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• Subarachnoid space


  Space filled with cerebrospinal fluid, connected to the interior of the brain through the ventricular system
• The subarachnoid space and ventricular system is where cerebrospinal fluid is produced and circulates
• Conditions capable of producing motor speech disorders (MSDs) involving the meninges and meningeal spaces

  • Infection
  • Venous vascular disorders
  • Hydrocephalus
  • Trauma with associated hemorrhage and edema
• Major anatomic levels of the nervous system

  Relate to the boundaries of the skull and spinal column, demarcated by the meninges, ventricular system, and vascular system

  
• The major anatomic levels and their skeletal, meningeal, ventricular, and vascular characteristics, as well as their relationship to the major types of MSDs, are summarized in Table 2-1
• Supratentorial level


  Located above the tentorium cerebelli, includes the paired frontal, temporal, parietal, and occipital lobes of the cerebral hemispheres, basal ganglia, thalamus, hypothalamus, and cranial nerves I and II

  
• Posterior fossa level


  Includes the brainstem (pons, medulla, and midbrain), the cerebellum, and the origins of cranial nerves III through XII

  
• Tectum


  Area of the posterior fossa dorsal to the aqueduct of Sylvius, includes the inferior and superior colliculi
• Tegmentum


  Area of the posterior fossa ventral to the aqueduct of Sylvius and fourth ventricle, contains white matter pathways and many nuclei, including the reticular formation
• Cerebellum


  Lies dorsal to the fourth ventricle, pons, and medulla, comprises a right and left hemisphere and a midline vermis
• Cranial nerves involved in speech production

  • III (oculomotor)
  • IV (trochlear)
  • V (trigeminal)
  • VII (facial)
  • IX (glossopharyngeal)
  • X (vagus)
  • XI (accessory)
  • XII (hypoglossal)
• Spinal level


  The adult spinal cord begins at the foramen magnum, surrounded by the bony vertebral column, 31 pairs of spinal nerves attached via dorsal (sensory) and ventral (motor) nerve roots

  
• Peripheral level


  Consists of the cranial and spinal nerves, most cranial nerves originate in the brainstem and exit the skull, spinal nerves emerge from the vertebral column

  
• Major functional longitudinal systems of the nervous system

  • Internal regulation (visceral) system
  • Cerebrospinal fluid (ventricular) system
  • Vascular system
  • Consciousness system
  • Sensory system
  • Motor system
• Internal regulation (visceral) system


  Includes the hypothalamus, limbic lobe, reticular formation, portions of cranial nerves, pathways in the brainstem and spinal cord, ganglia, receptors, and effectors, regulates visceral glands and organs
• Cerebrospinal fluid (ventricular) system


  Ventricles containing cerebrospinal fluid produced by choroid plexuses, connected to the subarachnoid space, cushions the CNS and helps maintain a stable environment
• Vascular system


  Provides oxygen and nutrients, removes metabolic wastes, major arteries include carotid and vertebrobasilar systems, vascular disturbances can lead to motor speech disorders
• The consciousness system is crucial for maintaining wakefulness, consciousness, awareness, and attention, malfunctions can affect cognition and motor actions including speech
• Sensory system


  Includes peripheral receptors, afferent nerves, ascending pathways, thalamus, and sensory cortex, responsible for processing sensory information
• Motor system


  Responsible for all voluntary motor activity, includes efferent connections of the cortex, basal ganglia, cerebellum, descending pathways, efferent nerves, and striated muscle, essential for reflexes, muscle tone, posture, and voluntary movement including speech
• Lesions in non-motor areas can indirectly affect speech through their effects on the motor system
• Structural elements of the nervous system

  • Neurons
  • Glial cells

  
• Neuron


  The most important cellular element, responsible for receiving, transmitting, and processing information, contains a cell body, dendrites, and an axon
• The neuron is the most important cellular element of the nervous system because its electrochemical activities drive the receipt, transmission, and processing of information
• Neurons in humans number on the order of 100 billion
• Neurons


  • They contain a cell body, dendrites, and an axon
  • The cell body is the central processing unit and is responsible for neuronal metabolic functions
  • Dendrites are usually numerous but short, with many branches, and are responsible for gathering information transmitted from surrounding neurons
  • Neurons have only one axon that may extend from the cell body for a few millimeters or for several feet, its diameter generally varying with its length
• Neuron-to-neuron communication


  1. Dendrites receive information

  2. Axon transmits information to other neurons

  3. Action potential moves through saltatory conduction
• Synapse


  Regions where most communication among neurons, or between neurons and muscles, takes place

  
• At the tip of the axon are tiny synaptic vesicles containing a chemical neurotransmitter that carries the axon's signal to neurotransmitter receptors that mediate excitatory, inhibitory, or modulatory effects on the receiving cell
• The message carried by a single axon to another neuron is either facilitates or inhibits the neuron receiving it from firing a message of its own, and the rate at which it is sent is the only thing that varies
• In the human nervous system, axons branch repeatedly, forming anywhere from 1,000 to 10,000 synapses, and their cell bodies and dendrites receive information from on the order of 1,000 other neurons, with the number of synapses in the brain may be on the order of 100 trillion

  
• Neurotransmitters


  • Glutamate (primary excitatory)
  • Gamma-aminobutyric acid (GABA) (primary inhibitory)
  • Dopamine
  • Acetylcholine
• Glutamate


  The primary excitatory neurotransmitter for all CNS neurons
• GABA


  A primary inhibitory neurotransmitter in the mature CNS that plays a major role in the regulation of muscle tone
• Dopamine


  A crucial neurotransmitter that originates in the substantia nigra and ventral tegmental area in the midbrain and projects to many areas of the brain, playing a role in movement, motivation and reward, cognition and learning, attention, mood, and sleep
• Acetylcholine (ACh)


  The only neurotransmitter involved in the PNS control of skeletal muscle functions, acting quickly and having excitatory effects
• Malfunction of the mechanisms that turn off neurotransmitters can be a source of neurologic disease
• Abnormalities of neurochemical systems are associated with numerous neurologic and psychiatric disorders, and can lead to motor speech and other neurologic communication disorders
• Oligodendroglia and Schwann cells


  • They form the insulation, or myelin, that surrounds axons in the CNS and PNS
  • Schwann cells in the PNS form myelin, which wraps around fibers in most peripheral nerves, with small gaps between each myelinated segment known as nodes of Ranvier
  • Oligodendroglia cells are the source of myelin in the CNS

  
• Astrocytes


  • Star-shaped cells widely distributed in the CNS, lying in proximity to both neurons and capillaries, that assist neuronal migration during development, help regulate neuronal metabolism, the chemical microenvironment, and synaptic transmission, and contribute to mechanisms of repair in response to injury
  • They are an important part of the blood-brain barrier