Structure and function of the nervous system - 2

Question 1

Frontal Lobe

Answer 1

• Includes all the cortex anterior to the central sulcus
• This region is especially large in humans, relative to other animals, and is reponsible for our unique ability to plan, reason and reflect on our own behaviours [Phineas Gage and frontal leucotomy psychiatric patients]

Question 2

Parietal Lobe

Answer 2

• Includes cortex located behind the central sulcus, caudal to the frontal lobe and dorsal to the temporal lobe.
• In left hemisphere, this region plays a special role in aspects of language comprehension and mental arithmetic; in the right hemisphere it is involved in representing the locations of salient (most noticeable or important) objects in space

Question 3

Temporal Lobe

Answer 3

• Includes cortex located ventral to the frontal and parietal lobes
• In the left hemisphere, this region plays a role in understanding the spoken and written word
• In the right hemisphere, it may be particularly involved in recognising complex objects and faes

Question 4

Occipital Lobe

Answer 4

• Includes the cortex at the back of the brain, caudal to the parietal and temporal lobes.
• Cortex in this area processes various aspects of visual information, such as motion, colour, shape and so on

Question 5

Cerebral Hemispheres

Answer 5

• Although the two cerebral hemispheres appear symmetrical anatomically, many functions are lateralised to just one hemisphere
• It has been suggested that cognitive and perceptual processing in the left hemisphere is piecemeal, analytic and serial
• Hence, it is argued that the left hemisphere is particularly efficient at extracting the parts that make a whole
• Consistent with the observation that the left hemisphere controls many aspects of language including talking, comprehension of speech, reading and writing. Damage to the left hemisphere typically impairs these abilities.
• It has been proposed that the right hemisphere is specialised for the synthesis of information i.e. putting together parts into wholes
• Consistent with the data that the right hemisphere damage can cause problems in constructing objects or drawing from pieces (e.g. completing a jigsaw puzzle)

Question 6

Corpus Callosum

Answer 6

• Although the two cerebral hemisphers perform different functions, our perception, memeory and thinking processes are unified
• This is made possible by a large bundle of axons that connects cortical areas of the two cerebral hemispheres, known as the corpus callosum. The corpus callosum contains about 200 million axons
• Some axons of the corpus callosum connect corresponding regions of cortex in the two hemisphers (homotopic fibres)
• Others connect different cortical regions of the two hemispheres (heterotopic fibres)
• Others connect adjacent regions within the same hemisphere (ipsilateral fibres)
• Patients with intractable epilepsy may have their corpus callosum surgically cut (callosotomy) to prevent abnormal electrical activity spreading from one hemisphere to the other. In such cases the two hemispheres essentially operate in isolation, with interesting consequences for behaviour

Question 7

Limbic system

Answer 7

• Buried inside the medial portion of each hemisphere resides a set of structures known collectively as the limbic system. The functions of this system were originally detailed by neuroanatomist Papez (1937). He suggested that the limbic structures formed a circuit whose primary functions are motivation and emotion
• The most important parts of the limbic system are the hippocampus (‘seahorse’) and the amygdala (‘almond’), which are lcoated adjacent to the lateral ventricle of each temporal lobe. A bundle of axons called the fronix connects these structures with other regions of the brain, most notably the mammillary bodies, two little nodules at the base of the brain that form part of the hypothalamus. A region of the cerebral cortex that lies above the corpus, known as the cingulate cortex, is also considered part of the limbic system. This part of the limbic system controls many functions, one of which is the emotional response to pain.
• Recent research has shown that the hippocampus and parts of the cortex that surround it are in fact involved in learning and memory rather than emotional behaviour. One of the most classic demonstrations of the role of the hippocampus and surrounding cortex in learning and memory comes from a neuropsychological patient with the initials H.M.. He had these structures removed for the relief of epileptic seizures, in an operation called a temporal lobectorm. After the surgery, H.M’s seizures improved but he was left densely amnesic, unable to learn or remember new facts (though he still recalled most of his life’s events up until around the time of his surgery). H.M’s problems were (and continue to be) specific to new learning and long-term memory. His intelligence is normal, as is his ability to perceive and to use and understand language.
• The amygdala, howeveer, is known to play a crucial role in mediating emotions

Question 8

Basal Ganglia

Answer 8

• The basal ganglia (the word ganglion means ‘a swelling’) are a collection of nuclei buried deep within each hemisphere
• They contain the cell bodies of collections of neurons and thus are classified as grey matter even though they are not part of the cerebral cortex
• The principal nuclei comprising the basal ganglia are the caudate nucleus (‘nucleus with a tail’), the putamen (‘shell’) and the globus pallidus (‘pale globe’)
• Together, the nuclei of the basal ganglia are responsible for controlling movement, particular those aspects that are highly automised or involuntary (such as walking)
• The basal ganglia are dysfunctional in patients with Parkinson’s disease, because of the degeneration of neurons in part of the midbrain that send their axons to the basal ganglia
• Parkinson’s disease is characterised by weakness, tremors, limb rigidity, poor balance and difficulty initiating movements

Question 9

Diencephalon (thalamus & hypothalamus)

Answer 9

• The second major division of the forebrain is the diencephalon. It surrounds the third ventricle, in the middle of the brain, and consists of two major parts:

1. Thalamus: (‘inner chamber’) forms the dorsal part of the diencephalon. It is a major relay station for sensory information being conveyed to the cerebral cortex. It is divided into several smaller nuclei, each with a specific function. For example, the lateral geniculate nucleus receives information from the retina of the eye and sends axons to the primary visual cortex, whereas the medial geniculate nucleus receives information from the inner ears and sends axons to the primary auditory cortex
2. Hypothalamus: (‘under the thalamus’), sits underneath the thalamus. It controls the ANS and the endocrine system; it also regulates behaviour necessary for survival, such as fighting, feeding, fleeing and mating. It is composed of several nuclei, each with its own specialised function

Question 10

Mesencephalon (tectum & tegmentun)

Answer 10

• The midbrain (mesencephalon) is located towards the base of the brain, and is anatomically the junction between the cerebrum and the spinal cord
• The dorsal part of the midbrain is called the tectum (‘roof’). It consists of the superior and inferior colliculi (singular: colliculus), which look like four little bumps on top of the brain stem