Muscles Lab Flashcards
occipitofrontalis (Epicranius m.)
overlies the dome of the cranium
occipitofrontalis is divided into
frontalis of the forehead
occipitalis at the rear of the head
orbicularis oculi
is a sphincter of the eyelid that encircles and closes the eye
Wink!
orbicularis oris
is a complex of muscles in the lips that encircle the mouth
Kiss
Muscles of Chewing
• Temporalis
• Masseter
Flexors of the Neck prime mover of neck flexion
sternocleidomastoid, a thick musc cord that extends from the upper chest (sternum and clavicle) to the mastoid process behind the ear
Muscles of the Head and Neck
Splenius capitus
Muscles of the Thoracic Region
3 layers of muscle lie between the ribs:
- External intercostal (superficial layer)
- Internal intercostal
- Innermost intercostal
Muscles of Anterior Abdominal Wall
• The external abdominal oblique (most superficial) fibers-downward and anteriorly
• The internal abdominal oblique (next deeper layer) fibers-upward and anteriorly
• The transverse abdominal (deepest layer) -horizontal fibers
Muscles of the Abdominal Wall 2
Anteriorly, a pair of vertical rectus abdominis muscles extend from sternum to pubis (six pack)
• Linea alba midline between the rectus muscles
• Inguinal ligament→is the aponeurosis of the external oblique
Muscles of the pectoral girdle Anterior Group:
• Pectoralis minor
arises by three heads from ribs 3 to 5 and converges on the coracoid process of the scapula
• Serratus anterior
arises from separate heads on all or nearly all of the ribs, wraps laterally around the chest, passes across the back between the rib cage and scapula, and inserts on the medial (vertebral) border of the scapula
Muscles acting on the scapula
Posterior Group
• The trapezius (superficial)
Deep muscles:
• levator scapulae
• rhomboideus minor
• rhomboideus major (the rhomboids)
Muscles acting on the arm-brachial region
Because they originate primarily on
the axial skeleton
• pectoralis major
• latissimusdorsi
Muscles Acting on the Arm-deltoid
• The deltoid, the thick triangular muscle that caps the shoulder.
• This is a commonly used site of drug injections
Muscles Acting on the Arm
The Rotator Cuff:
- Supraspinatus
- Subscapularis
- Infraspinatus
- Teres minor
The rotator cuff reinforces the joint capsule
and holds the head of the humerus in the glenoid cavity
Muscles Acting in the Forearm
Muscles with Bellies in the Arm (Brachium)
The principal elbow flexors
• the brachialis
• biceps brachii
• The triceps brachii is the prime mover of elbow extensor
Muscles Acting in the Forearm
Muscles with Bellies in the Forearm (Antebrachium):2
• The brachioradialis is in the lateral (radial) side of the forearm just distal to the elbow
Muscles acting in the hand
Most tendons of the extrinsic muscles of the forearm pass under a fibrous, bracelet-like sheet called the flexor retinaculum on the anterior side of the wrist or the extensor retinaculum on the posterior side.
• The carpal tunnel is a tight space between the flexor retinaculum and carpal bones
Muscles Acting on the Hip and Femur
Lateral and Posterior Muscles of the Hip are the tensor fasciae latae and three gluteal muscles
• The fascia lata is a fibrous sheath that encircles the thigh
• gluteusmaximus+tensorfasciaelatae=iliotibialband
The gluteal muscles are:
• gluteusmaximus • gluteusmedius
• gluteusminimus
Muscles Acting on the Hip and Femur
Fasciae divide the thigh into three compartments:
Anterior (extensor) compartment
Posterior (flexor) compartment
Medial (adductor) compartment
• Adductor Magnus
• Adductor Brevis
• Adductor Longus
• Gracilis
• Pectineus
Quadriceps femoris muscle, has four heads: (all converge on the patellar tendon)
- rectus femoris
- vastus lateralis
- vastus medialis
- vastus intermedius
Sartorius
longest muscle of the body
flexes the hip and knee joints and laterally rotates the thigh, as in crossing the legs
Muscles Acting on the Knee and Leg
Posterior (Flexor) Compartment of the Thigh
• Colloquially known as the hamstring muscles
1. Biceps femoris
2. Semitendinosus
3. Semimembranosus
Muscles Acting on the Foot
Posterior (Flexor) Compartment of the Leg
• Superficial group are plantar flexors:
• Gastrocnemius
• Soleus
These are collectively known as the triceps surae, insert on the calcaneus by way of the calcaneal (Achilles) tendon
What provides dorsiflexion of foot at ankle; inversion of foot?
