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SUMMARY Neurocognition (lectures)
- Instelling
- Universiteit Leiden (UL)
Summary of the course content: Neurocognition. Part of the master Clinical Neuropsychology. This summary is based on the lectures and the lecture slides.
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NeurocognitionWeek 1: The brain and cognition over the lifespan
There are different types of cells in the brain: neurons and glia cells. Neurons consist of:
- Cell body
- Axon
- Axon hillock (where the axon connects to the cell body)
- Dendrites
- Synapse / synaptic cleft
o Pre- and postsynaptic side
o Vesicles and receptors
- Myelin sheath
o Nodes of Ranvier
There are different types of neurons, which are categorized by shape and function:
- Sensory (afferent) neurons
- Interneurons (stellate, pyramidal, Purkinje)
- Motor (efferent) neurons
Action potentials are thresholded, non-decremental and an all-or nothing response. They are
triggered by summation of excitatory potentials and driven by varying ion permeability of the cell
membrane. The action potential propagates along the axon and can travel for a meter or more. At the
end of the axon, an action potential triggers neurotransmitter release into the synaptic cleft. Some
neurons can release more than one type of neurotransmitter, depending on the type of stimulation
(e.g., low vs high frequency stimulation). Types of neurotransmitters include:
- Acetylcholine
- Dopamine
- Norepinephrine
- Serotonin
- Glutamate
- Gamma-aminobutyric acid (GABA)
Receptor cells in the postsynaptic cleft can adapt to under- or overuse, which is a process of
psychopharmacology. The distribution of synapses connecting to a cell influences it excitability.
Along side neurons, there are also glia cells in the brain, which are non-nerve cells. They have
different shapes and functions:
- Astrocytes: blood-brain barrier, structural support
- Oligodendrocytes: produce myelin for CNS neurons
- Microglial cells: fight infections, waste disposal
- Ependymal cells: ventricular surface epithelium, create CSF
- Schwann cells: produce myelin for peripheral neurons
Different types of neurons are often organized in layers, also called cortical layers. Sensory,
interneurons and motor neurons are grouped. The organization of the layers is different in different
cortical areas, depending on the primary function of that area. Each layer has a specific function.
There are 6 layers, often interconnected, with subdivisions.
White matter tracts are bundles of myelinated axons connecting neurons throughout the central and
peripheral nervous system. This connection can be formed in several ways:
- Association fibres: connecting areas within a hemisphere
- Commissural fibres: crossing to the other hemisphere, to the same (homotopic) or a different
place (heterotopic)
- Projection fibres: connect outward, to subcortical regions, cerebellum, or the spinal cord
,The central nervous system consists of some major components:
- Forebrain (telencephalon)
o Both hemispheres
o Corpus callosum
o Subcortical deep structures: basal ganglia and limbic structures
- Diencephalon
o Thalamus: consists of many nuclei and is considered the relay station of the brain.
When a stroke occurs in the thalamus, anything can happen. The damage is dependent
on the location of the stroke.
o Hypothalamus
o Pituitary gland
- Midbrain (mesencephalon)
o Top of brain stem
o Superior and inferior colliculi: contribute to sensory processing
o Substantia nigra: contributes to movement initiation
- Hindbrain (metencephalon)
o Pons: crossing over many fibres in the motor and sensory pathways for contralateral
motor control
o Cerebellum: automated movement, balance, timing and time perception, sensorimotor
coupling, attention shifting, other cognitive functions
o Medulla oblongata: contributes to vital reflexes, damage is often fatal
- Spinal cord
Subcortical structures are structures that are below the/surrounded by the cortex. The basal ganglia
are such a subcortical structure. They consist of:
- Caudate nucleus
- Putamen
- Globus pallidus
- Subthalamic nucleus (STN)
- Substantia nigra (technically not in the telencephalon but considered as a part of the basal
ganglia because the SN and the basal ganglia work together very closely).
