Motor neuron

CGRP is widely distributed throughout the peripheral and central nervous systems and is found ia sensory neurons and ia the autonomic and enteric nervous systems. In many iastances CGRP is co-localized with other neuroregulators, eg, ACh ia motor neurons, substance P, somatostatin, vasoactive intestinal polypeptide (VIP), and galanin ia sensory neurons. It is also present ia the CNS, with ACh ia the parabigeminal nucleus and with cholecystokinin (CCK) ia the dorsal parabrachial area. CGRP functions as a neuromodulator or co-transmitter. 

Acetylcholine is a neurotransmitter at the neuromuscular junction in autonomic ganglia and at postgangHonic parasympathetic nerve endings (see Neuroregulators). In the CNS, the motor-neuron collaterals to the Renshaw cells are cholinergic (43). In the rat brain, acetylcholine occurs in high concentrations in the interpeduncular and caudate nuclei (44). The LD q (subcutaneous) of the chloride in rats is 250 mg/kg. 

The human brain is comprised of many millions of interconnected units, known individually as biological neurons. Each neuron consists of a cell to which is attached several dendrites (inputs) and a single axon (output). The axon connects to many other neurons via connection points called synapses. A synapse produces a chemical reaction in response to an input. The biological neuron fires if the sum of the synaptic reactions is sufficiently large. The brain is a complex network of sensory and motor neurons that provide a human being with the capacity to remember, think, learn and reason. 

ALS is a disorder of the motor neurons and the cortical neurons that provide their input. The disorder is characterized by rapidly progressive weakness and muscle atrophy. Most affected patients die of respiratory compromise and pneumonia after 2 to 3 years. There is prominent loss of motor neurons in the spinal cord and brainstem although the oculomotor neurons are spared. Large pyramidal motor neurons in layer V of motor cortex, which are the origin of the descending corticospinal tracts, are also lost. 

Episodic ataxia (EA) is an autosomal dominant disorder that brief episodes of ataxia can be triggered by physical or emotional stress. The symptom can occur several times during the day, last for seconds to minutes, and be associated with dysarthria and motor neuron activity, which causes muscle rippling (myokymia) between and during attacks. It is caused by a mutation in a neuronal voltage dependent Ca2+ channel. 

P2X6 CNS, motor neurons in spinal cord - (does not function as homomulti-mer) Intrinsic ion channel... 

The clinical and histopathological features of individual neurogenic muscle disorders are determined to a large extent by the balance of the opposing processes of denervation and reinnervation, at least as far as the muscle dysfunction is concerned. The involvement of upper motor neurons in some of these disorders is outside the scope of this chapter and will only be referred to in passing. 

Mulder, D.W. (1986). Motor neuron disease in adults. In Myology Volume II (Engel, A.G., Banker. 

W0 9 413 288 (Rhone-PoulencRorer appl. 10.12.1993 F-prior. 16.12.1992). use to treat motor-neuron diseases ... 

There is a dark side to receptor-mediated endocyto-sis in that viruses which cause such diseases as hepatitis (affecting liver cells), poliomyelitis (affecting motor neurons), and AIDS (affecting T cells) initiate their damage by this mechanism. Iron toxicity also begins with excessive uptake due to endocytosis. 

Motor neuron disease AIDS Subacute Motor dysfunction, muscle wasting with upper motor neuron signs bulbar dysfunction Possible immune mediated... 

Galassi G, Gentilini M et al (1998) Motor neuron disease and HIV-1 infection in a 30-year-old HIV-positive heroin abuser a causal relationship Clin Neuropathol 17(3) 131-135 Gherardi R, Lebargy F et al (1989) Necrotizing vasculitis and HIV replication in peripheral nerves. N Engl J Med 321(10) 685-686... 

The large diameter A/l-afferent fibre enters the dorsal horn of the spinal cord through the medial division of the dorsal root. It then descends through the medial region of lamina I or II, or alternatively, curves around the medial (central) edge of the dorsal horn down to the ventral horn. On reaching deeper laminae, laminae IV and V, the AjS-fibres ascend back up into laminae III and IV where they repeatedly subdivide and form a characteristic termination pattern. The densest arborisation appears to occur in lamina III. Axons originating from specialised muscle stretch receptors have collaterals that pass ventrally to make monosynaptic connections with neurons of laminae V, VI and VII. Some also extend to laminae VIII and IX of the ventral horn where they synapse directly onto motor neurons and form the basis of monosynaptic reflexes. 

Multiple sclerosis patients must be treated with agents specific for upper motor neuron spasticity. 

MS patients usually have upper motor neuron spasticity. This type of spasticity cannot be treated with muscle relaxants such as carisoprodol. MS patients must be treated with agents specific for upper motor neuron spasticity (Table 26—8).48 MS spasticity is classified as focal or generalized. If the spasticity primarily involves only one muscle group, it is focal and may benefit from botulinum toxin administration.11 Systemic medications are used for generalized spasticity. No clear conclusion can be reached regarding the superiority in efficacy of one antispasticity agent over another medication selection is usually based on adverse effects (see Table 26-8).11,48... 

Spinal and bulbar cerebellar cortex, brain stem Motor neurons, dorsal root ganglia 11-34 40-62 Androgen receptor NI (n)... 

Lou Gehrig s disease (amyotrophic lateral sclerosis ALS) displays motor neuron deposits of hyperphosphorylated neurofilament subunits in the sporadic disease. Familial ALS, some 20% of all cases of ALS, involves dominant superoxide dismutase SOD1 mutants that can form (3-barrel aggregates [49-51]. 

Cleveland DW. From Charcot to SOD1 mechanisms of selective motor neuron death in ALS. Neuron 1999 24 525-520. 

Desai, C., Garriga, G., Mclntire, S. L., andHorvitz, H. R. (1988). Agenetic pathway for the development of the Caenorhabditis elegans HSN motor neurons. Nature 336 638-646. 

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