Sophie Scott 12th January 2000
Neurology is the medical discipline interested in the diseases of the nervous system, and of the systems that impinge on the nervous system e.g. trauma, vascular disease and infections. Thus it has a very wide remit. In these lectures I will be giving you a basic overview of neurology.
1. The central nervous system - the anatomy and physiology of the brain, and the associated terminologys, with particular reference to the brain regions involved in communication (which is more of less all of it). What can go wrong with the nervous system, and how a clinical examination is carried out.
2. Brain imaging techniques: structural, functional, diagnostic
3. Aphasia, including sub-cortical aphasia and problems associated with aphasia
4. Traumatic head injury and dementia
5. Right hemisphere lesions; non-verbal processing and the role in recovery
6. Childhood aphasia and other Childhood language disturbances, neurological aspects of SLI, autism, dyslexia, stuttering
1. The central nervous system.
The CNS and PNS
CNS= brain and spinal cord
PNS= nerves that arise from the base of the brain and the spinal cord (12 cranial nerves and 31 pairs of spinal nerves). Spilts into the somatic and the autonomic
somatic = control of skeletal muscles
autonomic = regulation of involuntary structures (e.g. heart and gut). It is in fact both PNS and CNS. These distinctions are somewhat arbitrary and the system functions as a whole.
The nervous system is made up of nerve cells, neurones, which do not regenerate. They are supported by neuroglia. Signals are passed across synapses, involving neurotransmitters. There are many different types. drugs which are psychoactive (medical or recreational) influence different sets of these neurotransmitters. These are located presynaptically, and they pass across the synaptic cleft, to the other synapse, where they excite or inhibit the post synaptic neurone (turn it on or off). To activate something other than another neurone (e.g. a muscle cell), there is a neuroeffector junction; the post synaptic structure here is the surface of a muscle or gland.
Grey and white matter
Grey = cell bodies and dendrites
White matter = long processes of neurones.
Neuroglia and blood capillaries are throughout.
Most of the grey matter forms the outer layer of the brain, the cerebral cortex. This is very complex in humans, and forms distinct lobes.
Brain = CNS that is inside the skull. Largest and most complex mass of nervous tissue in the body weighs around 1400g. Surrounded by the meninges (three membranes) and it floats in the cerebrospinal fluid. There are cavities within the brain called ventricles. Spilt into three parts: the cerebrum, the brainstem and the cerebellum. The cerebrum and cerebellum are both split in two.
Cerebrum
Largest part of brain. (7/8ths of total weight). All sensory and motor activities are driven by areas located in the cerebrum. In humans the surface of the cerebrum is very convoluted. The up points of the convolutions are called gyri and the depressions in-between are called sulci. If they are really deep, they are called fissures; e.g. the longitudinal fissure between the two cerebral hemispheres.
Name the lobes and the fissures here!
The cerebral cortex is the layer of grey matter covering the surface of the hemispheres. This is grey matter, and makes up around 40% of the weight of the brain. It has been estimated to contain 15 billion neurones. The cellular structure of the cortex is not regular over the whole surface, and it is typically held that this neuroanatomical variation reflects some functional specialisation (not always thus : Lashley believed in mass action, that the whole brain was an undifferentiated organ). Experimental work with animals, with neuropsychological patients, with direct stimulation of the brain, with indirect stimulation of the brain and from functional imaging studies have tended to confirm this. Later in the course we will address several of these approaches. The neuroanatomical variation in cellular structure underlies one system of naming where in the brain we are: the Brodman areas.
This was developed by Brodman in the 1900’s. He was trying to correlate structure and function in the brain, and developed a number system to designate different brain regions, which have different cellular morphology. This enables us to describe different areas in terms of their function: sensory, motor and association cortex. Sensory = perception. Motor = output. Association: receive multiple inputs, many independent of perceptual input. This association cortex makes up 75% of the cortex, and the three main areas are:
prefrontal
anterior temporal
parietal/temporal/occipital.
