Neurophysiology: Neurons and Circuits Flashcards
Describe the difference between ionotropic and metabotropic receptors
- ionotropic: ligand-gated channels, fast response, direct ion flow
- metabotropic: GCPR, slower response, modulate ion channels indirectly
different classes of neurotransmitters
small-molecule neurotransmitters
amines
peptides
small-molecule neurotransmitters
small-molecular neurotransmitters (acts on ionotropic receptors, rapid responses, rapidly cleared from synaptic cleft)
amines
(released upon depolarisation and Ca2+ influx, can act on both ionotropic and metabotropic receptors, cleared by reuptake or enzymatic degradation)
peptides
(requires sustained stimulation to be released, typically acts on metabotropic receptors, thus slower and more prolonged responses, slow inactivation i.e. slower removal from synaptic cleft)
Explain graded changes in membrane potential from synaptic inputs
- synaptic inputs modulate the RMP
- can result in depolarisation (excitation) or hyperpolarisation (inhibition)
- information conveyed through chemical or electrical messages
Describe the difference between the different families of glutamate receptors
- AMPA, kainate and NMDA receptors
- subunits determine receptor chacterstics
- different subunit combinarions create various receptors
- AMPA receptors are non-selective cation channels mainly allowing Na+ influx
- NMDA contain an Mg2+ ion which blocks ions from flowing through channel so requires depolarisation before can function properly
Describe the steps in glutamate fast excitatory neurotransmission
- glutamate binds to ionotropic receptors AMPA and NMDA
- AMPA receptor activation leads to rapid Na+ influx and therefore depolarisation
- NMDA receptors allow Ca2+ entry after Mg2+ removal (triggered by teh depolarisation)
AMPA and NMDA receptors often work together for efficient transmission
Describe the different mechanisms for inactivating neurotransmitters
- recycling: glutamate removed, recycled and repackaged
- vesicular glutamate transporters (VGLUT) package glutamate into vesicles
- excitatory amino acid transporters (EATT) rapidly remove glutamate from the synaptic cleft
Describe the difference between electrical and chemical synapses
- chemical synapses: neurotransmitters released, bind to post-synaptic receptors
- electrical synapses: gap junctions physically connect neurons, allowign direct ionic passage
Describe the composition of gap junctions and the movement of ions through gap junctions
- gap junctions are composed of connexons with connexins
- connexons form a pore allowing bidirectional movement of ions
- communication of small molecules like calcium and ATP can occur through gap junctions
Discuss the Goldman and Nernst equations
- Goldman equation: calculates resting membrane potential, considering multiple ions and their permeabilities
- Nernst equation: calculates the equilibrium potential for a single ion based on its concentration
Describe how a potential is established across the neuronal membrane
- neurons exist in a state with a potential difference across their membrane
- changes in membrane potential occur due to excitatory or inhibitory inputs
- action potentials, triggered by reaching the threshold, allow long-distance communication
Identify the major constituent ions in intracellular and extracellular solution
- intracellular: High K+, low Na+, low Cl-, low Ca2+
- extracellular: low K+, high Na+, high Cl-, high Ca2+
Describe the electrical gradient, the chemical gradient and the electrochemical gradient
- electrical gradient: movement of charged particles along potential differences
- chemical gradient: movement along concentration differences
- electrochemical gradient: combined influence of electrical and chemical gradients
Define and explain why the plasma membrane is “semi-permeable”
- the neuronal plasma membrane allows some ions to pass through by restricts others
- ion channels play a crucial role in this selectivity
Explain how ions can move across the semi-permeable neuronal plasma membrane
- ions move along electrical and concentration gradients
- cell membrane is semi-permeable, allowing selective ion movement
- ion channels facilitate the passage of ions
Explain ion transporter, ion exchangers, ion pumps
- ion transporters (pumps) uses ATP to move ions agaisnt their concentration gradient
- ion exchangers utilise ion concentration gradients to move other ions without ATP
- the Na+/K+ pump, an ATPase pump, maintains ion concentration gradients
