Functional Anatomy andFunctional Anatomy and
PhysiologyPhysiology
Muscles and NervesMuscles and Nerves
Muscular System
There are 620 muscles in the body.
Muscles represent about 40– 50% of body weight.
Muscles perform four di...
Types of Muscle Tissue
Myology is the study of muscles
Muscle constitutes 50% of the total body weight.
Muscle tissue we...
2. Cardiac (involuntary)
 Intertwined fibres.
 Found only in the heart.
 Responsible for blood flow.
 Difficult to fat...
Muscle Tissue Characteristics
Excitability
Nerve stimuli controls muscle action. Muscles can
receive and respond to a stim...
Muscles of the body
Muscles of the body
Muscles of the body
Facial muscles
Anterior torso muscles
Posterior torso muscles
Upper arm muscles
Lower arm muscles
Upper leg muscles
Upper leg muscles
Lower leg muscles
Lower leg muscles
Skeletal muscle Architecture
Skeletal muscles can be classified according to the fibre
arrangement around the tendon.
The ...
Muscle Action
• Skeletal muscles produce movement by exerting a pulling force on a bone.
They have a more rigid attachment...
Muscle Fibre Types
There are two different types of muscle fibres:
1. Slow Twitch Muscle Fibres
• Red in colour
• Contract...
Types of Muscle contraction
Muscle contractions are classified according to the movement they cause:
1. Isotonic Contracti...
Muscle Action and Movements
During a particular movement, a muscle performs one of the following roles:
• Agonist or Prime...
Muscle Control
• Skeletal muscle can only pull to produce movement;
they cannot push. They pull by working in pairs or
gro...
MUSCLE ACTION EXERCISE/SKILL EG
Trapezius
Deltoid
Pectoralis major
Biceps brachii
Brachialis
Brachioradialis
Flexor carpi ...
PRINCIPAL MUSCLES OF THE BODY INVOLVED IN
GROSS MOTOR ACTIVITIES.
MUSCLE MAIN ATTACHMENT SITES MAIN ACTION
Abdominal Muscl...
PRINCIPAL MUSCLES OF THE BODY INVOLVED IN
GROSS MOTOR ACTIVITIES.
MUSCLE MAIN ATTACHMENT SITES MAIN ACTION
Forearm Movers:...
PRINCIPAL MUSCLES OF THE BODY INVOLVED IN
GROSS MOTOR ACTIVITIES.
MUSCLE MAIN ATTACHMENT SITES MAIN ACTION
Thigh movers:
G...
PRINCIPAL MUSCLES OF THE BODY INVOLVED IN
GROSS MOTOR ACTIVITIES.
MUSCLE MAIN ATTACHMENT SITES MAIN ACTION
Movers of the f...
Microscopic Structure of a Skeletal Muscle.
Skeletal muscle is covered with a layer of connective tissue
called the Epimys...
The Muscle Fibre
Each muscle fibre is surrounded by a cell
membrane called the Sarcolemma
Inside the sarcolemma is a gel-l...
Fundamentals of the Nervous System
You are driving down the freeway, and a horn blares to your right. You swerve to your l...
Nervous System
The Nervous System is the body’s control centre and communications
network.
• Functions:
• Sensory – It sen...
The nervous system is divided into two principle divisions:
Central Nervous System (CNS)
• Control centre for the entire s...
Nervous System
Neurons.
Neurons are the nerve cells and they are responsible for
conducting impulse from one part of the body to another....
There are two types of neurons:
1. Motor Neurons – they conduct impulses from
the brain and CNS to the muscles that cause
...
Nervous Control of Muscular Contraction.
• Nervous control facilitates the contraction of a muscle.
• The body receives in...
Motor Units.
• A motor unit consists of the motor nerve plus the
muscle fibre it stimulates.
• The number of fibres within...
The ‘All or Nothing’ Principle
• The ‘All or Nothing’ Principle states that the
nerve impulse will not stimulate the muscl...
