Brainstem
The brain stem is a critical anatomical structure that serves as a connection between the forebrain, cerebellum, and spinal cord. It plays an essential role in regulating involuntary bodily functions, including breathing and heart rate. The brain stem consists of three main parts: the midbrain, pons, and medulla, each contributing to various vital functions and facilitating communication between the brain and spinal cord. The medulla, located at the base, oversees essential processes such as heartbeat and reflex actions like coughing and sneezing. The pons, positioned above the medulla, is involved in motor control and sensory perception, while the midbrain aids in body and eye movement, as well as auditory and visual processing.
Moreover, the brain stem houses many cranial nerves that transmit motor and sensory signals throughout the body, with ten of the twelve pairs connecting to different regions of the brain stem. This structure is evolutionary ancient, present in many animal species, which underscores its fundamental role in survival and basic functionality. Understanding the brain stem's anatomy and function is crucial for comprehending how the central nervous system operates and maintains life-supporting activities.
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Brain stem
The brain stem is an anatomical structure of the brain. It links the forebrain, the cerebellum, and the spinal cord. The brain stem plays a vital role in bodily functions such as breathing and heart rate. It is mostly involved in regulating involuntary processes. The brain stem includes three main parts: midbrain, pons, and medulla. The parts help the body perform vital functions, and they send signals between the brain and the spinal cord.
Background
The brain stem is part of the central nervous system (CNS). The CNS is the system that controls all other parts of the body. The two main parts of the central nervous system are the spinal cord and the brain. The brain is housed and protected inside the bony skull. The spinal cord is protected inside a canal that runs through the vertebrae of the spine. The spinal cord is a bundle of nerves that sends signals to the body from the brain and from the brain to the body. The spinal cord is about 43 to 45 centimeters (16 to 18 inches) long and runs from the center of the back up to the skull. When the spinal cord enters the skull, it becomes the brain stem.
Two types of cells make up the parts of the central nervous system: neurons and glial cells. Neurons are cells that send signals throughout the CNS and other parts of the body. Glial cells make up most of the CNS, and they protect neurons, provide nutrients to neurons, create and move cerebral spinal fluid, and more. Neurons and glial cells are highly specialized, and many different types of each exist in different parts of the body. All neurons have the same basic structure. A neuron has a main part called the cell body. It has dendrites, which are small branches that project out from the cell body. It also has an axon, which stems from one side of the neuron. Axons can be very long. They send signals from the neurons to other cells.
The cells that make up the CNS are coated in a material called myelin. This material is white and is made mostly of lipids and proteins. The coating helps protect jelly-like glial and neuron cells. The brain stem, other parts of the brain, and the spinal cord are also bathed in cerebral spinal fluid. This clear, colorless fluid helps protect the CNS by cushioning blows and other injuries. The fluid is produced inside the brain, and is absorbed by the blood so that it can be replaced to ensure any waste products are taken away from the brain.
Overview
The brain stem begins when the bundle of nerves that is the spinal cord enters the bony skull. The section of the brain stem that is located nearest the spinal cord is called the medulla. The medulla, or medulla oblongata, is the lowest part of the brain stem. The medulla helps maintain some of the vital functions of the human body, such as breathing and heartbeat. It also helps control many reflex functions such as vomiting, coughing, and sneezing. This part of the brain stem includes the medullary pyramids, which are structures that include roughly one million corticospinal axons.
The pons, the middle section of the brain stem, is positioned above the medulla. This section of the brain stem is involved in motor control, such as control of some facial muscles, and sensory perception, such as understanding where one is in space. The pons also has parts that help regulate consciousness and sleep.
The midbrain, which is also called the mesencephalon, is the highest part of the brain stem. The top of the midbrain is called the tectum (or tectal area). This part of the midbrain connects to the cerebellum. The bottom of the midbrain is called the tegmentum. The midbrain is important for body movement, eye movement, vision, and hearing. It also plays a role in voluntary body movement.
The cerebellum is a brain structure that lies behind the brain stem. The brain stem is connected to the cerebellum via three peduncles. The inferior peduncle connects the cerebellum to the medulla. The middle peduncle, which is the largest, connects the cerebellum to the pons. The superior peduncle connects the cerebellum to the midbrain.
The brain stem is also the part of the brain where many cranial nerves (CNs) connect to the brain. Humans have twelve different pairs of CNs. CNs are nerves that send and receive motor and sensory signals between the brain and other parts of the body. Ten CNs connect to various parts of the brain stem.
- CN III (oculomotor nerve) connects to the midbrain. It helps control eye movement and pupil constriction.
- CN IV (trochlear nerve) connects to the midbrain. It also helps control eye movement.
- CN V (trigeminal nerve) connects to the pons. It sends sensory information from the face and head.
- CN VI (abducens nerve) connects to the pons. It helps control eye movement.
- CN VII (facial nerve) connects at the border between the pons and the medulla. It helps control muscles in the face.
- CN VIII (vestibulocochlear nerve) connects to the pons. This nerve sends auditory information and information about where a person is in space.
- CN IX (glossopharyngeal nerve) connects to the medulla. It sends sensory and motor information to parts of the tongue and throat.
- CN X (vagus nerve) connects to the medulla. It sends sensory and motor function information to some glands and organs.
- CN XI (spinal accessory nerve) connects to the medulla. It helps control head movement.
- CN XII (hypoglossal nerve) connects to the medulla. It helps control the muscles of the tongue.
The brain stem is one of the evolutionarily oldest parts of the brain. Many animals have brains that include parts similar to the human brain stem. Reptiles' brains include parts similar to the human brain stem, but they do not include more advanced parts, such as the cerebrum, which support higher-level thinking.
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