Quick question about involuntary nerve impulses?

[scilearner]

Hello everyone,

 

For example muscle tone is continuous and passive partial contraction of the muscles. This means there must be some involuntary nerve impulses. Now my question is I can understand how heart has leaky potassium channels and contract involuntary, but how does the brain make nerves contract involuntary without stimulus? Thanks

[Greippi]

Quick response off the top of my head:

 

Sometimes there is a stimulus, it's just subconscious. Other times, it's due to local stimuli - for example in some disorders involving involuntary muscle contraction, the neurotransmitter receptors may be more sensitive than normal (due to the fact that different neurotransmitters causing the receptor to be more or less sensitive, and an imbalance of neurotransmitters), resulting in contraction even at low concentrations of neurotransmitter.

[scilearner]

Quick response off the top of my head:

 

Sometimes there is a stimulus, it's just subconscious. Other times, it's due to local stimuli - for example in some disorders involving involuntary muscle contraction, the neurotransmitter receptors may be more sensitive than normal (due to the fact that different neurotransmitters causing the receptor to be more or less sensitive, and an imbalance of neurotransmitters), resulting in contraction even at low concentrations of neurotransmitter.

 

Hey thanks for the response . What do you mean a subconscious stimulus? Could you give me an example. Thanks

[Greippi]

As in you're not aware you're consciously making the decision to move the muscle.

[Double K]

A few thing that can cause this.

Multiple Sclerosis

Muscle misfolding

Muscular distrophy

Muscle tetanus

 

MS. (multiple sclerosis) is a well known cause, where the myelin sheath surrounding the axon of a nerve cell is basically scarified. This causes misfiring of the nerve.

 

Multiple sclerosis (MS) is a chronic disease that affects the central nervous system.

http://www.healthinsite.gov.au/topics/Multiple_Sclerosis

"In multiple sclerosis, the body incorrectly directs antibodies and white blood cells against proteins in the myelin sheath, which surrounds nerves in the brain and spinal cord. This causes inflammation and injury to the sheath and ultimately to the nerves that it surrounds. The result may be multiple areas of scarring (sclerosis) and eventually this damage can slow or block the nerve signals that control muscle coordination, strength, sensation and vision"

 

 

Muscle misfolding (which is a pretty new idea)

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2140035/

"An overactive neuron can cause protein aggregation in its target cell, according to new work by Susana Garcia, Richard Morimoto (Northwestern University, Evanston, IL), and colleagues, indicating that actions of one cell may disrupt protein homeostasis in another.

 

The authors discovered that mutations in a transcription factor found only in neurons increased aggregation of polyglutamine-containing proteins in muscle cells in C. elegans. This factor, UNC-30, boosts synthesis of GABA, which inhibits neuronal firing. Increased protein aggregation also resulted from other GABA-reducing (and thus neuronal stimulating) mutations, including one in the muscle cell's GABA receptor.GABA's normal actions are counteracted by the stimulatory neurotransmitter acetylcholine. Mutation-induced overactivity of the acetylcholine system had the same effect on polyglutamine aggregation as too little GABA activity. Small molecules also had similar effects: nicotine, which stimulates neurons, promoted aggregation, as did an insecticide called lindane, which inhibits GABA."

 

Muscle tetanus

You can also read about muscular distrophy and Myasthenia Gravis at the link below.

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Muscles.html#Tetanus

"Another one is muscle twitch & tetanus response (not the disease Tetanus)

The process of contracting takes some 50 msec; relaxation of the fiber takes another 50–100 msec. Because the refractory period is so much shorter than the time needed for contraction and relaxation, the fiber can be maintained in the contracted state so long as it is stimulated frequently enough (e.g., 50 stimuli per second). Such sustained contraction is called tetanus."

Edited May 17, 2010 by Double K