Initiation of Muscular Activity ‘The Sliding Filament Theory’
1. A nerve impulse arrives at the neuromuscular junction, ca...
Microfilaments
The microfilaments that have been most extensively studied are
those found in the skeletal muscle of animal...
Microfilaments cont…
When the sarcomere is fully shortened, the thin microfilaments
overlap somewhat in the centre, and th...
Microscopic Structure of a Skeletal Muscle.
Reflex Arc
• Involuntary or automatic responses are called reflex responses
• These responses involve both sensory and mot...
Examples of Reflexes.
1. Knee Jerk Reflex
– Impulses travel to L2 – L4 in
the spinal cord.
– Stretch on the tendon
causes ...
Examples of Reflexes.
2. Plantar Reflex
– Downward flexion (curling)
of the toes. This is normal.
– Babinski’s sign – toes...
Examples of Reflexes.
3. Abdominal Reflex
– Stroking the skin of the lateral
abdomen above the umbilicus can
cause contrac...
FA&P Muscles and Nerves
FA&P Muscles and Nerves
FA&P Muscles and Nerves
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FA&P Muscles and Nerves

  1. 1. Functional Anatomy andFunctional Anatomy and PhysiologyPhysiology Muscles and NervesMuscles and Nerves
  2. 2. Muscular System There are 620 muscles in the body. Muscles represent about 40– 50% of body weight. Muscles perform four different important functions for the body. Movement The majority of movements are the result of muscle contractions. For example, blood circulation, respiration, digestion and locomotion. Posture Maintenance Muscles work continuously to maintain varying postures against forces of gravity. Joint Stability Even as muscles pull on bones to cause movement they ‘stabilise’ joints of the skeleton, particularly the knee and the shoulder Heat Generation Muscles generate heat as they contract. This is vitally important in maintaining normal body temperature.
  3. 3. Types of Muscle Tissue Myology is the study of muscles Muscle constitutes 50% of the total body weight. Muscle tissue weighs more than fat tissue. Muscle consists of 30% protein and 70% salt solution. 1. Skeletal Muscle (voluntary) Long, cylindrical and striped.  They make up the form of the body.  Attached to the bone by tendons.  Characterised by short-term rapid contractions.  Initiates the movements of locomotion and manipulation.  Examples are triceps, hamstrings and gluteals.
  4. 4. 2. Cardiac (involuntary)  Intertwined fibres.  Found only in the heart.  Responsible for blood flow.  Difficult to fatigue. 3. Smooth (involuntary) Long and spindle shaped. Characterised by slow and sustained rhythmic contractions. Found in the walls of organs with hollow cavities. Examples are the digestive tract and urinary tract. Responsible for moving substances throughout the body.
  5. 5. Muscle Tissue Characteristics Excitability Nerve stimuli controls muscle action. Muscles can receive and respond to a stimulus from a nerve cell. Contractibility Muscle changes shape due to a stimulus. That is, can become shorter and thicker. Elasticity Muscle returns to normal length when force is removed. That is, after is has been contracted. Extensibility Muscles have the capacity to stretch when a force is applied. Atrophy – muscles can decrease in size as a result of injury, illness or lack of exercise. Hypertrophy – muscles can increase in size with an increase in physical activity.