Tibialis Anterior
What is flexion?
• movement that decreases a joint angle, usually in the sagittal plane
What is extension?
movement that straightens a joint and generally returns a body part to the zero position
What is abduction?
movement of a body part in the frontal plane away from the midline of the body
What is adduction?
movement in the frontal plane back toward the midline
What is elevation?
movement that raises a body part vertically in the frontal plane
What is depression?
lowers a body part in the same plane
What is protraction?
anterior movement of a body part in the transverse (horizontal) plane
What is retraction?
posterior movement
What is Circumduction
one end of an appendage remains fairly stationary while the other end makes a circular motion
What is supination?
of the forearm is a movement that turns the palm to face anteriorly or upward
What is pronation?
is the palm to face posteriorly or downward
Dorsiflexion and plantar flexion
What is rotation?
• Is a movement in which a bone spins on its longitudinal axis
– medial (internal) rotation
– lateral (external) rotation
3 Types of Muscle Tissue
Skeletal, cardiac, smooth
Functions of Skeletal Muscles
- Produce skeletal movement
- Maintain body position
- Support soft tissues
- Guard openings
- Maintain body temperature
- Store nutrient reserves
3 Characteristics of Skeletal Muscle
• Excitability: ability to respond to a stimulus by changing electrical membrane potential
• Contractility: exhibited when filaments slide past each other
▪ Enables muscle to cause movement
• Elasticity: ability to return to original length following a lengthening or shortening
Skeletal Muscle Defined
voluntary striated muscle that is usually attached to one or more bones
• Exhibits alternating light and dark transverse bands, or striations
• Voluntary→subject to conscious control
Myofiber→Skeletal muscle cell
Skeletal Muscle Structures muscle and connective tissue
• Epimysium: Surrounds the entire muscle and connect to tendons.
• Perimysium: surrounds bundles of muscle fibers separating them into fascicles
• Endomysium: surrounds each muscle fiber
The Muscle Fiber
Sarcolemma→is the plasma membrane of a muscle fiber
Sarcoplasm→is the cytoplasm
• Is occupied mainly by long protein cords called myofibrils • Contains glycogen, stored form of energy
• Contains a red pigment myoglobin, which stores oxygen until needed for muscular activity
The muscle fiber longitudinal section and cross section
The Muscle Fiber
The smooth endoplasmic reticulum, here called the sarcoplasmic reticulum (SR)
• The sarcolemma has tubular infoldings called transverse (T) tubules
• The smooth ER is a reservoir of calcium ions; which activates the muscle contraction process
Myofilaments
Each myofibril is a bundle of parallel protein called myofilaments 3 kinds
Thick filaments→made of myosin
Thin filaments→made of actin
– Each actin has an active site that can bind to myosin molecule
– It has a protein called tropomyosin which blocks the active sites of actins and prevents myosin from binding to them during muscle relaxation
• Each tropomyosin molecule, in turn, has a smaller calcium-binding protein called troponin bound to it
Elastic filaments→are made of titin
– Anchor thick filaments to Z disc at one end and M line at the other
Sarcomere
Striations
Striated muscle has dark A bands alternating with lighter I bands (think “dArk” and “LIght”)
A band = thick filaments
• In the middle of the A band, there is a lighter region called the H band into which the thin filaments do not reach
Sarcomere→the functional contractile unit of the muscle fiber, goes from one Z disc to the next
The Nerve–Muscle Relationship
• Skeletal muscle never contracts unless it is stimulated by a nerve (or artificially with electrodes)
• If its nerve connections are severed or poisoned, a muscle is paralyzed
