What is the Brainstem?
A Quick Description
From top to bottom, the brainstem includes the midbrain, the pons, and the medulla. Each of these sections contains nerve pathways, many of which travel throughout the whole brainstem. Cranial nerve roots are located in the brainstem, and each pair of the 12 cranial nerves emerge from the brainstem and join many parts of the body.
The brainstem is the area of the brain at the base of the brain which lies between the deep structures of the cerebral hemispheres and the cervical spinal cord. It serves a critical role in regulating certain involuntary actions of the body, including heartbeat and breathing. The brainstem is divided into three sections in humans: the midbrain, the pons, and the medulla oblongata.
The brainstem houses many of the control centres for vital body functions, such as swallowing, breathing, and blood vessel control. All of the cranial nerve nuclei, except those associated with olfaction and vision, are located in the brainstem, providing motor and sensory function to structures of the cranium, including the facial muscles, tongue, pharynx and larynx, as well as supplying the senses of taste, equilibrium, and hearing.
The Functions of the Brainstem
Many parts of the brain communicate with each other via parts of the brainstem. The majority of the automatic functions in the body are controlled by the brainstem.
Because of the important neural structures concentrated in this small portion of the nervous system, even very small lesions of the brainstem may have profound effects. Speech disorders, vestibular disturbance, abnormal consciousness, dysphagia, and respiratory disturbance are a few examples of possible outcomes of brainstem disorders. Complete loss of brainstem function is regarded by some experts as equivalent to brain death.
The Midbrain
All neuronal transmissions that pass through the body, to and from the brain, pass through the midbrain.
These are some of the functions performed by the midbrain:
*Management of auditory and visual information
*Moderation of the limbic system - emotions, behaviour, long term memory, motivation, learning scent, avoidance behaviour, anxiety
*Motor reflexes associated with auditory and visual stimuli (audio-/visual-spinal reflex)
*Connects brainstem to cerebrum
*Connects the brainstem to the cerebellum
*Contains an aqueduct which allows cerebrospinal fluid to flow from the 3rd to the 4th ventricle
*It is involved with coordination of movements
*The major coordinate system for auditory and somatosensory (voluntary) nerves
*It is involved in the suppression of pain
*It is involved with maintaining alertness
*Controls muscle tone, body position, and gait
*Planning and execution of voluntary movements
*Reception of visual sensory information from the retina
*Controls the orientation of the eyes and head
*Regulation of many autonomic (not consciously controlled body functions) such as: heart rate, blood pressure, smooth muscle contraction, production of vocalisations, the fight or flight response, and more
*Motor control
*Dopamine production and distribution
*Reward based learning patterns
*Circadian cycles also known as the sleep - wake cycle
*Relaying processed signals to various parts of the brain
*Involved in Rapid Eye Movement (REM)
*Fine motor skills
*Proprioception - the body’s ability to sense its position in the environment and in relation to other parts of the body
*Involved in cognitive ability
*Body temperature regulation
*Two cranial nerves control the movement of the eye and pupils’ light reflex
*Formation of visual memory
The Pons
In Latin pons means “bridge,” referring to the function and anatomical location of this structure – connecting the two hemispheres of the cerebrum. The pons also serves to connect the cerebral cortex to the medulla oblongata via the cerebral peduncles.
*Involved in many autonomic and sensory functions
*Arousal (staying awake)
*Respiration processes including diaphragm and intercostal muscles of breathing
*Fine motor control
*Equilibrium
*Muscle tone
*Circadian cycle (specifically regulating sleep)
*Many cranial nerves arise from the Pons including both sensory and motor
*Trigeminal, abducens, facial, and vestibulocochlear nerves arise from the Pons
*Trigeminal nerve - opthalmic, maxillary (upper jaw), and mandibular (lower jaw), includes controlling chewing, tongue movements, shrugging/shoulder movements, pharynx movement (voice box/vocal cords)
*Abducens nerve - controls the movement of the eyes, blinking reflex, gaze
*Facial nerve - controls expressions of the face, sensations of the face
*Vestibulocochlear nerve - regulates equilibrium, balance, and auditory sensations
*Connects the brainstem to the cerebellum and is the main source of the incoming messages from the body to the cerebellum. These primarily include planning and execution of fine movements of the arm, forearm, and hand.
*Coordination of movement
*Bladder control
*Posture
*Connects the spinal cord to the thalamus
*Transport of motor activity signals to the cerebellum and cerebral cortex
*Many major nerve pathways pass through the pons from the spinal cord to other parts of the brain
*Production of neurotransmitters
*Sensory and motor functions
*Consciousness
*Regulates activities in several areas of the brain
*Production of: dopamine, serotonin, acetylcholine, and more. These are related to sensory perception, motor control, and behavioural responses to various stimuli
*Corticospinal tract controls many motor functions including spinal reflexes and voluntary movements in parts of the body furthest from the brainstem
*Fine tactile sensation, detection of vibration, and proprioception (awareness of the position of body parts)
*Transmits information regarding pain, temperature, and touch
The Medulla
The medulla oblongata is essential to communications between the peripheral and central nervous systems as nearly all neuronal signals are sent through this organ. It controls various autonomic functions in the body.
*Controls respiration, digestion, heart rate, blood vessel functions, swallowing, sneezing
*Essential to communications between the central nervous system and the peripheral nervous system
*Connects the nerves from the pons which are responsible for autonomic sensory signals and so controls the coordination of somatosensory signals (the ability to interpret bodily sensation. Sensation takes a number of forms, including touch, pressure, vibration, temperature, itch, tickle, and pain) which regulate the sleep-wake cycle or circadian rhythm.
*Allows the flow of CFS from the brain ventricles and cisterns to the spinal cord
*Motor function, learning, auditory sensation
*Connects the pons, spinal cord, and cerebral cortex
*Connects the brainstem to the sacral, lumbar, and lower thoracic vertebrae. Transmits information on tactile and proprioception
*Connects brainstem to the upper thoracic and cervical vertebrae
*regulates many of the vital functions of the human body including respiration, heart rate, and blood pressure. Regarding its role in the circulation of blood throughout the body, the medulla oblongata works with the nucleus of the solitary tract. It is the first site through which sensory information related to taste and nerves going to the internal organs pass.
*Gastrointestinal function
*Vomiting
*Detection of toxic substances in the blood this can trigger the above mentioned function of vomiting
*The cranial nerves which arise from the medulla are:
1) glossopharyngeal (sensory - eustachian tube, middle ear, taste and other sensations to back third of the tongue, carotid sinus (blood pressure monitoring), carotid body (elects changes of arterial blood including oxygen, carbon dioxide, pH, and temperature), pharynx, controls the muscle which elevates the larynx and pharynx plus swallowing, carotid salivary glands
2) Vagus nerve: reception of sensory signals, visceral sensation to the heart and abdominal organs, taste to the epiglottis and tongue
*Innervates the muscles of the pharynx, soft palate, and larynx.
*Innervates the parasympathetic muscles of the trachea, bronchi, gastrointestinal tract, and heart
3) Accessory Nerve: control of innervating the trapezius muscles
4) Hypoglossal nerve: controls motor activity of the tongue