The introduction briefly talks about the hindbrain, its location, structure and highlights its main functions. It also talks about how the hindbrain is divided. The next topic is about Structure and Function. It first starts with the functions of the hind brain and then mentions each and every function of the brainstem, that it, the medulla, pons and the cerebellum. It also mentions the functions of the cranial nerves. The next section is on Injury and Disorder. Here it is mentioned, as a list, the various disabilities that the brainstem could have. These include the consequences when a stroke occurs in that region. The final section is on the recent research that has been done in the hindbrain. There are five research articles cited in this section. Introduction
The hindbrain is the oldest part of the brain. It is located in the lowermost region of the brain and is found in between the spinal cord and the brain hemispheres. It is also known as rhombencephalon, since this is the name given to the developing hindbrain in the embryonic stage. It consists of medulla, pons, the cerebellum and majority of the cranial nerves. These three combined together are called the brainstem and control the body’s autonomic system. It connects the brain to the spinal cord.
The hind brain coordinates some of the major functions for survival, such as respiratory rhythm, motor activity, sleep, and wakefulness. The hindbrain can be subdivided in a number of transversal swellings called rhomberes. In an embryo, eight rhomberes can be identified, from caudal to rostral: Rh8-Rh1. (Rhombencephalon, 2015) The hindbrain can also be subdivided into the myelencephalon, which is the area where medulla developed, and metencephalon, where pons and the cerebellum developed. Structure and Function
The functions of the hindbrain cover the primitive instincts and vital bodily functions such as heartbeat, breathing and digestion. The hindbrain also controls involuntary digestive and respiratory reflexes such as vomiting, coughing, swallowing and sneezing to expel dust and other foreign particles from the body. (What are the functions of the hindbrain?, n.d.) Each of the three major regions of the hindbrain have particular functions: The Medulla is placed at the base of the skull just above the spinal cord and below the cerebellum. It is found in the myelencephalon region of the hindbrain. The rhomberes Rh8-Rh4 form the myelencephalon. It carries information between the spinal cord and the higher parts of the brain. It also controls autonomic functions such as heartbeat and respiration.
It controls the contraction and expansion of the diaphragm and lungs and the dilation and contraction of the blood vessels by working with the hypothalamus to ensure homeostasis is maintained. It also helps in maintaining the upright position of our body. All these functions of medulla is possible with the help of cranial nerves. The medulla houses a portion of the reticular formation. Reticular formation is a set of interconnected nuclei that are located throughout the brainstem. The respiratory centre in the medulla oblongata is affected by various types of drugs including opioids such as morphine. These types of drugs often suppress the activity of the neurones in the respiratory nuclei. (Hindbrain – Anatomy & Physiology, 2012)
Because of its location at the brain stem, trauma to this area can be detrimental to survival of any kind. Research shows lesions resulting from trauma can cause pulmonary edemas due to the medullas association with pulmonary function. Similarly, ischemia can also result from lesions to the medulla affecting vasomotor function. (Hindbrain, 2014) The pons is found in the metencephalon region of the hind brain. It is located in the brainstem, directly above the medulla and acts as a link to the cerebellum. It is partly made up of tracts that connect the spinal cord with higher brain levels, and it also contains cell groups that transfer information from the cerebrum to the cerebellum. Some of those cell groups are part of the reticular formation, a network of neurons extending throughout the brainstem that regulates alertness, sleep, and wakefulness. (Hindbrain, 2015).
These are also controlled by the nuclei along with respiration, swallowing, bladder function, equilibrium, eye movement, facial expressions and posture. To accomplish these functions, pons coordinates with the autonomic nervous system. The other functions that pons occurs in pons is, sexual arousal, sensory analysis, motor control and auditory input that first makes contact with pons. The Pons have many axons which cross from one side of the brain to the other side. This is the reason why the right hemisphere controls the muscles on the left side of the body and the left hemisphere control muscles on the right side. Pons, to a certain extent, is able to influence the respiratory movements and many digestive processes.
It coordinates the hindbrain with the midbrain and forebrain. One of the most functions of pons is sleep paralysis reflex in which it prevents movements during sleep and ensures that we don’t sleepwalk. The cerebellum is located at the bottom of the brain and resembles the whole brain and is the largest portion of the hindbrain. It is found above the medulla and behind the pons contains a number of Purkinje cells and granule cells. The Purkinje cells, which are large in size, help in coordinating motor activity. The function of granule cells, which are comparatively smaller in size, is still unclear but they are shown to have an important role in motor learning. It is seen that without the cerebellum, the person is unable to walk in a straight line, that is, it handles walking and balance.
It controls the bodily balance, does analysis and coordination of sensory information to problem solving and coordinates the fine muscle movements. Damage to this area would impair the fine motor skills. The occipital lobe and the rest of the cerebrum work with the cerebellum to provide hand-eye coordination. Emotions and the associated physical stimuli such as increased heart rate are under the control of the cerebellum, as is long-term and short-term memory. (What are the functions of the hindbrain?, n.d.). Functions of the hindbrain are possible because of the wrinkled surface of the cerebellum. Neural network is connected to the wrinkles found on the cerebellum. Higher the number of wrinkles, better the neural network.
