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Chapter 10 Lecture Outline
10.1 General Characteristics of the Nervous System
Overview of Nervous System Function:
Master Regulatory System: Governs all bodily functions.
Sends and Receives Information: Critical for communication within the body.
Sensory Input:
Definition: Detects changes in the internal and external environment.
Integration and Processing:
Function: Involves processing incoming sensory data and making decisions based on that information.
Motor Output:
Function: Sends commands to muscles and glands to elicit responses.
Maintains Homeostasis:
Definition: Ensures stability in internal conditions despite external changes.
Acts as Center for Thought, Learning, and Memory:
Functionality: Enables higher cognitive functions.
Main Cell Types of Nervous System:
Neurons (Nerve Cells):
Function: Respond quickly to stimuli by conducting electrical impulses.
Mechanism: Communicate via neurotransmitters.
Neuroglia:
Function: Provide protection, support, insulation, and nourishment to neurons.
Characteristics: Do not conduct electrical impulses like neurons.
10.2 Nervous Tissue Cells: Neurons and Neuroglia
Neurons:
Variation: Vary in size and shape; differ in axon and dendrite structure.
Structural Features:
Cell Body (Soma or Perikaryon):
Contents: Contains nucleus, cytoplasm, organelles, neurofilaments, chromatophilic substance (Nissl bodies).
Dendrites:
Function: Branched structures that receive signals; neurons may have multiple dendrites.
Axon:
Function: Transmits impulses and releases neurotransmitters; usually only one axon per neuron.
Axons
Structural Features of Axons:
Axon Hillock: Cone-shaped area from which the axon arises.
Collaterals: Branches that extend from the axon.
Axon Terminal: Specialized endings of axons, where synaptic transmission occurs.
Synaptic Knob: Rounded ending at the terminal end of axons.
Schwann Cells:
Role: Neuroglia in the PNS that wrap around axons, forming myelin layers.
Myelin: Mixture of fats and proteins that insulates axons.
Myelin Sheath: Wrapped coating around some PNS axons that acts as an electrical insulator.
Nodes of Ranvier: Gaps in the myelin sheath between Schwann cells.
Myelinated and Unmyelinated Axons
Myelinated Axons:
Characteristics:
Coated by a myelin sheath produced by Schwann cells in PNS and oligodendrocytes in CNS.
Found in white matter of CNS.
Increase conduction speed of electrical impulses.
Unmyelinated Axons:
Characteristics:
Encased by Schwann cell cytoplasm without a myelin layer.
Groups found in gray matter of CNS.
Clinical Application 10.2: Multiple Sclerosis
Description: Destruction of myelin sheaths in the CNS due to an autoimmune response.
Mechanism: Myelin is targeted by the body's own antibodies, leading to scleroses that impair neuronal impulse conduction.
Consequences:
Loss of muscle contraction leading to atrophy.
Other symptoms include fatigue, mood disorders, blurred vision, and limb weakness/numbness.
Treatments: Drugs that suppress immune system activity.
Classification of Neurons
By Structure
Multipolar Neurons:
Features: Many processes from cell body (many dendrites, one axon); 99% of neurons.
Locations: Most CNS neurons, some in autonomic NS.
Bipolar Neurons:
Features: Two processes (one dendrite and one axon); less common.
Locations: Primarily found in sensory organs (eyes, ears, nose).
Unipolar (Pseudounipolar) Neurons:
Features: One process that bifurcates into peripheral and central processes functioning as a single axon.
Locations: Found in ganglia of PNS.
By Function
Sensory (Afferent) Neurons:
Function: Carry impulses from peripheral to CNS.
Characteristics: Most are unipolar; some are bipolar with sensory receptors.
Interneurons (Association or Internuncial Neurons):
Function: Relay information within the CNS; link different neurons.
Characteristics: Predominantly multipolar, may cluster into nuclei.
Motor (Efferent) Neurons:
Function: Carry impulses from the CNS to effectors (muscles or glands).
Characteristics: Typically multipolar; control voluntary and involuntary actions.
Classification of Neuroglia
General Functions of Neuroglia:
Support: Provide structural support for neurons.
Development: Guide neurons into position during embryonic development, stimulating specialization.
Nutrition: Produce growth factors to nourish neurons, regulate ionic compositions, and remove excess neurotransmitters/ions.
Synapse Formation: Aid in synaptic development.
Neuroglia of the CNS
Astrocytes:
Function: Connect neurons to blood vessels, form scar tissue, regulate ion concentrations (part of Blood Brain Barrier).
Oligodendrocytes:
Function: Produce myelin sheaths around CNS axons and provide structural support.
Microglia:
Function: Phagocytic cells providing immune defense, alongside structural support.
Ependyma/Ependymal Cells:
Function: Line brain ventricles and central canal of spinal cord, assist in regulating cerebrospinal fluid composition (ciliated cells).
Neuroglia of the PNS
Schwann Cells:
Function: Form myelin sheath around peripheral axons and assist in impulse transmission speed.
Satellite Cells:
Function: Support neuron cell bodies in ganglia and maintain ionic balance.
10.3 Cell Membrane Potential
General Concept
Definition: The cell membrane is typically electrically charged or polarized.
Polarity: Charge difference across the cell membrane; typically negative inside compared to outside.
Significance: This charge difference is essential for impulse conduction in excitable tissues (neurons and muscle fibers).