NEUROSCIENCE ACTUAL EXAMS SCRIPT QUESTIONS
AND ANSWERS SURE A+
✔✔Cell Body - ✔✔soma, perikaryon
support and metabolic center for neuron
highly active
∙transcription/translation
∙euchromatic nucleus
∙prominent nucleolus
∙extensive Golgi complex
∙extensive rough ER, polyribosomes (basophilic Nissl substance)
∙high energy metabolism
∙large numbers of mitochondria
varies in size/shape due to function
✔✔Axon - ✔✔arises from cell body at the axon hillock
transmits information (action potential)
∙to other neurons
∙to effector cells (i.e. muscle)
,cytoplasm/axoplasm
∙contains dense bundles of microtubules & neurofilaments
∙play a key role in transport of metabolites & organelees
typically devoid of ribosomes
∙distinguishes axons from dendrites
∙developing, regenerating & mature neuron axons support protein translation
generally single axon
∙range from short (few mm) to long (>1.5m)
∙accounts for ~99.8% of total neuron volume
smooth surface
often end in fine branches: terminal arbors
∙in most neurons, axon terminal is capped with a small terminal bouton
axons end at synapses
large axons are myelinated
∙CNS = oligodendrocyte
∙PNS - Schwann cell
smaller axons are less myelinated, while the smallest axons are unmyelinated
∙all axons still have intimate contact with oligodendrocytes or Schwann cell
myelin serves to increase AP conduction
∙salutatory conduction
∙nodes of Ranvier
✔✔Axon hillock - ✔✔last site in soma where graded membrane potentials are
summated before being transmitted to the axon
✔✔Initial segment of axon (AIS) - ✔✔earliest site of action potential initiation
first ~50-100 μm of axon
✔✔Node of Ranvier - ✔✔lower membrane resistance
node rich in Na+ channels (juxtaparanode rich in K+ channels)
salutatory conduction: the AP traveling along the length of the axon jumps from one
node to another
,✔✔Action Potential - ✔✔inputs to neuron (receptor or synaptic) alter membrane
potential
summation reaches critical point = action potential
∙occurs at axon hillock (or 1st node of Ranvier for sensory neurons)
AP propagation
∙unidirectional (anterograde)
∙small, unmyelinated axons = aided by general distribution of ion channels
∙myelinated axons = aided by nodes of Ranvier
at synapse, AP results in activation of voltage gated Ca+ channels, which results in
vesicular release of neurotransmitter
✔✔Synapse - ✔✔axons branch extensively near target regions
axons end as terminal boutons
synaptic contacts may also form along axon length
composed of pre- and post-synaptic elements, synaptic cleft
variety of types
✔✔Synthesis & Trafficking of Axonal Proteins - ✔✔translated primarily in cell body and
proximal dendrites
proteins translocated across rER during synthesis
∙membrane, lumenal, transmembrane proteins
synthesized as pre-propeptides
large dense core vesicles and synaptic vesicles
✔✔Axonal Transport - ✔✔IMPORTANT:
∙maintaining function of axon/synapses
∙trophic support for neuron (back to cell body)
bi-directional
∙anterograde/orthograde - from cell body towards synapse
∙retrograde - from terminals towards cell body
✔✔Anterograde: toward synapse - ✔✔fast (100-400mm/day)
∙kinesin: moves vesicles & mitochondria along microtubules
slow (~1mm/day)
, ∙less well understood
∙moves cytoskeletal & cytosolic components
✔✔Retrograde: toward cell body - ✔✔fast (50-400mm/day)
dynein: moves trophic support molecules (growth factors), axon recycling
growth factors are taken up near the axon terminal by vesicle-mediated pinocytosis,
receptor-mediated endocytosis
✔✔Axonal transport: Clinical relevance - ✔✔can be important clinically (i.e. rabies virus,
tetanus toxin are retrogradely transported)
✔✔Classification of Neurons - ✔✔multiple ways to classify
structural
∙unipolar
∙pseudounipolar
∙bipolar
∙multipolar
∙multipolar
∙amacrine
functional
∙sensory vs motor vs interneuron
∙afferent vs. efferent
anatomical
molecular properties
✔✔Structural Classification of Neurons - ✔✔pseudounipolar
∙bifurcated single process
∙central and peripheral branch
bipolar
∙single dendrite & axon
∙found in structures associated with special senses
multipolar
∙many dendrites, single axon
∙majority of neurons (~9%)
∙variety of shapes (fusiform, flask, triangular, polygonal, stellate)
