NEUROANATOMY

• The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS)
• The CNS includes the brain and spinal cord
• The spinal cord:

  • Centers where correlation and integration of nervous information occurs
  • Covered with meninges
  • Suspended in cerebrospinal fluid (CSF)
  • Protected by the skull and vertebral column
• The brain:

  • Composed of neurons and supported by neuroglia (glial cells)
  • Gray matter consists of nerve cells embedded in neuroglia
  • White matter consists of nerve fibers embedded in neuroglia
  • Tracts are bundles of nerve fibers found in the CNS
• The CNS lies in the cranial cavity and is surrounded by three meninges
• The brain is divided into primary vesicles, divisions, subdivisions, and adult structures
• The hindbrain consists of the medulla oblongata, pons, and cerebellum
• Medulla oblongata:

  • Conical in shape
  • Connects the pons superiorly and spinal cord inferiorly
  • Contains many nuclei that serve as conduits for ascending and descending tracts
• Pons:

  • Situated at the anterior surface of the cerebellum
  • Contains transverse fibers on its anterior aspect that connects the two cerebellar hemispheres
  • Contains many nuclei and descending nerve fibers
• Cerebellum:

  • Lies within the posterior cranial fossa of the skull
  • Connected to the brainstem via three peduncles
  • Has two laterally placed hemispheres connected by the vermis
• The midbrain connects the forebrain and hindbrain and contains the cerebral aqueduct of Sylvius
• The diencephalon consists of the dorsal thalamus and ventral hypothalamus
• The cerebrum is the largest part of the brain and consists of two cerebral hemispheres connected by the corpus callosum
• The cerebrum has lobes including the frontal, parietal, temporal, and occipital lobes
• The peripheral nervous system (PNS) consists of neurons that transmit signals between the CNS and receptors and effectors in the body
• There are sensory and autonomic ganglia in the PNS
• Nerve fibers in the PNS are named axons or dendrites of nerve cells
• In the PNS, myelin forms when a Schwann cell wraps its membrane around an axon up to 100 times
• Different types of nerve fibers in the PNS have varying functions and conduction velocities
• Clinically, tetanus toxin causes spastic paralysis by blocking presynaptic transmitter release in the CNS, while botulism causes flaccid paralysis by blocking the release of acetylcholine at the neuromuscular junction
• Myasthenia Gravis involves autoimmune destruction of acetylcholine receptors in the postsynaptic nerve ending, leading to muscle weakness
• In multicellular organisms, the distance for substances to enter cells is larger due to a higher surface area to volume ratio
• Multicellular organisms require specialised exchange surfaces for efficient gas exchange of carbon dioxide and oxygen
• Myasthenia Gravis:

  • Involves a lack of binding sites of acetylcholine leading to muscle weakness due to membrane depolarization failure
• Lambert Eaton Syndrome:

  • Involves autoimmune destruction of voltage-gated calcium channels in the pre-synaptic membrane
  • Leads to failure of fusion of synaptic vesicles with the pre-synaptic membrane, resulting in no acetylcholine release and muscle weakness
• Pyramidal Tract/Corticospinal Tract:

  • Originates from different areas of the brain
  • Descending fibers pass through the posterior limb of the internal capsule
  • Fibers decussate at the level of the pyramids in the medulla oblongata
• Final Common Pathways:

  • Control posture and movement
  • Output from CNS to effector muscles involves alpha motor neurons
  • Acetylcholine is the only neurotransmitter in the final common pathway
• Motor Unit:

  • Consists of a lower motor neuron and the muscle fibers under its control
  • Fasciculation and fibrillation are characteristics of motor unit activity
• Differentiating UMN vs LMN Lesions:

  • Features of upper motor neuron lesions and lower motor neuron lesions
• Spinal Cord Injuries:

  • Degree of injury at different vertebral levels
  • Partial or complete loss of function due to spinal cord injury
• Spinal Nerve Injuries:

  • Differentiating features of anterior horn cell, peripheral nerve, neuromuscular junction, and muscle involvement
• Lumbar Puncture:

  • Purpose of withdrawing CSF for examination or injecting drugs
  • Structures the needle passes through during lumbar puncture
• Head Injuries:

  • Effects of blows to the head, skull fractures, and brain injuries
• Intracranial Hemorrhages:

  • Types of intracranial hemorrhages and their causes
• Shaken Baby Syndrome:

  • Common cause of traumatic death in infancy
  • Symptoms and detection of subdural or subarachnoid hemorrhages
• Space Occupying Lesion within the Skull:

  • Includes tumors, hematomas, and abscesses
  • Impact of an expanding lesion on cerebrospinal fluid and the brain
• Diagnostic Imaging:

  • Computed Tomography, Magnetic Resonance Imaging, and Positron Emission Tomography for brain imaging
• Introduction and Organization of the Nervous System
• The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS)
• The CNS consists of the brain and spinal cord