Pathophysiology - Neuro

Overview of the Nervous System

  • Central Nervous System (CNS)

    • Comprises the brain and spinal cord.

    • Encased in protective structures:

      • Skull for the brain.

      • Vertebrae surrounding the spinal cord.

  • Peripheral Nervous System (PNS)

    • Composed of cranial nerves (12) and spinal nerves.

    • Includes pathways leading to skeletal muscles and organs.

    • Afferent Pathway: Ascending, sensory information to the CNS.

    • Efferent Pathway: Descending, motor commands from the CNS.

Divisions of the Peripheral Nervous System

  • Somatic Nervous System

    • Controls voluntary movements of skeletal muscles.

    • Involved with conscious control of bodily movements.

  • Autonomic Nervous System (ANS)

    • Functions automatically without conscious thought.

    • Regulates involuntary bodily functions including heartbeat, digestion, and respiratory rate.

    • Divided into:

      • Sympathetic Nervous System: Prepares the body for stress-related activities (fight or flight).

      • Parasympathetic Nervous System: Controls rest and digest functions.

Neurons in the Nervous System

  • Neurons: Primary functional units of the nervous system.

    • Types of Neurons:

      • Sensory Neurons: Afferent; transmit impulses from periphery to CNS.

      • Associational (Interneurons): Located within CNS; transmits impulses between neurons.

      • Motor Neurons: Efferent; transmit impulses from CNS to effectors (muscles/organs).

  • Neuromuscular Junction: Connection between motor neurons and skeletal muscles, essential for movement control.

  • Nerve Impulses:

    • Generated by neurons through electrical and chemical signaling.

    • Impulses induce neurotransmitter release to influence adjacent neurons.

  • Synapses: Junctions between neurons where impulse transmission occurs.

    • Presynaptic Neurons: Neurons sending the impulse.

    • Postsynaptic Neurons: Neurons receiving the impulse.

  • Neurotransmitters:

    • Chemical messengers in synapses.

    • Can be excitatory (stimulate response) or inhibitory (diminish response).

Protection of the Central Nervous System

  • Cranial Vault: Encloses the brain, composed of the skull and meninges.

    • Cerebrospinal Fluid (CSF): Cushions the CNS, providing further protection.

  • Vertebral Column: Composed of 33 vertebrae, protecting the spinal cord.

    • Injury location determines loss of function/movement below the injury point.

Blood Supply to the Brain

  • Cerebral Blood Flow: The brain receives ~20% of the body's cardiac output (~800-1000 mL/min).

    • Oxygen supplied through blood is essential for brain function.

    • Carbon Dioxide: A key regulator for blood flow; acts as a vasodilator.

  • Blood Supply Pathways:

    • Internal carotid and vertebral arteries provide primary blood flow.

  • Circle of Willis:

    • An arterial circle that allows alternative routes for blood supply if blockage occurs in one artery.

  • Venous Outflow:

    • Superficial and deep cerebral veins drain blood away from the brain.

    • Dural sinuses and internal jugular veins eventually connect to inferior vena cava.

  • Implications for Head Injuries:

    • Understanding venous drainage is crucial; blockage increases intracranial pressure.