Question

Trace the sensory pathway from the receptors of the skin to the sensory area of the cerebrum.

Trace the motor pathway from the motor area of the cerebrum to the muscles.

Please type answers, I'm awful at reading others handwriting.

Answer 1

Sensory Pathway-

1-Sensory Receptors in skin such as Pacinian corpuscles, meissner's corpuscles, free nerve endings get stimulated.

2-The stimulus are carried by the afferent nerves and they reach the dorsal root gangloin.

3-From dorsal root ganglion, First order neuron emerges and enter the dorsal horn of spinal cord. Pain and temperature fibres relay in substantia Gelatinosa. Proprioception First order neuron fibres enter in posterior column of spinal cord and carried as fasciculus gracilis and fasciculus cuneatus and relay high up in medulla oblongata in their respective nucleus.

4- From substantia gelatinosa a second order neuron emerges,ascends 2-3 segments and then crosses to opposite side and ascends upwards in spinal cord as spinothalamic Tract till they reach Thalamus. From medulla oblongata second order neuron emerges from nucleus gracilis and cuneatus, cross to opposite side , ascend up as medial lemniscus to reach Thalamus.

5- Thalamus is relay area for sensory fibres. From Thalamus, third order neuron emerges and reaches sensory cortex(area 3,1,2).

Motor Pathway.

1- From Motor cortex (area 4) , the fibres descends through internal capsule, then midbrain, then pons, then medulla.

2- In lower medulla, 85% of these fibres decussate ,that is cross to opposite side, 15% do not. Crossed fibres descend as lateral Corticospinal tract in spinal cord and uncrossed as Anterior corticospinal tracts in spinal cord. Eventually these fibres also cross and join crossed fibres ,that is 100% decussation acheived.

4- From spinal cord efferent nerves emerge and reach the muscles. The level from which they emerge depends on muscles they reach.