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- Generate forces to move bones or prevent movement.
- Produce heat for thermoregulation.
- Generate electricity - amplified in electric eels.
- Modified muscles.
- Current stuns prey or defends against attack.
- Forms field around animal for detection of nearby objects.
Many animals have electric organs
- Electric eel (Electrophorus), Electric catfish (Malapterus), Torpedo ray (Torpedo), Elephant nose, Gymnarchus, Skate (Raja), Stargazer (Uranoscopus).
- Evolved independently several times.
- Fiber color (red, white, pink)
- Somatic muscles move body segments/regions.
- Visceral muscles control organs, ducts and glands.
- Voluntary muscles=conscious control.
- Involuntary muscles=autonomic control.
- Muscle fiber types:skeletal, cardiac and smooth
move body segments/regions
control organs, ducts and glands.
Muscle fiber types
skeletal, cardiac=functional syncitium and smooth muscle fibers lack striations of striated muscle
Muscle structure determines what
Cross sectional area
maximum force a muscle can generate
Muscle belly and tendon locations
=proportional to x-sectional area of all sarcomeres of a muscle
Morphological cross section of a muscle
is perpendicular to long axis of muscle at thickest part
cross sectional area of all muscle fibers
is perpendicular to long axis=physiological cross-section.
Fiber orientation determines
amount of tension that can be generated by a muscle.
Parallel fibered muscles
all fibers lie along the line of tension generation.
Pinnate fibered muscle fibers
oblique to lines of a force and insert on a common tendon.
a motor neuron and all of the muscle fibers it innervates.
- Additional muscle fiber recruitment increases force amount generated.
- Also applies to recruitment of additional muscles to increase effectiveness of a particular movement.
- Muscle fibers or entire muscles causing a contraction can increase force of contraction in controlled manner.
- In contrast - motor unit response=all or none.
Velocity of muscle
- Shortening=greater for long muscle than short.
- Distance of shortening - sarcomere shortening in long muscle=additive; therefore can be longer than in short muscle.
- Longer muscles - move their attachments a greater distance than short muscles.
- Muscles cannot generate maximum tension at all lengthts
- Optimum=intermediate lengths but muscles can contract further or stretch more.
- Why different length muscles involved in completing movement from full extension to full flexion.
- Muscle force total output arises from active contraction of sliding filaments as well as the elastic component.
Synergistic effects of different length muscles required to produce peak tension
allow muscle force contraction maximization along entire range of movement.
- strength versus speed
- Attachments emphasize one or other- cannot maximize both.
strong movment, low speed.
fast movment, high gear
Two phases of muscle action
- Stance phase and swing phase
- Different muscles are active at different parts of stride
when rear or foot strikes ground until it is lifted again.
From time toe is lifted until heel strikes.
coordinates the pattern of movement and muscle activity=motor control program.
Muscle fiber types and numbers selected depends on
- the movement and types appropriate for the different levels of activity.
- synergists, agonists or antagonists, prime action, muscle origin.
Muscles with complementary actions.
- also antagonists
- Muscles which oppose each other.
Most important action of a muscle.
a relatively fixed point.
part that moves most
each site of origin of a muscle
muscles that stabilize joints
bend one part relative to other parts
straighten a body part
draw part toward midline
draw a part away from the midline
elevate the mandible
move the body part away from the opposite by opening a joint.
result in projection of a part.
bring a part backward.
turn a palm upward.
turn a part downward.
Constrictors or sphincters
Muscle homologies determined by
- shared origins/insertions and also shared innervations.
- Difficult to determine from fossils using only bone scars.
- Similar function may assist in homology determination.
Muscles in Embryology
- Muscles arise from mesenchyme, hypomere and paraxial mesenchyme.
- Appendicular musculature grows outward as myotomes grown downward in fishes.
- Axial muscles originate from myotomes which become the somites.
- Tetrapods have dorsal muscles (epaxial) divided by a septum from fentral muscles (hypaxial).
- During development, the myotomes expand into different areas of body.
- Differentation of muscle groups occurs according to locations.
