Exam II | Nervous System General Organization & Cytology Flashcards
At what level of the spine does the spinal cord end?
L1-L2
At what level of the spine does the dura mater end?
mid-sacrum
What is the filum terminale? Where does it begin and end?
- a specialized portion of the pia mater
- filum terminale internum begins at medullary cone and extends through dural sac
- filum terminale externum extends from bottom of dural sac to coccyx
What does the white matter of the cord primarily consist of? Gray matter?
- white consists of myelinated axons
- gray consists of cell bodies
What is the difference between tracts and nerves?
tracts are axon bundles in the CNS; nerves are axon bundles in the PNS
What are the buttons or ‘boutons’ of the neuron?
axon terminals
What are bipolar neurons, and where are they located?
- sensory motor neurons
- present in the eye and other specialized sensory structures
- e.g hair cells of the cochlea
What are pseudo-unipolar neurons, and where are they located?
- sensory motor neurons
- free nerve endings (e.g. dendrites extend up into dermis) that act as the receptor
- present in the somatosensory system
What are multipolar neurons?
motor neurons with a large number of dendrites
What are primary or alpha motor neurons, and where do they extend from?
- aka lower motor neuron (LMN) or last neuron
- the neuron that carries the final motor signal and is in contact with the effector (muscle)
- extends from ventral horn of cord to effector
What are primary or alpha sensory neurons?
- initial neuron in pathway the generates action potential
- carries initial sensory signal
- may also be the receptor cell (e.g. free nerve ending)
- or it may receive signals from a specialized receptor (such as a Merkel’s disk or corpuscle)
Where is the cell body of the afferent nerve?
DRG or cranial nuclei
Where is the cell body of the efferent nerve?
the ventral horn of the cord or cranial nuclei
What does the term “somatic” refer to?
- motor neurons of the PNS
- or to all motor and sensory neurons of the PNS that are not autonomic
Significance of dendritic spines
critical for interneuronal communication or LTP (learning, memory, association, etc.)
How many neurons and synapses form a disynaptic reflex arc?
- 3 neurons (efferent, interneuron, afferent)
- 2 synapses
What is the difference between nervous system ganglia and nuclei?
- Ganglia are in the PNS, nuclei are in the CNS
- exception is basal nuclei
How does a sensory ganglion differ from an autonomic ganglion?
autonomic ganglion have synapses, sensory ganglion do not
What is the difference between a motor unit and a myotome?
- a motor unit is a motor NEURON and all the muscle FIBERS innervated by it
- a myotome is a range of MUSCLES that are generally innervated by MORE THAN ONE spinal NERVE
What is the neurotransmitter and receptor at the neuromuscular junction?
Ach; nicotinic
What is a motor endplate?
- the neuromuscular junction
- a depression in myocyte (muscle fiber) membrane
Give an example of a motor end plate (MEP) pathology
myasthenia gravis
What are the glial cells of the CNS?
- astrocytes
- ependymal cells
- microglia
- oligodendrocytes
What is a satellite sell?
supportive cells in sensory and autonomic ganglia analogous to astrocytes
astrocytic processes
- surround dendrites, nodes of Ranvier, synapses, and capillaries
- form much of the structural framework of neuropil
What is the glia limitans?
thick layer made up of interlocking astrocyte processes that surrounds brain and spinal cord
How do astrocytes compare to neurons in the CNS in terms of size and abundance?
- more astrocytes than neurons in the brain
- astrocytes are smaller than neurons
Where do most brain tumors originate from?
astrocytes
7 astrocyte functions
1) controls what passes from blood to neuron (nutrients, wastes)
2) contribute to structural integrity of BBB
3) maintain GABA, glutamate, and CNS ion (Na+ and K+) levels
4) involved in Ca2+ dependent exocytosis
5) developmentally induce formation of endothelial tight junctions
6) facilitate neuronal metabolism (mediate PO4- transfer
7) contribute to CNS healing after injury or degeneration
What is gliosis?
- Glial scar formation after injury to the central nervous system
- astrocytes increase in number and release inflammatory cytokines following injury or degeneration
What are the immune cells of the CNS? What is their mechanism of action?
- microglia
- they relocate to site of injury/infection, alter cell structure, and proliferate
- phagocytic
- release inflammatory cytokines
What percent of brain cells are microganglia?
15%
What is a ramified glial cell?
- resting glial cell (not functioning as a macrophage)
- soma is usually fixed with motile processes
- typical of healthy CNS
What causes dystrophic microglia?
deterioration of microglia is due to age-related processes
What happens in reactive gliosis?
- injury or infection becomes so severe that efforts of microglia to control it actually begin to promote it
- -microglia hypertrophy due to acute injury
What are ‘gitter’ cells?
activated microglia (macrophages) which have consumed as much as possible
What is an activated microglia?
- microglia that has turned into a macrophage
- cell acquires an amoeboid shape and becomes a pro-inflammatory, motile cell
What are 2 demyelinating diseases of the CNS?
- Leukodystrophies
- MS
Do oligodendrocytes make up white or gray matter of CNS?
- white matter
- although satellite oligodendrocytes are part of gray matter
What is the majority of myelin made up of?
80% lipids
How many neuronal fibers can an oligodendrocyte myelinate compared to a Schwann cell?
- oligodendrocyte can contribute to myelination of up to 50
- Schwann cell just one
By how much does saltatory conduction increase conduction speed?
10 fold
What 4 signals trigger oligodendrocyte precursor cells (OPCs) to myelinate an axon?
- ATP
- glutamate
- GABA
- cell adhesion molecules
What is the structure of ependymocytes and where are they found?
- have microvilli and primary cilia on apical surfaces
- line central canal of cord and also portions of the ventricles
Function of ependymocytes
- produce CSF in choroid plexus
- selectively secrete capillary filtrate into the ventricles
- regulate flow of CSF with cilia
- regulate levels of CSF with microvilli for absorption
- remove waste products from CSF and adjust its composition over time
- contribute to BBB
How many times does a myelinating neurolemma wrap around an axon?
up to 100X
What is a Remak bundle?
- non-myelinating neurolemma that envelops several small fibers
- does not necessarily increase the speed of conduction
What is myelin made up of?
water and collagen
What is a neurofibroma?
a tumor with multiple cell types, including Schwann cells, mast cells, and fibroblasts
(From video) 3 approaches to getting CNS neurons to regenerate
1) Making environment around neurons favorable ( inhibiting CSPGs)
2) introducing factors that directly boost neuron’s capacity to heal itself (integrins, IGF, osteopontin)
3) Combination of 1 and 2 (mesenchymal stem cells)
(From video) How can mesenchymal stem cells help with CNS axon regeneration?
- naturally hone in on site of injury and protect against secondary damage caused by immune system
- may promote axon regeneration and myelin repair
- may directly transform into new neurons
