Introduction
A reflex is defined as an involuntary response of an organism to a specific stimulus. Reflexes are broadly categorized into two primary groups: unconditioned reflexes and conditioned reflexes. Unconditioned reflexes are those which we are born with and normally operate during our whole life. (throughout our entire lives) These reflexes operate autonomously, independent of conscious awareness or volitional control.Because of this, we may not notice them in our life, thus not assessing their importance for us. In this article, we will look at some vital unconditioned reflexes we encounter every day.
1. Accommodation Reflex
Accommodation reflex is linked to eyes, vision of an object, and the precise visual focusing of objects. Structures that are involved in a work of this reflex are: ciliary muscles, lenses, and pupils. The neuronal signaling pathway of this reflex involvesthe reception of visual information by the eye, whichsubsequently transmits a signal to the central nervous system. These signals transform into others specifically aimed at the eye muscles [1]. As a result, we can quickly focus on the near objects when they suddenly appear in front of us. We also can feel our eyes getting tensed while focusing.
This reflex seems too simple at first glance: however, it helps usnot only to distinguish objects we see but also to understand within a couple of seconds whether an object poses a danger.
2. Tendon Reflexes
Tendon reflexes, also known as stretch reflexes, are characterized as involuntary muscular responses. They involve afferent (sensory) and efferent (motor) pathways of neuronal signaling, starting from an initial application of performing a stimulus to a muscle’s mechanical receptors. These receptors then transfer the signal along the reflex arc to the central nervous system. The response of such reflexes is a resist to stretch, which occurs via the efferent pathway by the activated muscles [2].
Tendon reflexes can be observed in many muscles. It is sufficient to apply a stimulus to a specific tendon to receive themuscle response. For example, there are biceps reflex (biceps tendon), triceps reflex (triceps tendon), knee jerk reflex (patellar tendon), ankle jerk reflex (Achilles tendon), and jaw jerk reflex(mandibular tendon). They all maintain posture and coordination. [2, 3]. Notably, knee jerk reflex is a widespread one, and individuals can test it on themselves.
Figure 1. Knee jerk reflex scheme with afferent and efferent pathways [1]
3. Acoustic Reflex
In order to obtain an acoustic reflex, a person is exposed to an acoustic stimulus, such as a loud and irritating sound. Such stimuli cause the contraction of the middle ear muscles, thereby reducing pressure on the inner ear, which is located deeper within a cranium. Two types of muscles contract: stapedial muscles and tensor tympani muscles. Basically, contraction of form is the main response to the reflex due to the weaker contraction of the tensor tympani muscle. However, as it also contracts and does it before the stapedius muscle, its performing can point at some problems of health [4].
This reflex helps overcome the tension exposed on the inner ear by sound, transferring it to the middle ear, where respective muscles resist the unfavorable sounds. However, despite of the fact that the acoustic reflex protects us from further damagefrom too loud noise, we also should understand that this reflex has its own limits of decibels absorption [5]. That means that being exposed to the loud noise for a long time causes serious damage, and we should avoid such situations or use protective equipment.
Figure 2. Anatomy of a middle ear. The stapedius muscle is accentuated [2]
4. Salivary Reflex
When we eat, the whole process is accompanied by salivary production. Not only eating but also seeing or smelling food can make us produce increased salivary unintentionally. Yet, in all cases of normal functioning of major and minor salivary glands,we produce saliva because of food taste. There are four main types of taste: sweet, salty, sour, and bitter. These kinds of taste are the main stimuli for variety of salivary reflexes, such as agustatory-salivary reflex, a masticatory-salivary reflex, an olfactory-salivary reflex, and an esophageal-salivary reflex [6].
Saliva is essential in order to taste, masticate, and swallow thefood. It is released much or less dependently on which taste stimulus taste receptors meet. For instance, a sour taste has larger scales of the saliva presented. It presents a high neutralization rate of acidity of some food [6].
Consequently, this reflex helps us understand which food we can accept eating in more amounts and which is considered to beeaten in less amounts. Also, producing saliva is the response which maintains oral microflora.
Conclusion
The unconditioned reflexes are the significant features of living beings, including humans. They primarily protect us from different kinds of danger by distinguishing stimuli and responding in ways which preserve our health. Life would be harder and more fragile without unconditioned reflexes. After reading this article I believe you will notice that something that you might counted before as unimportant and disturbing will seem much more valuable in your life.
References
1. Motlagh M, Geetha R. Physiology, Accommodation. [Updated 2022 Nov 15]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK542189/
2. Rodriguez-Beato FY, De Jesus O. Physiology, Deep Tendon Reflexes. [Updated 2023 Aug 28]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK562238/
3. Walker, H. K. (1990). Deep Tendon Reflexes. In H. K. Walker (Eds.) et. al., Clinical Methods: The History, Physical, and Laboratory Examinations. (3rd ed.). Butterworths.
4. Barozzi, S., Zanetti, D., Di Berardino, F., Aldè, M., & Cantarella, G. (2021). Acoustic reflex preshoot: A sign of contraction of the tensor tympani muscle? Medical Hypotheses, 155, 110660. https://doi.org/10.1016/j.mehy.2021.110660
5. Feeney MP, Schairer KS, Putterman DB. Wideband Acoustic Reflex Measurement. Semin Hear. 2023 Mar 14;44(1):84-92. doi: 10.1055/s-0043-1763296. PMID: 36925659; PMCID: PMC10014201.
6. Satoh-Kuriwada S, Shoji N, Miyake H, Watanabe C, Sasano T. Effects and Mechanisms of Tastants on the Gustatory-Salivary Reflex in Human Minor Salivary Glands. Biomed Res Int. 2018 Jan 31;2018:3847075. doi: 10.1155/2018/3847075. PMID: 29651428; PMCID: PMC5832054.
Figures
1.Knee jerk reflex scheme with afferent and efferent pathways.
Suri, V. (2021). Reflexes. In: Clinical Neurological Examinationand Localization . Springer, Singapore. https://doi.org/10.1007/978-981-16-1228-2_7
(Date Taken: 14.05.2025, 13:20)
2.Anatomy of a middle ear. The stapedius muscle is accentuated
https://www.miracle-ear.com/blog-news/middle-ear-myoclonus
(Date Taken: 14.05.2025, 13:20)
Denetleyen: Esma Zehra SAĞLAM
