What receptors detect pain and which sensory tract takes APs to the somatosensory cortex?
- Nociceptors (found on the membranes of high threshold neurones)
- Spinothalamic tract
What does ‘contralateral arrangement’ refer to?
How the left side of the brain gets information from the right side and vice versa
What is affective neuroscience?
It describes how different regions of the brain, when stimulated, can initiate a physiological response.
What are the 3 different type of stimuli that nociceptors can receive?
- mechanical (pressure)
- thermal
- chemical (reacts to cytokines at sites of inflammation)
What immediately happens to the nociceptor when it detects one of the stimuli?
The nociceptors undergo a conformational change which allows ions to enter, thus creating an AP.
How are the 2 paths of the spinothalamic tract different?
- Fast path that detects sharp pain (neospinothalamic)
- Slow path that detects dull pain (paleospinothalamic tract)
What type of fibres are found in the fast path?
alpha fibres
What type of fibres are found in the slow path?
c fibres
Describe the path of the general spinothalamic tract and where the neurones synapse
Nociceptors -> Dorsal horn -> decussation of neurones (contralateral movement) -> thalamus -> somatosensory centre
Which of these tracts also passes through the reticular formation, before going to the thalamus?
The slow path that carries signals for dull pain
What are some of the causes of lower back pain (lumbago)?
Issues with the…
- lumbar muscles + vertebrae
- spinal cord/ nerve roots
- aorta
- kidneys
- pancreas
What is referred pain?
- There are afferent nerves (that can detect pain) running from the viscera to the spinal cord/brain.
- However, these visceral afferents converge (convergence theory) with somatic afferents on their way to the CNS.
- This means that the brain misinterprets the pain signals from the viscera as pain signals coming from a muscle/skin (e.g. pain from the heart could be received as though it were coming from the skin/muscle)
What is the convergent theory?
Afferent signals from the viscera converge with the somatosensory system.
What is mechanical back pain?
- Where the source of the back pain is the vertebrae/soft tissues.
- There shouldn’t be any neurological features (i.e. parasthesia)
What is radiculopathy?
- Unilateral pain produced by the pinching of a nerve root in the spinal column.
What is the most common cause of radiculopathy?
Age-related degeneration of the foramina
What is Cauda Equina Syndrome?
The impinging of the nerves at the end of the spinal cord
What are the (red flag) symptoms of Cauda Equina Syndrome?
- sudden onset usually
- Bilateral neurogenic sciatica
- Altered bladder function (urinary retention)
- Reduced perineal sensation (saddle numbness)
- Sexual dysfunction
- Bowel dysfunction
- Laxity of the anal sphincter
- Severe bilateral neurological deficit of the legs
What is the most common cause of this syndrome?
Compression arising from lumbar disc herniation at L4/L5 or L5/S1 regions.
Why do herniations usually occur at that level?
This area is taking the largest load-bearing effort.
How does Cauda Equina syndrome affect the micturition reflex?
- Cauda Equina generally takes place at L4/L5 level.
- The sympathetic innervation (T1-L2) is NOT going to be affected by the compression (above L4/5).
- The parasympathetic innervation will be affected because parasympathetic nerves are found in the sacral region. These nerves innervate the bladder and help you pee. If they become compressed/damaged, the bladder can’t empty.
What is the function of the sympathetic nerves in the bladder?
Promote…
- detrusor relaxation
- internal sphincter contraction
This stops you peeing.
What is the function of the parasympathetic nerves in the bladder?
Promote…
- detrusor contraction
- internal sphincter relaxation (inhibit Sympathetic NS)
This allows you to pee.
The somatic NS controls contraction/relaxation of the external sphincter.
Why is bowel dysfunction a red flag symptom?
Autonomic nerves innervate the bowels but if the parasympathetic nerves are compressed, they can’t carry out their function.
