Clinical aspects of the nervous system

Clinical Neuroanatomy

Prof. Vajira Weerasinghe

Professor in Neurophysiology, Faculty of Medicine, University of Peradeniya

& Consultant Neurophysiologist, Teaching Hospital, Peradeniya

www.slideshare.net/vajira54

Why study nervous system?

• Neurological diseases are very disabling and very little treatment is available

• Understanding the structure and function of the nervous system helps to understand the pathophysiological basis of these diseases

Functional Subdivisions

• Sensory functions feeling, eg. pain

• Motor functionsmovement, eg. walking

• Integrative functionseg. reflexes

• Autonomic functionscontrol of blood pressure

• Higher functionsmemory, learning

Anatomical Subdivisions• Central Nervous system

Brain and spinal cord

• Peripheral Nervous systemCranial Nerves & Peripheral Nerves

• Autonomic systemsympathetic & parasympathetic

Disorders of the nervous system based on an anatomical divisions

Type of disorder example 1. Peripheral neuropathies

1. Polyneuropathies diabetic polyneuropathy 2. Mononeuropathies carpal tunnel syndrome

2. Neuromuscular junction disorders1. Presysnaptic disorders botulism 2. Postsynaptic disorders myasthenia gravis

3. Anterior horn cell diseases MND (motor neuron disease) 4. Plexus, spinal root or spinal cord disorders Erb’s palsy, cervical

spondylosis, intervertebral disc prolapse

5. Brainstem disorders Tumors 6. Strokes CVA 7. Basal ganglia disorders Parkinsonism 8. Cerebellar disorders Cerbellar ataxia 9. Memory and cognitive function disorders Alzheimer Disease 10. Cranial nerve lesions Bell’s palsy 11. Others Multiple sclerosis

Peripheral neuropathies • Peripheral nerves are affected

• Types: Polyneuropathies or mononeuropathies

• Components: Sensory, motor, autonomic or mixed

• Distribution: Symmetrical or asymmetrical

• Cause: Trauma, demyelination, degeneration

• Examples: Diabetes mellitus vitamin deficiency alcoholism carpal tunnel syndrome ulnar nerve lesions wrist drop foot drop tarsal tunnel syndrome

NMJ disorders• Myasthenia gravis

Antibodies to Ach receptors Post synaptic disorder

• Lambert Eaton Syndrome (myasthenic syndrome) Presynaptic disorder (antibodies against Ca channels)

• Botulism Presynaptic disorder Binds to the presynatic region and prevent release of Ach

NMJ disorders

• Snake venom (Presynaptic or postsynaptic disorder)Krait (bungarotoxin)

Postsynaptic disorder

CobraPostsynaptic disorder

Russell’s viperPresynaptic disorder

Snake venom

• Common Krait (bungarus caeruleus)Produces neurotoxin known as

bungarotoxin Very potent

Causes muscle paralysis and death if not treated

• Cobra venom contain neurotoxin

Myasthenia gravis• Serious neuromuscular disease

• Antibodies form against acetylcholine nicotinic postsynaptic receptors at the NMJ

• Characteristic pattern of progressively reduced muscle strength with repeated use of the muscle and recovery of muscle strength following a period of rest

• Present with ptosis, fatiguability, speech difficulty, respiratory difficulty

• Treated with cholinesterase inhibitors

Anterior cell diseases

• Relatively rare

• Affect any age

• Muscle wasting

• Example: Poliomyelitis

• Adults: MND (motor neuron disease), also called ALS (amyotrophic lateral sclerosis) Speech difficulty (dysarthria)Typical features in EMG test

• Infants: SMA (spinal muscular atrophy) Breathing difficulty

MND dysarthria video clip

Plexus, spinal root or spinal cord disorders

• Plexopathies: brachial plexus, lumbosacral plexus Erb’s palsy

• Radiculopathies: cervical, thoracic, lumbar, sacral roots

• Myelopathies: cervical, thoracic

• Cauda equina lesions

Brainstem disorders • Sensory motor dysfunction and other features associated with brainstem

