Nervous System of Rat

Anatomy of Earthworm,Cockroach & Frog of Class 11

Nervous System

Nervous system consists of:

Central Nervous system — Brain & spinal cord

Peripheral Nervous system — Cranial nerves & spinal nerves

Autonomic Nervous system — Sympathetic & parasympathetic nervous system

Brain has well developed cerebrum and cerebellum. Cerebrum is divided into two cerebral hemispheres linked by corpus callosum.

Optic lobes are divided by a transverse fissure into 4 lobes, collectively called corpora quadrigemina.

Hindbrain includes cerebellum and medulla oblongata. Cerebellum has five lobes namely a median vermis, two lateral and two floccular lobes.

Medulla oblongata is the posterior part of hindbrain.

Rat has 12 pairs of cranial nerves and 33 pairs of spinal nerves originating from the spinal cord. Brain is contained in the cranium that is connected with the first vertebra (atlas) by a single occipital condyle.

Sympathetic ganglia are linked to form a chain of ganglia which lies near spinal cord. Parasympathetic ganglia are present near or inside visceral organ.

Sympathetic nervous system increases defence system of body against stressful conditions.

Parasympathetic nervous system provides relaxation, comfort, pleasure at the time of rest. It helps in the restoration and conservation of energy.

Sensory System

Eyes are the sense organs for vision and called photoreceptors. Eyeball is made up of three layers

(i) Sclera

(ii) Choroid (uvea) and

(iii) Retina

Light enters through the cornea part of the eye. Choroid is also called pigmented layer of the eye. It absorbs light rays and not reflected back out of the eyeball.

Focussing of image is brought about by altering lens curvature.

Ear consists of three parts — external, middle and internal

External ear consists of pinna (auricle) and auditory canal (external auditory meatus). External ears are characteristic of mammals.

Pinna collects the sound waves, external ear and internal ear are separated by tympanic membrane or eardrum.

Internal ear is called the labyrinth and consists of three parts

(1) Body proper

(2) Semicircular canal

(3) Cochlea

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