Chapter 2: Cells of the Nervous System

What is the neuron doctrine

The neuron doctrine states that neurons are separate independent cells that communicate across synapses and are not physically continuous with one another

What is a multipolar neuron

A multipolar neuron has one axon and many dendrites and is the most common type in the central nervous system

What is a bipolar neuron

A bipolar neuron has one dendrite and one axon and is found in sensory systems such as vision and olfaction

What is a unipolar neuron

A unipolar neuron has a single branch that splits into two directions and carries touch and pain information from the body

What are the four functional zones of a neuron

Input zone, integration zone, conduction zone, and output zone

What occurs in the input zone

The input zone contains dendrites that receive information from other neurons

What occurs in the integration zone

The integration zone usually at the axon hillock integrates incoming signals and decides whether to generate an action potential

What occurs in the conduction zone

The conduction zone is the axon where the action potential is actively propagated

What occurs in the output zone

The output zone contains axon terminals where neurotransmitter is released

What is the soma or cell body

The soma contains the nucleus and is responsible for maintaining cell metabolism

What are dendritic spines

Dendritic spines are tiny protrusions on dendrites that form synapses and change shape with learning reflecting neural plasticity

What is the axon hillock

The axon hillock is the region where the axon originates and where action potentials are initiated

What is axonal transport

Axonal transport is the movement of materials such as proteins and mitochondria along microtubules inside the axon

What is anterograde axonal transport

Anterograde transport carries materials from the SOMA toward the axon terminals

What is retrograde axonal transport

Retrograde transport carries materials from the AXON TERMINALS back to the soma

What is the function of sensory neurons

Sensory neurons carry information from the body or environment into the central nervous system

What is the function of motor neurons

Motor neurons send commands from the central nervous system to muscles and glands

What is the function of interneurons

Interneurons connect other neurons and process information within the brain and spinal cord

What are glial cells

Glial cells are non neuronal cells that support nourish insulate and protect neurons

What do astrocytes do

Astrocytes provide metabolic support regulate extracellular ions help form the blood brain barrier and modulate synaptic activity

What do microglia do

Microglia act as the immune cells of the central nervous system removing debris and responding to injury or infection

What do oligodendrocytes do

Oligodendrocytes myelinate axons in the central nervous system

What do Schwann cells do

Schwann cells myelinate axons in the peripheral nervous system

What is myelin

Myelin is a fatty insulating sheath that speeds up action potential conduction

What is a node of Ranvier

A node of Ranvier is a gap in the myelin sheath where ion channels are concentrated

What is saltatory conduction

Saltatory conduction is the jumping of the action potential from node to node increasing speed

What is multiple sclerosis

Multiple sclerosis is a disease in which the immune system attacks myelin leading to slowed communication and neurological symptoms

What is a synapse

A synapse is the cellular junction where information is transferred from one neuron to another

What is the presynaptic membrane

The presynaptic membrane is on the axon terminal and releases neurotransmitter

What is the postsynaptic membrane

The postsynaptic membrane is on the dendrite or soma and contains receptors for neurotransmitter

What is the synaptic cleft

The synaptic cleft is the small gap between the pre and postsynaptic membranes

What are neurotransmitters

Neurotransmitters are chemical messengers released from presynaptic terminals that bind to receptors on postsynaptic cells

What is neural plasticity

Neural plasticity is the ability of the nervous system to change its structure physiology and synaptic connections in response to experience or injury

How do dendritic spines relate to plasticity

Dendritic spines grow shrink and change shape in response to learning forming the basis for long term synaptic changes

What is the role of mitochondria in neurons

Mitochondria provide ATP needed for ion pumps neurotransmitter release and axonal transport

What is the cytoskeleton

The cytoskeleton is made of microtubules and neurofilaments that give the neuron structure and allow axonal transport

Why are neurons highly polarized cells

They have clearly separated functional regions such as dendrites input and axons output

What is selective expression of genes in neurons

Only certain genes are turned on in each neuron which determines which neurotransmitters receptors and proteins it makes

Why is the neuron considered the basic unit of the nervous system

Because it is the smallest cell type capable of processing and transmitting information

What evidence supports the neuron doctrine

Golgi staining electron microscopy and recordings show neurons are separate cells not a continuous network

What was Golgi’s reticular theory

Golgi believed neurons physically merged into a continuous network which was later disproven

Who proved the neuron doctrine

Ramon y Cajal proved neurons were separate independent cells using detailed staining techniques

What is presynaptic facilitation

Presynaptic facilitation increases neurotransmitter release at a synapse often due to modulatory input

What is presynaptic inhibition

Presynaptic inhibition decreases neurotransmitter release by reducing calcium entry or altering vesicle fusion

What are neurotransmitter vesicles

Vesicles are membrane bound packages that store neurotransmitter for release into the synaptic cleft

What triggers vesicle release

Arrival of an action potential opens voltage gated calcium channels and calcium entry triggers vesicle fusion

What determines whether a neuron fires an action potential

The neuron must reach threshold at the axon hillock where excitatory and inhibitory inputs are summed

What are excitatory postsynaptic potentials

EPSPs are depolarizing inputs that increase the chance of reaching threshold

What are inhibitory postsynaptic potentials

IPSPs are hyperpolarizing inputs that decrease the chance of reaching threshold

What is temporal summation

Temporal summation is the addition of inputs arriving at slightly different times

What is spatial summation

Spatial summation is the addition of inputs arriving at different synapses on the neuron

Why is neuronal integration important

It allows the neuron to compute whether to send a signal based on all incoming information

What does it mean that neurons vary widely in shape

Neurons can have different numbers of dendrites axon lengths and branching patterns depending on their function

Why do neurons require high metabolic support from glial cells

Neurons cannot store energy and need constant regulation of ions nutrients and neurotransmitter clearance supplied by glia

What happens when microglia are overactive

Overactive microglia can contribute to inflammation and neurodegenerative disease

What is myelin’s effect on conduction velocity

Myelin greatly increases conduction speed by reducing current loss and allowing saltatory conduction

What happens when axonal transport is disrupted

Disrupted transport leads to buildup of proteins and organelles which can cause neurodegeneration