Neurons and the Brain Flashcards
- What is the anatomical organization of the human brain? - How is cognition reflected in the structure of the brain? - How to model and simulate the brain?
How many neurons are in the human brain?
86 billion
How much power does the human brain consume?
13 W
What are the two subsystems of the vertebrate nervous system?
- Central Nervous System (CNS)
- Peripheral Nervous System (PNS)
What is the Central Nervous System?
Brain and spinal cord; the central information processing system. It collects and distributes data throughout the body.
What is the Peripheral Nervous System?
The PNS transmits signals between sensory organs, muscles, internal organs and the CNS.
Divided into
- autonomic nervous system (self-regulation)
- somatic nervous system (sensory nervous system for voluntary body control)
What is the cerebrum?
The cerebrum is the largest part of the brain containing the cerebral cortex, as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb.
It accounts for sensory integration, voluntary motion and higher-level cognitive functions.
It is split into two hemispheres that are connected by the corpus callosum.
What is the corpus callosum?
The corpus callosum is a wide, thick bundle of fibers beneath the cerebral cortex. It connects the left and right cerebral hemispheres.
What is the cerebral cortex?
The cerebral cortex is the folded outer layer of the cerebrum.
It is the center of higher cognitive function (attention, perception, awareness, thought, memory, language, and consciousness).
What is white matter?
White matter is the inner part of the cerebrum, a core of nerve fibers that connect the cortical regions.
What are the three anatomical features on the surface of the cerebral cortex?
- gyri: ridge formed by the convoluted surface
- sulci: fissures surrounding a gyrus
Major gyri and sulci divide each hemisphere into four lobes:
- anterior: frontal lobe
- superior: parietal lobe
- posterior: occipital lobe
- inferior: temporal lobe
What is the brainstem?
The brainstem connects the cerebrum with the spinal cord.
It is divided into four sections:
- Diencephalon
- Epithalamus
- Thalamus
- Hypothalamus
- Subthalamus
- Midbrain (Mesencephalon)
- Pons
- Medulla Oblongata
What is the diencephalon?
Top-most part of the brainstem. It consists of four sub-structures:
- Epithalamus: secretion of melatonin (hormone that regulates the sleep-wake cycle)
- Thalamus (largest part): relay and distribution of sensory (except smell) and motor signals to the different regions of the cerebral cortex; “gateway to consciousness”
- Hypothalamus: control of autonomic functions (temperature regulation, appetite), behavior, and hormone production
- Subthalamus: regulates skeletal muscle movements
What is the epithalamus?
Part of the diencephalon, which is part of the brain stem.
Secretion of melatonin (hormone that regulates the sleep-wake cycle)
What is the thalamus?
Largest part of the diencephalon, which is part of the brain stem.
Relay and distribution of sensory (except smell) and motor signals to the different regions of the cerebral cortex; “gateway to consciousness”
What is the hypothalamus?
Part of the diencephalon, which is part of the brain stem.
Control of autonomic functions (temperature regulation, appetite), behavior, and hormone production
What is the subthalamus?
Part of the diencephalon, which is part of the brain stem.
Regulates skeletal muscle movements
What is the midbrain?
Part of the brainstem.
Involved in the the control of eye movements, auditory processing, and visual processing.
What is the pons?
Part of the brainstem, inferior to the midbrain.
The pons is comprised of nerve fibers that connect the medulla oblongata and the cerebral cortex with the cerebellum (motor control).
It also transmits sensory and motor signals between the brain and the facial region.
What is the medulla oblongata?
Part of the brainstem, inferior to the pons.
It connects the brain with the spinal cord.
What is the autonomic nervous system?
The ANS is responsible for self-regulation (homeostatis) and operates largely unconsciously.
Two (antagonist) subsystems:
- sympathetic nervous system (“fight or flight”)
- parasympathetic nervous system (“rest and digest”)
What does the sympathetic nervous system do?
Promotes a fight-or-flight response.
- prepares the organism for stress (adjust heart rate, blood flow etc.)
It connects internal organs to the brain
What does the parasympathetic nervous system do?
The parasympathetic nervous system promotes a “rest and digest” response, promotes calming of the nerves return to regular function, and enhancing digestion.
It consists mainly of cranial nerves (nerves that emerge from the brain) and lumbar spinal nerves.
What is a connectonome?
A connectome is a comprehensive map of neural connections in the brain, and may be thought of as its “wiring diagram”.
What is a diffuse nervous system?
A nervous system that is distributed throughout the body, e.g. jellyfish.
What is the endocrine system?
The endocrine system (hormone system) in humans is a regulatory system that works in parallel to the nervous system.
What are some myths about the human brain?
- only 10% of the brain is used
- the brain does not produce new neurons in adults
- the size of the brain is related to intelligence
What is the encephalization quotient?
The encephalization quotient is a between-species measure of relative brain size, calculated as the ratio of actual to predicted brain mass for a given species relative to body mass.
It has been used as a proxy for intelligence and thus as a possible way of comparing the intelligences of different species. For this purpose it is a more refined measurement than the raw brain-to-body mass ratio, as it takes into account allometric (shape, anatomy, physiology) effects.
What is the function of the frontal lobe?
Short-term memory, action planning, movement control
What is the function of the parietal lobe?
Integrates sensory information among various modalities
spatial sense, navigation, touch, pain
What is the function of the occipital lobe?
