Neuroglia and Nervous System Physiology

Neurons and Neuroglia

  • Neuron Structure:

    • Consists of three main parts:
    • Dendrites: Short branches that collect information and send it to the soma.
    • Soma (Cell Body): Responsible for integrating information.
    • Axon: Long extension that can both collect information and respond to stimuli.

  • Neuroglia:

    • Support cells for neurons in the nervous system.
    • Approximately 50 neuroglial cells for every neuron, known to aid but not directly assist in neuronal function.

Nervous System Physiology

  • Functions:

    1. Sensory: Collection of information via receptors (e.g. photoreceptors in the eyes).
    2. Integration: Decision-making process in the CNS regarding responses to collected information.
    3. Motor Response: Actions initiated based on CNS decisions.

  • Function Definitions:

    • Physiology: Refers to functions.
    • Afferent: Sensory inputs that carry information to the CNS.
    • Efferent: Motor outputs that carry responses from the CNS.

Nervous System Divisions

  • Central Nervous System (CNS):

    • Comprises the brain and spinal cord.
    • Not including peripheral nerves.

  • Peripheral Nervous System (PNS):

    • Consists of all nerves outside the CNS, totaling 86.

  • Additional Nervous Systems:

    • Enteric Nervous System
    • Autonomic Nervous System (divided into sympathetic and parasympathetic systems).

Sympathetic vs. Parasympathetic Systems

  • Sympathetic Nervous System: Activates fight or flight responses, prepares body for action (e.g., increases heart rate, adrenaline rush).
  • Parasympathetic Nervous System: Reverses sympathetic actions, responsible for rest and digest (e.g., reduces heart rate, increases digestion).

Neuroanatomy

  • Neuroglial Cells in CNS:
    1. Astrocytes: Form blood-brain barrier (BBB), regulate nutrient supply and waste removal.
    2. Microglia: Act as immune cells in the brain, scavenging debris and pathogens.
    3. Ependymal Cells: Produce cerebrospinal fluid (CSF).
    4. Oligodendrocytes: Form myelin sheath around axons, increasing speed of impulse transmission (known as white matter).

Neuroglial Cells in PNS

  • Satellite Cells: Maintain a stable environment for neurons, provide nutrients and remove waste.
  • Schwann Cells: Form the myelin sheath for peripheral nerves (equivalent to oligodendrocytes in CNS).

Axonal Transport and Impulse Transmission

  • Myelination: The process of wrapping axons with myelin to insulate them, allowing for faster signal transmission.
    • Multiple Sclerosis (MS): A condition characterized by the loss of myelin in the CNS, leading to impaired nerve function due to disrupted signals.

Reflex Arc

  • Reflex Actions: Involuntary responses that occur without direct input from the brain, involving only the spinal cord for quick reactions (e.g., hitting brakes when a person runs in front of you).
  • Longer Processing: Involves carrying signals to the brain for conscious response, which takes more time than reflex actions.

Cranial and Spinal Nerves

  • Cranial Nerves: 24 total, associated with various functions, including sensory, motor, and mixed functions.
  • Spinal Nerves: 62 total, divided into 31 pairs, facilitating communication between the spinal cord and body segments.