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Key Highlights
- Corporal Quadrigemina are the four pairs of colliculi located on the dorsal surface of the midbrain.
- It is used to control the position of the eyes and head with respect to auditory, visual, auditory, and somatic stimuli.
- The colliculi formed in corporal quadrigemina are respectively called the inferior and superior colliculus.
- The region composed of four colliculi is called tectum.
- The correlation centres for visual reflexes are in the superior pair, while the correlation centres for auditory reflexes are in the inferior pair.
Corpora quadrigemina is located on the tectum of the dorsal side of the midbrain and consists of four pairs of colliculi—two inferior and two superior.
- These colliculi are visual and auditory reflex centres.
- When you turn around when someone calls your name represents a reflex action called the corpora quadrigemina.
Key Terms: Corpora Quadrigemina, Midbrain, Colliculi, Tectum, Inferior Colliculi, Superior Colliculi, Brain
What is Corpora Quadrigemina?
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The corpora quadrigemina are reflex centres located on the posterior side of the midbrain, just below the thalamus. It consists of groups of nerve cells called the brachium scattered in white matter.
- As the word ‘quad’ stands for four, corpora quadrigemina is composed of four colliculi.
- It is also known as the colliculi.
- The upper two colliculi are called superior colliculi, and the lower colliculi are inferior colliculi.
- The corpora quadrigemina are four circular swellings that make up the dorsal section, i.e. the back portion of the midbrain.
- It is used to control the posture of the head and eyes in response to visual, auditory, and somatic stimuli.
- The corpora quadrigemina delivers auditory impulses to the auditory centre in the cerebral cortex.
- The paramedian pontine reticular formation and the spinal cord receive descending projections from both colliculi.
- This allows them to engage in stimulus reactions faster than cortical processing permits.
Corpora Quadrigemina
Characteristics of Corpora Quadrigemina
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Important features of Corpora Quadrigemina are as follows:
- Corpora quadrigemina is the Latin term for the quadruple bodies, also known as the colliculi.
- These spherical eminences are located on the posterior surface of the midbrain, just below the thalamus.
- The whole region made up of the four colliculi is referred to as the tectum or tectal plate.
- Superior colliculi are important in the visual system, while inferior colliculi are important in the hearing system.
- The brachium connects each quadruple body to a bundle of nerve fibres.
- The superior brachium establishes the connection between the two superior colliculi, the lateral geniculate body, and the optic tract.
- The inferior brachium connects the two inferior colliculi to the medial geniculate body, which leads to the auditory cortex.
Superior Colliculi
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The superior colliculi are made up of seven layers of grey and white matter arranged in seven levels from peripheral to deep. Their most significant function is the visual body reflexes.
- Scanning while reading, shielding your eyes in bright regions, or tilting your head towards abrupt and unexpected visual stimulation are examples of automatic and involuntary actions.
- The sensations reach the superior colliculi through the visual pathway.
- During these reflexes, they are conveyed to the anterior grey column of the spinal cord and the motor nuclei of the cranial nerves through the tectospinal and retrobulbar tracts, respectively.
Components of Superior Colliculi
Various components of Superior Colliculi are as follows:
Zonal
Zonal is composed of fibres that originate primarily from the primary visual cortex and arrive as the external corticotectal tract.
Superficial Grey
It is the synapsing site of the corticotectal fibres and comprises multipolar interneurons.
Optic
This layer receives fibres originating in the optic tract, more specifically the retina. They are arranged precisely to form a retinotopic map of the contralateral (opposite) field of vision.
Intermediate Grey
Fibres originate from a range of places in this layer. It mostly absorbs fibres from the visual association cortex. As a result, the zonal layer makes it possible to perceive an image, while the intermediate grey layer makes it possible to analyse it. The intermediate grey layer also receives fibres from the spinal cord, the inferior colliculi, locus coeruleus, and raphe nuclei.
Deep Grey
This layer, along with the deep white one, comprises the parabigeminal nucleus. The key places where efferent information leaves the superior colliculi are deep grey and white.
Superior Colliculi
Inferior Colliculi
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The inferior colliculus has a grey matter nucleus in the centre. The nucleus has two zones, dorsomedial and ventrolateral, surrounded by a dorsal cortex and an external cortex.
- The inferior colliculi receive auditory information from the cochlear nuclei via the terminal nerve fibres of the lateral lemniscus.
- An example of such reflexes could be us tilting our head when hearing a loud, sudden sound.
Functions of Inferior Colliculus
- The inferior colliculi control the reflex component of the auditory system.
- Small efferent projections that go via the superior colliculi interact with the tectospinal and tectobulbar tracts.
- The auditory reflex is involuntary and allows us to react to sudden sounds.
Inferior Colliculus
Sample Questions
Ques. What is corpora quadrigemina present? (2 marks)
Ans. Corpora quadrigemina are part of the midbrain. As the word ‘quad’ stands for four, corpora quadrigemina is made up of four bodies. It is found in the midbrain's distal part. It is divided into two parts where the upper two calculi are called superior calculi and lower calculi are called inferior calculi. Corpora quadrigemina is present in the midbrain section of the brain. Corpora quadrigemina is the Latin terminology for the quadruple bodies, also known as the colliculi.
Ques. What are the components of corpora quadrigemina? (2 marks)
Ans. The corpora quadrigemina is divided into two parts, the superior (upper) colliculi and the inferior (lower) colliculi.