  6. 6. Muscles of the body
  7. 7. Muscles of the body
  8. 8. Muscles of the body
  9. 9. Facial muscles
  10. 10. Anterior torso muscles
  11. 11. Posterior torso muscles
  12. 12. Upper arm muscles
  13. 13. Lower arm muscles
  14. 14. Upper leg muscles
  15. 15. Upper leg muscles
  16. 16. Lower leg muscles
  17. 17. Lower leg muscles
  18. 18. Skeletal muscle Architecture Skeletal muscles can be classified according to the fibre arrangement around the tendon. The three classifications are Fusiform muscles – Run the length of the muscle belly – Designed for mobility because they produce contractions over a large range, yet produce low force – Example – sartorius. Pennate muscles – designed for strength and power and run at angles to the tendon, they are further divided into: Unipennate • Found on only one side of a central tendon • Example – tibialis anterior bipennate • run on either side of a central tendon • example rectus femoris in the quadriceps multipennate • branch out from several tendons • enable great force to be generated • example – deltoid Radiate muscles – Radiate from the main tendon – Compromise between fusiform and pennate – Capable of producing strength and power yet retain their mobility – Example – pectoralis major
  19. 19. Muscle Action • Skeletal muscles produce movement by exerting a pulling force on a bone. They have a more rigid attachment to a bone at one end, and they are attached across a joint to another bone that is usually more moveable. • The muscle’s point of attachment to the more stationary bone is called the origin and tends to be closer to the main mass of the body. • The origin of a muscle is often quite widespread because it helps anchor the muscle. • The muscles more moveable point of attachment is called the insertion and tends to be located away from the mass of the body. It usually attaches to the bone near the joint that is to be moved by the muscle. • When a muscle contracts, the origin and insertion are drawn together, shortening the muscle. • The bones attached to the muscle produce movement in a specific direction. This movement is called the muscle’s action. • For example, the action of raising your arm by your side (abduction) is caused by contraction of the deltoid muscle, where the insertion of the muscle at the humerus moves toward the muscle’s origin at the scapula.
  20. 20. Muscle Fibre Types There are two different types of muscle fibres: 1. Slow Twitch Muscle Fibres • Red in colour • Contract slowly but can contract repeatedly for prolonged periods of time. Therefore endurance fibres. • Smaller than fast twitch fibres 2. Fast Twitch Muscle Fibres • White in colour • Contract rapidly but easily exhausted • Suited for speed and strength • Larger than slow twitch fibres Your genetic inheritance of fibres determines your speed or endurance potential. Training will increase the efficiency of what you predominantly have – not increase the amounts of certain fibre type.
  21. 21. Types of Muscle contraction Muscle contractions are classified according to the movement they cause: 1. Isotonic Contraction – This is where the muscle length changes throughout the range of movement as force is being developed – It is the most common form of contraction. Examples include push-ups, sit- ups, throwing, kicking and most sporting movements. – There are two types of isotonic contractions: • Concentric – the muscle length shortens during the contraction. • Eccentric – the muscle lengthens while the force is developed. This occurs in activities that resist gravity, and it will slow the limb or trunk movement. 1. Isometric Contraction – This occurs when force is developed (tension), but there is no change in the length of the muscle. Is referred to as applying a force against an immoveable object. – Examples include gripping a cricket bat – the forearm muscles perform an isometric contraction, and holding a weight in a stationary position. 1. Isokinetic Contraction – This develops maximal velocity throughout the entire range of motion. – Highly specialised equipment, such as Cybex machines are required to perform these contractions. – The amount of force applied by these machines always equals the amount of force applied by the muscle and this is done over the muscle full range of motion.
  22. 22. Muscle Action and Movements During a particular movement, a muscle performs one of the following roles: • Agonist or Prime Mover – This muscle causes the major action. There is usually more than one prime mover in a joint action, and there are prime mover muscles for all moveable joints. • Antagonist – This muscle must relax and lengthen to allow a movement to occur. It causes an opposite reaction to that caused by the agonist. Generally, muscle flexors and extensors work in an agonist – antagonist relationship. • Synergist or assistant – This muscle assists the agonist to produce the required movement to reduce any excessive or unnecessary movements. • Stabiliser or fixator – these muscles ensure that the joint remains stable while the agonist and antagonist are working. The muscle will shorten just slightly during contraction, causing only minimal movement to allow the action to be performed more effectively. Example – In flexing the elbow joint, as in curling a dumbbell, the prime mover is the brachialis. Its assistant, or synergist, is biceps brachii. The brachialis is the prime mover because it has a better mechanical advantage than the biceps due to its lower origin on the humerus and its attachment to the more rigid ulna rather than the radius, which rotates. To make flexion of the elbow possible, the antagonist to the elbow flexors, triceps brachii, must be inhibited from contracting. Further, in flexing the elbow with the palm of the hand over the top of the dumbbell instead of under it, the supinators of the elbow must be prevented from acting. Therefore the elbow pronators (pronator teres) act as neutralisers to resist the contractions of the supinators. Finally, the shoulder girdle must be prevented form drooping as the weight is lifted, so there are fixator muscles, principally the trapezius in this case, that literally hold the shoulder up.
