Sensory system and Pain Flashcards
What is the function of perception?
- Provides information about an individuals position in space
- Provides information about the environment surrounding the individual
Describe a sensory pathway sequence
- Sequence of three neurones between peripheral receptor and cortex
- First order neurone in dorsal root ganglion (spinal nerves)
- Second order neurone in spinal cord grey matter
- Third order neurone in contralateral thalamus
What are the types of sensory pathways?
- Proprioception and fine touch
- Pain and temperature
- Auditory pathways (hearing)
- Olfactory pathways (smell)
- Visual pathways (sight)
- Gustatory pathways (taste)
Which pathway is myelinated and which one is not?
-Dorsal column- medial lemnsical system= myelinated
Spinothalamic tract= smaller myelinated fibres/ unmyelinated
Describe Proprioception
-Mediated by mechanoreceptors in muscle and joint so change in length of muscle (contraction increases rates of firing)
=muscle spindles
=Golgi tendon organs
=joint capsule receptors
-Fibres run in dorsal columns (position sense and kinaesthesia) ventral and dorsal spinocerebellar tracts (co-ordination of movements)
-Stationary information: limb position sense
-Sense of limb movement: kinaesthesia
What are the main sensory pathways and their sensory modalities?
-Dorsal column/ medial lemniscal pathway
=Proprioception and fine touch
-Spinothalamic pathway
=Pain and temperature sensation
What are the types of cutaneous mechanoreceptors in glabrous skin?
- Meissner corpuscle (high in dermal/ epidermal junction)
- Pacinian corpuscle (dermis and epidermis)
- Ruffini’s corpuscle
- Merkel’s disks
- Free nerve endings (scattered)
How do we get fine touch?
- Not fine touch= activated large numbers of neurones, amplified by network of free nerve endings, pressure applied over wide area
- Fine touch= neurone activated, talks to other free nerve endings, interneuron cells that switch off/ inhibit adjacent fibres to localise
Describe the dorsal column pathway
- Dorsal root ganglion
- Dorsal spinal nerve root
- Travel in dorsal column
- Cervical medullary junction
- Nucleus cuneatus/ Gracilis
What are the types of pain receptors?
Nociceptors -Thermal -Mechanical -Chemical Action potential travelling up the ascending pain pathway
Periphery substances released by cellular damage that interact with nociceptors
Activate: -K+ -5-HT -Bradykinin Sensitize: -Prostaglandins -Leukotrienes Further/ blood vessel dilation: -Histamine -Substance P
Describe the spinothalamic pathway
Dorsal root ganglion
Second order in spinal grey matter
Decussate
Thalamic nuclei
What is the substantia gelatinosa?
Cell type region of grey matter in spinal cord
Spinothalamic pathway= substantia gelatinosa (layers two and three) in dorsal column
What are the thalamic nuclei?
- Ventral posterior- general sensory afferents
- Ventral anterior and lateral- efferents to motor cortices
- Medial geniculate- auditory afferents relayed to primary auditory cortex
- Lateral geniculate- visual afferents relayed to primary visual cortex
What is the sensory cortex?
- Primary somatosensory cortex is the post-central gyrus in the parietal lobe
- Contralateral half of the body is represented in a somatotopic pattern
- Parietal association cortex important for the interpretation of general sensation
What are the stimuli of visceral pain?
- Hollow organ distention
- Ischaemia
- Inflammation
- Muscle spasm
- Traction
- But not cuts, burns etc
Describe headaches and facial pain (trigeminal thalamic pathway)
- General somatic pain from the head is conveyed by the trigeminal nerve (V)
- The afferent fibres pass to the trigeminal ganglion (first order neurones). From here axons pass into the pons and terminate in trigeminal sensory nuclei (second order neurones). The trigeminothalamic pathway ascends mostly with the medial lemniscal pathway.
What are the causes of headache?
- Direct stimulation of nociceptors via trigeminal nerve- sinuses, toothache, ocular, skin
- Stimulation of; periosteum, arteries, venous sinuses, areas of the dura, muscle
- Unknown causes- migraine
What are the disorders of general sensation?
-Spinal cord: =dorsal columns; tabes dorsalis, SCDC =spinothalamic tracts; syringomyelia -Thalamus =thalamic pain -Cerebral cortex =sensory seizures =agnosia/ dyspraxia
Describe subacute combined degeneration
Vitamin D deficiency
- Chronic alcoholics
- Degeneration of dorsal columns= reduced proprioception
- Wide gait, feet with increased pressure
- Low copper levels also a cause
Describe Tabes Dorsalis
- Syphilis infection
- Degeneration of dorsal columns
- Now rare
Describe syringomyelia
Fluid filled cavity develops in the spinal cord
- Central enlargement of spinal cord
- Second order neurones cant decussate in the spinothalamic pathway
- Pain and temperature perception affected
What is pain?
- Perceived nociceptive input to the CNS
- A sensory and emotional subjective experience of discomfort
- ‘Pain is pain’ regardless of whether there is a noxious stimulus causing it or not
- Most pain in clinical practice cannot be easily tied down to a specific lesion, injury or area of damage
What is the purpose of pain?
- Pain occurs before injury occurs – to prevent damage.
- To learn that something is harmful
- Pain sets limits on activity, forces inactivity or rest which is required for healing
What is the mechanism of pain?
- Activation of nociceptors does not automatically lead to the perception of pain
- Pain is a cortical emotion
- The nociceptive pathway may be modulated in the spinal cord
How do descending pathways modulate the transmission of nociceptive signal
Fibres arise in the periaqueductal grey matter
-To nucleus raphe magnus
so synapse in dorsal grey matter of spinal cord
Describe the gate theory of pain
- Nociceptive fibre activates second order neurone in spinothalamic pathway
- Nociceptor fibres inhibit the inhibitory interneuron to switch on secondary neurone
- Overcome inhibition of inhibitory interneuron by innocuous stimulus= activate large myelinated afferent fibre, switch on inhibitory interneuron to stop secondary neurone
- Rub banged elbow to provide innocuous stimulus
What causes pain?
-Characteristics of host =Biological: genetics, sex, endogenous pain control =Psychological: anxiety, depression, coping, behaviour =Cognitive -Disease =History =Present disease -Environment =Socialisation =Lifestyle =Traumas =Cultural expectations, upbringing, roles
What do we ask about pain?
- Location - Where is it?
- Radiation - Does it go anywhere else?
- Character – What is it like?
- Exacerbating factors – what makes it worse?
- Relieving factors –what makes it better?
- What do you think is causing it?
- How have you been feeling since you had the pain?
What are the drugs in the Analgesic ladder?
-Paracetamol
-Codeine containing drugs (coproxamol)
-Morphine
=NSAID aspirin, ibuprofen at any stage
Describe the placebo effect
- Placebo is still one of the best therapies in medicine
- Response rates of 30% in most conditions common
- The effect can be blocked by naloxone, a competitive antagonist of opioid receptors.
- Not ethical to prescribe
