LOCOMOTION AND MOVEMENT IN MAN
Living organisms possess a characteristic phenomenon called locomotion. It is more prominently observed in unicellular as well as multicellular animals. It distinguishes the animals from the plants.
LOCOMOTION
It is the displacement of the body from one place to another. The animal performs locomotion with the help of locomotory organs. Locomotion is performed by walking, running, swimming, hopping, flying, swimming, crawling etc. The purpose of locomotion is to search for food, water, shelter and partners for reproduction, to avoid unfavourable conditions and predators or to reach favourable places etc.
MOVEMENT
It is the movement (or change of direction) of the body parts, in relation to the long axis of the body. Movement is generally marked in the different parts of the body, keeping the main body fixed. It is related to the change of body posture. The head, trunk, limbs, and other appendages move against gravity to maintain the body posture. The jaws, tongue, teeth, tentacles, snout etc. move to collect and ingest food materials. The eyeballs move for vision and ear pinna moves to collect sound. The internal organs also move to carry out different functions. The stomach moves to grind and propels food materials. The heart moves to circulate the blood inside the body.
Movement is also seen in the unicellular organisms. The cytoplasm of these organisms shows streaming movements. In the multicellular animals even the leukocytes and macrophages show amoeba-like movement. The sperms move in a specific direction.
In higher animals movement Occurs due to the action of muscle cells which can contract and expand.
Significance of Locomotion
1. Locomotion helps to find food materiais.
2. It helps to avoid unfavourable conditions.
3. It helps to escape from predators.
A. It occurs as a reaction to the stimuli.
5.Jt is required to find out the mate.
6. In some animals spontaneous locomotion is also seen.
LOCOMOTION IN MAN
In man, locomotion is affected by the muscles of the body. These muscles are always associated with the skeletal system with high tensile strength. The musculo-skeletal system comprises of the bones, cartilages, muscles, tendons (cordlike structure which connects muscles with the bones) and ligaments (connects bones with bonesS)
SKELETAL SYSTEM IN MAN (COLOURED PLATE) – (III)
The human skeleton can be divided into axial and appendicular parts.
Axial Skeleton
1. Skull. It is a bony case containing brain, eyes, ears etC.
I. Cranium.
The cranium or brain box contains 8 bones. These are occipital (1), parietal
(2), frontal (1), temporal (2), sphenoid (1) and ethmoid (1).
II. Face.
The face contains 14 bones, 6 ear ossicles (Malleus, Incus, Stapes in each ear
and one hyoid bone.
2. Vertebral Column.
It consists of 26 bones in adult (33 bones in a baby) with five distinct regions viz. 7 cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae with one sacral (5 vertebrae in baby fused) and one coccyx (4 rudimentary vertebrae in baby) vertebrae
3.Thorax.
The thoracic region contains 24 rib bones with one sternum.
Appendicular Skeleton
1. Pectoral Girdle.
It consists of one ‘S’-shaped clavicle and one flattened triangular scapula, enclosing a glenoid cavity. The humerus fits into the glenoid cavity.
2. Pelvic Girdle.
Each half of the pelvic girdle called osinnomina m. ade into up which, ofilium, ischium and pubis which unite in the centre forming a socket like aceta head of femur fits. The two halves of pelvic girdle unite in the middle by pubic syip
3. ForeLimb.
Each forelimb consists of 30 bones viz., humerus (one), radius ulna carpals (eight small bones), metacarpals (five bones), phalanges (fourteen i.e. 3 in eaCn ai8 car and two in pollex).
4. Hind Limb.
Each hind limb contains 30 bones viz. femur (one), patella (one), tibia and fibula (two), tarsals (seven), metatarsals (five), phalanges (fourteen, i.e. 3 in each digit and 2 in hallux).
Function:- Skeletal system has the following important functions
(i) This endoskeleton gives rigidity to the body and supports the total weightage of the
body.
(ii) It protects internal organs, (Example-cranium or brain box contains the brain) like lungs, spinal cord etc. against mechanical injury.
(iii) It stores calcium and phosphate.
(iv) The skeletal muscles are inserted into the bones by a strong band of flexible connective tissue, called tendons.
4, JOINTS (Coloured Plage-IV)
Two bones are fitted with each other at joints.
