35.11: The Central Nervous System - Midbrain and Brain Stem
- Explain the structure and function of the non-cerebral cortex portions of the brain
Basal Ganglia
Interconnected brain areas called the basal ganglia (or basal nuclei) play important roles in movement control and posture. Damage to the basal ganglia, which occurs in Parkinson’s disease, leads to motor impairments such as a shuffling gait when walking. The basal ganglia also regulate motivation. For example, when a wasp sting led to bilateral basal ganglia damage in a 25-year-old businessman, he began to spend all his days in bed and showed no interest in anything or anybody. But when he was externally stimulated, as when someone asked to play a card game with him, he was able to function normally. Interestingly, he and other similar patients do not report feeling bored or frustrated by their state.
Thalamus
The thalamus (Greek for “inner chamber”) acts as a gateway to and from the cortex. It receives sensory and motor inputs from the body and also receives feedback from the cortex. This feedback mechanism can modulate conscious awareness of sensory and motor inputs depending on the attention and arousal state of the animal. The thalamus helps regulate consciousness, arousal, and sleep states. A rare genetic disorder, fatal familial insomnia, causes the degeneration of thalamic neurons and glia. This disorder prevents affected patients from being able to sleep, among other symptoms, and is eventually fatal.
Hypothalamus
Below the thalamus is the hypothalamus. The hypothalamus controls the endocrine system by sending signals to the pituitary gland, a pea-sized endocrine gland that releases several different hormones that affect other glands as well as other cells. This relationship means that the hypothalamus regulates important behaviors that are controlled by these hormones. The hypothalamus is the body’s thermostat: it makes sure key functions like food and water intake, energy expenditure, and body temperature are kept at appropriate levels. Neurons within the hypothalamus also regulate circadian rhythms, sometimes called sleep cycles.
The limbic system is a connected set of structures that regulates emotion, as well as behaviors related to fear and motivation. It plays a role in memory formation and includes parts of the thalamus and hypothalamus as well as the hippocampus. One important structure within the limbic system is a temporal lobe structure called the amygdala (Greek for “almond”). The two amygdale are important both for the sensation of fear and for recognizing fearful faces. The cingulate gyrus helps regulate emotions and pain.
Cerebellum
The cerebellum (Latin for “little brain”) sits at the base of the brain on top of the brainstem. The cerebellum controls balance and aids in coordinating movement and learning new motor tasks.
Brainstem
The brainstem connects the rest of the brain with the spinal cord. It consists of the midbrain, medulla oblongata, and the pons. Motor and sensory neurons extend through the brainstem, allowing for the relay of signals between the brain and spinal cord. Ascending neural pathways cross in this section of the brain, allowing the left hemisphere of the cerebrum to control the right side of the body and vice versa. The brainstem coordinates motor control signals sent from the brain to the body. It also controls several important functions of the body including alertness, arousal, breathing, blood pressure, digestion, heart rate, swallowing, walking, and sensory and motor information integration.
Key Points
- The basal ganglia control movement and posture; they also appear to be involved in self-motivation.
- The thalamus communicates information from the cerebral cortex to the rest of the body and also helps regulate the states of consciousness versus sleep.
- The hypothalamus regulates the pituitary gland, which controls the release of hormones throughout the body; it indirectly regulates functions such as water intake, body temperature, and sleep cycles.
- The limbic system includes the amygdala, the hippocampus, and parts of the thalamus and hypothalamus; it regulates emotion, fear, and motivation.
- The cerebellum controls motor reflexes and is, therefore, involved in balance and muscle coordination.
- The brainstem connects and transmits signals from the brain to the spinal cord, controlling functions such as breathing, heart rate, and alertness.
Key Terms
- cingulate gyrus : a section of the cerebral cortex, belonging to the fornicate gyrus, which arches over the corpus callosum
- limbic system : part of the human brain involved in emotion, motivation, and emotional association with memory
- endocrine system : a control system of ductless glands that secrete hormones which circulate via the bloodstream to affect cells within specific organs