Tag: biology

Retina forms the innermost layer of eyeball and mainly contains rods and cones, the photoreceptors, along with nerve fibres. 

Brain cells remain in the beginning stage of interphase of cell reproduction for their life, and never divide, and instead develop by forming new synapses with other neurons. They lack cellular machinery for cell division. So, the correct answer is option A. 

Brain cells are extremely sensitive to a lack of oxygen. Some brain cells start dying less than 5 minutes after their oxygen supply disappears. As a result, brain hypoxia can rapidly cause severe brain damage or death. 

• The limbic system often referred to as the "emotional brain", is found buried within the cerebrum. 
• Like the cerebellum, evolutionarily the structure is rather old. This system contains the thalamus, hypothalamus, amygdala, and hippocampus. 

The cerebrum or cortex is the largest part of the human brain, associated with higher brain function such as thought and action. The cerebral cortex is divided into four sections, called "lobes". The frontal lobe, parietal lobe, occipital lobe, and temporal lobe. 

• Hippocampus is the portion of the cerebral hemispheres in basal medial part of the temporal lobe. 
• This part of the brain is important for learning and memory, for converting short term memory to more permanent memory and for recalling spatial relationships in the world about us. 

• Amygdala is a part of the telencephalon, located in the temporal lobe, involved in memory, emotion, and fear. 
• The amygdala is both large and just beneath the surface of the front, medial part of the temporal lobe where it causes the bulge on the surface called the uncus. 
• This is a component of the limbic system. 

• Pons is a part of the metencephalon in the hindbrain. It is involved in motor control and sensory analysis. 
• For example, information from the ear first enters the brain in the pons. It has parts that are important for the level of consciousness and for sleep. 
• Some structures within the pons are linked to the cerebellum, thus are involved in movement. 

The meninges are the layers that are closely present around the brain. The dura mater is an outermost tough and fibrous layer. It closely lines the cranium. It is followed by the arachnoid mater that forms the middle meninx. The piamater is the innermost meninx which adheres closely to the surface of the brain. It is highly vascular due to the rich supply of the blood vessels. So, it provides oxygen and nutrients to the cells of the brain.