Question

Starting with a Meissner’s corpuscle in the index finger (digit 2) trace the afferent pathway to the brain and then the efferent pathway to the flexor digitorum profundus muscle that enervates the flexion of the index finger. For the afferent pathway be sure to describe the peripheral afferent nerves and the spinal nerve plexus involved. Then describe the three afferent systems, the anterolateral system (ALS), the dorsal column-medial lemniscal pathway (DCML), and the somatosensory pathway to the cerebellum of the spinal cord. Which pathway carries the fine touch sensory information from Meissner’s corpuscles up the spinal cord? What is the major afferent processing center in the diencephalon? What is the final destination of the fine touch sensory information in the cerebral cortex? Is this fine touch sensation conscious or unconscious sensation? How does the brain respond to generate a motor or efferent response? For the efferent pathway start with the primary motor cortex in the precentral gyrus. For the efferent pathways be sure to describe the pyramidal and extrapyramidal efferent pathways. Which is involved in fine motor control? What plexus and arm nerve is involved in this motor control of the flexor digitorum profundus muscle? What role does the cerebellum play in the flexion or the index finger?

Answer 1

1) Meissner’s corpuscle in the index finger --> carries light touch stimulus via sensory nerve to dorsal root ganglion --->1st order neuron enters the spinal cord through dorsal root and synapse on second order neuron --> Second order neruon gives rie to axon that corosses to the opposite side ascends --> fasiculus cuneatus of dorsal coumn --> synapse with nuclus cuneatus in medulla oblongata --> axons of the seond order neurons called internal arcuate fibers corss -->Asent in medial lemniscus through medulla , pons and midbrain --> VPL (venteroposterolatral) nucleus of thalamus ---> third order neuron --> cerebral cortex.

2) Efferent pathway - it is via corticospinal tract ::: Cerebral cortex --> corticospinal tract --> internal capsuele -->  80% fibers cross & 20 % remains uncrossed at pyramid --> 80% fiber become latral corticospinal tract and innervate the distal muscle whiel the remaining 20 % continue in ipsilateral side as ventral corticospinal tract --> at the spinal leve synapse with interneuron -->crosses over and supply to proximal muscle.

3) Dorsal coulmn medial leminiscus sytem - Carreis fine touch, pressure, vibration, proprioception and two point Discrimination

AnterionSpinothalamic tract - Carries crude touch and pressure, sexual senstion,tickle and itch

Lateral spinothalamic tract - carreis pain and temprature.

Which pathway carries the fine touch sensory information from Meissner’s corpuscles up the spinal cord?

answer - Dorsal coulmn medial leminiscus system

What is the major afferent processing center in the diencephalon?

Answer - Thalamus

What is the final destination of the fine touch sensory information in the cerebral cortex?

answer - Somesthetic area in the post central gyrus of cerebral cortex

Is this fine touch sensation conscious or unconscious sensation?

It is a concious sensation

Which is involved in fine motor control?

Pyramidal pathway

What plexus and arm nerve is involved in this motor control of the flexor digitorum profundus muscle?

Brachial plexus

What role does the cerebellum play in the flexion or the index finger?

Co-ordination and sequencing of movement