The surfaces of two bones, involved in the process, are in apposition with each other. In some cases the articulating surfaces of the bones move upon each other. This movement involves the muscles which are attached with the bones by tendons. The ligaments form the basis of articulation. These are made up of white fibrous connective tissue.
The joints are classified into three distinct types, according to their mobility, such as, fixed, slightly fixed and freely movable joints.
1. Fixed or Fibrous Joints. In this type of joint, the articulating bones are joined together by ligaments. In these joints the articulating bones do not move at all, their saw-like edges are joined by ligaments.Fibrous or immovable synarthrosis
These are of 3 types.
(a) Sutures. These are special fibrous joints present in the skull, These joints are tight due to interlocking of bones and are joined by ligaments.
Example. skull bone
(b) Gomphosis. This type of joint is present between the conical process of one bone and the socket of the other.
Example. It is a joint between the root of the tooth and the socket of the jaw bone.
(c) Schindylesis. This type of joint occurs when the crest of a bone fits into the groove of another bone.
Example. This type of joint is seen between the ethmoid and vomer bone of the skull.
2. Slightly Movable or Cartilaginous Joints. The articulating bones of these joints are joined together by a thin layer of hyaline cartilage (white fibrous cartilage). It allows limited movement at the joints like bending and slight rotation.
Example. Vertebrae.
3. Freely Movable or Synovial Joints.
In this type of joint, the articulating bones freely move upon each other. The ends of these articulating bones are covered by small pieces of hyaline cartilage. The space in between these hyaline cartilages is called a synovial cavity, which is filled with a slippery, lubricating fluid called synovial fluid. The synovial cavity is covered by a synovial membrane. The synovial membrane, fluid and space form the synovial capsule.
The synovial joints are classified into the following types, according to their structure and type of movements.
Immovable Joints
(1) These are called synarthroses.
(ii) Synovial cavity is absent.
(iii) These are of 3 types.
(a) Sutures-In-skull bone.
(b) Gomphosis-Ex-root of tooth socket and jaw bone.
(c) Schindylesis-Ex-joint between ethmoid and vomer.
Movable Joints
(i) These are called diarthrosis.
(ii) Synovial cavities may be present.
(iii) These are 6 types.
(a) Spheroidal joints-Ex-Pelvic girdle & femur,
(b) Hinge joints-In-Ankle.
(c) Pivot joints-Ex-upper-ends of radius and ulna
(d) Gliding joints-Ex-Palm
(e) Ellipsoid joints-Ex-Sole of foot
(f) Saddle joints-Ex-carpals and metacarpals
1. Ball and Socket Joint or Spheroidal Joints.
In this type of joint the ball like the head of one bone fits into the cup like the socket of another bone. This type of joints allows all sorts of movements like, stretching (extend), rotation, folding (flex), drawing the body to the middle line (adduct) and moving away (abduct).
Example. Pectoral and pelvic girdle joints.
2. Hinge Joints or Ginglymus Joints
In this type of JOINTS, one bone a another like a hinge. It resembles the hanging of a door on the side post of the door-frame. The bones are articulated by strong ligaments. The movement occurs on a single plane only.
Example. Ankle, knee and elbow joints.
3. Pivot Joints or Trochoid Joints.
In this type of joints, one bone moves freely over the cher bone which is fixed and acts as the pivot. This movement is restricted to rotation around the pivot.
Example. The upper ends of radius and ulna articulate in a pivot joint.
4. Gliding Joints.
In this type of joints, the articulating bones are flat and can glide or slide
over each other.
Example. It is seen in some bones of the palm and foot.
5. Ellipsoid Joints.
It is somewhat similar to gliding joints. But the two articulating bones move around two axes.
Example. It is seen among the toe bones and some bones of the sole of the foot.
6. Saddle Joints or Sellar Joints. It is similar to ball and socket joints. But the movements are somewhat restricted due to poorly developed balls and sockets.
Example. It is the joint between carpals and metacarpals of the thumb.
MUSCLES IN MOVEMENT OF MAN
The muscular system of humans consists of three types of muscles.
LOCOMOTION AND MOVEMENT IN MAN
(a) Cardiac Muscles are present in the heart.oel
(b) Smooth or Non-striated Muscles Are involuntary muscles present in the visceral organs Such as urinary bladder, alimentary canal etc.
