1) The document discusses the muscular system, describing the different types of muscle tissue (skeletal, cardiac, smooth), muscle characteristics (excitability, contractibility, elasticity), and the major muscle groups of the body.
2) It also covers muscle architecture (fusiform, pennate, radiate), types of muscle contractions (isotonic, isometric, isokinetic), and the roles muscles can play in movement (agonist, antagonist, synergist, stabilizer).
3) Finally, the document lists many of the principal muscles of the body, describing their main attachment sites and actions in gross motor activities.
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. 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. 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. 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.
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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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.
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. 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. 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.
39. 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
40. 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.
41. 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.
42.
43. 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.
44. 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.
46. 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.
47.
48. 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.
49. 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
50. 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.