The other important function of cerebellum is controlling the ability to shift attention between sound and sight stimuli. Damage to this area can affect the person’s ability to judge time, so if a person is presented with a rhythm which is faster than another rhythm, that person would not be able to differentiate. It also plays part in some cognitive functions such as attention, language, regulating fear and pleasure responses. (Hindbrain, 2014) Cranial nerves III to XII exit from the brain stem and act to innervate parts of the head, neck, viscera and the thoracic and abdominal cavities. Although most of these nerves contain both sensory and motor fibres, the sensory fibres all have their cell bodies in ganglia outside the brain stem. (Hindbrain – Anatomy & Physiology, 2012)
Injury and Disorders Injuries which affect this part of the brain, can result in a high number of disorders and disabilities. When an injury happens in the cerebellum, the damages include: •Ataxia- inability to coordinate movement
•Difficulties in speed •Gait impairments and problems with leg coordination •Vertigo- sensation of giddiness while looking down from a height •Disequilibrium- uncomfortable state for individuals •Loss of balance •Hypotonia Injuries or disease affecting the cerebellum usually produce neuromuscular disturbances, in particular ataxia, or disruptions of coordinated limb movements. The loss of integrated muscular control may cause tremors and difficulty in standing. (Cerebellum , 2014). Cerebellar atrophy can be seen in many other neurological disorders including Huntington’s disease, multiple sclerosis, essential tremor, progressive myoclonus epilepsy, and Niemann–Pick disease. Exposure to toxins like heavy metals or drugs (medical or recreational) are also causes of cerebellar atrophy. A damage in pons can cause:
•Alteration of smell, taste, hearing or vision (total or partial) •Urinary incontinence •Drooping of eyelid (ptosis) and weakness of ocular muscles •Decreased reflexes: swallow, gag and pupil reactivity to light •Decreased sensation and muscle weakness of the face •Weakness in tongue •Nystagmus- involuntary eye movement •Alteration of breathing pattern Central pontine myelinosis is a demyelination disease that causes difficulty with sense of balance, walking, sense of touch, swallowing and speaking. In a clinical setting, it is often associated with transplant or rapid correction of blood sodium. Undiagnosed, it can lead to death or locked-in syndrome. (Pons, 2015) An injury in the medulla can cause:
•Loss of bowel control and constipation •Alteration of heart rate •Alteration of breathing pattern •Blood pressure changes (Najaib, 2011) A blockage (such as in a stroke) will injure the pyramidal tract, medial lemniscus, and the hypoglossal nucleus. This causes a syndrome called medial medullary syndrome. Lateral medullary syndrome can be caused by the blockage of either the posterior inferior cerebellar artery or of the vertebral arteries. (Medulla Oblongata, 2015) Injuries or disease affecting the middle portion of the medulla may produce paralysis of the opposite side of the body, loss of the senses of touch and position, or partial paralysis of the tongue. Injuries or disease of the lateral medulla may cause loss of pain and temperature sensations, loss of the gag reflex, difficulty in swallowing, vertigo, vomiting, or loss of coordination. (Medulla Oblongata, 2013)
Recent Research
1.The Effect of Hindbrain Orexin A Signalling on Brown Adipose Tissue Thermogenesis and Physical Activity: This research basically looks at how brain’s defence acts against obesity. With obesity being a cultural syndrome in the US, there is a necessity to find solutions for it. Previous work has emphasized the importance of neuropeptides (protein neurotransmitters) in controlling obesity triggering factors such as ingestion and energy expenditure. The orexins (orexin A and orexin B) are a family of neuropeptides important in promoting physical activity, and have also recently been shown to increase energy expenditure through effects on thermogenesis. The research looks at the hindbrain signalling orexin A helps in controlling energy expenditure via thermogenesis. (Lee, 2014)
2.Constructing the hindbrain: insights from the zebrafish:
The hindbrain’s main functions include controlling respiration and heartbeat. In addition, cranial nerves projecting from the hindbrain control muscles in the jaw, eye, and face, and receive sensory input from these same areas. The hindbrain passes through a phase of segmentation, where there a series of seven bulges- the rhombomeres- were formed. The current understanding of vertebrate hindbrain development comes from integrating data from several model systems. Work on the chick has helped us to understand the cell biology of the rhombomeres, whereas the power of mouse molecular genetics has allowed investigation of the molecular mechanisms underlying their development. This review focuses on the special insights that the zebrafish system has provided to our understanding of hindbrain development. The research has identified genes required for hindbrain segmentation. (Kinkhabwala, et al., 2011)
3.Antecedent Hindbrain Glucoprivation Does Not Impair the Counterregulatory Response to Hypoglycemia: Recurrent hypoglycaemia impairs hormonal counter regulatory responses (CRRs) to further bouts of hypoglycaemia. The hypothalamus and hindbrain are both critical for sensing hypoglycaemia and triggering CRRs. Hypothalamic glucose sensing sites are implicated in the pathogenesis of defective CRRs; however, the contribution of hindbrain glucose sensing has not been elucidated. Using a rat model, the researchers compared the effect of antecedent glucoprivation targeting hindbrain or hypothalamic glucose sensing sites. These results show that hindbrain glucose sensing is not involved in the development of defective CRRs. However, neural substrates surrounding the third ventricle are particularly sensitive to glucoprivic stimulation and may contribute importantly to the development of defective CRRs. (Nicole M. Sanders, 2007)
4.Cell lineage restrictions in the chick embryo hindbrain:
It is seen that when a chick’s embryo is being developed, early neuronal differentiation and axonogenesis in the hindbrain follow a segmented pattern. Cell marking experiments have shown that the segments or rhombomeres, are lineage-restriction units each constructing a defined piece of the hindbrain. The metamerism is able to generate these anatomical structures with great precision. For many invertebrates, lineage ancestry becomes important for the determination of cell fate. (Lumsden, 1991)
5.Medulla Types of Hair: a Population Study:
This research took place in India. It looks at the pattern between hair growth and medulla. 400 individuals were selected (200 from each gender) between the ages of 5 to 55 years. The types have been classified as Absent, Fragmented, Discontinuous and Continuous types. Results showed that the maximum number men belonged to the Discontinuous category, whereas for women, most of them belonged to the mixed category. (Kaur, Thakkar, & Chattopadhyay, 1993)