Intro to Brain Anatomy Flashcards
Central Nervous System (CNS)
Brain and spinal cord
Peripheral Nervous System (PNS)
All parts of the nervous system outside of the brain and spinal cord
Two components of the brain
- Grey matter
2. White matter
Grey matter
what makes it grey?
Density of the cell bodies of the neurons
White matter
the axons of the neurons
-what makes it white?
The myelin sheath –> a fatty substance to enhance
conduction of the electrical signal down the axon
cerebral cortex
the seat of higher cognitive processes
• Technically a continuous sheet of tissue, but it is not
homogenous –> cytoarchitectonic areas
• The cerebral cortex has expanded immensely over
evolution. The human cortex is the most convoluted
of any primate brain!
• Folded into: sulci (the valleys), gyri (the hills), and
fissures (deeper valleys)
Subcortical structures
more primitive controls than cerebral cortex (e.g., breathing, heart rate, alertness, etc.)
Mapping cortical folds – early studies
- Mapping cortical folds started in the 19th century when it became possible to harden brain tissue using alcohol.
• These early studies demonstrated relatively consistent patterns across individuals
• Certain correlations with functional processes - limited to post-mortem specimens. This meant mainly surface analysis and a restricted sample size!
Mapping cortical morphology – recent advances
- With the advent of neuroimaging tools, it became possible to study the cortical folds of many subjects (who were alive!) in 3D.
- Using Magnetic Resonance Imaging (MRI), one can follow a sulcus on the surface of the cortex to its depth
- Can make use of a standard space
Frontal Lobe
• Voluntary motor control
• Working memory functions (monitoring/tracking
information, selective attention, active memory retrieval)
• Broca’s area for speech production
Parietal Lobe
- Somatosensory processing
- Dorsal stream of vision - “where” pathway
- Reading functions
- Writing functions
Occipital Lobe
Visual processing
Temporal Lobe
- Auditory processing
- Wernicke’s area for language comprehension
- Ventral stream of vision – “what” pathway
- Smell processing (medial side)
- Memory consolidation (medial side)
Penfield’s stimulations
• Dr. Wilder Penfield stimulated these areas using
electrodes directly on the cortex during awake
surgery:
-precentral gyrus = motor cortex (“M1”)
-postcentral gyrus = somatosensory cortex (“S1”)
• Mapped the somatotopic organization of these gyri –>
motor and somatosensory homunculi
Paracentral lobule
- motor and somatosensory processing of the foot
• Dr. Penfield then discovered a totally different motor homunculus on the medial surface of the
frontal lobe that he referred to as “M2” or the Supplementary Motor Area (SMA)
Hippocampus
- technically only one layer of neurons
- aka archicortex (first cortex)
Limbic cortex
• Phylogenetically old cortex
• Used to be called the “limbic lobe”
- limbus = ring
Insula
• Insula –> “island”, sometimes referred to as it’s
own lobe
• Found within the Sylvian Fissure – cannot see
from the lateral view itself because covered by
the frontal, parietal, and temporal opercula
• Has a central sulcus
• 3 short gyri: motor processing
• 2 long gyri: somatosensory processing
• Notice how it sits under the pre and postcentral gyri
of the lateral surface
anterior commissure
Communication of the cortex of the anterior temporal lobes
Occipito-frontal fasciculus
connects frontal and occipital lobes
Superior longitudinal fasciculus
connects frontal with parietal lobes
Arcuate fasciculus
connects lateral PFC with lateral posterior temporal lobes
Inferior longitudinal fasciculus
connects temporal and occipital lobes
Temperal-frontal extreme capsule fasciculus
lateral mid-temporal with lateral frontal cortex, part of the
extreme capsule
Uncinate fasciculus
orbitofrontal cortex and temporal poles
traditional language pathway
Norman Geschwind, 1970’s Boston –>
aphasiologist who emphasized the importance of the arcuate fasciculus to connect Broca’s area and Wernicke’s area in the language dominant hemisphere
Subcortical structures
Thalamus, striatum, basal ganglia
Thalamus
“grand central station”, consists of many
nuclei that regulate different types of information
Striatum
Putamen, Caudate Nucleus, Globus Pallidus
“pale globe”
Putamen and Caudate Nucleus
neostriatum
Globus Pallidus
paleostriatum
Basal ganglia
includes the striatum and amygdala and nucleus accumbens, and other structures important for motor learning and procedural memory
White matter connectivity
- cortico-cortical connections: connect one
area of cortex to another, either
• Within the same hemisphere - association
fibres (e.g., arcuate fasciculus)
• Between hemispheres - commissural fibres
(e.g., corpus callosum) - cortico-subcortical connections: also referred to as projection fibres
External capsule
motor cortex primarily to putamen (uni-directional)
Internal capsule
a massive white matter highway connecting subcortex (e.g., thalamic nuclei) to cortex and vice versa, i.e. bidirectional
Cortical cytoarchitecture – early studies
By hardening a brain using alcohol, one could section the tissue very thinly and stain the tissue for microscopic analysis.
• It became obvious that the cortex is not a homogeneous sheet of tissue, but rather can be subdivided based on its cytoarchitecture (“cyto” = cell; “architecture” = structure).
Golgi stain
- only stains about 10% of neurons but you can see the entire morphology of the neuron
- The Golgi stain is what Ramon y Cajal perfected and how he was able to demonstrate that the neuron is the individual unit of the brain. Generated beautiful illustrations of neurons using this stain
Nissl stain
stains the cell bodies of all neurons – great for cytoarchitecture studies because can determine cell densities
Weigert stain
stains the axons, i.e. the white matter (myelo-architecture)
Neocortex can be divided into how many layers?
6
2 main types of neurons in cortex
Pyramidal neurons – soma is shaped like a pyramid. These neurons have basal dendrites, an apical
dendrite, and a long axon that exits the cortex to
form the white matter. They are the typical cortical
neuron.
Granule/stellate neurons – much smaller, rounder
cells. Axons usually do not leave the cortex
(intrinsic) as they mainly distribute information to
neighbouring layers.
