Tenth lecture

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Tenth lecture
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c- Telany If the muscle fibres exposed to a
contimuous stimulus, resulted either complete or
incomplete tetany.
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Effect of temperature on the muscle
Warming of a muscle leads to a stronger
contraction than normal, with shortening of all
phases of the simple muscle twitch. Due to
acceleration of the metabolic reactions needed to
provide energy for muscle contraction. Warming
decreases the viscosity of the muscle facititales
the process of contraction. During muscular
exercise the muscle temperature rises which makes
contraction stronger and more rapid. Cooling of
the muscle produce the opposite effects.
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Effect of Fatigue Rapid and repeated
stimulation leads to muscle fatigue manifested by
decrease in strength of contraction and
prolongation of all phases of the simple muscle
twitch specially the relaxation phase which
becomes in complete (contracture).
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Contracture is a state of sustained muscle
contraction which occurs where the muscle become
extremely fatigued. It is due to depletion of
ATP which is important for muscle relaxation.
In isolated muscles, fatigue occurs rapidly
because of the following Fatigue of the
excitation contraction coupling mechanism due to
decreased ATP. Decreased active transport of Ca
ions into the sarcoplasmic reticulum. Decreased
energy stores inside the muscle (ATP, Cr-P and
glycogen). Accumulation of metabolites e.g. CO2
and lactic acid. Decreased O2 supply. Decreased
pH of the muscle cells. Electrolyte disturbance.
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Smooth Muscle (Unstriated) Smooth muscle cells
are spindle-shaped, with centrally placed
nucleus, In uterus. Vascular smooth muscle. They
are contractile tissue present in the hollow
viscera, blood vessels, the bronchi, exocrine
glandular ducts and certain structure in the eye
and skin. It possesses no visible
cross-striation. Smooth muscles are arranged in
bundles and layers. Vertebrate smooth muscles are
divided into two main types multi-unit and
single unit.
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a- Multi-Unit smooth muscles it include the
radial muscle of the iris of the eye, the ciliary
muscles, the pronotor muscle of the skin and the
muscle of some blood vessels. These muscles
contracts normally in response to excitation of
their extrinsic motor nerve each cell is
separately innervated, repetitive stimuli are
needed for maximal contraction.
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b- Single-Unit smooth muscles (Visceral) It
include muscles of the gastro-intestinal tract,
the ureter and uterus. They are characterized by
continuous rhythmic activity (contraction
relaxation which is not dependent on extrinsic
innervation). In visceral smooth muscles, there
are junctions between the cells which are
comparable with the intercalated disc in cardiac
muscles. These junctions facilitate conduction
from one cell to another allow activity to
spread from area of excitation to surrounding
regions. The vas defrens are intermediate between
multi and single unit types.
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Physiological properties the speed of
contraction in smooth muscles are very slow and
the duration is often prolonged than with little
expenditure of energy as sphincter muscle of the
bladder that relax for urination. Persistent
contraction of smooth muscle may be myogenic in
origin, or neurogenic.