Sensory Receptors, Nervous System, and Endocrine Functions in Animals

Posted on Dec 17, 2024 in Biology

Sensory Receptors

Receptors are cells specialized in capturing certain stimuli and transforming them into nerve impulses.

Characteristics

• Specificity or differential sensitivity: Each type of receptor is sensitive to a particular stimulus.
• Range: Each stimulus needs to act for long enough and at a certain intensity.
• Adaptation: The ability of certain receptors, when a stimulus persists for some time, to soften or eliminate the intensity of feeling.

Cell Types

The cells may be:

• Epithelial: In this case, they receive the stimulus at one end and are in contact with a sensory nerve fiber at the other.
• Neuronal origin: A neuron is modified, and on one side is a prolongation of dendritic type, which is the recipient of stimuli, and on the other, an axon synapses with other neurons.

The cells may be isolated but generally group together and with other accessory cells, leading to complex structures: the sense organs.

Types of Receptors

There are two types of receptors:

• Exteroceptors: Capture stimuli from outside.
• Interoceptors: Receive information from the interior of the body. These can be:
  • Proprioceptors: Report changes in posture.
  • Visceroceptors: Report visceral activity and changes in the internal environment.

Classification Based on Stimuli

Depending on the nature of the stimuli received:

• Chemoreceptors: Sensitive to chemical substances.
• Mechanoreceptors: Sensitive to stress.
• Thermoreceptors: Sensitive to temperature changes.
• Photoreceptors: Respond to light stimuli.

Nervous System Functions

• Conductor function: It is a center of reflex actions.
• The medulla oblongata: Plays a leading role. It is a reflex center for some vital functions like breathing, blood pressure, etc.
• The cerebellum: Coordinates muscle tone, so voluntary contractions are performed smoothly, and controls position and balance.
• The thalamus: Processes sensory information and also evaluates the quality of sensation.
• The hypothalamus: Contains nerve nuclei that regulate the functions of vegetative life.
• The brain: Is an associative center where information is processed and integrated before an appropriate response occurs. It is the center of the higher functions: intelligence, memory, and desire. The primary motor area is where the orders leave for voluntary movements.

Hormonal System

Hormones are organic compounds produced by the endocrine glands in evolved animals. They are discharged into the circulation and transported to an organ or a cell. The organs or cells where the hormones exert their action are known as target organs or cells. In the cell membrane or cytoplasm of the target cells are localized specific receptors, protein molecules that are stimulated by the presence of a particular hormone. They act in small quantities and degrade rapidly. An excess (hyperfunction) or default (hypofunction) can cause hormonal imbalance. The animal organism has mechanisms regulating hormone levels through nervous control, other endocrine glands, or the concentration of a substance in the blood. The regulation takes place by feedback; if there is a high concentration of the released hormone, the gland receives the information directly or indirectly. There are neurohormones produced by neurons, and pheromones are also varied. Many mammals use them to demarcate their territories. They also act in the breeding season, allowing the location of males to females kilometers away.

Other Endocrine Glands