Nervous System Overview and Neuron Physiology

Nervous System Overview

• The nervous system is responsible for coordinating and controlling bodily functions.
• It comprises the central nervous system (CNS) and the peripheral nervous system (PNS).
• The CNS consists of the brain and spinal cord, while the PNS includes nerves branching out from the CNS.
• Neurons are the fundamental units of the nervous system, specialized cells for communication.

Neuron Structure

• Neurons possess a cell body (soma) containing the nucleus.
• Dendrites are branching extensions receiving signals from other neurons.
• The axon transmits signals away from the cell body.
• Myelin sheaths, formed by glial cells, insulate axons and speed up signal transmission.
• Nodes of Ranvier are gaps in the myelin sheath, crucial for saltatory conduction.
• Synaptic terminals release neurotransmitters at the synapse, enabling communication with target cells.

Neuron Physiology

• Resting Membrane Potential: The difference in electrical charge across the neuronal membrane when the neuron is not transmitting a signal. Typically around -70 mV.
• Action Potential: A rapid, self-propagating sequence of changes in membrane potential. This is the fundamental signal transmitted by neurons.
• Depolarization: A change from the resting membrane potential to a less negative value, triggered by excitatory signals.
• Repolarization: Restoration of the resting membrane potential after depolarization by changes in ion permeability across the membrane.
• Hyperpolarization: A temporary increase in the negativity of the membrane potential, often following repolarization. This can result from inhibitory signals.
• Threshold Potential: The critical level of depolarization required to trigger an action potential.
• All-or-None Principle: Once a threshold is reached, an action potential of a consistent magnitude is generated.
• Refractory Period: A short period after an action potential where another action potential cannot be generated. This ensures unidirectional signal propagation.

Conduction Mechanisms

• Continuous Conduction: In unmyelinated axons, action potentials propagate along the entire length of the axon segment by sequential depolarization of adjacent sections. This method is slower, needing continuous ion movement.
• Saltatory Conduction: In myelinated axons, action potentials "jump" between nodes of Ranvier, significantly increasing conduction velocity. Myelin prevents ion leakage, concentrating depolarization at the nodes, where voltage-gated ion channels are densely packed.

Factors Affecting Conduction

• Axon Diameter: Larger diameter axons have faster conduction velocities due to reduced resistance to ion flow.
• Myelination: Presence of myelin substantially enhances conduction speed by reducing the amount of membrane that needs depolarization.
• Temperature: Increased temperature generally speeds up the rate of ion movement, which in turn increases conduction velocity but only up to a certain point.

Synaptic Transmission

• Synaptic Cleft: The narrow gap separating the presynaptic and postsynaptic neurons.
• Neurotransmitters: Chemical messengers released from synaptic vesicles in the presynaptic terminal.
• Receptor Binding: Neurotransmitters bind to specific receptors on the postsynaptic membrane.
• Postsynaptic Potentials: Changes in the postsynaptic membrane potential resulting from neurotransmitter binding. These can be excitatory (depolarizing), or inhibitory (hyperpolarizing).
• Synaptic Integration: The combined effect of multiple excitatory and inhibitory postsynaptic potentials. This determines whether an action potential is triggered in the postsynaptic neuron.

Explore the intricate details of the nervous system, including its structure and function. This quiz covers the central and peripheral nervous system and delves into the anatomy and physiology of neurons. Test your knowledge about neuron types, signal transmission, and the roles of various neuron components.