notes on

Functional Neuroanatomy lecture by Roland Brandt egon w. stemle ([email protected]) WS 2002/2003∗

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25. October 2002

1.1

How is the nervous system organized in the simple model organisms Hydra and Caenorhabditis elegans?

• hydra has a nervous system characterized by a nerve net, i.e. a collection of separate but ’connected’ neurons; no CNS • C. elegans has – a body axis – a specialized head region1 – an accumulation of nerve cells in the head region2 – 302 neurons, a nerve ring and a segmented dorsal and ventral strand

1.2

Which principle mechanisms operate to control the development of neurons?

1. hard-wired molecular programs, i.e. the genetic code completely predicts the development of cells 2. epigenetic processes, i.e. the connection pattern of neurons is determined by means of other factors; e.g. neurotrophic factors3

1.3

Why is the white matter white?

it’s made up of longitudinal tracts of myelinated neurons...4 myelin is the insulation of the nervous system, rich in fat and therefor white. ∗ last

modified 30. Januar 2003

1 cephalization 2 centralization 3 limiting 4 ...that

amount of neurotrophins determines the number of surviving neurons form the ascending and the descending pathways

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1.4

How many divisions form the vertebrate brain? How did it develop?

5 divisions: Tel-, Di-, Mes-, Met- and Myelencephalon

What is the Corpus callosum5 and why is it important?

1.5

the Corpus callosum is the primary pathway for interhemispheric communication. it’s a massive bundle of axonal fibers connecting the two hemispheres.

1.6

What could be learnt from the two Goldmann experiments?

1. Blood-Brain Barrier 2. Blood-Liquor Barrier

1.7

What are thought to be the main functions of the CSF6 ?

1. removing potentially harmful brain metabolites, 2. a mechanical cushion and 3. by it’s buoyant action the CSF allows the brain to float and thereby reducing the effective weight

1.8

What makes the blood-brain barrier?

endothelial cells forming the brain’s microvessels are the principle anatomic site of the blood-brain barrier7 . Astrocyte foot processes are believed to influence barrier-specific endothelial differentiation.

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1. November 2002

2.1

Which kind of mechanoreceptors do you know? How do pain receptors look like?

a. free nerve endings 1. Merkel Disc 2. Hair Receptor b. encapsulated nerve endings 1. Meissner’s Corpuscle 2. Pacinian Corpuscle c. Mixed Nerve endings 1. Ruffini endings 2. Bare nerve Ending (pain receptors) 5 dt.:

Balken

6 cerebrospinal

fluid, dt.: Gehirn-R¨ uckenmarksfl¨ ussigkeit Ort der Blut-Hirn-Schranke ist das Kapillarendothel, das bei den Hirnkapillaren eine geschlossene Wand ohne Fensterung bildet 7 der

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2.2

What is nociceptive, what neuropathic pain?

nociceptive pain due to direct activation of nociceptors neuropathic pain due to direct injury of nerve cells

2.3

What distinguishes A- and C-fibers and where are they found?

A-fibers are myelinated; e.g. mechanoreceptors, some nociceptors, some thermoreceptors C-fibres are non-myelinated, have a small diameter; e.g. some nociceptors, some thermoreceptors myelinated (fast) vs. non-myelinated (slow)

2.4

What are peptide transmitters and how do they contribute to pain?

Nociceptors respond indirectly8 to one or more chemicals (e.g. substance P or histamine) released from cells in the traumatized tissue. This contributes to kinds of unlocalizable pain.

2.5

Which differences in the pathways of mechanoreceptor and nociceptive information do you know?

2.6

What are primary, secondary and tertiary fibers with respect to the processing of mechanoreceptor information?

2.7

What is somatotopy and at which level does it occur? Give examples?

somatotopy is the orderly distribution of inputs from different portions of the body, i.e. the relative positions are preserved it occures at all levels, e.g. fibres, thalamus, somatosensory cortex

2.8

Give an example of parallel processing of somatosensory information? What is it good for?

Somatic sensation involves the parallel analysis of different stimulus attributes in different cortical areas, where parallel processing allows different neuronal pathways and brain relays to deal with sensory information in slightly different ways. e.g. the primary somatosensory cortex has 4 complete maps of the body surface. 8 directly

to some noxious stimuli

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3

8. November 2002

3.1

What is a motor unit, what a motor nucleus?

motor unit is a single motoneuron9 and the muscle fibres that it innervates motor nucleus is the cluster of motor neurons in the ventral spinal cord that innervate one muscle

3.2

What does the sliding filament hypothesis state?

each sarcomere10 is organized into a regular matrix of thick and thin filaments. sliding filament hypothesis states that in a contracting muscle adjacent thick and thin filaments slide past each other

3.3

Explain, how Ca-Ions regulate muscle movement?

Action Potential activates second messenger Ca2+ → Ca2+ binds to F-Actin/Tropomyosin complex → change of position → Myosin activated by ATP binds to F-Actin/tropomyosincomplex → thin filaments move into thick filaments

3.4

What is an alpha, what a gamma motor neuron?

α-motor neuron sind Motorneurone, die die extrafusale11 Arbeitsmuskulatur innervieren γ-motor neuron sind Motorneurone, die die intrafusale Muskulatur innervieren; eine Aktivierung bewirkt eine Kontraktion an beiden Enden der Muskelspindel12

3.5

What is a reflex and what distinguishes it from voluntary movement?

reflex is an automatic (i.e. involuntary), stereotyped (i.e. pattern of muscle contraction and relaxation) movement in response to stimulation of peripheral receptors. however, we now know that under normal conditions reflexes can be modified via supraspinal signals

3.6

How can a monosynaptic pathway be distinguished from a polysynaptic one?

by means of measuring the reflex latency after stimulation;