Diseases of the Neurosensory System

• Problems w/ Nervous System:

  • Peripheral nerves - trapped nerve or generalised neuropathies (dysfunction of the nerve)
  • Spinal cord -  syringomyelia , degeneration of the spinal cord (dorsal columns), blockage of blood flow in the spinal cord, and transverse myelitis 
  • Brain - lesioning or a lack of blood supply to the brainstem or cortex (primary somatosensory cortex = loss of sensation down the contralateral side of the body)

  *Positive symptoms = pins and needles, pain

  *Negative symptoms = numbness or analgesia (loss of pain sensitivity)

  • Can be acute or degenerative (sudden or gradual)
• Brain Injuries:

  • Damage to occipital lobe =complete/partial blindness
  • Sensory symptoms = temporary (concussion) or permanent (contusion/bruise)
  • Subdural or subarachnoid haemorrhage = bleeding from ruptured blood vessels in brain

  *increased intracranial pressue = compresses brain (sensory). force the brainstem through the foramen magnum (where the spinal cord enters the skull), death

  • Treatments:

  *brain surgery to remove the haemotoma (an area of blood that collects outside of the vessels), repair ruptured vessels, relieve the pressure within the skull.
• Cerebrovascular accidents (stroke):

  • caused by a blockage of blood circulation to the brain, leads to ischaemia (death of brain tissue due to a decrease in oxygen and nutrients)

  *risk factors: atherosclerosis = old, males, smokers, high levels of cholesterol.

  •  Blockage in anterior cerebral artery = loss of somatosensation in the contralateral leg
  • Blockage in posterior cerebral artery = loss of one visual field (homonymous hemianopia)
  • Transient ischaemic attack (TIA) = temporary numbness to the body 
  • Treatments = Thrombolysis (drugs that dissolve blood clots) AND Thrombectomy (surgery)
• Neurogenerative Disorders:

  • involve a progressive loss of neurons in the CNS over time
  • more commonly associated with impariment to cognition (e.g. Alzheimer's disease) and movement (e.g. Parkinson's disease), there are sometimes sensory symptoms that can accompany neurodegeneration
  • no cures for neurodegenerative diseases, and thus sensory symptoms may persist throught the lifetime of sufferers*deep brain stimulation in Parkinson's disease may help to alleviate symptoms
  • neurodegeneration may be caused by an inflammatory response in the CNS (MS) or genetic variation 
• Alzheimer's disease:

  • problems with object recognition, colour discrimination, peripheral vision, and depth perception - cell death within the retina, optic nerve, visual cortices and higher visual centres of the brain (posterior cortical atrophy)
  • hearing loss - mitochondrial dysfunction

  *energy-demanding neurons and vestibulocochlear hair cell death

  • Beta-amyloid plaques (prevent communication b/w cells) and neurofibrillary tangles of tau proteins (inside cells)

  *caused by misfolding of proteins which causes chain reaction - plaques and tangles proliferate throughout the brain.
• Parkinson's Disease:

  •  degeneration of dopamine neurons in the substantia nigra (in midbrain responsible for movement) which leads to overactivation of the basal ganglia

  *abnormalities w/ mitochondria protiens

  • significant increase in tactile and thermal thresholds and a significant reduction in mechanical pain perception
  •  peripheral deafferentation (a loss of input from peripheral nerves) = reduction in touch and smell sensations
• Neural Physiological Disorders:

  • Epilepsy = suddent bursts of abnormal electrical activity in the brain disrupt normal brain function and cause seizures and fits

  *Generalised = seizure starts in both hemispheres of the brain at the same time

  *Focal = seizures start in one hemisphere of brain (generalise by crossing to other brain regions via midline structures)

  *Simple seizure = px aware

  *Complex seizure = impaired awareness

  • a generalised epileptic fit is usually associated with a tonic (muscle stiffening) clonic (jerking of limbs) phase, followed by a period of unconsciousness.
• Causes of Epilepsy:

  • Temporal lobe seizures - olfactory and/or auditory hallucinations, such as hearing tones or ringing (i.e. similar to tinnitus).
  • Parietal lobe seizures - pins and needles, numbness, and dizziness / imbalance.
  • Occipital lobe seizures - visual symptoms of flashing lights or amaurosis (temporary vision loss without damage to the eye).
  • Ictogenesis = sensory stimulation

  *most common = photosensitivity to flashing lights.

  • causes: genetic causes, head injuries, strokes, or drug and alcohol abuse.
• Treatment of Epilepsy:

  • Increase inhibition by enhancing the action of GABA receptors, reduce inactivation of GABA , increase brain GABA levels 

  *medication: barbiturates , benzodiazepines, vigabatrin

  • Reduce excitation by reducing the release of glutamate from pre-synaptic neurones
  • Inhibit the repetive firing of neurones by blocking of sodium and calcium channels
  • Surgery =  temporal lobe resection (removal of part of brain where seizures are generated) or a corpus callosatomy (severing the connective tissue between the two hemispheres of the brain)
• Neuroimmunological Disorders:

  • CNS has relative immulogical privilege compared to the rest of the body due to the blood-brain barrier which prevents lymphocytes (white blood cells), macrophages and antibodies from entering

  *immune system in the brain can be activated by damage (stroke) which is then amplified by the release of cytokineswhich causes the BBB to open up and triggers a larger immune response. 

  • Autoimmune disease = immune system loses its ability to distinguish b/w foreign antigens and cells

  *produces antibodies and cytotoxic T cells that attack and destroy the cells of the body
• Neuroimmunological Disorders:

  • Acute disseminated encephalomyelitis = secondary inflammatory demyelinating diseases of the CNS and monophonic (once-occurring, can be fatal)

  *RABIES AND MEASLES

  • Guillan-Barré syndrome = unserious infection can cause an immune response which attacks peripheral nerves

  *PNS is not as protected from infection as CNS = more susceptible to infections and immune related diseases

  *leads to demyleniation of the peripheral nerve = numbness, pins and needles, and pain
• Neuroimmunological Disorders: MULTIPLE SCLEROSIS

  • inflammatory response gradually destroys myelin sheaths that surround neurones in the CNS, which leads to non-functional hardened lesions (or scarring) called scleroses
  • symptoms = loss of vision and colour blindness, numbness, tingling, pain

  *loss of myelin prevents the fast transmission of action potentials

  • Lesions in MS can heal through remyelimation:

  *Demyleinated axons can upregulate sodium ion channels

  *Periods of remission (symptom-free) = neurones attempt to heal and compensate for reduced nerve impulse conduction
• MULTIPLE SCLEROSIS TREATMENTS:

  • corticosteroids = during acute relapses use of anti-inflammatory medicines
  • immunotherapy using drugs that target T cells

  ! these cannot work in later stages of the disease

  
  

  
  

  CAUSES:

  • genetics
  • environment

  
  

  
  
• Neurogenetic Disorders:

  • Gene deletions - hereditary sensory neuropathies (peripheral nerve loss).
  • Gene duplications - sensory neuropathy.
  • Gene variants - nonsyndromic hearing loss 
  • Genetic imprinting - differential expression of a gene depending on whether the gene came from which parent, autism
  • Mitochondrial disorders - neurodegenerative, optic+peripheral neuropathy,strokes, epilepsy, and deafness.
  • Trinucleotide repeat disorders -large abnormal expansion of three bases in the genome (protein doesn't work correctly) , Friedreich's ataxia (loss of vibration sense and proprioception)