Nerve 1

Question 1

Describe the cell body of the typical neuron

Answer 1

-portion of the cell with the nucleus and other organelles (e.g, noiseless bodies- rER)

Question 2

Describe the nerve fibers of the typical neuron(dendrite)

Answer 2

Dendrite:
-Unmyelinated arborizations extending from a neuronal cell body

• receive stimulus from the environment and other neurons and carries impulse towards the cell body from another neuron
• contains cytoplasmic contents similar to the perinulcear

Question 3

Describe the nerve fibers of the typical neuron (axon)

Answer 3

• myelinated portion of nueron
• output portion of a neuron that carries nerve impulse from the cell body toward another neuron, muscle cell or gland
• contains microtubules, microfilaments, mitochondria, vesicles (with proteins including neurotransmitters )

Question 4

What are the fibers of the typical neuron ?

Answer 4

Dendrite and axon

Question 5

What are the categories of neurons ?

Answer 5

• sensory
• type of fiber =afferent (so,stick or visceral)
• structure- pseudo polar or unipolar
• carry - sensory (voluntary/involuntary) impulses

Interneurons

• type of fiber- afferent and/or efferent
• structure= multipolar
• carry- sensory/motor impulses

Motor

• type of fiber: efferent( somatic or visceral)
• structure: multipolar
• carry motor (voluntary/involuntary ) impulses

Question 6

What is the normal structure of a sensory neuron ?

Answer 6

a) general sensory- pseudo-unipolar), e.g. pain, (with cell bodies in DRG)
b) special sensory (bipolar) e.g. eyes (with cell bodies in retina

Question 7

What is the general structure of a motor neuron?

Answer 7

a) somatic voluntary (e.g., skeketal muscle)

b) autonomic involuntary (e.g. smooth muscle)

Question 8

What are the structures of integrative (communicating network ) neurons?

Answer 8

A. Pyramidal

B. Interneuron

C. Purkinje

Question 9

Summarize the interaction of a sensory neuron

Answer 9

Have part of their nerve fibers (axons) begin in the skin or an organ in the PNS and the other part of their axons are directed towards the CNS. Cell bodies are in the dorsal root ganglia (DRG)

Question 10

Summarize the interactions of integrative neurons

Answer 10

Interconnect eg. Interneurons in spinal cord. Have cell bodies in dorsal horn of spinal cord

Question 11

Summarize the interactions of motor neurons

Answer 11

Have their cell bodies located in the CNS eg. Ventral and intermediolateral horns of the spinal cord, and their axons are directed towards the peripheral nervous system (PNS) eg. to skeletal muscles or smooth muscles, cardiac muscles and glands

Question 12

What is axonal transport?

Answer 12

Bidirectional movement of materials between cell body and processes

Question 13

What are the types of axonal transport ?

Answer 13

Anterograde:

• motor protein involved-kinesin
• slow or fast

Retrograde:

• motor protein involved- Dynein
• fast

Clinical importance: route used by toxins abs viruses to enter nervous system

Question 14

Contrast anterograde and retrograde axonal transport

Answer 14

Anterograde: towards synapse; flow of synaptic vesicles, mitochondria etc.

Retrograde: towards CB; recycled membrane vesicles , neuromodulators

Question 15

Contrast ganglia and nuclei

Answer 15

Ganglia are clusters of nerve cell bodies outside the CNS

Nuclei are clusters of nerve cell bodies inside the CNS

Question 16

Summarize location and structure of sensory neurons

Answer 16

Location- craniospinal (DRG, cranial nerves)

1. Pseudo-unipolar neurons (general sensory)
   
   • larger cell bodies
   • close together
   • thick fascicles of fibers alternating with bundles of cell bodies
2. Bipolar neurons (for special senses)

Question 17

Summarize the autonomic nervous system

Answer 17

Sympathetic and parasympathetic nervous system

Multipolar neurons
-relatively smaller cell bodies

• further apart from each other
• diffuse nerve fibers between cell bodies

Question 18

Summarize the histology of sensory ganglia- DRG

Answer 18

• centrally located cell bodies
• large pale staining central nuclei
• No synaptic connections
• Groups of pseudo-unipolar cell bodies alternating with thick fascicles of nerve fibers (axons)

Question 19

Summarize the histology of sympathetic ganglia

Answer 19

• eccentric cell bodies with multiple processes
• random bundles of fibers mingled with the somas
• dispersed multipolar cell bodies
• Synapsing occurs between neurons

Question 20

Explain in DETAIL neuroglia

Answer 20

Neuroglia Or glia - are non- neuronal cells that support, insulate or nourish neurons. They can be found in both the central nervous system (CNS) and the peripheral nervous system (PNS). Peripheral neuroglia includes- Schwann cells and satellites cells. Central neuroglia includes- astrocytes, oligodendrocytes, ependymal cells and microglia cells

Question 21

What is the function of a protoplasmic astrocyte?

