Spinal Cord and Periphery Flashcards
Describe the cross-sectional anatomy of the spinal cord.
central ‘H-shaped’ grey matter and peripheral white matter- dorsal horn of grey matter= sensory fibres enter and ventral horn of grey matter= cell bodies of motor neurones which leave through ventral root
Describe the arrangement of white matter.
arranged in 3 columns= posterior, lateral and anterior - each column has bundles called tracts of axons, ascending tracts= sensory and descending tracts= motor, different tract carry different information
what are the ascending tracts?
they have spino- in the name and the ones need to know are lateral spinothalamic and dorsal/posterior column
what are the descending tracts?
end in spinal and the one need to know is corticospinal tract
what does the dorsal/posterior column carry?
carries touch, tactile localisation, vibration sense and proprioception
what is the pathway of the dorsal column?
found in the posterior white matter of the spinal cord- ascending tract which carries sensation from the periphery to the cerebral hemisphere- 1st order neurone ends by synapsing with the cell body of the 2nd neuron which is situated in the lower prt of the medulla - the 2nd order neurone decussated in the medulla and the tract is now called the medial lemniscus and passes through the brainstem to the thalamus - the 3rd of neuron starts from the thalamus and axons pass through the IC and radiate to the post-central gyrus
what does the lateral spinothalamic tract carry?
pain and temperature (noxious stimuli= dangerous stimuli so want to react more rapidly than other stimuli)
what is the pathway of the lateral spinothalamic tract?
1st order neurone enters into the grey matter and ends at the same level - the 2nd order neurones cross over torch the lateral column and is now called the lateral spinothalamic tract - the 2nd order neurone ends in the thalamus and the 3rd order neurone passes through the IC and radiates to the post-central gyrus
what does the corticospinal/pyramidal tract carry?
carries motor impulses form the motor cortex to skeletal muscles so control of voluntary skilled movements
what is the pathway of the corticospinal tract?
starts one the motor cortex (area 4) - form a radiating bundle and pass through the IC and the brainstem - some fibres leave the tract in the brainstem but most continue down and form the pyramids in the medulla and decussate in the lower part of the medulla so that they lie in the lateral column of the spinal cord and form the lateral corticospinal tract- the axon enters the grey matter and synapses triggering another neuron whose cell body is present in the ventral horn of the grey matter and passes out through the ventral root to the skeletal muscles
does all sensory information from the periphery need to be sent to the brain for decisions?
no, in certain circumstances where an immediate response is needed the spinal cord and other lower centres can take these decisions
what is a reflex?
an involuntary stereotypical pattern of response brought about by a sensory stimulus - many are mediated at the level of the spinal cord= spinal reflex and can be monosynaptic or polysynaptic
describe the stretch reflex.
knee-jerk reflex where the knee is bent and you hit just under the kneecap with a hammer and the leg will jerk forwards, when the hammer hits the tendon it is stretched which stretches some of the muscles fibres in the quads as well and triggers the intramural muscles fibres which are proprioceptors and carry sensory input of the muscles stretching back to the spinal cord via sensory neurones which triggers an effector neurone which causes the muscle to contract
describe the reciprocal innervation of the stretch reflex.
quadriceps are innervated by the femoral nerve (L2,3,4) from the lumbar plexus but some innervation passes down to the sacral section of the spinal cord and inhibits neurones innervating the hamstring muscles in order to relax them
what is the stretch reflex important for?
control of muscle tone and posture eg prevents falling on an uneven path
