Structure of the Nervous System

Updated for 1999

Structure of the Nervous System

(Chapter 3)

Although I won’t be lecturing on it, still you should be sure to know: blood supply, development of the CNS

You don’t need to know all the cranial nerves, but are responsible for the key words (in bold) in the PNS section

neuraxis - imaginary line drawn through the spinal cord up to the front of the brain, between the eyes

anterior/posterior

rostral/caudal

dorsal/ventral

lateral/medial

ipsilateral/contralateral

cross-section - like slicing pepperoni

horizontal section - parallel to the ground; like slicing hoagie bun

sagittal section - perpendicular to ground and parallel to the neuraxis; like slicing off your left arm and left leg

meninges - 3 layers:

dura mater (hard mother-actually refers to tough swaddling)
arachnoid membrane (looks like spider web)
pia mater (pious mother - actually delicate swaddling)

subarachnoid space - below arachnoid membrane, filled with CSF, cushions brain

ventricles:

lateral
third - connected to fourth by cerebral aqueduct
fourth

CSF - manufactured by the choroid plexus, lining the ventricles, flows from lateral through to fourth ventricle to subarachnoid space and then around CNS; reabsorbed into blood supply by arachnoid granulations

hydrocephalus - obstructive vs. ex vacuo

I. FOREBRAIN

telencephalon

cerebral cortex
sulci (small grooves), fissures (large grooves)
gyri (bulges, or bumps between grooves)
lobes: frontal, parietal, occipital, temporal
corpus callosum
primary motor/somatosensory/visual/auditory cortex
association areas
limbic system - motivation and emotion
hippocampus - memories
amygdala
basal ganglia - involved in the control of movement
Parkinson’s disease

diencephalon - it surrounds the third ventricle

thalamus - central relay station - projection fibers
lateral geniculate nucleus - visual "light"
medial geniculate nucleus - auditory "music"
hypothalamus - four Fs

II. MIDBRAIN/mesencephalon - surrounds the cerebral aqueduct

tectum - dorsal portion (roof)
superior colliculi - vision
inferior colliculi - auditory
tegmentum - below tectum
recticular formation - involved in arousal
periaqueductal gray matter - includes neurons involved in pain suppression
red nucleus - involved in movement
substantia nigra - dopamine secretion - degeneration associated with Parkinson’s disease

III. HINDBRAIN - surrounds the fourth ventricle

metencephalon

cerebellum - motor
pons - sleep and arousal

mylencephalon

medulla oblongata - vital functions

Neuroanatomical/Neurochemical Techniques

(Chapter 5)

EXPERIMENTAL ABLATION:

lesions by radio frequency current - problem?

excitotoxic lesions - how is it done? what’s the advantage?

"trojan horse" lesions - 6-hydroxydopamine - taken up by catecholaminergic neurons

sham lesions

reversible lesions - cooling or anesthetic

STEREOTAXIC SURGERY: stereotaxic atlas - roadmap for brain surgery

stereotaxic apparatus - allows for precise positioning of cannula or electrode into brain

HISTOLOGICAL METHODS: FIXATION
perfused - like embalming with salt solution

formalin - liquid version of formaldehyde

SECTIONING
freezing - soak in sugar solution, then chilled

embedding - parafin (wax) - brain soaked in xylene, which dissolves parafin, then dipped in increasing concentrations of parafin, then placed in small container of liquid parafin and allowed to cool

microtome - for slicing very thin

STAINING
1) Cell-body

Nissl stains - methylene blue or cresyl violet - all cell bodies, not just neurons

2) Myelin

Weil stain

3) Membrane

Golgi-Cox stain - silver, only stains a few of the neurons in an area, but allows for good views of their axons, dendrites, and synaptic connections

ELECTRON MICROSCOPY - beam of electrons passed thru tissue, shadow cast on photographic film (see figure 5.10 on page 127 for scanning-electron micrograph - pretty cool, eh?)

TRACING

1) anterograde labeling methods-used in animal research

PHA-L - protein (actually produced by the kidney bean), injected into nuclei in the brain, taken up by the dendrites, transported throughout cells within a couple of days (by fast axoplasmic transport)

immunocytochemical methods - used to identify peptides or proteins; attach antibodies to a dye, the antibodies then seek out and attach to particular peptides or proteins (antigens); for example, place slices of brain previously injected with PHA-L in dye containing antibodies to PHA-L

2) retrograde labeling methods-used in animal research

chemical injected into brain region, taken up by terminal buttons, and transported back to the cell body

fluorogold - commonly used, fluoresces in ultraviolet light

STUDY OF THE LIVING HUMAN BRAIN: 1) CT scan - x-ray; two-dimensional

2) magnetic reasonance imaging - magnetic field

3) Positron Emission Tomography (PET scan) - radioactive 2-DG injected, which emits positrons when decaying

TABLE 5.1 (page 133) IS A VERY NICE SUMMARY - CERTAINLY A GREAT SOURCE FOR EXAM QUESTIONS!

RECORDING NEURAL ACTIVITY:

Microelectrodes

Amplifiers - could then be displayed on oscilloscope and stored in computer

Macroelectrodes - as in EEG

RECORDING METABOLIC ACTIVITY:

Autoradiography

Fos - protein produced in nucleus of neuron following synaptic stimulation - How is this useful? MEASURING BRAIN SECRETIONS: Microdialysis - used to analyze chemicals in the interstitial (extracellular) fluid STIMULATING NEURAL ACTIVITY: Multibarreled micropipette - used for microiontophoresis

Recording microelectrode - records reaction to exposure to each substance

LOCALIZING NEUROCHEMICALS:

1) directly - if a peptide, by direct immunocytochemical methods (antibodies)

2) by enzymes that produce them - if not a peptide, then can use antibody to enzyme that produces the neurochemical

3) by "in situ hybridization" - slices of brain tissue exposed to a radioactive synthetic RNA, which sticks to the particular messenger RNA - viewed by autoradiography (like developing photos)

4) double labeling - combination of one of the 3 above, which identifies the particular neurotransmitter, and a/n anterograde/retrograde stain which identifies the cell