Histology Of The CNS

Question 1

Describe the dendrites of a neuron

Answer 1

Numerous dendrites extend from the perikaryon
Extensive branching/arborization
Numerous dendritic spines increase receptive area
Spines are plastic

Question 2

What is a neutropil?

Answer 2

Dense network of nerve fibers and their branches and synapses, together with glial processes

Question 3

What are Nissl bodies/substances?

Answer 3

A large granular body found in neurons

Site of protein synthesis

Question 4

What is a multipolar neuron?

Answer 4

Numerous poles associated with the extensive amount of dendrites
An axon on the other side

Question 5

What is a bipolar neuron?

Answer 5

Centrally located cell body
Two processes extending on each side (one with dendrites and the other axon)
Found in the retina

Question 6

What are unipolar neurons?

Answer 6

Sensory neurons
One cell body
One process extending from the cell body which branches (peripheral and central process)

Question 7

What is an anaxonic neurons?

Answer 7

Single cell body with multiple dendrites surrounding it but no clear axon

Question 8

Describe synaptic communication

Answer 8

Nerve impulses are transmitted from one neuron to effector cells
Synaptic transmission is unidirectional
Converts an electrical signal (nerve impulse) from a presynaptic cell —> chemical signal that affects the postsynaptic cell
Most act by releasing NTs

Question 9

What does the presynaptic terminal button contain?

Answer 9

Mitochondria and synaptic vesicles which release NTs via exocytosis

Question 10

What separates pre and postsynaptic membranes?

Answer 10

Synaptic cleft

Question 11

What does the postsynaptic cell membrane contain?

Answer 11

Receptors for the NT

Ion channels to initiate new impulse

Question 12

What are the different types of synapses?

Answer 12

Axodendritic
Axosomatic
Axoaxonic

Question 13

Describe an electrical synapse

Answer 13

Direct passive flow of electrical current between neurons via gap junctions
Link pre and postsynaptic membranes
Contain connexon proteins which link pre and postsynaptic membranes

Question 14

Describe astrocytes

Answer 14

Large number of long branching processes

Proximal regions are reinforced with intermediate filaments made of glial fibrillary acid protein (GFAP)

Question 15

What is the function of astrocytes?

Answer 15

Form a vast network of delicate terminals contacting synapses and other structures
Terminal processes of a single astrocyte typically associate 1M+ synaptic sites
Involved in the BBB
Structural and metabolic support of neurons especially at synapses
Repair processes

Question 16

What are ependymal cells?

Answer 16

Columnar or cuboidal cells that line the brain ventricles and the central canal of the SC
Apical end may have cilia and long microvilli which facilitate movement of CSF and likely involved in absorption
Joined apical by apical junctional complexes
No basal lamina present

Question 17

Describe the choroid plexus

Answer 17

Found in the roofs of the 3rd and 4th ventricles and parts of lateral ventricular walls
Thin elaborated folded layer of well vascularized pia mater covered by cuboidal ependymal cells

Question 18

What is the function of choroid plexus?

Answer 18

Removes H2O from blood and release it as CSF
Contains Na+, K+, Cl-
Very little protein
Only cells include sparse lymphocytes

Question 19

What contributes to the blood CSF barrier?

Answer 19

Tight junctions (zonula occludens) between epithelial cells

Question 20

Describe the villous structure observed when identifying the choroid plexus

Answer 20

Branching system of blood vessels which run in fronds composed of a fibrous core covered by cuboidal/columnar epithelium

Question 21

Describe microglia

Answer 21

Less numerous oligodendrocytes or Astrocytes
Migratory, will remove damaged or inactive synapses or other fibrous components
Major mechanism of immune defense in the CNS removing any microbial invaders
Originate from monocytes

Question 22

Describe oligodendrocytes

Answer 22

Extend processes that enwrap nearby axons in myelin
Enwrap axons from multiple neurons
A single axon may be entrapped by many oligodendrocytes
Usually appear as small cells with rounded condensed nuclei and sustained cytoplasm

Question 23

What are peripheral glia?

Answer 23

Includes neurolemmocytes (Schwann cells) and satelittle cells 
Both NCC derived

Question 24

What is the function of neurolemmocytes (Schwann cells)?

Answer 24

Myelinate peripheral nerves and provide electrical insulation

Question 25

What is the function of satellite cells?

Answer 25

Provide structural and metabolic support for neuronal cell bodies

Question 26

What are the different central glial cells?

