A traumatic brain injury (TBI) is a form of brain injury caused by an external physical force.  In addition to direct injury at the site of an impact, the rapid acceleration-deceleration of the head may cause the brain to move within the skull and result in injury to the part of the brain opposite the impact site.  This is known as a contrecoup injury.If an impact to the head also results in a skull fracture, the injury is classified as an open TBI.  If there is no skull fracture, the injury is classified as a closed TBI.  The type of TBI can be predicted from the collision duration and the average acceleration of the head.  The thresholds for open and closed TBI are shown in Figure 1.Figure 1  Thresholds for open and closed TBIIn an experiment to study head collisions with projectiles, researchers equipped the head of a crash test dummy with sensors that measured acceleration on multiple axes.  The crash test dummy was stationary before its head was subjected to controlled collisions with incoming projectiles of varying mass and impact velocity.  The linear acceleration of the crash test dummy's head was recorded during and after the impact.  The results for a trial in which the impact lasted for 10 ms are shown in Figure 2.Figure 2  The acceleration of the head during and after a 10-ms collision Question 4A baseball traveling at 20 m/s strikes a player running at 5 m/s.  The relative speed of the ball with respect to the player depends on the direction of travel of the ball relative to the player's direction of travel.  What is the difference between the minimum and maximum possible speeds of the ball relative to the player?A.10 m/sB.15 m/sC.20 m/sD.25 m/s

type of Head injury: occurs on the opposite side of the brain from the site of impact. aCoup injury bcontrecoup injury cskull fracture dICP

A 54-year-old female with symptoms of persistent fatigue and impaired cognitive function was examined by her physician.  During the exam, the patient expressed concern over increased body fat and, under questioning, reported having suffered a concussion during a soccer match in college.  Based upon the patient's symptoms and responses to questions, the physician ordered a panel of tests.A concussion is a mild traumatic brain injury (TBI) that results from impact to the skull.  TBI occurs most frequently in male patients, typically due to accidents; however, there is growing appreciation that TBI also occurs in male and female athletes during sporting events.  In addition, previously unrecognized chronic responses to TBI (eg, hormonal deficiencies) are now better understood.As part of the examination, the patient underwent a test to evaluate growth hormone (GH) secretion.  The brain participates in regulating GH secretion, and roughly half of the GH secreted into the blood is bound to a binding protein that increases the half-life of GH by inhibiting its urinary elimination.  Furthermore, lipid-soluble sex hormones, such as estradiol, augment GH secretion.During the GH secretion test, GH-releasing hormone (GHRH) was administered to the patient along with arginine.  GHRH is an endogenous stimulator of GH secretion, and arginine inhibits secretion of somatostatin, an endogenous inhibitor of GH secretion.  When administered together in healthy individuals, GHRH and arginine strongly stimulate GH secretion into the blood.  However, this patient exhibited an abnormally small response to GHRH and arginine, leading the physician to start the patient on GH therapy.  After a year, the patient's symptoms had improved, and body composition testing showed that her lean body mass had increased. Question 36Based on the passage, a likely mechanism by which GH therapy relieves chronic symptoms associated with TBI is by:A.stimulating protein synthesis in multiple tissues.B.inhibiting protein synthesis in multiple tissues.C.stimulating GHRH release by the pituitary.D.inhibiting GHRH release by the pituitary.

Describe what happens in the brain when a traumatic brain injury occurs.

Traumatic brain injury (TBI) while riding roller coasters can occur when external forces cause the brain to accelerate or decelerate rapidly, damaging the brain tissue. TBI is a major cause of death and disability, but the extent to which riding a roller coaster poses an increased risk for TBI is unclear.Riders of coasters experience gravitational forces that may be too large for their body to withstand. Yet, gravitational forces alone cannot predict TBI. The body can endure large gravitational forces if they occur over periods of less than 25 seconds. Predicting the probability of a TBI requires the identification of kinematic parameters such as ride duration, coaster velocity, and acceleration, as well as those forces experienced by the body as a result.Measures such as the Head Injury Criterion (HIC) and Head Impact Power (HIP) are used to aid in TBI predictions. HIC is calculated using acceleration over a certain time interval (usually t = 15 ms) to estimate the likelihood of injury arising from an impact. HIC evaluates only linear acceleration, while HIP accounts for both linear and rotational acceleration. To compare the TBI risk of different activities, scientists often use the following equation:HIC = F x ∆tEquation 1where F is the average linear force and ∆t is the time interval. Scientists conducted an experiment to test the TBI risk of several activities in comparison to roller coasters. The linear accelerations, linear velocities, angular accelerations, and angular velocities of participants’ heads were measured and averaged for four participants across five activities: three roller coaster rides, a pillow fight, and a five m/s bumper hit (see Table 1). The linear acceleration of a pillow fight's results is graphed in Figure 2. Finally, the probability of a concussion, the most common and the least serious type of TBI, was graphed as a function of HIC. Participants 1, 2, 3, and 4 weigh 800, 350, 400, and 750 N, respectively.Table 1 Study resultsFigure 1 Head linear acceleration during pillow fightFigure 2 Predicted risk of concussionQuestion 40Which of the following situations would present Participant 3 with the greatest risk for TBI? A.A linear acceleration of 10 m/s2 for 2 ms in a car crashB.A single punch to the head causing acceleration of 100 m/s2 for 3 msC.Riding a roller coaster of 9 m/s2 sustained for 40 sD.Total body acceleration of 15 m/s2 for 1 ms

describe common mechanisms that contribute to extracranial and intracranial traumatic brain injuries, including intracranial hematomas.