  23. 23. Muscle Control • Skeletal muscle can only pull to produce movement; they cannot push. They pull by working in pairs or groups – that is, as a muscle contracts on the front side of the body (anterior), usually the muscles at the back (posterior) with the opposite action relax. • Reciprocal Inhibition – states that when one muscle is contraction, the opposite muscle in the pair is relaxing. It is a balanced process of relaxation and contraction of the agonist and antagonist.
  24. 24. MUSCLE ACTION EXERCISE/SKILL EG Trapezius Deltoid Pectoralis major Biceps brachii Brachialis Brachioradialis Flexor carpi radialis Flexor digitorum Superficialis Sartorius Rectus femoris Tibialis anterior Soleus Serratus anterior External oblique Rectus abdominis Adductor longus Vastus medialis Gracilis Vastus lateralis Teres major Triceps brachii Gluteus maximus Biceps femoris Semitendinosus Semimembranosus Gastrocnemius Latissimus dorsi Erector spinae Raises and adducts shoulder blade Flexion, extension, rotation and adduction of the shoulder Flexion, rotation and abduction of the shoulder Elbow flexion and forearm supination Elbow flexion Forearm flexion Flexion of wrist and forearm and abduction of the hand flexion of fingers, forearm and hand flexion and rotation of the thigh hip flexion and knee extension plantar flexion and inversion of foot plantar flexion abduction and rotation of scapulae compresses abdominals trunk flexion and rotation adduction, flexion and lateral rotation of thigh hip flexion and knee extension adduction of thigh and leg flexion extension of leg adduction, extension & rotation of arm elbow extension hip extension, external rotation and abduction hip extension and knee flexion flexion and rotation of leg, thigh extension as above plantar flexion and knee flexion extension, internal rotation and adduction of the shoulder Trunk extension Bench press, dumbbell fly, pecdec machines Bicep curls Preacher curls Wrist curls Breastroke kick Kicking a football Freestyle kick Calf raises on toes Tennis serve Trunk twists Sit ups Inside foot pass in soccer Triceps kick back Cycling Leg curls, squats Rowing Calf raises Lat pull-downs, upright rowing Tennis serve
  25. 25. PRINCIPAL MUSCLES OF THE BODY INVOLVED IN GROSS MOTOR ACTIVITIES. MUSCLE MAIN ATTACHMENT SITES MAIN ACTION Abdominal Muscles: External Oblique Internal Oblique Rectus Abdominus Transversus Abdominus Movers of the Shoulder Girdle: Serratus Anterior Trapezius Rhomboids Arm Movers: Pectoralis major Deltoid Latissimus Dorsi Rotator Cuff: Subscapularis Supraspinatus Infraspinatus Teres minor Lower 8 ribs to the pubis and illium Illium to last 3 or 4 ribs Pubis to 5th – 7th ribs Illium and 6 lower ribs to sternum and pubis Upper 8 – 9 ribs to the scapula Base of the skull, 7th cervical and all thoracic vertebra to the clavicle and scapula 7th cervical and first 4 – 5 thoracic vertebrae to the scapula Clavicle, sternum and cartilage of ribs to the humerus Clavicle and scapula to the humerus Lower 6 thoracic and all lumbar vertebrae, sacrum, illium and lower 3 – 4 ribs to humerus All 4 extend from parts of the scapula to the humerus Flexes spine, compresses abdomen Flexes spine, compresses abdomen Flexes spine, compresses abdomen Compresses abdomen Rotates and abducts scapula Draws head back to the side; adducts scapula, rotates scapula Adducts and rotates scapula downward slightly Flexes, adducts and medially rotates arm at the shoulder Extends, flexes and abducts the abducts the arm at the shoulder Adducts, extends and medially rotates arm; draws shoulder backward and downwards As a group, the 4 muscles strengthen and stabilize the shoulder joint and act as the chief rotators of the arm
