Neurological System Overview

  • Specialists in Neurological Conditions

    • Neurologist vs. Neurosurgeon:
    • Neurologists diagnose and manage non-surgical neurological disorders.
    • Neurosurgeons perform surgical interventions.
    • Example: A migraine is treated by a neurologist, not a neurosurgeon.

  • Functions of the Nervous System:

    • Sensory Function:
    • Responsible for receiving sensory information.
    • Associated with afferent pathways (inbound to the brain).
    • Motor Function:
    • Relates to body actions and movements.
    • Associated with efferent pathways (outbound from the brain).
    • Integrative Function:
    • Involves interneurons that process and relay messages between sensory and motor pathways.

  • Parts of the Nervous System:

    • Central Nervous System (CNS):
    • Comprises the brain and spinal cord.
    • Peripheral Nervous System (PNS):
    • Encompasses all other neural tissue.
    • Contains mixed nerves (both sensory and motor fibers).
    • Cranial and Spinal Nerves:
    • Both are parts of the PNS despite emerging from the CNS.

  • Subdivisions of the PNS:

    • Somatic Nervous System:
    • Controls voluntary movements and skeletal muscles.
    • Autonomic Nervous System:
    • Regulates involuntary body functions.
    • Subdivided into:
      • Sympathetic: Emergency response (fight or flight).
      • Parasympathetic: Rest and digest responses.
      • Enteric: Governs the gastrointestinal system.

  • Neurons and Neuroglia:

    • Neuron: Main signaling cell.
    • Neuron Structure:
    • Soma (cell body): Contains nucleus.
    • Dendrites: Receives input.
    • Axon: Conducts signals away from the cell body.
    • Neuroglia: Support cells for neurons.
    • Types include oligodendrocytes (CNS), Schwann cells (PNS), microglia, and astrocytes.
    • Oligodendrocytes myelinate CNS axons, while Schwann cells do so in the PNS.

  • Myelination and Signal Propagation:

    • Myelin Sheath:
    • Provides insulation and increases signal conduction speed.
    • Nodes of Ranvier allow for saltatory conduction (faster transmission).
    • Neuroplasticity: Ability of the nervous system to adapt through structural changes.

  • Neuronal Signaling:

    • Action Potentials:
    • Must reach a certain threshold (typically around −55-55mV) for signals to propagate.
    • Depolarization and repolarization phases involved, with sodium channels opening to cause depolarization primarily, followed by potassium channels to repolarize the neuron.
    • Graded Potentials:
    • Local changes in membrane potential that may or may not lead to an action potential (if they do not reach threshold).

  • Types of Ion Channels:

    • Leakage Channels: Allow ions to pass freely without energy.
    • Ligand-Gated Channels: Open in response to specific neurotransmitter binding.
    • Voltage-Gated Channels: Open in response to changes in membrane potential.
    • Mechanically Gated Channels: Respond to physical deformation of the receptor.

  • Synaptic Transmission:

    • Chemical synapses use neurotransmitters like acetylcholine.
    • Excitatory vs. Inhibitory:
    • Excitatory neurotransmitters (e.g., glutamate) promote action potentials.
    • Inhibitory neurotransmitters (e.g., GABA) prevent action potentials.
    • Summation:
    • Temporal (timing) and spatial (different locations) summation dictate whether an action potential occurs based on inputs from multiple signals.

  • Major Neurotransmitters:

    • Acetylcholine: Excitatory in muscle contractions, inhibitory elsewhere.
    • Glutamate: Main excitatory neurotransmitter.
    • GABA: Main inhibitory neurotransmitter.
    • Norepinephrine and Epinephrine: Neurotransmitters involved in stress response.
    • Dopamine: Associated with pleasure and reward.

  • Medications and Neurotransmission:

    • Can affect neurotransmitters through enhancing or blocking their release, synthesis, degradation, and receptor activation.

  • Healing and Nerve Damage:

    • CNS cannot repair itself efficiently after damage, while PNS has a limited ability to repair damaged axons.

  • General Reminder:

    • Care and caution needed to avoid spinal injuries from accidents.