Nervous System Overview Quiz

Nervous System Overview

• Composed of two main parts:

  • Central Nervous System (CNS): Brain and spinal cord
  • Peripheral Nervous System (PNS): Everything else, including nerves and ganglia

• PNS subdivided into:

  • Sensory (afferent) neurons: Carry information toward the CNS
  • Motor (efferent) neurons: Carry information from the CNS
    • Somatic motor division: Controls skeletal muscles
    • Autonomic division: Controls smooth and cardiac muscles, glands (exocrine and some endocrine), and some adipose tissue (visceral nervous system)

Neurons

• Carry electrical signals

  • Dendrites: Receive incoming signals
  • Axon: Carries outgoing information
  • Cell body: Contains the nucleus and other organelles, essential for protein synthesis, but outside the direct path of signals

• Types of neurons;

  • Peripheral sensory neurons: Pseudounipolar, with cell bodies near the CNS and long processes extending to receptors
  • Interneurons: Located entirely within the CNS, often with complex branching to communicate with other neurons

• Axon hillock: Specialized region of the cell body where the axon originates

• Axon Terminal: Contains mitochondria and vesicles with neurocrine molecules, transmits outgoing electrical signals to the end of the axon.

• Synapse: Region where an axon terminal meets its target cell

  • Presynaptic cell: Neuron delivering the signal
  • Postsynaptic cell: Cell receiving the signal
  • Synaptic cleft: The narrow space between the two cells

Glial Cells

• Support and protect neurons
  • PNS: Schwann cells and satellite cells
  • CNS: Oligodendrocytes, microglia, astrocytes, and ependymal cells
  • Schwann cells: Form myelin sheaths around axons in the PNS, speeding signal transmission, have Nodes of Ranvier
  • Satellite cells: Non-myelinating, forming capsules around nerve cell bodies
  • Oligodendrocytes: Form myelin sheaths around axons in the CNS
  • Astrocytes: Abundant in the brain, regulate extracellular environment (e.g., K+ uptake), part of the blood-brain barrier
  • Microglia: Specialized immune cells; remove damaged cells and foreign invaders
  • Ependymal cells: Form epithelial layer (ependyma) separating fluid compartments

Action Potential Generation

• Main steps:
  • Graded depolarization brings membrane to threshold
  • Sodium channel activation
  • Sodium influx: Further depolarization
  • Sodium channel inactivation
  • Potassium channels open: Repolarization
  • Temporary hyperpolarization
  • Sodium channels return to normal
• Types of ion channels (mechanically gated, chemically gated, voltage-gated)

Spinal Cord

• Integrating center for simple reflexes
• Major pathway for information between brain and body (skin, joints, muscles)
  • Dorsal roots: Sensory input
  • Dorsal root ganglia: Contain sensory neuron cell bodies
  • Ventral root: Motor output
  • White matter: Tracts of axons (ascending – sensory; descending – motor; propriospinal – within cord)

Brain Stem

• Includes midbrain, pons, and medulla oblongata
• Medulla oblongata: Controls involuntary functions (e.g., breathing, blood pressure)
• Pons: Relay station for cerebellum and cerebrum, breathing coordination
• Midbrain: Control of eye movement, auditory and visual reflexes

Cerebellum

• "Little brain"
• Coordinates movement

Diencephalon

• Contains centers for homeostasis
  • Thalamus: Sensory relay station, integrates information
  • Hypothalamus: Maintains homeostasis, regulates body temperature, osmolarity, reproductive functions, hunger & thirst, interacts with the limbic system, cardiovascular function, hormones, etc

Brain Functions

• Receives, integrates, processes sensory information to create a response; includes sensory, cognitive, behavioural state systems.

Pathophysiology

• Guillain-Barré syndrome: Rare paralytic condition
• Alzheimer's disease: Neurodegenerative disorder
• Parkinson's disease: Movement disorder due to dopamine neuron degeneration
• Multiple sclerosis (MS): Autoimmune disease damaging myelin sheath.