  26. 26. PRINCIPAL MUSCLES OF THE BODY INVOLVED IN GROSS MOTOR ACTIVITIES. MUSCLE MAIN ATTACHMENT SITES MAIN ACTION Forearm Movers: Biceps brachii Triceps brachii Supinator Pronator teres Movers of the Hand & Fingers: Common wrist extensor (Extensor carpi) muscles Common wrist flexor (Flexor carpi) muscles Flexor digitorum muscles Extensor digitorum Movers of the Vertebral Column: Quadratus lumborum Erector spinae group: Iliocostals Longissimus and Spinalis Scapula to the radius Scapula and humerus to ulna Humerus and ulna to the radius Humerus and ulna to the radius This group of muscles extend from the ulna and humerus to the metacarpal bones This group of muscles extend from the humerus and ulna to the metacarpal and 2 carpal bones These muscles extend from the humerus, ulna and radius to the phalanges of each finger Humerus to the middle and distal phalanges of the finger Illium to 12th rib and upper 4 lumbar vertebrae Three groups of muscles, each consisting of a series of overlapping muscles, located posteriorly along the spine and torso Flexes forearm at elbow and supinates hand Extends forearm at elbow Supinates hand Pronates hand Extend and either adduct or abduct the hand at the wrist Flexes and either abduct or adduct the hand at the wrist Flex the phalanges of each finger and flex the Hand at the wrist Extends the phalanges of each finger Flexes vertebral column sideways These muscles act to extend various sections of the spine
  27. 27. PRINCIPAL MUSCLES OF THE BODY INVOLVED IN GROSS MOTOR ACTIVITIES. MUSCLE MAIN ATTACHMENT SITES MAIN ACTION Thigh movers: Gluteal (buttock muscles): Gluteus maximus Gluteus medius and minimus Iliopsoas Tensor fasciae latae Adductor longus Lateral Rotators Leg Movers: Quadricep femoris: Rectus femoris Vastus lateralis, vastus medialis And vastus intermedius Hamstrings: Biceps Femoris Semitendonosus and Semimembranosus Illium, sacrum and coccyx to the femur and Illiotibial band Illium to the femur Composed of 2 muscles which extend from the lumbar vertebrae, illium and sacrum to femur Illium to the tibia (via the iliotibial tract) A group of 4 muscles which extend from parts of the pubis and ischium to the femur A group of 6 small muscles extending from the pelvis and sacrum to the Illium to the patella Femur to the patella Ischium and femur to the fibula and tibia Ischium to the tibia Extends and laterally rotates the thigh at the hip Both muscles abduct and rotate the thigh at the hip Flex and rotate the thigh at the hip, flex the lumbar spine Flexes and abducts thigh at the hip Adduct, flex and rotate the thigh at the hip Laterally rotate the thigh at the hip Extends leg at the knee and flexes thigh at the hip Extend the leg at the knee Flexes and laterally rotates leg at the knee; extend thigh at the hip Flex and medially rotate leg at the knee; extend thigh at the hip
  28. 28. PRINCIPAL MUSCLES OF THE BODY INVOLVED IN GROSS MOTOR ACTIVITIES. MUSCLE MAIN ATTACHMENT SITES MAIN ACTION Movers of the foot: Gastrocnemius Soleus Peroneus longus and peroneus brevis Tibialis anterior Tibialis posterior Femur to the calcaneous (via Achillies tendon) Fibula and tibia to calcaneous (via Achilles) Two muscles which extend from the fibula and tibia to the metatarsals and a cuneiform bone Tibia to the 1st metatarsal and 1st cuneiform Tibia and fibula to 2nd and 4th metatarsals and several ankle bones Plantar flexes foot at ankle, flexes leg at knee Plantar flexes foot at ankle Both muscles act to plantar flex and evert the foot at the ankle Dorsiflexes and inverts foot at the ankle Plantar flexes and inverts the foot at the ankle
  29. 29. Microscopic Structure of a Skeletal Muscle. Skeletal muscle is covered with a layer of connective tissue called the Epimysium. The epimysium thickens as it reaches the ends of the muscle to form tendons. Skeletal muscle consists of thousands of muscle fibres (long, narrow and thread like) which run the length of the muscle and are arranged in bundles called Fasciculi. Each individual muscle fibre is surrounded by a connective tissue called the Endomysium, which binds the fibres together to from the bundles. The fasciculi are surrounded by a layer of connective tissue called the Perimysium, which helps to bind the fasciculi together. Each fibre is composed of many microscopic threads called myofibrils, which are responsible for muscle contraction. By further division, myofibrils become myofilaments, which have thick filaments (called myosin) and thin filaments (called actin). They are bound together by connective tissue and are contained in a fluid called sarcoplasm.