(c) Striated (or skeletal muscles) are the voluntary muscles which are responsible for the movement of the body of man. The structure and function of these muscles are described in the chapter -Animal tissue).
TYPES OF MUSCLES (Coloured Plate-III)
The striated muscles are divided into the following categories according to their function.
1. Flexor. A part of these muscles bends upon each other. The contraction brings about flexion or bending
Example. Biceps bends forearm towards upper arm.
2. Extensor. Extension of body parts is brought about by the contraction of these muscles,
Example. Triceps extend the forearm
3. Elevators. These muscles contract to raise the body parts.
Example. The masseter muscles contract to raise the lower jaw.
4. Depressors. These muscles contract to lower the body parts.
Example. The depressor mandibularis muscle of the lower jaw contracts to open the mouth.
5. Abductors. These muscles move away the body parts.
Example. The deltoid muscles of the arm moves the arm forward.
6. Adductors. These muscles bring the body parts towards the body.
Example. Latissimus dorsi brings the arm near the body.
7. Rotators for Pronators. It causes rotation of body parts.
Example. Pyriformis rotates the femur
8. Constrictor. These muscles close the aperture.
Example. The sphincter muscles of anus close anal aperture.
9. Dilators. These muscles contract to dilate the aperture.
Example. The cloacal aperture is dilated by dilator
10. Supinator. These muscles turn the body part in the opposite direction.
Example. These muscles bring about the movement of the hand by which the palm is turned upwards
11. Pronator. It is antagonistic to the supinators. It brings about the body parts to normal state.
Example. These muscles bring about the movement of the hand by which the palm is turned upside down.
12. Sphincter. These sets of muscles narrow or close an aperture or orifice.
Example, Pyloric sphincter is present between stomach and duodenum and and sphincter anus
There are nearly 700 muscles in human body which perform different functions. Some honest with oppositely acting antagonist muscles. The biceps and tr’ ceps act in opposite direction.
General Properties of Muscles
1. Excitability. The muscles receive stimuli and react.
2. Contractibility. The contraction of muscles makes it short and thick.
3. Elasticity and Extensibility. The muscles can extend and come back to their original shape due to elasticity.
4. Tonicity. It is the involuntary resistance to passive stretch. All muscles are found in a partial sustained stage of contraction called muscle tonus.
Structure of Muscle
In the body of the vertebrates three types of muscles are present. They are:
(a) striped or striated muscles
(b) unstriped or unstriated muscles
(c) cardiac or heart muscles.
The striated muscles form the main bulk of the vertebrate body, It shows striations in the form of alternate light and dark bands and hence the name striated muscle. It is attached to the bone by a connective tissue called tendon, thus it is known as skeletal muscle. The working of this muscle is under the control of will, hence it is also called as voluntary muscle.
The muscle is formed of a large number of muscle cells. These muscle cells are called muscle fibres. The muscle fibres are long (1.0-40 mm), unbranched cells. Its cell membrane is called sarcolemma and it contains many nuclei and longitudinal protein filaments called myofibrils.
Ultrastructure of Myofibril (Coloured Plate-V)
A myofibril under high magnification shows alternate light bands and dark bands. The light band or -band is isotropic under polarized light. The dark band or A-band is anisotropic to polarized light. In the centre of the I-band a Z-line or Krause’s membrane is present. It is derived from a German term, Zwischenscheibe (= between disc).
In the middle of the A-band, a light region called H-Zone or Hensen’s Zone is present. The portion of myofibril between oneZ-line and the next Z-line is called a Sarcomere Sarcomere is the functional unit of myofibril and is about 2 to 3 u in length. A sarcomere includes two 1/2 1-bands on the sides and an A-band in the centre. Electron microscopic study revealed that a sarcomere consists of two types of filaments-a thick filament (nearly 100 A in
diameter) or myosin filament or primary filament and a thin filament called actin filament or secondary filament about 50 A° in diameter). The thick myosin filaments are present only in
the dark bands while thin actin filaments occupy the light band and part of the dark band. Absence of action from the central portion of dark band accounts for the less dense H-zone. Tho acting filaments are attached to the Z line at one end; their other ends extend towards the middle of the sarcomere and are free. The myosin filaments lie midway between Z Lines and are unattached to them.