Beneath the cerebral cortex is white matter. Within this, there are small areas of grey matter, called the basal nuclei, or more often, the basal ganglia (although ganglia are groups of nervous tisse OUTSIDE the central nervous system. They are very important and if damaged seem to impact on motor systems (e.g. Parkinson’s disease), or chorea (type of dyskinesia, breifer, peripheries, small fleeting movement, speech and swallowing), atheostis (writhing, arm and shoulder twist around, incl. posturing) and dyskinesia (abnormal involunary movement, can’t repress), all of which can impact on speech. These regions are also important in other aspects of processing e.g. emotional processing.
The white matter itself is organised into tract, joining regions of the brain together. Three types.
The two hemispheres are mirrors of each other structurally and functionally, with a couple of provisos. There is also cross over, so the left hemisphere is largely concerned with motor and sensory aspects of the right side of the body and vice versa. Speech and language are (for most people) dominantly represented on the left side, and right hemisphere with other stuff, such as space, attention, non-verbal aspects of perception e.g. recognising a key by the feel of it. This is not mediated linguistically. Also, maybe, non verbal communication. But also, it’s important to note that most of it is pretty similar. When people speak of the dominant hemisphere, they tend to mean the one that is specialised for speech and language, which for 97% of right handers is the left.
The two hemispheres are joined by commissures. The largest is the corpus collosum, then there are the fornix, the anterior commissure and the posterior commissure.
Each hemisphere is divided into lobes. The frontal, parietal, occipital temporal, central (insular) and limbic (?). These are separated by major sulci, or fissures. You can see the frontal, occi., parietal and temporal lobes from the outside (lateral) view of the brain. Go through where they all are in a figure, and include the way that the fissures separate them.
The central lobe, or insula, is not visible from a lateral view, it is on the inside of the lateral fissure. This includes the frontal, occipital and temporal opperculi
Limbic lobe is an old fashioned term for the ring of gyri on the medial aspect of each hemisphere, incl. the hippocampus, parahippocampal gyrus and the cingulate gyrus. Mostly, the cingulate would be treated differently, and the hippocampus, etc. would be considered to be medial temporal lobe structures, and not really discussed in terms of lobes..
Describe the medial differentiation of the lobes
Functional specialisation in the cortex
There is a lot of functional specialisation across the brain regions. E.g. frontal lobes - control of behaviour and movement, Anterior to the central sulcus is the precentral gyrus, or primary motor area, or motor strip or Brodman area 4 - carry voluntary nerve impulses to the brainstem and spinal cord - i.e. cells here are responsible for movement of skeletal muscles on the opposite side of the body. If you stimulate these areas (e.g. with TMS) the muscle of the opposite side contracts. The nerves that leave this area and pass to the brainstem of spinal cord form the pyramidal pathways.
The parts of the body responsive to voluntary muscular control are represented on this strip in a roughly spatial array. A map of this array has been determined using direct brain stimulation in patients having a brain operations under local anaesthetic. It is called the motor homunculus. The body is roughly inverted.. The area involved is not correlated to the size of the corresponding body part, but more concerned with fine motor control. A large part of the fingers and around half of it to the control of the face articulators and vocal tract! NB a lot of plasticity is possible in this organisation.
There are other motor areas: the pre-motor area (Brodman area 6), supplementary motor area, secondary motor area and frontal eye field (BA 8). The premotor area lies anterior to the pre-central sulcus. It contributes fibres to the descending motor pathways, and also influences the activity in primary motor cortex. Stimulation here activates groups of muscles, e.g. vocalisation, or rhythmic leg movements, chewing, swallowing, contortions of the body. It seems to be involved in skilled motor activity and directs the primary motor cortex as to the patterns of activation of the motor system required.
Secondary motor area is located in the dorsal wall of the lateral fissure below the precentral sulcus. Its functional significance is unknown. Supplementary motor area seems to be important in speech production, and is located within the longitudinal fissure on the medial aspect of the hemisphere anterior to the leg portion of the primary motor area. The frontal eye field is anterior to the premotor area and is involved in voluntary eye movements.
Broca’s area is in the frontal lobe, and is important for language: BA 44/45, in the inferior (3rd) gyrus of the frontal lobe, necessary for fluent, well articulated speech. we’ll be coming back to this area later!
