Answer: Colliding action potentials cancel each other out because the refractory period of either spike prevents the continuation of an impulse in either direction. Answer: It depends on what segment of the spinal cord and which plane you measure:.
Reference: Carpenter, M. Answer: Ballismus comes from the Greek word "ballismos" meaning "a jumping about" or "dancing. Answer: Gray matter consists primarily of neuron cell bodies. For example, in the brain, gray matter forms the outside layers of cortex and nuclei deep within the brain. White matter consists of myelinated axons.
Answer: The knee jerk reflex helps with posture. When the knee bends, it stretches the leg muscle quadriceps femoris. The muscle stretch starts the reflex and the leg straightens. However, Liechti et al. Blood pressure increases caused by MDMA are higher in men than in women. Reference: Liechti, M. Gender differences in the subjective effects of MDMA. Psychopharmacology Berl.
Answer: It depends on the drug and the test. Urine tests are the most common way drugs are detected. However, samples of a person's blood, saliva, breath, sweat and hair can also be tested to detect drug use. The presence of breakdown products metabolites in a sample is an indication of drug use. According to The Medical Letter , August 19, Volume 44 , the following drugs can be detected in urine :. According to Keltner, N. Louis: Elsevier Mosby, :. I am looking for a list of brain neurological disorders to use as a reference for students doing research projects.
There is a link at the top of that page "Request mailed brochures" where you can have free publications about various neurological disorders mailed to you. Answer: Yes, there are case reports of visual disturbances after methamphetamine use. At the same time, try to draw a "6" in the air with your right hand. This is difficult to do!
Answer from Dr. Pat F. Neuroscientist Network member : The motor coordination between upper and lower limbs is interconnected, both unilaterally and bilaterally. These interconnections are a holdover from our quadrupedal gait patterns. They are an evolutionary holdover, but are functional early in life. Both nerves and tracts are made up of axons; the long, slender projections of neurons. Nerves are the bundles of axons in the peripheral nervous system.
They basically make the electrochemical pathways to transmit nerve signals between sensory organs and central nervous system.
Axons are slender projections of neurons that make the nerve network in the body. Usually a single nerve contains many axons, hence referred to as nerve fibers. Each axon is covered with a connective tissue called endoneurium. Cranial nerves are typically assigned Roman numerals from 0 to Peripheral nerve fibers are grouped based on the diameter, signal conduction velocity, and myelination state of the axons.
These classifications apply to both sensory and motor fibers. Fibers of the A group have a large diameter, high conduction velocity, and are myelinated. The A group is further subdivided into four types A-alpha, A-beta, A-delta, and A-gamma fibers based on the information carried by the fibers and the tissues they innervate. Fibers of the B group are myelinated with a small diameter and have a low conduction velocity. The primary role of B fibers is to transmit autonomic information.
Fibers of the C group are unmyelinated, have a small diameter, and low conduction velocity. The lack of myelination in the C group is the primary cause of their slow conduction velocity.
Saltatory conduction : Demonstrates the faster propagation of an action potential in myelinated neurons than that of unmyelinated neurons. C fiber axons are grouped together into what is known as Remak bundles. These occur when an unmyelinated Schwann cell bundles the axons close together by surrounding them.
The Schwann cell keeps them from touching each other by squeezing its cytoplasm between the axons. C fibers are considered polymodal because they can often respond to combinations of thermal, mechanical, and chemical stimuli.
A-delta and C fibers both contribute to the detection of diverse painful stimuli. Because of their higher conduction velocity, A-delta fibers are responsible for the sensation of a sharp, initial pain and respond to a weaker intensity of stimulus. These nerve fibers are associated with acute pain and therefore constitute the afferent portion of the reflex arc that results in pulling away from noxious stimuli. An example is the retraction or your hand from a hot stove.
Slowly conducting, unmyelinated C fibers, by contrast, carry slow, longer-lasting pain sensations. Privacy Policy. Skip to main content. Peripheral Nervous System. Search for:. Structure of a Nerve A nerve is the primary structure of the peripheral nervous system and is composed of bundles of axons.
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