HOW FAST

How Fast are you

How fast are you

Aim: In this experiment we are to test our reflex actions and voluntary actions

Background:

Reflex action also known as involuntary actions do not involve the brain in making decisions, they are automatic. An example would be to put your hand on a hot object. In this case a sensory receptor from our finger would pick up an impulse, and the travel along the spinal cord, this cell is called a sensory neurone, because it is carrying an impulse from a sensory receptor.(Jeff Franklin 2005) It is well recognized that aging affects the performance of motor tasks, such as the maintenance of posture and balance control (Bohannon et al., 1984; Horak et al., 1989). It is presumed that both the central and peripheral nervous systems contribute to these phenomena, but the precise mechanisms are still unknown (Stelmach et al., 1989). Stretch reflex, a simple neural circuit that responds to the sudden stretch of a muscle, might be also affected by aging. Some investigations have paid attention to the effect of aging on the spinal reflex modulation of the soleus (SOL) muscle, which is a key muscle for postural control and bipedal walking (Koceja et al., 1995; Angulo-Kinzler et al., 1998; Chalmers and Knutzen, 2002; Kawashima et al., 2004). We previously demonstrated that elderly subjects show augmented short stretch reflex response in the SOL muscle at rest as compared to those in young subjects (Kawashima et al., 2004). It has also been demonstrated that elderly subjects lack the ability to modulate the SOL motoneuronal excitability for instance, Koceja et al. (1995) showed abnormal modulation of the motoneuronal excitability by postural changes. On the other hand, recent studies have suggested that the stretch reflex of the tibialis anterior (TA), the antagonistic muscle of the SOL muscle, also has an important role in stabilizing the ankle joint during upright standing (Nakazawa et al., 2003), and the early stance phase of walking (Christensen et al., 2001; Nakazawa et al., 2004). However, to the best of our knowledge, only one study has examined the changes of the TA muscle due to aging. Although Nardone et al. (1995) reported that the amplitude of the reflex action obtained in the TA muscle during upright standing did not depend on age; it remains unknown how the stretch reflex function of the TA muscle changes with age, and whether or not the aging process of this muscle is identical to those in other muscles. It is well known that each of the SOL and TA muscle have different neuronal characteristics, such as different degrees of connection to the motor cortex (Bawa et al., 2002), and different modulation effects on the spinal reflex excitability (Katz et al., 1988). Interestingly, in contrast to the SOL muscle, the TA stretch reflex shows a larger long-latency reflex (LLR) component, which presumably involves the transcortical pathway (Petersen et al., 1998). Given these facts, it is very likely that the aging process of the stretch reflex in the TA muscle is ...