  30. 30. The Muscle Fibre Each muscle fibre is surrounded by a cell membrane called the Sarcolemma Inside the sarcolemma is a gel-like fluid called sarcoplasm. This fluid contains: • Mitochondria – site of aerobic energy production • Myoglobin – removes oxygen from blood and transports it to the mitochondria. • Fat, carbohydrate and protein – energy nutrients. • Adenosine triphosphate (ATP) – immediate energy source. • Enzymes – chemicals to speed up energy production. • Actin and Myosin filaments – the contractile proteins.
  31. 31. Fundamentals of the Nervous System You are driving down the freeway, and a horn blares to your right. You swerve to your left. You are dozing and your infant son makes a soft cry. Instantly you awaken. What do all these events have in common? They are everyday examples of the functioning of your nervous system, which has your body cells humming with activity nearly all the time. The nervous system is the master controlling and communication system of the body; every thought, action and emotion reflects its activity. Along with the endocrine system, it is responsible for regulating and maintaining homeostasis; of the two systems it is by far the more rapid acting and complex. Cells of the nervous system communicate by means of electrical signals, which are rapid and specific, usually causing almost immediate responses. In contrast, the endocrine system typically brings about its effects in a more leisurely way through the activity of hormones released into the body. The nervous system has three overlapping functions: (1) It uses millions of sensory receptors to monitor changes occurring both inside and outside the body; the gathered information is called sensory input; (2) It processes and interprets the sensory input and makes decisions about what should be done at each moment – a process called integration; and (3) it effects a response by activating muscles or glands; the response is called the motor output. Eg when you are driving and see a red light just ahead (sensory input), your nervous system integrates this information (red light means ‘stop’), and your foot goes for the brake (motor output).
  32. 32. Nervous System The Nervous System is the body’s control centre and communications network. • Functions: • Sensory – It senses the changes within the body and in the outside environment. • Integrative – Interprets the changes. • Motor – Responds to the interpretation by initiating action in the form of muscular contractions or glandular secretions. Through sensation, integration and response the nervous system represents the body’s most rapid means of maintaining homeostasis. Its split-second reactions can normally make adjustments necessary to keep the body functioning efficiently. (The Nervous System shares the maintenance of homeostasis with the endocrine system).
  33. 33. The nervous system is divided into two principle divisions: Central Nervous System (CNS) • Control centre for the entire system • Consists of the brain and spinal cord Peripheral Nervous System (PNS) • Consists of nerves connecting the CNS with receptors, muscles and glands • It is divided into two systems – Afferent System (sensory neurons) – conveys information from receptors to the CNS. – Efferent System (motor neurons) – conveys information from the CNS to muscles and glands. The Efferent System can be further divided: • Somatic Nervous System – conducts impulses from the CNS to skeletal muscle tissue. This is voluntary • Autonomic Nervous System – conveys impulses from the CNS to smooth muscle tissue, cardiac muscle tissue and glands. This is involuntary.