The parietal lobe is involved in many sensory functions. Heat, cold, pain, touch, pressure and position of the body all input to here (possibly also taste). In the post central gyrus is the primary sensory strip, or somesthetic area, BA 3,1,2. This receives sensory signals from the opposite side of the body (face is a bit ipselateral). As in the motor system, we can map out this strip, and as in the motor system the map is roughly inverted. The size of the area on the strip correlates with the number of sensory receptors in that body part. This map is called the sensory homunculus. So the thumb and lips are large areas, and the trunk and legs are smaller.
In the supra marginal gyrus, at the posterior end of the lateral fissure, and the angular gyrus is at the end of the superior temporal gyrus. They form part of a posterior language area, in the dominant hemisphere, involved in spoke and written language. Again, we will be coming back to this.
The temporal lobe is involved with audition, and there are also a lot of speech and language related areas here. The primary auditory area is located within the lateral fissure (the sylvian fissure), in anterior transverse temporal gyri called Hescl’s convolutions (BA 41 and 42). The posterior part of the lateral surface of the STG and the area behind Hescl’s gyrus (planum temporale) form auditory association cortex. Beneath this, in the STS is Wernike’s area, also important in speech perception. There are also auditory association areas anterior to HG: running anteriorly down the STG into the STS.
The occipital lobe is principally involved in vision. The primary visual area is right at the back, BA17 and surrounds the calcerine sulcus.
The bits of the brain called the limbic lobe are involved in smell, attention and lots of memory and emotion stuff, all fairly separately. Some of these at least can cause speech perception problems, esp. of non verbal aspects of communication, like the perception of intonation and vocal emotional expressions.
The Brainstem
Going rostrally (head) down to the caudal end (tail) there is :
The diencephalon - thalamus and hypothalamus. The thalamus is spilt into two by the third ventricle In most people it forms two egg shaped thalami connected by an interthalamic adhesion (intermediate mass). Each thalamic mass contains over 30 nuclei, which are incredibly important in sensory and motor functions. It forms a massive sensory integration area, all input (except smell) passing through this body. It is also involved in the inhibition and facilitation of motor impulses (and more complex output?). It is thus involved in some forms of aphasia
Beneath the thalamus is the hypothalamus, a very small but very important brain region. It controls and integrates the autonomic nervous system, e.g. cardiac muscle and gland secretions. It is very involves in mind/body interactions, e.g. the effect of a cognitive emotional state on the body activity. Also body temp., and eating and drinking and sexual behaviour.
Mid Brain
smallest part of mid brain, contains many regions involved in the processing of sound and eye movements (and in other animals, ear movements). Deals with the way everything changes when we move our head.
Pons
Between mid brain and medulla oblongata and anterior to the cerebellum.
Medulla oblongata
Most caudal part of brainstem, it is continuous with the spinal cord. Mostly forms white matter tracts.
Reticular formation
Runs up the middle of the brainstem. Very important in wakefulness; if stimulated in a sleeping person, they instantly wake. Damage to this area causes coma, and the subject cannot be woken.
Cerebellum
2 hemispheres connected by the vermis. Connects to the brain stem via 3 bundles of nerves or peduncles. It is involved in the production and refinement of muscle movements, esp. the timing involved in co-ordination. Very very important in speech production; it may also be involved in more high level aspects of speech and cognition.
Definitions of language disorders
Speech production involves the concept and symbolic expression of the things to be spoken - disruption here is called aphasia
The symbolically formed speech concept has to be realised as a motor programme or act - disruption here is a dysarthria
Before this programme is externalised, it must be correctly sequenced in terms of muscle contractions: a disorder at this level is an apraxia.
Rarely are these seen as separate problems!
Neuropathological substrate of neurogenic speech and language disorders.
Can be anything that damages the brain. It is the area damaged, not the method, which typically causes the speech deficit.
Disorders involving the blood supply to the brain are the most common cause of neurological disease, and thus of related speech and language disorders. When there is spontaneous disruption, this is called a cardiovascular accident, or stroke. The three features of this are:
There are two forms of stroke: ischaemic stroke and haemorrhagic stroke.
