Lecture 6 - Nervous System Flashcards
CNS vs PNS
Central nervous system - includes brain and spinal cord
Peripheral Nervous System- includes nervous tissue outside brain and spinal cord (ie. cranial nerves, spinal nerves, ANS)
Cell body (Know Alt. Names)
Aka soma, perikaryon
function: supports metabolic and synthetic needs of the neuron
Dendrite
provides increased surface area for synaptic input from the other neurons
Axon
single axon conducts info away from cell body via action potential
Parts: axon hillock, initial segment, node of ranvier, internodal segment, axon terminal
Axon hillock
the ANATOMICAL region where the axon rises from the soma
Initial segment
PHYSIOLOGIC trigger zone for an AP; located bw the axon hillock and beginning of myelin sheath
Node of Ranvier
Between myelinated segments
conducts AP
internodal segment
myelinated segments
Axon terminal
conveys info to other neurons via synapses
Multipolar neuron
most common
present throughout nervous system
multiple dendrites emerge from the soma
SINGLE axon emerges from soma
Pyramidal Neuron
type of multipolar neuron
-large triangular shaped soma
-single apical dendrite extends toward pial surface (the outside of brain)
-multiple basal dendrites
singla axon
-location: cerebral cortex and hippocampus
Bipolar neuron
has 2 processes that emerge from soma -single dendrite -single axon Few locations in CNS -associated with CN-I (olfactory neurons) -CN II- retinal bipolar cells) CN VIII
Unipolar neurons
aka pseudounipolar
one process emerges from the soma
-bifurcates into peripheral (receives signals) and central branch (enters the CNS)
-both branches are morphologically axons and can propagate an AP
Location: mainly in the PNS (dorsal root ganglia, cranial nerve ganglia)
Neuronal Cell Body
nucleus, rough er, free ribosomes, golgi apparatus, mitochondria, microfilaments, neurofilaments, microtubules
Cell nucleus
has euchromatin (dispersed chromatin- available for transcription) -well defined nucleolus is common (center for ribosomal RNA synthesis and formation of ribosomal subunits
Cytoplasm In a Neuron
contains rER for prot synth
Free ribosomes are scattered within it
Golgi apparatus in a Neuron
prominent
packages newly synthesized proteins
mitochondria in a neuron
numerous
meet energy requirements
cytoskeletal elements in a neuron
microfilaments & neurofilaments, microtubules
Nissl stain
light microscopy
BASIC stain - visualization of cell body/soma
Nissl bodies
NB: the light microscopic term for aggregates of rER and polyribosomes
Axons does not have Rough ER
Presence of Nissl Bodies location in neuron
High in the Soma
presence of NB in Proximal dendrite
-diminishes distally
-Absent in axon
Free ribosomes & Nissl stain
may be located in axons and distal dendrites, but do not aggregate and cannot be seen with light microscope
-do not form Nissl Body
Ganglion vs Nucleus
ganglion: collection of neuronal cell bodies outside CNS
- Note: their cell bodies are surrounded by small support cells called satellite cells (glial cells)
Nucleus: collection of neuronal cell bodies within CNS
Dendrites
receive signals
- extensive branching pattern allows dendrites to receive input from many neurons simultaneously
- dendritic spines increase surface area for synaptic contact
- base of dendrites contain typical organelles EXCEPT golgi apparatus
- many organelles become absent distally
- contain cytoskeletal elements: micro and neurofilaments, microtubules
axons
arise from soma as a single process, may extend long distances
NO golgi apparatus
-may see occasional ribosomes, not large aggregates
contain cytoskeletal microfilaments, neurofilaments and microtubules
Cytoskeletal elements
microfilaments
Neurofilaments
Microtubules
(small ->large)
microfilaments
smallest diameter, actin filaments
location: mainly along the cell membrane around the soma
function: provides structural support to the cell and maintains cell shape
neurofilaments
intermediate filament
function: provides structural support of cell
Microtubules
largest diameter
function: key role in an intracellular transport system toward and away from the cell body
Axonal transport
- energy dependent transport
- moves to and from axon terminal along microtubules
- too long to allow efficient movement of substances between the soma to the axon terminal by simple diffusion
- dendrites have capacity to transport substances but is not as extensive as in the axon
anterograde vs retrograde transport
Anterograde- from soma to axon terminal
Retrograde - from terminal to soma
anterograde transport
involves KINESIS, a microtubule associated protein that moves along microtubules
Kinesin
‘molecular motor’
interacts with both the microtubule and element to be transported in anterograde motion from soma to axon terminal
retrograde transport
involves DYNEIN and moves from axon to soma
dynein
microtubule associated protein
moves vesicles along microtubles but in retrograde
Synapse
