Structure and Function of Neurons

1 CHAPTER 1 Structure and Function of Neurons Varieties of Neurons General Structure Structure of unique Neurons Internal operations and the functioning of a neuron Subcellular organelles Protein synthesis Neuronal transport: shipping and receiving molecules and organelles throughout the neuron SummaryNeurons are the cells of chemical communication in the brain. Human brains com-prise tens of billions of Neurons , each linked to thousands of other Neurons . Thus,the brain has trillions of specialized connections known as synapses. Neuronshave many sizes, lengths, and shapes, which determine their functions. Localization withinthe brain also determines Function . When Neurons malfunction, behavioral symptoms mayoccur. When drugs alter neuronal Function , behavioral symptoms may be relieved, wors-ened, or produced. Thus, this chapter briefly describes the Structure and Function of normalneurons as a basis for understanding psychiatric disorders and their of neuronsGeneral structureAlthough this textbook will often portray Neurons with a generic Structure (such as thatshown in Figure 1-1A and B), the truth is that many Neurons have unique structures (seeFigures 1-2 through 1-8).

2 All Neurons have a cell body, known as the soma, and are setup structurally to receive information from other Neurons through dendrites, sometimesvia spines on the dendrites, and often through an elaborately branching tree of dendrites(Figure 1-1A and B). Neurons are also set up structurally to send information to otherneurons via an axon, which forms presynaptic terminals as the axon passes by en passant (Figure 1-1A) or as it ends (in presynaptic axon terminals) (Figure 1-1A). Structure of unique neuronsMany Neurons in the central nervous system have unique structures. For example, eachpyramidal cell has a cell body shaped like a triangular pyramid (Figure 1-2A is a somewhatStructure and Function of Cambridge University PressCambridge University Press978-0-521-8570 2-4 - Stahl s Essential Psychopharmacology: Neuroscientific Basis and PracticalApplications, Third EditionStephen M. StahlExcerptMore informationdendritic spinesdendritescell body (soma)axonpresynaptic axonterminalsdendritic spinesen passantpresynapticaxon terminalsdendritesdendritic treeaxongeneral Structure of the neuronanother general Structure of the neuroncell body (soma)ABFIGURE 1-1A and B Generic Structure of is an artist s conception of the generic Structure of aneuron.)

3 All Neurons have a cell body known as the soma, which is the command center of the nerve and containsthe nucleus of the cell. All Neurons are also set up structurally to both send and receive information. Neuronssend information via an axon, which forms presynaptic terminals as it passes by (en passant) or as it ends (A). Neurons receive information from other Neurons through dendrites, sometimes via spines on the dendrites, andoften through an elaborately branching tree of dendrites (B). Although all Neurons share these properties, theycan have unique structures that, in turn, dictate specialized depiction and 1 2B is an icon of a pyramidal cell); each also has an extensivelybranched spiny apical dendrite and shorter basal dendrites (Figure 1-2B) as well as a sin-gle axon emerging from the basal pole of the cell body. Pyramidal Neurons are discussedextensively in this textbook because they make up most of the Neurons in the functionallyimportant prefrontal cortex as well as elsewhere in the cerebral cortex .

4 Several other neu-rons are named for the shape of their dendritic tree. For example, basket cells are so namedbecause they have widely ramified dendritic trees that look rather like baskets (Figure 1-3 Ais a somewhat realistic depiction and 1 3B is an icon of a basket cell). Basket cells functionas interneurons in the cortex , and the wide horizontal spread of their axons can make manylocal inhibitory contacts with the soma of other cortical Neurons . Double bouquet cells arealso inhibitory interneurons in the cortex and have a very interesting vertical bitufted appear-ance, almost like two bouquets of flowers (Figure 1-4A is a somewhat realistic depiction and1 4B is an icon of a double bouquet cell). Each double bouquet cell has a tight bundle ofaxons that is also vertically oriented, with varicose collaterals that innervate the dendrites ofother cortical Neurons , including other double bouquet cells, and supply inhibitory input tothose Neurons . Spiny Neurons , not surprisingly, have spiny-looking dendrites (Figure 1-5A2 Essential Cambridge University PressCambridge University Press978-0-521-8570 2-4 - Stahl s Essential Psychopharmacology: Neuroscientific Basis and PracticalApplications, Third EditionStephen M.)

5 StahlExcerptMore informationbasal dendritespresynaptic axon terminal apical dendritepyramidal cellbodyaxonpyramidal cellbody (soma)recurrent collateral (axon)motor cortexaxonpresynaptic axonterminalrealistic pyramidal cellicon of pyramidal celldendritictreeABFIGURE 1-2A and B Pyramidal cells (depicted somewhat realistically inAand iconically inB)have a cell body shaped like a triangular pyramid, an extensively branched spiny apical dendrite, shorter basaldendrites, and a single axon emerging from the basal pole of the cell body. The majority of the Neurons in thecerebral cortex , particularly in the prefrontal cortex , are pyramidal a somewhat realistic depiction and 1 5B is an icon of a spiny neuron). Spiny Neurons arelocated in the striatum in large numbers and have a highly ramified dendritic arborizationthat radiates in all directions and, of course, is densely covered with spines, which receiveinput from cortex , thalamus, and substantia nigra.