- Superior colliculi: It plays a role in preliminary visual processing and eye movement control.
- Inferior colliculi: It receives input from numerous brainstem nuclei and projects to the medial geniculate nucleus of the thalamus, which transfers auditory information to the primary auditory cortex.
Ques. What is the function of corpora quadrigemina in the brain? (2 marks)
Ans. The corpora quadrigemina are reflex centres involving vision and hearing: superior colliculi: involved in preliminary visual processing and control of eye movements.
Ques. What is the importance of corpora quadrigemina? (3 marks)
Ans. The corpora quadrigemina are four rounded elevations on the dorsal surface of the midbrain. The two superior colliculi are involved in visual reflexes and the two inferior colliculi are relay centres for auditory reflexes that operate when it is necessary to move the head to hear sounds more distinctly.
Ques. What is neural coordination? (3 marks)
Ans. Neural coordination:When higher animals respond to various stimuli, each response to a specific stimulus generally involves many organs of their bodies. Therefore, it is necessary that all the concerned organs of the body should work in a systematic manner to produce the response. The working together of various organs of the body of a multicellular organism in a proper manner to complement the functions of each other is called coordination. This is achieved by three overlapping processes of nervous system-sensory input, integration and motor output.
Ques. What is forebrain? (3 marks)
Ans. Forebrain: It consists of: Olfactory lobes, the paired structures concerned with the sense of smell. The cerebrum is the largest and most complex of all the parts of the human brain. It is divided by a cleft into left and right cerebral hemispheres which are connected by a large bundle of myelinated fibres. The outer cover of the cerebral hemisphere is called the cerebral cortex. It consists of sensory and motor areas. The Hypothalamus region of the forebrain contains centres that control body temperature, hunger and also contains a group of neurosecretory cells.
Ques. What is Midbrain? (3 marks)
Ans. The midbrain is located between the thalamus/hypothalamus of the forebrain and pons of the hindbrain. A canal called the cerebral aqueduct passes through the midbrain. The dorsal portion of the midbrain consists mainly of four round swellings (lobes) called corpora quadrigemina. Midbrain and hindbrain form the brainstem.
Ques. Write short notes on Hindbrain? (3 marks)
Ans. The hindbrain comprises the pons, cerebellum and medulla. Pons consists of fibre tracts that interconnect different regions of the brain. Cerebellum has a very convoluted surface in order to provide the additional space for many more neurons. The medulla of the brain is connected to the spinal cord. The medulla contains centres that control respiration, cardiovascular reflexes and gastric secretions.
Ques. Answer the following: (3 marks)
(a) Which part of the ear determines the pitch of a sound?
(b) Which part of the human brain is the most developed?
(c) Which part of our central neural system acts as a master clock?
Ans. (a) The part of the ear that determines the pitch of a sound is the cochlea
(b) The part of the human brain that is the most developed is the cerebrum
(c) The part of the central neural system that acts as a master clock is the hypothalamus
Ques. Are corpora quadrigemina a mammalian character? (2 marks)
Ans. Yes, the corpora quadrigemina is a mammalian character. The quadrigemina means quadruplet bodies. So, the small, solid and four lobes or colliculus called corpora quadrigemina are found in mammals.
Ques. What is the function of medulla oblonganta? (4 marks)
Ans. The function of medulla oblonganta are as follows:
- Breathing: The medulla oblongata acts as the command center for respiration by monitoring blood levels. It sends signals to the muscles involved in breathing, ensuring regular breathing and adequate oxygen intake.
- Heart Rate and Blood Pressure: It regulates your heart rate and blood pressure by controlling nerve cells.
- Swallowing: It coordinates the complex muscle movements involved in swallowing, ensuring food is safely transferred from the mouth to the esophagus.
- Digestion: The medulla oblongata controls the digestive processes by sending signals to the stomach and intestines.
Ques. What are the four structures of the corpora quadrigemina? (2 marks)
Ans. The corpora quadrigemina, also known as the quadruplet bodies, are a group of four structures located on the posterior surface of the midbrain. These structures, called colliculi, are further divided into two superior colliculi and two inferior colliculi.
Ques. What is colliculi? (3 marks)
Ans. Colliculi are a pair of rounded structures located in the midbrain, and together, they form the corpora quadrigemina. There are two main types of colliculi, each with distinct functions:
- Superior Colliculi: These are located on the upper part of the midbrain and are involved in visual processing, especially controlling the movements of the head and eyes. They regulate the reflexes triggered by visual stimuli, such as your rapid eye movements when something catches your eye.
- Inferior Colliculi: It is situated below the superior colliculi and is involved in auditory processing. They receive auditory information from the ears and are involved in controlling the movements of the head and body in response to sounds.
Ques. Is corpora quadrigemina part of the diencephalon? (2 marks)
Ans. No, corpora quadrigemina is not part of the diencephalon. It is actually a structure located in the midbrain. The diencephalon is located above the midbrain and contains components like the thalamus, hypothalamus, and pituitary gland. On the other hand, the midbrain contains structures like the corpora quadrigemina and cerebral aqueduct.
Ques. What damage would the corpora quadrigemina interfere with? (2 marks)
Ans. Damage to the corpora quadrigemina can interfere with various functions which are as follows:
- It can hamper the visual reflexes, ability to voluntarily control eye movements and spatial orientation.
- Damage to the corpora quadrigemina can disrupt reflexes triggered by visual or auditory stimuli.
- It also affects your balance or coordination of movements.
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