Cerebral Cortex
last authored: Sept 2009, David LaPierre
The cerebral cortex has a surface area of about 2200 cm2 and contains an estimated 1.5-2 x 1010 neurons. There are an estimated 3 x 1014 synapses (Boron and Boulpaep, 2006). Much gray matter is located on the brain surface, but some is inside. The basal ganglia are gray matter deep in the brain.
The cortex is highly folded, with each ridge called a gyrus and each groove called a sulcus. Brains differ considerably, though there are some fairly constant major features. It is divided into 5 lobes, as well as other smaller structures:
- frontal
- prefrontal
- parietal
- temporal
- occipital
- limbic
- insula
Frontal Cortex
structures
- lies in front of the central sulcus (of Rolando) and above the lateral sulcus; separated from the limbic lobe by the cingulate sulcus
functions
- the precentral gyrus contains the primary motor cortex and the premotor and supplementary motor areas
- Broca's area, usually the left inferior frontal gyrus, is involved in production of written and spoken language
- prefrontal cortex involved in personality, insight, foresight
Prefrontal Cortex
The prefrontal cortex is associated with mood and executive decisions involving social behaviour.
dorsolateral - establishes and maintians social goals
medial - empathy and regulates negative emotion
orbitofrontal - assigns emotional value to a situation following decision-making projections from amygdala and thalamus
connections
The PFC has connections with:
Parietal Cortex
structures
- extends from central sulcus to an imaginary line separating it from the occipital lobe
- medially, bounded by calcarine sulci
- postcentral gyrus contains primary somatosensory cortex
functions
- associated with somatosensation, processing of tactile and proprioreceptive information, and integration with experience and emotion
- inferior lobe, usually left, associated with language comprehension
- complex aspects of spatial orientation and perception
Temporal Cortex
strutures
- Located below the lateral fissure
functions
- primary auditory cortex located on superior temporal lobe; processes auditory information
- Wernicke's area, usually on the left temporal lobe, important in language comprehension
- much of temporal lobe, especially inferior surface, associated with higher order processing of visual information
- medial aspects associated with learning and memory
Occipital Cortex
strutures
- No clear demarcation laterally, though separated from the parietal lobes by the parietoccipital fissure.
- primary visual cortex contained in walls of calcarine sulcus, separating parietal and temporal lobes
functions
Limbic Cortex
structures
- encircles the cortex-diencephalon junction
- contains cingulate and parahippocampal gyri, the latter which forms a medial bump called the uncus.
- hippocampus is folded into temporal lobe
functions
Insula
structure
lies buried within lateral sulcus
functions
- gustatory and autonomic functions
- may be involved in visceral function and nociception, though it is unclear.
Cortical Output
Output axons from the cortex come primarily from the pyramidal cells of layer V, which synapse in the brainstem and spinal cord, and from layer VI, which projects back to the thalamus.
The internal capsule connects the cortex with the rest of the CNS, particularly the thalamus and the brainstem. Internal capsule is continuous with the cerebral peduncles in the midbrain.
The corpus collosum is a massive collection of white matter connecting the two hemispheres.