BIOL5_Ch7_NervousSys_I (1)

The Nervous System Overview

• Chapter 7

Introduction to the Nervous System

• Nervous System (NS) Divisions:

  • Central Nervous System (CNS)

    • Composed of the brain and spinal cord

  • Peripheral Nervous System (PNS)

    • Composed of cranial and spinal nerves

Neurons and Supporting Cells

• Key Components:

  • Neurons:

    • Functional units of the NS, responsible for gathering and transmitting information

    • Classification:

      • Sensory/Afferent neurons: conduct impulses into CNS

      • Motor/Efferent neurons: carry impulses out of CNS

      • Association/Interneurons: integrate NS activity, located entirely within CNS

  • Supporting Cells (Glial Cells):

    • Maintain homeostasis in the NS and outnumber neurons by 5-7 times

• Functions of Supporting Cells:

  • PNS includes Schwann and satellite cells, where Schwann cells myelinate axons

  • CNS includes oligodendrocytes, microglia, astrocytes, and ependymal cells.

    • Oligodendrocytes myelinate multiple CNS axons

    • Ependymal cells act as neural stem cells

Neuron Structure and Function

• Neurons consist of:

  • Cell body: contains the nucleus and is the nutritional center of the neuron

  • Dendrites: receive information and convey it to the cell body

  • Axon: conducts impulses away from the cell body

    • The axon hillock is the site of action potential initiation

• Electrical Activity in Neurons:

  • Neurons generate and conduct electrochemical impulses

  • Action potentials involve changes in membrane potential due to ion flow

Action Potentials and Electrical Activity

• Resting Membrane Potential (RMP):

  • Neurons maintain a negative internal charge of -70 mV through ion gradients

  • Sodium/Potassium (Na+/K+) channels play a crucial role in maintaining RMP

Key Concepts in Action Potentials

• Action Potential Generation:

  • A rapid depolarization occurs when Na+ ions flood into the neuron, creating a positive feedback loop

  • Following depolarization, K+ ions rush out, causing repolarization.

• All-or-None Principle:

  • Action potentials are fired if the threshold is reached, maintaining uniform amplitude despite variations in stimulus strength

Axonal Conduction

• Propagation Speed Factors:

  • Cable properties and myelination affect conduction velocity

  • Types of Conduction:

  • Continuous conduction in unmyelinated axons is slower

  • Saltatory conduction in myelinated axons is faster

Synaptic Transmission

• Types of Synapses:

  • Chemical synapses utilize neurotransmitters for signal transmission

  • Electrical synapses allow direct ion flow via gap junctions

• Graded Potentials and Action Potentials:

  • Graded potentials are local changes in membrane potential, mainly occurring in dendrites

  • Summation of EPSPs and IPSPs determines if an action potential is generated at the axon hillock

Neurotransmitter Action

• Receptor Types:

  • Ionotropic receptors have direct NT binding and channel activation

  • Metabotropic receptors require G-proteins to open channels

• Neurotransmitter Lifecycle:

  • Includes production, release, reuptake, and inactivation in the synaptic cleft

Conclusion

• Understanding the nervous system dynamics involves exploring neuron structure, signaling mechanisms, and synaptic interactions. Action potentials act as vital signals for neuron communication and integration.