human nervous system is the most complex system in the human body
which is composed of trillions of cells distributed in a network through the brain, spinal cord and periphery. It functions to gather information from sensory organs and integrates it to determine appropriate reaction the body should make (Guyton & Hall, 2006, p.555) and maintain homeostasis by coordinating the function of internal organs as well as meditating sensation and controlling movement (Widmaier, Raff, Strang, 2006, p.138). This essay will be mainly discussing about mechanisms involved in the control of normal movement with relation to underlying pathological changes in a 65 year old gentleman who has been diagnosed with Parkinson's disease (PD) 5 years ago, having increased difficulty in getting up out of a chair.
The nervous system can be divided into two main parts, central nervous system (CNS) which include brain and spinal cord and peripheral nervous system (PNS) which consist of cranial nerves and spinal nerves that connects the brain and spinal cord with body's muscles and sensory organs (Snell, 2010, p.2 ; Widmaier, Raff, Strang, 2006, p.138). The brain can be divided into cerebrum, cerebellum and brain stem. The cerebral hemisphere in cerebrum consists of cerebral cortex and basal ganglia. The primary motor cortex, located on the precentral gyrus carries out individual movement of different part of body on the contralateral side. The premotor cortex in cerebrum located in front of primary motor area stabilises the shoulders during upper limb tasks and hips during walking (Lundy-Ekman, 2007, p.442). The supplementary motor cortex which lies mainly on the longitudinal fissure is important for initiation of movement, planning bimanual and sequential movement.
Cerebellum, which is located on the posterior part of brain stem, is involved in coordination of movement of limbs, trunk and head. During a highly skilled movement, cerebellum will be informed by motor cortex via signal sent about the anticipated movement which allows cerebellum to make continuous adjustment, resulting in smooth movement (Porth & Matfin, 2009, p.1207). Besides, it facilitates sequencing of movements in conjunction with motor cortex beforehand. Cerebellum also supervises and provides anticipatory postural changes when the body is moving so that it is balanced with the motor impulses transmitted by motor cortex and other components of brain by evaluating the actions planned by motor cortex with the movements being executed as presented by peripheral sensory feedback information.
Caudate nucleus (CN), putaman (PT), globus pallidus(GP), substantia nigra (SN) and subthalamic nucleus (STN) are masses of gray matter that are collectively known as basal ganglia (BG) (Guyton & Hall, 2006, p.707) which is located deep within the cerebral hemisphere (Tortora & Derrickson, 2009, pg. 517). They function as initiator and terminator of a movement in the body besides suppressing unwanted movements and regulate muscle tone. Many aspects of cortical functions including sensory, limbic, cognitive, and linguistic functions have involvement of BG. According to Lundy-Ekman (2007, p.244), GP and PT are known as lentiform nucleus whereas CN and PT form striatum based on anatomic positions. There are two pathways that could be taken for the transmission of impulses, the putamen and caudate pathways. The putamen circuit functions to control complex patterns of motor activity in association with corticospinal tract (CST). BG function in association with this system is to control complex patterns of motor activity needed to perform a highly skilled movement which is mostly done subconsciously (Guyton & Hall, 2006, p.708). The impulse usually begins in premotor cortex, supplementary motor cortex and somatosensory motor cortex. Then the impulse will be sent to PT through CN, then to the GP and to thalamus, located in the center of cerebrum. Finally, the impulse returns to primary motor cortex, and part of premotor and supplementary motor area associated with primary motor cortex. Lesions with putamen circuit at GP, PT or STN may results in athetosis, chorea or hemibalismus respectively (Guyton & Hall, 2006, p.709).
The caudate circuit of basal ganglia is responsible for cognitive control of sequences of motor patterns. The impulses are being sent from cerebral cortex to GP through CN then again to thalamus, finally back to prefrontal, premotor and supplementary motor areas of cerebral cortex where cognitive control of motor activities occur. This circuit permits responds to subconscious and complex pattern of movements that should be carried out simultaneously (Lundy-Ekman, 2007, p.246).
