Anatomy and pathology of the nervous system is understood by directly visualizing it. This is best accomplished by handling the brain (or model of the brain as the case may be) and dissecting or taking it apart for direct examination. The purpose (for the clinician) of understanding neuroanatomy and neurophysiology is to be able to use that knowledge to solve clinical problems. The first step in solving a clinical problem is anatomical localization. So, if one cannot directly inspect the patient's brain, how is this localization accomplished? The "window" to the patient's brain is the neurological examination. The neuro exam is a series of tests and observations that reflects the function of various parts of the brain. If the exam is approached in a systematic and logical fashion that is organized in terms of anatomical levels and systems then the clinician is lead to the anatomical location of the patient's problem.
almost 11 years ago
Introduction Examination of the cranial nerves allows one to "view" the brainstem all the way from its rostral to caudal extent. The brainstem can be divided into three levels, the midbrain, the pons and the medulla. The cranial nerves for each of these are: 2 for the midbrain (CN 3 & 4), 4 for the pons (CN 5-8), and 4 for the medulla (CN 9-12). It is important to remember that cranial nerves never cross (except for one exception, the 4th CN) and clinical findings are always on the same side as the cranial nerve involved. Cranial nerve findings when combined with long tract findings (corticospinal and somatosensory) are powerful for localizing lesions in the brainstem. Cranial Nerve 1 Olfaction is the only sensory modality with direct access to cerebral cortex without going through the thalamus. The olfactory tracts project mainly to the uncus of the temporal lobes. Cranial Nerve 2 This cranial nerve has important localizing value because of its "x" axis course from the eye to the occipital cortex. The pattern of a visual field deficit indicates whether an anatomical lesion is pre- or postchiasmal, optic tract, optic radiation or calcarine cortex. Cranial Nerve 3 and 4 These cranial nerves give us a view of the midbrain. The 3rd nerve in particular can give important anatomical localization because it exits the midbrain just medial to the cerebral peduncle. The 3rd nerve controls eye adduction (medial rectus), elevation (superior rectus), depression (inferior rectus), elevation of the eyelid (levator palpebrae superioris), and parasympathetics for the pupil. The 4th CN supplies the superior oblique muscle, which is important to looking down and in (towards the midline). Pontine Level Cranial nerves 5, 6, 7, and 8 are located in the pons and give us a view of this level of the brainstem. Cranial Nerve 6 This cranial nerve innervates the lateral rectus for eye abduction. Remember that cranial nerves 3, 4 and 6 must work in concert for conjugate eye movements; if they don't then diplopia (double vision) results. The medial longitudinal fasciculus (MLF) connects the 6th nerve nucleus to the 3rd nerve nucleus for conjugate movement. Major Oculomotor Gaze Systems Eye movements are controlled by 4 major oculomotor gaze systems, which are tested for on the neurological exam. They are briefly outlined here: Saccadic (frontal gaze center to PPRF (paramedian pontine reticular formation) for rapid eye movements to bring new objects being viewed on to the fovea. Smooth Pursuit (parietal-occipital gaze center via cerebellar and vestibular pathways) for eye movements to keep a moving image centered on the fovea. Vestibulo-ocular (vestibular input) keeps image steady on fovea during head movements. Vergence (optic pathways to oculomotor nuclei) to keep image on fovea predominantly when the viewed object is moved near (near triad- convergence, accommodation and pupillary constriction) Cranial Nerve 5 The entry zone for this cranial nerve is at the mid pons with the motor and main sensory (discriminatory touch) nucleus located at the same level. The axons for the descending tract of the 5th nerve (pain and temperature) descend to the level of the upper cervical spinal cord before they synapse with neurons of the nucleus of the descending tract of the 5th nerve. Second order neurons then cross over and ascend to the VPM of the thalamus. Cranial Nerve 7 This cranial nerve has a motor component for muscles of facial expression (and, don't forget, the strapedius muscle which is important for the acoustic reflex), parasympathetics for tear and salivary glands, and sensory for taste (anterior two-thirds of the tongue). Central (upper motor neuron-UMN) versus Peripheral (lower motor neuron-LMN) 7th nerve weakness- with a peripheral 7th nerve lesion all of the muscles ipsilateral to the affected nerve will be weak whereas