Describe how ion channels are gated and selective
- ion channels can be voltage-gated, ligand-gated or mechanically gated
- selectivity means specific ion channels allow specific ions to pass through
- channels open and close in response to various stimuli
Explain what is meant by the “equilibrium potential” of an ion
- equilibrium is reached when electrical and chemical gradients balanc
- no net movement of an ion at equilibrium
- membrane potential at equilibrium is the equilibrium potential
functional phenotype
- describes what a neuron does e.g. excites skeletal muscle cells for motor function
- identified through electrophysiology or observing its effect on post-synaptic cells
name the different types of glial cells and briefly describe their role in the nervous system
- oligodendrocytes (CNS) and Schwann cells (PNS) form myeline sheaths
- microglia act as local immune cells
- astrocytes support CNS, contribute to the blood-brain barrier and regulate ion balance
- ependymal cells create barriers and produce neural stem cells
- radial glia guid neuronal migration during development
chemical phenotype
- involves neurotransmitters produced/used (e.g. acetylcholine in motor neurons)
- identified through direct labelling, mRNA analysis, or genetic markers
combined phenotype example
cholinergic motor neuron is both functionally excitatory and uses acetylcholine
Describe the key characteristics of neurones
- Neurons are excitable cells, capable of changing their membrane potential
- classified based on their morphology, location, chemical signature and function
- information usually flows from dendrites to cell body to axon
- communicate at synapses
describe the key roles of astrocytes within the central nervous system
- regulate neurotransmission fidelity by removing excess neurotransmitters
- maintain extracellular ion homeostasis
- spatial buffering via gap junctions
- regulate blood vessel diameter and neural activity
- contribute to the blood-brain barrier
- release gliotransmitters for active communication
describe the importance of astrocytes in neuronal function and well-being
- astrocytes regulate neuronal function, blood flow and the blood-brain barrier
- actively participate in neurotransmission through gliotransmitters
- support homeostasis, ensuring proper neural activity and extracellular ion balance
describe and identify the common regions of neurones
all neurons have synapses, dendrites (mostly), cell body/soma, axo hillock and axon
describe the direction of the flow of information in neurons
- information flows from dendrites to cell body to axon
- special cases dendrites are skipped
determine the output of a simple neural circuit
- output is the sum total of all inputs within the circuit
- excitatory neurons increase post-synaptic cell activity
- inhibitory neurons decrease post-synaptic cell activity
explain the difference between excitatory and inhibitory neurons
- excitatory neurons
- increase activity of post-synaptic cell
- release neurotransmitters that enhance neural activity
- inhibitory neurons
- decrease activity of post-synaptic cell
- release neurotransmitters that suppress neural activity
Ion channel fundamentals:
- Determinants: Electrochemical gradient (chemical and electrical gradients).
- Effect on Membrane Potential: Inhibitory ion channels lead to hyperpolarization.
- Equilibrium Potential: Membrane potential with no net ion movement through open channels.
- GABA’s Dual Role: Context-dependent excitatory or inhibitory function.
Inhibitory neurons:
- Role: Coordinate muscle groups, selective activation, and modulation of neural activity.
- Neurotransmitters: GABA and glycine.
- Differentiation: Receptors recognize subtle structural differences.
GABA’s dual role
GABA is not always inhibitory; in some contexts, such as the enteric nervous system of invertebrates, it can be excitatory. This shift is attributed to changes in GABA’s intracellular concentration during maturation.
Explain the concept of equilibrium potential
Equilibrium potential, also known as reversal potential, is the membrane potential at which there is no net movement of a specific ion through its open channel. The electrochemical gradient, determined by the Nernst equation, dictates the equilibrium potential for an ion.
Describe the effect of activating inhibitory ion channels on membrane potential
Activating inhibitory ion channels, such as GABA and glycine receptors, leads to hyperpolarization of the membrane potential.