6 Spiny Neurons have long axons thateither leave the striatum or circle back as recurrent collaterals to innervate neighboring spinyneurons. Finally, Purkinje cells from the cerebellum form a unique dendritic tree that, infact, looks very much like a real tree (Figure 1-6). This dendritic tree is extensively bran-ched and fans out from an apical position, with a single axon emerging from the basal poleof the least one type of neuron is named for its unique axonal Structure : the chandelierneuron (Figure 1-7A is a somewhat realistic depiction and 1 7B is an icon of a chandelierneuron). The axons of this cell look like an old-fashioned chandelier, with odd-appearingaxon terminals shaped like vertically oriented cartridges, each consisting of a series ofaxonal swellings linked by thin connecting pieces. Chandelier Neurons are yet another typeof inhibitory interneuron in the cortex , where the characteristic chandelier endings of theiraxons have a specific Function and location namely, to serve as inhibitory contacts close tothe initial segment of axons of pyramidal cells.

7 Thus, chandelier Neurons terminate in whatStructure and Function of Cambridge University PressCambridge University Press978-0-521-8570 2-4 - Stahl s Essential Psychopharmacology: Neuroscientific Basis and PracticalApplications, Third EditionStephen M. StahlExcerptMore informationaxondendrites (dendritictree shaped like a basket)dendrites (dendritictree shaped like a basket)presynaptic axonterminalspresynaptic axonterminalsaxonbasket cell bodybasket cell bodyrealistic basket cellicon of basket cellABFIGURE 1-3A and B Basket Neurons are named for their widely ramified dendritic trees, whichresemble baskets (depicted somewhat realistically inAand iconically inB). They are cortical interneurons withaxons that spread horizontally to make many inhibitory contacts with the soma of other bodybouquet shapeof dendritic treeaxonrealistic double bouquet cellicon of double bouquet celldendritesspinesaxonbouquet shapeof dendritic treepresynaptic axonterminalpresynaptic axonterminalcell bodyABFIGURE 1-4A and B Double bouquet bouquet cells are so called because of their vertical bituftedappearance, which resembles two bouquets of flowers (depicted somewhat realistically inAand iconically inB).

8 Like basket Neurons , double bouquet cells are inhibitory interneurons in the cortex . They have a tight bundle ofaxons that is oriented vertically, with varicose collaterals that innervate the dendrites of other cortical Neurons ,including other double bouquet Cambridge University PressCambridge University Press978-0-521-8570 2-4 - Stahl s Essential Psychopharmacology: Neuroscientific Basis and PracticalApplications, Third EditionStephen M. StahlExcerptMore informationrealistic spiny neuronicon of spiny neuronpresynaptic axonterminalaxonspiny neuroncell bodyspiny dendritesaxonpresynaptic axonterminalspinydendritesspiny neuroncell bodyABFIGURE 1-5A and B Spiny dendrites of spiny Neurons radiate in all directions and are denselycovered with spines (depicted somewhat realistically inAand iconically inB). Spiny Neurons are located in thestriatum in large numbers and receive input from cortex , thalamus, and substantia nigra. The axons of spinyneurons are long and either leave the striatum or circle back as recurrent collaterals to innervate neighboringspiny Purkinjedendritic treecell bodyaxonpresynaptic axon terminalPurkinje cellFIGURE 1-6 Purkinje from the cerebellum haveextensively branched dendritic treesfanning out from an apical position,with a single axon emerging from thebasal poll of the called an axoaxonic synapse.

9 Since the initial segment of a pyramidal cell s axon is themost influential location in determining whether that axon will fire or not, the chandelierneuron can potentially provide the most powerful inhibitory input to a pyramidal neuron,possibly even being able to completely shut down a pyramidal cell s firing. Many chandelierStructure and Function of Cambridge University PressCambridge University Press978-0-521-8570 2-4 - Stahl s Essential Psychopharmacology: Neuroscientific Basis and PracticalApplications, Third EditionStephen M. StahlExcerptMore informationrealistic chandelier neuronicon of chandelier neuronchandelieraxonterminalsdendritesce ll bodyaxonchandelieraxonterminalsdendritic treecell bodyaxonABFIGURE 1-7A and B Chandelier chandelier neuron is named for its unique axonal Structure (depicted somewhat realistically inAand iconically inB). The axons resemble an old-fashioned chandelier withaxon terminals shaped like vertically oriented cartridges, each consisting of a series of axonal swellings linkedtogether by thin connecting pieces.

10 Like basket Neurons and double bouquet cells, chandelier Neurons areinhibitory interneurons in the cortex . The chandelier endings of their axons come into close contact with theinitial segments of pyramidal cell axons, forming what is called an axoaxonic synapse. The chandelier neuron canpotentially provide powerful inhibitory input to a pyramidal neuron via this synapse, possibly even completelyshutting down a pyramidal cell s firing. Many chandelier Neurons provide input to a given pyramidal cell, andeach chandelier neuron can provide input to several pyramidal provide input to a given pyramidal cell, and each chandelier neuron can provideinput to several pyramidal operations and the functioning of a neuronSubcellular organellesIn order to do its duties, the neuron contains various internal working parts that havespecialized functions, from subcellular organelles and protein synthetic machinery to inter-nal superhighways for transport of these materials into dendrites and axons on specializedmolecular motors.