with a "central 7th ", only the muscles of the lower half of the face contralateral to the lesion will be weak because the portion of the 7th nerve nucleus that supplies the upper face receives bilateral corticobulbar (UMN) input. Cranial Nerve 8 This nerve is a sensory nerve with two divisions- acoustic and vestibular. The acoustic division is tested by checking auditory acuity and with the Rinne and Weber tests. The vestibular division of this nerve is important for balance. Clinically it be tested with the oculocephalic reflex (Doll's eye maneuver) and oculovestibular reflex (ice water calorics). Medullary Level Cranial nerves 9,10,11, and 12 are located in the medulla and have localizing value for lesions in this most caudal part of the brainstem. Cranial nerves 9 and 10 These two nerves are clinically lumped together. Motor wise, they innervate pharyngeal and laryngeal muscles. Their sensory component is sensation for the pharynx and taste for the posterior one-third of the tongue. Cranial Nerve 11 This nerve is a motor nerve for the sternocleidomastoid and trapezius muscles. The UMN control for the sternocleidomastoid (SCM) is an exception to the rule of the ipsilateral cerebral hemisphere controls the movement of the contralateral side of the body. Because of the crossing then recrossing of the corticobulbar tracts at the high cervical level, the ipsilateral cerebral hemisphere controls the ipsilateral SCM muscle. This makes sense as far as coordinating head movement with body movement if you think about it (remember that the SCM turns the head to the opposite side). So if I want to work with the left side of my body I would want to turn my head to the left so the right SCM would be activated. Cranial Nerve 12 The last of the cranial nerves, CN 12 supplies motor innervation for the tongue. Traps A 6th nerve palsy may be a "false localizing sign". The reason for this is that it has the longest intracranial route of the cranial nerves, therefore it is the most susceptible to pressure that can occur with any cause of increased intracranial pressure.
over 10 years ago
SCRUBS Surgical Society (University of Nottingham) Presents: Prof Hope Neuroanatomy Series Podcast 2 - Brain Stem and Cranial Nerves This lecture covers the anatomy of the brain stem and cranial nerves, with key focus on clinical relevance. Prof Hope is a talented, and very entertaining consultant neurosurgeon based at QMC, Nottingham. He personally designed this lecture series for Nottingham Medical Students on behalf of SCRUBS to be packed full of important clinical neuroanatomy and surgery. This lecture is perfect for any final year medical students, or those studying for their pre-clinical neuroanatomy exams.
over 7 years ago
Facial Nerve - USMLE - Neuroanatomy - Get 1 Year Online Access to 400+ Hours of videos on Basic Medical Sciences. Limited Time Offer: $99 ONLY! http://drnajeeblectures.com/
over 7 years ago
An easy way to draw the basic components of the brachial plexus. On paper, it's pretty easy to draw the brachial plexus using this method in around 10 seconds. I know I fumbled on a few words here and there but that shouldn't distract from how easy it can be to draw the brachial plexus.
over 7 years ago
Can you imagine being able to search for locations in the human body in the same way you can on Google Maps? This thinking lead Programmer Rich Stoner to create this amazing video of a 21st Century Map of the Brain which was our most popular tweet last week. A 21st Century Map of the Brain http://t.co/tkojzJBW55 via @brianglanz #openscience— Meducation (@Meducation) October 18, 2013 Rich writes in his blog - “Now we can quickly search Google Maps for a location, ask what is nearby, and even see what it looks like using StreetView. Now, imagine if something like that existed for the human brain: an interactive environment to search, visualize, and explore layers upon layers of neuroanatomy. This is the dream of cortical cartographers (also known as neuroanatomists). 10 years ago, one of the largest brain mapping initiatives was founded by Paul Allen with a single goal: to build a 21st Century Map of the Brain.” Click here to read more. The mapping of the brain is a working progress and therefore not 100% accurate. Even so the video gives us an insight into the innovate ways we will be able to interact with science in the future. You can follow Meducation on twitter to see more tweets like this at twitter.com/meducation.
almost 8 years ago
Trochlear Nerve and its Clinical Correlates by Dr. Najeeb. Watch 400+ hours of Medical Lectures at http://www.DrNajeebLectures.com
over 6 years ago
http://www.anatomyzone.com Neuroanatomy tutorial on the sympathetic nervous system. In this short tutorial, we take a look at the basic configuration of the ...
over 6 years ago