This inhibitory effect results from the movement of chloride ions, which makes the interior of the cell more negative.
Explain what determined the movement of ions through an ion channel
The movement of ions through an ion channel is determined by the electrochemical gradient, which includes both the chemical concentration gradient and the electrical potential gradient across the cell membrane.
The Nernst equation describes the equilibrium potential for an ion, determining the direction of ion movement.
Identify the major fast inhibitory neurotransmitters
The major fast inhibitory neurotransmitters are GABA (gamma-aminobutyric acid) and glycine.
Describe and identify the difference between GABA and glutamate
GABA and glutamate are both neurotransmitters, but GABA is the principal fast inhibitory neurotransmitter, while glutamate is the principal fast excitatory neurotransmitter. The structural difference between them lies in a carboxyl group, and GABA is synthesized from glutamate by the enzyme glutamic acid decarboxylase (GAD).
Describe the mechanism that allows receptors to differentiate between very similar molecules
Receptors differentiate between similar molecules through their specific structural configurations and binding sites.
Even though GABA and glutamate are structurally similar, the receptors have evolved to recognize subtle differences, allowing for the precise and selective binding of neurotransmitters to their respective receptors.
Describe and explain why inhibitory neurons are important in neural circuits
Inhibitory neurons play a crucial role in neural circuits by causing hyperpolarization, which inhibits or prevents the firing of neurons.
This allows for the coordination of antagonistic muscle groups, selective activation of specific behavioural pathways, and modulation of neural activity, contributing to the overall fine-tuning and control of neural circuits.
Identify the enzymes and transporters specific to catecholamine
- the enzymes used in catecholamine pathways are tyrosine hydroxylase, DOPA decarboxylase, DBH and PNMT
- transporters used are DAT (an Na+ co-transporter that takes up dopamine), NA/A (NET also a Na+ co-transporter that take sup dopamine) and vesicular monoamine transporter (VMAT that takes up all monoamines)
Name the major monoamine neurotransmitters in the central nervous system
dopamine, noradrenaline, GABA, adrenaline
Describe the synthetic pathway for catecholamines
- tyrosine is converted to DOPA via the enzyme tyrosine hydroxylase
- DOPA is then converted to dopamine via DOPA decarboxylase enzyme
- dopamine is then converted to norarenaline via DBH enzyme
- finally, noradrenaline is converted to adrenaline via PNMT enzyme
Identify the different second messengers utilised in GPCR signalling pathways
Second messengers include Ca2+, cyclic nucleotides (cAMP), IP3, DAG, etc.
Describe the common effect of presynaptic GPCRs
Metabotropic receptors alter neuronal activity between receptors and ion channels.
Identify the effect of different intracellular pathways activated by GPCRs
- Gαq-PLC pathway may lead to Ca2+ release and activation of multiple pathways.
- Gαs can stimulate adenylyl cyclase, increasing cAMP.
Describe the intracellular signalling pathways in response to activation of metabotropic receptors
- Metabotropic receptors interact with different intracellular pathways.
- G-proteins (e.g., Gαq) activate effectors (e.g., phospholipase C).
- Different effectors produce second messengers (e.g., IP3, DAG).
Describe the difference between ionotropic and metabotropic receptors
- Ionotropic receptors directly open ion channels upon ligand binding.
- Metabotropic receptors activate intracellular signaling pathways in response to ligand binding
Describe the key ion movements involved in changes in membrane potential
During changes in membrane potential, key ion movements involve the passive diffusion of ions such as K+ through leak channels. This movement is influenced by both concentration and electrical gradients.
Explain ‘graded potential’
Graded potentials are based on the stimulus received by the neuron, particularly how it is influenced by other neurons. These potentials represent local changes in membrane potential, with the strength of the stimulus determining the magnitude of the response.
Describe how and where action potentials are initiated
Action potentials are initiated at the axon hillock, specifically in the axon initial segment (AIS). This is where the membrane potential reaches the threshold, leading to the opening of voltage-gated Na+ channels.
