Stimulus (physiology)

A stimulus or stimulus ( plural: stimuli) is a physical or chemical parameter of the internal or external environment, acting by changing their energy amounts to living systems.

Within the meaning of the neurobiology is therefore an influence on a sense cell that causes a change in the membrane potential -threshold of the cell membrane ( depolarization or hyperpolarization ), and so causes an action potential.

• 2.1 stimulus-response chain in animals
• 2.2 irritability in plants

Kinds of stimuli

Adequate stimuli

Those stimuli that trigger an action potential in the receptor cell with the lowest energy is known as adequate stimuli. For example, affect the sensory cells that are optimized for such stimuli. For example, respond to the rods and cones in the eye to light stimuli.

Inadequate stimuli

Inadequate stimuli can also cause a potential change. You are stimuli that do not match the sensory cell and thus cause only with high energy or no excitement. One example is for a high pressure ( shock) on the eye, which is usually causes the perception of white spots; also applying a direct voltage can cause a sensation in the central nervous system.

Subliminal stimuli

In such adequate stimuli, the amount of energy is not enough to excite the sensory cell of ( all-or- nothing principle). Meet them but in small temporal or spatial intervals, they can be a suprathreshold stimulus and the receptor excite by summation. Example: the continuing drop of a leaky faucet can be stressful in the long run.

Suprathreshold stimuli

In this case, sufficient amount of energy of an appropriate stimulus to achieve the full reaction. There is no increase possible ( all-or- nothing principle).

Stimulus processing

Feelings and sensations arise only in the central nervous system and are not directly measurable ( black box). They can be detected only with psychological methods. Perceptions arise by combining the sensations with experiences and their own person.

Living things respond to both external (coming from the environment) as well as internal (ie by the organism itself triggered ) stimuli. At a adequate stimulus a reaction follows ( which is, however quite inhibited by subsequent interconnections; see also: stimulus filtering). This principle allows the interaction between the subsystems of an organism and between organisms and the environment. In animals, a sensory cell is addressed, which is connected via synapses with a centralized or decentralized ganglia. In this the stimulus is processed and eventually leads to a reaction.

Stimulus-response chain in animals

A stimulus acts on the receptors ( sensory cells ) or acceptors ( sense organs ) of an organism and is by the sensory afferent ( sensory) nerve forwarded to the central nervous system ( spinal cord and / or brain) and processed there. The information is then relayed via efferent motor nerves to the effector ( target organ ), eg muscle or gland. Finally here is done, the answer to the knitted- stimulus, such as a muscle contraction.

Irritability in plants

→ Main article: Plant movement

In plants, the signal transmission is almost exclusively chemically, here is primarily the light a very important stimulus, but also the temperature, chemical materials, among others gravitational influences lead to reactions. In the processing of different stimuli can interact.

Modes of perception and its charms

Perception is adapted to spectrum and intensity of the stimuli needed (eg, hearing ). Thus man knows the following external senses and the associated stimuli:

• Keys (skin) - pressure / touch, temperature,
• Taste ( tongue ) - salty, sour, sweet, bitter, umami, fat
• Smell (nose) - fragrance molecules ( also share in the sense of taste )
• Seeing ( eyes) - Brightness ( light) and color
• Hearing ( ears) - sound waves ( tones, sounds )

In business - especially in the consumer advertising and trade psychology - the entire stimulus spectrum is used to arouse interest in goods and in addition initiate purchase actions.

Added to this are the senses that serve the self-perception ( for a review see sensibility (medicine) ):

• Proprioception
• Entero - or Viszerozeption

However, there also exist countless other stimulus qualities such as magnetism and ultrasound, which man can not perceive.

Demarcation: stimulus and arousal

A stimulus ( for example heat, pressure, pain, etc. ) is an external force, which is received, for example, in the skin by the sense cells ( receptors). An irritant effect on the postsynaptic nerve cells, the formation of electrical pulses, which are referred to as excitation. A " conduction " does not exist, as only the electrical pulses can be forwarded from the fibers. For impulse formation in the heart and the excitement forwarding through the fibers of the conduction system but no appeal is necessary.