Introduction to Gross Topography: Brain and Brainstem week 2 Flashcards
What is gray matter? What color is gray matter in life and why?
Gray matter designates areas in the CNS consisting primarily of neuron cell bodies (and dendrites) which are clustered in various arrays; e.g. nuclei of the brainstem, central gray matter of the spinal cord, and the cortical layers of the cerebrum and cerebellum. The space surrounding the neuron cell bodies is occupied by dendrites and synaptic arrays that form local circuits and establish connections between neurons. In life, the “gray matter” is actually pinkish in color due to its abundant blood supply.
Define the following terms:
cortex
gyri
folia
sulci
fissures
Nuclei: This term does not refer to the nucleus of a cell, but rather to specific regions of gray matter where groups of neuron cells bodies are often functionally related.
Cortex: This term refers to a layered surface that covers some part of the CNS, specifically the external mantle of the cerebrum or cerebellum. During development, cells undergo extensive expansion and the cortical surfaces fold to accommodate the increases in surface area producing bumps or gyri of the cerebral cortex (and folia of the cerebellum). The infoldings between gyri are called sulci and deeper grooves are called fissures. Approximately 2/3rds of the cerebral cortex cannot be seen from the surface and lies within these sulci.
What is white matter?
In the cerebrum, what is the location of white matter in relation to gray matter?
In the cerebrum, white matter is deep to the cortical gray matter. This underlying white matter is the means by which inputs and outputs access the cortex and determine connectivity between one area and another (e.g. between the cortex and the spinal cord). White matter contains many myelinated axons which transmit information from one location to another.
Define the following terms:
pathways/tracts
fasiculi
funiculi
peduncles
lemnisci
columns
projections
decussations
commissures
modality
- Pathways and tracts are collections of hundreds to millions of myelinated axons that generally have long trajectories. “Tracts” usually refer to an individual segment of a pathway that arises from a cell body in one location and terminates on a target in another location.
- Structures containing tracts and fiber bundles in the CNS white matter are referred to as fasciculi (little bundles), funiculi (strings), peduncles (little feet), lemnisci (ribbons), columns, or projections.
- Decussations are axon bundles that cross midline going from a location on one side to a different location on the contralateral side.
- Commissures are axon bundles that cross midline but connect comparable locations.
- Efferent fibers refer to fibers leaving one location and projecting to another. Fibers entering a target location would be afferent.
- The term modality refers to the type of information being conveyed along a pathway (touch, proprioception, temperature, etc.). This term is most often applied to sensory pathways that show sensitivity to a particular stimulus based on the associated neuronal receptors.
What surface of the cerebrum is ventral? dorsal?
What surface of the cerebellum is ventral? dorsal?
Within the brainstem and spinal cord, the superior inferior axis is synomous with what axis? The anterior-posterior axis is synonymous with what axis?
Terms such as anterior, dorsal, and rostral change their meaning depending on which region of the nervous system is being described.
Within the brainstem and spinal cord, the “superior-inferior” axis is synonymous with the “rostral-caudal” axis and the “anterior-posterior” axis is synonymous with the “ventraldorsal” axis.
The reason for this change in terminology relates to embryologic development of the nervous system. There is an approximately 80 degree bend between the long axis of the spinal cord and brainstem and the long axis of the cerebrum. This bend is a consequence of the cephalic flexure which appears early in development and persists in the adult brain.
Identify the indicated parts of the gross brain.
Identify the indicated parts of the gross brain.
What connects the 2 hemispheres of the brain? What kind of axons does it contain?
What separates the frontal from parietal lobe? What functions does this separate?
The cerebral cortex consists of two hemispheres interconnected by interhemispheric commissural fibers (axons) of the corpus callosum. Each hemisphere has four major lobes (frontal, parietal, occipital, temporal) subdivided into component gyri. There is a fifth insular lobe buried deep to the lateral fissure.
The frontal lobe is separated from parietal lobe by the central sulcus. This essentially is the landmark delineating motor and behavioral functions of the frontal lobe anteriorly from sensory processing in the more posterior parietal-occipital-temporal regions.
What function is the inferior gyrus of the frontal lobe associated with? On what side of the brain is it located in most people? What is the specific name for this area of the brain?
The frontal lobe has three main gyri: 1) superior, 2) middle, and 3) inferior; with the inferior gyrus being further divided into triangular, opercular, and orbitolfrontal. The inferior gyrus (specifically the triangular and opercular regions) is associated with motor language on the left in most people. This area is functionally referred to as Broca’s area (the area for motor speech-expressive language).
What term is used for the most anterior regions of the frontal lobe? What functions is this area of the cortex involved in?
What general term is used for areas of the cortex just anterior to the precentral gyurs?
