Understanding Genetic Mutations and the Nervous System
Genetic Mutations
In genetics and biology, a mutation is an alteration or change in the genetic information (genotype) of a living organism. This change occurs suddenly and spontaneously, and can be transmitted to offspring. The gene, the unit of hereditary information, is capable of mutating.
Types of Mutations
Somatic Mutations
A somatic mutation affects the individual’s somatic cells, resulting in a mosaic individual with two different cell lines and genotypes. Once a cell mutates, all cells derived from it by mitotic divisions inherit the mutation (cell inheritance). The earlier the mutation occurs in development, the greater the proportion of affected cells. For instance, if a mutation occurs after the first zygote division, half of the adult individual’s cells will have one genotype and the other half another. Somatic mutations are not transmitted to the next generation.
Germ Line Mutations
Germ line mutations affect the cells that produce gametes. These mutations are passed on to the next generation and have significant evolutionary implications.
The Nervous System
The nervous system is divided into the central nervous system (CNS), the peripheral nervous system (PNS), and the autonomic nervous system (ANS).
The Central Nervous System (CNS)
The CNS consists of the brain and spinal cord.
The Brain
The brain, encased within the skull and protected by three membranes called meninges (dura, pia, and arachnoid), is composed of the cerebrum, cerebellum, and medulla oblongata.
The Cerebrum
The cerebrum, the largest part of the brain, consists of gray matter (outside) and white matter (inside). Its surface has wrinkles called convolutions and grooves called fissures (the most notable being the Sylvian and Rolando fissures). A cleft divides the cerebrum into two cerebral hemispheres, each containing lobes named after the bones they contact. Weighing about 1200 grams, the cerebrum controls and regulates other nerve centers, receives sensations, and forms conscious responses. It also governs intellectual faculties like attention and memory.
The Cerebellum
Located behind the cerebrum, the smaller cerebellum (120 grams) resembles a butterfly with spread wings. It consists of two cerebellar hemispheres and a vermiform body. Gray matter covers the outside, while white matter forms a tree-like structure inside called the ‘tree of life’. The cerebellum coordinates muscle movements during activities like walking.
The Medulla Oblongata
The medulla oblongata, a continuation of the spinal cord that thickens as it enters the skull, regulates heart and respiratory muscle function, as well as chewing, coughing, sneezing, and vomiting. Injury to the medulla oblongata can cause instant death due to cardio-respiratory arrest.
The Spinal Cord
The spinal cord, a white, cylindrical nerve column within the vertebral column, transmits nerve impulses between the brain and the rest of the body.
The Peripheral Nervous System (PNS)
The PNS is subdivided into the somatic and autonomic nervous systems.
The Somatic Nervous System
The somatic nervous system controls voluntary bodily functions. Spinal nerves send sensory information (touch, pain) from the trunk and extremities to the CNS and receive motor commands from the spinal cord to control skeletal muscle. There are 31 pairs of spinal nerves, each with a sensory and motor root. Cranial nerves send sensory information from the neck and head to the CNS and receive motor commands for the skeletal muscles of the neck and head. There are 12 pairs of cranial nerves.
The Autonomic Nervous System (ANS)
The ANS regulates involuntary bodily functions, controlling smooth muscle, the heart, intestines, and glands. It has two branches:
- Sympathetic Nervous System: Involved in activities requiring energy expenditure.
- Parasympathetic Nervous System: Responsible for storing and conserving energy, and gastric motility.
- Enteric Nervous System: Regulates gastrointestinal activity and coordinates the peristaltic reflex.
The ANS is composed of roots, plexuses, and nerve trunks.