A myosin filament is composed of about 500 tadpole shaped myosin molecules. Each molecule has two parts:
(i) a long double helical tail and
(ii) a laterally projecting head. The head is joined with the tail by a short shaft. The head is a modified myosin called meromyosin and has a binding site for actin. The tails together form myosin filament The globular heads project outside, forming cross bridges.
A thin actin filament consists of three proteins :actin, tropomyosin and troponin. Actin has a molecular weight of about 70,000. It occurs in two forms, a globular or G-form and filamentous or fibrous F-form. In the presence of salts, actin attains globular form. These G-forms polymerise in presence of KCl and ATP to form fibrous or F-actin. Tropomyosin is a double stranded helical structure present in the groove of two actin strands Troponin consists of three globular molecules having calcium ion binding sites. This troponin and Cat* helps in the formation of cross bridges between actin and myosin. However, tropomyosin and troponin inhibit cross bridge formation
MECHANISM OF MUSCLE CONTRACTION (PLATE VI & VII)
The muscles are contractile in nature. The process by which the muscles contract is known as muscle contraction. Muscles contract in response to various stimuli such as mechanical, electrical and thermal. The mechanism of muscle contraction can be discussed under three bases:
(a) Physical
(b) Molecular
(c) Biochemical.
Physical Basis of Muscle Contraction
The Sliding Filament Theory proposed independently by two groups of scientists H.E. Huxley and Hanson (1954) ; and A.E Huxley and R. Niedergerve best explains the mechanism of muscle contraction
This widely accepted theory has the following features:
1. According to this theory the length of actin and myosin filaments remain constant
2. During contraction the length of the A-band remains constant while the length of I-band and H-zone gradually decrease and finally disappear .
3. The Z-lines touch the end of myosin filament.
4. When the thin actin filaments slide over the thick myosin filaments, the width of H-zone between the ends of actin filaments become smaller and finally disappear. Thus, the thin actin filaments of opposite sides meet in the centre of sarcomere.
5. The sliding of filaments takes place by means of quick formation of cross bridges and their breakdown.
6. The sarcomeres are shorter in length as a result of which the muscles shorten and contract.
Molecular Basis of Muscle Contraction
The thick myosin filament consists of myosin molecules. The myosin molecule acts as an enzyme (an ATPase). Electron micrographs show that myosin molecule consists of a double-headed globular region joined to double stranded helical Tall. The myosin molecule splits by trypsin into two fragments, called light meromyosin (LMM) and heavy meromyosin (H MM). LMM lacks ATPase activity and does not combine with action. H MM catalyses the hydrolysis of ATP and binds to actin.
The thin actin filaments have three constituents Actin, Tropomyosin and Troponin. In solutions of low ionic strength, actin is formed of numerous globular subunits called G-actin. As the ionic strength is increased the G-actin polymerizes into fibrous form called F-actin. An F-actin fibre looks like two strings of beads wound around
Biochemical Basis of Muscle Contraction:
The biochemical events associated with the muscle contraction have been worked out, Gyorgyl and some other workers. These events are outlined below
(I) A nerve impulse stimulates a muscle fibre by releasing acetylcholine at the neuromuscular junction motor end plate.
(II) Acetylcholine causes the release of calcium ions from the sarcoplasmic reticulum (= endoplasmic reticulum) of the muscle into the interior of muscle fibre.
(ii) The calcium ions bind to the calcium binding subunit of troponin (TpC) and produce conformational change in actin filament.
(iv) Myosin molecules now bind with actin to form actomyosin. The heads of the myosin molecules form cross bridges with actin molecules. The cross bridges temporarily hook to pull the filaments a short distance and then release them.
(v) The globular double head of myosin molecule has two active sites, one for actin and other for ATP The active site for ATP has ATPase activity which splits ATP into ADP + Pi
Muscle Relaxation:
It is not a passive process and like contraction it requires ATP. When a muscle is stimulated, the sarcoplasmic reticulum gives out the calcium ions. When such stimulation stops, the calcium ions return to sarcoplasınic reticulum by the process of active transport utilising ATP.
During the process, the muscle glycogen is broken down into lactic acid releasing some ATP. In some cases lactic acid is oxidized to liberate energy, CO2 and water. This is described as Cori Cycle
Muscle Glycogen- Lactic acid (muscle)
Electrical Events During Muscle Contraction
When the muscle is at rest, the outside of sarcolemma of muscle fibre is rich in sodium
ions and is positively charged. On the inner side of sarcolemma potassium ion is profusely present and the inside is negatively charged. This potential difference across the sarcolemma is called resting potential and the sarcolemma is in a polarised state.
