Scenario (2) Reflexes Flashcards
Functions of spinal cord an spinal nerves
- White matter= sensory and motor tracts “highways” for conduction of sensory to the brain and motor from the brain
- Grey matter summing of EPSPs and IPSPs
- Spinal nerves and branches connect CNS to PNS
Reflex
Fast involuntary muscle contraction in response to a specific stimulus
> Inborn reflex: pulling hand away from something hot
> Learned/ Acquired reflex e.g emergency stop in driving
What is a spinal reflex
When integration takes place in the grey matter of spinal cord
E.g patellar reflex (knee jerk)
What is a cranial reflex
Integration occurs in the brain stem rather than spinal-cord
E.g tracking movements of your eyes when reading
What is a somatic reflex
Contraction of skeletal muscle
Autonomic (visceral) reflexes
Not consciously perceived
Responses of smooth+cardiac muscle and glands
E.g heart rate, digestion
Complete and incomplete spinal cord injuries
Permanent damage to the area of the spinal cord that is affected. Spinal cord fully severed
Paraplegia or tetraplegia are results of complete spinal cord injuries.
No Bladder and bowel control.
Partial damage to the spinal cord. The ability to move and the amount of feeling depends on the area of the spine injured and the severity of the injury. Some bladder control
2 types of intrafusal muscle fibres
Nunclear bag: annulospiral (primary) nerve ending - group 1a afferent nerve fibres. *Velocity speed and extent of change. Phasic rapid change, patellar tap.
Nuclearchain: flower spray (secondary) nerve endings- group la and II afferent. *change in muscle length. Tonic= posture and sustained. More sustained
Stimulus sent to CNS
Gamma motor neurones
Controls sensitivity of stretch receptors
Why are reflexes below the spinal lesion brisk
Alpha and motor neurones are under the influence of the descending pathways
Abnormal activity of descending pathways influences change in sensitivity of stretch reflexes
>tendon reflexes
>muscle tone
***Upper motor neurone damage: causes over activity of dynamic gamma neurones- tendon reflexes are hypersensitive
Working too well not getting info to say you don’t need to contract
Descending control isn’t working minimal inhibition a lot more forceful no control.
Problem CNS not controlling
Ascending and descending pathways
Spinal cord and cortex
Ascending: carries impulses from pain,thermal,tactile,muscle and joint receptors to the brain. Some reaches a conscious level in the cerebral cortex some goes to the subconscious centres cerebellum
Descending: originates from the cerebral cortex and brainstem. Control of movement,muscle tone, spinal reflexes. Control of voluntary controlled movements. How sensitive stretch reflex. Gamma neurone
Spinal injury bilateral+sensory loss
Second order neurones (pain) are damaged they decussate in the ventral white commissars close to central canal causes selective loss of sensation. Dissociated sensory loss
Cross spinal level or can cross in brain stem
Sensory impulses crosses at varying levels = bilateral
Abscent
Peripheral nerve injury most likely
Don’t know whether it’s motor or sensory
How is sensory info classed
Special senses ( cranial nerves) olfactory hearing etc
General senses (spinal nerves) touch pressure pain temperature
General sensation pathway
Sensory receptor at periphery and perception of sensation at cerebral cortex pathway
- First order primary neurone: enters spinal-cord through spinal nerve through trigeminal on same side of body as peripheral receptor
cell body = dorsal root ganglion of spinal nerve
Within CNS neurone remains on the same side as synapse
- Second order neurone: cell body in the spinal-cord exact location depends on modality concerned
Axon crosses over to the other side within CNS and ascends thalamus where is terminates
- Third order neurone: cell body in thalamus Axon projects into somatosensory cortex in postcentral gryus of parietal lobe of cerebral hemisphere
