Cellular Structures: Neurons and Glial Cells

Flashcards covering the structural components of neurons, the specialized types of dendritic spines, neuronal communication, glial cell types, and the macroscopic organization of the nervous system as detailed in the lecture.

Soma

The cell body of a neuron, part of the gray matter in the CNS, containing cellular components like the nucleus, DNA, and ribosomes to keep the cell alive.

Dendrites

Neuronal processes that often make synaptic contacts with neighboring neurons to receive information at small protrusions known as dendritic spines.

Neural Plasticity

configuration of synapses on dendrites and cell body is constantly changing in response to

• Dendritic spines, which increase surface area for synapses, can be rapidly altered

• Neurons receive neurotransmitter stimulation at synapse

Axon hillock

Also known as the axon initial segment, this is the 'decision making area' of the neuron where a dense concentration of sodium channels facilitates threshold responding and initiates action potentials.

Axon

carry action potentials from the axon hillock (the trigger zone) to the axon terminals.

Myelin Sheath

A conductive and insulative material that covers axons to increase the effectiveness and efficiency of cellular transmissions by preventing ions from leaking out.

Nodes of Ranvier

Un-myelinated segments or breaks between bundles of myelin with a dense concentration of sodium (Na+) and potassium (K+) channels; the site of saltatory conduction.

Axon terminals

Also called boutons, these are the ends of axon collaterals and the site where electrical signals are converted into chemical signals via the release of neurotransmitters.

Stubby Spines

belived to be precursor of other spine types (anything less than 1 um)

Filopodia

Dendritic spines characterized by a length ($L$) of more than $2\,\mu m$, believed to be the precursor of other spine types.

Thin Spines

Dendritic spines that appear and disappear in a few days; due to their flexible structure, they are referred to as 'learning spines.'

Mushroom Spines

Stable dendritic spines that can last for months and contain more AMPA receptors; they are referred to as 'memory spines.'

AMPA Receptors

Glutamate receptors that act as ion channels; when glutamate binds, they open to let sodium (Na+) ions in, depolarizing the membrane and creating an excitatory postsynaptic potential (EPSP).

• More AMPA Receptors = More Sodium Entry — leads to a larger postsynaptic potential (EPSP).

Confocal Microscopy

Works by shining a laser onto the sample, like a focused beam of light.

• This laser light scans across the sample, and as it hits the dendritic spines, it bounces back and is detected by a special detector

• The detector captures the light and creates a high-resolution image of the spines, showing theirshape, size, and other details.

Multipolar Neurons

The most common type of neuron, consisting of one axon and many dendrites, allowing for the collection of large amounts of information.

Bipolar Neurons

Neurons with one axon and one dendrite; commonly found in the olfactory epithelium, the retina, and the vestibulocochlear nerve ganglia.

Pseudo-Unipolar Neurons

Neurons with a single extension that branches into two directions (one toward the periphery and one into the spinal cord); commonly found in dorsal root ganglia to send touch information.

Afferent Neurons

Sensory neurons that carry information from the peripheral nervous system (PNS) and sensory receptors to the central nervous system (CNS).

Efferent Neurons

Motor neurons that carry information from the central nervous system (CNS) to the motor organs, such as muscles.

Interneurons

Neurons found only in the CNS that transmit motor and sensory info; relay types have long axons for far-away targets, while local types stay within a specific area.

$A\delta$ (A-delta) fibers

Large-diameter, myelinated neurons that carry pain information at fast speeds up to 30m/s

C fibers

Small-diameter, unmyelinated neurons that carry pain, temperature, and itching information slowly at approximately 1m/s (that residual, achy pain you get long after an injury)

Exocytosis

The process of neurotransmitter release mediated by specialized proteins such as SNAREs and synaptotagmin.

Synaptotagmin

A protein that binds to entering calcium (Ca2+) and catalyzes membrane fusion by binding to the SNARE complex and the plasma membrane.

Gray Matter

Regions of the CNS rich in neuronal cell bodies, dendrites, and synapses.

White Matter

Regions of the CNS rich in myelinated axons, appearing white due to the presence of myelin.

Nucleus (CNS)

A cluster of neuronal cell bodies within the central nervous system that share a common function.

Ganglion

A cluster of neuronal cell bodies found in the peripheral nervous system (PNS), with the basal ganglia being a notable CNS exception.

Astrocytes

Star-shaped glial cells that provide mechanical and metabolic support, form the blood-brain barrier, and release gliotransmitters like glutamate and ATP to modulate neuron function.

• contain sucker-like extensions that contact blood vessels

Microglia

Immune cells of the CNS that protect the brain by cleaning up debris and performing synaptic remodeling or 'pruning' via phagocytosis.

Ependymal Cells

Glial cells that form the inner lining of the ventricles and facilitate the production of cerebrospinal fluid (CSF).

Oligodendrocytes

Glial cells in the CNS that form the myelin sheath around segments of 30 to 40 different axons.

Schwann Cells

Glial cells in the PNS that create a single myelin segment for one axon.

Satellite Cells

Thin, flattened glial cells that surround the soma of peripheral neurons, supplying nutrients and regulating the ionic environment.

Saltatory Conduction

The process where a membrane depolarization 'jumps' from one node of Ranvier to the next, accelerating the speed of nerve impulses up to 120 m/s

Multiple Sclerosis

The immune system attacks the protective sheath (myelin) that covers nerve fibers and causes communication problems between your brain and the rest of your body.

Input Zone

1. Dendrites

2. Dendritic Spines

3. Soma

Integration Zone

1.Axon initial segment/axon hillock

Conduction Zone

1.Axon

2. Myelin Sheath

3. Nodes of Ranvier

Output Zone

1.Axon terminals

Cortex

Layered sheet of neuronal cell bodies (CNS)

Tract

A bundle of axons with a common origin and destination (CNS)

Fasciculus

Small/medium bundle of axons within a larger structure (CNS)

Funiculus

A large region of white matter containing multiple fasciculi (CNS)

Column

Often used synonymously with funiculus in the spinal cord (CNS)

Lemniscus

A ribbon-like tract of axons (CNS - brainstem)

Peduncle

A stalk-like bundle of axons connecting brain regions (CNS)

Action Potential

Originate in the axon hillock, propagate at high speed along the axon, the greater the stimulus, the greater the response (before threshold)—the change in potential is called a graded response

• Local potentials play a crucial role in neuronal communication; serve as the initial signals that can either initiate or inhibit the generation of action potentials.

Electrical Synapses

potential jumps directly to the postsynaptic region without using chemicals

Synaptic Transmission

1. Action potential arrives at axon terminal.

2. Voltage-gated calcium channels open and Ca2+ ions enter.

3. Synaptic vesicles fuse with membrane and release transmitter into the cleft.

4.Transmitter crosses the cleft and binds to postsynaptic receptors, which opens ion channels.