The most anterior regions of the frontal lobe are termed the prefrontal cortex. The prefrontal cortex is involved in higher executive functions, attention, judgment, foresight, and motivation. Those areas of cortex just anterior to the precentral gyrus are termed premotor areas.
What is the function of the precentral gyrus? What is the homunculus within the precentral gyrus?
Where are frontal eye fields (FEF)? What is their function?
The precentral gyrus is the primary motor area and possesses a distorted and inverted representation (homunculus) of the contralateral side of the body. The precentral gyrus is the principal outflow pathway for descending motor fibers that will activate motor neurons in the brain and brainstem.
FEF moves eyes to the opposite side. Located within the frontal cortex (see attached)
What lobe is the postcentral gyrus located in? What are the 2 lobules of this lobe?
What is the function of the postcentral gyrus? What is the homnuculus within it?
What do the supramarginal and angular gyri do?
The parietal lobe is located posterior to the central sulcus and possesses a postcentral gyrus, as well as superior and inferior parietal lobules.
The postcentral gyrus is the primary somatosensory cortex, and possesses an inverted representation of the sensory homunculus for the contralateral side of the body.
Two other significant gyri are the supramarginal and angular gyri. These are important sensory association areas for processing of sensory inputs.
In what lobe is the primary auditory area of the brain located? Specifically, what gyrus of this lobe is it found in?
Where is Werneicke’s area located? What is it’s function?
The temporal lobe has three major gyri visible on the lateral surface, namely the superior, middle, and inferior gyri. The primary auditory area is located in the middle of the superior temporal gyrus. Behind this at the posterior margin of the lateral fissure is Wernicke’s area (receptive speech).
Identify the indicated gross brain structures.
What lobe is the primary visual cortex found within? Specifically, in what part of this lobe?
What is the function of the paracentral lobule? What parts of the body are represented in this region?
The occipital lobe is mostly visible on the medial surface (mid-sagittal view). The primary visual cortex is located at the upper and lower margins of the calcarine fissure.
Note the paracentral lobule where the primary motor and somatosensory areas overlap onto the medial surface of the brain. The leg and foot are represented in this region.
Identify the indicated structures.
Identify the indicated parts of the basal surface of the brain.
Where is the hippocampus located? What is the function of the hippocampus?
What demarcates the lateral boundary of the hippocampus?
Where is the uncus? What is it associated with? What can cause uncal herniations? What is the result of an uncal herniation?
A key structure of the temporal lobe is the parahippocampal gyrus beneath which is the hippocampus, involved in memory acquisition. It is demarcated at its lateral boundary by the collateral sulcus.
The uncus, a bump on the medial (mesial) portion of the parahippocampal gyrus, is associated with primary olfactory cortex. Physically this is an important structure since swelling or displacement of the brain can produce uncal herniations through the tentorial notch into the posterior cranial fossa. This tissue can damage the IIIrd nerve (cranial nerve III) and compress the upper brainstem resulting in coma.
State the Brodmann numbers and associated cortical areas (cytoarchitectonic map of the cortex) along with their functions.
Identify the parts of the brainstem.
What CN exits between the crus cerebri (cerebral peduncles)?
What is the basis pontis? What is the function of it?
Explain the travel of fibers of the crus cerebri/cerebral peduncles.
Where do fibers of the medullary pyramids travel?
What does the olive of the medulla correspond to?
What is the purpose of fibers of the cerebellar peduncles?
The crus cerebri (cerebral peduncles) are fiber bundles seen externally on the ventral brainstem. CN III (oculomotor) exits between the crus cerebri.
The bulge of the pons is the basis pontis and consists of transverse fibers that are an important input to the cerebellum.
Fibers of the crus cerebri pass into the bulging base of the pons and then re-emerge as the pyramids at the medullary level.
The medullary pyramids contain fibers as they exit from the pons en route to the spinal cord.
The olive is the conspicuous bump located posterolaterally to the pyramid on each side. It corresponds to a large internal nucleus (collection of neuron cell bodies) called the inferior olivary nucleus (more on this later).
On the dorsal aspect of the brainstem note the cerebellar peduncles which are fiber projections passing to and from the cerebellum. These fiber bundles are a physical connection of the cerebellum to the brainstem.
Identify the cranial nerves exiting from the brainstem.
State the specific parts of the brainstem that each CN exits from.
Midbrain:CN III and IV (CN IV is the only cranial nerve to exit dorsally from the brainstem).
Pons: CN V
Medulla: CN VI, VII, and VIII exit at the pontomedullary junction, CN IX, X, XI and XII exit is association with the olive. Cranial nerves IX, X, XI exit as rootlets posterior to the olive. Cranial nerve XII emerges between the pyramids and olive.
