The nervous system





Anatomy and physiology


The nervous system consists of the brain and spinal cord (central nervous system, CNS) and the peripheral nerves (peripheral nervous system, PNS). The PNS includes the autonomic nervous system, responsible for control of involuntary functions.


The neurone is the functional unit of the nervous system. Each neurone has a cell body and axon terminating at a synapse, supported by astrocytes and microglial cells. Astrocytes provide the structural framework for the neurones, control their biochemical environment and form the blood–brain barrier. Microglial cells are blood-derived mononuclear macrophages with immune and scavenging functions. In the CNS, oligodendrocytes produce and maintain a myelin sheath around the axons. In the PNS, myelin is produced by Schwann cells.


The brain consists of two cerebral hemispheres, each with four lobes (frontal, parietal, temporal and occipital), the brainstem and the cerebellum. The brainstem comprises the midbrain, pons and medulla. The cerebellum lies in the posterior fossa, with two hemispheres and a central vermis attached to the brainstem by three pairs of cerebellar peduncles. Between the brain and the skull are three membranous layers called the meninges: dura mater next to the bone, arachnoid and pia mater next to the nervous tissue. The subarachnoid space between the arachnoid and pia is filled with cerebrospinal fluid (CSF) produced by the choroid plexuses. The total volume of CSF is between 140 and 270 mL and there is a turnover of the entire volume 3–4 times a day; thus CSF is produced at a rate of approximately 700 mL per day.


The spinal cord contains afferent and efferent fibres arranged in discrete bundles (pathways running to and from the brain), which are responsible for the transmission of motor and sensory information. Peripheral nerves have myelinated and unmyelinated axons. The sensory cell bodies of peripheral nerves are situated in the dorsal root ganglia. The motor cell bodies are in the anterior horns of the spinal cord ( Fig. 7.1 ).




Fig. 7.1


Anatomy of the central nervous system.

A Lateral surface of the brain. B Spinal cord, nerve roots and meninges. C Cross-section of the spinal cord. D Spinal motor neurone. The terminals of presynaptic neurones form synapses with the cell body and dendrites of the motor neurones.




The history


For many common neurological symptoms such as headache, numbness, disturbance/loss of consciousness and memory loss, the history is the key to diagnosis, as the examination may be either normal or unhelpful. Some symptoms, including loss of consciousness or amnesia, require an additional witness history; make every effort to contact such witnesses.


Remember the two key questions: where (in the nervous system) is the lesion and what is the lesion?


Neurological symptoms may be difficult for patients to describe, so clarify exactly what they tell you. Words such as ‘blackout’, ‘dizziness’, ‘weakness’ and ‘numbness’ may have different meanings for different patients, so ensure you understand what the person is describing.


Ask patients what they think or fear might be wrong with them, as neurological symptoms cause much anxiety. Patients commonly research their symptoms on the internet; searches on common benign neurological symptoms, like numbness or weakness, usually list the most alarming (and unlikely) diagnoses such multiple sclerosis, motor neurone disease or brain tumours first, and almost never mention more common conditions such as carpal tunnel syndrome or functional disorders.


Time relationships


The onset, duration and pattern of symptoms over time often provide diagnostic clues: for example, in assessing headache ( Box 7.1 ) or vertigo (see Box 9.3 ).



7.1

Clinical characteristics of headache syndromes





















































Onset Duration/periodicity Pain location Associated features
Primary syndromes
Migraine Evolves over 30–120 mins Usually last < 24 h, recurrent with weeks/months symptom-free Classically unilateral but may be anywhere including face/neck Aura (usually visual), nausea/vomiting, photophobia and phonophobia
Cluster headache Rapid onset, often waking patient from sleep 30–120 mins, 1–4 attacks within 24 h, clusters usually last weeks to months, with months to years of remission Orbital/retro-orbital; always same side during cluster, may switch sides between clusters Autonomic features, including conjunctival injection, tearing, nasal stuffiness, ptosis, miosis, agitation
Stabbing headache Abrupt, rarely from sleep Very brief, seconds or less Anywhere over head Common in migraineurs
Secondary syndromes
Meningitis Usually evolves over a day or two, can be abrupt Depends on cause and treatment, usually days to weeks Global, including neck stiffness Fever, meningism, rash, false localising signs, signs of raised intracranial pressure
Subarachnoid haemorrhage Abrupt, immediately maximal, rare from sleep May be fatal at onset, usually days to weeks Anywhere, poor localising value 20% isolated headache only; nausea/vomiting, reduced consciousness, false localising signs, III nerve palsies
Temporal arteritis Gradual onset of temple pain and scalp tenderness Continuous Temple and scalp Usually in those > 55 years; unwell, jaw pain on chewing, visual symptoms, tender temporal arteries, elevated erythrocyte sedimentation rate and C-reactive protein



Ask:




  • When did the symptoms start (or when was the patient last well)?