Describe the phase of the action potential, including the ions and their direction of movement
- Resting Phase: Voltage-gated Na+ channels are closed at -65mV.
- Depolarization: Channels open around -55mV, allowing an influx of Na+, causing depolarization.
- Repolarization: At +30mV, K+ channels open, leading to repolarization.
- Undershoot Phase: Slight overshoot due to the activity of Na+ and K+ leak channels.
Describe the role and phases of different ion channels in the phases of action potential generation
- In the phases of action potential generation, voltage-gated Na+ channels play a crucial role. They open during depolarization, allowing Na+ influx, and then become inactive, contributing to the peak of the action potential.
- Voltage-gated K+ channels open during the falling and undershoot phases, facilitating repolarization.
Describe the importance of the myelin sheath and node of Ranvier
The myelin sheath, formed by oligodendrocytes (CNS) or Schwann cells (PNS), insulates axons, allowing action potentials to skip from one node of Ranvier to the next. This saltatory propagation enhances the speed of action potential transmission.
Compare propagation of action potential between myelinated and unmyelinated fibres
Propagation of action potentials differs between myelinated and unmyelinated fibers. Myelinated fibers exhibit saltatory propagation, skipping nodes, leading to faster transmission compared to the continuous propagation in unmyelinated fibers.
Name and identify the specialised proteins that can be used to identify the AIS
Specialized proteins such as B4-Spectrin and Ankyrin-G are crucial for organizing the axonal cytoskeleton and clustering voltage-gated channels, particularly sodium and potassium channels, at the AIS. Mutations in these proteins can lead to severe neurodevelopmental disorders.
Describe the contribution of voltage-gated channels in action potential generation
Voltage-gated channels, particularly NaV and Kv, contribute significantly to action potential generation. They are highly expressed within the AIS and nodes of Ranvier, facilitating the rapid transmission of action potentials over long distances.
Describe and compare EPSP and IPSP
- Excitatory Postsynaptic Potentials (EPSP) and Inhibitory Postsynaptic Potentials (IPSP) are variations in membrane potential caused by synaptic inputs.
- EPSP tends to depolarise the membrane, making it more likely to generate an action potential
- IPSP hyperpolarises, reducing the likelihood of action potential generation. Both are crucial in integrating signals in dendrites and soma.
Describe what is myelin is
myelin is a multi-layered, compacted membranous sheath that surrounds and insulates axons in the nervous system, facilitating rapid nerve impulse conduction
Name the cells responsible for the production of myelin
In the Peripheral Nervous System (PNS), Schwann cells are responsible for myelinating axons. In the Central Nervous System (CNS), oligodendrocytes perform the myelination process.
Describe what myelin is composed of
myelin is composed of lipids, cholesterol, phospholipids and glycolipids, forming a dense and tough membranous sheath that appears white. unique proteins like MAG and MOG are present, attracting and compacting adjacent myelin layers
Describe the general organisation of myelin
Myelin is organized into internodes separated by nodes of Ranvier. Internodes consist of compacted myelin sheaths, while nodes of Ranvier are exposed areas with a higher density of sodium channels.
Explain the roles and importance of the node of Ranvier, paranoid, juxtaparanode
- Node of Ranvier: Contains clusters of voltage-gated sodium channels, facilitating saltatory conduction.
- Paranode: Adjacent to nodes, it forms the junction between non-compacted myelin loops and the axolemma, contributing to axonal structure.
- Juxtaparanode: Located between paranodes and internodes, it contains voltage-gated potassium channels, influencing ion movement.
Explain and describe the advantage myelin confers to neurons, including how it gives rise to the ‘speedy’ conduction of action potentials
Myelin enables saltatory conduction by reducing capacitance at internodes, allowing rapid activation of sodium channels at nodes. This results in faster propagation of action potentials, enhancing efficiency and metabolic benefits.
