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.
basal ganglia
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.
Subscribe to:
Posts (Atom)
