Neural System
* Coordination between organ systems and the functions of the organs is crucial to maintain a physiological balance, called homeostasis.
* The neural system and the endocrine system maintain homeostasis in our body.
* Neurons are called the structural and functional units of the neural system.
* The human neural system is divided into the central neural system (CNS) and the peripheral neural system (PNS).
* The brain and spinal cord from the central neural system, and the cranial and spiral nerves form the peripheral neural system.
* The peripheral neural system can be divided into somatic neural system and the autonomic neural system.
* The autonomic neural system is further classified into the sympathetic neural system and the parasympathetic neural system.
* A neuron is a branched nerve cell and is the longest cell in the body.
* The two main parts of a neuron are the cyton and nerve processes.
Generation and Conduction of Nerve Impulse
* The nerve impulse is the sum of mechanical, chemical and electrical disturbances created by s stimulus in a neuron.
* The nerve impulse can be divided into resting membrane potential and action membrane potential.
* The electrical potential difference across the neural membrane in an unexcited nerve fibre is called resting potential, and the neuron is called a polarized nerve fibre.
* The reversal of polarity across the two sides of the membrane is called depolarisation.
* The action potential travels as a wave of depolarization along the length of a nerve fibre in a particular direction and is called a nerve impulse.
* The junctions that help transmit a nerve impulse from one neuron to another are called synapses.
* Synapses are of two types-chemical synapses and electrical synapses.
* The synaptic cleft is a fluid-filled gap between the axon terminal and the Dendron of another neuron.
Central Neural System
* The brain and spinal cord of vertebrates are collectively known as the central neural system.
* The brain is divided into forebrain, midbrain and hindbrain.
* The forebrain consists of the cerebrum, thalamus and hypothalamus.
* The thalamus is located between the forebrain and midbrain and acts as a major coordinating centre for sensory and motor signaling.
* The hypothalamus is situated at the base of the thalamus and it contains the centers that control body temperature, the urge to eat and drink and the circadian rhythms.
* The collection of structures within the forebrain, including the amygdale and hippocampus, is known as the limbic system.
* The midbrain is located between the thalamus/hypothalamus of the forebrain and pons of the hindbrain.
* The hindbrain is formed of the pons, cerebellum and medulla Oblongata.
* The midbrain and the hindbrain form the brain stem. It acts as a relay station for auditory and visual information. That is, every impulse conducted between brain and spinal cord passes through the brainstem.
* An involuntary response to an external stimulus that occurs without any conscious effort or thought and requires the involvement of a part of the central neural system is called reflex action.
The Eye
* Human beings have a pair of spherical eyes located I eye sockets or orbits of the skull.
* The wall of the human eye ball is composed of three layers-sclera, choroid and retina.
* The retina contains three layers- ganglion, bipolar and photoreceptor cells.
* Rods and cones are the two types of photoreceptor cells.
* The cones are responsible for colour vision and daylight vision, which is also known as photopic vision.
* The rods are responsible for twilight vision, which is also known as scotopic vision.
* The optical part of the retina contains two spots known as the blind spot and the fovea.
* An inverted image forms on the retina and the impulse is carried to the visual cortex of the brain, where it is perceived in its correct form.
The Ear
* Anatomically, the ear is divided into three sections- the outer ear, the middle ear and the inner ear.
* The outer ear comprises the pinna and the external auditory meatus.
* The middle ear consists of the tympanic cavity that separates the external and inner ears.
* The Eustachian tube connects the tympanic cavity to the pharynx and helps maintain equal air pressure on both sides of the eardrum.
* The inner ear consists of a bony and membranous labyrinth, which consists of the cochlea and vestibular apparatus.
* The crista and macula are the specific receptors of the vestibular apparatus that maintain body balance and posture.