When a muscle fibre is stimulated the sarcolemma becomes permeable to ions. Sodium ions from outside move to the inside and potassium ions from the inside move to the outside of the sarcolemma . As a result the inside is positively charged and the outside is negatively charged. This change is called action potential and the sarcolemma is said to be depolarized. Due to depolarization the muscle fibre contracts.
TERMS RELATED TO MUSCLE CONTRACTION
Threshold Stimulus. Each muscle contracts due to some stimulus. The nerves supply nerve impulses to muscles. Nerve impulse is the change in the electrical potentials. The adequate strength of stimulus shortens the muscle fibre. Besides nerve impulse, the muscle fibres can be stimulated by other stimuli like chemical, mechanical stimuli etc. The muscle fibres remain limp or relaxed when it is not stimulated. The specific minimum strength required muscle contraction is called a threshold stimulus. It differs from fibres to fibres and muscles to muscles.
The stimulus which is unable to bring contraction is called subliminal stimulus and the stronger stimulus is known as supraliminal stimulus. The period between two successive stimulations is called a refractory period.
Single Twitch. The single nerve impulse or an electrical shock of sufficient amount, brings about contraction in a single muscle fibre. It is known as muscle twitch.
Summation. When a second stimulus is given to the muscle fibre after the first one (already contracted muscle fibre), it brings about more shortening or contraction than the first one. Thus it adds to the contraction strength of the first stimulus. It is known as summation.
Tetanus. When a series of stimuli are given to the muscle fibre in a quick succession, the contraction of muscle fibres continues. This continued state of contraction is known as tetanus.
The daily activities of man are carried out by tetanic contraction of muscles.
Muscle Fatigue. By repeated stimulation, the muscles lose irritability and fail to contract. It is known as fatigue. It happens due to exhaustion of energy and accumulation of lactic acid Rigor Mortis. Due to non-availability of ATP, enzymes, oxygen and food, the muscles remain contracted after death. It is called rigor mortis.
RED AND WHITE MUSCLE
Red Muscle Fibre. It is dark red in colour, due to the presence of myoglobin. It stores oxygen as oxymyoglobin. It is rich in mitochondria. It shows a slow rate of contraction and can contract without muscular fatigue.
Example. Extensor muscles present on the back of the human body. Fight muscles of kite
White Muscle Fibres. These are light red in colour due to lack of myoglobin.They show fast rate of contraction but for a short period only. They are poor in mitochondria. They depend on anaerobic metabolism or glycolysis only, accumulating lactic acid.
Examples. Flight muscles of birds, muscles of the eyeball of humans etc.
CONTROL OF MUSCLE MOVEMENT
The muscular contraction is controlled by the nervous system. The motor nerves are connected with muscle fibres. It releases acetylcholine at the neuromuscular junction. The sensory nerves Iso innervate the muscles which act as receptors of strain and stretch. The stimulus is mostly aired by sensory nerves to spinal cord, which restricts excessive stretching
OXYGEN DEBT
During strenuous work, or exercise, the muscles does not get sufficient oxygen to meet the energy needs immediately. So, the muscle gets energy from anaerobic glycolysis. It results in accumulation of large amounts of lactic acids in the muscles. During the recovery, the oxygen consumption of the muscle is more than when it is in normal state. The extra oxygen consumed during the recovery period is called the oxygen debt of the muscle. The oxygen is used in oxidising lactic acid aerobically.
DISORDERS
1. ARTHRITIS. Inflammation or swelling of the joints is referred to as arthritis. It is an integral term which can be applied to as many as twenty-five malfunctions of joints. It is a common disease of old age. Its common symptoms are pain and stiffness in the joints. It is used either due to bacterial infection, injury, allergy or due to hormonal imbalance. There common forms of arthritis are described below :
(I)Rheumatoid arthritis. It is the most common arthritic disease. It is the inflammation
of the synovial membrane in synovial joints. When this synovial membrane is
inflamed, it produces too much fluid. As a result the joints swell causing extrema
pain in joints. Fever, anaemia, loss of weight and morning stiffness are the other symptoms of rheumatoid arthritis. Generally this disease starts at the age of 20-40 yen and affects women more often than men. Rest and prescribed exercises give relief
(ii) Osteoarthritis. At the joints, the end of bones are covered over by smooth cartilage Due to years of use the smooth cartilages are replaced by uneven bony mass. As.a result the joint becomes inflamed, its movement becomes painful and restricted. it is common in old persons and mainly affects weight bearing joints.
