Introduction to the Nervous System and Nervous Tissue: Study Notes

Introduction to the Nervous System and Nervous Tissue

Overview of the Nervous System

The nervous system is a complex network responsible for coordinating the body's activities by transmitting signals to and from different parts of the body. It is divided into the central nervous system (CNS) and the peripheral nervous system (PNS), each with distinct structures and functions.

• Major Functions: The nervous system regulates sensory input, integration, and motor output.

• Central Nervous System (CNS): Composed of the brain and spinal cord; responsible for processing and integrating information.

• Peripheral Nervous System (PNS): Consists of nerves and ganglia outside the CNS; transmits signals between the CNS and the rest of the body.

• Functional Divisions of PNS:

  • Somatic Nervous System: Controls voluntary movements.

  • Autonomic Nervous System: Regulates involuntary functions (e.g., heart rate, digestion).

Nervous System Structure and Function

The nervous system is composed of specialized cells called neurons and supporting cells known as neuroglia. Each component has a unique structure that supports its function.

• Neurons:

  • Cell Body (Soma): Contains the nucleus and organelles; site of metabolic activity.

  • Dendrites: Receive incoming signals from other neurons.

  • Axon: Transmits electrical impulses away from the cell body.

• Types of Neurons:

  • Sensory (Afferent) Neurons: Carry information toward the CNS.

  • Motor (Efferent) Neurons: Transmit signals from the CNS to effectors (muscles/glands).

  • Interneurons: Connect neurons within the CNS; involved in processing information.

• Neuroglial Cells:

  • CNS Neuroglia: Astrocytes, oligodendrocytes, microglia, ependymal cells.

  • PNS Neuroglia: Schwann cells, satellite cells.

• Function of Neuroglia: Support, protect, and nourish neurons; maintain homeostasis.

Electrophysiology of Neurons

Neurons communicate via electrical signals generated by ion movement across their membranes. This process is essential for the development of action potentials and signal transmission.

• Voltage-Gated Ion Channels: Proteins that open or close in response to changes in membrane potential, allowing ions (Na+, K+) to flow.

• Action Potential: A rapid change in membrane potential that propagates along the axon. $\text{Action Potential:} \quad \text{Depolarization} \rightarrow \text{Repolarization} \rightarrow \text{Hyperpolarization}$

• Refractory Periods:

  • Absolute Refractory Period: No new action potential can be generated.

  • Relative Refractory Period: A stronger stimulus is required to generate an action potential.

• Conduction Types:

  • Continuous Conduction: Occurs in unmyelinated axons; slower.

  • Saltatory Conduction: Occurs in myelinated axons; faster due to jumping between nodes of Ranvier.

• Factors Affecting Conduction Velocity: Axon diameter and myelination increase speed.

Neuronal Synapses

Synapses are junctions where neurons communicate with other neurons or effectors. They can be electrical or chemical, each with distinct mechanisms.

• Electrical Synapses: Direct transfer of ions through gap junctions; rapid communication.

• Chemical Synapses: Use neurotransmitters to transmit signals across a synaptic cleft.

• Structure of Chemical Synapse: Presynaptic terminal, synaptic cleft, postsynaptic membrane.

• Neurotransmitter-Receptor Relationship: Neurotransmitters bind to specific receptors, triggering a response.

• Synaptic Transmission Events:

  1. Action potential arrives at presynaptic terminal.

  2. Neurotransmitter released into synaptic cleft.

  3. Neurotransmitter binds to postsynaptic receptor.

  4. Postsynaptic potential generated (EPSP or IPSP).

• EPSP (Excitatory Postsynaptic Potential): Depolarizes the postsynaptic membrane, increasing likelihood of action potential.

• IPSP (Inhibitory Postsynaptic Potential): Hyperpolarizes the postsynaptic membrane, decreasing likelihood of action potential.

Neurotransmitters

Neurotransmitters are chemical messengers that transmit signals across synapses. Their effects depend on the type of receptor they bind to.

• Excitatory vs. Inhibitory: A neurotransmitter can be excitatory at one synapse and inhibitory at another, depending on the receptor.

• Major Classes:

  • Amino Acids: e.g., glutamate (excitatory), GABA (inhibitory).

  • Monoamines: e.g., dopamine, serotonin.

  • Peptides: e.g., substance P, endorphins.

  • Others: e.g., acetylcholine.

• Common Neurotransmitters in CNS:

  • Excitatory: Glutamate.

  • Inhibitory: GABA.

Example:

Glutamate is the most common excitatory neurotransmitter in the CNS, while GABA is the most common inhibitory neurotransmitter.

Additional info: Academic context was added to expand brief points into full explanations, including definitions, examples, and relevant details for each topic.