More importantly still, the brain stem is the origin of a multitude of fibre systems, ascending to higher levels as well as those descending into the spinal cord, passing into the cerebellum, or, just as richly, terminating elsewhere within the brain stem.
Similarly, signals relating to the sense of touch or limb movement ( somatic sensation and proprioception) are relayed in cells within the medulla. It is also a relay for certain categories of movement commanded by the motor cortex, as instanced by signals related to hand clenching conveyed in the ‘rubrospinal tract’, with its neuronal cell bodies at the upper end of the brain stem. The brain stem is very much more than simply a viaduct for the long nerve fibre tracts directly linking brain and spinal cord. These two nerves also carry important information from receptors in the lungs, heart, and blood vessels essential to the reflex regulation of these structures.īy virtue of its nerve connections the brain stem mediates important reflexes, including protection of the eyes by closure of the lids, protection of the throat by gagging, and elimination of irritant bodies by sneezing and coughing. The ninth ( glossopharyngeal) and tenth ( vagus) nerves also contain the special system of ‘parasympathetic’ motor fibres of the autonomic nervous system that innervate not only structures around the head and neck (such as the salivary glands) but also, in the case of the vagus nerves, the thoracic and abdominal organs (heart, bronchi, gut). The eighth ( auditory) cranial nerve carries mainly sensory fibres from two highly specialized structures, the cochlear and vestibular apparatus, concerned respectively with hearing and balance.
The brain stem consists of the skin#
Most of these nerves also carry incoming information: the massive fifth cranial nerve ( trigeminal) has a rich abundance of sensory fibres contributing to the exquisite tactile sensitivity of the facial skin at the mouth, eyes, cornea and, less agreeably, ones from the dental pulp and gums to cause dental pain. Damage to the seventh cranial ( facial) nerve on one side for example, creates the characteristic asymmetry of the ‘set’, smile or grimace in ‘Bell's Palsy’, while motorneuron disease affecting other cranial nerves interferes with speech. These contain motor nerves to skeletal muscle fibres that move the eyes, to the facial muscles responsible for the familiar expression or ‘set’ of a face, and to those controlling the movements of the jaw, the tongue, and the larynx. From above down these are the midbrain a bridge-like structure, the pons and the medulla oblongata, which merges below with the spinal cord.įrom the brain stem emerge pairs of cranial nerves, analogous to the spinal nerves that innervate the limbs and trunk. The brain stem itself consists of three distinct parts. The brain stem forms a bridge between cerebrum and spinal cord and also carries the major pathways ( peduncles) for signals to pass to and from the cerebellum. With the cerebellum behind and above it, it occupies the smaller, back part of the skull cavity. And at the base of the cerebrum, emerging like the stalk from a mushroom cap, is an elongated structure, the brain stem. The cerebral hemispheres ( cerebrum) of the brain occupy the larger, front part of the cavity of the skull. The hindbrain, also referred to as the brainstem, is made of the medulla, pons, cranial nerves, and back part of the brain called cerebellum.Brain stem The brain within the skull and the spinal cord within the vertebral column constitute the central nervous system.
The midbrain consists of various cranial nerve nuclei, tectum, tegmentum, colliculi, and crura cerebi. The structures in the forebrain include the cerebrum, thalamus, hypothalamus, pituitary gland, limbic system, and the olfactory bulb. The forebrain, midbrain and hindbrain make up the three major parts of the brain. The brain works as a single organ but is divided into areas of special expertise and function. Our emotions, memory and personality as well as our senses-sight, touch, hearing, taste, smell-originate in our brain. The brain controls both voluntary actions, like talking and running, and involuntary actions like breathing and reflexes. The major parts of the brain are made up of different structures each of which has a unique and important function.
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