Spinal pathways Flashcards by Hugh Murray

Which mechanoreceptors are high density?

Merkel and Meissner

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What do the mechanosensory neurons do at the caudate medulla?

They synapse with the gracile and cuneate nuclei and the their axons crosses over

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What is the main role of golgi tendon organs?

Sense tension/force in muscle

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What type of signal, excitatory or inhibitory, do interneurons generally produce?

Inhibitory

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Which subregion of the primary somatosensory cortex receives the most from the ventrio-posterio-lateral thalamus?

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What are muscle spindles found?

Amongst muscle fibres

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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

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What is anaesthesia

No innervation

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Which nuclei does mechanosensory information from the upper body travel to?

The cuneate

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Why is the vertebral column longer than the spinal cord?

The vertebral column extends faster than the spinal cord

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What is a motor neuron pool?

All the neurons that innervate a whole muscle

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Which mechanoreceptors are low density?

Ruffini and Pacinian

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Where do the gracile and cuneate nuclei send their axons to?

The ventero-posterio-lateral nucleus of the thalamus

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Where is information from the primary somatosensory cortex sent to?

The secondary somatosensory cortex mainly but also parietal areas 5 and 7

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What is the function of muscle spindles?

Modified muscle fibres that are surrounded by sensory nerves - to detect stretch in muscle

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Having more receptor fields allows for what?

The ability to distinguish finer details

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Which side of the spinal cord do axons for nociception travel?

Opposite to the side of the receptor

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Where is the primary somatic sensory cortex located?

Postcentral gyrus

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What is dysaesthesia?

Abnormal, unpleasant sensation

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What is a motor unit?

A neuron and the muscle fibres it innervates

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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)

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What is hypoesthesia?

Reduced sense of touch

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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

1. Tapping the tendon causes stretch of the muscle which is detected by the muscle spindle. 2. An action potential is sent up to the motor neuron for the corresponding muscle, producing an excitatory signal. 3. The same AP synapses with a interneuron that sends an inhibitory signal to the antagonistic muscle of that pair. 4. 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