• Cranial nerve nuclei could be affected

• Tumors or trauma

Motor homunculus

First discoveredbyPenfield

Brodmann areas Primary motor cortex Area 4

Primary somatosensory Cortex, Area 3b, 1

Primary visual cortexBroca’s area area 44

Supplementary motor areaPremotor cortex

Secondary sensory area

Motor cortex

• different areas of the body are represented in different cortical areas in the motor cortex

• Motor homunculus– somatotopic representation – not proportionate to structures but proportionate

to function – distorted map– upside down map

Motor cortical areas

• primary motor cortex (MI)– precentral gyrus

• secondary motor cortex (MII)– premotor cortex– supplementary motor area (SMA)

Stroke • Also called CVA (cerebrovascular accident) or brain attack

• 2nd most common cause of death worldwide (WHO)

• 4th most common cause of death in Sri Lanka

• Commonly hemiplegia occurs

Types of strokes

• Ischaemic strokes (acute ischemic stroke is caused by thrombotic or embolic occlusion

of a cerebral artery and is more common than hemorrhagic stroke)

Large vessel strokes Lacunar strokes

• Haemorrhagic strokes (In hemorrhagic stroke, bleeding occurs directly into the brain

parenchyma due to a leakage from small intracerebral arteries damaged by chronic hypertension)

Intracerebral haemorrhage (ICH)Subarachnoid haemorrhage (SAH)

CT images

Ischaemic strokes Haemorrhagic strokes

Lacunar Stroke

• Lacunar infarcts or small subcortical infarcts result from occlusion of a single penetrating artery and account for one quarter of cerebral infarctions

Cerebral blood vessels • Anterior and middle cerebral arteries carry the anterior circulation and arise

from the supraclinoid internal carotid arteries

• Anterior cerebral artery (ACA) supplies the medial portion of the frontal and parietal lobes and anterior portions of basal ganglia and anterior internal capsule

• Middle cerebral artery (MCA) supplies the lateral portions of the frontal and parietal lobes, as well as the anterior and lateral portions of the temporal lobes, and gives rise to perforating branches to the globus pallidus, putamen, and internal capsule

• MCA is the dominant source of vascular supply to the hemispheres

• Posterior cerebral arteries (PCA) arise from the basilar artery and carry the posterior circulation

• PCA gives rise to perforating branches that supply the thalami and brainstem and the cortical branches to the posterior and medial temporal lobes and occipital lobes

Cerebellar arteries

• Inferiorly by the posterior inferior cerebellar artery (PICA), arising from the vertebral artery

• Superiorly by the superior cerebellar artery

• Anterolaterally by the anterior inferior cerebellar artery (AICA), from the basilar artery

Lacunar infarct• Pure motor stroke/hemiparesis

This is the most common (33-50%) lacunar syndrome usually occurs with infarction of the posterior limb of the internal capsule, which carries the descending corticospinal and corticobulbar tracts, or the basis pontis. It is marked by hemiparesis or hemiplegia that typically affects the face, arm, or leg of one side. Dysarthria, dysphagia, and transient sensory symptoms may also be present.

• Ataxic hemiparesis This is the second most frequent lacunar syndrome and usually occurs with infarction of the posterior limb of the internal

capsule, basis pontis, and corona radiata. It displays a combination of cerebellar and motor symptoms, including weakness and clumsiness, on the ipsilateral side of the body. It usually affects the leg more than it does the arm; hence, it is known also as homolateral ataxia and crural paresis. The onset of symptoms is often over hours or days.

• Dysarthria/clumsy hand This is sometimes considered a variant of ataxic hemiparesis (above), but usually still is classified as a separate lacunar

syndrome. The lesion is in the pons and the main symptoms are dysarthria and clumsiness (i.e. weakness) of the hand, which often are most prominent when the patient is writing.

• Pure sensory stroke Marked by persistent or transient numbness, tingling, pain, burning, or another unpleasant sensation on one side of the

body, this infarct is usually in the contralateral thalamus.

• Mixed sensorimotor stroke This lacunar syndrome involves hemiparesis or hemiplegia with ipsilateral sensory impairment, with infarct typically in the

thalamus and adjacent posterior internal capsule.

