Rheobase is the lowest current that will initiate an action potential. the chronaxie is the maximum stimulus duration when the current is 2X reheobase. Rheobase and chronaxie define the shape of the strength-duration relationship. A slowly inceasing depolarizing current may not initiate an action potential even though it may rise to an intensity much greater than threshold level. A maintained depolarization causes the threshold to rise towards 0 mV. This called as accomadation.
It is not possible to elicit a second action potential after brief period of first action potential. This period is called as absolute refractory period. in this period all Na channels again can be aplicable for activation, this period is called as relative refractory period.
properties of excitable cell
myelination
first one, in the central nervous system, myelin is formed by the oligodendrocytes. One oligodendrocyte can contribute to the myelin sheath of several axons.
myelination II: in the peripheral nervous system, myelin is formed by Schwann cells. Each Schwann cell associates with only one axon, when forming a myelinated intermode.
vertebrate nervous system
The organization of the vertebrate nervous system is different from invertebrates. Vertebrates have a well-organized hollow dorsal nervous system. The central nervous system included a brain and spinal cord. The peripheral nervous system comprise peripheral nerves extending from spinal cord and peripheral ganglia. nervous
EPSP's and IPSP's
If transmitter opens a cation influx, the resulting depolarization is called an Excitatory Post Synaptic Potential (EPSP). These individual potentials are sub-threshold. If the transmitter opens an anion influx, the resulting hyperpolarization is called an Inhibitory Post synaptic potential (IPSP). All these potentials are additive. ıf some of the synapses are inhibitory in type. The cell produce action potential according to the algebric some of both excitatory and inhibitory synapses. The neurotransmitter GABA causes postsynaptic inhibition because its rceptor gated, postsynaptic membrane channels allow CL-flow.
Repitative stimulation of postsynaptic nerve from single synaptic region can also produce action potential. This kind of summation is called as temporal summation. Sometimes even the cell do not produce action potential, it can be come close to threshold potential , this is called as faciltation. Synaptic depression or fatique occur due to the depletion of synaptic vesicles as a result of repitetive stimulation. Continuous stimulation may led to the decline of postsynaptic potential.
basal ganglia
Basal ganglia is composed of some nuclei in the diencephelon; caudate nucleus, putamen, globus pallidus and substantia nigra. These are neural structure is related with motor function. Basal ganglia receive afferents from motor cortex and send efferents to the thalamus and then to the cortex. Basal ganglia controls the motor impulses conducted from cortex to the spinal cord. The complex fine movements is coordinated by the nasal ganglia. In the failure of the nasal ganglia, spontenous contraction occur in the extremity muscle.
autonomic nervous system
in simple animal autonomic fibers directly originate the segmentally arranged nerve cord and travel to the visceral organ as like peripheral nerves. In higher vertebrate and mammals, there are postganglionic ganglia in the periphery near to the inervated organ. Autonomic nerves innervate involuntary internal organs of the body.
After they emerge from spinal cord, it relays on a ganglia and the postganglionic fibers goes to the organ. When the autonomic nerves of a smooth muscle are cut, the smooth muscle continue to contruct and no athropy seen. But somatic nerve is destroyed, atrophy occur in the innervated organ. Autonomic nervous system is divided into two functional branches: the parasymphatetic branch and symphatetic branch. The preganglionic fibers of the parasymphatetic system exit the central nervous and synapse at the peripheral organs. Nervous system
The preganglionic fibers of symphatetic nerves leave the spinal cord via throracic and lumbar spinal nerves and synaplse on to the ganglia close to the spinal cord or synapse in more peripheral sympathetic ganglia. The symphatetic and parasymphatetic systems have antoganistic actions. In general the symphatetic nervous system preparres the body for response to stressful or dangerous situations; it initiates the fight of flight reactions, elevation of heart rate and increased force of contruction, peripheral vasoconstriction, and sweating.
