Central nervous system (CNS) is composed of the brain and the spinal cord, including the nuclei and cell bodies of most nerve cells. The brain is the organ that controls the body. It is also the center of consciousness. It is divided into three areas: the cerebrum, cerebellum, and brainstem. The cerebrum, which contains about 75% of the brain’s total volume, controls a wide variety of activities, including most voluntary motor function and conscious thought. It is the main part of the brain and is divided into two hemispheres with four lobes. The cerebellum coordinates balance and body movements. The brainstem controls all the functions that are necessary for life, including the cardiac and respiratory systems and nerve function transmissions. The spinal cord carries messages between the brain and the body via the gray and white matter. Gray matter is composed of neural cell bodies and synapses, which are connections between nerve cells. White matter consists of fiber pathways. To protect the brain and spinal cord, the skull is covered by layers of muscle called superficial fascia. The spinal canal is surrounded by a thick layer of skin and muscles, further protected by the meninges, which are three distinct layers of tissue that suspend the brain and the spinal cord. Long nerve fibers link these cells to the body’s various organs through openings in the spinal column. These nerve fibers constitute the PNS. The brain is a layered structure starting with the skin, then the fascia, followed by muscle, skull outer and inner table, then the meninges. The outer layer of the meninges is called the dura mater, which is a tough fibrous layer that closely resembles leather. This layer forms a sac to contain the CNS, with small openings through which the peripheral nerves exit. The inner two layers of the meninges are called the arachnoid and pia mater. They contain the blood vessels that nourish the brain and spinal cord. Cerebrospinal fluid (CSF) is produced in a chamber inside the brain called the third ventricle. CSF acts mainly as a shock absorber. If a patient has what looks like a runny nose or reports a salty taste at the back of the throat, you should assume that the fluid is CSF. Serious bleeding within the skull is referred to as intracranial hemorrhage.
The Peripheral Nervous System has two anatomic parts: 31 pairs of spinal nerves and 12 pairs of cranial nerves. These 31 pairs of spinal nerves conduct sensory impulses from the skin and other organs to the spinal cord. They also conduct motor impulses from the spinal cord to the muscles. The brachial plexus controls the arms, and the lumbosacral plexus controls the legs. The 12 pairs of nerves that emerge from the brainstem perform special functions in the head and face, including sight, smell, taste, hearing, and facial expression. There are two major types of peripheral nerves: sensory nerves, with endings that perceive only one type of information, and motor nerves, with short fibers, which allow the cells on either end to exchange simple messages. If a sensory nerve detects an irritating stimulus, it will bypass the brain and send a direct message to a motor nerve.
Voluntary activities are the actions that we consciously perform, in which sensory input determines the specific muscular activity. Involuntary activities are the actions that are not under our conscious control, such as breathing. The nervous system that regulates or controls our voluntary activities, including almost all coordinated muscular activities, is called the somatic (voluntary) nervous system. The brain interprets the sensory information that it receives from the peripheral and cranial nerves and responds by sending signals to the voluntary muscles. Body functions that occur without conscious effort are controlled by the autonomic nervous system, which is divided into two sections. The sympathetic nervous system reacts to stress with the fight-or-flight response, causing pupils to dilate, smooth muscle in the lungs to dilate, heart rate to increase, and blood pressure to rise. The body also shunts blood to vital organs and to skeletal muscle—epinephrine (adrenaline) is released. The parasympathetic nervous system has the opposite effect on the body, causing blood vessels to dilate, slowing the heart rate, and relaxing the muscle sphincters. The body shunts blood to the organs of digestion.
The skull is composed of the cranium and the facial bones. The cranium is occupied by 80% brain tissue, 10% blood supply, and 10% CSF. The spinal cord is divided into 5 sections, the first being the cervical (7), next the thoracic (12), followed by the lumbar (5), then the sacral (5), and finally the coccygeal (4). Each vertebra consists of a round, solid block of bone called the vertebral body; the back part forms a bony arch. The series of arches forms a tunnel running the length of the spinal column. This tunnel is the spinal canal, which encases and protects the spinal cord. Vertebrae are connected by ligaments and separated by cushions called intervertebral disks. When the spinal cord and its nerves are left unprotected, injury can occur. Therefore, keep the spine aligned throughout transport.
More than 50% of all traumatic deaths result from a head injury. There are two types of head injuries. In a closed head injury, the brain has been injured but there is no opening to the brain. In an open head injury, an opening exists from the outside world to the brain. Obvious skull deformity with a break in the skin is a sign of an open head injury. Even a small laceration can quickly lead to significant blood loss. Occasionally, bleeding may be severe enough to cause hypovolemic shock. These injuries are often an indicator of deeper, more serious injuries.
Significant force applied to the head may cause a skull fracture. Additional signs of skull fracture that you may see include ecchymosis that develops under the eye (raccoon eyes) or behind one ear over the mastoid process (Battle sign). Linear skull fractures account for 80% of all fractures. If the brain is uninjured and there are no scalp lacerations, then linear fractures are not life-threatening. However, if there is a scalp laceration with a linear fracture—making it an open fracture—there is a risk of infection and bleeding inside the brain. Depressed skull fractures result from high-energy direct trauma to the head with blunt objects. Bony fragments may be driven into the brain, resulting in injury. Patients with depressed skull fractures often present with signs of neurologic injury (such as a loss of consciousness). Basilar skull fractures result from diffuse impact to the head (falls, motor vehicle crashes) and form from the extension of a linear fracture. CSF drainage from the nose or ears indicates rupture of the tympanic membrane in the ear. Patients with leaking CSF from either the nose or the ear are at risk for bacterial meningitis. You should also see raccoon eyes and Battle sign, but they may not appear until up to 24 hours after. In open skull fractures, brain tissue may be exposed to the environment, which significantly increases the risk of a bacterial infection.