A. ischaemic stroke = when there is suddenly insufficient blood supply to part of the brain for cells to survive. Two patterns behind this:
Both of these forms of stroke deprive the brain of oxygen, leading to the death of cells (infarct). Embolitic infarctions develop more quickly than thrombitic infarcts. The white matter is less sensitive to ischemia than the grey matter (cortex). The centre of an infarct is totally destroyed but at the periphery white matter tracts may be preserved and there may be areas were the cells are disrupted but do not die. This can lead to peri-infarct activation after some time, one candidate route for post-stroke recovery. The centre of the infarct becomes a cyst-like zone with no neural activity.
The severity of these attacks can vary enormously. If a major vessel is occluded, by thrombosis or embolism, the effects can be terrible. Or the ischemic can be transient, and may not last long enough to cause brain damage, e.g. TIA’s repetitive stereotyped attacks of focal neurological function followed by complete recovery. These were thought to be due to a spasmodic narrowing of blood vessels, more likely to be a repeated embolisation of small particles from proximally located atherosclerotic plaques in the neck (e.g. the internal carotid arteries)
B. haemorrhagic stroke = when a blood vessel ruptures and blood rushes through destroying tissue (intra-cerebral haemorrhage) or collects outside the brain between the meninges, causing compression of the brain within the skull. This may have a sudden onset with evolution to maximum deficit occurring in a smooth fashion over several hours. When associated with cardiovascular disease, (rather than trauma) , is most often associated with hypertension, but also other pathologies of the cerebral blood vessels, aneurysm, angioma (tumour of blood vessel), arterio-venous malformation, abnormality of clotting factors (such as mild leukaemia, inherited problems with clotting, certain cancers and infections) or arterisis (inflammation of blood vessel wall – auto-immune diseases). Anti-coagulant therapy (e.g. warfarin therapy) is a frequent cause of cerebral haemorrhage.
Most occur during activity and without warning. Onset is abrupt and is associated with a severe headache, vomiting and loss of consciousness. Most common site of intra-cerebral haemorrhage is the region of the internal capsule. Patient complains of something wrong, headache, aphasia and/or dysarthria, paralysis down the opposite side of the body and variable state of consciousness. With brainstem haemorrhage there is a rapid loss of consciousness and often death. Cerebellar haemorrhages are associated with vertigo, nausea, ataxia followed by coma and often death. The prognosis for haemorrhagic stroke is poorer than for ischemic strokes.
Intra-cerebral haemorrhages involve deeper structures of the brain than the cerebral cortex, and cause damage by local destruction and brain tissue compression. The force of the blood from the ruptured vessel directly damages the cells and forms a clot called a haematoma, which increases in size and displaces brain tissue. As the brain is in a box, the intra cranial pressure rises as the clot develops causing compression. This can lead to a secondary rupture into the ventricular system or subarachnoid space. This is why removing the clot can become of value in the relief of symptoms in some cases.
In addition to hypertension, the rupture of intra-cranial aneurysms is another cause. An aneurysm is a thin-walled enlargement of blood vessels (usually found in the circle of Willis or its major branches). They tend to occur at junctions and may represent congenital deficiencies in the development of the vessel wall. They increase in size and can produce cranial nerve palsies or focal seizures prior to rupture, which occurs during activity and produces headache, collapse and unconsciousness. The bleeding tends to occur into the subarachnoid space, but may also go into the brain tissue, leading to intra-cerebral haemorrhage.
Intra cranial tumours are the third most common disorder of the nervous system after cardiovascular disorders and infections. They are not uncommon in aphasia producing lesions. Tumours can be benign or malignant. They are primary if they develop from cells within the cranial cavity, or secondary (metastases) if the travel to the brain from a primary tumour elsewhere. They produce symptoms in three ways:
Two forms of intra-cranial tumours:
Intra-cerebral = involve cerebral tissues majority of these are gliomas which develop from the neuroglial cells.
Extra-cerebral = involve tissues outside the brain itself (e.g. meninges, skull bones).
