Question

In a sheep brain, we see that the thalamus acts as a relay point for all sensory processing and noted the very large size of this structure.

A. Do you think there are differences between the sensory systems of the sheep and the human? For example, do humans and sheep use each sensory system the same amount, or are there certain senses that are more prominent in sheep or in humans?

B. How would this manifest anatomically?

C. write 2-3 sentences* describing:

(i) its location in the brain

(ii) its neurological relationship to nearby structures

(iii) any neurologic disorders associated with its dysfunction.

Answer 1

Ans .(A) The Sheep , like many mammals, has a more developed sense of smell, or olfaction, than humans do. The olfactory bulb is the part of the brain located underneath the frontal lobe that is responsible for relaying sensory information from nose to the rest of the brain.

The olfactory bulb in sheep is two to three times the size of human olfactory bulb, despite the sheep brain being much smaller overall. This reflects the importance of sense of smell to the sheep. In addition to helping it understand its surrounding and avoid danger, sense of smell also plays a crucial role in establishing the bond between mother and infant , known as imprinting.

The Optic chiasm is more pronounced in the sheep brain because sheep , like many prey animals, have eyes toward the sides of head that operate more independently , giving the sheep a much wider field of vision.Therefore most of the visual information from each eye crosses over. Humans have more frontal eyes, and share information from each eye more evenly between the brain hemispheres to enable complex visual processing tasks, such as depth perception.

Ans .(B) A sheep's brain is elongated in shape, whereas a human brain is rounded. The human brain stem is towards the backbone and downwards , because in the human body the backbone is vertical ; compared to a sheep's backbone which is horizontal, and its brain is directed outwards.

The optic chiasm is the part of the brain where optic nerves cross. The optic nerves of the left and the right eye meet in the body midline, ventral to the brain.

Ans .(C) (i) The optic chiasm is located at the bottom of the brain immediately inferior to the hypothalamus. It is located at the junction of anterior wall and floor of the hypothalamus.

The olfactory bulb lies on the ventral aspect of the frontal lobes.

Ans .(C) (ii) The optic chiasm lies immediately ventral to the suprachiasmatic nucleus and the third ventricle.

The accessory olfactory bulb resides on the dorsal- posterior region of main olfactory bulb and forms a parallel pathway.

Ans .(C) (iii) Chiasmal syndrome is the set of signs and symptoms that are associated with lesions of optic chiasm, manifesting as various impairments of the sufferer's visual field according to location of lesion along the optic nerve.

Noniatrogenic causes of olfactory nerve injury include diseases of nose and paranasal sinuses, recent upper respiratory tract infection , and head trauma.