  • Are they persistent or intermittent?



  • If persistent, are they getting better, getting worse or staying the same?



  • If intermittent, how long do they last, and how long does the patient remain symptom-free in between episodes?



  • Was the onset sudden or gradual/evolving?



Precipitating, exacerbating or relieving factors





  • What was the patient doing when the symptoms occurred?



  • Does anything make the symptoms better or worse, such as time of day, menstrual cycle, posture or medication?



Associated symptoms


Associated symptoms can aid diagnosis. For example, headache may be associated with nausea, vomiting, photophobia (aversion to light) and/or phonophobia (aversion to sound) in migraine; headache with neck stiffness, fever and rash may be associated with meningitis ( Box 7.1 ).


Common presenting symptoms


Headache


Headache is the most common neurological symptom and may be either primary or secondary to other pathology. Primary (idiopathic) causes include:




  • migraine



  • tension-type headache



  • trigeminal autonomic cephalalgias (including cluster headache)



  • primary stabbing, cough, exertional or sex headache



  • primary thunderclap headache



  • new daily persistent headache.



Secondary (or symptomatic) headaches are less common, but include potentially life-threatening or disabling causes such as subarachnoid haemorrhage or temporal arteritis. One of the key history aspects is rapidity of onset; isolated headache with a truly abrupt onset may represent a potentially serious cause such as subarachnoid haemorrhage or cerebral vein thrombosis, whereas recurrent headache is much more likely to be migraine, particularly if associated with other migrainous features like aura, nausea and/or vomiting, photophobia and phonophobia ( Box 7.1 ). Asking patents what they do when they have a headache can be instructive. For example, abandoning normal tasks and seeking a bed in a dark, quiet room suggest migraine, whereas pacing around the room in an agitated state, or even head banging, suggests cluster headache.


Transient loss of consciousness


Syncope is loss of consciousness due to inadequate cerebral perfusion and is the most common cause of transient loss of consciousness (TLOC). Vasovagal (or reflex) syncope (fainting) is the most common type and precipitated by stimulation of the parasympathetic nervous system, as with pain or intercurrent illness. Exercise-related syncope, or syncope with no warning or trigger, suggests a possible cardiac cause. TLOC on standing is suggestive of orthostatic (postural) hypotension and may be caused by drugs (antihypertensives or levodopa) or associated with autonomic neuropathies, which may complicate conditions such as diabetes.


Seizure


An epileptic seizure is caused by paroxysmal electrical discharges from either the whole brain (generalised seizure) or part of the brain (focal seizure). A tonic–clonic seizure (convulsion) is the most common form of generalised seizure, and typically follows a stereotyped pattern with early loss of consciousness associated with body stiffening (tonic phase) succeeded by rhythmical jerking crescendoing and subsiding over 30–120 seconds (clonic phase); this is followed by a period of unresponsiveness (often with heavy breathing, the patient appearing to be deeply asleep) and finally confusion as the patient reorientates (postictal phase). The history from the patient and witnesses can help distinguish syncope from epilepsy ( Box 7.2 ). Focal seizures may or may not involve loss of awareness (complete loss of consciousness is less typical) and are characterised by whichever part of the brain is involved: for example, a focal motor seizure arising from the motor cortex, or temporal lobe seizures characterised by autonomic and/or psychic symptoms, often associated with automatisms such as lip smacking or swallowing. Functional dissociative attacks (also known as non-epileptic or psychogenic attacks, or pseudoseizures) are common, and may be difficult to distinguish from epileptic seizures. These attacks are often more frequent than epilepsy, sometimes occurring multiple times in a day, and may last considerably longer, with symptoms waxing and waning. Other features may include asynchronous movements, pelvic thrusts, side-to-side rather than flexion/extension movements and absence of postictal confusion. The widespread availability of videophones allows witnesses to capture such events and may prove invaluable.



