Parts and Functions of Nervous System

Both Parts and functions of nervous system are very important and interesting for biology class 12.You will find all the important details about this topic in this given article.

The human nervous system is classified into three main parts. These are -

1.Central Nervous System

2.Peripheral Nervous System

3.Autonomous Nervous System

1.Central Nervous System - It consists of the brain and the spinal cord. It is found along the middle line of the body.

2.Peripheral Nervous System - It consists

mainly of the nerves that arise from the central nervous system. These nerves are of two types -

(A)Cranial Nerves - These nerves arise from the brain. They emerge from the cranium through the brain. These nerves generally innervate the parts of head and nerves except the vagus nerve. There are 12 pairs of cranial nerves in humans. The names and serial number of the nerves can be remembered with the help of the word 'Oooptafagvah'. These nerves are-

*Olfactory nerve - It is a sensory nerve. It arises from the olfactory epithelium of the nose and goes to the olfactory lobes of the brain after passing through the olfactory tract. It carries smell impulses from the nasal epithelium.

*Optic nerve - It is a sensory nerve. This nerve arises from the retina of the eye. From the crossing of two nerves i.e optic chiasma and innervates the diencephelon. It carries the sight impulses from the eye to the brain.

*Oculomotor nerve - It is a type of motor nerve. It arises from the floor of the mid brain. The four eye muscles innervated by this nerve are inferior oblique, inferior rectus, superior rectus and internal rectus. It is responsible for the movement of eye ball.

*Pathetic or Trochlear nerve - It is a motor nerve. It arises from the floor of mid brain. It supplies nerve fibres to the superior oblique eye muscles. It controls the rotation of the eye ball.

*Trigeminal nerve - It is a mixed nerve and the largest of all the cranial nerves. This nerve originates from the central side of pons varolii. It has a trigeminal ganglion at its base. It has three branches- (a) Opthalmic - It is sensory in nature. It innervates the lacrimal glands, eyelids, conjuctiva of the eye and the skin of the forehead.

(b) Maxillary - It is sensory in nature. It innervates the gums, upper teeth, cheeks and the lower eye lids.

(c) Mandibular - This branch is mixed . It innervates the tongue,lower lip, pinna of the ear and the gums and teeth of lower jaw.

*Abducens nerve - It is a motor nerve. It arises from the mid-ventral side of the medulla oblongata of the mid brain. The external rectus muscles of the eye ball are innervated by this nerve. It helps in the movement of the eye ball.

*Facial nerve - It is a mixed nerve. It originates from the lateral side of the medulla oblongata of the hind brain. The face and the neck muscles and the taste buds of the tongue are innervated by this nerve. It is responsible for controlling the facial expressions.

*Auditory nerve - It originates from the internal side of the ear and innervates the medulla oblongata posterior to 7th nerve. It has two branches. These are -

(a) Vestibular - It is sensory in nature. It originates from the vestibule of the internal ear. It is responsible for the equilibrium of the body.

(b) Cochlear - It is sensory in nature. It originates from the cochlea of the internal ear. It is responsible for the function of hearing.

*Glosso-pharyngeal nerves - It is a mixed nerve. It arises from the side of medulla oblongata. It innervates the muscles and mucuous membrane of the pharynx and the tongue.The sense of taste, saliva secretion and movement of pharynx are controlled by this nerve.

*Vagus nerve - It is a mixed nerve. It arises from the side of medulla oblongata. The organs innervated by this nerve are larynx, pharynx, lungs, oesophagus, heart, stomach and intestines. It controls the visceral movements and sensations.

*Accessory spinal nerve - It is a motor nerve. It originates from the side of medulla oblongata and innervates the larynx, pharynx, neck and shoulder muscles. It controls the movements if these organs.

*Hypoglossal nerve - It is a motor nerve. It originates from the ventral side of the medulla oblongata of the brain. It regulates the movements of the tongue.

(B) Spinal nerves - Humans have 31 pairs of spinal nerves. The spinal nerves are mixed. Basically these nerves are made up of medullated nerve fibres. These nerves are classified into five groups -

(a) Cervical - It has 8 pairs of nerves.

(b) Thoracic - It has 12 pairs of nerves.

(d) Sacral - It has 5 pairs of nerves.

(e) Coccygeal - It has 1 pair of nerves.

Structure of spinal nerves

All the spinal nerves are connected to the spinal cord by anterior or ventral root and posterior or dorsal root. The sensory fibres enter inside the spinal cord in the form of posterior root and the motor fibres emerge out of the spinal cord in the form of anterior root. The posterior root bears a posterior root ganglia which consists of bodies of sensory neurons inside it. The grey matter consists of bodies of motor neurons. The mixed spinal nerve is formed by the joining of anterior and posterior roots of the spinal nerves in the vertebral canal of the vertebral column that emerges out from the paired apertures called Intervertebral foramina.

3.Autonomous Nervous System - It generally controls involuntary functions in the body. It has two parts -

(a) Sympathetic Nervous System - It has paired chains of ganglia that arises from the foramen magnum and goes up to the coccyx on either side of the vertebral column. Its all trunks have interconnected chain ganglia present at equal intervals (3 cervical ,12 thoracic, 5 lumbar and 1 sacral). It has consolidated components and a distinct anatomical entity. The pre-ganglionic fibres are only emerged with the spinal nerves and are shorter than post ganglionic fibres. The pre-ganglionic fibres branch and enter many ganglia. They produce a widespread effect by transmitting nerve impulses to several post ganglionic. fibres.Post ganglionic fibres are generally adrenergic.

(b) Parasympathetic Nervous System - It consists of -

*Pre-ganglionic fibres - These axons of neurons are found in the mid brain, brain stem and the lateral sacral region of the spinal cord. These fibres emerge with the spinal and cranial nerves.

*Parasympathetic ganglia - They are generally found close to or within the viscera. They don't form any chain and their neurons synapse with parasympathetic pre-ganglionic fibres.

*Post-ganglionic fibres - These axons of neurons are present in the parasympathetic ganglia. The non-striated muscles and glands of viscera are innervated by these fibres. These are generally cholinergic.

Functions of a Nervous System

Different parts of the nervous system serve different functions in regulating the voluntary and involuntary activities of the body. All the important functions of a nervous system can be understood by clicking on the above given link.

Hope this article Parts and functions of nervous system for notes of biology class 12 would be quite helpful to you. You can also practice this topic using Worksheets for ScienceWorksheets for Science. Please share and comment if you want article on any topic.

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