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11.7A: Overview of the Cerebrum

With the assistance of the cerebellum, the cerebrum controls all voluntary actions in the body.

 

LEARNING OBJECTIVE

 

Describe the function of the cerebrum

 

KEY TAKEAWAYS

Key Points

 

  • The cerebrum is the largest and most developed of the five major divisions of the brain.
  • The brain contains two hemispheres, the left and the right, connected by a bundle of nerve fibers called the corpus callosum.
  • The cerebrum directs the conscious or volitional motor functions of the body. Damage to this area of the brain can result in loss of muscular power and precision rather than total paralysis.
  • The primary sensory areas of the cerebral cortex receive and process visual, auditory, somatosensory, gustatory, and olfactory information.
  • Each hemisphere of the mammalian cerebral cortex can be broken down into four functionally and spatially defined lobes: frontal, parietal, temporal, and occipital.

 

Key Terms

 

  • sulci: Any of the grooves that mark the convolutions of the surface of the brain (plural of sulcus).
  • cerebral cortex: The cerebrum’s outer layer of neural tissuecomposed of folded gray matter. The cerebral cortex plays a key role in memory, attention, perception, awareness, thought, language, and consciousness.
  • olfactory bulb: A neural structure of the vertebrate forebrain involved in olfaction (sense of smell).
  • Broca’s area: A region in the frontal lobe of the dominant hemisphere of the human brain with functions linked to speech production.
  • Wernicke’s area: Involved in the comprehension or understanding of written and spoken language.
  • aphasia: A combination speech and language disorder often caused by a stroke.
  • gyri: A ridge on the cerebral cortex (plural of gyrus).

 

Cerebrum Animation

 

Cerebrum Animation: Location of the cerebrum (in red).

The cerebrum, which lies in front or on top of the brainstem, comprises a large portion of the brain. In humans, it is the largest and best-developed of the brain’s five major divisions. The cerebrum is the newest structure in the phylogenetic sense, with mammals having the largest and most developed among all species.

The cerebrum contains the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb. In larger mammals, the cerebral cortex is folded into many gyri and sulci, which allows it to expand in surface area without taking up much greater volume. With the assistance of the cerebellum, the cerebrum controls all voluntary actions in the body.

Cerebral Cortex

The cerebral cortex

 

The cerebral cortex: The cerebral cortex is the outer layer depicted in dark violet. Notice the folded structure of the cortex: the “valleys” of the cortex are known as sulci.

The cortex is composed of two hemispheres, right and left, separated by a large sulcus. A thick fiber bundle, the corpus callosum, connects the two hemispheres, allowing information to be passed from one side to the other. The right hemisphere controls and processes signals from the left side of the body, while the left hemisphere controls and processes signals from the right side of the body.

The Four Brain Lobes

Each hemisphere of the mammalian cerebral cortex can be broken down into four functionally and spatially defined lobes: frontal, parietal, temporal, and occipital.

The frontal lobe is located at the front of the brain, over the eyes, and contains the olfactory bulb. The frontal lobe also contains the motor cortex, which is important for planning and implementing movement.

This diagram of the cerebral lobes delineates the frontal lobe, temporal lobe, medulla oblongata, spinal cord, cerebellum, occipital lobe, parietal lobe, somatosensory cortex, and somatomotor cortex.

 

Cerebral Lobes: Locations of the cerebral lobes

 

Two of the parietal lobe’s main functions are processing somatosensation (touch sensations such as pressure, pain, heat, cold) and proprioception (the sense of how parts of the body are oriented in space).

The temporal lobe is located at the base of the brain by the ears. It is primarily involved in processing and interpreting sounds. It also contains the hippocampus, which processes memory formation.

The occipital lobe is located at the back of the brain. It is primarily involved in vision: seeing, recognizing, and identifying the visual world.

Cerebrum Function

The cerebrum directs the conscious or volitional motor functions of the body. These functions originate within the primary motor cortex and other frontal lobe motor areas where actions are planned. Upper motor neurons in the primary motor cortex send their axons to the brainstem and spinal cord to synapse on the lower motor neurons, which innervate the muscles. Damage to motor areas of cortex can lead to certain types of motor neuron disease. This kind of damage results in loss of muscular power and precision rather than total paralysis.

The olfactory sensory system is unique in that neurons in the olfactory bulb send their axons directly to the olfactory cortex, rather than to the thalamus first. Damage to the olfactory bulb results in a loss of the sense of smell. The olfactory bulb also receives “top-down” information from such brain areas as the amygdala, neocortex, hippocampus, locus coeruleus, and substantia nigra. Its potential functions can be placed into four non-exclusive categories: discriminating among odors, enhancing sensitivity of odor detection, filtering out background odors, and permitting higher brain areas involved in arousal and attention to modify the detection or the discrimination of odors.

Speech and language are mainly attributed to parts of the cerebral cortex. Motor portions of language are attributed to Broca’s area within the frontal lobe. Speech comprehension is attributed to Wernicke’s area, at the temporal-parietal lobe junction. Damage to the Broca’s area results in expressive aphasia (non-fluent aphasia) while damage to Wernicke’s area results in receptive aphasia.