amacrine
∙"axonless"
AND ANSWERS SURE A+
✔✔Cell Body - ✔✔soma, perikaryon
support and metabolic center for neuron
highly active
∙transcription/translation
∙euchromatic nucleus
∙prominent nucleolus
∙extensive Golgi complex
∙extensive rough ER, polyribosomes (basophilic Nissl substance)
∙high energy metabolism
∙large numbers of mitochondria
varies in size/shape due to function
✔✔Axon - ✔✔arises from cell body at the axon hillock
transmits information (action potential)
∙to other neurons
∙to effector cells (i.e. muscle)
,cytoplasm/axoplasm
∙contains dense bundles of microtubules & neurofilaments
∙play a key role in transport of metabolites & organelees
typically devoid of ribosomes
∙distinguishes axons from dendrites
∙developing, regenerating & mature neuron axons support protein translation
generally single axon
∙range from short (few mm) to long (>1.5m)
∙accounts for ~99.8% of total neuron volume
smooth surface
often end in fine branches: terminal arbors
∙in most neurons, axon terminal is capped with a small terminal bouton
axons end at synapses
large axons are myelinated
∙CNS = oligodendrocyte
∙PNS - Schwann cell
smaller axons are less myelinated, while the smallest axons are unmyelinated
∙all axons still have intimate contact with oligodendrocytes or Schwann cell
myelin serves to increase AP conduction
∙salutatory conduction
∙nodes of Ranvier
✔✔Axon hillock - ✔✔last site in soma where graded membrane potentials are
summated before being transmitted to the axon
✔✔Initial segment of axon (AIS) - ✔✔earliest site of action potential initiation
first ~50-100 μm of axon
✔✔Node of Ranvier - ✔✔lower membrane resistance
node rich in Na+ channels (juxtaparanode rich in K+ channels)
salutatory conduction: the AP traveling along the length of the axon jumps from one
node to another
,✔✔Action Potential - ✔✔inputs to neuron (receptor or synaptic) alter membrane
potential
summation reaches critical point = action potential
∙occurs at axon hillock (or 1st node of Ranvier for sensory neurons)
AP propagation
∙unidirectional (anterograde)
∙small, unmyelinated axons = aided by general distribution of ion channels
∙myelinated axons = aided by nodes of Ranvier
at synapse, AP results in activation of voltage gated Ca+ channels, which results in
vesicular release of neurotransmitter
✔✔Synapse - ✔✔axons branch extensively near target regions
axons end as terminal boutons
synaptic contacts may also form along axon length
composed of pre- and post-synaptic elements, synaptic cleft
variety of types
✔✔Synthesis & Trafficking of Axonal Proteins - ✔✔translated primarily in cell body and
proximal dendrites
proteins translocated across rER during synthesis
∙membrane, lumenal, transmembrane proteins
synthesized as pre-propeptides
large dense core vesicles and synaptic vesicles
✔✔Axonal Transport - ✔✔IMPORTANT:
∙maintaining function of axon/synapses
∙trophic support for neuron (back to cell body)
bi-directional
∙anterograde/orthograde - from cell body towards synapse
∙retrograde - from terminals towards cell body
✔✔Anterograde: toward synapse - ✔✔fast (100-400mm/day)
∙kinesin: moves vesicles & mitochondria along microtubules
slow (~1mm/day)
, ∙less well understood
∙moves cytoskeletal & cytosolic components
✔✔Retrograde: toward cell body - ✔✔fast (50-400mm/day)
dynein: moves trophic support molecules (growth factors), axon recycling
growth factors are taken up near the axon terminal by vesicle-mediated pinocytosis,
receptor-mediated endocytosis
✔✔Axonal transport: Clinical relevance - ✔✔can be important clinically (i.e. rabies virus,
tetanus toxin are retrogradely transported)
✔✔Classification of Neurons - ✔✔multiple ways to classify
structural
∙unipolar
∙pseudounipolar
∙bipolar
∙multipolar
∙multipolar
∙amacrine
functional
∙sensory vs motor vs interneuron
∙afferent vs. efferent
anatomical
molecular properties
✔✔Structural Classification of Neurons - ✔✔pseudounipolar
∙bifurcated single process
∙central and peripheral branch
bipolar
∙single dendrite & axon
∙found in structures associated with special senses
multipolar
∙many dendrites, single axon
∙majority of neurons (~9%)
∙variety of shapes (fusiform, flask, triangular, polygonal, stellate)
amacrine
∙"axonless"
