Cerebral Cortex

The cerebral cortex is the largest and most developed part of the human brain and CNS. Occupying the upper part of the cranial cavity, the cerebral cortex has 4 lobes and is divided into 2 hemispheres that are joined centrally by the corpus callosum. The cortex contains gyri that are separated by sulci. The cerebral cortex provides the neural substrate for the conscious experience of sensory stimuli.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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General Features

Overview

The cerebral cortex is the part of the brain that is both superficial and supratentorial:

  • It is the most superficial of the brain structures, lying deep to the meninges Meninges The brain and the spinal cord are enveloped by 3 overlapping layers of connective tissue called the meninges. The layers are, from the most external layer to the most internal layer, the dura mater, arachnoid mater, and pia mater. Between these layers are 3 potential spaces called the epidural, subdural, and subarachnoid spaces. Meninges.
  • It is located above the tentorium cerebri, which are paired dural reflections superior to the cerebellum Cerebellum The cerebellum, Latin for "little brain," is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum.
  • It is derived embryologically from ectoderm. 
  • There are 4 paired lobes of the cerebrum.
  • The cerebrum are divided by sulci (indentations) and gyri (prominences) that are individually named and contain unique functions.
  •  The cerebrum is the largest and most developed part of the human brain:
    • Located in the upper cranium
    • Connected to the spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord via the brainstem
  • Embryology: Dorsal ectoderm → neural tube → prosencephalon → telencephalon
Brain vesicle

The embryonic development of the cerebrum: note the lineage starting from the neural tube → prosencephalon → telencephalon → cerebrum

Image: “Brain Vesicle” by Phil Schatz. License: CC BY 4.0

Lobes

  • Frontal lobe
  • Parietal lobe
  • Occipital lobe
  • Temporal lobe

Notable sulci

  • Medial longitudinal fissure: separates left and right cerebral hemispheres 
  • Lateral sulcus (or Sylvian fissure): separates parietal and temporal lobes 
  • Central sulcus (of Rolando): separates parietal and frontal lobes 
  • Collateral sulcus: separates fusiform gyrus and hippocampal gyrus
  • Calcarine sulcus: separates occipital lobes horizontally into the cuneus (superior) and lingual (inferior) gyri
  • Parieto-occipital sulcus: separates the parietal and occipital lobes

Notable gyri

  • Precentral gyrus: in the frontal lobe, controls voluntary motor movement
  • Postcentral gyrus: in the parietal lobe, site of somatosensory cortex
  • Cingulate gyrus: located above the corpus callosum and forms part of the limbic system Limbic system The limbic system is a neuronal network that mediates emotion and motivation, while also playing a role in learning and memory. The extended neural network is vital to numerous basic psychological functions and plays an invaluable role in processing and responding to environmental stimuli. Limbic System 
  • Fusiform gyrus; in the temporal and occipital lobes, thought to play a role in facial and word recognition
  • Inferior temporal gyrus: involved with auditory processing
  • Hippocampal gyrus (parahippocampal gyrus) → fold on the inner surface of the temporal lobe that borders the hippocampus
Lobes of cerebral cortex

The image demonstrates the location of some key structures, including each of the 4 lobes, the precentral and postcentral gyrus, and the central, lateral, and parieto-occipital sulci.

Image: “Lobes of Cerebral Cortex” by OpenStax Anatomy and Physiology. License: CC BY 4.0

Microscopic Structure and Neurovasculature

Microscopic structure

  • Outer gray matter
  • Inner white matter consisting of 2 parts:
    • Neocortex: 
      • Larger and evolutionarily newer
      • Composed of 6 layers of neurons
    • Allocortex:
      • Smaller and evolutionarily older
      • Composed of 4 layers of neurons

Vascular system

  • Arterial supply:
    • Arterial supply is by the paired internal carotid and vertebral arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries, which anchor and give rise to the circle of Willis.
    • The circle of Willis gives rise to 3 primary cerebral arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries:
      • Anterior cerebral artery: supplies anteromedial surface
      • Middle cerebral artery (MCA): supplies lateral surface
      • Posterior cerebral artery (PCA): supplies posterior and inferior surfaces
  • Venous drainage:
    • Cerebral veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins drain into large venous channels that run through the dura mater.
    • All empty into the confluence of sinuses, transverse sinuses, sigmoid sinuses, and terminally into the jugular veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins.

Frontal Lobe

The frontal lobe is the most anterior/superior aspect of the supratentorial brain. It controls many of the higher-order functions of the brain, including motor function, executive thought, and speech.

