The eye is a complex sensory organ that allows us to see the world around us. The eye works by gathering light from the environment and converting it into electrical signals that can be interpreted by the brain. The basic structure of the eye includes the cornea, iris, pupil, lens, retina, and optic nerve. The cornea is the transparent outer layer of the eye that helps to focus incoming light. The iris is the colored part of the eye that regulates the amount of light that enters the eye through the pupil, which is the black circular opening in the center of the iris. The lens is a clear, flexible structure located behind the iris that helps to focus light onto the retina. The retina is a thin layer of tissue that lines the back of the eye and contains photoreceptor cells called rods and cones. These cells convert light into electrical signals that are sent to the brain via the optic nerve. The rods are responsible for the low light vision and detecting motion, while the cones are ...
It is made of myocardium that is specialized in for initiation and conduction of the cardiac impulse. Its fibers are finer than other myocardial fibers, these are completely cross striated and possess special nerve-like properties (= self excitatory neuromuscular pathway).
The conducting system has the following parts:-
S.A. Node (Pacemaker) → Internodal pathway → A.V. Node → Bundle of His → Purkinje fibres (Rt & Lt)
* Speed of conduction is fastest in Purkinje fibres and slowest in AV node.
1) Sinuatrial node (SA node). It is known as the "pacemaker" of the heart. It is present in the right upper corner of the atrium. It generates impulses at the rate of about 72 per minute and initiates a heartbeat.
2) Internodal pathway that connects the SA node to the AV node.
3)Atrioventricular node (AV Node). It is situated in the lower-left corner of the right atrium close to the atrioventricular septum. It is capable of generating impulse at a rate of about 40/min.
4) Bundle of His (AV Bundle). It is the connection between the atrial and ventricular musculature. It begins at the AV node and then divided into left and right branches as it descends down toward ventricles. Branches of the Av bundle descends on the interventricular septum and is distributed to the ventricle after dividing it into Purkinje fibres.
5) The Purkinje fibres. These are distributed through the endocardium of the ventricles and propagate the impulse in the entire ventricle musculature. (18-25 per min.)
* The SAN can generate the maximum number of action potentials, i.e., 70-75 per min, and is responsible for initiating and maintaining the rhythmic contractile activity of the heart. therefore, it is called the pacemaker. Our heart normally beats 70-75 times in a minute (average 72 beats per min).
* Rhythmic contraction and relaxation of the heart are called heartbeat. Actually, contraction and relaxation occur separately in atria and ventricles. However, ventricular movements are Quite prominent and forceful. Therefore, the heartbeat is synonymous with ventricular or apex beat. It increases temporarily with activity and disease. In animals, the heartbeat is connected with size. In mammals, smaller animals have a higher heartbeat,
Adult human - 72 per min.
Rabbit - 210 per min.
Newborn - 120-140 per min.
Note: Heart rate is higher in women, children, and infants and lower in aged persons.
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