7.2

Features that help discriminate vasovagal syncope from epileptic seizure







































Feature Vasovagal syncope Seizure
Triggers Typically pain, illness, emotion Often none (sleep deprivation, alcohol, drugs)
Prodrome Feeling faint/lightheaded, nausea, tinnitus, vision dimming Focal onset (not always present)
Duration of unconsciousness < 60 s 1–2 mins
Convulsion May occur but usually brief myoclonic jerks Usual, tonic–clonic 1–2 mins
Colour Pale/grey Flushed/cyanosed, may be pale
Injuries Uncommon, sometimes biting of tip of tongue Lateral tongue biting, headache, generalised myalgia, back pain (sometimes vertebral compression fractures), shoulder fracture/dislocation (rare)
Recovery Rapid, no confusion Gradual, over 30 mins; patient is often confused, sometimes agitated/aggressive, amnesic



Stroke and transient ischaemic attack


A stroke is a focal neurological deficit of rapid onset that is due to a vascular cause. A transient ischaemic attack (TIA) is the same but symptoms resolve within 24 hours. TIAs are an important risk factor for impending stroke and demand urgent assessment and treatment. Hemiplegia following middle cerebral artery occlusion is a typical example but symptoms are dictated by the vascular territory involved. Much of the cerebral hemispheres are supplied by the anterior circulation (the anterior and middle cerebral arteries are derived from the internal carotid artery), while the occipital lobes and brainstem are supplied by the posterior (vertebrobasilar) circulation ( Fig. 7.2 ).




Fig. 7.2


The arterial blood supply of the brain (circle of Willis).


A useful and simple clinical system for classifying stroke is shown in Box 7.3 .



7.3

Clinical classification of stroke


Total anterior circulation syndrome (TACS)





  • Hemiparesis, hemianopia and higher cortical deficit (e.g. dysphasia or visuospatial loss)



Partial anterior circulation syndrome (PACS)





  • Two of the three components of a TACS



  • OR isolated higher cortical deficit



  • OR motor/sensory deficit more restricted than LACS (see below)



Posterior circulation syndrome (POCS)





  • Ipsilateral cranial nerve palsy with contralateral motor and/or sensory deficit



  • OR bilateral motor and/or sensory deficit



  • OR disorder of conjugate eye movement



  • OR cerebellar dysfunction without ipsilateral long-tract deficits



  • OR isolated homonymous visual field defect



Lacunar syndrome (LACS)





  • Pure motor > 2 out of 3 of face, arm, leg



  • OR pure sensory > 2 out of 3 of face, arm, leg



  • OR pure sensorimotor > 2 out of 3 of face, arm, leg



  • OR ataxic hemiparesis




Isolated vertigo, amnesia or TLOC are rarely, if ever, due to stroke. In industrialised countries about 80% of strokes are ischaemic, the remainder haemorrhagic. Factors in the history or examination that increase the likelihood of haemorrhage rather than ischaemia include use of anticoagulation, headache, vomiting, seizures and early reduced consciousness. Haemorrhagic stroke is much more frequent in Asian populations. Spinal strokes are very rare; patients typically present with abrupt bilateral paralysis, depending on the level of spinal cord affected. The anterior spinal artery syndrome is most common and causes loss of motor function and pain/temperature sensation, with relative sparing of joint position and vibration sensation below the level of the lesion.


Dizziness and vertigo


Patients use ‘dizziness’ to describe many sensations. Recurrent ‘dizzy spells’ affect approximately 30% of those over 65 years and can be due to postural hypotension, cerebrovascular disease, cardiac arrhythmia or hyperventilation induced by anxiety and panic. Vertigo (the illusion of movement) specifically indicates a problem in the vestibular apparatus (peripheral) or, much less commonly, the brain (central) (see Box 9.3 and p. 174 ). TIAs do not cause isolated vertigo. Identifying a specific cause of dizziness is often challenging but may be rewarding in some cases, including benign paroxysmal positional vertigo (BPPV), which is eminently treatable. As a guide, recurrent episodes of vertigo lasting a few seconds are most likely to be due to BPPV; vertigo lasting minutes or hours may be caused by Ménière’s disease (with associated symptoms including hearing loss, tinnitus, nausea and vomiting) or migrainous vertigo (with or without headache).


Functional neurological symptoms


Many neurological symptoms are not due to disease. These symptoms are often called ‘functional’ but other (less useful and more pejorative) terms include psychogenic, hysterical, somatisation or conversion disorders. Presentations include blindness, tremor, weakness and collapsing attacks, and patients will often describe numerous other symptoms, with fatigue, lethargy, pain, anxiety and other mood disorders commonly associated. Diagnosing functional symptoms requires experience and patience ( p. 363 ). Clues include symptoms not compatible with disease (such as retained awareness of convulsing during non-epileptic attacks, or being able to walk normally backwards but not forwards), considerable variability in symptoms (such as intermittent recovery of a hemiparesis), multiple symptoms (often with numerous previous assessments by other specialties, particularly gynaecology, gastroenterology, ear, nose and throat and cardiorespiratory) and multiple unremarkable investigations, leading to numerous different diagnoses. The size of a patient’s case notes can sometimes be a clue in itself! Beware of labelling symptoms as functional simply because they appear odd or inexplicable. Like disease, most functional neurological disorders follow recognisable patterns, so be cautious when the pattern is atypical.


