Choroid Plexus and Cerebral Hemispheres

Neuroglia

• Glial cells do not transmit nerve impulses but aid in neuronal function.
• Neuroglia retain the ability to divide throughout life; most brain tumors stem from these cells (gliomas).
• Supporting cells in the Central Nervous System (CNS) include:
  • Astrocytes: Anchor neurons to blood capillaries, providing structural support.
  • Microglia: Act as scavengers that remove debris such as dead cells and bacteria.
  • Ependymal Cells: Circulate cerebrospinal fluid (CSF) and form a protective cushion around the CNS.
  • Oligodendrocytes: Produce the myelin sheath that insulates neuronal axons.
• Supporting cells in the Peripheral Nervous System (PNS):
  • Schwann Cells: Generate myelin sheaths around nerve fibers.
  • Satellite Cells: Provide protection and cushioning for neuronal cell bodies.

Physiology of Nerve Impulses

• Neurons exhibit two primary functional properties:
  • Irritability: Ability to respond to stimuli and convert them into nerve impulses.
  • Conductivity: Capability to transmit impulses to neurons, muscles, or glands.
• Saltatory Conduction: Fast transmission in myelinated fibers where impulses jump between nodes of Ranvier due to insulation from myelin.
• Impairments of Conduction: Influenced by alcohol, sedatives, anesthetics, cold temperatures, and sustained pressure.

Reflex Arc

• Reflex: An involuntary response to stimuli.
  • Somatic Reflex: Involves skeletal muscles.
  • Visceral Reflex: Involves smooth muscle, cardiac muscle, or glands.
  • Spinal Reflex: Conducted by spinal cord neurons without immediate brain involvement.

Anatomy of the Spinal Cord

• Comprises 31 pairs of spinal nerves, bridging the brain and most body parts.
• Functions:
  • Connects the brain with the body.
  • Facilitates spinal reflex actions (both somatic and visceral).
• It extends from the foramen magnum to the first lumbar vertebra, approximately 47 cm long.
• Contains significant anatomical features, including:
  • Cervical and Lumbosacral enlargements: Indicate regions of increased neural processing.
• Meninges: Three protective layers surrounding the spinal cord:
  • Dura Mater: Tough outer layer.
  • Arachnoid: Middle layer that extends to S2 vertebra.
  • Pia Mater: Innermost vascular layer.
• Spaces:
  • Epidural Space: Contains blood vessels and fat.
  • Subdural Space: Minimal space between dura and arachnoid, no cerebrospinal fluid (CSF).
  • Subarachnoid Space: Contains CSF and blood vessels.

Cerebrospinal Fluid (CSF)

• A clear, watery fluid derived from blood, produced primarily in the choroid plexus of the brain.
• Provides cushioning and nutrient supply for the brain and spinal cord.

Internal Structure of the Spinal Cord

• Central Canal: Contains CSF.
• Gray Matter: Dark, H-shaped region including dorsal and ventral horns.
• White Matter: Composed of myelinated fiber tracts, categorized into:
  • Posterior Column: Carries sensory input to the brain.
  • Anterior and Lateral Columns: Responsible for motor output.

The Cerebral Hemispheres

• Gyri: Elevated ridges of tissue.
• Sulci: Shallow grooves between gyri; larger grooves are termed fissures.
• Critical areas:
  • Somatic Sensory Area: Located in the parietal lobe, processes touch, pain, and temperature sensations.
  • Primary Motor Area: Located in the frontal lobe, responsible for voluntary movement.
  • Broca's Area: Associated with speech production.

Structures of the Brainstem

• Midbrain: Controls motor movement and processes auditory and visual information; consists of:
  • Cerebral Aqueduct: Connects third and fourth ventricles.
  • Cerebral Peduncles: Transmit impulses.
  • Corpora Quadrigemina: Involved in reflex actions for vision and hearing.
• Pons: Contains nuclei essential for breathing regulation and neurological pathways.
• Medulla Oblongata: Regulates vital autonomic functions and contains many neural tracts.

Nerves

• Mixed Nerves: Carry both sensory and motor fibers.
• Afferent Nerves: Sensory nerves transmitting signals to the CNS.
• Efferent Nerves: Motor nerves transmitting information from the CNS.

Autonomic Nervous System (ANS)

• A subdivision of the PNS that automates bodily functions: heart rate, digestion, and respiratory rate.
• Comprises two motor neurons:
  • Preganglionic Neuron: Located in the CNS.
  • Postganglionic Neuron: Resides in ganglia outside the CNS.
• Has two divisions:
  • Sympathetic Division: Mobilizes the body during stress ("fight or flight").
  • Parasympathetic Division: Promotes relaxation and energy conservation ("rest and digest").

Functionality of ANS

• Organs receive input from both divisions and produce antagonistic effects.
• Neurotransmitters:
  • Parasympathetic fibers release acetylcholine (cholinergic fibers).
  • Sympathetic fibers release norepinephrine (adrenergic fibers).