Lesson 1.2: Central Nervous System

• Our brain is a very delicate organ. Even though it is protected by the skull, it is important that we keep both of them from injuries because the brain controls many functions—our body processes, thoughts, emotions, and actions.
• The brain cannot function well without the spinal cord. Together, they make up the central nervous system
• The brain and spinal cord form the largest part of the nervous system.
• The adult human brain weighs about 1.4 to 1.6 kilograms and is approximately the size of two fists joined together.
• The brain is the largest and most complex mass of nervous tissue in the body. Because of this, it is commonly discussed in terms of its four major regions — the cerebrum, diencephalon, brain stem, and cerebellum
• The cerebrum is the most superior part of the brain as it controls many functions, such as intelligence, emotions, learning, and critical thinking.
• It is divided into two equal halves called the cerebral hemispheres
• Cerebral Hemispheres

  • These hemispheres are separated by a single deep longitudinal fissure but are connected by a thick bundle of axons called the corpus callosum.
• The entire surface of the cerebral hemispheres exhibits elevated ridges called gyri and shallow fissures called sulci.
• Deeper sulci divide the cerebrum into four major lobes—the parietal, occipital, temporal, and frontal lobes
• Frontal lobe

  • Near the forehead
  • Memory, motivation, cognition, reasoning, voluntary movement of skeletal muscles
• Temporal lobe

  • Behind the ears
  • Hearing, smell
• Occipital lobe

  • The rear portion of the skull
  • Vision, color recognition
• Parietal lobe

  • Top of the cerebrum (behind the frontal lobe and in front of the occipital lobe)
  • Taste, touch, reading, temperature and pressure perception
• The cerebrum also contains two areas that are very important in our sensory perception and motor actions. They are the primary somatosensory and motor cortices
• The somatosensory cortex is located in the parietal lobe. All the impulses traveling from the body receptors are localized and interpreted in this area of the brain
• On the other hand, the motor cortex is located in the frontal lobe. It allows us to consciously move our skeletal muscles.
• The somatosensory cortex and motor cortex form the cerebral cortex
• The diencephalon, also called the interbrain, lies atop the brain stem and almost entirely surrounded by the cerebral hemispheres. Its major structures are the thalamus, epithalamus, and hypothalamus.
• The thalamus is a mass of nervous tissue that serves as a relay station for sensory impulses that pass through the sensory cortex. It processes these impulses and sends them to the cerebrum
• The epithalamus connects the part of the brain that controls emotions to other parts of the brain. It has the pineal gland that secretes melatonin, which helps in maintaining our sleep-wake patterns
• The hypothalamus plays a role in the regulation of body temperature, water balance, and metabolism. It is also the center for the control of emotions and pleasure. It also controls the pituitary gland by sending hormones to trigger the gland’s functions.
• The brainstem is the stalk-like lower portion of the brain at about the size of a thumb in diameter and approximately 3 inches long. It regulates the essential survival functions such as breathing and heartbeat. Its structures are the midbrain, pons, and medulla oblongata.
• The midbrain is a small part of the brain stem composed of two bulging fiber tracts that serve important functions in eye movements and in auditory and visual processing.
• The pons is the rounded structure protruding below the midbrain. It serves as a message station between the cortex and the cerebellum. Without the pons, messages in the brain would not be transmitted
• The medulla oblongata is the lowest portion of the brain stem. It is a control center for respiration and blood circulation. It helps in the regulation of breathing, heart and blood vessel functions, digestion, and even sneezing.
• The reticular formation is a diffuse mass of nuclei that extends in the entire length of the brainstem. Its neurons are involved in motor control of the visceral organs. It also performs many important functions including the regulation of sleep, the formation of sensory habits, and the control of our motor actions and pain. Damage to this area may result in permanent unconsciousness or coma.
• Behind the brainstem is the cauliflower-like structure of the brain called the cerebellum. It is the Latin word for “little brain.” This portion of the brain refines motor messages and coordinates our muscle movements subconsciously. It is because of the cerebellum that our body movements are smooth and well-coordinated.
• Enclosed within the bony armor of the vertebral column or backbone is the cylindrical spinal cord.
• The Spinal Cord

  • approximately 17-inch (42 cm) white neural tissue emerges from the base of the brain that extends along the back of the body and ends just below the ribs (lumbar vertebra).
• The Spinal Cord

  • From this point, a collection of spinal nerves called cauda equina extends toward the end of the vertebra. Its name literally translates to “horse’s tail” because of its hair-like structure.
• The spinal cord transmits information between the body and the brain. It is also the major center for our reflexes
• A reflex is a rapid, involuntary response to a stimulus without the need for integration in the brain.
• The spinal cord is divided into five sections based on their location in the vertebral column, namely cervical thoracic, lumbar, sacral, and coccygeal cord.
• The cervical cord is found at the base of the neck, followed by the thoracic cord located in the upper torso.
• The lumbar cord follows, which is found in the lower rib area. The sacral cord is located in the hip area, while the coccygeal cord is found at its terminal part. Each section is organized into 31 segments: 8 cervical, 12 thoracics, 5 lumbar, 5 sacral, and 1 coccygeal. Each segment is defined by 31 pairs of spinal nerves that run on both sides of the body.
• Like the brain, the spinal cord is a delicate neural tissue that needs to be protected. It is sheathed with layers of protective tissues called the meninges that keep the spinal cord from shock, dehydration, and injury. The meninges are composed of the dura, arachnoid, and pia mater.
• The dura mater is the most external of all the meningeal layers. It is tough and inflexible, giving it the responsibility of protecting the spinal cord from being displaced.
• Beneath the dura is the delicate membrane called the arachnoid mater, followed by the innermost meningeal layer called the pia mater.
• The two layers are separated by the subarachnoid space that contains the cerebrospinal fluid (CSF).