Wait – Why Do Sheep Have One Cerebellum **BRAINS**

As a general Rule, All Sheep have one Cerebellum that controls, Balance, and Posture in Sheep. It also coordinates all voluntary muscle control and motor responses. It is responsible for Sheep’s Learning abilities. Humans have two sections, but Sheep’s Brains are less developed than people, and only have one.

Why Do Sheep Have One Cerebellum

Why Do Sheep Have One Cerebellum

The human cerebellum controls human behavior and motor control, which is why it is divided into two portions, and the sheep have only one. The sheep’s behavior and motor control are less complex than humans.

Sheep brains, although smaller than human brains, have similar features as human and sheep brains are similar in function so the sheep brain can be utilized for the study of brain physiology and anatomy. A sheep brain dissection is perfect for anatomy and brain structure studies.

Dissection of Sheep Brain 

             A scalpel is used for dissection of sheep’s brain and the following structures can be analyzed that include the cerebrum, cerebellum, spinal cord, corpus callosum, pituitary gland, pineal gland, sulci, gyri, olfactory bulbs, brain stem, temporal lobe, frontal lobe, parietal lobe, occipital lobe, rhinencephalon lobe and other major structures and parts of brain look alike.

   This plain preserved sheep brain specimen comes with the cranial nerve attached.

The Function of the Cerebellum in Sheep

            The cerebellum in sheep helps in coordinating the voluntary movements. Most movements are composed of several different muscle groups acting together in a temporally coordinated fashion.

One major function of the cerebellum is to coordinate the timing and force these different muscle groups to produce fluid limb or body movements. Cerebellum has different functions that are discussed below.

• Maintenance of balance and posture
• Coordination of voluntary movements
• Motor learning
• Cognitive functions

Maintenance of Balance and posture

       The cerebellum is important for making postural adjustments to maintain balance. Through its input from vestibular receptors and proprioceptors, it modulates command to motor neurons to compensate for shifts in body position or changes in load upon muscles.

Sheep with cerebellar damage suffer from a balance disorder, and they can often develop often stereotyped postural strategies to compensate for this problem.

Coordination of Voluntary Movements

Most movements are composed of several different muscle groups acting together in a temporally coordinated fashion. One major function of the cerebellum is to coordinate the timing and force of these muscle groups to produce fluid limb or body movements.

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Motor Learning 

                 The cerebellum is important for motor learning. The cerebellum plays a major role in adapting and fine-tuning motor programs to make accurate movements through trial and error processes.

Cognitive Functions 

Although the cerebellum is most in terms of its contribution to the motor canal, it is also involved in certain cognitive functions, such as language. Thus, like the basal ganglia, the cerebellum is considered as part of the motor system, but its functions extend beyond control in many ways that are not yet well understood.

Cerebellar Gross Anatomy 

 The cerebellum consists of two major parts. The deep cerebellar nuclei are the sole output structures of the cerebellum. These nuclei are encased by a highly convoluted sheet of tissue called the cerebellar cortex, which contains almost all of the neurons in the cerebellum.

A cross-section through the cerebellum reveals the intricate pattern of folds and fissures that characterize the cerebellar cortex. Like the cerebellar cortex, cerebellar gyri are reproducible across individuals and have been identified and named. The only concerned topics are the larger divisions of the cerebellar cortex.

Divisions of the Cerebellum 

Two major fissures running mediolaterally divide the cerebellar cortex into three primary subdivisions.

Posterolateral Subdivision 

The posterolateral fissure separates the flocculonodular lobe from the corpus cerebelli, and the primary fissure separates the corpus cerebelli into the posterior lobe and an anterior lobe. The cerebellum is also divided sagittally into three zones that run from medial to lateral.

The vermis is located along the midsaggital plane of the cerebellum. Directly lateral to the vermis is the intermediate zone. Finally, the lateral hemispheres are located lateral to the intermediate zone.

