4. Histology of the CNS Flashcards
- Describe the anatomy of a neuron:
cells that respond to stimuli through electrochemical mechanisms (excitable or inhibitory)
Cell body- large with large euchromatic nucleus with well-developed nucleolus; nissl substance/bodies scattered throughout cytoplasm, indicative of protein synthesis
numerous dendrites extend from perikaryon, with extensive branching/arborization, numerous spines (increasing receptive area) which are PLASTIC
long axon covered by myelin emerging from axon hillock
2a. Describe how neurons are classified (structural)
multipolar- most common throughout CNS; multiple dendrite branches, one axon
bipolar- sensory neurons of retina, olfactory mucosa, and inner ear; one dendrite, one axon (2 processes)
Uni/pseudounipolar- other sensory neurons, including DRG and cranial ganglia; single short process of axon–> branches into central and peripheral processes; restricted at dendrites
Anaxonic neurons of CNS lack true axons and do not produce Action Potentials, but regulate local electrical changes of adjacent neurons
3a. Describe and distinguish anatomy of chemical synapses: what does it contain and its function?
presynaptic terminal bouton- contains mitochondria and synaptic vesicles–> which releases NT via exocytosis
Synaptic cleft= 20-30 nm wide intercellular space separating pre and postsynaptic membranes; when fuse with axons, contents released here
Postsynaptic cell membrane= contains receptors for NT and ion channels to initiate new impulse
greater in number than electrical !!**
- Describe the mechanisms of axonal transport, what are the types?
substances needed in axons and dendrites are synthesized in cell body and require transport
Bidirectional mechanism carrying molecules along MT and Intermediate filaments from axon terminal –> nerve cell body and from nerve cell body –> axon terminal
Anterograde transport: nerve cell body–> periphery; KINESIN, MT-associated motor protein with ATP use
Retrograde transport: axon terminal and dendrites–> nerve cell body; DYNEIN, MT associated motor protein
- Identify types of glial cells found in brain:
Astrocytes
Ependymal Cells
Microglial Cells
Oligodendrocytes
Where does the axon originated from and what is terminal arborization? what is usually at the ends?
Originates from axon hillock; initial segment= site where excitatory or inhibitory stimuli are initiated; long in length, constant diameter
Terminal Arborization: distal end of axon; some have branching, collateral branches
ends of axons usually have TELEDONDRIA (dilation of branch ends and contact postsynaptic cell)
2b. Describe how neurons are classified (functional):
Sensory neurons (aff)–> receive stimuli from receptors throughout body
Motor neurons (eff)–> send impulses to effector organs
Somatic: neurons under voluntary control and innervate skeletal muscle (motor neurons)
Autonomic: control involuntary or unconscious activities of glands, cardiac muscle, and SM
Interneurons: establish relationships among other neurons, forming complex functional circuits (99% of all neurons in adults)
4b. How does rate affect axonal transport?
Also characterized by rate!!
SLOW:
-conveys substances from CB–> terminal bouton (anterograde only!!)
FAST:
- conveys substances in both directions (20-400 mm/day); -anterograde= membrane-limited organelles, sER stuff, synaptic vesicles, and mitochondria
- retrograde= membrane limited organelles and molecules endocytosed at axon terminal; path followed by toxins and viruses
What is synapse communication?
nerve impulses transmitted from one neuron to effector cells
unidirectional transmission
converts electrical signal (nerve impulse) from PRESYNAPTIC CELL–> chemical signal affecting POSTSYNAPTIC CELL
most act via NTS
3b. Describe and distinguish anatomy of electrical synapses: jxns? What does it contain and permit?
Permit direct, passive flow of electrical current from one neuron to another; potential difference generated locally by presynaptic AP
current flow occurs via GAP jxns, link pre- and postsynaptic membrane (2 nm)
contains connexon proteins= permit diffusion of small molecules and electric current flow
What are the types of synapses?
Axosomatic (to CB), axodendritic, and axoaxonic synapses
connectivity creates responses!
- Describe histological changes associated with Alzheimers disease:
most common neurodegenerative disease, incidence increases with age (>70 usually)
sx: memory failure, progressing steadily to involve motor skills, speech, and sensation; some genetic association
Other: striking thinning of gyri, particularly those of frontal and temporal lobes
Histo: B-amyloid plaques (amorphous pink masses in cortex), neurofibrillary tangles (abnormal accumulation of TAU), neuronal loss!!
What are the types of synapses?
Axosomatic (to CB), axodendritic, and axoaxonic synapses
connectivity creates responses!
What are the types of synapses?
Axosomatic (to CB), axodendritic, and axoaxonic synapses
connectivity creates responses!
5a. What is the origin and functions (5) of astrocytes?
Origin and info: large number of long, branching processes; GFAP; forms vast network of delicate terminals contacting synapses and other structures; terminal processes of a single astrocyte typically associate 1M+ synaptic sites
Functions:
- processes can affect formation, function, and plasticity of synapses; help form BBB (wrap vasculature or axon processes, prevent leakage)
- regulate extracellular ionic concentrations around neurons (especially in buffering extracellular K+)
- guide and physically support movements and locations of differentiating neurons during CNS development; neural development assistance
- extend fibrous processes with expanded perivascular feet that cover capillary endothelial cells and modulate BF and help move nutrients, wastes, and other metabolites bw neurons and capillaries
- filling tissue defects after CNS injury by proliferation to form an astrocytic scar
