Forebrain

Forebrain is divided into the diencephelon and thelencephelon. the dorsal portion of the diencephelon is the epithalamus, the lateral portion the thalamus and the ventral portion is the hypothalans.

The epithalamus contains a small nucleus that transmits olfactory information to the brain stem, the pineal and parapineal bodies, and the anterior choroid plexus.

In lower vertebrates epithalamus is well developed and importantt for the transmission of impulses from periphery to cerebral cortex, but in mammales most of sensory information is transferred to the cerebral cortex via thalamus.

properties of excitable cell

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.

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/