Answer 21

• prevalent in the gray matter
• branching cytoplasmic processes
• maintain the blood CSF barrier

-contains GFAP (protein of the intermediate filament family) helps provide structural support/strength to cells

Question 22

What is the function of fibrous astrocytes?

Answer 22

• prevalent in white matter
• Has straight cytoplasmic processes
• contain GFAP

Question 23

What do fibrous and protoplasmic astrocytes have in common?

Answer 23

• support and regulate movement of metabolites and wastes in neurons
• maintain the blood-brain barrier
• protect bare areas of neurons

Question 24

What are microglia?

Answer 24

Smallest type of central microglia

• originate from hematopoietic (blood cell line)
• functions in phagocytosis of bacteria, removal of debris & injured tissue
• Has abundant spikes/ ruffled border cytoplasmic processes

Question 25

What are oligodendrites?

Answer 25

- myelinate axons in the CNS - have tongue-like cytoplasmic processes - larger nodes of fancier - increases efficiency of nerve conduction - one oligodendrocyte myelinates portions of several axons

Question 26

What is the function of ependymal cells?

Answer 26

- epithelium lining of the CNS cavities - cuboid to columnar cell type - have characteristic of fluid transporting/absorbing cells ( cilia, microvilli, basal in folding) - found in choroid plexus- modified cells that interact with capillaries and help secrete cerebrospinal fluid

Question 27

What is the Schwann cell?

Answer 27

- myelinate neurons in PNS. Several Schwann cells myelinate portions of the axon - provide support for both myelinated and unmyelinated axons in the PNS - clean up debris - scaffolding for regeneration of nerve tissue

Question 28

What are satellite cells?

Answer 28

- small cuboidal cells - surround the cell body of neurons in PNS - regulate the perineuronal environment - electrical insulator, does NOT MAKE MYELIN - Regulate metabolic exchange

Question 29

What is myelin?

Answer 29

- lipid rich layer around the axons of neurons - formed by the mesoaxon of the Schwann cells - serves to insulate/ support axons of nerves fibers from the environment surrounding the endoneurium - facilitates rapid conduction of nerve impulses

Question 30

What are the myelinating cells?

Answer 30

- Schwann cells (PNS) | - Oligodendrocite(CNS)

Question 31

Explain the formation of myelin sheath

Answer 31

-Axon lies in a groove of the Schwann cell’s surface - Schwann cell plasma membrane forms two distinct polarized domains - abaxonal plasma membrane - adaxonal plasma membrane Mesoaxon-formed when the abaxonal and adaxonal membranes connects, which closes off the extracellular environment - Concentric sheaths of myelin are laid around the axon - Thickness of the myelin sheath is determined by the diameter of the axon, regulated by neuregulin-1 protein As myelin is laid down, the sheaths contain small amounts of cytoplasm allowing for connections within the Schwann cell: -inner collar of Schwann cell cytoplasm +between axon and myelin - Schmidt-Lanternmann clefts - small islands of cytoplasm within lamellae of myelin Perinodal cytoplasm at node of fancier - Outer collar of Schwann cell cytoplasm - around myelin (most times where cell nucleus is located)

Question 32

Contrast myelin vs nerves

Answer 32

Myelinated nerves- -they have multiple concentric layers of myelin sheath around one axon -the nerves are devoid of myelin at the nodes of ranvier, axon hillock, and terminal arborizations Unmyelinated nerves - Axon/axons rests in a cleft of Schwann cell cytoplasm, each with a single mesoaxon - No myelin sheaths formed

Question 33

What is impulse conduction?

Answer 33

- Impulses received by the dendrites are conducted to the cell body - Action potential is triggered - Nerve impulse is conducted along the axon - Wave of depolarization passes along the axon through the nodes of Ranvier - Faster in myelinated vs Unmyelinated axons