Cerebral Cortex: Focus on the Frontal Lobe

Boundaries of the Frontal Lobe

• Separated from the Parietal Lobe by the Central Sulcus
• Separated from the Temporal Lobe by the Lateral Sulcus or Sylvian Fissure

Functional Anatomy of the Frontal Lobe

Primary Motor Cortex (Pre-central gyrus)

• Location: Anterior to the central sulcus
• Function: Involved in voluntary movement of skeletal muscles
• Broadman Area: 4
• Major Pathways:
  • Corticospinal Tract: Connects to muscles of limbs and trunk
  • Corticobulbar Tract: Connects to cranial nerve nuclei for head and neck muscles
• Motor Homunculus: Maps different body areas; larger parts indicate more motor units and fine control
  • Medial: Lower limbs
  • Lateral: Upper extremities, head, neck
• Clinical Correlation: Stroke in the Anterior Cerebral Artery affects lower limbs; Middle Cerebral Artery affects upper limbs, head, neck

Motor Association Cortex

• Components:
  • Pre-motor Cortex: More lateral
  • Supplementary Motor Area: More medial
• Function: Planning, sequencing, and execution of movement. Fine motor control of axial and proximal muscles
• Broadman Area: 6

Frontal Eye Fields

• Function: Voluntary rapid eye movements (saccades)
• Pathway: Right frontal eye field sends signals to left paramedian pontine reticular formation; stimulates left lateral rectus and right medial rectus for leftward gaze
• Lesion Effects: Causes ipsilateral conjugate gaze deviation
• Broadman Area: 8

Prefrontal Cortex

• Functions:
  • Personality and behavior: Communicates with limbic system, hypothalamus, amygdala
  • Memory: Working memory, hippocampus interaction
  • Cognition, reasoning, judgment: Influences decision-making, ventral tegmental area (reward system)
  • Motor planning: Communicates with posterior association area and basal ganglia
• Clinical Correlation: Frontotemporal dementia affects personality, memory, decision-making, can develop Parkinsonian symptoms
• Broadman Areas: 8-14, 24, 25, 32, 45-47

Broca's Area

• Location: Inferior frontal gyrus on the dominant hemisphere (usually left for right-handed individuals)
• Function: Motor control of speech muscles
  • Pathway: Coordinates with Wernicke's area via arcuate fasciculus; sends signals via corticobulbar tract
  • Muscles Involved: Orbicularis oris, muscles of pharynx, larynx, soft palate, uvula, tongue
• Lesion Effects: Broca's aphasia, non-fluent and grammatically incorrect speech, intact language comprehension
• Alternative Name: Expressive aphasia