  34. 34. Nervous System
  35. 35. Neurons. Neurons are the nerve cells and they are responsible for conducting impulse from one part of the body to another. They consist of three distinct parts: 1. Cell Body (soma) – It contains the nucleus and nucleolus surrounded by granular cytoplasm. It directs the neurons activities. 2. Dendrites – Highly branched, thick extensions of the cytoplasm of the cell body. Their function is to conduct impulses toward the cell body. 3. Axon – A single, highly specialised long, thin process that conducts impulses away from the cell body to another neuron or tissue.
  36. 36. There are two types of neurons: 1. Motor Neurons – they conduct impulses from the brain and CNS to the muscles that cause movement. 2. Sensory Neurons – they conduct impulses from the sense receptors to the brain. A nerve impulse is a message that is carried along a nerve fibre. The impulse from a nerve causes a muscle to be stimulated and hence contract. Neural chains are made up of several neurons linked together. They transmit messages from the brains to muscles over long distances in various parts of the body.
  37. 37. Nervous Control of Muscular Contraction. • Nervous control facilitates the contraction of a muscle. • The body receives information from the environment via the sense organs (receptors) • Proprioceptors found in the muscles, tendons and joints provide additional information about your body. For example pain and temperature. • This information is sent to the brain where it is processed and organised. The individual then decides on an action and this message is transmitted down the spinal cord to the specific muscles (effectors), where the action is undertaken. • Messages are sent via nerve impulses, which are transmitted by neurons. • Messages must travel long distances throughout the body. Neurons are linked in neural chains to ensure all muscle fibres receive the messages from the brain. • A synapse is the junction between the dendrite of one neuron and the axon of the next neuron in these chains. • A neuromuscular synapse is the junction between the axon and the muscle where the nerve impulse stimulates the muscle.
  38. 38. Motor Units. • A motor unit consists of the motor nerve plus the muscle fibre it stimulates. • The number of fibres within each motor unit varies according to the precision of the movement required. • Generally muscles which perform gross motor movements, such as gluteus maximus, have large motor units. That is it consists of skeletal muscles having a nerve to muscle ratio of 1:1000 – with powerful contractions but no possibility of controlled and refined contractions. • Generally, muscles that require fine motor movements, such as the facial muscles, have small motor units. That is they have a ratio of 1:10, generating
  39. 39. The ‘All or Nothing’ Principle • The ‘All or Nothing’ Principle states that the nerve impulse will not stimulate the muscle fibres until it reaches a certain threshold level. • Once the nerve impulse reaches this threshold, all fibres of the motor unit will contract at the same time and maximally. • If the impulse is too weak, no fibres will contract at all. • The intensity of the muscular contraction can vary in two ways: – By varying the number of motor units stimulated. This depends on the degree of strength required. – By varying the frequency at which the impulses arrive at the motor unit. The greater the frequency, the greater the contractions of the muscle.
  40. 40. Initiation of Muscular Activity ‘The Sliding Filament Theory’ 1. A nerve impulse arrives at the neuromuscular junction, causing a release of a chemical called Acetylcholine from the nerve ending. 2. Acetylcholine travels along the synaptic cleft between the nerve and the muscle, stimulating another impulse, which travels along the sarcolemma, and changing the permeability of the sarcolemma to calcium. 3. Small openings inside the sarcolemma carry the impulse through channels within the fibre to the myofibril level. This channel system is called the sarcoplasmic reticulum. 4. Calcium is stored in the sarcoplasmic reticulum. Once the impulse reaches the site calcium is released. 5. The release of calcium allows the cross bridges on the myosin to make contact with the actin, allowing ATP to break down and release energy. 6. This energy causes the cross bridge cycling, shortening the sarcomere and thereby shortening the muscle. 7. When no nerve impulse is detected, the sarcoplasmic reticulum draws the calcium ions back, preventing the cross bridges from working and allowing the muscle to relax.
