L1 - Anatomy Flashcards
1
Q
What is the cerebral cortex? What are its subdivisions (types of cortex) and how many layers does each contain?
A
- A heavily folded, 2-4 mm thick sheet of neurons
- Isocortex has 6 layers and makes up 90% of the cortex
- Paleocortex and Archicortex has 3-4 layers and makes up 10% (hippocampus)
2
Q
How many neurons, synapses and Hebbian synapses exist in the cortex?
A
- Neurons: 1.5 x 10^9
- Synapses: 2.4 x 10^9
- Hebbian circuits: exceeds the number of particles in the universe
3
Q
What are the major types of cells of the neocortex?
A
- Neurons: Information processing components
- Glia: support vegetative physiology and provide BBB infrastructure, also involved in information processing
4
Q
What is the ratio of neurons and glia in the neocortex? Explain the method that is used to accurately calculate this ratio.
A
- There is about an equal number of neurons and glia
- Isotropic fractionator: put brain tissue into a vile with enzymes that break down the connective tissue. Then a blending process occurs that makes all bits of tissue the same. Method prevents sampling error – blends neurons and glia together to create an average ratio.
5
Q
List and describe the 4 types of glial cells.
A
- Astrocytes: Most abundant glial cell in grey matter. It is star-shaped with foot processes (Glia Limitans) that make tight arterial junctions to form the BBB. They also supply nutriments to neurons, remove excess NTs, and help the migration of neurons during brain development.
- Oligodendrocytes: Found adjacent to axons and provide myelination to neurons. Unlike Schwann cells, they are capable of myelinating several axons. Unable to repair itself if injured.
- Microglia: Small cells of mesenchymal origin that have an elongated nucleus with little cytoplasm. In response to tissue damage, they transform into large, phagocytic cells. They protect neurons from disease processes and act as ‘scavengers’ of the nervous system.
- Ependymal cells: Forms the epithelial lining of the ventricles and the central canal of the spinal cord. Produce and assist in the circulation of CSF.
6
Q
Name a disease that is associated with abnormalities in the 4 glial cells.
A
- Astrocytes: Can produce tumours called astrocytomas. Tumour is encased in the skull so it creates increased intracranial pressure and tissues begin to squirt out of skull. Increased pressure can kill you because of a cut off blood supply.
- Oligodendrocytes: Autoimmune disease MS can attack myelin, causing demyelination. Once demyelination occurs, it remains for a lifetime since oligodendrocytes cannot repair themselves.
- Microglia: In autoimmune diseases, cells recognize own tissues as foreign and attack them. Treatments are drugs that suppress immunity, which results in immune compromisation. This results in diseases emerging that were previously suppressed by microglia, such as spongiform encephalopathy.
- Ependymal cells: Abnormalities can occur where canals are blocked CSF cannot be drained. Ependymal cells don’t know how to shut off production go CSF, so fluid begins to accumulate inside the skull and results in hydrocephalus. Cortical surface gets pushed away and ventricles become enlarged.
7
Q
List and describe the 5 types of cortical neurons.
A
- Pyramidal cells: Output neurons of the cortex, found in layers 5 and 6. Have long axons that project to other cortical areas or subcortical areas. Have apical dendrites that are studded with spines.
- Stellate cells: The main interneurons of the cortex that contain short axons. They are small and multipolar. Cortical spiny stellate cells of V1 receive inputs from thalamus in Layer 4 and send excitatory outputs to Layers 2/3. Easy to study because they can be identified through regular firing patterns.
- Cells of Martinotti: Small, polygonal neurons with few, short dendrites that synapse with pyramidal neurons.
- Cajal-Retzius Horizontal cells: Small spindle shaped neurons oriented parallel to the cortical surface and found only in layer 1. They are prominent during development but disappear after birth.
- Fusiform cells: Spindle shaped cells oriented at a right angle to the cortical surface and function similarly to pyramidal cells.
8
Q
Explain the 6 layers of the isocortex in terms of cell type, cell size, and population density.
