Question

What is the relationship between the central and peripheral nervous systems and the sensory organs?

How does the autonomic nervous system help to maintain homeostasis in the body?

Can you provide an example of a disease that is a result of autonomic nervous system imbalances? Explain.

Answer 1

Peripheral nervous system includes cranial and spinal nerves that connect the central nervous system with receptors and effectors of the body.  The peripheral nervous system sends information gathered by the body's sensory receptorsto the CNS. The peripheral nervous system or PNS contains the nerves, which leave the brain and the spinal cord and travel to certain areas of the body -

• Afferent nerve fibres conduct sensory impulses from the receptors present in the peripheral tissue towards the central nervous system. Sensory neurons (afferent in nature) conduct sensory impulses from receptors or sense organs and evoke sensations.
• Efferent nerve fibres conduct motor impulses from central nervous sytem to effectors. Motor neurons, efferent in nature, conduct motor impulses to effectors such as muscles and glands.

Sensory nerve conducts impulses from receptors to CNS and motor neurons conducys motor impulses from CNS to effectors to produce reactions.

Autonomic nervous system -

The autonomic nervous system regulates the activities of involuntary smooth muscle, cardiac muscle and glands. The system consists of preganglionic fibres from CNS, ganglia and post ganglionic fibres. This system helps to control arterial pressure, secretion of certain glands, sweating, body temperature etc.

Autonomic nervous system is part of peripheral nervous system and controls the function of muscles, glands and organs within the body.

The autonomic signals are transmitted to various organs of the body through two subsystems – sympathetic nervous system and parasympathetic nervous system.

Sympathetic nervous system –

The sympathetic nervous system maintains homeostasis and mediates fight or flight response. This occurs by preganglionic sympathetic nerves that ends in the adrenal medulla and secrete acetylcholine. Acetylcholine triggers the secretion of epinephrine and norepinephrine into the blood stream. Epinephrine and norepinephrine then binds to adrenergic receptor on tissue resulting in fight or flight response with various effects such as –

• Increased basal metabolic rate
• Increased blood glucose concentration
• Increased heart rate
• Blood vessel constriction
• Increased blood pressure
• Pupillary dilation
• Increased peristalsis in esophagus
• Increased sweating

Parasympathetic nervous system –

The parasympathetic nervous system regulates organ and body function during rest and it counteracts the effects of sympathetic nervous system. It is responsible for “rest and digest” response. On stimulation, the preganglionic nerves secrete acetylcholine which binds with the receptor present on the effector cells. In parasympathetic nervous system, acetylcholine binds to two types of receptor – nicotinic receptor and muscarinic receptor present on the effector or target organ.

Effects of parasympathetic nervous system –

• Counterbalance the effects of sympathetic nervous system.
• Decrease heart rate.
• Muscles relax.
• Pupils constrict.
• Increases stomach movement and secretions.
• Saliva production increases.
• Increase in urinary output

The sympathetic and parasympathetic nervous system acts antagonistically to each other to maintain homeostasis. Therefore stimulation of sympathetic nervous system excites a particular organ whereas at the same time stimulation of parasympathetic nervous system inhibits it.