Cerebellar Nuclei 

                   All outputs from the cerebellum originate from the deep cerebellar nuclei. Thus, a lesion to the cerebellar nuclei has the same effects as a complete lesion of the entire cerebellum. It is important to know the inputs, outputs, and anatomical relationships between the different cerebellar nuclei and subdivisions of the cerebellum.

• Fastigial nuclei
• Interposed nuclei
• Dentate nucleus
• Vestibular nuclei

Fastigial Nuclei 

                  The fastigial nuclei are the most medially located of the cerebellar nuclei. It receives input from the vermis and from cerebellar afferents that carry vestibular, proximal somatosensory, auditory, and visual information. It projects to the vestibular nuclei and the reticular formation.

Interposed Nuclei 

The interposed nuclei comprise the emboliform nuclei and the globose nucleus. They are situated lateral to the fastigial nucleus. They receive input from the intermediate zone and from cerebellar afferents that carry spinal, proximal somatosensory, auditory, and visual information. They project to the contralateral red nucleus.

Dentate Nucleus

                    The dentate nucleus is the largest of the cerebellar nuclei, located lateral to the interposed nuclei. It receives input from the lateral hemisphere and from cerebellar afferents that carry information from the cerebellar cortex. It projects to the contralateral red nucleus and the ventrolateral thalamic nucleus.

Vestibular Nuclei 

             The vestibular nuclei are located outside the cerebellum, in the medulla. Hence, they are not strictly cerebellar nuclei, but they are considered to be functionally equivalent to the cerebellar nuclei because their connectivity patterns are identical to the cerebellar nuclei.

The vestibular nuclei receive input from the floccunoduar lobe and the vestibular labyrinth. The project to various motor nuclei and originate the vestibulospinal tracts.

                In addition to these inputs, all cerebellar nuclei and all regions of the cerebellum get special inputs from the inferior olive of the medulla.

               It is convenient to remember that the anatomical locations of the cerebellar nuclei correspond to the cerebellar cortex regions from which they receive input.

Thus, the medially located fastigial nucleus receives input from the medially located vermis, the slightly lateral interposed nuclei receive input from the slightly lateral intermediate zone, and the most lateral dentate nucleus receives input from the lateral hemispheres.

Cerebellar Peduncles 

               Three fibre bundles carry the input and output of the cerebellum.

• Inferior cerebellar peduncle
• Middle cerebellar peduncle
• Superior cerebellar peduncle

1. Inferior Cerebellar Peduncle

The inferior cerebellar peduncle primarily contains afferent fibers from the medulla, as well as efferents to the vestibular nuclei.

2. Middle Cerebellar Peduncle 

             The middle cerebellar peduncle primarily contains afferents from the pontine nuclei.

3. Superior Cerebellar Peduncle

The superior cerebellar peduncle primarily contains different fibers from the cerebellar nuclei, as well as some afferents from the spinocerebellar tract.

Thus, the inputs to the cerebellum are conveyed primarily through the inferior and middle cerebellar peduncles, whereas the outputs are conveyed primarily through the superior cerebellar peduncle.

The input arises from the ipsilateral side of the body, and the outputs also go to the ipsilateral side of the body. Thus, cerebellar outputs to the red nucleus affect the ipsilateral side of the body by a double-crossed pathway.

Unlike the cerebellar cortex, the cerebellum receives input from, and controls output to, the ipsilateral side of the body, and damage to the cerebellum, therefore, results in deficits to the ipsilateral side of the body.

Functional Subdivision of the Cerebellum 

                               The anatomical subdivisions described above correspond to three major functional subdivisions of the cerebellum.

• Vestibular cerebellum
• Spinocerebellum
• Cerebrocerebellum

1. Vestibular Cerebellum 

                   The vestibular cerebellum comprises the flocculondular lobe and its connection with the lateral vestibular nuclei. Phylogenetically, the vestibulocerebellum is the oldest part of the cerebellum. As the name implies, it is involved in vestibular reflexes.

