3.1 Neuronal structure and function
3 min read•august 7, 2024
The nervous system's building blocks are neurons, specialized cells that transmit signals. These cells have a , dendrites for receiving signals, and an for sending them. Understanding their structure is key to grasping how our nervous system functions.
Neurons communicate through action potentials, electrical signals that travel along axons. These signals are generated by changes in ion concentrations across the cell membrane. Myelin sheaths and specialized help speed up signal transmission, allowing for efficient .
Neuron Structure
Components of a Neuron
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- Neurons are the basic functional units of the nervous system that transmit electrical and chemical signals
- Consist of a cell body (soma) which contains the nucleus and other organelles necessary for cellular function
- Have specialized projections called dendrites that receive signals from other neurons and transmit them towards the soma
- Possess a single long projection called an axon that transmits signals away from the soma to other neurons or effector cells (muscles, glands)
Axon Structure and Function
- Axons are long, thin, cable-like projections that extend from the soma and transmit electrical signals to other neurons or effector cells
- Axons are surrounded by a lipid-rich insulating layer called the which is produced by in the peripheral nervous system and oligodendrocytes in the central nervous system
- The myelin sheath is interrupted at regular intervals by gaps called which allow for faster signal transmission via (jumping from node to node)
- Axons terminate at synapses where are released to communicate with other neurons or effector cells (neuromuscular junctions)
Neuronal Signaling
Action Potential Generation and Propagation
- Neurons transmit signals through changes in their membrane potential called action potentials
- At rest, neurons maintain a negative membrane potential (around -70 mV) due to the unequal distribution of ions (primarily K+ and Na+) across the membrane
- When a receives a sufficiently strong depolarizing stimulus, voltage-gated Na+ channels open allowing Na+ to flow into the cell, further depolarizing the membrane
- If the membrane potential reaches a threshold value (around -55 mV), an is generated and propagates down the axon
- After the peak of the action potential, voltage-gated K+ channels open allowing K+ to flow out of the cell, repolarizing the membrane back to its resting potential
Ion Channels and Saltatory Conduction
- Ion channels are proteins embedded in the neuronal membrane that allow specific ions to flow in or out of the cell
- (Na+ and K+) are essential for the generation and propagation of action potentials
- (such as those activated by neurotransmitters) are important for synaptic transmission
- In myelinated axons, action potentials jump from one node of Ranvier to the next in a process called saltatory conduction
- Saltatory conduction allows for faster signal transmission compared to continuous conduction in unmyelinated axons because the action potential is regenerated only at the nodes of Ranvier (less energy and time required)
Key Terms to Review (16)
Action Potential: An action potential is a rapid and transient electrical signal that travels along the membrane of a neuron or muscle cell, allowing for the transmission of information and communication between cells. This process involves a series of changes in membrane potential due to the movement of ions across the membrane, which is essential for various physiological processes including muscle contraction and synaptic transmission.
Axon: An axon is a long, slender projection of a neuron that conducts electrical impulses away from the neuron's cell body. It plays a crucial role in transmitting signals to other neurons, muscles, or glands, and is essential for communication within the nervous system. The axon is often covered by a myelin sheath, which enhances signal transmission speed and efficiency.
Dendrite: A dendrite is a branched extension of a neuron that receives signals from other neurons and transmits this information toward the cell body. Dendrites are crucial for neuronal communication, allowing for the integration of synaptic inputs and the processing of information within the nervous system.
Depolarization: Depolarization is a process during which the membrane potential of a cell becomes less negative, moving towards a more positive value. This change in charge across the cell membrane is crucial for the initiation and propagation of action potentials in neurons and muscle cells, including cardiac myocytes. It plays a key role in various physiological functions, such as transmitting signals between neurons and coordinating heartbeats.
Ion Channels: Ion channels are integral membrane proteins that facilitate the selective passage of ions across cell membranes, playing a crucial role in various physiological processes. They are essential for maintaining the electrochemical gradient within cells, enabling cellular communication, and mediating responses to environmental stimuli through sensory transduction. Their activity directly influences neuronal signaling, muscle contraction, and the overall functionality of cells.
Ligand-gated ion channels: Ligand-gated ion channels are specialized protein structures embedded in cell membranes that open or close in response to the binding of specific chemical signals, known as ligands. These channels play a crucial role in neuronal communication by allowing ions to flow into or out of the cell, leading to changes in membrane potential and initiating action potentials or synaptic transmission.
Myelin sheath: The myelin sheath is a fatty layer that surrounds the axons of many neurons, acting as an insulating material that enhances the speed and efficiency of electrical signal transmission along the nerve fibers. This sheath is crucial for maintaining proper neuronal function, as it prevents the loss of electrical signals and facilitates faster communication between neurons through a process called saltatory conduction.
Neural communication: Neural communication refers to the process by which neurons transmit information through electrical impulses and chemical signals. This intricate system allows for the transfer of signals across synapses, enabling the brain and nervous system to coordinate bodily functions, respond to stimuli, and facilitate complex behaviors.
Neuron: A neuron is a specialized cell in the nervous system that transmits information through electrical and chemical signals. These cells are fundamental to processing and transmitting information throughout the body, forming the basis of communication within the nervous system, which controls everything from muscle movement to sensory perception.
Neurotransmitters: Neurotransmitters are chemical messengers that transmit signals across synapses from one neuron to another, playing a crucial role in the communication within the nervous system. They help regulate various physiological processes, including mood, sleep, and movement, by binding to specific receptors on the postsynaptic neuron. The balance and function of neurotransmitters are essential for normal brain function and can influence behavior and bodily functions.
Nodes of Ranvier: Nodes of Ranvier are small gaps in the myelin sheath of myelinated neurons that facilitate rapid signal transmission along the axon. These nodes are crucial for saltatory conduction, where action potentials jump from one node to the next, significantly increasing the speed of nerve impulse propagation compared to unmyelinated fibers. Their presence allows for efficient communication between neurons and enhances overall neural signaling.
Repolarization: Repolarization is the process by which a neuron returns to its resting membrane potential after depolarization, primarily involving the movement of potassium ions (K+) out of the cell. This is a crucial phase in action potential generation, as it restores the negative internal environment of the neuron, enabling it to be ready for subsequent action potentials. It plays a key role in the overall excitability and signaling capability of neurons.
Saltatory conduction: Saltatory conduction is the process by which action potentials jump from one node of Ranvier to another along myelinated axons, allowing for faster and more efficient transmission of electrical signals in neurons. This mechanism enhances signal speed compared to continuous conduction in unmyelinated fibers, leading to quicker communication between neurons and improved overall neural function.
Schwann cells: Schwann cells are specialized glial cells in the peripheral nervous system that are essential for the formation of myelin sheaths around nerve fibers. These cells not only facilitate the rapid transmission of electrical signals along axons but also play a crucial role in the repair and regeneration of damaged neurons. By insulating the axons, Schwann cells enhance the efficiency of nerve impulse conduction and contribute to overall neuronal function.
Soma: The soma, also known as the cell body, is the central part of a neuron that contains the nucleus and organelles essential for cellular function. It serves as the control center of the neuron, integrating incoming signals from the dendrites and generating outgoing signals to the axon. The soma is crucial for maintaining the overall health and metabolic functions of the neuron.
Voltage-gated ion channels: Voltage-gated ion channels are specialized proteins embedded in the cell membrane that open or close in response to changes in membrane potential, allowing ions to flow across the membrane. These channels play a crucial role in generating and propagating electrical signals in neurons, facilitating communication throughout the nervous system.