Logan Steele
The tongue is a muscular organ located in the mouth that is essential for chewing, swallowing, and speaking. It is made up of eight muscles combined into one, which provide multiple movements and allow the tongue to move in all kinds of directions. The tongue is anchored inside the mouth by webs of strong tissue and is covered by mucosa, a moist, pink lining that covers certain organs and body cavities. The tongue is also covered with different types of papillae (bumps) and taste buds. While the tongue is flexible and powerful, it is not the strongest muscle in the body.
| Characteristics | Values |
|---|---|
| Definition | The pupil is the black opening in the middle of the colored part of your eye (iris). |
| Function | The pupil lets light enter the eye. |
| Control | The muscles of the iris control the size of the pupil. |
| Muscles Involved | Two muscles are involved: the circumferential sphincter muscle and the iris dilator muscle. |
| Nerve Involvement | The oculomotor nerve connects and synchronizes both eyes so they have the same direction and pupillary response. |
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What You'll Learn
The pupil is the black opening in the middle of the iris
The pupil is the black opening at the center of the iris, the colored part of the eye. The iris is a contractile structure, consisting mainly of smooth muscle, surrounding the pupil. The pupil is not itself a muscle, but its size is controlled by the activity of two muscles in the iris: the circumferential sphincter muscle and the iris dilator muscle.
The sphincter muscle is innervated by the parasympathetic nervous system and causes the pupil to constrict when it contracts. This is known as miosis. The dilator muscle, on the other hand, is innervated by the sympathetic nervous system and causes the pupil to dilate when it contracts. This is known as mydriasis.
The pupil plays a crucial role in vision by controlling the amount of light that enters the eye. In bright light, the pupil constricts to prevent aberrations of light rays and attain the expected acuity. In low light conditions, the pupil dilates to allow more light to enter the eye. This adjustment of the pupil size in response to light is known as the pupillary light reflex and is an important test of brainstem function.
The size of the pupil can also be influenced by factors other than light, such as emotional arousal, cognitive load, and certain drugs. Additionally, some individuals can voluntarily control their pupil size, dilating or constricting them on command without changes in lighting conditions.
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The iris contains muscles that control the size of the pupil
The pupil is the black opening in the middle of the iris, the coloured part of the eye. The iris is made up of muscles and nerves that work together to control the size of the pupil. This process happens without any conscious thought and adjusts the amount of light that enters the eye.
The iris contains two types of muscles with opposing functions: the dilator muscle and the sphincter muscle. The dilator muscle, or iris dilator, opens the pupil from the inside out, resembling a sun with rays. This muscle enlarges the pupil by pulling the iris radially. The sphincter muscle, or iris sphincter, is a circular muscle that encircles the pupil and controls its closure. It contracts the pupil in a circular motion, constricting the pupil in bright light and controlling the amount of light that reaches the retina.
The iris sphincter is innervated by the parasympathetic nervous system, which causes pupillary constriction and accommodation. The parasympathetic fibres that serve the sphincter originate from the Edinger-Westphal nucleus of cranial nerve III. On the other hand, the dilator muscle fibres contain α-adrenergic sympathetic receptors that respond to changes in sympathetic tonus and blood levels of circulating catecholamines. The sympathetic system, originating from the superior cervical ganglion, also promotes sphincter muscle relaxation, which is crucial for low-light conditions or night vision.
The size of the pupil is determined by the activity of these two muscles. The contraction and relaxation of the sphincter and dilator muscles, respectively, allow the pupil to adjust to different lighting conditions, ensuring optimal vision.
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The pupil lets light into the eye
The pupil is the black opening in the middle of the iris, the coloured part of the eye. The pupil lets light into the eye, and the iris regulates the amount of light by controlling the size of the pupil. This is known as the pupillary light reflex. The iris contains two groups of smooth muscles: the sphincter pupillae and the dilator pupillae.
The sphincter pupillae is a circular group of muscles that constrict the pupil, reducing its size. This occurs in response to bright light, preventing aberrations of light rays and allowing the eye to attain its expected acuity. The parasympathetic nervous system innervates these muscles.
The dilator pupillae, on the other hand, is a radial group of muscles that dilate the pupil, increasing its size. This occurs in low-light conditions to allow more light into the eye. Sympathetic nerves from the superior cervical ganglion innervate these muscles.
The size of the pupil can also be influenced by factors other than light, such as emotional arousal, cognitive load, and certain drugs. For example, opioids cause constriction, while LSD, MDMA, and cocaine cause dilation. The pupil is a crucial part of the vision system, and issues with its function can indicate various diseases or conditions, such as Adie syndrome or Horner syndrome.
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The pupil works with the lens to send light to the retina
The pupil is the black opening in the middle of the iris, the coloured part of the eye. The iris controls how much light the pupil lets in by changing its shape, thanks to the muscles in the iris. The pupil is the pathway that lets light get to the retina.
The retina is a light-sensitive layer of tissue at the back of the eye. When light hits the retina, special cells called photoreceptors turn the light into electrical signals. These electrical signals travel from the retina through the optic nerve to the brain. The brain then turns these signals into images. This is how we are able to see.
The pupil changes size to adjust for the amount of light available. When it is very dark, our pupils get bigger to let in more light, and when it is bright, they get smaller to let in less light. This opening and closing of light into the eye is much like the aperture in a camera, which lets in more or less light depending on the conditions.
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The pupil size can be impacted by drugs
The pupil is the black opening in the middle of the coloured part of the eye (iris). The pupil gets bigger or smaller in response to changes in light. The size of the pupil is controlled by the activities of two muscles: the circumferential sphincter muscle, found in the margin of the iris and innervated by the parasympathetic nervous system; and the iris dilator muscle, which runs radially from the iris root to the peripheral border of the sphincter.
Drugs can impact the size of our pupils, causing them to either constrict or dilate. This is due to the effect of drugs on the autonomic nervous system, which regulates the size of the pupils. The autonomic nervous system controls automatic functions such as heart rate and blood pressure, and its balance can be disrupted by substance use.
Stimulants, such as cocaine and amphetamines, often cause pupil dilation. These drugs stimulate the sympathetic nervous system, leading to an increase in the release of norepinephrine, resulting in heightened arousal and increased energy levels. On the other hand, depressant drugs like opioids and benzodiazepines tend to cause pupil constriction. This is because opioids and other depressants have a sedating effect on the body, slowing down the central nervous system and causing the pupils to become smaller and appear pinpoint in size.
Hallucinogens, such as LSD and psilocybin mushrooms, can induce both dilation and constriction, depending on factors like dosage and individual sensitivity. Cannabis use is also known to cause pupil dilation due to the presence of psychoactive compounds like THC.
It is important to note that changes in pupil size alone do not provide a definitive diagnosis of drug use, and other factors and behavioural cues should be considered. Additionally, pupil size can be influenced by factors unrelated to drug use, such as lighting conditions and emotional states.
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Frequently asked questions
The pupil is the black opening in the middle of the coloured part of your eye (iris).
The pupil lets light into your eye as the muscles of your iris change its shape. The pupil controls the amount of light that enters the eye so that you can see clearly.
The pupil gets bigger or smaller in response to changes in light. The iris contains two groups of smooth muscles: a circular group called the sphincter pupillae, and a radial group called the dilator pupillae. When the sphincter pupillae contracts, the iris decreases the size of the pupil. The dilator pupillae dilates, increasing the size of the pupil when in low light.
If your pupils don't work properly, you may experience photophobia (eye discomfort in light) or hemeralopia (an inability to see clearly in light).