The impulse for control of contraction of skeletal muscles starts in anterior part of premotor cortex in cerebrum then passes to posterior premotor cortex where excitation of patterns of muscles activity occurs. Impulses is then transmitted to primary motor cortex, and then sent to spinal cord via CST, one of main pathway arising from primary motor cortex. CST is the most important output pathway which directly sends the signal from the cortex to spinal cord in performing muscle contraction (Ganong, 2005, p.204). CST fibers descend and decussations occur at pyramids of medulla. This leads to innervations and controlling of contralateral side of body by brain. They synapse in brain stem or spinal cord with lower motor neurons which terminate at skeletal muscles.
In this discussion, the patient is diagnosed with Parkinson's disease (PD). PD is a chronic, progressive neurologic disorder characterized by key features of rigidity, bradykinesia, tremor and postural instability which is associated with dopamine deficiency in the striatum and loss of dopaminergic neurons in the substantia nigra (Gancher, 2010). An extensive destruction of portion of SN which sends dopamine-secreting nerve fibers to CN and PT occur in the brain. Dopamine (DA) is an inhibitory neurotransmitter which inhibits the GABAergic neurons, maintaining the activation of motor control system. This balance between both excitatory and inhibitory impulse of motor cortex and BG results in smooth, purposeful muscle activity (Porter, 2003, p.451) As dopaminergic neurons degenerate, DA secretion decreases and there is a loss of GABAergic neuronal inhibition, which will then allows the CN and PT to become overly active and possibly causes continuous output of excitatory signals to the corticospinal motor control system, leading to decreased voluntary movements producing excessive contraction of postural muscles (Sullivan & Schmitz, 2007, p.855 ; Lundy-Ekman, 2007, p.248). Lewy bodies, characteristic cytoplasmic inclusion bodies develop as the disease progresses (Umphred, 2007, p.782).
A normal inhibitory on function of GP and PT activity is another role of DA. In PD, dopaminergic neuronal destruction will have a constant firing of excitatory impulses from GP and PT to CST. This will causes an over excitation of muscles resulting in rigidity, an increase resistance to movements in muscles. Bradykinesia, decrease in motion characterised by inability to initiate and perform purposeful movements is a result of decrease activation of supplementary motor cortex, premotor cortex and motor cortex (Umphred, 2007, p.782). Tremor is an involuntary oscillation of a body part at a slow frequency. Patient with PD is usually seen with resting tremor as it presents at rest and disappears during voluntary movements (Sullivan & Schmitz, 2007, p.857). Rigidity, bradykinesia and tremor will later affect in postural abnormalities and imbalance in a PD patient.
Berg balance scale (BBS) is chosen to assess the patient's performance in the functional task of sitting to standing due to wide acceptance and reliability of this test (Qutbuddin et al, 2005). BBS has 14 multitask item which is used for evaluation of effective interventions and for quantitative descriptions of function in clinical practice and research. The BBS consists of 14 tasks of varied difficulty, graded on a 5-point ordinal scale ranging from 0 to 4 (Conradson et al., 2007) where 0 indicates the patient is unable to perform and 4 indicating the patient could perform independently, meeting time and distance criteria. PD patients usually have difficulties in transition between movements, especially during series of repetitive movements (Umphred, 2007, p.783). The patient should be placed in sitting position, and instructed to stand without trying to use his hands or any other support. As the whole process of standing up is considered as complex movements, the patient might do it at a slower pace and it is advisable for a physiotherapist to stand beside him. While the patient is carrying out the activity, the therapist must note the accomplishment of the activity as well as how long it takes to do so (Umphred, 2007, p.787). As a result from poor motor controls, a PD patient can be usually seen having a festinating gait. It is characterised by forward trunk flexion and short steps of rapid cadence (clinical gait ana Kirtley, 2006, p.).
In conclusion, the nervous system is accountable to perform tasks in activities of daily living. Disturbance in any of the part of brain may lead to dysfunction as can be seen in PD. PD is a progressive disease associated with dopamine deficiency affecting basal ganglia and motor cortex, resulting in poor motor control. This leads to difficulty in completing activities of daily living (ADL) in which, PD patient needs not only psychological support but sociological support as well. BBS can be used for assessment of functional task for PD patient as it is both valid and reliable to assess the patient.
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