Types of Muscle Fibres

In mammals and birds the skeletal muscle has two types of fibres:

Slow (Red) fibres:

• Thin, dark reddish in colour and slower in contraction, these fibres have large amount of myoglobin. It undergoes long  sustained contractions hence also called as onic fibres.

• Number of mitochondria is very high, myoglobin stores O2 and releases for utilization.

• It produces mainly aerobic contractions, without lactic acid accumulation.

• Extensor muscle of back consists mainly of red fibres;Avian flight muscles are of this kind.

• Long, marathon race is performed by this muscle.

Fast (White) fibres:

Thick, light colored and fast contracting muscles have very fewer number of mitochondria and very less myoglobin.

It depends mainly on anaerobic contractions, accumulates lactic acid hence soon gets fatigued.

Due to short contraction phase it is also called as witch or phasic fibre.

Fast actions like short sprinting (100-200 mtr race) is made by this muscle.

Other examples of this kind are eye muscles of man, flight muscle of sparrow.

Sperm is the only cell in human body which is having flagellum

Sharpey’s fibres are collagenous fibres holding bones and teeth.

Human foot is arched for ideal distribution of weight. It has longitudinal arch and transverse arch.

Weberian ossicles are small bones present in fishes.

In birds endoskeleton is fully ossified, light but strong and without epiphyses. Long bones pneumatic or hollow without bone marrow. Synsacrum is formed by fusion of posterior thoracic, lumbar sacral and

anterior caudal vertebrae. Tail vertebrae are few compressed laterally and last 3 or 4 fused into a ploughshare bone called pygostyle. Ribs are double headed (bicephalous) and bear posteriorly directed uncinate

processes. Both clavicles and single interclavicle are fused to form a V shaped bone called furcula or wishbone or merrythought bone.

Epiphyseal plates at the extremities of long bones help in elongation of bone.

Fabella of knee and pisiform of hand are also sesamoid bones other than Patella. Total number of sesamoid bones is 6. Patella is formed by ossification in tendon of quadriceps femoris muscle.

Contracture is extremely slow relaxation of a muscle due to over stimulation.

Kymograph is an instrument used to record muscle contraction.

Colle’s fracture is a fracture of distal end of radius.

Chevron bones are present in reptiles and birds.

If the bone can move only in one plane, the joint is said to monaxial, if it can move in two planes, joint is said to be biaxial and if three planes it is said to be multiaxial (polyaxial)

Bones having both compact and spongy regions are called Diploic bones Eg. Humerus, Femur.

Largest foramen in skull is foramen magnum.

Half of the pelvic girdle is known as os-innominatum.

Zygomatic arch of rabbit is formed of the bones maxilla, squamosal and jugal.

Longest bone of frog is tibio fibula.

Olecranon fossa is a posterior depression in humerus bone that receives olecranon (olecranon process) of ulna when the forearm is extended. Proximal end of ulna presents an olecranon process which forms

the prominence of elbow.

Pterygoid is a wing like extension of sphenoid bone of cranium.

Human skeleton is S-shaped.

Total 4 ball and socket joints are present in human body.

Paranasal sinuses are paired cavities in certain cranial and facial bones near nasal cavity. (Frontal, sphenoid, Ethmoid and maxillae). Paranasal sinuses are lined with mucous membranes that are continuous with

lining of nasal cavity. Besides producing mucus, the paranasal sinuses lighten the skull bones and serve as resonant chambers for sound as we speak or sing. An inflammation of membrane due to an allergic

reaction of infection is calledSinusitis. If the membrane swells enough to block drainage into nasal cavity, fluid pressure builds up in the paranasal sinuses and sinus headache results.

Muscle Twitch : It is a single isolated contraction of a muscle fibre in response to a single stimulus and relaxation. Latent period (= period of latent excitation) is the interval between the application of appropriate stimulus and initiation of contraction. It is 0.01 sec in a skeletal muscle and upto 3 sec in a visceral muscle. During latent period the stimulus is converted into chemical excitation, spread of chemical excitation to all parts and liberation of chemicals required for contraction. Relaxation period is the interval required for the contracted muscle to regain its original relaxed/elongated state. It is 0.05 sec for a skeletal muscle and 2-3 sec for visceral muscle.