Past medical history


Symptoms that the patient has forgotten about or overlooked may be important; for example, a history of previous visual loss (optic neuritis) in someone presenting with numbness suggests multiple sclerosis. Birth history and development may be significant, as in epilepsy. Contact parents or family doctors to obtain such information. If considering a vascular cause of neurological symptoms, ask about important risk factors, such as other vascular disease, hypertension, family history and smoking.


Drug history


Always enquire about drugs, including prescribed, over-the-counter, complementary and recreational/illegal ones, as they can give rise to many neurological symptoms (for example, phenytoin toxicity causing ataxia; excessive intake of simple analgesia causing medication overuse headache; use of cocaine provoking convulsions).


Family history


Obtain a family history for at least first-degree relatives: parents, siblings and children. In some communities, parental consanguinity is common, increasing the risk of autosomal recessive conditions, so you may need to enquire sensitively about this. Many neurological disorders are caused by single-gene defects, such as myotonic dystrophy or Huntington’s disease. Others have important polygenic influences, as in multiple sclerosis or migraine. Some conditions have a variety of inheritance patterns; for example, Charcot–Marie–Tooth disease may be autosomal dominant, autosomal recessive or X-linked. Mitochondria uniquely have their own DNA, and abnormalities in this DNA can cause a range of disorders that manifest in many different systems (such as diabetes, short stature and deafness), and may cause common neurological syndromes such as migraine or epilepsy. Some diseases, such as Parkinson’s or motor neurone disease, may be either due to single-gene disorders or sporadic.


Social history


Social circumstances are relevant. How are patients coping with their symptoms? Are they able to work and drive? What are their support circumstances, and are these adequate?


Alcohol is the most common neurological toxin and damages both the CNS (ataxia, seizures, dementia) and the PNS (neuropathy). Poor diet with vitamin deficiency may compound these problems and is relevant in areas affected by famine and alcoholism or dietary exclusion. Vegetarians may be susceptible to vitamin B 12 deficiency. Recreational drugs may affect the nervous system; for example, nitrous oxide inhalation causes subacute combined degeneration of the cord due to dysfunction of the vitamin B 12 pathway, and smoking contributes to vascular and malignant disease. Always consider sexually transmitted or blood-borne infection, such as human immunodeficiency virus (HIV) or syphilis, as both can cause a wide range of neurological symptoms and are treatable. A travel history may give clues to the underlying diagnosis, such as Lyme disease (facial palsy), neurocysticercosis (brain lesions and epilepsy) or malaria (coma).


Occupational history


Occupational factors are relevant to several neurological disorders. For example, toxic peripheral neuropathy, due to exposure to heavy or organic metals like lead, causes a motor neuropathy; manganese causes Parkinsonism. Some neurological diagnoses may adversely affect occupation, such as epilepsy in anyone who needs to drive or operate dangerous machinery. For patients with cognitive disorders, particularly dementias, it may be necessary to advise on whether to stop working.




The physical examination


Neurological assessment begins with your first contact with the patient and continues during the history. Note facial expression, demeanour, dress, posture, gait and speech. Mental state examination ( p. 320 ) and general examination ( p. 20 ) are integral parts of the neurological examination.


Assessment of conscious level


Consciousness has two main components:




  • The state of consciousness depends largely on integrity of the ascending reticular activating system, which extends from the brainstem to the thalamus.



  • The content of consciousness refers to how aware the person is and depends on the cerebral cortex, the thalamus and their connections.



Do not use ill-defined terms such as stuporose or obtunded. Use the Glasgow Coma Scale (see Box 18.5 ), a reliable and reproducible tool, to record conscious level.


Meningeal irritation


Meningism (inflammation or irritation of the meninges) can lead to increased resistance to passive flexion of the neck (neck stiffness) or the extended leg (Kernig’s sign). Patients may lie with flexed hips to ease their symptoms. Meningism suggests infection (meningitis) or blood within the subarachnoid space (subarachnoid haemorrhage) but can occur with non-neurological infections, such as urinary tract infection or pneumonia. Conversely, absence of meningism does not exclude pathology within the subarachnoid space. In meningitis, neck stiffness has relatively low sensitivity but higher specificity. The absence of all three signs of fever, neck stiffness and altered mental state virtually eliminates the diagnosis of meningitis in immunocompetent individuals.