Brain injuries are capable of producing physical, intellectual, emotional, social, and vocational changes. There is primary (direct) injury and secondary (indirect) injury. Primary injury is when the brain and its associated structures are injured as a result of impact to the head. Secondary brain injury refers to a multitude of processes that increase the severity of a primary brain injury and have a negative outcome; it may be caused by cerebral edema, intracranial hemorrhage, increased intracranial pressure (ICP), cerebral ischemia, and infection. Hypoxia and hypotension are the two most common causes. When the brain slams into the rear of the skull, this type of injury is known as a coup-contrecoup injury. Cerebral edema is the swelling of the brain and may not develop until several hours following the initial injury. Low oxygen levels in the blood aggravate cerebral edema, so provide oxygen before cyanosis or other obvious signs of hypoxia. Be prepared to manage seizures in all patients who have had a head injury.
The skull is rigid and doesn’t allow expansion of the intracranial contents. Therefore, the accumulation of blood within the skull or swelling of the brain can rapidly lead to an increase in intracranial pressure (ICP). Cheyne-Stokes respirations (respirations that become fast and then become slow, with intervening periods of apnea) are signs of increased ICP. Central neurogenic hyperventilation is another abnormal breathing pattern associated with high ICP; it is characterized by deep, rapid breathing. The pattern is similar to Kussmaul respirations; however, there is no acetone breath smell. Other signs are decreased pulse rate, headache, nausea, vomiting, decreased alertness, bradycardia, sluggish or nonreactive pupils, decerebrate posturing, and an increased or widened pulse pressure. The triad of increased systolic blood pressure, decreased heart rate, and irregular respiration is called the Cushing reflex.
Intracranial hemorrhage is bleeding inside the skull and can increase pressure. Epidural hematoma is an accumulation of blood between the skull and dura mater. It is almost always a result of a blow to the head that produces a linear fracture in the thin temporal bone; the meningeal artery runs along a groove in that bone. Arterial bleeding into the epidural space will rapidly progress symptoms. Often the patient will lapse in and out of consciousness. Death will follow rapidly without surgery to evacuate the hematoma. Subdural hematoma is the accumulation of blood beneath the dura mater but outside the brain. It may or may not be associated with a skull fracture. It is venous bleeding, so the increased ICP typically develops more gradually than with an epidural hematoma. Patients often experience a fluctuating level of consciousness or slurred speech. Intracerebral hematoma is bleeding within the brain tissue itself; once symptoms appear, the patient’s condition often deteriorates quickly and has a high mortality rate. Subarachnoid hemorrhage is bleeding occurring in the subarachnoid space where the CSF circulates. It results in blood in the CSF and signs of meningeal irritation (such as neck rigidity or headache). Common causes are trauma or rupture of an aneurysm. Signs include decreased level of consciousness, changes in the pupils, vomiting, and seizures.
Concussions are mild TBIs. They are traumatic brain injuries without demonstrable physical damage to the brain. A concussion is a functional change, not a structural change. Patients with a concussion may be confused or have amnesia—occasionally the patient can remember everything but the events leading up to the injury; this is called retrograde amnesia. A patient who cannot remember events after injury is said to have anterograde (posttraumatic) amnesia. Ask about dizziness, weakness, visual changes, or changes in mood. Nausea and vomiting may occur, and patients may have delayed motor functions. Contusions are often more serious because there is swelling from injured blood vessels. Other brain injuries include blood clots or hemorrhages that can also cause brain injuries. Be very alert when there is an altered mental status.
Force that compresses the patient’s vertebral body can cause the herniation of disks, subsequent compression of the spinal cord and nerve roots, and fragmentation into the spinal canal. Trauma can overextend or hyperflex the cervical spine and damage the ligaments and joints. Rotation-flexion injuries of the spine result from rapid acceleration forces—likely to happen at C1 and C2. Injuries to this area of the spine are considered unstable because of the location on the body and lack of bony and soft-tissue support. When a spine is pulled along its length (hyperextension), it can cause fractures in the spine as well as ligament and muscle injuries. When the bones of the spine are altered from traumatic forces, they can fracture or move out of place; when these injuries pinch, pull, or penetrate the spinal cord, permanent damage may occur. Less commonly, you may feel or observe a deformity of the spine, sometimes referred to as a “step-off” of the spinous process. If you feel this, take extra precautions when immobilizing the spine, both manually and with adjuncts.
A helmet that fits well and prevents the patient’s head from moving should be left on if there are no impending airway or breathing problems, it doesn’t interfere with assessment and treatment of airway or ventilation problems, and you can immobilize the spine. It should also be left on if taking it off would injure the patient more. Remove a helmet if it is a full-face helmet, it makes assessing or managing airway problems difficult, it prevents you from properly immobilizing the spine, and allows for excessive head movement. When removing, make sure to keep the body in an inline position if the person is wearing something like shoulder pads.
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