Module 4: Cerebral cortex - Organization and Anatomy

Behavior occurs…

through neural network processing and neural processing is a system of connectivity and modularity

Neurons in different regions….

behave differently

2 cerebral hemispheres

• right

• left

Cerebrum

• the largest segment of the CNS; most complex

• split into 2 symmetrical regions called the cerebral hemispheres by the longitudinal cerebral fissure

• possesses characteristic grooves and hills, called sulci and gyri

• serves as information processing hub and center of all integrative operations of the cerebrum

Hemispheres are joined together via…

a massive tract of axons located at the bottom of the longitudinal fissure called the corpus callosum

4 lobes of the cerebral hemisphere

frontal, parietal, occipital, temporal

subcortical structures also part of the cerebrum

• basal ganglia

• hippocampus

• amygdala

• insula

• white matter associated with afferent and efferent signals passing to and from regions of gray matter

Cerebral cortex diagram

Cerebral cortex

All conscious thought and behavior originates in the cerebral cortex

Cerebral Cortex: Frontal Lobe nomenclature

• precentral gyrus

• superior, middle, and inferior frontal gyrus

• superior, inferior frontal sulcus

3 parts of the inferior frontal gyrus

• pars opercularis

• pars triangularis

• pars orbitalis

Traditional brocas area

Pars opercularis and Pars triangularis

Sylvian fissure

Divides frontal and temporal lobes, and a little parietal

Cerebral Cortex: Frontal Lobe Nomenclature diagram

Prefrontal Cortex

Remainder of the frontal lobe rostral (front) to the premotor areas

Executive function of prefrontal cortex

Judgement, future planning, the sense of purpose in action (ex: stopping yourself from cursing), the notion of personal responsibility, adherence to social norms and constructs

Massive interconnections of the prefrontal corex

• *motor-related regions: premotor areas, cerebellum, basal ganglia

• *sensory-related regions: parietal and temporal association areas

• thalamus, memory systems, limbic systems, neuromodulatory systems

Cerebral Cortex: Parietal Lobe Nomenclature

• postcentral gyrus

• postcentral sulcus

• intraparietal sulcus

• parieto-occipital sulcus

• superior temporal sulcus

• superior and inferior parietal lobe

Cerebral Cortex: Parietal Lobe Nomenclature diagram

2 parts within the inferior parietal lobule

• supramarginal gyrus

• angular gyrus

They are involved in reading network along with the temporal lobe structures

Superior view of cerebral cortex diagram

Somatopic Organization of M1 and S1 diagram

Dorsal

towards the top

Ventral

towards the bottom

Neurons in the M1

Neurons in the primary motor cortex transmit signals to contract muscles of the body including muscles for speech production and feeding

Neurons in the S1

Neurons in the primary somatosensory cortex receive signals from the muscles/skin about touch, proprioception, motion, temperature, and pain

Are muscles in the ventral or dorsal area of the M1 that active speech?

Ventral

Electrical stimulation of M1 neurons

• low level electrical stimulation of M1 neurons produces contraction of discrete muscles in the body

• high level electrical stimulation of M1 neurons begins coordinated and purposeful actions such as reaching or grabbing

M1 characteristics

• somotopically organized in a gross manner along the precentral gyrus

• integrative hub for inputs related to movement from cerebellum, basal ganglia and pre-motor area

• obtains somotosensory input from thalamus and S1

• combinations of inputs from associated motor and somotosensory structures is thought to provide M1 with required info to produce skilled and goal directed actions

Cerebral cortex: temporal lobe nomenclature diagram

Cerebral cortex: temporal lobe nomenclature

• superior, middle, inferior temporal gyrus

• superior and inferior temporal sulcus

Cerebral Cortex: lateral view diagram

Thalamus diagram

Axon fiber pathways

• corpus callosum

• anterior commisure

• posterior commisure

Connect right and left hemispheres

Thalamus

• has connections to ALL cortical regions

• thalamo-corticol fibers transmit signals from all senses except smell

• modulates incoming sensory info and influences attentiveness of the cerebral cortex to specific features of incoming sensory info

• important in motor control, emotional regulation, memory, and autonomic functions

Organization of nervous system

• anatomic approach

• developmental approach

Anatomical approach

Based on the gross anatomy of the nervous system

• CNS

• PNS - cranial and spinal nerves

Developmental Approach

Based on the development of the nervous system and neurodevelopmental terms

Developmental approach example

Diencephalon: thalamus, hypothalamus, epithalamus

Cortical (cortex) organization

• primary sensory and motor regions to association cortex

• the cortex is organized into layers (rows) or columns for organized signal transmission

• Brodmann’s organization: cell architecture

Each lobe possess…

segments that function as primary sites of raw information input & direct output to effectors of the body

M1, S1, V1, A1

primary motor cortex, primary somatosensory cortex, visual primary cortex, auditory cortex

Association Cortices diagram

Neurons react to more complex stimuli…

as you get more complex, they respond to different info

Hierarchical organization

Primary sensory/motor regions to association cortices to multi-modality regions and general processing regions

Hierarchial organization diagram

6 layers

Cerebral cortex is a grouping of 6 layers of cell bodies

6 layers of cerebral cortex diagram

Layer 1 and 2

• Layer 1 is surface of scalp

• They both communicate cortical layer to other cortical areas

Layer 3

• receives input from all other systems

• sends to opposite hemisphere

Layer 4

• information comes from thalamus to layer 4

• all sensory except smell

Layer 5 and 6

• Sends signals out to muscles, cerebellum, basal ganglia

• layer 5 - to brainstem and spinal cord

• layer 6 - to thalamus

Cortical Columns

fundamental processing and computational unit of the cortex is the cortical column

Korbinian Brodmann

• He created cytoarchitectonic maps

• cross sections of cortical tissue

• cell staining

• cells looked different across regions

Brodmann’s map of the lateral and medial cerebral cortex

Major Brodmann’s areas associated with speech, language and sensorimotor behavior

BA maps do NOT account for

• hidden regions (ex: within fissures)

• left - right asymmetries

• individual differences

BA4 and BA3

BA4 - primary motor cortex

BA3 - primary somatosensory cortex