🧠Neuromorphic Engineering Unit 2 – Neuroscience Fundamentals

Key Concepts and Terminology

• Neuroscience studies the nervous system, including the brain, spinal cord, and peripheral nerves
• Neurons are the primary functional units of the nervous system, responsible for processing and transmitting information
• Glia are non-neuronal cells that support and maintain the nervous system (astrocytes, oligodendrocytes, and microglia)
• Action potentials are electrical impulses generated by neurons to transmit information along their axons
• Synapses are specialized junctions between neurons where information is transmitted through chemical or electrical signals
• Neurotransmitters are chemical messengers released by neurons at synapses to communicate with other neurons (glutamate, GABA, dopamine)
• Neuroplasticity refers to the brain's ability to change and adapt in response to experience, learning, and injury
• Neuromorphic engineering aims to design artificial neural systems inspired by the principles of biological neural networks

Neuroanatomy Basics

• The central nervous system (CNS) consists of the brain and spinal cord, while the peripheral nervous system (PNS) includes nerves that extend throughout the body
• The brain is divided into several regions, each with specific functions:
  • Cerebral cortex: responsible for higher cognitive functions (perception, language, decision-making)
  • Cerebellum: involved in motor coordination and balance
  • Brainstem: regulates vital functions (breathing, heart rate, sleep)
• The spinal cord transmits sensory and motor information between the brain and the body
• White matter consists of myelinated axons that facilitate rapid information transmission, while gray matter contains neuronal cell bodies and synapses
• The blood-brain barrier is a selective barrier that regulates the passage of substances between the bloodstream and the brain, maintaining a stable environment for neurons
• Ventricles are fluid-filled cavities within the brain that produce and circulate cerebrospinal fluid (CSF)

Neuronal Structure and Function

• Neurons have a cell body (soma) containing the nucleus and organelles, dendrites that receive input, and an axon that transmits output
• Dendrites are branched extensions that receive signals from other neurons and integrate them at the soma
• The axon is a long, thin process that conducts electrical signals away from the soma to other neurons or effector cells (muscles, glands)
• The axon hillock is the site of action potential initiation, where the electrical signal begins
• Myelin is an insulating sheath around axons that enhances signal transmission speed and efficiency
• Ion channels are proteins embedded in the neuronal membrane that allow the selective passage of ions (sodium, potassium, calcium)
• The resting membrane potential of a neuron is typically around -70 mV, maintained by the unequal distribution of ions across the membrane

Synaptic Transmission

• Synapses can be chemical, where neurotransmitters are released, or electrical, where ions flow directly between neurons through gap junctions
• In chemical synapses, the presynaptic neuron releases neurotransmitters into the synaptic cleft, which bind to receptors on the postsynaptic neuron
• Neurotransmitter release is triggered by the arrival of an action potential at the presynaptic terminal, causing calcium influx and vesicle fusion
• Excitatory neurotransmitters (glutamate) increase the likelihood of the postsynaptic neuron firing an action potential, while inhibitory neurotransmitters (GABA) decrease it
• Neurotransmitters are cleared from the synaptic cleft by reuptake into the presynaptic neuron or degradation by enzymes
• Synaptic plasticity refers to the ability of synapses to strengthen or weaken over time, underlying learning and memory (long-term potentiation, long-term depression)

Neural Networks and Circuits

• Neural networks are interconnected groups of neurons that process and transmit information
• Feedforward networks have unidirectional information flow from input to output, while recurrent networks have feedback loops
• Parallel processing allows multiple neural pathways to process information simultaneously, enabling complex computations
• Oscillations and synchronization of neural activity are important for information processing and communication between brain regions
• Neuronal circuits can be excitatory, inhibitory, or modulatory, depending on the types of neurons and neurotransmitters involved
• Cortical columns are vertical arrangements of neurons in the cerebral cortex that process similar information

Neuroplasticity and Learning

• Neuroplasticity enables the brain to adapt and reorganize in response to experience, learning, and injury
• Synaptic plasticity, including long-term potentiation (LTP) and long-term depression (LTD), underlies learning and memory formation
  • LTP strengthens synaptic connections through repeated activation, while LTD weakens them
• Structural plasticity involves changes in neuronal morphology, such as the growth or pruning of synapses and dendrites
• Critical periods are developmental windows of heightened plasticity when the brain is particularly sensitive to environmental input (visual system, language acquisition)
• Adult neurogenesis is the formation of new neurons in specific brain regions throughout life, contributing to plasticity and learning
• Neuroplasticity can be harnessed for rehabilitation after brain injury or stroke, as intact brain regions can compensate for damaged areas

Neurotransmitters and Neuromodulators

• Neurotransmitters are chemical messengers released by neurons to transmit signals across synapses
• Glutamate is the primary excitatory neurotransmitter in the CNS, involved in learning, memory, and synaptic plasticity
• GABA (gamma-aminobutyric acid) is the main inhibitory neurotransmitter, regulating neuronal excitability and preventing excessive activity
• Dopamine is involved in reward, motivation, and motor control, and its dysregulation is associated with disorders like Parkinson's and addiction
• Serotonin modulates mood, sleep, and appetite, and is targeted by antidepressant medications (SSRIs)
• Acetylcholine is involved in attention, learning, and muscle control, and its deficiency is linked to Alzheimer's disease
• Norepinephrine is involved in arousal, attention, and stress response, and is part of the sympathetic nervous system
• Neuromodulators are substances that modify the effects of neurotransmitters, altering neuronal excitability and synaptic transmission (endocannabinoids, neuropeptides)

Linking Neuroscience to Engineering

• Neuromorphic engineering seeks to design artificial neural systems that mimic the principles and functions of biological neural networks
• Artificial neural networks (ANNs) are computational models inspired by the structure and function of biological neurons and networks
  • ANNs consist of interconnected nodes (artificial neurons) that process and transmit information
• Brain-machine interfaces (BMIs) enable direct communication between the brain and external devices, with applications in prosthetics, rehabilitation, and communication
• Neuroprosthetics aim to restore or enhance sensory, motor, or cognitive functions by interfacing with the nervous system (cochlear implants, retinal prostheses)
• Neuromorphic sensors and processors emulate the efficient processing and energy consumption of biological neural systems
• Neurorobotics combines neuroscience, robotics, and AI to create robots with brain-inspired control systems and learning capabilities
• Computational neuroscience uses mathematical models and simulations to study the function and dynamics of neural systems, informing neuromorphic designs
• Neuromorphic engineering can advance our understanding of the brain by providing testable models and platforms for experimentation