Neurobiology
From Medical-Wiki
The study of neurobiology covers a wide range of topics and disciplines, from neuroanatomy, to biophysics and electrophysiology, and systems biology. Each discipline has its own practices, but they combine to provide a basic description of the beautiful workings of the nervous system.
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[edit] Introduction
The nervous system controls almost every aspect of our body's responses to the world. Central to this control is the flow of information from the sensory periphery through the central nervous system and back out to the periphery. As a general introduction to the nervous system let's follow (at a very simplified level) the effects of seeing an old flame at your 10 year high-school reunion:
Let's say you hear his/her voice before you see them:
- Mechanosensors in the ear split the voice into many auditory channels, each carrying a narrow range of sound frequencies. The auditory nerve carries the information in these channels to nuclei in the brainstem that calculate the location of the sound source. The information is then relayed to the thalamus, where a decision is made whether to send it on up to your cerebral cortex or to let it dissipate. If it passes on to your auditory cortex, the information gets processed and passed onto higher cortical areas as well as to "subcortical" (that is, not in the cerebral cortex) areas.
One subcortical area is the superior colliculus, that along with other areas, coordinates the rapid movement of your eyes. The superior colliculus orients your gaze to the sound source - you have now spun to check him/her out.
- Photopigments in the eye break contrasting color regions in the image into different neuronal streams in the retina, and the retinal neurons project through the optic nerve to the thalamus. Again, at the thalamus the information is either blocked (which would happen if you were asleep) or allowed to pass on up to the visual cortex. The image is initially parsed into tiny segments - in which color, orientation and brightness are encoded by the activity of individual neurons. The primary visual cortex projects to higher visual areas, each combining the input from the previous area into a more complex and larger representation. Eventually the information gets to your inferior temporal lobe and fusiform face area, in which complex features, like faces, are encoded. It's him/her (the example would be much more compelling if I knew the interest of the reader).
- At this point information is starting to make its way to the frontal cortex, where executive decisions and value judgments are made. Did I lose enough weight on my diet to talk to him/her? Should I play it cool? What is my spouse going to say when he/she realizes who I'm looking at? and so on.
- The decision is made - play it cool and turn back around.
- Just then, that old perfume/cologne makes its way onto your nasal epithelium. Again the stimulus, this time a complex set of odorants, activates a unique set of receptors, each encoding a small range of chemical structures. The olfactory input, unfortunately, goes directly to olfactory cortex - which is primitive and bypasses the thalamus. The olfactory cortex plugs directly into the limbic system, which controls emotions.
- Your decision to play it cool, well reasoned as it was, has been over-ruled.
- The limbic system plugs into the hypothalamus, which controls your body's homeostasis. Your hypothalamus is being bombarded by potent signals and it starts to activate your autonomic nervous system - your eyes dilate and the blood flow to your intestines shuts down, peripheral vascular tone decreases (your cheeks flush, your ears turn red).
- All these systems feed into associational areas in the cerebral cortex, which, now that the decision to speak has been made, send signals to motor areas. Primary motor cortex will control how your body and arms move around to face the subject of interest, your superior colliculus will control gaze direction, and Broca's area will determine motor outputs of speech.
- Motor commands, descending from primary motor cortex through midbrain and pons send copies of the motor command to the cerebellum, which is in charge of making sure commanded motions match actual motions. In this case, unfortunately, your cerebellum is a bit slow because of the open bar, and as you turn to speak to him/her you spill your drink (a pink frozen daiquiri) all over your shirt.
- He/she smirks and turns away. Now you're left to deal with much higher cortical functions - like how to get out as fast as possible.
[edit] Neuroanatomy
Blood supply
Ventricles and cisternae
Limbic system
Cerebellum
Brainstem
[edit] Cranial nerves
[edit] Neurodevelopment
[edit] Electrophysiology
Action potential
Synaptic transmission
Neuro-muscular junction
Neural plasticity
[edit] Sensory systems
Introduction to sensory systems
Central regulation of pain
Visual system
Auditory system
Vestibular system
Olfaction
Gustation
[edit] Motor systems
Spinal reflexes
Central pattern generators
Motor cortex and descending pathways
Basal ganglia
Cerebellum
[edit] Autonomic nervous system
Sympathetic system
Parasympathetic system
[edit] Neuroendocrinology
[edit] Neuropharmacology
Glutamate, the major excitatory neurotransmitter.
GABA, the major inhibitory neurotransmitter.
Acetylcholine, neurotransmitter found at the neuro-muscular junction and within the CNS.
Serotonin
Dopamine
Norepinephrine and Epinephrine
[edit] Neuroradiology
[edit] The Neuro exam
[edit] High-yield neuro topics
These are topics that are often covered and tested in early medical neurobiology courses. They require an understanding of specific neuro-anatomical and systems concepts, while at the same time have clinical relevance.
Bell's Palsy - a common disorder that has different manifestation depending on whether the lesion is central or peripheral. Requires knowledge of the organization of the Facial nerve (CN VII).
Lesions of the visual pathway - lesions at different levels of the visual pathway produce specific visual defects. Requires knowledge of the organization of CN II as well as the more central visual pathway.
Pupillary reflexes - sensory or motor lesions have different effects on pupillary reflexes. Requires knowledge of CN II, parasympathetic and motor pathways, and midbrain nuclei.
Hearing loss - distinguish between the two major classes of hearing loss, sensorineural and conductive.
Aphasia - distinguish between major types of aphasias, including Wernicke's and Broca's. Requires knowledge of auditory and speech pathways, as well as blood supply patterns.
Brown-Sequard syndrome - caused by a hemi-transection of the spinal cord, this produces classic and specific sensory and motor deficits. Requires knowledge of spinal cord anatomy and tract decussation locations.
Myesthenia gravis - an auto-immune disorder. Requires knowledge of synaptic neurotransmission and neuropharmacology.
Cortico-spinal tract - the major descending motor tract.
Spino-thalamic tract - the ascending pathway for pain and temperature information.
Dorsal column - medial lemniscus - the ascending pathway for touch and vibratory sensation.
Intracranial bleeds - among the most common neurological problems. Requires knowledge of brain coverings (dura, arachnoid) as well as brain vessels.
