🧠Intro to Brain and Behavior Unit 2 – Neurophysiology

Key Concepts and Terminology

• Neurons are the fundamental units of the nervous system that process and transmit information
• Glia are non-neuronal cells that support and protect neurons, including astrocytes, oligodendrocytes, and microglia
• Action potentials are electrical impulses generated by neurons that allow for rapid communication over long distances
• Synapses are specialized junctions between neurons where information is transmitted through chemical or electrical signals
• Neurotransmitters are chemical messengers released by neurons that bind to receptors on target cells to influence their activity
• Neuroplasticity refers to the brain's ability to change and adapt in response to experience, learning, and injury
• Homeostasis is the maintenance of a stable internal environment within the body, regulated by the nervous system
• Neurological disorders are conditions that affect the structure or function of the nervous system (Alzheimer's disease, Parkinson's disease, multiple sclerosis)

Neuron Structure and Function

• Neurons are specialized cells that transmit electrical and chemical signals throughout the nervous system
• The soma, or cell body, contains the nucleus and organelles necessary for cellular function
• Dendrites are branched extensions of the soma that receive signals from other neurons
  • Dendritic spines are small protrusions on dendrites that form synapses with axon terminals
• The axon is a long, thin extension of the neuron that conducts electrical impulses away from the soma
  • Axons are often insulated by a myelin sheath, which increases the speed of signal transmission
• Axon terminals are the endpoints of axons that form synapses with other neurons or target cells
• Neurons can be classified by their structure (unipolar, bipolar, multipolar) or function (sensory, motor, interneurons)
• Sensory neurons detect stimuli from the environment and transmit signals to the central nervous system
• Motor neurons transmit signals from the central nervous system to muscles or glands to initiate movement or secretion

Electrical Properties of Neurons

• The neuronal membrane is selectively permeable, allowing certain ions to pass through ion channels
• The resting membrane potential of a neuron is typically around -70 mV, maintained by the unequal distribution of ions across the membrane
• Graded potentials are small, localized changes in membrane potential that can be excitatory (depolarizing) or inhibitory (hyperpolarizing)
  • Graded potentials are generated by the opening or closing of ligand-gated or voltage-gated ion channels
• Action potentials are all-or-none electrical impulses that propagate along the axon when the membrane potential reaches a threshold value
  • Action potentials involve the rapid opening and closing of voltage-gated sodium and potassium channels
• The refractory period is a brief time after an action potential during which the neuron cannot generate another action potential
• Myelin sheaths, produced by oligodendrocytes in the CNS and Schwann cells in the PNS, insulate axons and facilitate rapid signal transmission
  • Nodes of Ranvier are gaps in the myelin sheath where action potentials are regenerated, allowing for saltatory conduction

Synaptic Transmission

• Synapses are specialized junctions between neurons where information is transmitted through chemical or electrical signals
• Chemical synapses involve the release of neurotransmitters from the presynaptic neuron, which bind to receptors on the postsynaptic neuron
  • Synaptic vesicles containing neurotransmitters fuse with the presynaptic membrane and release their contents into the synaptic cleft
• Electrical synapses are gap junctions that allow direct electrical coupling between neurons, enabling rapid and bidirectional communication
• Neurotransmitter receptors can be ionotropic, directly opening ion channels, or metabotropic, activating intracellular signaling cascades
• Excitatory postsynaptic potentials (EPSPs) depolarize the postsynaptic membrane, increasing the likelihood of action potential generation
• Inhibitory postsynaptic potentials (IPSPs) hyperpolarize the postsynaptic membrane, decreasing the likelihood of action potential generation
• Synaptic plasticity refers to the ability of synapses to strengthen or weaken over time, underlying learning and memory
  • Long-term potentiation (LTP) is a persistent increase in synaptic strength, while long-term depression (LTD) is a persistent decrease