(iii) Gout. It is another form of arthritis caused due to the deposition of excess amounts of uric acid and crystals of sodium urate in the synovial joints. It is very painful particularly at night, and makes movement difficult. Gout generally affects the foot. This arthritis is related to diet and persons suffering from gout should avoid meat
There is no cure for arthritis. Persons suffering from arthritis are advised to take
pain relieving or analgesic drugs and take rest.
2. OSTEOPOROSIS (Gk. Osteon = bone, poros = pore, osis = condition) Osteoporosis is the loss of minerals and fibres from the matrix of the bone causing weakening of the bone. It results from excessive reabsorption of calcium and phosphorus from the bone. It leads to crushing fractures of vertebrae and neck of femur. OsteoporOsis occurs in elderly women experiencing post menopause. This disease is more common in women than men, and older than middle aged persons. Smoking, excessive drinking, and decreased exercise may lead to osteoporosis. Pain in bone, particularly back and lower vertebrae are the common symptoms. Food rich in calcium, calcium supplying drugs, sex hormones and exercise reduce osteoporosis.
3. FRACTURE. Fracture is a break in bone. Due to deposition of minerals the bones of
an adult person becomes hard and brittle. So the old persons are more liable to fracture of bones
than children.
4. SLIPPED DISC. It is the displacement of vertebrae from their normal position. It may
be due to mechanical injury or defects of ligaments holding the vertebrae together.
5.SPRAIN AND STRAIN. Twisting of a joint without dislocating it is called a sprain. h
causes damage to the ligaments and also to tendons, muscles, blood vessels and nerves and
produce severe pain. Strain is less severe stretching or twisting of a joint.
ADDITIONAL INFORMATION FOR ENTRANCE EXAMINATION
- Smallest bone in Human body is the stapes in the middle ear.
- Longest bone in Human body is the Femur.
- Largest foramen is the Foramen magnum in the skull.
- Smallest muscle is the Stapedius of the stapes.
- Largest muscle is Gluteus maximus (Buttock).
- Strongest muscle is the Masseters of the lower jaw.
- Kinesiology is the study of body movement.
- Cardiology is the study of the skull.
- Knee joint is the largest synovial joint.
- “All or none law” is associated with muscle fibre.
- Protein found in thick filaments of skeletal muscle is Myosin.
- Only one molecule of oxygen is attached to one molecule of myoglobin.
- Kymograph is the apparatus used in recording muscle contraction.
- Rigidity that develops in the muscle after death is known as Rigor mortis.
- The most abundant mineral element in the muscle is potassium.
- Muscle fatigue is due to lactic acid.
FAQ~
- WHAT IS THE MEANING OF LOCOMOTION ?
Ans:- It is the displacement of the body from one place to another. The animal performs locomotion with the help of locomotory organs. Locomotion is performed by walking, running, swimming, hopping, flying, swimming, crawling etc. The purpose of locomotion is to search for food, water, shelter and partners for reproduction, to avoid unfavourable conditions and predators or to reach favourable places etc.
- WHAT IS THE MEANING OF MOVEMENT ?
Ans :- It is the movement (or change of direction) of the body parts, in relation to the long axis of the body. Movement is generally marked in the different parts of the body, keeping the main body fixed. It is related to the change of body posture. The head, trunk, limbs, and other appendages move against gravity to maintain the body posture. The jaws, tongue, teeth, tentacles, snout etc. move to collect and ingest food materials. The eyeballs move for vision and ear pinna moves to collect sound. The internal organs also move to carry out different functions. The stomach moves to grind and propels food materials. The heart moves to circulate the blood inside the body.
- WHAT IS THE SIGNIFICANCE OF LOCOMOTION ?
Ans:-
1. Locomotion helps to find food materiais.
2. It helps to avoid unfavourable conditions.
3. It helps to escape from predators.
A. It occurs as a reaction to the stimuli.
5.Jt is required to find a mate.
6. In some animals spontaneous locomotion is also seen.