The peripheral nervous system (PNS) consists of a network of nerves and ganglia. The PNS connects the CNS to the rest of the body, enabling communication between the central nervous system and sensory organs, muscles, glands, and other tissues. The autonomic nervous system and the somatic nervous system are the two divisions of the peripheral nervous system.
Autonomic Nervous System
Regulation of physiological functions is controlled by involuntary responses, which are under the authority of the autonomic nervous system (ANS). Smooth muscles, such as those of the heart, exocrine, bladder, and endocrine-related organs, are connected to the central nervous system of the brain and spinal cord by ganglionic neurons. It is divided into two types of systems, which are given below:
Sympathetic Nervous System
- In situations where physical danger and mental stress are encountered, the sympathetic nervous system gets activated.
- During such conditions, activities like digestion, which are not so important for survival at that time, are reduced, and heart rate and blood flow are increased in some areas, like muscles, because of the release of norepinephrine and epinephrine, which are neurotransmitters.
- Some parts of the body take a rest, and some parts become active as the system is independent of each other.
Parasympathetic Nervous System
- The parasympathetic system turns the body into a rest and digest stage when acetylcholine is used as a mediator, which is a neurotransmitter.
- There is an increase in metabolic activities of digestion and salivation.
- There is a decrease in sympathetic responses and heart rate when the body is dominated by the parasympathetic system.
- In humans, there are some voluntary controls in the parasympathetic system, unlike the sympathetic system.
- Defecation and urination are the best examples of this.
Somatic Nervous System
The brain transmits signals to end organs like muscles, and it is done voluntarily by the somatic nervous system. Signals from senses such as touch, smell, and taste are sent to our brain and spinal cord through the sensory nervous system, which is a part of the somatic nervous system. It is divided into two types of systems, which are given below:
Sensory(Afferent) Somatic System
- Carries sensory impulses from receptors → to the CNS (brain and spinal cord).
- Involved in conscious sensations such as touch, pain, temperature, pressure, and proprioception (body position).
- Receptors involved as photoreceptors (eyes), mechanoreceptors (touch, pressure), thermoreceptors (temperature), and nociceptors (pain).
- Allows the body to sense and become aware of changes in the internal and external environment.
Motor(Efferent) Somatic System
- Carries motor commands from CNS → to skeletal muscles.
- Controls voluntary movements such as walking, writing, speaking, and lifting objects.
- There are two types of motor actions as voluntary actions(e.g., picking up an object) and reflex actions (fast, involuntary responses controlled by reflex arcs).
- Initiates and regulates skeletal muscle contraction.
Diseases
Diseases | Description | Symptoms |
|---|---|---|
Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) | The inflammation of nerve roots and nerves. Due to the inflammation, myelin can be destroyed, which is the protective covering of nerves. | Pain and numbness in different areas, tiredness, weakness in legs and arms, and slow reflexes |
Ganglioneuroma | It is a rare, benign (non-cancerous) tumour that develops from mature nerve cells of the autonomic nervous system, specifically from sympathetic ganglion cells. | Difficulty in breathing, chest pain if the tumour is in the chest, bloating and abdominal pain |
Autonomic Neuropathy | Nerves that control the autonomic body functions seem to be damaged when this disease occurs. | Loss of appetite, constipation, nausea, vomiting, abdominal bloating, and heartburn. |