Conduction of impulse in chemical synapse :
- The axon terminals contains vesicles filled with chemicals called neurotransmitters.
- When the action potential arrives at the axon terminals, it stimulates the movement of synaptic vesicles towards the membrane.
- Synaptic vesicle fused with the pre-synaptic membrane and releases the neurotransmitter into the synaptic cleft.
- The neurotransmitter binds with the receptors located on the post-synaptic membrane.
- Activation of receptors on post-synaptic membrane makes it permeable to Na+ and generates action potential as it done by stimulus.
- The new potential developed may be either excitatory or inhibitory depends on the nature of the neurotransmitter.
CENTRAL NERVOUS SYSTEM :
- Brain is the central control and command system in neural coordination.
- The human brain is well protected by the skull.
- Inside the skull the brain is covered by cranial meninges.
- Meninges consists of following layers –
- Outer layer – dura mater.
- Middle layer – thin arachnoid.
- Inner layer – pia mater remain close contact with the brain.
- The human brain is divided into three major parts –
- Fore brain.
- Cerebrum.
- Thalamus.
- Hypothalamus.
- Mid brain.
- Hind brain.
- Pons.
- Cerebellum
- Medulla oblongata.
Fore brain :
- Cerebrum is the major part of the fore brain.
- Deep median fissure divides the cerebrum into two equal cerebral hemisphere.
- The hemispheres are connected by tract of nerve fibres called corpus callosum.
- The thin layers of cells covers the cerebral hemispheres called cerebral cortex and are thrown into prominent folds.
- The cerebral cortex is referred as the grey matter.
- The cerebral cortex differentiated into –
- Motor areas – sends information to the body
- Sensory areas – receives information from the body
- Association area-neither sensory nor motor (co-ordinates the information)
- Interior of the brain is called white matter due to myelin sheath of tract of nerve fibres.
- The cerebrum is wraps around a structure called thalamus, which is a major coordinating centre for sensory and motor signaling.
- At the base of the thalamus is the hypothalamus.
- The hypothalamus have following functions –
- Control body temperature.
- Urge for eating and drinking.
- Neurosensory cells secrete different hormones.
- The inner part of the cerebral hemispheres and a group of associated deep structures like amygdala, hippocampus etc. forms complex structure called the limbic lobe or limbic system.
- Along with the hypothalamus it is involved in the regulation of sexual behaviour, expression of emotional reactions (excitement, pleasure, rage and fear) and motivation.
Mid brain:
- The mid brain is located between the thalamus and pons of the hind brain.
- A canal called cerebral aqueduct passes through the mid brain.
- The dorsal part of the mid brain consists of four swelling called corpora quadrigemina.
Hind brain:
- Comprises pons, cerebellum and medulla oblongata.
- Pons consists of fibre tracts that interconnect different regions of the brain.
- Cerebellum has very convoluted surface in order to provide the additional space for many more neuron.
- Medulla of the brain is continued as spinal cord.
- Medulla contains centers which control respiration, cardiovascular reflexes and gastric secretion.