Watershed

• A watershed stroke or watershed infarct is defined as an ischemia, or blood flow blockage, that is localized to the border zones between the territories of two major arteries in the brain

• Watershed locations are those border-zone regions in the brain supplied by the major cerebral arteries where blood supply is decreased

Basal Ganglia disorders

• Parkinsonism

• Athetosis

• Chorea

• Hemiballismus

Basal ganglia disorders are also called extrapyramidal disorders

Basal ganglia• Caudate nucleus • Putamen• Globus pallidus

–(internal and external)• Subthalamic nuclei• Substantia nigra

International Basal Ganglia Society

(Ref. Guyton)

thalamus

globus pallidus

putamencaudate

Basal ganglia• caudate nucleus

• putamen

• globus pallidus

• subthalamic nuclei

• substantia nigra

corpus striatum

lentiformnucleus

Parkinsonism• due to destruction of dopamine secreting pathways from

substantia nigra to caudate and putamen. also called “paralysis agitans” or “shaking palsy” first described by Dr. James Parkinson in 1817.

• In the west, it affects 1% of individuals after 60 yrs

Classical Clinical features:

• Tremor, resting

• Rigidity of all the muscles

• Akinesia (bradykinesia): very slow movements

• Postural instability

Chorea• Lesions in the caudate

nucleus

• jerky movements of the hand, face and other parts

• patient is unable to control them

• may get worse with anxiety

• disappears in sleep

Athetosis

• Lesions in putamen

• spontaneous slow writhing movements (twisting movements) of fingers, hands, toes, feet.

Hemiballismus

• Lesions in subthalamus

• violent, flailing movements of arm & leg on one side of the body

Features of cerebellar disorders

• ataxia incoordination of movementsataxic gait

broad based gaitleaning towards side of the lesion

• dysmetriacannot plan movements

• past pointing & overshoot

• decomposition of movements

• intentional tremor

Features of cerebellar disorders

• dysdiadochokinesisunable to perform rapidly alternating movements

• dysarthriaslurring of speech

• nystagmusoscillatory movements of the eye

Features of cerebellar disorders

• hypotonia reduction in tone

due to excitatory influence on gamma motor neurons by cerebellum (through vestibulospinal tracts)

• decreased reflexes

• head tremor

• head tilt

• ReboundIncreased range of movement with lack of normal recoil to

original position

Memory and cognitive function disorders

• Amnesia Retrograde amnesia

unable to recall events that occurred before the development of the amnesia for example due to head injury

Antegrade amnesiadifficulty in the learning and retention of information encountered after brain

damage, previous memories unaffectedCould occur in head injury, hippocampal lesions, alcoholism,

A combination of both

• Dementia Alzheimer’s disease

Loss of Ach pathways Alcoholism

Degeneration of nerve pathways Senile dementia

Old age

limbic system

• nuclei– amygdala– septal nuclei– mammillary body– hypothalamus

• cortical areas– hippocampal gyrus– cingulate gyrus– dentate gyrus– entorhinal, amygdaloid cortex

• paralimbic structures• orbital gyrus, insula, nucelus accumbens, thalamic nuclei, superior

temporal gyrus,

• fibre tracts: fornix, medial forebrain bundle

limbic cortex

• consist of 3 layered cortex (in contrast to 6 layered cortex of the neocortex)

Dementia

• Loss of memoryAlzheimer’s dementia

degeneration of brain areas (hippocampus)decreased acetylcholine

Alcoholism limbic system (hippocampus) is affected

In old agesenile dementia

Alzheimer’s disease

video

Alzheimer’s disease

• A progressive, degenerative and fatal brain disease

• in which cell to cell connections in the brain are lost

• as a result, the death of brain cells occur

• Rapid cognitive impairment

Other conditions

• Internuclear ophthalmoplegiaEye movement disorder Affected eye weak adduction, other eye nystagmusMedial longitudinal fasciculus (MLF) which connects

abducens and occulomotor pathways affected

Horner’s syndromeresults from an interruption of the sympathetic nerve supply to the eye and is characterized by the classic triad of miosis (ie, constricted pupil), partial ptosis, and loss of hemifacial sweating (ie, anhidrosis).

Klippel–Feil syndrome

• This is a rare disease, initially reported in 1912 by Maurice Klippel and André Feil from France characterized by the congenital fusion of any 2 of the 7 cervical vertebrae