The Human Nervous System: Structure and Function
Central Nervous System
The central nervous system (CNS) is formed by the brain and spinal cord. It is responsible for processing received information and controlling body functions.
Peripheral Nervous System
The peripheral nervous system (PNS) is formed by a set of nerves that connect the CNS with the rest of our body organs. Its function is to transmit information and conduct the CNS’s orders to the organs responsible for executing them.
Brain
The brain is located in the skull. It consists of the cerebrum, cerebellum, and medulla.
Cerebrum
The cerebrum is divided into two hemispheres. Its surface has convolutions and crevices. The cerebral cortex contains gray matter. The cerebral cortex receives information from the senses and prepares response orders. It also stores and processes information. The innermost zone contains white matter.
Cerebellum
The cerebellum is located below the brain. It is divided into two cerebellar hemispheres and has convolutions. It coordinates movement and allows us to maintain balance.
Medulla
The medulla binds the top of the brain with the spinal cord. The medulla controls body functions, such as blood flow through blood vessels or the movements of the respiratory and digestive tract.
Spinal Cord
The spinal cord is situated in the interior of the spine. The outer part is composed of more white matter, and the internal part is gray matter. The cord is a nerve pathway through which messages ascend to the brain and through which orders descend from the brain to the rest of the organs. It gives off spinal or spinal nerves. The medulla is responsible for reflex movements.
Somatic Nervous System
The somatic nervous system is formed by nerves that connect the skeletal muscles with the CNS. It is responsible for voluntary acts.
Autonomic Nervous System
The autonomic nervous system includes nerves that connect to the viscera with the CNS. It regulates involuntary organ functions. The organs receive antagonistic orders through two nerves: parasympathetic and sympathetic nerves.
Stimuli and Receptors
Environmental changes may be detected by the body. Stimuli are captured by sensitive nerve cells called receptors.
Types of Receptors
- Internal: Report on the state and functioning of our internal organs.
- External: Capture external stimuli, and are located on the surface of the body.
Reported Types of Stimuli Received
- Mechanoreceptors: React to pressure changes.
- Thermoreceptors: Perceive temperature changes.
- Chemoreceptors: Identify chemicals.
- Photoreceptors: Are sensitive to light.
Skin
The skin is an organ where tactile receptors can be found.
The Skin
The skin is formed by two layers: the epidermis (the surface) and the dermis (the deeper layer). The epidermis is formed by layers of epithelial tissue. The superficial cells are dead layers and impregnated with corneal substances, keratin, which waterproofs the skin. These cells are continuously renewing. There are also melanocytes, cells that produce a pigment, melanin, which gives the skin its color. Epidermal structures include nails (protective function), insulating hairs, sebaceous glands (produce fat to cover the hair), and sweat glands (secrete sweat to cool the skin).
Tactile Receptors
Tactile receptors are free nerve endings or enclosed in capsules that are scattered throughout the skin.
- Meissner’s corpuscle: Light contact pressures.
- Pacinian corpuscle: Strong pressures and vibrations.
- Ruffini’s corpuscle: Touch, pressure, and increasing temperature.
- Krause’s corpuscle: Decreasing temperature.
- Free nerve endings: Feel pain, heat, and temperature.
Smell
The sense of smell is located in the nasal cavities. These cavities are covered by the nasal mucosal epithelium, which is called the pituitary.
We distinguish two regions:
- Red Pituitary: Covers the bottom half of the nasal cavity and contains blood capillaries to heat the air we breathe.
- Yellow Pituitary: Is situated in the upper part of the nostrils.
The olfactory receptors are formed by cells responsible for receiving and transporting the stimuli. Olfactory receptors are sensitive to gaseous or volatile substances in the inspired air.
Taste
Taste