Sensory reception, or the recognition of a stimulus by sensory cells, is the first step in a sensory pathway. Each sensory cell is either a specialized neuron or a non-neuronal cell that acts as a regulator for a neuron (as shown in the image attached). Some sense cells live alone, whereas others are grouped together form sensory organs, such as the mole's star-shaped nose in the image attached.

The word sensory receptor refers to both the sensory cell or organ and the subcellular component that detects inputs. Some sensory receptors respond to internal cues such as blood pressure and body posture. Others sense external stimuli such as heat, light, pressure, or chemicals. Some of these receptors are sma-sensitive.

The attached image shows categories of sensory receptors.

The shift in ion flow across the membrane that results affects the membrane potential. The shift in membrane potential is referred to as a receptor potential, and the process of converting the stimulus to a receptor potential is referred to as sensory transduction.

It is worth noting that receptor potentials are graded potentials: Their magnitude is proportional to the intensity of the stimulus.

When action potentials enter the brain via sensory neurons, neuronal circuits analyze the information, resulting in the awareness of the stimuli.

The characteristics of an action potential caused by light striking the eye are the same as those of an action potential triggered by air vibrating in the ear. So, how do humans discriminate between sights, sounds, and other stimuli? The solution can be found in the connections that connect sensory receptors to the brain.

Sensory receptor action potentials pass along neurons that are dedicated to a certain stimulus; these dedicated neurons make synapses with specific neurons in the brain or spinal cord. As a result, the brain only differentiates inputs like sight and sound.

Sensory receptors convert stimulus energy and send it to the central nervous system.

Sensory transduction, the change in the membrane potential of a sensory receptor in response to a stimulus, occurs before stimulus recognition. The resultant receptor potential regulates action potential transmission to the CNS, where sensory input is processed to create perceptions.

The number of activated axons and the frequency of action potentials in an axon influence stimulus intensity. The kind or quality of the stimulus is encoded by the identification of the axon conveying the signal.

Pressure, touch, stretch, motion, and sound are all stimuli that mechanoreceptors respond to.

The magnitude of a receptor potential grows in proportion to the strength of the stimulus. A higher receptor potential leads to more frequent action potentials if the receptor is a sensory neuron (as shown in the attached image). If the receptor is not a sensory neuron, a higher receptor potential typically results in the release of more neurotransmitters.

Many sensory neurons produce action potentials spontaneously at a low rate.

A stimulus does not turn on or off the generation of action potentials in these neurons but rather affects how frequently an action potential is produced, alerting the nervous system to variations in stimulus intensity.

Sensory information can be processed before, during, and after-action potential transmission to the CNS.

In many situations, sensory integration occurs as soon as the information is received. Receptor potentials generated by stimuli given to various sections of a sensory system

Applying light pressure, Added stress and the number of action potentials per receptor is low.

A high number of action potentials are generated per receptor.

The image attached shows a single sensory receptor encodes input intensity

Mechanoreceptors detect flowing fluid or settling particles in hearing and balance. Most invertebrates use statocysts to determine their orientation in relation to gravity. Specialized hair cells serve as the foundation for hearing and balance in humans, as well as water movement sensing in fish and aquatic amphibians.

In mammals, the tympanic membrane (eardrum) sends sound waves to the bones of the middle ear, which then transmit the waves to the fluid in the coiled cochlea of the inner ear via the oval window.

The fluid's pressure waves shake the basilar membrane, depolarizing hair cells and generating action potentials that go to the brain through the auditory nerve.

Light-absorbing pigments are required for the various visual sensors of animals.

Light detectors invertebrates include simple light-sensitive eyespots, image-forming complex eyes, and single-lens eyes. A single lens in the vertebrate eye focuses light on photoreceptors in the retina. Both rods and cones have a pigment called retinal that is linked to a protein (opsin).

Light absorption by the retina initiates a signal transduction pathway that hyperpolarizes the photoreceptors, leading them to release fewer neurotransmitters. Synapses carry information from photoreceptors to cells that integrate information and send it to the brain through the optic nerve's axons.

Taste and smell both rely on comparable sets of sensory receptors.

The sensations of taste (gustation) and smell (olfaction) are dependent on the activation of chemoreceptors by tiny dissolved molecules. Sensory cells in taste buds in humans express a receptor type that is unique to one of the five flavor perceptions: sweet, sour, salty, bitter, and umami (elicited by glutamate).

The top portion of the nasal canal is lined with olfactory receptor cells. Over 1,000 genes are known to code for membrane proteins that bind to certain types of odorants, and each receptor cell seems to express just one of those genes.

Muscle function is dependent on the physical interaction of protein filaments.

Myofibrils are made of thin filaments of (mainly) actin and thick filaments of myosin in the muscle cells (fibers) of vertebrate skeletal muscle. Sarcomeres are repeating units made up of these filaments. Myosin heads that have been activated by ATP hydrolysis attach to thin filaments, form cross-bridges, and then release upon binding ATP again. The thick and thin filaments move past each other when the cycle repeats, shortening the sarcomere and contracting the muscle fiber.

Acetylcholine is released by motor neurons, which causes action potentials in muscle fibers, which promote the release of Ca2+ from the sarcoplasmic reticulum. When Ca2+ binds to the troponin complex, tropomyosin shifts, exposing the myosin-binding sites on actin and triggering cross-bridge formation.

A motor unit is made up of a motor neuron and the muscle fibers it regulates.

A twitch is caused by a single action potential. Slow-twitch or fast-twitch skeletal muscle fibers can be oxidative or glycolytic.

Cardiac muscle is present in the heart and is made up of striated cells that are electrically linked by intercalated disks. Nervous system input regulates the pace at which the heart contracts, but it is not necessarily necessary.

Muscle contraction is converted into movement via skeletal systems.

Skeletal muscles flex and pull against the bones, typically in antagonistic pairs. Skeletons can be hydrostatic and supported by fluid pressure, as in worms; hardened into exoskeletons, as in insects; or endoskeletons, as invertebrates.

Each mode of locomotion—swimming, walking, or flying—presents a unique set of challenges. Swimmers, for example, must overcome friction but face less of a barrier from gravity than creatures that move on land or fly.