Describe the process of ion movement and the propagation of action potentials with and without myelin
- With Myelin: Saltatory conduction occurs, where action potentials “whip” through internodes due to reduced capacitance, activating sodium channels at nodes, resulting in faster and more metabolically efficient conduction.
- Without Myelin: Action potentials propagate more slowly along the entire axon, requiring continuous sodium influx, leading to higher capacitance and reduced speed.
Explain the role of the SNARE complex in vesicle fusion
the SNARE complex acts as a molecular machinery responsible for bringing synaptic vesicles in close proximity to the presynaptic membrane and mediating their fusion, leading to the release of neurotransmitters into the synaptic cleft. This process is tightly regulated and essential for efficient synaptic transmission.
Explain the role of VGCCs (voltage-gated calcium channels) in neurotransmitter release
VGCCs facilitate neurotransmitter release by allowing calcium influx into the presynaptic terminal upon membrane depolarization. Calcium influx triggers vesicle fusion with the presynaptic membrane, leading to the exocytosis of neurotransmitters into the synaptic cleft.
Define co-release and co-transmission
Co-release refers to the simultaneous release of multiple neurotransmitters from the same synaptic terminal, possibly from the same vesicle. Co-transmission, on the other hand, involves distinct neurotransmitters released from separate vesicles or boutons, mediating different synaptic effects.
Describe the process of vesicular recycling and the proteins involved
Vesicular recycling involves multiple steps such as docking, priming, fusion, and endocytosis. Proteins like synaptotagmin, SNAREs, clathrin, and dynamin play crucial roles in these processes, ensuring the efficient recycling of synaptic vesicles for neurotransmitter release.
Describe the sequence of events in neurotransmitter release
- Synthesis and storage of neurotransmitters.
- Action potential depolarizing the nerve terminal.
- Opening of voltage-gated calcium channels, leading to calcium influx.
- Calcium triggering vesicle fusion with the presynaptic membrane.
- Exocytosis of neurotransmitters into the synaptic cleft.
- Binding of neurotransmitters to receptors on the postsynaptic membrane
Compare and contrast the key differences between classical and non-classical neurotransmitters
Classical neurotransmitters are small molecules synthesized and stored at nerve terminals, released from small vesicles, and act rapidly for short durations. Non-classical neurotransmitters, in contrast, are larger peptides or gases synthesized at the cell body, stored in large dense core vesicles, and have slower and longer-lasting effects.
Describe the criteria that goes towards determining is a substance is a neurotransmitter
- Synthesis within neurons.
- Storage within vesicles.
- Release upon stimulation.
- Interaction with postsynaptic receptors to induce a biological effect.
- Mechanism for inactivation post-release.
- Ability to mimic the effect when applied directly to the postsynaptic membrane.
Key types of synaptic proteins
Key synaptic proteins include SNAREs (e.g., synaptobrevin, syntaxin, SNAP-25) involved in vesicle fusion, synaptotagmin for calcium binding, and various other proteins responsible for vesicle recycling (e.g., clathrin, dynamin).
Vesicles and their roles
Synaptic vesicles store neurotransmitters and are crucial for neurotransmitter release. They undergo cycles of docking, priming, fusion, and recycling. Proteins like synaptotagmin and SNAREs are involved in vesicle fusion, while others like clathrin mediate endocytosis for vesicle recycling.
Roles and types of Ca2+ channels
Voltage-gated calcium channels (VGCCs) play a crucial role in neurotransmitter release. Main types include N-type (Cav2.2) and P/Q-type (Cav2.1). These channels couple membrane depolarization to calcium influx, which triggers vesicle fusion and neurotransmitter release.
The organisation of a nerve terminal
The nerve terminal is organized with synaptic vesicles containing neurotransmitters. These vesicles are docked and primed at the presynaptic membrane, ready for release upon stimulation. Proteins like synapsin keep vesicles tethered within the reserve pool, while SNARE proteins facilitate vesicle fusion during exocytosis.