Neural Networks and Circuits

• Neural networks are interconnected groups of neurons that process and transmit information
• Feedback loops are circuits in which the output of a neuron influences its own input, either directly or indirectly
  • Positive feedback loops amplify signals, while negative feedback loops regulate and stabilize activity
• Convergence occurs when multiple presynaptic neurons synapse onto a single postsynaptic neuron, allowing for integration of information
• Divergence occurs when a single presynaptic neuron synapses onto multiple postsynaptic neurons, allowing for distribution of information
• Parallel processing involves the simultaneous processing of information by multiple neural pathways or circuits
• Neuronal oscillations are rhythmic patterns of activity in neural networks that are associated with various cognitive and behavioral states
• Neural circuits can be modified by experience and learning, leading to changes in synaptic strength and connectivity
• Disorders of neural networks and circuits can lead to conditions such as epilepsy, schizophrenia, and autism spectrum disorder

Neurotransmitters and Neuromodulators

• Neurotransmitters are chemical messengers released by neurons that bind to receptors on target cells to influence their activity
• Glutamate is the primary excitatory neurotransmitter in the CNS, involved in learning, memory, and synaptic plasticity
• GABA (gamma-aminobutyric acid) is the primary inhibitory neurotransmitter in the CNS, regulating neuronal excitability
• Acetylcholine is a neurotransmitter involved in muscle contraction, attention, and memory formation
  • Cholinergic neurons in the basal forebrain play a crucial role in attention and arousal
• Dopamine is a neurotransmitter involved in reward, motivation, and motor control
  • Dysfunction of dopaminergic systems is associated with Parkinson's disease and addiction
• Serotonin is a neurotransmitter involved in mood, sleep, and appetite regulation
  • Selective serotonin reuptake inhibitors (SSRIs) are commonly used to treat depression and anxiety disorders
• Norepinephrine is a neurotransmitter involved in arousal, attention, and stress responses
• Neuromodulators are substances that modify the effects of neurotransmitters or the excitability of neurons
  • Examples include endocannabinoids, neuropeptides, and hormones such as cortisol and estrogen

Neuroplasticity and Learning

• Neuroplasticity refers to the brain's ability to change and adapt in response to experience, learning, and injury
• Synaptic plasticity involves changes in the strength and number of synaptic connections between neurons
  • Long-term potentiation (LTP) and long-term depression (LTD) are forms of synaptic plasticity that underlie learning and memory
• Structural plasticity involves changes in the structure of neurons, such as the growth of new dendrites or the formation of new synapses
• Adult neurogenesis is the formation of new neurons in specific regions of the adult brain, such as the hippocampus and olfactory bulb
• Critical periods are developmental windows during which the brain is particularly sensitive to specific experiences or stimuli
• Enriched environments and cognitive stimulation can promote neuroplasticity and enhance cognitive function
• Neuroplasticity can be harnessed for rehabilitation after brain injury or stroke
  • Constraint-induced movement therapy (CIMT) is an example of a rehabilitation technique that promotes plasticity in the motor cortex

Clinical Applications and Disorders

• Neurodegenerative disorders, such as Alzheimer's disease and Parkinson's disease, involve the progressive loss of neurons and synaptic connections
  • Alzheimer's disease is characterized by the accumulation of amyloid plaques and neurofibrillary tangles, leading to cognitive decline and memory loss
• Neurodevelopmental disorders, such as autism spectrum disorder and attention-deficit/hyperactivity disorder (ADHD), involve atypical development of neural networks and circuits
• Psychiatric disorders, such as depression, anxiety, and schizophrenia, are associated with imbalances in neurotransmitter systems and altered brain connectivity
• Neuroimaging techniques, such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), allow for the visualization of brain activity and structure
  • These techniques can be used to study the neural basis of behavior and to diagnose and monitor neurological and psychiatric disorders
• Optogenetics is a technique that uses light to control the activity of genetically modified neurons, allowing for precise manipulation of neural circuits
• Deep brain stimulation (DBS) is a surgical treatment that involves the implantation of electrodes to modulate the activity of specific brain regions
  • DBS is used to treat movement disorders such as Parkinson's disease and dystonia, as well as psychiatric disorders such as depression and obsessive-compulsive disorder (OCD)