Examination sequence





  • Position the patient supine with no pillow.



  • Expose and fully extend both of the patient’s legs.



Neck stiffness





  • Place your hands on either side of the patient’s head, supporting the occiput.



  • Flex the patient’s head gently until their chin touches their chest.



  • Ask the patient to hold that position for 10 seconds. If neck stiffness is present, the neck cannot be passively flexed and you may feel spasm in the neck muscles.



  • Flexion of the hips and knees in response to neck flexion is Brudzinski’s sign.



Kernig’s sign





  • Flex one of the patient’s legs to 90 degrees at both the hip and the knee, with your left hand placed over the medial hamstrings ( Fig. 7.3 ).




    Fig. 7.3


    Testing for meningeal irritation: Kernig’s sign.



  • Extend the knee while the hip is maintained in flexion. Look at the other leg for any reflex flexion. Kernig’s sign is positive when extension is resisted by spasm in the hamstrings. Kernig’s sign is absent with local causes of neck stiffness, such as cervical spine disease or raised intracranial pressure.




Speech


Dysarthria refers to slurred or ‘strangulated’ speech caused by articulation problems due to a motor deficit.


Dysphonia describes loss of volume caused by laryngeal disorders.



Examination sequence





  • Listen to the patient’s spontaneous speech, noting volume, rhythm and clarity.



  • Ask the patient to repeat phrases such as ‘yellow lorry’ to test lingual (tongue) sounds and ‘baby hippopotamus’ for labial (lip) sounds, then a tongue twister such as ‘The Leith police dismisseth us.’



  • Ask the patient to count to 30 to assess fatigue.



  • Ask the patient to cough and to say ‘Ah’; observe the soft palate rising bilaterally.




Disturbed articulation (dysarthria) may result from localised lesions of the tongue, lips or mouth, ill-fitting dentures or neurological dysfunction. This may be due to pathology anywhere in the upper and lower motor neurones, cerebellum, extrapyramidal system, or nerve, muscle or neuromuscular junction.


Bilateral upper motor neurone lesions of the corticobulbar tracts cause a pseudobulbar dysarthria, characterised by a slow, harsh, strangulated speech with difficulty pronouncing consonants, and may be accompanied by a brisk jaw jerk and emotional lability. The tongue is contracted and stiff.


Bulbar palsy (see Box 7.5 later) results from bilateral lower motor neurone lesions affecting the same group of cranial nerves (IX, X, XI, XII). The nature of the speech disturbance is determined by the specific nerves and muscles involved. Weakness of the tongue results in difficulty with lingual sounds, while palatal weakness gives a nasal quality to the speech.


Cerebellar dysarthria may be slow and slurred, similar to alcohol intoxication. Myasthenia gravis causes fatiguing speech, becoming increasing nasal, and may disappear altogether. Parkinsonism may cause dysarthria and dysphonia, with a low-volume, monotonous voice, words running into each other (festination of speech), and marked stuttering/hesitation.


Dysphonia usually results from either vocal cord pathology, as in laryngitis, or damage to the vagal (X) nerve supply to the vocal cords (recurrent laryngeal nerve). Inability to abduct one of the vocal cords leads to a ‘bovine’ (and ineffective) cough.


Dysphasias


Dysphasia is a disturbance of language resulting in abnormalities of speech production and/or understanding. It may involve other language symptoms, such as writing and/or reading problems, unlike dysarthria and dysphonia.


Anatomy


The language areas are located in the dominant cerebral hemisphere, which is the left in almost all right-handed people and most left-handed people.


Broca’s area (inferior frontal region) is concerned with word production and language expression.


Wernicke’s area (superior posterior temporal lobe) is the principal area for comprehension of spoken language. Adjacent regions of the parietal lobe are involved in understanding written language and numbers.


The arcuate fasciculus connects Broca’s and Wernicke’s areas.



Examination sequence





  • During spontaneous speech, listen to the fluency and appropriateness of the content, particularly paraphasias (incorrect words) and neologisms (nonsense or meaningless new words).



  • Show the patient a common object, such as a coin or pen, and ask them to name it.



  • Give a simple three-stage command, such as ‘Pick up this piece of paper, fold it in half and place it under the book.’



  • Ask the patient to repeat a simple sentence, such as ‘Today is Tuesday.’



