Question

Describe the mode of transmission of neural impulses involved with the sensations of pain, vision, and hearing

Answer 1

Neural Impulses: A neural impulse is a spike of electric charge or signal that travels along with a nerve fiber in response to a stimulus a transmit a record of sensation from the target site to an effector cell.. the electric signal generated by a different type of chemical signals from nearby cells.

Mode of transmission of neural impulses: Sensation of Pain:

Pain has been considered as a sensation that can be felt by the body by surrounding.

Receptors of pain sensation are the free nerve endings present in each part of the body.

Order of Neurons: From skin and deeper structures

First order neuron: These are the cells in posterior nerve root ganglia and get impulses of pain sensation through their dendrites. Then it transmitted to spinal cord by axons of these neurons.

Pain Fibers: Two types a. Fast pain fibers b. Slow pain fibers.

a. Fast pain fibers: A Delta type afferent fibers which synapse with neurons of the marginal nucleus in the posterior gray horn.

b. Slow pain fibers: C type afferent fibers, It synapse with neurons of Substantia gelatinosa of rolando in the posterior gray horn.

Second-Order Neuron: Neurons from the Marginal nucleus and substantial gelatinosa of rolando from the second-order neurons.

Now fibers from these neurons ascend in the form of the spinothalamic tract (Lateral form).

Fast pain fibers: fibers arise from marginal nucleus then cross the midline via anterior gray commissure. after that they reach the lateral white column of the opposite side and ascend.

These fibers come from neospinothalmic fibers in lateral spinothalamic tract and terminate in the ventral posterolateral nucleus of the thalamus. some terminate in the ascending reticular activating system of the brainstem.

Slow Pain fibers: fibers origin is substantial gelatinosa then cross the midline and run along the fibers of fast pain as paleospinothalamic fibers in the lateral spinothalamic tract.

some (ONE FIFTH) fibers terminate in the ventral posterolateral nucleus of the thalamus.

And the remaining one terminates in different area which is mentioned below:

1.Nuclei of the reticular formation in the brain.

2.tectum of the midbrain.

3.Adueduct of sylvius (Gray matter portion surround it).

Third Order Neurons:

neurons of third order in pain pathways are:

1.thalamic nucleus

2.Reticular formation

C. Tectum.

4.Adueduct of Sylvius gray part only.

Axons from these neurons meet the sensory area of the cerebral cortex. some reach the hypothalamus.

Center for pain sensation: Postcentral gyrus of parietal cortex.

Pain sensation from face: Carried by the trigeminal nerve.

Pain sensation from Viscera: Sympathetic (THORACOLUMBAR) nerves- thoracic and abdominal viscera.

Pain from the esophagus, pharynx, trachea is carried by the vagus and glossopharyngeal nerves.

Pain from Pelvic region: Sacral parasympathetic nerves.

Neurotransmitters involved in pain sensation: Glutamate and Substance P, which are secreted by pain nerve ending.

Neuron Fibers:A Delta afferent fibers- Fast Pain-Glutamate.

Neuron Fibers: C type fibers- slow pain- substance P.

Neuron system with the sensation of vision:

The visual pathway or optic pathway: Neurons transmits impulses from the retina visual center in the cerebral cortex.

Visual receptors: Rods and Cons.

First-order neurons: Bipolar cells in the retina.

axons from the bipolar cells synapse with dendrites of ganglionic cells.

Second-order neurons; Ganglionic cells (retina)

Third Order Neurons: Occurs in the lateral geniculate body. then it reaches in the visual cortex.

Visual pathway:

Receptors in the retina (Visual receptors)------first-order neurons(Bipolar cells in inner nuclear layer-----second-order neurons(Ganglionic cells------optic nerve-------optic chiasma-------optic tract-------third-order neurons(Lateral geniculate body-----optic radiation and finally in VISUAL CORTEX.

Neuron system with the sensation of Hearing:

fibers from the ear auditory pathway pass through the Cochlear division of the Vestibulocochlear nerve that is the VIII cranial nerve.

Another name: auditory nerve.

Major Pathway: major pathways of auditory lies in the medulla oblongata, midbrain, and thalamic region.

HIGHER CENTER OF HEARING: Temporal lobe of the cerebral cortex.

Receptors: Hair cells in organ of Corti.

First-order neurons: Bipolar cells of the spiral ganglion(present in modiolus of cochlea.

Dendrites of the hair cells are distributed as afferent fibers in the organ of Corti then enter cochlear nerve fibers and enter medulla oblongata. Here, it divided into two groups: Which end on the ventral cochlear nucleus and the dorsal cochlear nucleus of the similar side of medulla oblongata.

Efferent nerve-fibers of hair cells come from superior olivary nucleus.

Second-order neurons: Neurons of dorsal and ventral cochlear nuclei in the medulla oblongata:

Axons of this order run in four different groups:

a. The first group crosses the midline and run to the opposite side and make TRAPEZOIDS BODY. The fibers from this body go to the superior olivary nucleus.

b.This group terminates: at superior olivary nucleus from the same trapezoids body.

c.The third group of fibers: It runs in lateral lemniscus of the same side, and termination in the nucleus of lateral lemniscus of the same side.

d.Form reticular, cross the midline as intermediate trapezoid fibers.

and finally, join the nucleus of the lateral lemniscus of the opposite side.

Third-order neurons; Superior olivary nuclei and nucleus of the lateral lemniscus.

Ending: in the medial geniculate body, forms subcortical auditory center.

The fibers of auditory radiation help in the reflex movement of the head, and in response to auditory stimuli.

Cortical Auditory Center: Temporal lobe of the cerebral cortex.

Thanks and God Bless You.