The Central Nervous System-2

Major Parts of the Brain

Brain Stem:

The area between the spinal cord and diencephalon is known as the brain stem. The mid brain, the pons, and the medulla oblongata make up this structure. The medulla oblongata is located near the base of the brain stem. The pons is located directly above the medulla, and the midbrain is located above that. The brain stem's three sections all serve as two-way conduction pathways. Motor fibers conduct impulses down from the brain to the cord, while sensory fibers conduct impulses up from the cord to various areas of the brain.

Functions of the Brain Stem:

• It is in charge of the automatic actions.
• Gives fiber tracts a means to travel between higher and lower brain areas.

Medulla Oblongata:

The expanded inferior portion of the brain stem is known as the medulla oblongata. It starts at the foramen magnum, a sizable opening in the occipital bone, and continues to the pons' inferior boundary.

Large corticospinal tracts or fibers that descend from the cortex produce the two pyramid-shaped structures that make up the medulla. Before entering the spinal cord, these fibers make a switch to the other side. Each side of the brain controls the movements on the opposite side of the body because of this point of intersection, known as the decussation of pyramids.

The medulla houses the vital centers, also known as the cardiac, respiratory, and vasomotor centers. The cardiovascular center controls the heart's pace, force, and blood vessel diameter. To control the pace and depth of breathing, the respiratory center collaborates with other regions of the brain. The medulla still has other centers that regulate processes including swallowing, hiccoughing, vomiting, and sneezing. The medulla also houses the nuclei of the cranial nerves VIII, IX, X, XI, and XII.

Functions of the Medulla Oblongata:

• It regulates the essential bodily processes.
• The cardiovascular center controls both the blood vessel and heart size.
• The respiratory center controls how quickly and deeply we breathe.
• The medulla is also in charge of controlling hiccoughing, sneezing, vomiting, and swallowing.
• Fiber tracts can travel through it and then descend into the spinal cord.

Pons

The word "pons" is Latin for "bridge." It is the area that connects the medulla to the midbrain. It is located beneath the midbrain and above the medulla. It is situated behind the pituitary gland and ahead of the cerebellum in the sagittal plane. Two respiratory centers, the pneumotaxic region and the apneustic area, which aid in controlling breathing, are also found in the pons. There are also nuclei for cranial nerves V through VIII in the pons.

There are several fibers that travel through the pons and transport impulses from the cerebrum to the cerebellum.

The coordination of free motions depends on these fibers.

Functions of the Pons:

• The respiratory center and the medulla oblongata control how quickly and deeply we breathe.
• It offers a two-way conduction conduit between various brain regions and various bodily parts.

Midbrain:

The midbrain is situated inferior to the pons and superior to the diencephalon. Two bundles of fibers, known as cerebral peduncles, are located on the inferior surface of the midbrain and transmit sensory and motor impulses from the spinal cord to the thalamus as well as motor impulses from the cerebral cortex to the pons.

The midbrain also houses the nuclei of cranial nerves III and IV, which regulate eye movement. The substantia nigra and red nucleus, two more significant nuclei that are involved in motor processes, are also found in the midbrain.

Functions of the Midbrain:

• It links the cerebrum to the pons and the cerebellum.
  It serves as a bidirectional conduction route that relays both auditory and visual impulses.

Diencephalon

Between the cerebrum and the midbrain, on the inferior side of the brain, is a tiny but significant region known as the diencephalon. It is split into two sections:

• Sub-thalamus (ventral thalamus) and hypothalamus make up the ventral part, or pars ventralis.
• The thalamus (dorsal thalamus), the metathalamus, and the epithalamus make up the dorsal part, or pars dorsalis.

Pineal body, Habenular nuclei, medial and lateral nuclei are among the epithalamic structures. stria habenularis (stria medullaris thalami) and posterior commissure of the habenula.

Thalamus:

The thalamus, which resembles a dumbbell, is located just above the hypothalamus. The third ventricle is directly lateral to it. It is mostly made up of gray matter since it is filled with a wide variety of neurons. Up to 80% of the diencephalon is made up of it. The dendrites and cell bodies of neurons with axons reaching up to the sensory regions of the cerebrum make up the majority of the thalamus.

Functions of the Thalamus:

• It aids in the creation of touch, temperature, and pain sensations. Its neurons transmit impulses from the body's sensory organ to the cerebral cortex.
• It links emotions and sensations. Almost all sensations are accompanied by an unpleasant or pleasant feeling to some extent.
• It contributes to the alerting or arousal process.
• It comprises crucial nuclei like the medial and lateral geniculates, which are in charge of the auditory and visual senses, respectively.
• The thalamus works as a hub for the fusion of motor processes thanks to its connections with the cerebellum and basal ganglia.

Hypothalamus:

As its name suggests, the hypothalamus is situated beneath the thalamus. The infundibulum, a stalk of hypothalamic tissue, serves as the direct connection between the hypothalamus and the posterior portion of the pituitary. This link enables the hypothalamus to affect pituitary gland operations. Because it has such a strong influence over almost all internal organs, the hypothalamus might be referred to as the center for the maintenance of homeostasis.

Functions of the Hypothalamus:

• Control of the autonomic nervous system:
  • In this capacity, it controls the heart rate, blood pressure, breathing rate, digestive tract motility, eye pupil size, and other visceral functions.
• Body temperature regulation:
  • The hypothalamus makes adjustments that return the body temperature to normal as it rises or falls.
• Food intake control:
  • It controls food intake in response to fluctuating blood levels of the hormones insulin and glucose.
• Controlling thirst:
  • As blood osmotic pressure rises, the hypothalamus is stimulated, which results in a thirst sensation and a desire to drink fluids.
• Sleep-wake cycle regulation:
  • It adjusts the time in response to daylight and darkness and controls the sleeping and waking cycle.
• Controlling emotional reactions and behavior:
  • It participates in the sense of pleasure, fear, fury, pain, aggression, and sexual arousal along with the limbic system.
• Control of endocrine system activities:
  • It regulates the anterior pituitary gland's hormone releases. Additionally, it makes the antidiuretic hormone and oxytocin, which are then transported to the posterior pituitary gland and released there.