Chapter 2 - Cells of the Nervous System

Question 1

Neuron doctrine

Answer 1

• 1890s
• theorized that the brain was composed of individual, highly specialized cells called neurons
• – and that these neurons were not connected continuously (like wires) but separated by functional space through which they communicate with each other called a synapse

Question 2

Parikaryon

Answer 2

• aka soma or cell body
• metabolic center
• much like other cells in body

Question 3

Neurites

Answer 3

• cellular fibers emerging from the soma

- e.g. dendrites, axon

Question 4

Pre-synaptic terminals, branches, or boutons

Answer 4

• lie at the end of the axon
• contain synaptic vesicles which store neurochemical signals (neurotransmitters) that are essential for neuronal function

Question 5

Dendrites

Answer 5

receive messages from other cells

Question 6

Cell body

Answer 6

the cell’s life-support center

Question 7

Axon

Answer 7

passes messages away from the cell body to other neurons, muscles, or glands

Question 8

Neural impulse

Answer 8

electrical signal traveling down the axon

Question 9

Myelin sheath

Answer 9

covers the axon of some neurons and helps speed neural impulses

Question 10

Terminal branches of axon

Answer 10

form junctions with other cells

Question 11

Neuronal action at the synapse

Answer 11

neurotransmitters are released from the pre-synaptic terminal and they cross the synapse to bind neurotransmitter receptors that are embedded in the membrane of the next neuron, forming the communicating link between neurons

Question 12

Synapses

Answer 12

• communication between neurons usually occurs at space between the axon terminal and receptive region of postsynaptic neuron (an area called the synapse)
• diverse in shape and properties
• – can either be inhibitory or excitatory synapses

Question 13

Different types of neurons in the nervous system

Answer 13

• neurons are characterized according to how many neurites originate from the soma
• – can be unipolar (one neurite), bipolar (two neurites), or multipolar (many neurites) nerve cells

Question 14

Types of synapses

Answer 14

• information flows from the dendrite to soma to axon, then to:
• – axodendritic connections (synapses) – usually excitatory (presynaptic terminal to dendrite)
• – axosomatic synapses (presynaptic terminal to soma)
• – axo-axonal synapses (presynaptic terminal to axon)
• – axo-synaptic synapses – usually inhibitory (presynaptic terminal to presynaptic terminal)

Question 15

Neuronal groups and connections

Answer 15

• neuronal cell bodies are grouped into clusters or groups within the brain called nuclei
• each nucleus contains:
• – projection neurons
• – interneurons

Question 16

Projection neurons

Answer 16

• the neuron’s axon projects to other parts of the brain

- – axons project as part of tracts (fasciculi) or lemnisci (brain) or columns (spinal cord)

Question 17

Interneurons

Answer 17

• neurons and their axons that project within a nucleus
• – called neuropil
• – these are short relays of information within a brain region

Question 18

Neurglia

Answer 18

• macroglia and microglia
• – cells in nervous system that do not form synapses
• – dominate the nervous system
• —– play an important role in myelin formation, controlling ion balance, guidance of developing neurons, reuptake of neurotransmitters, and neuroimmunity

Question 19

Glial cells

Answer 19

made up of macroglia and microglia

Question 20

Macroglia

Answer 20

made up of oligodendrocytes and astrocytes

Question 21

Microglia

Answer 21

made up of microglial cells

Question 22

Oligodendrocytes

Answer 22

• predominate in white matter within the CNS only
• extend multiple dendritic arms to myelinate many axons, insulating cells in the CNS
  (in the PNS, this function is done by the Schwann cell)

Question 23

Astrocytes

Answer 23

• provide structural support
• act as glial guide wires for neurons during development
• maintain ion balance around neurons
• participate in reuptake of neurotransmitter adjacent to synapse
• surround blood vessels to act as an integral part of the blood brain barrier
• migrate to site of neuronal injury and proliferate to aid in repairing damaged neuronal tissue (specialized set of astrocytes called Reactive Astrocytes (still maintain all other astrocyte functions as well))
• – unfortunately, if unsuccessful can lead to gliosis

Question 24

Microglial cells

Answer 24

• macrophages (scavengers)
• – mobile glial cells that survey the CNS to combat infection
• – activate and infiltrate injured zones of CNS to scavenge for infection and damage
• – some exist within the CNS and others infiltrate from the blood

Question 25

Gliosis

Answer 25

glial scarring where glial cells dominate injury site

Question 26

Protoplasmic astrocytes

Answer 26

• delicate astrocytes with many branched processes
• occur in gray matter
• respond to neural damage

Question 27

Fibrous astrocytes

Answer 27

• more fibrous and robust astrocytes
• radiate long processes in all directions from soma
• surround blood vessels (blood brain barrier)
• exist in white matter areas of CNS
• cover exterior surface of CNS

Question 28

Wallerian degeneration

Answer 28

• if axon is cut –> the distal end of the axon degenerates
• – cell body reaction (chromatolysis) is swelling and breakdown of Nissl substance (ribosome studded ER with free polyribosomes - site of translation)
• – axon reaction is loss of structural integrity (degeneration), detachment of synapses, swelling of neighboring astrocytes, and activation of microglia

Question 29

Regeneration in the nervous system

Answer 29

• peripheral nerves
• – axonal regeneration (ligation or repair) of severed axons performed by Schwann cells
• CNS
• – axonal regeneration is aborted
• – oligodendrocytes produce inhibitory factors (NoGo)
• collateral sprouting
• – regenerative sprouting in CNS and PNS (F2-F15) in response to partial severing
• – remaining axons form new collaterals that try to reinnervate end organ