• If the connection is not restored, the paralyzed muscle undergoes a shrinkage called denervation atrophy
Motor Neurons and Motor Units
• Skeletal muscles are served by nerve cells called somatic motor neurons, whose cell bodies are in the brainstem and spinal cord
• axons, called somatic motor fibers, lead to the skeletal muscles
• One nerve fiber and all the muscle fibers innervated by it are called a motor unit
The Neuromuscular Junction 1 of 2
The point where a nerve fiber meets its target cell is called a synapse
• When the target cell is a muscle fiber, the synapse is called a neuromuscular junction (NMJ), or motor end plate
The Neuromuscular Junction 2 of 2
The electrical signal (nerve impulse) traveling down a nerve fiber causes the synaptic vesicles to undergo exocytosis, releasing ACh into the cleft
• ACh thus functions as a chemical messenger from the nerve cell to the muscle cell
Excitation
• Action potential arrives at axon terminal at neuromuscular junction
• Ach released: binds to receptors on sarcolemma
• Ion permeability of sarcolemma changes
• Local change in mb voltage (depolarization) occurs
• Local depolarization (end plate potential) ignites action potential in sarcolemma
Excitation-Contraction Coupling
Sequence of events by which transmission of an action potential along the sarcolemma leads to the sliding of myofilaments
Excitation- Contraction Coupling 2
• Action potential travels across the entire sarcolemma
• Action potential travels along T tubules
• Sarcoplasmic Reticulum releases Ca2+ which binds to Troponin
• Troponin–tropomyosin complex changes shape→actin filaments bind to myosin heads→CONTRACTION BEGINS
Relaxation
When its work is done, a muscle fiber relaxes and returns to its resting length
• Nerve signals stop arriving at the neuromuscular junction, so the synaptic knob stops releasing ACh.
• As ACh dissociates (separates) from its receptor, AChE breaks it down into fragments that cannot stimulate the muscle
• In the SR, Ca2+ is been pumped from the cytosol back into the cisternae. Ca binds to a protein called calsequestrin and is stored until the fiber is stimulated again
• As calcium ions dissociate from troponin
• Tropomyosin moves back into the position where it blocks the active sites of the actin filament. Myosin can no longer bind to actin, and the muscle fiber ceases to produce or maintain tension
Sarcomere Shortening
Rigor Mortis
Is the hardening of the muscles and stiffening of the body that begins 3 to 4 hours after death
It occurs partly because the deteriorating sarcoplasmic reticulum releases calcium into the cytosol, and the deteriorating sarcolemma admits more calcium from the extracellular fluid
The calcium activates myosin–actin cross-bridging.
Once bound to actin, myosin cannot release it without first binding an ATP molecule, and of course no ATP is available in a dead body.
Thus, the thick and thin filaments remain rigidly cross- linked until the myofilaments begin to decay.
peaks about 12 hours after death and then diminishes over the next 48 to 60 hours.
Contraction of a Skeletal Muscle 2 types
• Isometric→develops tension but not movement
• Isotonic→develops tension and muscle shortening occurs
Tension
force exerted by a contracting muscle on an object
Load
the opposing exerted on the muscle by the weight of the object to be moved
Muscle Twitch
Muscle Twitch
Muscle Twitch→Is a motor unit’s response to a single action potential of its motor neuron
Graded muscle response
Increase the firing rate of neurons
• Temporal summation→muscles maintain prolonged contraction by adding numerous individual contractions back-to-back
• Incomplete tetanus→in which each stimulus causes a contraction to be initiated when the muscle has only partly relaxed from the previous contraction
• Complete tetanus→in which stimuli to a particular muscle are repeated so rapidly that decrease of tension between stimuli cannot be detected
