Question

In: Anatomy and Physiology

A needle is inserted into the right somatosensory nucleus of the thalamusin the central nervous system...

A needle is inserted into the right somatosensory nucleus of the thalamusin the central nervous system and the area is injected with GABA.

1. Through what structure does a primary sensory neuron from the hand enter the central nervous system?

2. Where does the first synapse for this somatosensory pathway occur?

3. Describe the type(s) of sensory information carried by this pathway.

4. Name and describe two different classes of primary sensory receptors that are associated with this pathway.

5. Discuss the common features that all primary sensory receptors possess.

6. If an adrenergic substance had been injected instead of GABA, how would this have altered neural transmission? Explain.

Solutions

Expert Solution

1. Primary sensory neuron from the hand enter the central nervous system through the dorsal nerve root of the spinal cord. the cell bodies that carry somatic sensations are present in the dorsal nerve root ganglion.

2. The first synapse for different somatic sensations occur at different levels

The lateral spinothalamic tract carries pain and temperature sensations; first synapse for this sensation occur at the posterior
horn cells in the region of substantia gelatinosa of spinal cord

The ventral /anterior spinothalamic tract carries light touch, pressure, tickle, and itch sensations; first synapse for this sensation occur at the posterior horn cells in the region of substantia gelatinosa of the spinal cord but about 8 to 10 spinal segments above or below the entered spinal segment.

Dorsal column medial lemniscal pathways carries conscious proprioception that is the sensations of proprioception, two-point discrimination as well as vibrations; first synapse for this sensation occur in the nucleus gracilis and nucleus cuneatus.

3. The type of sensation carried by this pathways are Touch both fine touch & crude touch, Temperature, Pain, Pressure, Tactile localization, Tactile discrimination, Vibratory sensation, Stereognosis (ability to identify an object by feeling/ touching it)

4. Receptors are sensory nerve endings that ends in peripheral organs as capsulated or non-encapsulated structures which when stimulated produce a series of impulses & are transmitted via afferent nerves to the central nervous system

Basically there are two types of receptors; Exteroceptors & Interoceptors

Exteroceptors

  • They are those receptors which give response to the stimulus arising from ouside of the body
  • Example: Cutaneous receptors/ Mechanoreceptors like Meisnner's corpuscle(Touch), Merkel disk(Touch), Pacinian Corpuscle(Pressure), Ruffini end organ (temperature) & free nerve endings(Pain)

Interoceptors

  • They are those receptors which give response to the stimulus arising from within the body
  • Example: Proprioceptors like Muscle spindle in the muscle, Golgi tendon organ in the tendon of muscles, etc..

5. The common features that all primary sensory receptors possess are

  1. Specificity of response is also known as also known as Muller's law. according to this for each type of response there is specific receptors, that means a temperature receptor will give response only to temperature not to any other response.
  2. Sensory Adaptation is defined as the decline in discharge of sensory impulses when a receptor is stimulated continuously with constant strength. that means the receptor will adapt to a certain stimuli if it is constant
  3. RESPONSE TO INCREASE IN STRENGTH OF STIMULUS :- During the stimulation of a receptor, if the response given by the receptor is to be doubled, the strength of stimulus must be increased many fold.
  4. SENSORY TRANSDUCTION :- Sensory transduction is the process by which the energy from the stimulus in the environment is converted into electrical impulses or action potentials in nerve fiber.
  5. RECEPTOR POTENTIAL :- it is the transmembrane potential difference that develops when a receptor is stimulated. It is also known as generator potential. it is is short lived.

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