Intra-cerebral tumours cause more speech and language disorders than extra-cerebral tumours. However in neither is aphasia a major complaint until quite late in the disease. This is because the intra cerebral neoplasms infiltrate the cerebral tissues widely before causing focal destruction. Also, extra-cerebral tumours develop slowly, allowing a lot of accommodation by the brain tissue before functions are disrupted. If aphasia symptoms do appear early, it is normally because the tumour has disrupted the cerebral blood flow. Compression or distortion of tissue due to a tumour can occur at a site distal to the tumour, which is why aphasic signs are not necessarily a use indicator of tumour localisation. Surgical removal of tumours can also be the cause of speech and language deficits, as can radiotherapy.
A very common cause of problems, esp. in young adult males, in this country at this time, this is mostly due to motor accidents (as opposed to gunshot wounds). They can be categorised into closed and open head injuries. Closed head injuries often cause diffuse damage, often to a region distal to the point of impact, due to the movement of the brain inside the skull. Open head injuries are more severe, and vary widely based on the site and extent of the damage.
All of these are characterised clinically by a progressive deterioration of neurological function and pathologically by cellular depletion with atrophy of nervous tissue. Those affecting the cerebrum and esp. the cortex are characterised by progressive dementia in the middle or later decades of life and include Alzheimer’s disease and Pick’s disease. Both of these are associated with an initial ‘dulling’ of intellectual abilities with confusion and memory problems. Language problems are a common occurrence. Deterioration occurs over months and years, leading to profound dementia, immobility, and death from secondary infections (you don’t die from dementia). You don’t get focal signs, such as hemiparesis, hemianasthesia, cranial nerve palsies.
Some degenerative diseases are associated with atrophy in the basal ganglia, e.g. Parkinson’s disease, Huntington’s chorea. This latter is an inherited disorder involving mental deterioration and choriform movements which may involve speech disturbances in the form of hyperkinetic dysarthria. Parkinson’s disease has prominent motor system involvement with minimal (although some) mental effects, demonstrating tremor, muscular rigidity, bradykinesia, a mask like face, shuffling gait and hypokinetic dysarthria.
Posions – produced with the body (e.g. when kidneys fail) or introduced from outside e.g. drugs (barbiturates, tranquillisers, some antibiotics, some anti-depressants), heavy metals (lead, mercury, arsenic), organic phosphates and alcohol. Some of these produce speech and language problems as part of their pattern of impairment. In Wernike-Korsakoff syndrome get memory loss, paralysis of eye movements, ataxia, confusion. They confabulate and think they are much younger than they are. It is a complication of chronic alcoholism.
This refers to spontaneous degeneration of the myelin sheaths of nerve fibres. In the CNS is the primary pathological alteration. Multiple sclerosis is the most important disorder in this category. Typically, various symptoms of focal damage to the CNS appear and disappear over a prolonged period, due to numerous patches of demyelination, occurring almost anywhere in the system. It rarely causes a language deficit, and when it does, it is normally word-finding, and tends to co-occur with dementia and/or amnesia. It causes speech problems, typically mixed dysarthria.
7. Infectious disorders
Classified by major site of involvement and type of infecting organism. Infection of the meninges is called meningitis, while inflammation of the brain is called encephalitis. If both area infected, it is meningo- encephalitis. Inflammation of the spinal cord is myelitis.
There are 3 types of meningitis – bacterial, tuberculous and viral. Bacterial involves fever, headache, nausea, vomiting, photophobia, neck stiffness (a positive Kernig’s sign) and alterations in level of consciousness. Viral meningitis is less severe but similar.
Encephalitis can be caused by bacteria or a virus, and around the world can also include forms of parasite. Signs include moderate headache, vomiting, confusion, delirium and drowsiness leading to coma. Kernig’s sign is negative and there is no neck stiffness.
Any language disorder is typically lost amongst the range of neurobehavioral signs and symptoms. Sometimes an aphasia can be traced to an infection, typically herpes simplex encephalitis. Aphasia can also arise from intra-cranial abscesses, typically found in the frontal and temporal lobes. Prior to antibiotic drugs, which was a common form of aphasia secondary to chronic ear infections.