There are two main types of neurotransmitters:
- Classical neurotransmitters: These include small molecules like amino acids (e.g., glutamate, GABA, glycine) and monoamines (e.g., noradrenaline, dopamine, serotonin, acetylcholine).
- Non-classical neurotransmitters: These are larger peptides (e.g., substance P, neuropeptide Y) or gases (e.g., nitric oxide) synthesized at the cell body and typically involved in modulatory functions.
What is a postsynaptic density?
A postsynaptic density (PSD) is a specialized region in the postsynaptic neuron that contains a high concentration of membrane and cytoplasmic proteins clustered opposite the release sites or active zones of synapses. It appears dense in electron microscopy due to its protein concentration.
Neuroligins and other CAMs form key parts of the density and signal via different pathways
Neuroligins, a type of cell adhesion molecule (CAM), play crucial roles in organizing postsynaptic densities. They act as ligands for β-Neurexins located presynaptically. This interaction helps mediate the formation and maintenance of synapses between neurons, highlighting the importance of CAMs in synaptic signaling.
Definition of a neurotransmitter
A neurotransmitter is a chemical signal released from the presynaptic nerve terminal into the synaptic cleft. It affects the postsynaptic cell by binding to receptors, thereby altering the properties of the target cell temporarily.
Postsynaptic densities differ according to the type of synapse
Indeed, postsynaptic densities vary depending on the type of synapse. For example, excitatory synapses typically have different protein compositions compared to inhibitory synapses. This variation contributes to the functional diversity of synapses.
PSD95 is a core organising molecule due to its 3 PDZ domains and other signalling/binding domains
PSD95, a membrane-associated guanylate kinase (MAGUK) protein, is a central organizing molecule in postsynaptic densities. It possesses three PDZ domains, which allow it to bind to various synaptic proteins and receptors, facilitating the assembly and stabilization of the postsynaptic complex
Identify the major elements of post-synaptic densities and their roles in synaptic transmission
Major elements of postsynaptic densities include ligand-gated ion channels, anchoring proteins, cytoskeletal proteins, and regulatory proteins. These components are crucial for organizing and regulating synaptic transmission, ensuring proper signaling between neurons.
Discuss mechanisms that organise post-synaptic densities and key proteins involved
Post-synaptic densities are organized by a complex interplay of proteins, including MAGUKs like PSD95, cytoskeletal proteins like Shank, and cell adhesion molecules like neuroligins. These proteins interact to form a scaffold that anchors receptors and signaling molecules, contributing to the structural and functional integrity of the synapse.
Cytoskeletal proteins like Shank can have important signalling functions
Cytoskeletal proteins such as Shank play crucial roles in synaptic signaling and organization. Shank proteins interact with the actin cytoskeleton and other synaptic proteins, modulating synaptic function and facilitating communication between neurons.
Discuss trans-synaptic mechanisms by which postsynaptic density proteins help organize presynaptic active zones.
Trans-synaptic interactions mediated by proteins like neuroligins and neurexins play a crucial role in organizing both postsynaptic densities and presynaptic active zones. These interactions facilitate the alignment and stabilization of synaptic components, ensuring efficient neurotransmission between neurons.
Define sensory transduction
Sensory transduction is the process by which external or internal stimuli are converted into electrical signals that can be detected by the brain. It involves a change in the membrane potential of a sensory neuron terminal, ultimately leading to the generation of action potentials.
Identify mechanisms of sensory transduction
Sensory transduction mechanisms involve the interaction of the environment with structures capable of detecting stimuli and converting these interactions into changes in the properties of sensory neurons. These mechanisms vary depending on the sensory modality and the specific sensory structures involved.
Identify stimulus modalities that produce overall sensation
The main stimulus modalities include chemical (e.g., taste, smell, pain), electromagnetic (e.g., vision), and mechanoreceptors (e.g., touch, proprioception, audition). These modalities contribute to overall sensation by activating specific sensory pathways and neural circuits.
