The Nervous System of Frog | Diagram

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The nervous system of a frog, like other vertebrates, is composed of the central nervous system (CNS), the peripheral nervous system (PNS), and the sympathetic nervous system or the autonomic nervous system. In this article, we will learn about the nervous system of frog.

The Nervous System of Frog

The nervous system of a frog consists of three main parts:-

1. The central nervous system
2. The peripheral nervous system &
3. The sympathetic or Autonomic nervous system.

The Central Nervous System of Frog

The central nervous system consists of –

1. 1. 1. The brain and
      2. The spinal cord.

The Brain of Frog

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• • • The brain is lying inside the cranium of the skull and it is well protected there.
    • It is surrounded by two meninges. The outer one is called piamater and the inner one is called duramater.
    • The whole brain is differentiated into three parts. They are the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain).
    • The anteriormost part is called the prosencephalon which is subdivided into two parts and they are telencephalon and diencephalon.
    • The telencephalon comprises a pair of small olfactory lobes and a pair of cerebrum or cerebral hemispheres. Olfactory lobes are responsible for the sense of smell.
    • The rest of the telencephalon comprises two lobes called the cerebrum or cerebral hemispheres. 
    • The roof of the cerebrum is very thin and the floor of the cerebrum is very thick. 
    • Behind the cerebrum, the depressed part of the brain is called the diencephalon.
    • The ventral side of the diencephalon bears ‘X’ shaped optic chiasma which is formed by the optic nerves and responsible for the sense of sight.
    • Optic thalami are present on the lateral sides of the diencephalon.
    • The midbrain remains undivided.
    • The optic lobes are present in the midbrain.
    • The posteriormost part of the brain, the rhombencephalon is divided into two parts 1. Metencephalon and 2. Myelencephalon.
    • A thin transverse band like the cerebellum is present in the metencephalon. 
    • Medulla oblongata is present in the myelencephalon.
    • The cerebellum coordinates the movement of the body and the medulla oblongata controls and regulates some vital processes like regulation of heartbeat, metabolism, respiration and etc.
    • Some well-formed internal cavities, called ventricles, are present in the brain.

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The Spinal Cord

1. 1. 1. The spinal cord is a hollow tube.
      2.  It extends posteriorly from the medulla oblongata.
      3.  It remains encased within the neural canal of the vertebral column. 
      4. The spinal cord has a dorsal fissure and a ventral fissure on its middorsal and midventral lines.
      5. The cavity of the spinal cord is known as neurocoel.

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The Peripheral Nervous System of Frog

• The peripheral nervous system comprises of the cranial nerves and spinal nerves arising from the cerebrospinal axis.
• The nerve fibers are of two types and they are 1. afferent or sensory nerve fibers and 2. efferent or motor nerve fibers.
• The sensory fibers convey the information from the receptor organs to the central nervous system and the motor fibers carry impulses from the central nervous system to the effector organs.
• Mixed-type nerves are also present which are composed of both sensory and motor nerve fibers.
• The peripheral nervous system comprises-

1. Cranial Nerves &

2. Spinal Nerves.

1. Cranial Nerves of Frog

(Click here if you face a problem seeing the full table – cranial nerves of frog)

Serial	Name	Origin	Type		Distribution
I	Olfactory nerve	Olfactory lobes	Sensory		It gives branches to the mucous membrane of the nose.
II	Optic nerve	Optic lobes	Sensory		It gives nerves to the retina.
III	Oculomotor nerve	Ventral side of the mid brain(mesencephalon)	Motor		It sends nerves to the muscles of the eyes.
IV	Trochlear nerve	Dorsal side of the mid brain(mesencephalon)		Motor	To the superior oblique muscle of the eyeball.
V	Trigeminal nerve	Lateral side of the medulla oblongata		Mixed	It gives sensory fibres to the upper and lower eyelid, anterior part of the head, mucous membrane of the nose and upper jaw, upper lip etc.It gives motor nerve fibres to the floor of the buccal cavity.
VI	Abducens nerve	Ventral side of the medulla oblongata		Motor	It supplies the external rectus muscle of the eye.
VII	Facial nerve	Medulla oblongata		Mixed	It gives nerve fibres to the roof of the mouth, tympanum, mandibular joint, and floor of the buccal cavity.
VIII	Auditory nerve	Lateral side of the medulla oblongata		Sensory	It sends nerves to the internal ear.
IX	Glossopharyngeal nerve	Lateral side of the medulla oblongata		Mixed	To the floor of the buccal cavity and tongue.
X	Vagus nerve	Medulla oblongata		Mixed	It sends nerve fibres to the heart, lungs, alimentary canal, etc.

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2. Spinal Nerves of Frog

1. 1. •  There are ten pairs of spinal nerves present in the toad.
      •  All the spinal nerves are mixed types.
      •  The first spinal nerve, hypoglossal, supplies to the muscles of the tongue.
      •  The second and third spinal nerves of a toad form the brachial plexus.
      •  The fourth, fifth, and sixth spinal nerves of a toad supply the integument and the muscles of the trunk region.
      •  The seventh, eighth, ninth, and tenth spinal nerves form the sciatic plexus.

The Autonomic Nervous System of Frog

1.  The activities of the autonomic nervous system are somewhat independent. 
2.  This nervous system regulates the involuntary activities of the body like heartbeat and peristalsis of the alimentary canal.
3.  The autonomic nervous system consists of two sympathetic trunks.
4.  The sympathetic trunks are located on either side of the dorsal aorta.
5.  The sympathetic trunks supply the branches to innervate the cardiac muscles, blood vessels, and alimentary canal. 

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