  • Borders:
    • Anteriorly by the frontal bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Structure of Bones
    • Superiorly by the frontal and parietal bones
    • Posteriorly by the central sulcus
    • Inferiorly by the anterior cranial fossa
  • Frontal lobe location:
    • Posteriorly delineated by the central sulcus
    • Medially delineated by the longitudinal fissure
    • Inferolaterally delineated by the lateral fissure
  • Motor homunculus: neurological map in the primary motor cortex representing the proportion of the brain dedicated to processing sensory function
    • Lower extremities represented most medially
    • Trunk, upper extremities, and face located most laterally
    • The size of the feature on the homunculus relates to the relative size of the brain region dedicated to that specific feature.
  • Blood supply:
    • Lateral frontal lobe: MCA
    • Medial/superior frontal lobe: Anterior cerebral artery
Table: Frontal lobe internal structure
Name Location Brodmann
number
Function
Primary motor cortex Precentral gyrus 4 Dictates contralateral motor control
Premotor cortex Anterior to primary motor cortex 6 Programming of motor events; neurons activate prior to primary motor neurons
Supplementary motor cortex Midline surface of the hemisphere anterior to leg Leg The lower leg, or just "leg" in anatomical terms, is the part of the lower limb between the knee and the ankle joint. The bony structure is composed of the tibia and fibula bones, and the muscles of the leg are grouped into the anterior, lateral, and posterior compartments by extensions of fascia. Leg representation of primary motor cortex 6 Planning of complex motor movements
Prefrontal cortex Anterior portion of frontal lobe 8–14, 24, 25, 32, 44–47 Olfaction Olfaction The sense of smell, or olfaction, begins in a small area on the roof of the nasal cavity, which is covered in specialized mucosa. From there, the olfactory nerve transmits the sensory perception of smell via the olfactory pathway. This pathway is composed of the olfactory cells and bulb, the tractus and striae olfactoriae, and the primary olfactory cortex and amygdala. Olfaction and executive function (problem-solving, judgment, planning, behavior, and emotions)
Frontal eye field Intersection of the middle frontal gyrus with precentral gyrus 8
  • Coordination of voluntary eye movements
  • Receives afferents from the primary and secondary visual cortices
  • Provides efferents to the brain muscle nuclei of the cranial nerves Cranial nerves There are 12 pairs of cranial nerves (CNs), which run from the brain to various parts of the head, neck, and trunk. The CNs can be sensory or motor or both. The CNs are named and numbered in Roman numerals according to their location, from the front to the back of the brain. Overview of the Cranial Nerves III, IV, and VI → superior colliculus → innervation of the eye muscle nuclei
Broca area Inferior frontal gyrus of the dominant hemisphere 44, 45 Word production (motor speech)
Primary motor cortex

Note the primary motor cortex (the most posterior structure of the frontal lobe) with the overlaid homunculus, detailing the proportions of the cortex dedicated to processing each specific motor function.

Image by Lecturio.

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Parietal Lobe

The parietal lobe lies posterior to the frontal lobe and superior to the occipital lobe. It is associated with the processes of sensation and language comprehension. 

  • Borders:
    • Anteriorly by the central sulcus
    • Superiorly by the parietal bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Structure of Bones,
    • Posteriorly by the parieto-occipital sulcus
    • Inferiorly by the Sylvian fissure. 
  • Parietal lobe location: posterior to the central sulcus on the superolateral and medial surfaces of the cerebral hemisphere
  • Sensory homunculus: neurological map in the primary somatosensory cortex representing the proportion of the brain dedicated to processing sensory function
    • Lower extremities represented most medial
    • Trunk, upper extremities, and face located most lateral
    • Size of feature on homunculus = size of brain region dedicated to that specific feature
  • Blood supply:
    • Medial: middle cerebral artery (MCA) and Anterior cerebral artery (ACA)
    • Posterior: posterior cerebral artery (PCA) 
Table: Parietal lobe internal structure
Name Location Brodmann
number
Function
Primary somatosensory cortex Postcentral gyrus 3, 1, 2 Receives contralateral somatosensory input from the ventral posteromedial nucleus and ventral posterolateral nucleus of the thalamus Thalamus The thalamus is a large, ovoid structure in the dorsal part of the diencephalon that is located between the cerebral cortex and midbrain. It consists of several interconnected nuclei of grey matter separated by the laminae of white matter. The thalamus is the main conductor of information that passes between the cerebral cortex and the periphery, spinal cord, or brain stem. Thalamus
Parietal association areas Posterior parietal 5, 7 Stereognosis and awareness of contralateral self and surroundings
Wernicke Area Superior temporal gyrus of the dominant hemisphere 22 Comprehension of language
Primary somatosensory cortex

The primary somatosensory cortex (labeled in dark blue) marks the anterior-most region of the parietal lobe.

Image by Lecturio.

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Occipital Lobe

The occipital lobe is the most posterior lobe of the supratentorial brain. It is primarily involved with visual processing.

  • Borders: 
    • Anteriorly by the temporal lobe
    • Superiorly by the parieto-occipital sulcus
    • Posteriorly by the occipital bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Structure of Bones
    • Inferiorly by the tentorium cerebelli
  • Occipital lobe location: posterior to the temporal and parietal lobes
    • The parieto-occipital sulcus separates its medial surface from the temporal and parietal lobes.
    • The lateral parietotemporal line separates its lateral surface from the temporal and parietal lobes.
  • Blood supply: branches of PCA
Table: Occipital lobe internal structure
Name Location Brodmann
number
Function
Primary visual cortex Posterior occipital lobe 17 Vision and acuity (input from lateral geniculate nucleus via optic radiations)
Visual association cortex Extrastriate cortex 18, 19 Processes inputs related to form, color, motion, depth, and spatial relationships
Primary visual cortex

Note the location of the primary visual cortex in the most posterior region of the brain in the occipital lobe.

