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CNX is the vagus nerve; it is involved in the gag reflex and is tested with CNIX generic abana 60caps amex. CNXI controls the movement of the sternocleidomastoid and trapezius muscles of the neck and shoulders buy abana 60 caps. Evaluation of arm drift is a sensitive test for weakness in the upper extremities. Other sensitive tests for extremity weakness include hand grasp, plantar flexion of the foot, and dorsiflexion of the foot. Atrophy—observe large muscle groups for symmetry and deter- mine if their size is appropriate for the person’s age. Rigidity presents as stiffness regardless of the rate of passive movement. Basic sensory examination consists of pain, light touch, proprioception, stereognosis, and vibration: 1. Proprioception measures posterior column defects (position of toe—up or down, etc. Stereognosis is dependent on touch and position sense (identification of a familiar object in one’s hand). Vibration sense is tested by placing a vibrating tuning fork over the distal interphalangeal joint of a finger and the great toe. The cerebellum organizes and coordinates movements but does not control individual muscles. Smooth, coordinated movements depend on the normal functioning of the cerebellum. Tests include finger to nose, heel-knee-shin, the Romberg test, and gait assessment.

Although both phenylalanine and tyrosine are found in the brain it is tyrosine which is the starting point for NA and DA synthesis cheap abana 60 caps amex. It appears to be transported into the brain after synthesis from phenylalanine (phenylalanine hydroxylase) in the liver rather than from phenylalanine found in the brain discount abana 60caps. Despite the fact that the concentration of tyrosine in the brain is high (561075 M) very little body tyrosine (1%) is used for the synthesis of DA and NA. This is the rate-limiting step (K 561076 M) in DA synthesis, it requires molecular O and m 2 Fe2‡ as well as tetrahydropterine (BH-4) cofactor and is substrate-specific. It can be inhibited by a-methyl-p-tyrosine, which depletes the brain of both DA and NA and it is particularly important for the maintenance of DA synthesis. Since the levels of tyrosine are above the Km for tyrosine hydroxylase the enzyme is normally saturated and so it is not possible to increase DA levels by giving tyrosine. Dopa decarboxylase By contrast, the cytoplasmic decarboxylation of dopa to dopamine by the enzyme dopa decarboxylase is about 100 times more rapid (K :461074 M) than its synthesis and m indeed it is difficult to detect endogenous dopa in the CNS. This enzyme, which requires pyridoxal phosphate (vitamin B6) as co-factor, can decarboxylate other amino acids (e. Controls of synthesis It is possible to deplete the brain of both DA and NA by inhibiting tyrosine hydroxylase but while NA may be reduced independently by inhibiting dopamine b- hydroxylase, the enzyme that converts DA to NA, there is no way of specifically losing DA other than by destruction of its neurons (see below). In contrast, it is easier to augment DA than NA by giving the precursor dopa because of its rapid conversion to DA and the limit imposed on its further synthesis to NA by the restriction of dopamine b-hydroxylase to the vesicles of NA terminals. The activity of the rate-limiting enzyme tyrosine hydroxylase is controlled by the cytoplasmic concentration of DA (normal end-product inhibition), presynaptic dopamine autoreceptors (in addition to their effect on release) and impulse flow, which appears to increase the affinity of tyrosine hydroxylase for its tetrahydropteridine co-factor (see below). METABOLISM Just as the synthesis of DA and NA is similar so is their metabolism. They are both substrates for monoamine oxidase (MAO) and catechol-O-methyl transferase (COMT). In the brain MAO is found in, or attached to, the membrane of the intraneuronal mitochondria. Thus it is only able to deaminate DA which has been taken up into nerve endings and blockade of DA uptake leads to a marked reduction in the level of its deaminated metabolites and in particular DOPAC.

Single-unit Smooth Muscles smooth muscles also display intrinsic 60 caps abana with visa, or myogenic buy 60caps abana with amex, electrical ac- Smooth (visceral) muscle tissue is arranged in circular layers tivity and contraction in response to stretch. For example, the around the walls of blood vessels, bronchioles (small air passages stretch induced by an increase in the luminal contents of a small in the lungs), and in the sphincter muscles of the GI tract. How- artery or a section of the GI tract can stimulate myogenic con- ever, both circular and longitudinal smooth muscle layers are traction. Such contraction does not require stimulation by auto- found in the tubular GI tract, the ureters (which transport urine), nomic nerves. By contrast, contraction of multiunit smooth the ductus deferentia (which transport sperm), and the uterine muscles requires nerve stimulation. The alternate contraction of circu- smooth muscles are compared in table 13. Autonomic Innervation of Smooth Muscles Smooth muscle fibers do not contain sarcomeres (which The neural control of skeletal muscles and that of smooth mus- account for striations in skeletal and cardiac muscle). A skeletal muscle fiber has only one junc- muscle fibers do, however, contain a great deal of actin and some tion with a somatic nerve fiber, and the receptors for the myosin, which produces a ratio of thin-to-thick myofilaments of neurotransmitter are localized at the neuromuscular junction about 16:1 (in striated muscles the ratio is 2:1). By contrast, the The long length of myosin myofilaments and the fact that entire surface of smooth muscle fibers contains neurotransmitter they are not organized into sarcomeres helps the smooth muscles function optimally. Smooth muscles must be able to exert ten- sion even when greatly stretched—in the urinary bladder, for ex- ample, the smooth muscle cells may be stretched up to two and a myogenic: Gk, mys, muscle; genesis, origin Van De Graaff: Human V. Autonomic Nervous © The McGraw−Hill Anatomy, Sixth Edition Coordination System Companies, 2001 438 Unit 5 Integration and Coordination Sympathetic ganglion (paravertebral ganglion) Rami FIGURE 13. Neurotransmitter molecules are released along STRUCTURE OF THE AUTONOMIC a stretch of an autonomic nerve fiber that is located some dis- tance from the smooth muscle fibers. The regions of the auto- NERVOUS SYSTEM nomic fiber that release transmitters appear as bulges, or Both the sympathetic and parasympathetic divisions of the auto- varicosities, and the neurotransmitters released from these vari- nomic nervous system consist of preganglionic neurons with cell cosities stimulate a number of smooth muscle fibers. However, the specific Knowledge Check origin of the preganglionic neurons and the location of the ganglia differ in the two subdivisions of the autonomic nervous system. How does the neural regulation of cardiac and smooth muscle fibers differ from that of skeletal muscle fibers? How Objective 4 Describe the origin of preganglionic sympathetic are these three types of muscle tissue affected by the exper- neurons and the location of sympathetic ganglia.