Nervous System: CNS, PNS, Neurons & Neuroglia

• The Central Nervous System (CNS) includes the brain and spinal cord, acting as the body's main control center.
• The CNS receives, processes, and integrates information from the peripheral nervous system.
• The Peripheral Nervous System (PNS) consists of nerves extending from the CNS to the rest of the body.
• The PNS relays sensory information to the CNS, and motor commands from the CNS to muscles and glands.
• Nervous tissue is composed of two main cell types: neurons and neuroglia.

Neurons

• Neurons are the functional units of the nervous system, specialized to conduct nerve impulses.
• Neurons are incapable of cell division.

Neuroglia (Glial Cells)

• Neuroglia support and protect neurons.
• Neuroglia are capable of cell division.

Cell Body (Soma)

• The cell body contains the nucleus and essential organelles for neuronal function.
• Clusters of cell bodies are called nuclei in the CNS and ganglia in the PNS.

Dendrites

• Dendrites are branched extensions that receive incoming signals, conducting them toward the cell body.

Axon

• The axon is a long, slender projection transmitting nerve impulses away from the cell body to other neurons, muscles, or glands.

Axon Terminals (boutons)

• Axon terminals are specialized endings releasing neurotransmitters into the synapse.

Myelin Sheath

• The myelin sheath serves as a fatty insulating layer around some axons, increasing the speed of nerve impulse conduction.
• Oligodendrocytes in the CNS and Schwann cells in the PNS form the myelin sheath
• Nodes of Ranvier are gaps in the myelin sheath.

Neurilemma

• The neurilemma is the outermost layer of the Schwann cell in the PNS, which aids in axon regeneration.
• The CNS lacks a neurilemma, limiting the regenerative capacity of CNS axons.

Axonal Transport

• Axonal transport is the process that moves materials along the axon using anterograde and retrograde transport
• Anterograde transport moves materials from the cell body to the axon terminal.
• Retrograde transport moves materials in the opposite direction.
• Kinesin and dynein are motor proteins involved in axonal transport.

Neurotrophins

• Neurotrophins are proteins supporting neuronal survival, growth, and differentiation.
• Examples include nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and glial-derived neurotrophic factor (GDNF).

Resting Membrane Potential

• Resting membrane potential denotes the electrical potential difference across the neuronal membrane, typically around -70 mV.

Depolarization

• Depolarization involves a decrease in the membrane potential, caused by an influx of sodium ions (Na+).

Hyperpolarization

• Hyperpolarization involves an increase in the membrane potential, typically caused by an efflux of potassium ions (K+) or an influx of chloride ions (Cl-).

Threshold Potential

• Threshold potential is the membrane potential that must be reached to trigger an action potential, usually around -55 mV.

Action Potential

• An action potential is a rapid, all-or-none change in the membrane potential that propagates along the axon.

All-or-None Law

• The all-or-none law states that an action potential either occurs completely or not at all, independent of stimulus strength.

Refractory Period

• The refractory period is the time after an action potential when another action potential cannot be initiated.

Saltatory Conduction

• Saltatory conduction enables the rapid propagation of action potentials along myelinated axons, "jumping" between the Nodes of Ranvier.

Synapse

• A synapse is the junction between two neurons or between a neuron and a target cell such as a muscle or gland.
• Electrical and chemical synapses exist.

Electrical Synapse

• An electrical synapse involves direct electrical coupling between cells via gap junctions; transmission is fast and bidirectional.

Chemical Synapse

• A chemical synapse requires neurotransmitter release from the presynaptic neuron to the synaptic cleft.
• Neurotransmitters then bind to receptors on the postsynaptic neuron; transmission is slower and unidirectional.

Neurotransmitter

is a chemical messenger released that binds to receptors to cause a change in its membrane potential on the postsynaptic neuron.

Synaptic Vesicles

• Synaptic vesicles are membrane-bound sacs in the axon terminal that store and release neurotransmitters.

Synaptic Cleft

• The synaptic cleft represents the space between the presynaptic and postsynaptic neurons.

Receptor

A receptor is a protein on the postsynaptic membrane that binds to a neurotransmitter and initiates a cellular response.

Postsynaptic Potential

• A postsynaptic potential is a change in the membrane potential caused by neurotransmitter binding to its receptor.
• Excitatory postsynaptic potentials (EPSPs) cause depolarization.
• Inhibitory postsynaptic potentials (IPSPs) cause hyperpolarization.

Spatial Summation

• Spatial summation means the summation of postsynaptic potentials happens from multiple synapses at the same time.

Temporal Summation

• Temporal summation means the summation of postsynaptic potentials happens coming from a single synapse over time.

Synaptic Plasticity

• Synaptic plasticity describes the ability of synapses to change their strength over time, involving long-term potentiation (LTP) and long-term depression (LTD).

Long-Term Potentiation (LTP)

• LTP involves an increase in synaptic strength due to repeated stimulation, often involving the insertion of AMPA receptors.

Long-Term Depression (LTD)

• LTD describes a decrease in synaptic strength due to reduced stimulation, often involving the removal of AMPA receptors.

Presynaptic Inhibition

• Presynaptic inhibition occurs when a neuron synapses onto the axon terminal of another neuron, reducing neurotransmitter release.

Postsynaptic Inhibition

• Postsynaptic inhibition occurs when an inhibitory neurotransmitter hyperpolarizes the postsynaptic neuron.

Facts

• CNS comprises the brain and spinal cord, and the PNS includes cranial and spinal nerves.
• Neurons conduct impulses, and neuroglia support neurons.
• Neurons consist of a cell body, dendrites, and an axon.
• Axonal transport is crucial for neuronal function through anterograde and retrograde processes.
• Sensory neurons are afferent, motor neurons are efferent, and interneurons integrate information.
• The typical resting membrane potential is -70 mV. Action potentials are all-or-none events.
• Myelin sheaths increase conduction speed through saltatory conduction.
• Chemical synapses involve neurotransmitter release into the synaptic cleft.
• EPSPs cause depolarization, while IPSPs cause hyperpolarization.
• Acetylcholine has nicotinic and muscarinic receptors.
• Monoamines use second messenger systems.
• Glutamate is the major excitatory neurotransmitter, and GABA is the major inhibitory neurotransmitter.
• Synaptic plasticity involves LTP and LTD.
• Spatial and temporal summation integrate synaptic inputs.
• Presynaptic and postsynaptic inhibition modulate neuronal activity.
• Neurotrophins are essential for neuronal survival and growth. G-protein coupled receptors utilize second messenger systems.
• Many drugs affect neurotransmitter systems functioning as agonists and antagonists.

Explore the central and peripheral nervous systems, including the roles of neurons and neuroglia. Learn about the structure and function of the CNS and PNS. Understand the function of cell bodies and dendrites.