2. Spinocerebellum

               The spinocerebellum comprises the vermis and the intermediate zones of the cerebellar cortex, as well as the fastigial and interposed nuclei.

As its name implies, it receives major inputs from the spinocerebellar tracts. Its output projects to the rubrospinal, vestibulospinal, and reticulospinal tracts. It is involved in the integration of sensory input with motor commands to produce adaptive motor coordination.

3. Cerebrocerebellum

              The cerebrocerebellum is the largest functional subdivision of the human cerebellum, comprising the lateral hemisphere and the dentate nuclei. Its name derives from its extensive connections with the cerebellar cortex, via the pontine nuclei and the VL thalamus (efferents).

It is involved in the planning and timing of the movements. Also, the cerebrocerebellum is involved in the cognitive functions of the cerebellum.

Sheep Brain Dissection 

          When the sheep brain is dissected, different structures present in the brain can be seen and observed, and their functions have been studied in accordance.

Choroid Plexus 

Location of choroid plexus

The choroid plexus is found in both lateral ventricles, third ventricle, and fourth ventricle of the brain in the meninges.

Function

             They provide cerebrospinal fluid and help to protect the brain and another central nervous system issue.

Folding of Cerebrum 

Folding of the cerebrum is important because it means more surface area. The more folds mean the more neurons brain holds. The human brain has more folds than a sheep brain. The human brain is rounded, larger, and heavier than the sheep brain. The human brain also makes us capable of thinking, writing, inventing, and creating, whereas the sheep brain cannot.

Division of Cerebellum 

Brain Stem  

           The brain stem in humans is towards the backbone and downwards compared to the sheep’s backbone, which is horizontal, and its brain is directed towards outside.

Difference Between Human and Sheep Brain

Sheep brains are readily available from scientific vendors for dissection, making them a popular choice in neuroanatomy classes, whereas the ultimate goal is to learn about the human brain.

This is because the human and sheep brain are very similar to each other. However, some key differences should be considered

Different Shape and Size 

                                          The sheep brain and human brain are very similar in overall structure, as are all mammalian brains. Each contains a cerebrum, cerebellum, and brain stem. The sheep brain is smaller weighing around 140g or about one-tenth of the weight of an adult human brain, though it is still large enough to be easily dissected.

The cerebrum is more elongated in sheep than in humans, and the cerebellum and brain stem are located behind the cerebrum, instead of being tucked below it. This is because sheep, being a four-legged animal, have a horizontal spine, while humans stand upright with their spines vertical.

Frontal Lobe 

           A major difference is that the frontal lobe in the sheep brain is much smaller relative to overall brain size, accounting for only a few percent by volume compared to about 25 percent in the human case. The frontal lobe is connected with higher cognitive functions, such as abstract thinking and analysis.

The relative size of the frontal lobe, as well as the number of the ridge in the cortex, are indicators of species intelligence. Though the sheep has generally been regarded as an unintelligent animal, it is increasingly recognized that sheep can perform some advanced tasks, such as remembering the faces of other sheep and humans for two years or longer.

Olfactory Bulb 

               The sheep, like many mammals, have a more developed sense of smell, or olfaction than humans do. The olfactory bulb is the part of the brain located underneath the front lobe that is responsible for relaying the sensory information from the nose to the rest of the brain.

The olfactory bulb in sheep is two to three times of the human olfactory bulb, despite the sheep brain being much smaller overall. This reflects the importance of the smell of sheep.

Optic Chiasm 

              The optic chiasm is a cross-shaped structure centrally located on the underside of the brain where optic nerve fibers from each eye partially cross over to the corresponding optical tract on the other side of the brain.

It is more pronounced in sheep because sheep, like many prey animals, have eyes towards the side of the head that operate more independently, giving the sheep a much wider field of vision. Therefore most of the visual information from each eye cross over. Human has more frontal eyes and shares information from each eye more evenly between the brain hemispheres to enable complex visual processing tasks, such as depth perception.

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