Lecture_14_flashcards

Introduction to the Nervous System

• Importance of the Nervous System: Extensive coverage in biology courses, with significant emphasis in biology 231 and 232.

• Chapters Overview: 5 chapters about the nervous system in total (Chapters 12 and 13).

Components of the Nervous System

• Extrinsic Regulation: The nervous system and endocrine system work to maintain homeostasis via negative feedback.

• Components:

  • Central Nervous System (CNS): Consists of the brain and spinal cord.

  • Peripheral Nervous System (PNS): Comprises nerves and ganglia.

  • Ganglia: Collections of neuron cell bodies in PNS, including dorsal root ganglia that transmit information to the spinal cord.

Functions of the Nervous System

Three Main Functions:

1. Sensory Function:

   • Interaction with stimuli (internal and external).

   • Receptors include exteroceptors (external) and interoceptors (internal).

2. Integration:

   • Processing and interpretation of sensory signals by the CNS.

3. Motor Function:

   • Transmission of commands to effectors (muscles and glands) to enact responses.

Functional Divisions of the Nervous System

• CNS vs. PNS:

  • CNS: Integration centers (brain and spinal cord).

  • PNS: Nerves, ganglia, and receptors outside the CNS.

• Divisions of PNS:

  • Sensory (afferent) Division: Carries signals to the CNS.

  • Motor (efferent) Division: Sends commands from the CNS to effectors.

Subdivisions of PNS

• Sensory Division:

  • Somatic Sensory Division: Signals from skin and skeletal muscle.

  • Visceral Sensory Division: Signals from internal organs.

• Motor Division:

  • Somatic Motor Division: Controls skeletal muscles (voluntary).

  • Visceral Motor Division (Autonomic Nervous System): Controls involuntary factors like cardiac muscle and glands.

Neurons and Their Functions

• Neurons: Major communicating cells of the nervous system, responsible for transmitting electrical impulses.

  • Types of Neurons:

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

    • Motor Neurons (Efferent): Convey commands from the CNS to effectors.

    • Interneurons: Connect sensory and motor pathways; primarily located in the CNS.

• Neuron Structure:

  • Dendrites: Receive signals.

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

  • Axon Terminals: Release neurotransmitters to communicate with other cells.

Structure of Neurons

• Multipolar Neurons: Most common, with one axon and multiple dendrites.

• Bipolar Neurons: One axon and one dendrite, found in special senses (e.g., retina).

• Unipolar Neurons: A single process that bifurcates, primarily sensory in function.

• Anaxonic Neurons: Lack axons, primarily found in the brain, involved in local circuits.

Glial Cells

• Types of Glial Cells in CNS:

  • Astrocytes: Support neurons, contribute to blood-brain barrier, maintain ion balance, and help recycle neurotransmitters.

  • Ependymal Cells: Produce and circulate cerebrospinal fluid (CSF).

  • Microglia: Immune function, cleaning up debris and responding to injury.

  • Oligodendrocytes: Myelinate axons in the CNS.

• Types of Glial Cells in PNS:

  • Satellite Cells: Provide structural support and help regulate ion concentrations around neuron cell bodies.

  • Neurolemmocytes (Schwann Cells): Myelinate axons in PNS; assist in repair of damaged nerves.

Myelination and Nerve Conduction

• Myelin Sheath: Insulates axons, speeds up conduction of action potentials (up to 30 times faster).

• Saltatory Conduction: Action potentials jump between the nodes of Ranvier on myelinated axons, allowing faster signal propagation.

• Continuous Conduction: Occurs in unmyelinated axons where action potentials must traverse the entire membrane.

Regeneration of Neurons

• CNS Neurons: Limited regeneration. Damaged cell bodies do not recover.

• PNS Neurons: Axons may regenerate if the cell body remains intact; the surrounding neurolemmocytes guide regrowth.

Conclusion

• Summary: Understanding the organization and functionality of the nervous system, including neuron types, glial cells, and the implications of myelination, is crucial for the study of biological systems.