In contrast, the parasymphatetic nervous system controls general bodily functions such as digestion. The neurotransmitter of postganglionic parasymphatetic synapse is acetylcholine, so the postsynaptyic receptors of these synapses are cholinergic.. http://nervous-system-info.blogspot.com/
The neurotransmitter of the symphatetic postganglionic synapse is usually norepinephrine, so there are adrenergic. The symphatetic neurotransmitter is epinephrine rather than norepinephrine rather than norepnephrine in some vertebrates. The neurotransmitter at the preganglionic synapse of both the parasymphatetic and symphatetic branches is acetylcholine.http://nervous-system-info.blogspot.com/
chemical synapses
The sequence of events during chemical synaptic transmission is :
1- the presynaptic action potential depolarizes the presynaptic membrane. 2- Ca+ permeability increase through the presynaptic membrane.
3-the elevated intracellular Ca+ concentration causes the release of neurotransmitter from synaptic vesicles in to synaptic cleft.
4- Neurotransmitter molecules diffuse across the synaptic cleft to the postsynaptic membrane and they reversibly bind to the specific receptors on the postsynaptic membrane.
Ca is very important in neurotransmitter release . The neuromucular junction is a typical chemical synapse. In this case two acetylcoline molecule are required to open the sodium channel. Postsynaptic membrane include acetycholine esterase to remove ACh.
In each postsynaptic end, a small depolarization is generated. That is called as end plate potential (EPP) or postsynaptic endplate potential.
These mini EPPs reflect the spontaneous release of one, or a few synaptic vesicles. Single EPPs does not generate in chemical synapsis . This ranges from 0.5 msec to 2.0 msec or even more.
electrical synapses
Electronic conduction is provided by gap junction between two neuronal membrane. these gap junctions are composed of numerous connections that allow direct movement of ions and small molecules. The direct electrical coupling of neurons is often observed when there is a requirement for the closesyncronization of effector organs. Examples are the cells of lobster heart, the electronic organ of mormyrid fish. the sound production muscle of toadfish and the escape response of some invertebrates.
http://nervous-system-info.blogspot.com/
There is no time delay, or latency in transmission of electrical depolarization in electrical synapses. The normal direction of synaptic transmission is from the presynaptic membrane to the postsynaptic membrane. Some electrical synapsis are inhibitory.
Synaptic Transmission
Action potentials are transmitted from one cell to another. There are two different mechanism for transfer of electrical from one cell to another .
1) electrical synapsis
2)chemical synapses
in electrical synapses, the action potential jumps electrotonically from the presynaptic cell membrane to the postsynaptic cell membrane. In the chemical synapsis, neurotransmitter released from one cell provide transmission of impulses.
What Happens To The Nervous System Under Stress?
The nervous system is the messenger between the brain and the other parts of the body. It is a labyrinth of connections that ensure that every signal transmitted by the brain triggers the necessary response in the body. Needless to say, it is an indispensable part of the body mechanism yet one of the most neglected ones. The nervous system remains active even when the rest of the body is in the resting state. It is also the main center for triggering the fight or flight response and the involuntary responses that keep us safe from potentially harmful stimuli.
When the nervous system is neglected i.e. by lack of proper sleep, stress and other factors, the repercussions are slowly but surely felt. The severity might vary from mood swings, poor hand eye co-ordination, fatigue to even depression and Alzheimer’s disease. The nervous system can also be affected adversely by improper food and sleeping patterns, lack of exercise, excessive exposure to stimulants such as coffee, certain medication and neglecting the need for relaxing activity. When the nervous system is not in ship shape, it can lead to the impairment of daily life and significantly increase the risk of occurrence of other medical conditions.
On the other hand, when the nervous system is performing to its full potential it fortifies the immune system, the ability to focus and multitask increases, the capacity to perform complicated tasks is enhanced and the risk of depression is significantly lowered. It also contributes towards a positive frame of mind and improving resistance towards stress. As the nervous system affects the body, the vice versa also holds true. Proper nutrition, rest and regular exercise release beneficial hormones such as endorphins into the system and help balance the several regulatory mechanisms of the body. A healthy body is truly run by a healthy nervous system.
Nervous System general
do you want to explore the nervous system ? this is general nervous system video.. there is a biochemical communications network of the human body, Revealing visuals are supported by informative features in which a neurologist discusses the chemistry of a nerve impulse.
The Nervous System video
The Nervous System video Animation from youtube . very great animation how nervous system works?
