
Sub Topics: Molecular and Cellular Neuroscience, Cognitive Neuroscience,...
Sub Tracks Clinical Neurology, Neurodegenerative...
Sub Tracks: The Functional Units
of the Nervous System, Ion Channels and Membrane Potential, Synaptic
Transmission, Glial Cells and Their Roles,Cellular Mechanisms of Learning and
Memory, Excitability and Ion Homeostasis, Neural Circuitry and Connectivity
Cellular
Neuroscience is a branch of neuroscience that focuses on
the study of the cells of the nervous system, particularly neurons and glial
cells, and how they function, communicate, and contribute to higher brain
functions. It deals with the physiological mechanisms that govern cellular
activity within the nervous system, including the electrical properties of
neurons, synaptic transmission, and the cellular changes that occur during
learning, memory, and disease processes.
1. Neurons: The
Functional Units of the Nervous System
Structure of Neurons:
Cell Body (Soma): Contains the nucleus and other organelles;
responsible for metabolic activities of the neuron.
Dendrites: Tree-like branches that receive electrical
signals from other neurons.
Axon: The long extension that transmits electrical impulses
away from the cell body to other neurons or muscles.
Axon Terminals: Release neurotransmitters to communicate
with other neurons or effector cells.
Myelin Sheath: Fatty layer surrounding the axon (formed by
oligodendrocytes in the CNS and Schwann cells in the PNS), which helps speed up
electrical signal conduction.
Types of Neurons:
Sensory Neurons: Transmit sensory information from receptors
(e.g., skin, eyes) to the central nervous system (CNS).
Motor Neurons: Carry signals from the CNS to muscles and
glands to elicit a response.
Interneurons: Located in the CNS, connecting sensory and
motor neurons, playing a critical role in processing information.
2. Ion
Channels and Membrane Potential
Resting Membrane Potential:
Neurons maintain a resting membrane potential of about
-70mV, which is created by differences in the concentration of ions inside and
outside the cell (mostly Na+, K+, and Cl- ions).
The sodium-potassium pump plays a key role in maintaining
these gradients by pumping 3 Na+ out of the cell for every 2 K+ in.
Action Potential:
Depolarization: When a neuron is stimulated, sodium channels
open, causing an influx of Na+ ions and a shift in membrane potential.
Repolarization: Potassium channels open, and K+ ions flow out
of the neuron, restoring the resting potential.
Hyperpolarization: The membrane potential becomes more
negative than the resting potential before returning to its resting state.
3.
Synaptic Transmission
Chemical Synapses:
Neurons communicate across synapses via the release of
neurotransmitters.
Pre-synaptic Neuron: Releases neurotransmitters into the
synaptic cleft after an action potential depolarizes the axon terminal.
Post-synaptic Neuron: The receptors on the postsynaptic
membrane bind neurotransmitters, leading to depolarization or
hyperpolarization.
Neurotransmitters:
Excitatory Neurotransmitters: E.g., Glutamate, which
promotes the firing of action potentials in the postsynaptic neuron.
Inhibitory Neurotransmitters: E.g., GABA, which inhibits
action potential firing.
Synaptic Plasticity:
Long-Term Potentiation (LTP): Strengthening of synaptic
connections, important for learning and memory.
Long-Term Depression (LTD): Weakening of synapses, thought
to play a role in forgetting and synaptic pruning.
4. Glial
Cells and Their Functions
Astrocytes: Support neurons, maintain the blood-brain barrier,
regulate blood flow, and help recycle neurotransmitters like glutamate.
Oligodendrocytes and Schwann Cells:
Oligodendrocytes form myelin in the CNS.
Schwann Cells form myelin in the PNS. Both myelinate axons,
speeding up signal transmission.
Microglia: The immune cells of the CNS, involved in inflammation,
immune responses, and clearing cellular debris.
Ependymal Cells: Line the ventricles of the brain and produce
cerebrospinal fluid (CSF), which cushions and protects the brain.
5. Signal
Transduction and Second Messengers
Receptor-Mediated Signaling:
Ionotropic Receptors: Directly linked to ion channels. For
example, NMDA receptors are involved in synaptic plasticity.
Metabotropic Receptors: Involved in G-protein coupled
signaling pathways. For example, dopamine receptors influence intracellular
pathways that affect gene expression and neural activity.
Second Messengers:
cAMP and calcium ions (Ca2+) are important intracellular
messengers that amplify and transduce signals.
Phosphorylation: The activation of proteins by the addition
of phosphate groups, often mediated by protein kinases, is a key part of signal
transduction.
6.
Synaptic Vesicle Release and Recycling
Vesicle Fusion: Neurotransmitters are packaged into synaptic
vesicles and released into the synaptic cleft when an action potential
depolarizes the presynaptic terminal.
Exocytosis: The process of neurotransmitter release into the
synaptic cleft, triggered by Ca2+ influx.
Reuptake: Neurotransmitters are removed from the synapse
either by transporters (reuptake) into presynaptic neurons or nearby glial
cells, or degraded by enzymes.
7.
Cellular Mechanisms of Learning and Memory
Synaptic Plasticity: Changes in synaptic strength (either
potentiation or depression) are believed to be the cellular basis of learning
and memory.
Calcium Signaling: Calcium ions play a critical role in both LTP and
LTD and are central to modulating synaptic strength.
Gene Expression: Learning can lead to changes in gene expression
that alter the structure and function of synapses, making them more efficient
at transmitting signals.