I\'m having a hard time putting all the concepts I learned in Physiology togethe

Question

I'm having a hard time putting all the concepts I learned in Physiology together with this question:

Describe the series of events that occur in response to deep pressure on the skin. Start with the events that activate the Pacinian corpuscle and stop with the first synapse in the dorsal horn of the spinal cord. Include all the events that occur from producing the receptor potential, producing and action potential, conduction to the axon terminal, neurotransmitter release, and effect on the post synaptic cell. Describe the ion channels involved and use proper terminology. You can use one of the primary sensory neurons in the figure below as a guide and assume the neurotransmitter is norepinephrine acting on alpha 1 and alpha 2 receptors.

Explanation / Answer

13. Pacinian corpuscles or lamellated corpuscles (Cutaneous receptors of the skin (exteroceptors)) are located deep in the dermis, and they respond to the deep pressure stimulus.

In the cross section of the spinal cord, the interior butterfly shaped or H shaped region represents the grey matter. The grey matter divides the white matter into anterior, posterior and lateral columns. The H- shaped grey matter contains anterior (ventral) and posterior (dorsal) horns. The anterior horn cells are concerned with motor functions. Anterior root of spinal nerves arise from the anterior horn. The posterior horn cells are sensory in function. The posterior root of spinal nerves enters the spinal cord through the posterior horns. The posterior root contains a ganglion called as “dorsal root ganglion,” an enlarged area that contains cell bodies the sensory neurons.

When any form of impulse strikes the nerve cell, it causes change in membrane potential by changing the ion permeability across the membrane. If the membrane potential reach threshold potential (the minimum potential difference to elicit a response), then the action potential is generated.

Electrophysiological events of nerve impulse conduction:

Depolarization: It is the influx of sodium ions, and the membrane potential moves towards positive side, when the membrane potential becomes more positive inside i.e., approximately, +35 to +45mV, the process of depolarisation stops by the closure of sodium channels. This phase is followed by repolarisation.

Repolarization: It is the efflux of potassium ions, and the membrane potential moves to the negative side. When it reaches normal resting membrane potential, the cell enters into the resting stage.

Refractory period: During refractory period, the nerve fibre does not respond to the stimuli because the sodium channels are in closed state (depolarisation ends by the closure of sodium channels, without depolarization, the impulse cannot be transmitted). Irrespective of the intensity of the stimulus, the nerve do not accept any impulses, this period is called as absolute refractory period (the period from the peak of depolarization to the point of reaching resting membrane potential).

When the action potential reaches the axon terminal, depolarization of the membrane causes opening of “voltage gated calcium channels.” Then the high concentrations of intracellular calcium causes synaptic vesicles to fuse with the membrane and releases neurotransmitters by a process called exocytosis, which diffuses through the synaptic cleft, and act on the post synaptic neuron’s receptors.

If the released neurotransmitter is excitatory and causes depolarization of post synaptic membrane, then EPSP (excitatory post synaptic potential) is generated. Or if, the released neurotransmitter is inhibitory and causes hyperpolarisation of post synaptic membrane, then IPSP (inhibitory post synaptic potential) is generated. Eg: Release of adrenalne causes excitatory post synaptic potential. Adrenaline acts on alpha and beta adrenergic receptors.

Primary sensory neurons carry the information towards the dorsal horn of spinal cord via secondary seonsory neurons, where the receival of sensory stimulus occurs.

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