Study Notes for Marieb Human Anatomy & Physiology Chapter 11

Marieb Human Anatomy & Physiology Chapter 11: Fundamentals of the Nervous System and Nervous Tissue

Introduction

• Prepared by Ashley Spring, Ph.D., Eastern Florida State College

• Copyright © 2025 Pearson Education, Inc. All Rights Reserved

11.1 The Nervous System Receives, Integrates, and Responds to Information

• The nervous system acts as the master controlling and communicating system of the body.

• Cell Communication:

  • Communicates via electrical and chemical signals.

  • These signals are rapid and specific, leading to almost immediate responses.

Functions of Nervous System (1 of 4)

1. Sensory Input

   • Information gathered by sensory receptors about internal and external changes.

2. Integration

   • Processing and interpretation of sensory input.

3. Motor Output

   • Activation of effectors (muscles and glands) produces a response.

Diagram: The Nervous System's Functions

• Sensory receptors detect a stimulus from inside or outside the body, leading to sensory input travel via afferent pathways.

• Integration occurs at a control center where sensory input is processed.

• Motor output travels via efferent pathways to effectors (muscles and glands) that cause a response.

Functions of Nervous System (2 of 4)

• Divisions of the Nervous System:

  • Divided into two principal parts:

  1. Central Nervous System (CNS)

     • Composed of the brain and spinal cord within the dorsal body cavity.

     • Acts as the integration and control center, interpreting sensory input and dictating motor output.

  2. Peripheral Nervous System (PNS)

     • Consists mainly of nerves extending from the brain and spinal cord.

     • Includes spinal nerves (to and from the spinal cord) and cranial nerves (to and from the brain).

     • Contains the enteric nervous system, comprising neurons in the walls of the gastrointestinal tract.

Functions of Nervous System (3 of 4)

• PNS Functional Divisions:

  • Two functional divisions:

  1. Sensory (Afferent) Division

     • Somatic Sensory Fibers: Convey impulses from skin, skeletal muscles, and joints to CNS.

     • Visceral Sensory Fibers: Convey impulses from visceral organs to CNS.

  2. Motor (Efferent) Division

     • Transmits impulses from CNS to effectors (muscles and glands).

     • Consists of:

       • Somatic Nervous System: Voluntary system controlling skeletal muscles.

       • Autonomic Nervous System (ANS): Involuntary system controlling smooth muscle, cardiac muscle, and glands, with two functional subdivisions:

       • Sympathetic Division

       • Parasympathetic Division

Functions of Nervous System (4 of 4)

• Somatic Nervous System (SNS):

  • Composed of somatic motor nerve fibers that conduct impulses from CNS to skeletal muscle for conscious control.

• Autonomic Nervous System (ANS):

  • Consists of visceral motor nerve fibers, regulating smooth muscle, cardiac muscle, and glands.

11.2 Neuroglia

• Nervous tissue consists of two principal cell types:

  • Neuroglia (Glial Cells): Small cells that support and wrap delicate neurons.

  • Neurons (Nerve Cells): Excitable cells that transmit electrical signals.

Neuroglia in the CNS (1 of 5)

• Four main types of neuroglia in the CNS:

  1. Astrocytes

  2. Microglial Cells

  3. Ependymal Cells

  4. Oligodendrocytes

Functions of Neuroglia in CNS (2 of 5)

• Astrocytes:

  • Most abundant, versatile, and branched glial cells.

  • Functions include:

  • Support and brace neurons.

  • Play a role in exchanges between capillaries and neurons.

  • Guide the migration of young neurons.

  • Control the chemical environment around neurons by cleaning up leaked potassium ions and recycling neurotransmitters.

  • Influence neuronal functioning.

Functions of Neuroglia in CNS (3 of 5)

• Microglial Cells:

  • Small, ovoid cells with thorny processes that monitor neurons.

  • Migrate toward injured neurons and transform to phagocytize microorganisms and neuronal debris.

Functions of Neuroglia in CNS (4 of 5)

• Ependymal Cells:

  • Shape varies from squamous to columnar, may be ciliated.

  • Line the central cavities of the brain and spinal column, forming a barrier between cerebrospinal fluid (CSF) and tissue fluid bathing CNS cells.

Functions of Neuroglia in CNS (5 of 5)

• Oligodendrocytes:

  • Branched cells with fewer processes than astrocytes that wrap CNS nerve fibers to form insulating myelin sheaths.

Neuroglia in the PNS

• Two major neuroglia in PNS:

  1. Satellite Cells: Surround neuron cell bodies in PNS and function similarly to astrocytes in CNS.

  2. Schwann Cells (Neurolemmocytes): Surround all peripheral nerve fibers and form myelin sheaths around thicker nerve fibers, vital for regeneration of damaged peripheral nerve fibers.

11.3 Neurons

• Neurons are the structural units of the nervous system, large cells specialized for conducting impulses.

• Special Characteristics:

  • Extreme longevity (can last a person's lifetime).

  • Amitotic (often lose ability to divide) with few exceptions.

  • High metabolic rate requiring continuous supply of oxygen and glucose.

  • Neurons have a cell body and one or more slender processes.

Neuron Cell Body

• The cell body (or soma) contains:

  • Spherical nucleus with nucleolus surrounded by cytoplasm.