  41. 41. Microfilaments The microfilaments that have been most extensively studied are those found in the skeletal muscle of animals with backbones. This type of muscle is also called striated muscle because of the striations (stripes) that divide it into light and dark bands. The striations result from alternating areas of overlap of thick and thin microfilaments. Each skeletal muscle cell is divided into numerous contractile units called sarcomeres. Each sarcomere is separated from the next by a partition called the Z-line or Z disc. Extending toward the centre of the sarcomere from the Z-line at each end are numerous thin microfilaments of a protein called actin, with smaller amounts of two other proteins, troponin and tropomyosin, attached. Between the thin microfilaments are thick microfilaments that extend from the centre of the sarcomere towards the Z-lines. The thick microfilaments are composed of a protein known as myosin and have numerous projections, which are commonly known as cross-bridges, since they appear to cross over and attach to the thin microfilaments. The current ‘sliding filament theory’ of muscular contraction is based on the belief that the cross-bridges attach to the thin microfilaments and pull them past the thick microfilaments so that the sarcomere shortens. Notice that in the contracted sarcomere, cross-bridges have attached to the thin microfilaments.
  42. 42. Microfilaments cont… When the sarcomere is fully shortened, the thin microfilaments overlap somewhat in the centre, and the Z-lines are drawn in until they almost touch the ends of the thick microfilaments. If enough sarcomeres shorten, the entire muscle shortens. The movement of the cross-bridges is often compared to the action of a ratchet. Each cross-bridge apparently reaches out and attaches to a thin microfilament at an angle of 90 degrees, then moves (in the power stroke) to an angle of 45 degrees, forcing the thin microfilament to move a short distance; then it detaches to return (in the recovery stroke) to the 90 degree position for a new attachment. With numerous cross-bridges going through the same process, the microfilaments are made to slide past one another, and the sarcomere shortens. Microfilaments are found in most cells, but in much less organized patterns than in muscle cells. In some cases they seem merely to provide a support to hold the cell in a particular shape and have come to be regarded as a sort of cytoskeleton (‘cell skeleton’). In other cases they seem to be involved in the movement of the cell or of parts within the cell and are referred to as cytomusculature (‘cell muscle system’). They are composed mostly of actin, but myosin is often present, particularly where movement is involved. Microtubules are generally more rigid than microfilaments and appear to have a larger role in determining cell shape, but they are also responsible for certain kinds of movement within the cell.
  43. 43. Microscopic Structure of a Skeletal Muscle.
  44. 44. Reflex Arc • Involuntary or automatic responses are called reflex responses • These responses involve both sensory and motor neurons. • A reflex arc is a pathway that the nerve impulses take by bypassing the brain to produce a quick response, often as the means of protection. Components of the reflex arc are: • The receptor – site of the stimulus action • Sensory neuron – transmits the afferent impulses to the CNS. • Integration centre – joins the sensory neuron to the motor neuron, where the CNS processes the incoming information and decides what to do. • Motor neuron – conducts impulses from the integration centre to the effector organ. • The effector – the muscle fibre or gland that responds to the impulse.
  45. 45. Examples of Reflexes. 1. Knee Jerk Reflex – Impulses travel to L2 – L4 in the spinal cord. – Stretch on the tendon causes impulses to travel vial afferent fibres in the muscles to motor neurons in the spinal cord causing stretched muscles to contract – Inhibitory synapses make the antagonist muscles (hamstring) relax and allow the reflex to occur.
  46. 46. Examples of Reflexes. 2. Plantar Reflex – Downward flexion (curling) of the toes. This is normal. – Babinski’s sign – toes dorsi flex (small toes fan laterally). – Babies until approximately 12 months old exhibit this due to nervous system incompletely myelinated. – This response checks the integrity of the spinal cord from L4 – S2
  47. 47. Examples of Reflexes. 3. Abdominal Reflex – Stroking the skin of the lateral abdomen above the umbilicus can cause contraction of abdominal muscles – This response checks the integrity of T8 – T12 4. Crossed Extensor Reflex – Reflex withdrawal of the body part on the stimulated side and extension on the other side. For example if someone suddenly grabs your arm, you extend the other arm to protect yourself or fend off.
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