Multiple circuits in the brain go through the basal ganglia. All of them are a part of the basal ganglia
but anatomically they are very different.
- Motor circuit: organizing voluntary movement through inhibitory and excitatory pathways
- Associative circuit: contributing to learning, predictive processing, sequencing
- Reward circuit: producing pleasure responses, motivational functions
The limbic system is another example of a subcortical structure. It consists of:
- Cingulate cortex (technically part of the cortex, not subcortical)
- Hippocampus
- Hypothalamus
- Amygdala
The telencephalon consists of the hemispheres, which are formed by the cortical lobes. Roughly:
- Frontal lobes: movement, attention, reward, short term memory, planning impulse control
and more
- Parietal lobes: sensory integration, association processes, language functions, spatial
processing, sense of touch, some visual processes and more
- Occipital lobes: mainly primary visual areas
- Temporal lobes: memory, emotion association, primary auditory areas, some visual processes
and more
, When looking at lateralization, many functions in the brain are the same across inter-hemispheric
homologues. There are some primary perception areas with cross-lateralized fields: vision and touch.
However, auditory perception of partly bilateral. On the other hand, there are some functional
asymmetries. Language is usually left-lateralized, whereas nonverbal material is on the right. Global
perception is usually right-lateralized, whereas local perception is on the left. The creative versus
logical contrast does not hold, most functions need both hemispheres to be performed correctly. There
is no such thing as ‘left/right’ brained, which is supported by split-brain studies.
The wrinkled surface of the cortex is described in terms of gyri and sulci. Other animals don’t have
this wrinkled surface. The purpose of the wrinkles is simply: wrinkled surface allows for more space.
Gyrus is the ‘bump’ or ‘ridge’ in the wrinkles. Sulcus is the ‘groove’ in the winkles, some are also
called ‘fissure’. Gyri, sulci, and fissures are recognizable landmarks:
- Longitudinal fissure: separating the hemispheres
- Central sulcus: between the primary motor and primary sensory cortex (also called the
Rolandic fissure)
- Lateral fissure: between temporal and frontal lobe (also called the Sylvian fissure)
- Precentral sulcus
- Postcentral sulcus
- Superior temporal gyrus (also called Heschl’s gyrus)
The ventricles in the brain allow for open spaces in the brain:
- Lateral ventricles (first and second ventricle)
- 3rd ventricle
- Cerebral aqueduct (connects 3rd en 4th ventricle)
- 4th ventricle
- Central canal (at the end of the 4th ventricle)
Cerebrospinal fluid (CSF) runs through the ventricles, as well as the subarachnoid space and the
venous sinus. CSF is created in the lateral ventricles from arterial blood in the choroid plexus and
ependymal cells.
The meninges are multiple membraned covering the brain and spinal cord from the outside:
- Dura mater (outer and inner layers)
- Arachnoid with subarachnoid space
- Pia mater
There are multiple ways of finding your way in the brain, also called naming conventions:
- Brodmann Areas: a histological way of naming, meaning that they are named after what they
look like, what the cells resemble. However, this only sometimes overlaps with functionally
distinct areas
- Functional names, e.g., ‘primary motor cortex’: the exact location can stay vague and assumes
only one function per area which is not always the case. One area can be involved in multiple
functions
- Relative locations, e.g., ‘dorsolateral frontal cortex’: the disadvantage is that you need to
know the directional planes
- Coordinate systems, e.g., values for x-, y-, and z-axes: the most exact way of finding your
way, but multiple coordinate systems exist
Directional planes represent anatomical localisation and planes in the human brain:
- Sagittal plane -> medial view
- Axial (horizontal) plane -> superior or inferior view
- Coronal plane -> frontal view
- Dorsal -> to the top
- Ventral -> to the bottom
- Anterior -> to the front
- Posterior -> to the back
- Lateral -> to the side
- Medial -> to the middle
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