sensory

• The nervous system is a major control system in the body, controlling rapid activities of the body and receiving information from the different sensory organs to determine the response to be made by the body.
• The nervous system is organized into the Central nervous system (CNS) consisting of the brain and spinal cord, and the Peripheral nervous system (PNS) consisting of nerve fibers that carry information between the CNS and other parts of the body (periphery).
• Neurons in the nervous system include afferent neurons which transmit information from the different parts of the body to the central nervous system, and efferent neurons which transmit information from the central nervous system to the different parts of the body.
• The nervous system is composed of three major parts: the sensory portion, the central nervous system or integrative portion, and the motor portion.
• The sensory portion of the nervous system is concerned with informing the person about his external or internal environment, detecting this information through special structures called receptors present at the peripheral terminals of afferent fibers.
• The sensory portion of the nervous system carries the information it detects to the cerebral sensory cortex through special pathways.
• Types of sensations include somatic sensations arising from skin, skeletal muscles, tendons, ligaments and joints, visceral sensations sensations from the viscera (mediated by autonomic fibers), organic sensations such as thirst and hunger, special sensations like vision, hearing, taste & smell, and emotional sensations like fear, sadness, pleasure.
• Pain sensation can be divided into cutaneous pain, which is due to stimulation of pain receptors in the skin, and deep pain, which is produced by stimulation of pain receptors in deep structures such as muscles, joints and ligaments.
• Cutaneous pain can be further divided into fast or immediate pain and slow or delayed pain.
• Deep pain may arise from inflammation of deep structures, trauma of deep structures such as bone fracture, ischemia, or muscle spasm.
• Visceral pain is produced from the viscera of the chest and abdomen and can be caused by ischemia, spasm of a hollow viscus, overdistention of a hollow viscus, or inflammation of the peritoneal covering of the organs.
• Referred pain is pain felt away from its original site, usually initiated in one of the visceral organs and referred to an area on the body surface.
• Examples of referred pain include cardiac pain felt at the left shoulder and left arm, gastric pain felt between the umbilicus and xiphoid process, gall bladder pain felt at the right shoulder, and appendicular pain felt around the umbilicus.
• Headache is a painful sensation at the head that is referred from other structures and may be either intracranial or extracranial in origin.
• Extracranial causes of headache include muscular spasm of scalp and neck muscles, irritation of nasal sinuses, eye disorders, toothache, and systemic disorders such as anemia.
• Intracranial causes of headache include meningeal irritation, brain tumors, constipation, hypertension, and distention of intracranial arteries.
• A reflex arc consists of a receptor that receives the stimulus, an afferent neuron that transmits the information to the CNS, a centre in the brain or spinal cord, an efferent neuron that transmits information to an organ, and an effector organ which will do the action.
• Pain is a specific unpleasant sensation that is elicited by stimuli which causes tissue damage, i.e. noxious stimuli, and is a protective mechanism against permanent damage because it initiates protective reflexes such as withdrawal reflex.