Recognise that some sensations depend on multiple modalities
Sensations often result from the integration of signals from multiple sensory modalities. For example, the perception of a complex event may involve inputs from vision, audition, and touch, among others.
Define a neuron receptive field and identify the types of information that form such fields
A neuron receptive field is the specific region of sensory space in which a stimulus can evoke a response from the neuron. The types of information that form receptive fields include the location, intensity, and modality of the stimulus.
Describe the types of sensory structures in the glabrous skin
Glabrous skin contains various sensory structures, including free nerve endings (pain, cool, and warm receptors), Pacinian corpuscles (vibration detectors), and Ruffini endings (slowly adapting receptors).
Describe the different types of firing properties of cutaneous sensors
Cutaneous sensors exhibit two main types of firing properties: rapidly adapting and slowly adapting. Rapidly adapting sensors fire transiently in response to stimulus onset, while slowly adapting sensors fire continuously throughout the duration of the stimulus.
Describe simple mechano-transduction
Simple mechano-transduction involves the activation of stretch-sensitive ion channels in sensory neuron terminals by mechanical deformation of specialized sensory structures. This process leads to the generation of generator potentials and, potentially, action potentials
Recognise that detection mechanisms can be in terminals of axons or in specialised receptor cells
Sensory detection mechanisms can be located either in the terminals of sensory axons or in specialized receptor cells associated with sensory structures. These mechanisms communicate with sensory axons to produce signals that affect behavior
Describe the different types of mechanoreceptor axons in skeletal muscle
There are three main types of mechanoreceptor axons in skeletal muscle: muscle spindles, Golgi tendon organs, and intrafusal muscle fibers. Muscle spindles encode muscle length, while Golgi tendon organs signal muscle tension.
Describe what happens when a muscle is stretched in terms of sensory transduction
When a muscle is stretched, mechanoreceptor axons within muscle spindles are deformed, leading to the opening of stretch-sensitive ion channels and the generation of action potentials. These action potentials encode information about the rate and magnitude of muscle stretch
Describe how Golgi tendon organs signal muscle tension
Golgi tendon organs, located at the junction between muscle fibers and tendons, detect muscle tension. When a muscle contracts, tension is applied to the Golgi tendon organ, deforming its terminals and depolarizing Ib afferents, which signal the muscle tension to the central nervous system.
Describe what taste is
Taste refers to the sensation evoked by chemical compounds, known as tastants, acting on the tongue.
Describe the mechanisms involved in this process
Taste transduction involves specific receptors in taste receptor cells (TRCs) on the tongue. These TRCs can be of different types, each expressing different taste receptors. Mechanisms of taste transduction include simple transduction in Type I TRCs, G-protein coupled receptor (GPCR) pathways in Type II TRCs, and transduction via otopetrin-1 in Type III TRCs.
Describe what olfaction is
Olfaction is the sense of smell, which involves the detection of volatile odorants in the air through olfactory receptors in the nasal cavity
Describe the mechanisms involved in this process
Olfactory transduction occurs in olfactory receptor neurons (ORNs) in the olfactory epithelium. Each ORN expresses olfactory receptors that bind to specific odorants. When odorants bind to receptors, they activate a G-protein coupled pathway, leading to the production of cyclic AMP (cAMP) and subsequent depolarization of the ORN membrane. This depolarization results in the generation of action potentials, which are transmitted to the brain via the olfactory nerve.
Describe what audition is
Audition refers to the sense of hearing, which involves the detection of sound waves by the ear and the conversion of these vibrations into electrical signals that can be interpreted by the brain.
Describe the mechanisms involved in this process
Auditory transduction occurs in the inner ear, specifically in the cochlea. Sound waves enter the cochlea through the oval window, causing vibrations of the basilar membrane. This movement stimulates hair cells in the organ of Corti, which convert mechanical stimuli into electrical signals. Hair cells release neurotransmitters onto auditory nerve fibers, which then transmit signals to the brain for processing.
