or +60 mV.

• After this spike, the neuron enters a refractory period where it cannot be stimulated again immediately until it returns to its resting state.

Propagation of Action Potentials

• The action potential propagates along the neuron's axon rapidly due to changes in polarity across the membrane, allowing communication between neurons.

• This process involves measuring action potentials through techniques like electroencephalograms (EEGs), which assess brain activity by detecting electrical signals.

Importance of Nutrition for Neural Function

• Proper nutrition is vital for neuronal health; deficiencies can lead to learning difficulties and other neurological issues.

• Essential nutrients such as lipids and proteins support ion channel functions necessary for maintaining neuronal excitability and overall brain health.

Learning Implications Related to Stimulation

• Effective teaching requires sufficient stimulus intensity; overstimulation can lead to fatigue and reduced responsiveness during learning processes.

Neuronal Action Potentials and Myelination

Understanding Action Potentials

• The process of returning to the resting state after an action potential is crucial for neuronal function, highlighting the brief duration of action potentials measured in milliseconds.

• Repeated stimulation can lead to a diminished sensation of pain due to the exhaustion of the pain stimulus, resulting in a refractory period where neurons cannot fire again immediately.

Muscle Contraction Mechanism

• When a neuron stimulates a muscle instead of another neuron, it triggers contraction through myosin proteins that respond to electrical impulses, demonstrating how stimuli can have different effects based on their target.

Role of Myelin Sheath

• The presence of myelin sheaths allows for faster transmission of electrical impulses along neurons by enabling saltatory conduction at nodes of Ranvier, rather than continuous conduction across the entire membrane.

Speed and Functionality in Neurons

• Myelinated neurons conduct signals much more rapidly compared to unmyelinated ones; white matter (myelinated axons) is associated with high-speed signal transmission while gray matter (unmyelinated cell bodies) generally has slower processing capabilities.

Importance of Study Topics