Vision
What is the function of the temporal lobe?
Hearing, emotion, learning, memory
What is the neocortex?
The center of higher cognitive functions and intelligence, part of the cerebral cortex.
Most parts are organized into six layers:
(I. outermost, VI. innermost - adjacent to white matter)
I. Molecular layer
II. External granular layer
III. External pyramidal layer
IV. Internal granule layer
V. Internal pyramidal layer
VI. Polymorphic / Multiform layer
The human visual system occupies 60% of the neocortex.
What is a cortical microcolumn?
A cortical minicolumn is a vertical column of 80-100 neurons through the cortical layers.
Neurons within the microcolumn receive common inputs, have common outputs, are interconnected, and may well constitute a fundamental computational unit of the cerebral cortex.
What is the cortical homunculus?
A cortical homunculus is a distorted representation of the human body, illustrating how much space the sensory representation of different parts of the body occupy on the cerebral cortex.
What is a nucleus?
A nucleus is a cluster of neurons in the brain.
What are the basal ganglia?
The basal ganglia are a group of nuclei located beneath the cerebral cortex, related to the motor system. They are engaged in the planning, execution and learning of actions.
What is the hippocampus?
A brain region with a seahorse-like shape.
Formation of episodic long-term memories
What is the amygdala?
A group of nuclei related to the analysis of the emotional or motivational significance of stimuli
almond-shaped
within the temporal lobe
What are pyramidal neurons?
Pyramidal neurons are a type of multipolar neuron found in areas of the brain including the cerebral cortex, hippocampus and amygdala.
What species has superior sequence learning capabilities?
Compared to other species, humans have superior capabilities of learning sequences of stimuli.
What is the hindbrain composed of?
- Pons
- Medulla oblongata
- Cerebellum
What is the neuron doctrine?
The neuron doctrine is the concept that the nervous system is made up of discrete individual cells.
Golgi and Cajal laid the foundations at the end of the 19th century.
1873: Camillo Golgi developed the silver nitrate method for making the morphology of neural cells visible
1889: Santiago Ramón y Cajal improved the staining methods of Golgi and documented the his findings on the microscopic structure of the nervous system in a famous series of drawings
What are whole brain models?
Whole brain models are executable hypotheses of the architecture and the functioning of the brain.
Many whole brain models are large-scale simulations of different building blocks of the thalamocortical system.
All brain models so far were built based on a specific set of assumptions and for a specific purpose. The manual engineering applied to derive these models makes it hard to
incorporate new findings or to extend the them to represent additional aspects.
There is a clear need for a flexible unified model that captures all knowledge about the brain available to date and which can be easily extended to accommodate new data!
What are simplified engineered brain models and detailed data-driven brain models?
Simplified engineered brain models are defined manually based on rules and statistics identified in datasets.
Detailed data-driven brain models are reconstructed from data based on an automatic toolchain.
Detailed modelling at large scale requires considerable amount of processing power and storage and therefore became possible only in recent years.
What is Visual Cortex (1992)?
One of the first large-scale brain models of the visual cortex.
The model is comprised of 10,000 neuronal groups (for efficiency) and 1,000,000 connections.
It receives input from a color camera and solves the binding problem.
What is the Thalamocortical System (2008)?
An engineered whole brain model based on MRI measurements and 3D neuron reconstructions.
- 1 million spiking multi-compartment neurons and 500 million synapses
- the model is able to reproduce typical patterns of brain activity
Izhikevich et. al (2008)
What is Spaun (2012)?
A functional spiking neuron-based whole brain model that was synthesized from abstract cognitive architecture.
- 2.5 million spiking neurons
- cognitive architecture implements cognitive functions such as image recognition, working memory, perception and action
Focus is on production of behavior
What is the Blue Brain Project (2015)?
The Blue Brain Project is a brain research initiative that aims to create a digital reconstruction of the brain by a data-driven reconstruction process for cortical microcircuits.
- 31,000 anatomically detailed neurons and 37 million snypases
- digital reconstruction that is based on both experimental data and predictions
- reproduces data recorded in experiments!
What are saccades?
Both voluntary and reflexive eye movements that direct the gaze towards objects and regions of interest (ROI).
What are the conceptual processing layers in the human visual system?
(What are the three levels of visual perception?)
- lower-level vision: basic image analysis (e.g. lines)
- mid-level vision: processing of objects, surfaces and orientations
- high-level vision: visual processing based on memory and intentions
What is top-down and bottom-up processing?
Visual input is processed both bottom-up (sensory inputs) and top-down (including memory and context through high-level vision).
What is the optic chiasm?
The optic chiasm is the part of the brain where the optic nerves emerging from the retinas cross.
From this point on, each hemisphere receives half the input of each of the eyes, a prerequisite for binocular vision.
What is the two-streams hypothesis of visual processing?
Visual information in primate brains is processed along two streams:
- dorsal stream: “where?” - fast
- ventral stream: “what?” - slow
What is the neocognitron?
The neocognitron is a hierarchical, multilayered artificial neural network proposed by Fukushima in 1979. It is able to recognize patterns by learning the shapes of objects.
It is the original deep convolutional neural network (CNN) architecture.
What is the difference between static and dynamic connectivity in the brain?
- static connectivity: anatomical connectivity
- dynamic connectivity: functional connectivity, dependent on the current cognitive task
What is Barlow’s dogma?
For each decision in the brain there is a dedicated neuron.
