c 17. Explain how the cascading effect of hormonal pathways amplifies the respon
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c 17. Explain how the cascading effect of hormonal pathways amplifies the response. 18. Compare the nervous and endocrine systems Solving Quantitative Exercises 1. Answer the following questions regarding conduction of action potentials using the velocities given on p. 100: r a. How long would it take for an action potential to travel 0.6 m along the axon of an unmyelinated neuron of the digestive tract? b. How long would it take for an action potential to travel the same distance along the axon of a large myelinated neuron innervating a skeletal muscle? c. Suppose there were two synapses in a 0.6 m nerve tract and the delay at each synapse is 1 msec. How long would it take an action potential and chemical signal to travel the 0.6 m now, for both the myelinated and unmyelinated neurons? d. What if there were five synapses? 2. Suppose point A is 1 m from point B. Compare the follow- i. A single axon spans the distance from A to B, and its ii. Three neurons span the distance from A to B, all three ing situations: conduction velocity is 60 m/sec. uolocity and the syn-Explanation / Answer
17] Cascading effect of hormones is characterised by a sequence of successive reactions which amplify the initial stimulus. A hormone cascade pathway is often the result of interactions between the hypothalamus, anterior pitiutary and the target endocrine gland This can be explained by the hormone cascade pathway on thyroid regulation.
Hypothalamus is the link between the nervous and the endocrine systems. The neurosecretory cells of hypothalamus are capable of converting neural signals into hormonal output. This is why they are also called neuroendocrine transductors.
* The stimulus activates the sensory neurons.
* The sensory neurons activate the neurosecretory cells of the hypothalamus.
* Hypothalamus secretes thyrotropin releasing hormone [TRH] into the blood stream.
* TRH stimulates the anterior pitiutary which in turn secretes thyroid stimulating hormone [TSH] or thyrotropin.
* TSH stimulates the thyroid gland to secrete thyroid hormone T3 and T4.
* When the level of thyroid hormone ,thyroxine, reaches the required level in the blood, a negative feedback is sent to the hypothalamus, which then stops secreting TRH.
* Lack of TRH in the blood signals the pitiutary to stop secreting TSH and in this way the secretion of thyroid hormone is regulated.
18] Difference between Nervous and Endocrine systems--
NERVOUS SYSTEM ENDOCRINE SYSTEM
1] Made up of the brain, spinal cord and 1] Made up of a set of ductless glands which
the nerve fibres. secrete chemicals called hormones.
2] It transmits signals via electical or chemical 2] Controls the activities of target cells or
impulse. organs by the hormones.
3] They are always quick acting 3] May be quick acting or acting with a lag
period.
4] They act through nerve fibers. 4] They send chemical messengers[hormones] through blood.
5] They act towards a specific direction 5] Hormones are released in blood from
i.e. effector organ or CNS. where are taken by specific receptor cell.
6] They are for quick reactions 6] They are for long term changes like
changes in body at the onset of puberty,
sustenance of pregnancy etc.
7] Their effect is for a short time. 7] Their effect is long lasting and maybe
for lifetime eg. secondary sexual
like reflexes. changes during puberty.
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