Refractory Period : It is the interval during which a muscle fibre fails to respond to a second stimulus. Refractory period is 0.002 - 0.005 sec in a skeletal muscle fibre and 0.1-0.2 sec in a cardiac muscle fibre.

Muscle Tension : The force produced during contraction of a muscle is known as muscle tension. It can do a job like lifting a load. Isometric contraction is the development of muscle tension without actual shortening due to nonaccomplishment of a job like pushing against an immovable object. Isotonic contraction involves shortening of a muscle in connection with doing a job like lifting a load. Treppe (Staircase Phenomenon). A stimulus of constant strength applied regularly at close intervals to a muscle produces a series of contractions, the first few of which are of increasing amplitude.

Motor Unit : It is a functional unit of muscle made of a single motor neuron and a group of muscle fibres (100-1900) innervated by it. Each muscle fibre receives a branch of the same neuron. All the muscle fibres of a motor unit contract and relax simultaneously. A muscle often contains a number of motor units.

Cholesterol content is highest in cardiac muscles.

Refractory period is the time interval between two subsequent contractions of a muscle fibre.

Muscular fatigue is due to lack of glycogen, ATP and excess of lactic acid.

In a smooth muscle striations are not seen because actin and myosin are not arranged into filaments.

Gastroenemius is the muscle of shank (Calf muscle)

Contraction of muscle of shortest duration is seen in eyelids.

Tendons connect muscles with bone and ligaments connect bones with bones. Sprain is due to overstretching of ligaments.

During muscle contraction energy is provided by phospagen (Creatine phosphate)

Potassium is most abundant mineral element in a muscle.

Dystrophin is a cytoskeletal protein that links thin filaments of sarcomere to integral membrane proteins of sarcolemma.

Stimulus of intensity below threshold value is called subliminal or sublimited stimulus. Stimulus stronger than threshold value is supraliminal or supralimited stimulus.

Largest muscle is Gluteus maximus (Buttock), smallest muscle is stapedius of stapes. Largest synovial joint is knee joint. Longest muscle is Tailor muscle (sartorius) Boxer’s muscle is serratus anterior.

Myalgia (Myodynia) is pain in muscles. Kinesalgia is pain on muscular contraction. Myositis is inflammation of a muscle.

Tendon is made up of white fibrous tissue, it is tough and inelastic. Ligament is made up of yellow elastic tissue with some collagen fibres. It is strong but elastic.

Myosin contributes 55% of muscles protein by weight.

In isotonic contraction, the tension remains same whereas change occurs in length of muscle fibres. The muscles shortens during contraction example is simple bending of arm.

In isometric contraction, length of muscle fibres remains same and tension is increased. Muscle does not shorten during contraction. Eg. is pulling any heavy object.

Deltoid muscle is in shoulder region and Latissimus dorsi is in back region. Hilton’s muscle is Aryepiglotticus muscle of Larynx.

EDTA (Ethylene diamine tetra acetic acid) when injected into muscles combine with Ca2+ and stops muscle contraction.)

Types of limbs in terrestrial mammals.

• Plantigrade type. The entire hands (=manus) and feet (=pes) remain in contact with the ground, both at rest and in locomotion. Examples : bears and certain insectivores.
• Digitigrade type : The proximal portions of hands and feet are permanently elevated on the ground so that the animal rests, walks or runs only on its fingers and toes. Examples : cats dogs, etc.
• Unguligrade type : Only the tips of one or two fingers and toes remain in contact with ground both at rest and during locomotion. Examples : ungulates (hoofed mammals) such as horses, cows, deer, etc.

Man remains plantigrade at rest and in walking, but running is attained by lifting the heel and using only the toes for contact with the ground (= digitigrade progression). Rabbits rarely walk and also use digitigrade progression in fast running by leaping. Thus men, and rabbits have subplantigrade type of limbs.