Nervous and Endocrine Systems: Functions and Disorders
The Peripheral Nervous System
The peripheral nervous system is the part of the nervous system outside the brain and the spinal cord. It consists of both sensory and motor nerves. The nerves that connect with the brain, such as the optical, are called cranial nerves, and those that connect with the spinal cord, such as the sciatic nerve, are called spinal nerves.
The peripheral nervous system has two major parts:
- The somatic nervous system transmits information to the skeletal muscles and is responsible for voluntary movements such as walking.
- The autonomic nervous system is responsible for the involuntary activity of internal organs such as digestion, heart rate and respiratory rate.
The autonomic nervous system consists of the sympathetic nervous system, which activates the organs, and the parasympathetic nervous system, which relaxes them.
Voluntary and Involuntary Actions
Voluntary actions result from orders that start in the brain and reach the effectors through the cranial and spinal nerves.
Involuntary actions: The quickest way to respond to a stimulus is through a reflex or involuntary response, this is known as a reflex action. These responses are produced in the spinal cord and take the shortest path from the receptor to the effector. The chain of neurons involved in this action consists of the sensory neuron. The impulse then passes to the interneuron, and then to the motor neuron. This chain of neurons is called the reflex arc.
Common Mental Disorders
A mental disorder is a disturbance of the intellectual functions.
- Depression is a mental illness that often takes the form of low mood and an inability to lead a normal life. In severe cases, sufferers may present destructive behaviour.
- Anxiety is a psychological disorder that causes fear, anguish and even hyperactivity.
- Schizophrenia is an illness that can occur after adolescence. It causes severe personality disorders, a tendency to disconnect from the outside world, delusions and hallucinations.
Neurodegenerative Diseases
These are diseases caused by the degeneration of nerve cells in certain areas of the brain that leads to the gradual loss of intellectual functions. They are more common in older people. The most significant are Parkinson’s disease and Alzheimer’s disease.
The Endocrine System
The endocrine system consists of cells that secrete substances directly into the blood. When these cells are grouped together, they form endocrine glands. The secreted substances are called hormones. They are distributed throughout the body, but only act on certain cells that recognise them. These are called target cells.
How the Endocrine System Works
The endocrine system depends to a large extent on the nervous system. The hypothalamus, a region of the brain connected to the pituitary gland, controls the body’s hormonal activity and acts as a link between the nervous and endocrine systems.
Hormone Functions
The coordination and regulation functions of hormones can be summarised as follows:
- They maintain homeostasis (a balanced internal environment). They regulate the levels of many substances in body fluids, such as blood sugar levels, pH and water balance.
- Along with the nervous system, they help control the body’s stress levels.
- They control growth and development.
- They control sexual development and reproduction.
Principal Glands and Hormones
- Pituitary gland or hypophysis: Produces numerous hormones, which control growth and many other metabolic processes.
- Thyroid gland: Produces two hormones. Thyroxine regulates metabolic processes. Calcitonin regulates the concentration of mineral salts in the blood, specifically calcium.
- Pancreas: Produces insulin and glucagon, which regulate blood sugar levels.
- Adrenal glands: Corticosteroids accelerate metabolism and help maintain the composition of salts in the blood. Adrenaline and noradrenaline are released by the medulla in response to a stressful event.
- Ovaries: They produce oestrogen that controls the development of female secondary sexual characteristics and the menstrual cycle.
- Testicles: They produce testosterone, which controls the development of male secondary sexual characteristics.