Answer 26

Astrocytes, ependymal cells, microglia and oligodendrocytes

Question 27

Describe the cerebral cortex

Answer 27

Biologically older parts of the cortex are arranged as archicortex (3 layered) Most of the cortex is neocortex and consists of 6 layers

Question 28

What are the 6 layers of the cerebral cortex (neocortex)?

Answer 28

1. Molecular layer (largely fibers and neuroglial cells) 2. External granular layer 3. External pyramidal layer 4. Inner granular layer 5. Ganglionic layer (extra large pyramidal cells - Betz cells - especially in motor areas) 6. Multiform (polymorphic) layer contains cells with diverse heaped)

Question 29

Describe Alzheimer’s disease

Answer 29

Most common neurodegenerative disease Sx: memory failure, progressing steadily to involve motor skills, speech and sensation Striking thinning of gyri particularly those of the frontal and temporal bones

Question 30

What are the different structures seen in someone with Alzheimer’s?

Answer 30

Plaques, neurofibrillary tangles and neuronal loss are identified on sections Amyloid beta plaques: amorphous, pink masses in cortex Neurofibrillary tangles: flame shaped skeins formed by abnormal accumulation of tau protein

Question 31

Describe the substantia nigra

Answer 31

Large mass of grey matter containing multipolar neurons w/ dark pigment Connections with the cortex, SC, corpus striatum and reticular formation Important role in fine control of motor movement

Question 32

What type of granules do neurons of the substantia nigra contain?

Answer 32

Granules of neuromelanin pigment | Neuromelanin contains dopamine -> inhibitory effects in brain areas dedicated to movement

Question 33

Describe Parkinson’s disease

Answer 33

Clinical features of tremor, slow movement and rigidity resulting from degeneration of neurons in the substantia nigra -> loss of dopamine

Question 34

What distinctive inclusions are seen in the remaining neurons in someone with Parkinson’s?

Answer 34

Lewy bodies Rounded pink staining inclusions with pale halo around them Composed of aggregates of the protein alpha synuclein and other proteins

Question 35

What are the three layers of the cerebellar cortex?

Answer 35

Molecular layer Purkinje layer Granular layer Organized into folia with the cerebellar medulla located deep

Question 36

What are characteristics of the molecular layer of the cerebellar cortex?

Answer 36

Has many neuropils and scattered neuronal cell bodies

Question 37

What are characteristics of the Purkinje layer of the cerebellar cortex?

Answer 37

Extend dendrites throughout the molecular layer as a branching basket of nerve fibers Conspicuous in H&E stained sections

Question 38

What are characteristics of the granular layer of the cerebellar cortex?

Answer 38

Contains various very small densely packed neurons (i.e. granule cells) and little neuropil

Question 39

Describe the spinal cord

Answer 39

Central masses of gray matter has the shape of a butterfly, ventral, dorsal and lateral horns Central canal lies in the central commissure of gray matter White matter consists of ascending tracts of sensory fibers and descending motor tracts

Question 40

Describe peripheral nerves

Answer 40

Bundles of nerve fibers individually surrounded by neurolemmocytes and CT Multiple layers of neurolemmocytes memrbane can unite as the myelin sheath

Question 41

Describe myelin sheath

Answer 41

Composed mainly of lipid bilayer and membrane proteins Amount of myelin is dependent on axon diameter Degraded by standard staining procedures

Question 42

What are nodes of Ranvier?

Answer 42

Intervening regions on an axon that lack myelin

Question 43

Describe the formation of the myelin sheath

Answer 43

1. Schwann cell becomes aligned along the axon and extends a wide cytoplasmic process to encircle it 2. Growing process completely encloses the axon but continues its spiral extension 3. Spiral wrappings become compacted layers of cell membrane (myelin) as cytoplasm leaves the growing process

Question 44

Describe unmyelinated axons

Answer 44

1. Schwann cell starts to envelop multiple axons | 2. The unmyelinated axons are enveloped by the Schwann cell but there are no myelin sheath warps around each axon

Question 45

What is endoneurium?

Answer 45

Immediately around the neurolemmocytes | Consist of reticular fibers, fibroblasts and capillaries

Question 46

What is perineurium?

Answer 46

Enwrap fascicles of axons, neurolemmocytes and endoneurium

Question 47

What is epineurium?

Answer 47

Dense, irregular fibrous coat in between fascicles and surrounding the peripheral nerve (continuous with spinal meninges)