Nervous System Detailed Notes

Central Nervous System (CNS)

• Composed of the brain and spinal cord.

Brain

• Brain Stem:
  • Medulla Oblongata
  • Pons
  • Midbrain
• Cerebellum
• Diencephalon
• Cerebrum:
  • Gyri and Sulci
  • Corpus Callosum (a deep fissure)

Peripheral Nervous System (PNS)

• Somatic Nervous System (SNS)
• Autonomic Nervous System (ANS)

Cells of the Nervous System

• Neurons
  • Different parts of the neuron
  • Different types of neurons
• Glia Cells
  • Central Glia
  • Peripheral Glia

Nerves and Nerve Tracks

• Nerves: Bundles of axons
• Coverings of Nerves:
  • Epineurium
  • Perineurium

Nerve Signals

• Receptors

Parkinson's Disease (PD)

Autonomic Nervous System (ANS)

• Conduction Pathways
• Neurotransmitters
  • Cholinergic Fibers: Use acetylcholine
  • Adrenergic Fibers: Use norepinephrine
    • Different effects due to different neurotransmitters

Peripheral Nervous System (PNS) Conditions

• Herpes Zoster (Shingles)
• Bell Palsy: Affects cranial nerve

Tumors

• Cancerous Tumors in the Brain:
  • Generally metastatic (originate elsewhere)
  • 90% of brain tumors are non-cancerous (benign)
• Benign Tumors:
  • Common in glial cells (gliomas)

Objectives: Central Nervous System (CNS)

• Brain and Spinal Cord
• Focus of neurosurgery
• Peripheral Nervous System (PNS)
  • Cranial nerves and spinal nerves
  • Autonomic Nervous System: Parasympathetic and sympathetic nervous system

Cells of the Nervous System: Neurons

• Neurons conduct neurotransmitters.
• Cell Body:
  • Main part of the neuron
• Dendrites:
  • Branching projections
  • Conduct impulses toward the cell body
• Axon:
  • Elongated projection
  • Conducts impulses away from the cell body

Types of Neurons

• Sensory (Afferent) Neurons:
  • Conduct impulses to the spinal cord and brain
  • Located in the periphery and senses (e.g., eyes, nose, taste)
• Motor (Efferent) Neurons:
  • Conduct impulses away from the brain and spinal cord to muscles and glands
  • Affect muscles (movement) or glands (secretion)
• Interneurons (Connecting Neurons):
  • Conduct impulses from sensory neurons to motor neurons
  • Bypass the brain and spinal cord for quick reactions (e.g., touching something hot)

Glia (Neuroglia) Cells

• Support cells:
  • Bring nervous tissue together structurally and functionally
• Central Nervous System (CNS) Glia:
  • Astrocytes: Star-shaped cells
    • Anchor blood vessels
    • Form the blood-brain barrier (protects brain tissue from chemicals in the blood)
  • Microglia: Small cells in inflamed brain tissue
    • Carry on phagocytosis (remove dead brain cells)
    • Immune system cells of the brain
  • Oligodendrocytes:
    • Form myelin sheaths on axons in the CNS
    • Insulators that speed up impulse conduction
• Peripheral Nervous System (PNS) Glia:
  • Schwann Cells:
    • Form myelin sheaths in the PNS
  • Myelinated Fibers:
    • Neurons with myelin-wrapped axons
    • Nodes of Ranvier: Gaps between adjacent Schwann cells
  • Neurolemma: Another protective covering for the axon

Disorders of Neural Tissue

• Multiple Sclerosis (MS):
  • Autoimmune condition (body attacks itself)
  • Characterized by myelin loss and destruction
  • Results in conduction impairments (weakness, incoordination, visual impairment, speech disturbances)
  • More common in genetic females between 20 and 40
  • Early detection improves outcomes
• Neuromas:
  • General term for any nervous system tumor
  • Most are gliomas (tumors from glia cells)
  • Neurofibromatosis:
    • Inherited disease with numerous benign neuromas
    • Can cause large, disfiguring fibrous tumors
• Malignant Tumors:
  • Most are secondary tumors resulting from metastasis (cancer cells from other organs)

Nerves and Nerve Tracts

• Nerve: Bundle of peripheral axons
• Tract: Bundle of central axons
• Fascicle: Group of wrapped axons
• White Matter:
  • Brain or spinal cord tissue
  • Composed primarily of myelinated axons (giving it a white look)
• Gray Matter:
  • Brain or spinal cord tissue
  • Composed primarily of cell bodies and unmyelinated fibers (darker look)

Nerve Impulses (Action Potential)

• Rapid communication between cells
• Reflex Arc:
  • Basic type of neuron pathway
  • One-way streets
• Two-Neuron Arc:
  • Simplest reflex arc (one sensory and one motor neuron)
• Ganglion:
  • Group of neuron cell bodies in the peripheral nervous system
  • Can act as a hub to send signals without brain involvement

Neuron at Rest

• Excess positively charged sodium ions (Na^+) outside the neuron's membrane.
• Stimulus opens sodium channels.
• Sodium (Na^+) enters the axon.
• If threshold is met, it triggers depolarization, sends signal.
• After firing, it goes into repolarization.
• During repolarization, the cells cannot be stimulated.

Salutatory Conduction

• How the impulses travel faster in the myelinated axons (impulses jump around the myelin).

Synapses

• Place where impulses are transmitted from one neuron to another.
• Sending neuron and receiving neuron.
• Three structures within:
  • Synaptic knob (sending end of the axon)
  • Synaptic cleft (gap between the sending and receiving axon)
  • Plasma membrane (postsynaptic neuron, receiving the signal)

Neurotransmitters

• Chemical compound needed to transfer impulses.
• Released from vesicles into synaptic cleft.
• Taken up by the receiving end.
• Types:
  • Acetylcholine: Released in the spinal cord and at neuromuscular junctions.
  • Norepinephrine, Dopamine, Serotonin (Amines):
    • Play a role in sleep, motor function, mood and pleasure.
  • Endorphins and Enkephalins:
    • Released at various spinal cord and brain synapses in the pain conduction pathway.
    • Morphine-like; inhibit that pain conduction impulse.

Parkinson’s Disease

• Chronic progressive nervous disorder.
• Caused by a deficiency of dopamine in certain parts of the brain.
• Disorder causes:
  • Rigidity
  • Trembling of the head and extremities
  • Forward tilt of trunk
  • Shuffling manner of walking
• Trembling resembles a tick
• Treatment:
  • Cocktail of medication geared towards that particular patint because no treatment is the same
  • Potentially neuroligcal procedures of re[lacement therapy will fix dopamine levels.