mediates info transfer bw neurons
-includes: presynaptic element and post synaptic element
presynapse
axon terminal/bouton
contains NT in membrane bound synaptic vesicles
presence of mitochondria
postsynapse
NT binds to receptor on post membrane
results in electrical signal in postsynaptic neuron
Types of synapses
axosomatic
axodendritic
axoaxonic
Axosomatic
axon forms a synapse with a cell body
axodendritic
axon forms a synapse with a dendrite
axoaxonic
axon forms a synapse with another axon
-synapses modulate activity of other two types
Neurological cells
astrocytes, microglia, oligodendrocyte, schwann cells
Astrocytes Function and location
located throughout CNS
cover most surfaces of neuron (soma, dendrite, node of ranvier) via cytoplasmic extensions (astrocytic processes/end feet) (END FEET)
- outer surface of brain and spinal cord is covered with astrocytic processes called glial limiting membrane
- every blood vessel in CNS is covered by astrocytic processes that seperate it from the neural tissue
-provide structural support in CNS
-protect neurons by removing ions and neurotransmitters (eg. glutamate) form extracellular space
glial limiting membrane
glial limiting membrane that covers brain and spinal cord
-a specific astrocyte
Just below the Pia Mater
Astrogliosis (gliosis)
transformation astrocytes from a quiescent to reactive state in response to CNS injury
cellular changes associated with astrogliosis: increased number of astrocytes, increased cell size, extension of cytoplasmic process, increased production of intermediate filaments
changes give rise to formation of a dense gliotic scar
can last weeks, months, years
If you see thesse you know there was an injury but you do not know when
Horseradish peroxidase
Enzyme injected into specific terminal and will be transported back to the cell body
Studies wanted to see if this retrograde motion would affect Primate teeth to find cell bodies
•Results -Labelled neurons in ipsilateral trigeminal ganglion, mesencephalic nucleus and superior cervical ganglion
clostridium tetani
Tetanus bacteria takes advantage of reterograde transport
- toxin can block inhibitory interneuron receptors and cause tetanic contraction
Rabies
travels retrograde to CNS
Alzheimer’s disease
Tau protein on microtubule becomes hyperphosphorylated
- becomes unstable and can no longer stabilize microtubules, depolymerizes
CTE
evidence of hyperphosphorylation of tau protein
Microglia
transform from a quiescent to reactive state in response to CNS injury; process is termed microgliosis
- remove foreign and degenerating cellular elements through phagocytosis
- microglia return to resting state once reactive process has ceased
- If you see them then you have a current active problem
Microgliosis
Key changes
Increased number of microglia
increased cell size
includes extension of cytoplasmic processes
Oligodendrocyte
responsible for producing and maintaining the myelin sheath around CNS axons
One Cell Body away from the nerve acting on multiple axons
ID on pic
Schwann Cells
form myelin sheath around axons in PNS
Each schwann cell myelinates a single internode (an internode is a myelinated axonal segment between two nodes of ranvier
- contact both myelinated and unmyelinated axons in the PNS
- unmyelinated are surrounded by the schwann cell plasma membrane (for protection)
Epineurium
conective tissue of nerve cell outermost layer Dense CT forming most of the CT investment Thickest of the three surrounds the entire nerve
perineurium
middle layer
dense CT layer that surround a bundle of axons within the nerve
ARound the nerve fassicle
Endoneurium
innermost layer
Loose CT that surrounds individual axons
Around an individual Nerve
PNS damage and regeneration
Retrograde: axon proximal to injury degenerates
Anterograde: axon distal to injury degenerates
local: axonal ends retract; macrophages and fibroblasts gather
neurolemma
the thin sheath surrounding a nerve axon maintained by the schwann
Regeneration of Nerve
within 96 hours of injury, the axon proximal to the lesion sends out sprouts
if the axonal sprouts reach the tube left by schwann cells, then the axon is guided to the target (1 mm/day)
The schwann cells maintain the path that the nerve should take and it follows this
Non continuous neurolemma Regeneration of Nerve
if the cut ends of the axon are separated such that there is a non continuous neurolemma (aka the schwann cells dont maintain the path), then the regrowth of the axon toward its target is disrupted and reinnervation of the target cannot occur
Nerve vs tract
nerve: collection of nerve fibers that carries info to and from the CNSd
Tract: collection of nerve fibers within the CNS
What Are the Morphological Classifications for Neurons
Multipolar
Pyrimidal
Bipolar
Unipolar (pseudounipolar)
Dorsal Horn
The location in which the axon enters the spinal chord
What are the connective tissue of peripheral Nerves
Epinerium, Perioneruium, Endoneurium