A
- Layer I (plexiform / molecular): contains few scattered neurons (cajal-retzius and spiny stellate), apical dendrites of pyramidal cells, horizontal axons, and glia. Inputs to apical tufts involved in feedback for associative learning and attention. Receives input from M-type neurons of the thalamus.
- Layer II (outer granular layer): Dense population of small pyramidal neurons and numerous stellate neurons. Also contains axonal and dendritic synapses.
- Layer III (outer pyramidal cell layer): Contains small and medium pyramidal neurons and neurons with vertically oriented axons through the cortex. Target of inter hemispheric afferents and sends efferents to other regions of cortex in same hemisphere.
- Layer IV (inner granular layer): Densely packed stellate and pyramidal neurons. Receives inputs from C-type neurons of the thalamus and cortical areas of the same hemisphere.
- Layer V (inner pyramidal layer): Large pyramidal neurons with axons that leave the cortex and synapse with subcortical structures like the BG. In M1, Betz cells form the corticospinal tract.
- Layer VI (polymorphic cell layer): Few large pyramidal neurons and many small spindle shaped neurons of various types. Sends outputs to the thalamus (one column connects with thalamic neurons that provide input to the same column). Neurons sends excitatory fibres to the thalamus and send collaterals to thalamic reticular nucleus that inhibit these same thalamus neurons / ones spatially adjacent.
9
Q
What are the 14 lobes of the cerebral cortex?
A
- Left frontal
- Right frontal
- Left temporal
- Right temporal
- Left occipital
- Right occipital
- Left parietal
- Right parietal
- Left superior limbic (mammillary bodies)
- Right superior limbic
- Left inferior limbic (amygdala and hippocampus)
- Right inferior limbic
- Left insular
- Right insular
10
Q
What are the 5 main fissures / sulci that separate the lobes?
A
- Fissure of Rolando: frontal / parietal
- Medial Longitudinal Fissure: Left and right hemispheres
- Lateral sulcus: Temporal, frontal, and parietal
- Parieto-occipital fissure: Parietal and occipital
- Calcarine fissure: superior and inferior occipital
11
Q
What are the 7 main divisions of the frontal lobes?
A
- Primary motor cortex
- Premotor cortex
- Supplementary motor cortex
- Frontal eye fields
- Prefrontal cortex
- Broca’s area
- Orbitofrontal cortex
12
Q
Compare and contrast the primary motor cortex and the premotor cortex.
A
- M1: Located in frontal lobes in BA 4. Neurons (Betz cells) connect directly with spinal motor neurons and motor nuclei of the cranial nerves. Focal lesions of a specific region leads to a loss of voluntary control of body part mapped to that region.
- Premotor cortex: Neurons connect with subcortical centres. Effects of lesions are less specific than M1 because the basic motor control processes are carried out by the BG, thalamus, and cerebellum. Lesions impair the integration of separate movements of the hands / limbs into fluid action sequences (e.g. involuntary resistance to limb movements, involuntary grasp of object placed in hand, changes in gait).
- Both project directly to the spinal cord so they can operate in parallel
13
Q
What are the 8 superficial landmarks of the temporal lobes?
A
- Superior temporal gyrus
- Middle temporal gyrus
- Inferior temporal gyrus
- Heschl’s gyrus
- Temporal pole
- Fusiform gyrus
- Parahippocampal gyrus
- Uncus
14
Q
What are the two major divisions of the parietal lobes?
A
- Anterior: Somatosensory cortex (S1 and S2, both located on the contralateral post central gyrus)
- Posterior: Superior parietal lobule and inferior parietal lobule, separated by the intraparietal sulcus.
15
Q
What are the limbic and insular lobes?
A
- Limbic: Arc-shaped region of cortex on medial surface of each cerebral hemisphere that consists of parts of the frontal, parietal, and temporal lobes.
- Insular: Folded deep within the lateral fissure and believed to be involved in consciousness, emotion, homeostasis, perception, motor control, self-awareness, cognition, and interpersonal experience.
