→ The neural system coordinates and integrates functions as well as metabolic and homeostatic activities of all the organs.
→ Neurons, the functional units of the neural system are excitable cells due to a differential concentration gradient of ions across the membrane.
→ The electrical potential difference across the resting neural membrane is called the ‘resting potential’.
→ The nerve impulse is conducted along the axon membrane in the form of a wave of depolarisation and repolarisation. A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron which may or may not be separated by a gap called the synaptic cleft. Chemicals involved in the transmission of impulses at chemical synapses are called neurotransmitters.
→ The human neural system consists of two parts
- Central neural system (CNS) and
- the Peripheral neural system.
→ The CNS consists of the brain and spinal cord. The brain can be divided into three major parts:
- Midbrain and
→ The forebrain consists of the cerebrum, thalamus, and hypothalamus. The cerebrum is longitudinally divided into two halves that are connected by the corpus callosum. A very important part of the forebrain called the hypothalamus control the body temperature, eating, and drinking.
→ Inner parts of cerebral hemispheres and a group of associated deep structures form a complex structure called the limbic system which is concerned with olfaction, autonomic responses, regulation of sexual behavior, expression of emotional reactions, and motivation.
→ The midbrain receives and integrates visual, tactile, and auditory inputs.
→ The hindbrain comprises the pons, cerebellum, and medulla. The cerebellum integrates information received from the semicircular canals of the ear and the auditory system.
→ The medulla contains centers, which control respiration, cardiovascular reflexes, and gastric secretions.
→ The pons consists of fiber tracts that interconnect different regions of the brain. The entire process of involuntary response to peripheral nerve stimulation is called reflex action.
→ Information regarding changes in the environment is received by the CNS through the sensory organs which are processed and analyzed. Signals are then sent for necessary adjustments. The wall of the human eyeball is composed of three layers.
→ The external layer except the cornea is called the sclera. The inside the sclera is the middle layer, which is called the choroid.
→ Retina, the innermost layer, contains two types of photoreceptor cells, namely rods and cones.
→ The daylight (photopic) vision and color vision are functions of cones and twilight (scotopic) vision is the function of the rods. The light enters through the cornea, the lens, and the images of objects are formed on the retina.
→ The ear can be divided into the outer ear, the middle ear, and the inner ear. The middle ear contains three ossicles called malleus, incus, and stapes.
→ The fluid-filled inner ear is called the labyrinth and the coiled portion of the labyrinth is called the cochlea. The organ of Corti is a structure that contains hair cells that act as auditory receptors and is located on the basilar membrane.
→ The vibrations produced in the eardrum are transmitted through the ear ossicles and oval window to the fluid-filled inner ear.
→ Nerve impulses are generated and transmitted by the afferent fibers to the auditory cortex of the brain.
→ The inner ear also contains a complex system located above the cochlea called the vestibular apparatus. It is influenced by gravity and movements and helps us in maintaining a balance of the body and posture.
→ Coordination is the process through which two or more organs interact and complement the functions of one another.
→ Neurons: The neural system of all animals is composed of highly specialized cells called ‘neurons.
→ Somatic neural system and autonomic neural system: The PNS is divided into two divisions called somatic neural system and autonomic neural system.
→ Synaptic knob: Each branch terminates as a bulb-like structure called a synaptic knob.
→ Nissl’s granules: The cell body contains cytoplasm with typical cell organelles and certain granular bodies called Nissl’s granules.
→ Nodes of Ranvier: The gaps between two adjacent myelin sheaths are called ‘nodes of Ranvier.
→ Synaptic cleft: At a chemical synapse, the membranes of the pre and post-synaptic neurons are separated by a fluid-filled space called the synaptic cleft.
→ Arachnoid: A very thin middle layer is called arachnoid.
→ Corpora quadrigemina: The dorsal portion of the midbrain consists mainly of four round swellings (lobes) called corpora quadrigemina.
→ Labyrinth: The fluid-filled inner ear called labyrinth consists of two parts, the bony and the membranous labyrinths.