  • Plasma membrane serves as receptive region receiving information from other neurons.

  • Biosynthetic and metabolic center of neuron includes:

  • Protein and membrane-making machinery.

  • Free ribosomes, Golgi apparatus, and rough endoplasmic reticulum (also called Nissl bodies).

Structure of a Motor Neuron

• A structural diagram details the components of a motor neuron, emphasizing the organization of dendrites, axon, and neuron cell body.

Neuron Processes

• Processes extend from the cell body:

  • Types of processes include:

  1. Dendrites: Receive signals and convey them toward the cell body as graded potentials.

  2. Axon: Conducts impulses away from the cell body, starting at the axon hillock.

     • Axons may branch into several terminal branches (axon terminals) that release neurotransmitters.

Myelin Sheath

• White fatty substance coating many axons, protective and electrically insulating.

  • Increases speed of nerve impulse transmission, associated with axons and not dendrites.

Neuron Classification

• Structural Classification:

  1. Multipolar Neurons: Many processes (1 axon and many dendrites), predominant in CNS.

  2. Bipolar Neurons: Two processes (1 axon and 1 fused dendrite), found in retina, ear, and olfactory mucosa.

  3. Unipolar Neurons: One process (T-shaped process) divides into two branches; mostly sensory neurons in PNS ganglia.

Functional Classification of Neurons

1. Sensory (Afferent) Neurons: Transmit impulses from sensory receptors to CNS.

2. Motor (Efferent) Neurons: Carry impulses from CNS to effectors.

3. Interneurons (Association Neurons): Shuttle signals through CNS pathways, mostly entirely within CNS (99% of body's neurons).

11.4 Membrane Potentials

• Neurons possess resting membrane potentials and can rapidly change this potential due to excitability.

Basic Principles of Electricity

• Voltage: Measure of potential energy generated by separated charge.

• Current: Flow of electrical charge.

• Resistance: Hindrance to charge flow; influenced by the type of substance (insulators vs. conductors).

• Ohm's Law: Relationship of voltage, current, and resistance.

  • Current is directly proportional to voltage and inversely proportional to resistance.

Ion Channels

• Plasma membranes house large proteins acting as channels for ion flow.

• Two main types of ion channels:

  1. Leakage (Nongated) Channels: Always open.

  2. Gated Channels: Open/close in response to specific stimuli (voltage-gated, chemically gated, mechanically gated).

Membrane Potential Changes

• Types include:

  • Depolarization: Decrease in membrane potential; makes inside less negative and increases likelihood of impulse.

  • Hyperpolarization: Increase in membrane potential; makes inside more negative and decreases likelihood of impulse.

11.5 Graded Potentials

• Short-lived, localized changes in membrane potential; triggered by stimulus opening gated ion channels.

• Types:

  • Receptor Potentials: Occur in sensory receptors.

  • Postsynaptic Potentials: Occur in neurons.

  • End-Plate Potentials: Trigger action potentials for muscle contractions.

11.6 Action Potentials

• Brief reversal of membrane potential (typical change in voltage);

• Sends signals over long distances in excitable membranes.

• Involves four main steps: Resting state, depolarization, repolarization, and hyperpolarization.

Generating an Action Potential

1. Resting State: All channels closed; resting membrane potential maintained by leakage channels.

2. Depolarization: Voltage-gated Na+ channels open allowing influx of Na+; results in positive feedback and AP spike.

3. Repolarization: Na+ channels inactivate, voltage-gated K+ channels open causing K+ efflux.

4. Hyperpolarization: Some K+ channels remain open, making inside more negative than resting state.

11.7 Synapses

• Connections between neurons allow information transfer.

  • Presynaptic Neuron: Conducts impulses toward synapse.

  • Postsynaptic Neuron: Transmits signals away from synapse.

Types of Synapses

• Electrical Synapses: Less common; rapid communication.

• Chemical Synapses: Most common; involve the release of neurotransmitters.

Information Transfer Across Chemical Synapses

1. Action potential arrives at the presynaptic terminal.

2. Voltage-gated Ca2+ channels open, Ca2+ influx.

3. Ca2+ causes synaptic vesicles to release neurotransmitter via exocytosis.

4. Neurotransmitter binds to receptors on postsynaptic membrane.

5. Ion channels open, creating graded potentials.

6. Termination of neurotransmitter effect by reuptake, degradation, or diffusion.

Postsynaptic Potentials

• EPSP: Exhibits depolarization, can trigger an action potential.

• IPSP: Exhibits hyperpolarization, inhibits action potential generation.

11.9 Neurotransmitters

• Over 50 identified neurotransmitters that exhibit diverse functions in the nervous system.

Classification by Chemical Structure

1. Acetylcholine (ACh)

2. Biogenic Amines (e.g., dopamine, norepinephrine)

3. Amino Acids (e.g., glutamate, GABA)

4. Peptides (e.g., endorphins)

5. Purines (e.g., ATP)

6. Gases and Lipids (e.g., nitric oxide)

Conclusion

• The nervous system operates through a highly coordinated network of neurons and supporting cells that facilitate rapid communication, sensory processing, motor response, and homeostasis regulation. This complex interaction among various cell types, neurotransmitters, and electrical signals underlies the functionality and adaptability of the nervous system across various physiological and behavioral contexts.