  • Ask the patient to read a passage from a newspaper.



  • Ask the patient to write a sentence; examine the handwriting.




Expressive (motor) dysphasia results from damage to Broca’s area. It is characterised by reduced verbal output with non-fluent speech and errors of grammar and syntax. Comprehension is intact.


Receptive (sensory) dysphasia occurs due to dysfunction in Wernicke’s area. There is poor comprehension, and although speech is fluent, it may be meaningless and contain paraphasias and neologisms.


Global dysphasia is a combination of expressive and receptive difficulties caused by involvement of both areas.


Dysphasia (a focal sign) is frequently misdiagnosed as confusion (non-focal). Always consider dysphasia before assuming confusion, as this fundamentally alters the differential diagnosis and management.


Dominant parietal lobe lesions affecting the supramarginal gyrus may cause dyslexia (difficulty comprehending written language), dyscalculia (problems with simple addition and subtraction) and dysgraphia (impairment of writing). Gerstmann’s syndrome is the combination of dysgraphia, dyscalculia, finger agnosia (inability to recognise the fingers) and inability to distinguish left from right. It localises to the left parietal lobe in the region of the angular gyrus.


Cortical function


Thinking, emotions, language, behaviour, planning and initiation of movements, and perception of sensory information are functions of the cerebral cortex and are central to awareness of, and interaction with, the environment. Certain cortical areas are associated with specific functions, so particular patterns of dysfunction can help localise the site of pathology ( Fig. 7.4A ). Assessment of higher cortical function can be difficult and time-consuming but is essential in patients with cognitive symptoms. There are various tools, all primarily developed as screening and assessment tools for dementia. For the bedside the Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA) are quick to administer, while the Addenbrooke’s Cognitive Examination is more detailed but takes longer. None of these bedside tests is a substitute for detailed neuropsychological assessment. The assessment of cognitive function is covered in more detail on page 323 .




Fig. 7.4


Cortical function.

A Features of localised cerebral lesions. B Somatotopic homunculus.


Frontal lobe


The posterior part of the frontal lobe is the motor strip (precentral gyrus), which controls voluntary movement. The motor strip is organised somatotopically ( Fig. 7.4B ). The area anterior to the precentral gyrus is concerned with personality, social behaviour, emotions, cognition and expressive language, and contains the frontal eye fields and cortical centre for micturition ( Fig. 7.4A ).


Frontal lobe damage may cause:




  • personality and behaviour changes, such as apathy or disinhibition



  • loss of emotional responsiveness, or emotional lability



  • cognitive impairments, such as memory, attention and concentration



  • dysphasia (dominant hemisphere)



  • conjugate gaze deviation to the side of the lesion



  • urinary incontinence



  • primitive reflexes, such as grasp



  • focal motor seizures (motor strip).



Temporal lobe


The temporal lobe contains the primary auditory cortex, Wernicke’s area and parts of the limbic system. The latter is crucially important in memory, emotion and smell appreciation. The temporal lobe also contains the lower fibres of the optic radiation and the area of auditory perception.


Temporal lobe dysfunction may cause:




  • memory impairment



  • focal seizures with psychic symptoms



  • contralateral upper quadrantanopia (see Fig. 8.5 (4))



  • receptive dysphasia (dominant hemisphere).



Parietal lobe


The postcentral gyrus (sensory strip) is the most anterior part of the parietal lobe and is the principal destination of conscious sensations. The upper fibres of the optic radiation pass through it. The dominant hemisphere contains aspects of language function and the non-dominant lobe is concerned with spatial awareness.


Features of parietal lobe dysfunction include:




  • cortical sensory impairments



  • contralateral lower quadrantanopia (see Fig. 8.5 (5))



  • dyslexia, dyscalculia, dysgraphia



  • apraxia (an inability to carry out complex tasks despite having an intact sensory and motor system)



  • focal sensory seizures (postcentral gyrus)



  • visuospatial disturbance (non-dominant parietal lobe).



Occipital lobe


The occipital lobe blends with the temporal and parietal lobes and forms the posterior part of the cerebral cortex. Its main function is analysis of visual information.


Occipital lobe damage may cause:




  • visual field defects: hemianopia (loss of part of a visual field) or scotoma (blind spot) (see Fig. 8.5 (6)).



  • visual agnosia: the inability to recognise visual stimuli



  • disturbances of visual perception, such as macropsia (seeing things larger) or micropsia (seeing things smaller)



  • visual hallucinations.





