Spinal pathways Flashcards
Which mechanoreceptors are high density?
Merkel and Meissner
What do the mechanosensory neurons do at the caudate medulla?
They synapse with the gracile and cuneate nuclei and the their axons crosses over
What is the main role of golgi tendon organs?
Sense tension/force in muscle
What type of signal, excitatory or inhibitory, do interneurons generally produce?
Inhibitory
Which subregion of the primary somatosensory cortex receives the most from the ventrio-posterio-lateral thalamus?
3a
What are muscle spindles found?
Amongst muscle fibres
At what level must damage occur for a limb to exhibit upper motor neuron symptoms?
At any level above the motor neurons for that limb
What is anaesthesia
No innervation
Which nuclei does mechanosensory information from the upper body travel to?
The cuneate
Why is the vertebral column longer than the spinal cord?
The vertebral column extends faster than the spinal cord
What is a motor neuron pool?
All the neurons that innervate a whole muscle
Which mechanoreceptors are low density?
Ruffini and Pacinian
Where do the gracile and cuneate nuclei send their axons to?
The ventero-posterio-lateral nucleus of the thalamus
Where is information from the primary somatosensory cortex sent to?
The secondary somatosensory cortex mainly but also parietal areas 5 and 7
What is the function of muscle spindles?
Modified muscle fibres that are surrounded by sensory nerves - to detect stretch in muscle
Having more receptor fields allows for what?
The ability to distinguish finer details
Which side of the spinal cord do axons for nociception travel?
Opposite to the side of the receptor
Where is the primary somatic sensory cortex located?
Postcentral gyrus
What is dysaesthesia?
Abnormal, unpleasant sensation
What is a motor unit?
A neuron and the muscle fibres it innervates
What is the function of the monosynaptic stretch reflex?
To maintain posture/position in response to changing stimuli.
eg. a load is placed on an outstretched hand which causes a reflex contraction of the bicep to account for the load (and relaxation of the triceps)
What is hypoesthesia?
Reduced sense of touch
At what level does the mechanosensory axons cross over the spinal cord?
Caudal medulla
What is the function of the golgi tendon organ feedback mechanism?
Send negative feedback (via an interneuron) to reduce the force of a movement if there is too much
T/F Somatosensory axons have the fastest signal transduction?
False, they’re fast, but still second to muscle spindle axons of proprioception
What are propriospinal connections?
Interconnections that occur within the spinal cord
Somatosensory neurons give off more than one axon, what are they?
One that travels to the CNS
One that synapses in the spinal cord
What is the name of the structure that is a continuation of the spinal cord?
Cauda equina
What senses does the somatosensory system mediate?
Sense of touch
Proprioception
What are the four types of mechanoreceptors of the skin?
Meissner corpuscles
Merkel complexes
Ruffini organs
Pacinian corpuscles
What is the main difference between golgi tendon organs and muscle spindles?
GTOs are in tendons while muscle spindles are within muscles
Which one of these are in series with the muscle, golgi tendon organs or muscle spindles?
Golgi tendon organs
List the sequence of events that occur in a monosynaptic stretch reflex
- Tapping the tendon causes stretch of the muscle which is detected by the muscle spindle.
- An action potential is sent up to the motor neuron for the corresponding muscle, producing an excitatory signal.
- The same AP synapses with a interneuron that sends an inhibitory signal to the antagonistic muscle of that pair.
- The result is contraction of the primary muscle and relaxation of the antagonist.
Which glabrous mechanoreceptors are closest to the surface of the skin?
Meissner corpuscles
Merkel complexes
What happens to the area of innervation after repair of a damaged peripheral nerve?
Abnormal sensation.
Feeling will usually be conscious in the area the repaired nerve previously innervated despite it innervating a new area now.
What type of reflex does stimulation of nociceptor elicit?
Flexion retraction - to move the affected body part away from the source of pain
Where does the ventral lateral posterior nucleus of the thalamus send axons with mechanosensory information to?
The primary somatic sensory cortex
How are the four subregions of the primary somatic sensory cortex differentiated?
Histologically
By where they receive input from
Which mechanoreceptors are fast adapting?
Pacinian and Meissner
T/F mechanoreceptors are free nerve endings
False, they have complex connective tissue structures
How are action potentials initiated with mechanoreceptors?
Vibrations are transmitted into their membranes which mechanically opens Na channels
Which tract does mechanosensory information from the lower body travel up?
The gracile
Which mechanoreceptors are slow adapting?
Merkel and Ruffini
Where are the cell bodies of glabrous mechanoreceptors?
The dorsal root ganglion
At what level must damage occur for a limb to exhibit lower motor neuron symptoms?
At the level of the limbs motor neuron
Describe the appearance of Pacinian corpuscles
Onion layers of connective tissue
What happens to the somatotopic distribution for finger when one is removed?
The other move into its space
Which level of the spinal cord has more white matter?
Higher up - There are more sensory afferents and motor efferents at that point
Where is the secondary somatosensory cortex located relatively?
Posterior to the primary one
How do rapidly adapting mechanoreceptors differ from slowly adapting?
Rapidly adapting generally only respond to changing stimuli
What is hyperesthesia?
Increase sensation
What type of symptoms does myathensia gravis cause, upper or lower motor neuron?
Lower (despite the neurons being fine)
What happens to the other limb in a pair when one responds to the nociception reflex?
Contraction of the extensor muscles to provide stabilisation
What is the name of the non-hairy surfaces of the body?
Glabrous
T/F golgi tendon organs act directly on motor neurons
False, they act through interneurons
Which side of the spinal cord do axons for somatosensory neurons travel?
The same side as the receptor
