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What are the basic characteristics of neural/nervous tissue?
It carries information in the form of electrical signals called action potentials.
It communicates with other neurons/cells by releasing chemicals called neurotransmitters.
Its cells do not divide by mitosis.
Neurons live your entire lifetime.
Neurons cannot repair damage or be replaced, meaning damage to nervous system organs is permanent [1cii].
There are very few exceptions to this.
It has a high metabolic rate.
It constantly demands oxygen and nutrients (glucose/sugar).
What are the two main parts of a neuron?
a cell body (soma) and extensions off the cell body
Describe the cell body (soma) of a neuron.
largest part of the neuron
It contains the nucleus and most organelles.
The nucleus has a prominent/dark nucleolus.
It contains extensive networks of rough ER that stain as dark spots called Nissl bodies. This indicates that lots of membrane proteins are required for neuron function.
The membrane contains lots of neurotransmitter receptors. The cell body is a receptive area of the neuron that can detect information in the form of neurotransmitter released by other neurons (“listening end”).
Most cell bodies are in the CNS, and those outside the CNS are usually in ganglia.
What are the two types of extensions attached to the neuron's cell body?
dendrites and axons
Describe the structure and function of dendrites.
are short extensions off the cell body that usually have lots of branches called dendritic spines
Like the cell body, dendrites have lots of neurotransmitter receptors in their membrane.
Dendrites increase the receptive surface area of the neuron that can detect information in the form of neurotransmitter released by other neurons (“Listening end”)
Describe the structure of axons.
are long extensions off the cell body that do not usually have lots of branches
The membrane of axons contains lots of ion channels that carry information in the form of electrical signals called action potentials. They are like wires that carry information from one place to another very quickly.
The beginning of the axon, where it attaches to the cell body, is called the Axon hillock.
The end of the axon is usually a disc-shaped region called the axon terminal. The axon terminal is the region of the axon that will release neurotransmitter to communicate with the next neuron/cell when stimulated by action potentials (“speaking end”). This happens in special structures called synapses.
What is axon myelination? What are the two types of axons based on myelination?
is the surrounding of axons by myelin sheaths.
with no myelin sheaths surrounding them are called non-myelinated axons. Bundles of non-myelinated axons are still surrounded by Schwann cells or oligodendrocyte processes but do not have myelin sheaths [5ei]. You previously learned that Schwann cells are glial cells found in the PNS that produce myelin sheaths, and oligodendrocytes are glial cells found in the CNS that produce myelin sheaths.
with myelin sheaths surrounding them are called myelinated axons. Schwann cells and oligodendrocyte processes form many myelin sheaths covering axons with small gaps between them called nodes of Ranvier.
What are the two types of axon branches? Describe them.
Axon collaterals are branches of the axon near the axon hillock. They carry the same info to many locations in different tissues at once.
Telodendria are branches of the axon near the axon terminal. They carry the same info to many cells within the same tissue.
What are the three functional neuron types/classes? Describe their general function and location.
Sensory neurons: not entirely within the CNS. They carry info from sensory receptors to the CNS. This relates to the sensory input function of the nervous system you learned about previously.
Motor neurons: not entirely within the CNS. They carry info from the CNS to effectors. This relates to the motor output function of the nervous system you learned about previously.
Interneurons: Entirely within the CNS. They carry info from place to place within the CNS. They make up 99.9% of all neurons in the body. This relates to the integration function of the nervous system you learned about previously
What are the three structural neuron types/classes? Give an example of each.
Unipolar/Pseudounipolar neurons: Neurons with a single extension off the cell body that splits into one long axon connecting dendrites to the axon terminals. Example: Somatic and Visceral sensory neurons [7bi]. You previously learned that the somatic sensory branch carries information from sensory receptors in the body wall, and the visceral sensory branch carries information from sensory receptors in internal organs.
Bipolar neurons: Neurons with two extensions off the cell body, one dendrite that extends away from the cell body and splits into many dendritic spines, and one axon that leads to the axon terminals. Example: Special sensory neurons [7bii]. You previously learned that the special sensory branch carries information from special sensory organs for senses like vision, hearing, taste, smell, and balance/equilibrium [Your Response to Me].
Multipolar neurons: Neurons with three or more extensions off the cell body, most of the extensions off the cell body are dendrites. Example: Interneurons, Motor neurons
What is a synapse?
a site where neurons communicate with one another
What is the most common type of synapse in the body? How does it communicate?
chemical synapses, which communicate using chemicals called neurotransmitters.
Define the pre-synaptic and post-synaptic neurons.
is the neuron that carries electrical signals to the
is the neuron that detects neurotransmitter and carries electrical signals away from the synapse.
Describe the basic process of synaptic communication.
Pre-synaptic axon terminals storing neurotransmitter in small synaptic vesicles.
When action potentials reach the axon terminal, small synaptic vesicles fuse with the membrane and release neurotransmitter by exocytosis.
Neurotransmitter is detected by neurotransmitter receptors, usually on the post-synaptic dendrites/cell body.
What are the two main functional types of neurotransmitters? How do they affect the post-synaptic neuron?
Excitatory neurotransmitters: Bind to excitatory receptors that produce depolarizations in post-synaptic neurons and possibly produce action potentials. The most abundant excitatory neurotransmitter in the CNS is the amino acid neurotransmitter glutamate.
Inhibitory neurotransmitters: Bind to inhibitory receptors that produce hyperpolarizations in post-synaptic neurons and make it harder to produce action potentials. The most abundant inhibitory neurotransmitter in the CNS is the amino acid neurotransmitter GABA.
What are some structural types of neurotransmitters?
Acetyl Choline
Amino acid neurotransmitters such as Glutamate, GABA, and Glycine
Biogenic amines such as Catecholamines (Dopamine, Norepinephrine, Epinephrine) and Serotonin
Neuropeptides such as Substance P, Endorphins, and Oxytocin
Dissolved gases such as Nitric oxide, Carbon monoxide, and Hydrogen sulfide (Note: their function is not well understood)
Purines such as ATP and Adenosine
Lipids such as Prostaglandins and Endocannabinoids
