Central nervous system | Neuromuscular system

Upper motor neuron units

Definitions

Upper motor neuron units: A network of neurons in which cell bodies originate in the cerebral cortex (brain), brainstem, and spinal cord. Characteristics of disease processes that are upper motor neuron units are weakness, hyperreflexia, and hypertonia.

Anatomy of the brain

The brain is divided into two (2) hemispheres, divided externally by the longitudinal fissure and internally by the corpus callosum
- Right hemisphere:
  - Spatial awareness
  - Emotional processing
  - Facial recognition
  - Creativity
  - Abstract thought
  - Controls the left side of the body
- Left hemisphere
  - Language
  - Logic and reasoning
  - Analytical thinking
  - Controls the right side of the body

The brain is divided into six (6) lobes with distinct characteristics that work collectively to assist function:
- Frontal lobe:
  - Executive function
  - Voluntary movement
  - Problem solving
  - Learning
  - Behavior
  - Impulse control
  - Personality
  - Social behavior
  - Expressive language (Broca’s area)
- Parietal lobe:
  - Awareness of somatic sense — touch, pain, temperature, pressure, vibration
  - Processing somatic sensation- analyzing, recognizing, and developing of memory of somatic sense
  - Spatial and body awareness
  - Coordination of visual, auditory, and somatosensory stimuli
- Temporal lobe:
  - Hearing
  - Receptive language (Wernicke’s area)
  - Memory
    - Declarative: memory regarding names of people, places, or things
    - Procedural: memory of how to perform activities such as brushing teeth, putting on makeup, etc.
- Occipital lobe:
  - Awareness of visual stimuli
  - Processing of visual stimuli
- Cerebellum:
  - Motor learning
  - Coordinate movement
  - Balance and equilibrium
  - Proprioception sense
  - Maintain posture
- Brainstem:
  - Ascending and descending tracts are located in the brainstem
  - Heart rate and respiration rate
  - Sleep and wake cycles
  - Digestion
  - Body temperature
  - Vomiting
  - Swallowing

Other important brain structures

Thalamus
- Receives sensory information from the body
- Sends these signals to the appropriate areas of the cerebral cortex for further processing.
- Helps coordinate movements by sending signals to the motor cortex.
- Assists with memory processing
Hypothalamus
- Maintains homeostasis within the body by regulation of hormones
Basal ganglia
- Initiation of movements
- Assists with maintaining posture and muscle tone
- Assists with controlling voluntary movements

Arterial circulation of the brain

Circle of Willis

A network of arteries that provides blood supply to the brain
Major arteries
- Anterior cerebral artery (ACA)
  - Supplies frontal, prefrontal, and supplementary motor cortex, as well as circulation to primary motor and sensory cortex
  - Injury to the ACA can cause hemiparesis with weakness of the lower extremity > upper extremity, with sparing of face, apraxia, abulia, akinetic mutism, and urinary incontinence
- Anterior communicating artery
  - The blood supply that connects the left and right ACA
  - Injury to the anterior communicating artery can cause visual disturbances, memory deficits, cognitive impairment, severe headache, altered mental status, and impaired executive function
- Middle cerebral artery
  - Blood supply to the frontal, temporal, parietal, and deeper structures
  - Injury to the middle cerebral artery can cause hemiparesis with weakness of the upper extremity > lower extremity; it innervates both Broca’s area and Wernicke’s area, and neglect
- Internal carotid artery
  - Provides oxygenation to the brain
  - Injury can lead to blurred vision, confusion, memory loss, hemiparesis, or sudden death
- Posterior cerebral artery
  - Supplies blood to the occipital and temporal lobes
  - Injury can cause visual field loss, visual impairment, headache, confusion, and memory impairment
- Posterior communicating artery
  - Connects the internal carotid artery to the posterior cerebral artery
  - Injury can cause visual field loss, ptosis, diplopia, headache, confusion, memory impairment, hemiparesis

Other Important arteries of the brain

Basilar artery
- Supplies: Brainstem, occipital lobe, cerebellum, thalamus, medial temporal lobes
- Functions: Supports autonomic regulation
- Injury Signs: Hemiparesis or quadriparesis, facial paralysis, dizziness, headache, dysarthria
- Involvement: Combines with vertebral artery → vertebrobasilar system → damage to both can cause locked-in syndrome
Vertebral artery
- Supplies: Brain and spinal cord
- Injury Signs: Headache, neck pain, dysarthria, dysphagia, seizures, impaired coordination, sensory/motor deficits to the face and body
- Involvement: Joins basilar artery → vertebrobasilar system → dual injury may result in locked-in syndrome
Posterior inferior cerebellar communicating artery (PICA, Wallenburg syndrome, or Lateral medullary syndrome)
- Supplies blood flow to the medulla, fourth ventricle, and cerebellum
- Injury can cause diplopia, ptosis, facial pain, vertigo, slurred speech, hoarseness, balance deficits, and sensory deficits on the same-side face and the contralateral body

Definitions

Locked-in syndrome: Paralysis of all voluntary muscles, with only eye movement remaining intact. The individual remains conscious but is unable to speak or move.