Cranial nerves


The 12 pairs of cranial nerves (with the exception of the olfactory (I) pair) arise from the brainstem ( Fig. 7.5 and Box 7.4 ). Cranial nerves II, III, IV and VI relate to the eye ( Ch. 8 ) and the VIII nerve to hearing and balance ( Ch. 9 ).




Fig. 7.5


Base of the cranial cavity.

The dura mater, with the cranial nerves and their exits from the skull. On the right side, part of the tentorium cerebelli and the roof of the trigeminal cave have been removed.


7.4

Summary of the 12 cranial nerves























































Nerve Examination Abnormalities/symptoms
I Sense of smell, each nostril Anosmia/parosmia
II Visual acuity
Visual fields
Pupil size and shape
Pupil light reflex
Fundoscopy
Partial sight/blindness
Scotoma; hemianopia
Anisocoria
Impairment or loss
Optic disc and retinal changes
III Light and accommodation reflex Impairment or loss
III, IV and VI Eye position and movements Strabismus, diplopia, nystagmus
V Facial sensation
Corneal reflex
Muscles of mastication
Jaw jerk
Impairment, distortion or loss
Impairment or loss
Weakness of chewing movements
Increase in upper motor neurone lesions
VII Muscles of facial expression
Taste over anterior two-thirds of tongue
Facial weakness
Ageusia (loss of taste)
VIII Whisper and tuning fork tests
Vestibular tests
Impaired hearing/deafness
Nystagmus and vertigo
IX Pharyngeal sensation Not routinely tested
X Palate movements Unilateral or bilateral impairment
XI Trapezius and sternomastoid Weakness of scapular and neck movement
XII Tongue appearance and movement Dysarthria and chewing/swallowing difficulties



Olfactory (I) nerve


The olfactory nerve conveys the sense of smell.


Anatomy


Bipolar cells in the olfactory bulb form olfactory filaments with small receptors projecting through the cribriform plate high in the nasal cavity. These cells synapse with second-order neurones, which project centrally via the olfactory tract to the medial temporal lobe and amygdala.



Examination sequence


Bedside testing of smell is of limited clinical value, and rarely performed, although objective ‘scratch and sniff’ test cards, such as the University of Pennsylvania Smell Identification Test (UPSIT), are available. You can ask patients if they think their sense of smell is normal, although self-reporting can be surprisingly inaccurate.


Hyposmia or anosmia (reduction or loss of the sense of smell) may result from upper respiratory infection, sinus disease, damage to the olfactory filaments after head injury or infection, local compression (by olfactory groove meningioma, for example; see Fig. 7.29C ) or invasion by basal skull tumours. Disturbance of smell may also occur very early in Parkinson’s and Alzheimer’s diseases. Patients often note hypogeusia/ageusia (altered taste) with anosmia too, as taste is crucially influenced by the sense of smell.


Parosmia is the perception of pleasant odours as unpleasant; it may occur with head trauma or sinus infection, or be an adverse effect of drugs. Olfactory hallucinations may occur in Alzheimer’s disease and focal epilepsies.



Optic (II), oculomotor (III), trochlear (IV) and abducens (VI) nerves


See Chapter 8 .


Trigeminal (V) nerve


The V nerve conveys sensation from the face, mouth and part of the dura, and provides motor supply to the muscles of mastication.


Anatomy


The cell bodies of the sensory fibres are located in the trigeminal (Gasserian) ganglion, which lies in a cavity (Meckel’s cave) in the petrous temporal dura (see Fig. 7.5 ). From the trigeminal ganglion, the V nerve passes to the pons. From here, pain and temperature pathways descend to the C2 segment of the spinal cord, so ipsilateral facial numbness may occur with cervical cord lesions.


There are three major branches of V ( Fig. 7.6 ):




  • ophthalmic (V 1 ): sensory



  • maxillary (V 2 ): sensory



  • mandibular (V 3 ): sensory and motor.




Fig. 7.6


The sensory distribution of the three divisions of the trigeminal nerve.

1, Ophthalmic division. 2, Maxillary division. 3, Mandibular division.


The ophthalmic branch leaves the ganglion and passes forward to the superior orbital fissure via the wall of the cavernous sinus (see Fig. 8.3 ). In addition to the skin of the upper nose, upper eyelid, forehead and scalp, V 1 supplies sensation to the eye (cornea and conjunctiva) and the mucous membranes of the sphenoidal and ethmoid sinuses and upper nasal cavity.


The maxillary branch (V 2 ) passes from the ganglion via the cavernous sinus to leave the skull by the foramen rotundum. It contains sensory fibres from the mucous membranes of the upper mouth, roof of pharynx, gums, teeth and palate of the upper jaw and the maxillary, sphenoidal and ethmoid sinuses.


