Cell Signalling, Signal Transduction, Nervous System Flashcards
what are the division of the nervous system and what are the components?
Nervous system is divided into the (CNS) and (PNS).
CNS: brain and spinal cord
PNS: Nerves and ganglia divided into,
Somatic- sensory and motor functions
Autonomic- sympathetic and parasympathetic
Etheric- digestive tract control
What are the main types of glial cells, and what are their functions?
Astrocytes: Regulate neurotransmitters, maintain synaptic functions
Ependymal cells: produce and circulate cerebrospinal fluid
Oligodendrocytes: myelinate axons in the CNS
Microglia: act as macrophages, clearing debris and pathogens
Schwann cells: Myelinate axons in the PNS
Describe the structure and function of a neuron
Primary signaling cells,
Dendrites: receive input signals
Cell body: integrates signals
Axon: Transmits action potential
Axon terminals: Release neurotransmitters to communicate with other cells.
What is an action potential, and how is it generated and propagated?
Resting potential: -70mv maintain by Na+/k+ pumps and leak channels
Threshold-depolarisation to -50mv triggers voltage-gated Na+ channels.
Depolarisation: Na+ influx makes the membrane potential more positive.
Repolarisation- K+ efflux restores negative potential
Hyperpolarisation- temporary over as K+ channels close slowly.
Restoration: Na+/K+ pump re-establishes resting potentials.
How does myelination affect action potential propagations?
Myelin sheaths produced by Schwann cells (PNS) or oligodendrocytes (CNS), insulate axons.
Action potentials jump between nodes of ranvier (saltatory conduction) increases speed.
What are refractory periods and why are they important?
Absolute refractory period: During repolarisation, no action potential can be generated
Relative refractory period: during hyperpolarisation a stronger stimulus is required to trigger an action potential.
Unidirectional flow of action potentials and prevent overlapping signals.
What are G protein-coupled receptors (GPCRs) and how they function?
GPCRs are cell surface receptors with 7transmembrane domains
Ligand binding activate the receptor causes G proteins activation
GDP is replaced by GTP on the Ga sub-unit
Ga dissociates from Gby, activating signalling cascades
What are second messengers, and why are they important?
Second messengers are small molecules that amplify and transmit signals within cells.
cAMP- activates PKA
Ca2+- modulates calmodulin and CaM kinases
IP3 and DAG - produced by phospholipase C affect calcium levels and PKC
Describe the adenylyl cyclase cAMP pathway
Addenylyl cyclase converts ATP to cAMP upon activation by G-protein.
cAMP activates protein kinase A (PKA) which phosphorylates targets alternating metabolism and gene expression
How do G proteins regulate ion channels
Indirectly modulate ion channels via second messengers (camp, iP3)
Directly bind ion channels to alter their activity
What are the differences between the G protein subtypes (Gs,Gi,Gq)
Gs-stimulates Adenylyl cyclase, increasing cAMP levels
Gi-inhibits adenylyl cyclase, reducing cAMP levels
Gq- activates phospholipase C, producing iP3 and DAG leading to increased calcium signalling.
What are receptor tyrosine kinases (RTKs), and how do they function ?
RTKs are transmembrane receptors with intracellular kinase domains.
Ligand binding induces dimerisation and autophosphorylation of tyrosine residues
Phosphorylated RTKs recruit and activate downstream signaling proteins
What is MAP kinase pathway and why is it significant
Cascade triggered by RTKs, involving sequential phosphorylation,
1. Activation of Ras (gtp enzyme)
2. Ras activates MAP kinase kinase kinase
3. MAPKKK activates MAP kinase kinase
4. MAPKK activates MAP kinase, modulates transcription factors
Regulates cell growth, differentiation and survival
What mechanism terminates signal transduction
Dephosphylation-phosphates remove phosphates from proteins
GTP hydrolysis- G-proteins return to inactive GDP bound state
Ligand receptor complexes are endocytosed and degraded
Negative feedback loops- reduce pathway activation over time
How do different receptor types coordinate cellular responses?
Ion channel-linked receptors cause rapid changes in membrane potential
GPCRs amplify signals via second messengers
RTKs - regulate long term changes like growth and differentiation through transcriptional modifications.
