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.