Question

What are the differences among exteroceptors, interoceptors and proprioceptors? What are their similarities? What is the difference between a somatic motor neuron and a visceral motor neuron?

Answer 1

Sensory receptors are divided in 3 major classes: exteroceptors, interoceptors and proprioceptors.

Differences:

Interoceptors provide information to the body regarding the internal state of the body. They regulate the voluntary musculature and the filling of the hollow organs. For example, regulation of blood pressure, plasma osmolarity, glucose concentration etc. The nerve endings are free in these receptors. The receptor activates insular cortex. They are involved in body homeostasis and regulated by feedback inhibition.

Exteroceptors provide information on external environment. They are located at or near the body surface. They are responsible for sight, sound, smell, and cutaneous sensation. Cutaneous sensation includes light touch, pressure, fine touch, superficial pain, temperature, itching, and tickling. They are further classified based on those present in skin and those in brain.

Proprioceptors provide information regarding position and posture of the body in space. They cause deep somatic sensation from beneath the skin, in muscles and joints, and inner ear. Proprioception senses movement, vibration, position, and equilibrium. Proprioceptors are subdivided into those present in the locomotor system and the special proprioceptors present in the brain. Golgi tendon organ is a propioreceptor in the tendon. The receptors are myelinated small nerves that activate somatosensory pathways.

Similarities: The exteroceptors, interoceptors and proprioceptors are sensory receptors that transmit signals to the regions of the forebrain for conscious perception. They are dendrites of nerves that receive specific kinds of stimuli. The stimuli are then transmitted to the brain for interpretation and perception.

Difference between somatic motor neuron and visceral motor neuron:

Somatic motor neuron transmits messages from CNS to skin, skeletal muscles, joints and tendons. They are located in the ventral horn of the gray of the spinal cord. They innervate the striated muscles of the axial skeleton and the muscles of the upper and lower limbs. Majorly they are alpha motor neurons while a few are gamma motor neurons that innervate the extrafusal muscle fibers within skeletal muscle.

Visceral motor neuron transmits messages from CNS to smooth muscle, cardiac muscle, and glands. They are located in intermediate horn of the spinal cord between the dorsal and ventral horns. They have two functional groups, sympathetic and parasympathetic. Sympathetic motor neurons are present in the thoracic and upper lumbar parts of the spinal cord. They innervate the smooth muscle of blood vessels, sweat glands, arrector pilii and adrenal medulla. The parasympathetic motor neurons are in the sacral spinal cord and innervate the pelvic viscera, hindgut, and plenic flexure of the colon.