The human brain is the main organ of the human central nervous system. It is located in the head, protected by the skull. It has the same general structure as the brains of other mammals, but with a more developed cerebral cortex. Large animals such as whales and elephants have larger brains in absolute terms, but when measured using a measure of relative brain size, which compensates for body size, the quotient for the human brain is almost twice as large as that of a bottlenose dolphin, and three times as large as that of a chimpanzee, though the quotient for a treeshrew's brain is larger than that of a human's. Much of the size of the human brain comes from the cerebral cortex, especially the frontal lobes, which are associated with executive functions such as self-control, planning, reasoning, and abstract thought. The area of the cerebral cortex devoted to vision, the visual cortex, is also greatly enlarged in humans compared to other animals.
about 5 years ago
Transcranial magnetic stimulation is a relatively new and sophisticated device-based therapy. TMS involves the skilful application of a strong magnetic field close to the surface of the scalp. The TMS device delivers strong and very brief magnetic pulses that stimulate the brain and its network of neurons. TMS is a relatively painless and non-invasive technique that stimulates parts of the brain (the cerebral cortex). Brain activity has been shown to differ in people with schizophrenia compared to other people.
over 5 years ago
Neurons grown from embryonic stem cells can contribute to repair of the damaged cerebral cortex in adult mice after brain transplant
As stem cell transplants show increasing promise to repair eye diseases of the cornea and retina, one of the next frontiers of regenerative medicine is using stem cells grown in the laboratory...
almost 6 years ago
In research published in the journal Cerebral Cortex, a team of scientists led by the University of Cambridge and the Medical Research Council (MRC) Cognition and Brain Sciences Unit...
almost 6 years ago
Huntington's disease is a neurodegenerative disorder that results in involuntary spastic movement and loss of control of voluntary motor function.
almost 6 years ago
Cerebellum (Section 3, Chapter 5) Neuroscience Online: An Electronic Textbook for the Neurosciences | Department of Neurobiology and Anatomy - The University of Texas Medical School at Houston
The cerebellum (“little brain”) is a structure that is located at the back of the brain, underlying the occipital and temporal lobes of the cerebral cortex (Figure 5.1). Although the cerebellum accounts for approximately 10% of the brain’s volume, it contains over 50% of the total number of neurons in the brain. Historically, the cerebellum has been considered a motor structure, because cerebellar damage leads to impairments in motor control and posture and because the majority of the cerebellum’s outputs are to parts of the motor system. Motor commands are not initiated in the cerebellum; rather, the cerebellum modifies the motor commands of the descending pathways to make movements more adaptive and accurate. The cerebellum is involved in the following functions:
over 6 years ago
Orientation, Memor Asking questions about month, date, day of week and place tests orientation, which involves not only memory but also attention and language. Three-word recall tests recent memory for which the temporal lobe is important. Remote memory tasks such as naming Presidents, tests not only the temporal lobes but also heteromodal association cortices. Attention-working memory Digit span, spelling backwards and naming months of the year backward test attention and working memory which are frontal lobe functions Judgement-abstract reasoning These frontal lobe functions can be tested by using problem solving, verbal similarities and proverbs Set generation This is a test of verbal fluency and the ability to generate a set of items which are frontal lobe functions. Most individuals can give 10 or more words in a minute. Receptive language Asking the patient to follow commands demonstrates that they understand the meaning of what they have heard or read. It is important to test reception of both spoken and written language. Expressive language In assessing expressive language it is important to note fluency and correctness of content and grammar. This can be accomplished by tasks that require spontaneous speech and writing, naming objects, repetition of sentences, and reading comprehension. Praxis The patient is asked to perform skilled motor tasks without any nonverbal prompting. Skills tested for should involve the face then the limbs. In order to test for praxis the patient must have normal comprehension and intact voluntary movement. Apraxia is typically seen in lesions of the dominant inferior parietal lobe. Gnosis Gnosis is the ability to recognize objects perceived by the senses especially somatosensory sensation. Having the patient (with their eyes closed) identify objects placed in their hand (stereognosis) and numbers written on their hand (graphesthesia) tests parietal lobe sensory perception. Dominant parietal lobe function Tests for dominant inferior parietal lobe function includes right-left orientation, naming fingers, and calculations. Non-dominant parietal lobe function The non-dominant parietal lobe is important for visual spatial sensory tasks such as attending to the contralateral side of the body and space as well as constructional tasks such as drawing a face, clock or geometric figures. Visual recognition Recognition of colors and faces tests visual association cortex (inferior occiptotemporal area). Achromatopsia (inability to distinguish colors), visual agnosia (inability to name or point to a color) and prosopagnosia (inability to identify a familiar faces) result from lesions in this area.
about 10 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.
about 10 years ago
Orientation, Memor This patient has difficulty with orientation questions. The day of the week is correct but he misses the month and date. He is oriented to place. Orientation mistakes are not localizing but can be due to problems with memory, language, judgement, attention or concentration. The patient has good recent memory (declarative memory) as evidenced by the recall of three objects but has difficulty with long term memory as evidenced by the difficulty recalling the current and past presidents. Attention-working memor The patient has difficulty with digit span backwards, spelling backwards and giving the names of the months in reverse order. This indicates a problem with working memory and maintaining attention, both of which are frontal lobe functions. Judgement-abstract reasoning The patient gives the correct answer for a house on fire and his answers for similarities are also good. He has problems with proverb interpretation. His answers are concrete and consist of rephrasing the proverb or giving a simple consequence of the action in the proverb. Problems with judgement, abstract reasoning, and executive function can be seen in patients with frontal lobe dysfunction. Set generatio Set generation tests word fluency and frontal lobe function. The patient starts well but abruptly stops after only four words. Most individuals can give more then 10 words in one minute. Receptive languag Patients with a receptive aphasia (Wernicke’s) cannot comprehend language. Their speech output is fluent but is devoid of meaning and contains nonsense syllables or words (neologisms). Their sentences are usually lacking nouns and there are paraphasias (one word substituted for another). The patient is usually unaware of their language deficit and prognosis for recovery is poor. This patient’s speech is fluent and some of her sentences even make sense but she also has nonsense sentences, made up of words and parts of words. She can’t name objects (anomia). She doesn’t have a pure or complete receptive aphasia but pure receptive aphasias are rare. Expressive languag This patient with expressive aphasia has normal comprehension but her expression of language is impaired. Her speech output is nonfluent and often limited to just a few words or phases. Grammatical words such as prepositions are left out and her speech is telegraphic. She has trouble saying “no ifs , ands or buts”. Her ability to write is also effected Patients with expressive aphasia are aware of their language deficit and are often frustrated by it. Recovery can occur but is often incomplete with their speech consisting of short phrases or sentences containing mainly nouns and verbs. Praxi The patient does well on most of the tests of praxis. At the very end when he is asked to show how to cut with scissors he uses his fingers as the blades of the scissors instead of acting like he is holding onto the handles of the scissors and cutting. This can be an early finding of inferior parietal lobe dysfunction. Gnosi With his right hand the patient has more difficulty identifying objects then with his left hand. One must be careful in interpreting the results of this test because of the patient’s motor deficits but there does seem to be astereognosis on the right, which would indicate left parietal lobe dysfunction. This is confirmed with graphesthesia where he definitely has more problems identifying numbers written on the right hand then the left (agraphesthesia of the right hand). Dominant parietal lobe functio This patient has right-left confusion and difficulty with simple arithmetic. These are elements of the Gertsmann syndrome, which is seen in lesions of the dominant parietal lobe. The full syndrome consists of right-left confusion, finger agnosia, agraphia and acalculia.
about 10 years ago