A2 OCR Biology: Types of Muscle

A2 OCR Biology: Types of Muscle

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  • Created on: 25-05-11 00:04
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Types of Muscle
Muscle Structure
Muscles are composed of elongated cells forming fibres.
All muscles contract and relax as they produce a force on contraction as they contain
filaments made of the proteins actin and myosin.
Types of Muscle
o Involuntary (Smooth muscle) muscle
o Cardiac muscle
o Voluntary (Striated/Skeletal Muscle)
muscle
Involuntary (Smooth) Muscle
Smooth muscle is innervated by neurones of the
autonomic nervous system. This means that contractions of this muscle are not
voluntary. Smooth muscle fibres can be found:
In walls of the intestine in circular and longitudinal bundles. Its purpose is to
move food along the intestine.
In the iris of the eye in circular and longitudinal bundles where it controls the
intensity of light entering the eye. To dilate the pupil, radial muscles contract. To
constrict the pupil, circular muscles contract.
In the walls of the arteries in circular bundles.
Smooth muscles contain small bundles of actin and myosin, and a nucleus. Cells in the
relaxed state measure around 500 µm long and 5 µm.
Cardiac Muscles
There are three types of cardiac muscle:
Atrial muscle and ventricular muscle
o Contract similarly to that of skeletal muscles but with a longer duration of
contraction.
Specialised excitatory and conductive muscle fibres.

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Contract feebly but conduct electrical impulses and control the rhythmic
heartbeat.
Some cardiac muscle fibres are capable of stimulating contraction without a nerve
impules, they are myogenic. However neurones of the autonomic system carry impulses
to the heart to regulate the rate of contraction. Sympathetic stimulation increases its
rate; parasympathetic stimulation decreases its rate.
The sinoatrial node is made of specialised excitatory and conductive fibres. It has the
greatest ability for self-excitation and the electrical activity generated there immediately
spreads into the atrial wall.…read more

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Questions
1. Circular smooth muscle contracts to reduce the diameter of the blood vessel but
when relaxed, the blood vessel increases in diameter. The dilation is done
automatically.
Muscle Type Structure Function
Made of individual muscle
Cardiac
cells in rows with
(Atrial, Ventricular and Myogenic; regulated by
intercalated discs and
Specialised, conductive autonomic system
junctions in between for fast
muscle fibres)
transfer of action potentials
Contain small bundles of
Non-conscious contractions;
actin and myosin, and a
innervated by neurones of
Smooth nucleus.…read more

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