Overview
This lecture provides an overview of the major brain lobes, their anatomical gyri and sulci, and key functional sensory areas such as sensory, visual, auditory, gustatory, and olfactory cortices.
Frontal Lobe Anatomy
- The frontal lobe is divided by two sulci into superior, middle, and inferior frontal gyri.
- The inferior frontal gyrus is subdivided into pars opercularis, pars triangularis, and pars orbitalis.
- The precentral gyrus lies immediately anterior to the central sulcus.
- On the medial surface, the superior frontal gyrus, paracentral lobule (anterior half), and cingulate gyrus form part of the frontal lobe.
Temporal Lobe Anatomy
- The temporal lobe contains superior, middle, and inferior temporal gyri, divided by two transverse sulci.
- Heschl's gyrus (transverse temporal gyrus) lies on the superior aspect, within the Sylvian fissure.
- Medially, the hippocampal gyrus, uncus, and parahippocampal gyrus are important landmarks.
Parietal and Occipital Lobes
- The parietal lobe is divided into superior and inferior parietal lobules by the interparietal sulcus.
- The inferior parietal lobule includes the supramarginal gyrus (caps Sylvian fissure) and angular gyrus (caps superior temporal sulcus).
- The occipital lobe is split by the lateral occipital sulcus and, medially, by calcarine and parieto-occipital sulci into cuneus and lingual gyrus.
Major Sensory Cortices and Their Functions
- Primary sensory cortex is in the postcentral gyrus (Brodmann areas 1, 2, 3) and receives thalamic input conveying touch, pain, temperature, proprioception, and vibration.
- The sensory homunculus represents the contralateral body, with face and tongue having bilateral representation.
- Lesions cause immediate sensory loss; pain and temperature may return due to thalamic input but discriminative touch is lost.
- Visual cortex (Brodmann 17) on the calcarine gyrus receives input from the lateral geniculate nucleus; lesions cause characteristic contralateral visual field defects.
- Primary auditory cortex (Brodmann 41, 42) is in Heschl's gyrus and receives bilateral input; lesions impair sound localization, more so contralaterally.
- The gustatory cortex (parietal lobe) processes taste from the thalamic VPM; lesions can cause taste disturbances and seizures may cause gustatory hallucinations.
- Olfactory cortex (pyriform cortex, periamygdaloid area) receives direct input from the olfactory bulb and is unique in bypassing the thalamus.
Key Terms & Definitions
- Gyrus (gyri) — ridge on the brain's surface.
- Sulcus (sulci) — groove or furrow on the brain's surface.
- Homunculus — a topographic representation of the body in the cortex.
- Brodmann areas — regions of the cerebral cortex defined by cytoarchitecture.
- Heschl's gyrus — primary auditory cortex.
- Calcarine sulcus — divides primary visual cortex in occipital lobe.
- VPL/VPN/VPM — thalamic nuclei relaying sensory input.
- Contralateral — opposite side of the body.
Action Items / Next Steps
- Review detailed pathways and field deficits of the visual system.
- Study secondary sensory, visual, and auditory association cortices.
- Read about clinical implications of lesions in primary sensory areas.