Changes

==Mechanism of seasonality==

==Mechanism of seasonality==

During the day lights levels are detected by the [[Special_Senses_-_Visual_-_Anatomy_%26_Physiology#Optics|retina]] which sends impulses to the [[Hypothalamus_-_Anatomy_%26_Physiology#Nuclei|suprachiasmatic nucleus]] of the [[Hypothalamus_-_Anatomy_%26_Physiology|hypothalamus]] and then to the superior cervical ganglion. Postganglionic nerve fibres synapse with inhibitory nerve fibres within the pineal gland. These fibres cause inhibition of the pinealocyte cells of the [[Pineal_Gland_-_Anatomy_%26_Physiology|pineal gland]] preventing synthesis of the hormone [[Endocrine System - Melatonin - Anatomy & Physiology|melatonin]]. At night there is reduced retinal firing and so reduced inhibition of pinealocytes by postganglionic superior cervical gangion fibres and so melatonin is synthesised and released. Melatonin stimulates the synthesis and release of GnRH from the hypothalamus leading to pulses of luteinising hormone release from the [[Pituitary_Gland_-_Anatomy_%26_Physiology|pituitary gland]]. High frequency, low amplitude LH pulses lead to breeding activity. Where as low frequency, high amplitude LH pulses lead to anoestrus and inactive gonads.

During the day lights levels are detected by the [[Eye - Anatomy & Physiology#Optics|retina]] which sends impulses to the [[Hypothalamus_-_Anatomy_%26_Physiology#Nuclei|suprachiasmatic nucleus]] of the [[Hypothalamus_-_Anatomy_%26_Physiology|hypothalamus]] and then to the superior cervical ganglion. Postganglionic nerve fibres synapse with inhibitory nerve fibres within the pineal gland. These fibres cause inhibition of the pinealocyte cells of the [[Pineal_Gland_-_Anatomy_%26_Physiology|pineal gland]] preventing synthesis of the hormone [[Endocrine System - Melatonin - Anatomy & Physiology|melatonin]]. At night there is reduced retinal firing and so reduced inhibition of pinealocytes by postganglionic superior cervical gangion fibres and so melatonin is synthesised and released. Melatonin stimulates the synthesis and release of GnRH from the hypothalamus leading to pulses of luteinising hormone release from the [[Pituitary_Gland_-_Anatomy_%26_Physiology|pituitary gland]]. High frequency, low amplitude LH pulses lead to breeding activity. Where as low frequency, high amplitude LH pulses lead to anoestrus and inactive gonads.

==Long day breeders==

==Long day breeders==