The mandibular branch (V 3 ) exits the skull via the foramen ovale and supplies the floor of the mouth, sensation (but not taste) to the anterior two-thirds of the tongue, the gums and teeth of the lower jaw, mucosa of the cheek and the temporomandibular joint, in addition to the skin of the lower lips and jaw area, but not the angle of the jaw (see Fig. 7.6 ).


The motor fibres of V run in the mandibular branch (V 3 ) and innervate the muscles of mastication: temporalis, masseter and medial and lateral pterygoids.



Examination sequence


Four aspects need to be assessed: sensory, motor and two reflexes.


Sensory





  • Ask the patient to close their eyes and say ‘yes’ each time they feel a light touch (you use a cotton-wool tip for this test). Do this in the areas of V 1 , V 2 and V 3 .



  • Repeat using a fresh neurological pin, such as a Neurotip, to test superficial pain.



  • Compare both sides. If you identify an area of reduced sensation, map it out. Does it conform to the distribution of the trigeminal nerve or branches? Remember the angle of the jaw is served by C2 and not the trigeminal nerve, but V 1 extends towards the vertex (see Fig. 7.6 ).



  • ‘Nasal tickle’ test: use a wisp of cotton wool to ‘tickle’ the inside of each nostril and ask the patient to compare. The normal result is an unpleasant sensation easily appreciated by the patient.



Motor (signs rare)





  • Inspect for wasting of the muscles of mastication (most apparent in temporalis).



  • Ask the patient to clench their teeth; feel the masseters, estimating their bulk.



  • Ask the patient to open their jaw and note any deviation; the jaw may deviate to the paralysed side due to contraction of the intact contralateral pterygoid muscle.



Corneal reflex


Routine testing of the corneal reflex is unnecessary, but may be relevant when the history suggests a lesion localising to the brainstem or cranial nerves V, VII or VIII. The afferent limb is via the trigeminal nerve, the efferent limb via the facial nerve.




  • Explain to the patient what you are going to do and ask them to remove their contact lenses, if relevant.



  • Gently depress the lower eyelid while the patient looks up.



  • Lightly touch the lateral edge of the cornea with a wisp of damp cotton wool ( Fig. 7.7 ).




    Fig. 7.7


    Testing the corneal reflex.

    The cotton-wool wisp should touch the cornea overlying the iris, not the conjunctiva, and avoid visual stimulus.



  • Look for both direct and consensual blinking.



Jaw jerk





  • Ask the patient to let their mouth hang loosely open.



  • Place your forefinger in the midline between lower lip and chin.



  • Percuss your finger gently with the tendon hammer in a downward direction ( Fig. 7.8 ), noting any reflex closing of the jaw.




    Fig. 7.8


    Eliciting the jaw jerk.



  • An absent, or just present, reflex is normal. A brisk jaw jerk occurs in pseudobulbar palsy ( Box 7.5 ).



    7.5

    Comparison of bulbar and pseudobulbar palsy







































    Bulbar palsy Pseudobulbar palsy
    Level of motor lesion Lower motor neurone Upper motor neurone
    Speech Dysarthria Dysarthria and dysphonia
    Swallowing Dysphagia Dysphagia
    Tongue Weak, wasted and fasciculating Spastic, slow-moving
    Jaw jerk Absent Present/brisk
    Emotional lability Absent May be present
    Causes Motor neurone disease Cerebrovascular disease, motor neurone disease, multiple sclerosis





Sensory symptoms include facial numbness and pain. Unilateral loss of sensation in one or more branches of the V nerve may result from direct injury in association with facial fractures (particularly V 2 ), local invasion by cancer or Sjögren’s syndrome. Lesions in the cavernous sinus often cause loss of the corneal reflex and V 1 or V 2 cutaneous sensory loss. Cranial nerves III, IV and VI may also be involved (see Fig. 8.3 ). Trigeminal neuralgia causes severe, lancinating pain, typically in the distribution of V 2 or V 3 . Reactivation of herpes varicella zoster virus (chickenpox) can affect any sensory nerve, but typically either V 1 or a thoracic dermatome ( Fig. 7.9 ). In herpes zoster ophthalmicus (affecting V 1 ) there is a risk of sight-threatening complications. Hutchinson’s sign, vesicles on the side or tip of the nose, may be present.


Dec 29, 2019 | Posted by in GENERAL & FAMILY MEDICINE | Comments Off on The nervous system
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