Image by Lecturio.

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Temporal Lobe

The temporal lobe is the most anterior/inferior aspect of the supratentorial brain. It is involved with the processes of hearing, olfaction, and memory.

  • Borders: 
    • Anteriorly by the sphenoid bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Structure of Bones
    • Superiorly by the Sylvian fissure
    • Posteriorly by the occipital lobe
    • Inferiorly by the middle cranial fossa
  • Temporal lobe location: occupies the middle cranial fossa
    • Extends superiorly to the Sylvian fissure and posteriorly to the lateral parietotemporal line
    • Separates the temporal lobe from the parietal lobe superiorly and the occipital lobe inferiorly
  • Blood supply:
    • Branches from the internal carotid system
    • Branches from the vertebrobasilar artery
Table: Temporal lobe internal structure
Name Location Brodmann
number
Function
Primary auditory cortex Superior temporal plane of temporal lobes within lateral sulcus 40, 41 Hearing
Middle and inferior temporal gyri Middle and inferior temporal lobe 20, 21 Long-term memory
Parahippocampal gyrus Medially located in the inferior temporo-occipital cortex 34 Short-term memory
Uncus Continuous with the hippocampal gyrus 34 Olfaction Olfaction The sense of smell, or olfaction, begins in a small area on the roof of the nasal cavity, which is covered in specialized mucosa. From there, the olfactory nerve transmits the sensory perception of smell via the olfactory pathway. This pathway is composed of the olfactory cells and bulb, the tractus and striae olfactoriae, and the primary olfactory cortex and amygdala. Olfaction
Fusiform Gyrus Occipitotemporal Medial Gyrus 37 Facial recognition

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Clinical Relevance

The following structures are closely related to the cerebral cortex by location or function:

  • Auditory and vestibular pathways: neural pathways that allow for the perception of sound. The auditory sense converts acoustic waves—meaning fluctuations in pressure in our surroundings—into electrical signals and, consequently, perceives tones, sounds, and noises.
  • Visual pathway Visual pathway The primary visual pathway consists of a relay system, beginning at the retina, whose ganglion cell axons form the optic nerve. The optic nerve fibers from each eye hemidecussate in the optic chiasm (OC), with nasal fibers joining the temporal fibers of the contralateral nerve. Signals are then transmitted to the primary visual cortex of the occipital lobe. The Visual Pathway and Related Disorders: the visual system, part of the CNS. The visual pathway encompasses multiple structures that together enable the visual perception of the world around us.
  • Brainstem: consists of the midbrain, pons, and medulla oblongata. The brainstem is a stalklike structure that connects the cerebrum to the spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord (SC) and is a major relay station for sensory, motor, and autonomic information.
  • Cerebellum: located in the posterior cranial fossa, dorsal to the pons and midbrain. The cerebellum Cerebellum The cerebellum, Latin for "little brain," is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum’s principle involvement is in the coordination of movements. The cerebellum Cerebellum The cerebellum, Latin for "little brain," is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. 
  • Cerebrovascular system Cerebrovascular system Blood supply to the brain can be divided into an anterior and a posterior circulation, which interconnect to form the circle of Willis. The anterior circulation is derived from the internal carotid arteries and consists mainly of the anterior and middle cerebral arteries. The posterior circulation is derived from the vertebral arteries and consists primarily of the cerebellar and posterior cerebral arteries. Cerebrovascular System: composed of the vessels supplying the brain. The brain receives approximately 750 ml of blood every minute, which is 15% of the cardiac output. The arterial supply of the brain is divided into 2 categories: the anterior circulation from the internal carotid artery system and the posterior cerebral circulation from the vertebrobasilar circulatory system.
  • Diencephalon: consists of 4 components, which are the thalamus Thalamus The thalamus is a large, ovoid structure in the dorsal part of the diencephalon that is located between the cerebral cortex and midbrain. It consists of several interconnected nuclei of grey matter separated by the laminae of white matter. The thalamus is the main conductor of information that passes between the cerebral cortex and the periphery, spinal cord, or brain stem. Thalamus, the epithalamus, the hypothalamus Hypothalamus The hypothalamus is a collection of various nuclei within the diencephalon in the center of the brain. The hypothalamus plays a vital role in endocrine regulation as the primary regulator of the pituitary gland, and it is the major point of integration between the central nervous and endocrine systems. Hypothalamus, and the subthalamus. Overall, the diencephalon coordinates unconscious vegetative and sensorimotor functions.
  • Limbic system: consists of several components: the hippocampus, parahippocampal gyrus with entorhinal cortex, the cingulate gyrus, the amygdala, and the mammillary bodies.

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