Jaw muscles arise from two sources
- Hypobranchial muscles
- Branchiomeric muscles.
from myotomes of somites, spinal nerve innervation.
from head somitomeres and cranial nerve innervations.
Extrinsic eye muscles
- Six total
- Originate from walls of orbit and insert on outer surface of eyeball.
- Arise form preotic myotomes.
- Innervated by cranial nerves I, II, and III.
- Differ from intrinsic ocular muscles that control structures within the eyes.
- Conservative across all vertebrate groups plus.
Myomere structure and orientation in Amphioxus and teleost fishes
- Horizontal septum that divides muscles into epaxial and hypaxial is absent from cyclostomes.
- Each myomere supplied by a spinal nerve which bifurcates into dorsal and ventral rami to epaxial and hypaxial muscles.
- Axial musculature is main generator of propulsive force in fishes.
- In tetrapods appendicular musculature takes over generation of most propulsive forces.
- Axial musculature of tetrapods is reduced and appendicular muscles increased in relative mass over fishes.
- On land, muscles needed to support body off ground because water buoyancy is no longer present.
- Waves of undulation pass posteriorly along fish body, throwing it into curves that press against water to provide propulsive thrust.
Fish vs tetrapods
- Fish have relativley undifferentiate epaxial and hypaxial muscle masses.
- Tetrapods show greater division and specialization.
- Salamanders have a single dorsal muscle mass, dorsalis trunci, but hypaxial muscles are separated into discrete groups.
- Lizards show greater specialization (body wall muscles)
- In reptiles the horizontal septum is reduced, although dorsal and ventral nerve rami are easily distinguished.
- Epaxial musculature reduced when later body undulation is reduced as limbs take over locomotor functions.
Reptiles show first epaxial musculature differentiation
Muscles of Sphenodon
- Living primitive reptile, shown superficial to deep.
- These muscles attach to vertebral processes.
- Hypaxial muscles attach to ribcage and assist in breathing and moving the trunk (of great importance in snakes)
Hypaxial muscles arise form four embryonic groups
- Dorsomedial muscles that become longus colli that moves the neck.
- Medial musculature that includes the transversus abdominus and internal oblique.
- Lateral musculature that is outside the ribcage consisting of external obliques and external intercostals.
- Medial and lateral muscles contribute to rectus abdominus.
External and internal intercostal muscles have opposite functions in respiration
- because the originate form different embryonic muscle masses.
- External intercostals function to assist diaphragm in inspiration.
- Internal intercostals are most active during expiration and innermost intercostals act with them.
- Oblique muscles are a continuous sheet only becuase ribs are absent in the abdomens of mammals.
Appendicular muscles in fishes arise from myotomes that grow out into fins in dorsal and ventral masses
- Dorsal muscles elevate fin (=levators)
- Ventral muscles depress fin (=depressors)
- Appendicular muscles in tetrapods more prominent and relatively larger.
- Receive contributions from axial muscles and branchiomeeric (=gill arch muscles)
- Fore and hind limb differences occur because of different attachments of girdles and limb purpose (body support, propulsion, etc.)
Four muscle sources and muscles then divide and increase specificity of actions as well as complexity at limb
- 1. Branchiometric
- 2. Axial musculature
- 3. Dorsal muscles
- 4. Ventral muscles
- trapiezius and mastoid group.
- In mammals this group includes: clavotrapezius, acromiotrapezius and spinotrapezius.
- In mammals the mastoid group includes: cleidomatoid and sternomastoid
- gives rise to levatator scapulae, rhomboideus complex and serratus muscles.
- With the trapezius complex these muscles provide the muscular sling that suspends the body between the scapulae.
- Tetrapod forelimbs are suspended by a muscular sling, with little or no bony connnection to the axial skeleton.
- Turtles are the exception to the forelimb suspension plan because the shoulder girdle in them is attached to the shell.
- In pterosaurs, birds and bats the shoulder girdle rests on the sternum as an adaptation for shoulder stability during flight.
- In fishes the pectoral girdle is usually attached to the rear of the skull, but in tetrapods it is not.
- insert on the humerus and move it turing the stepping cycle.
- Latissimus dorsi - originates from body wall outside limb.
- Teres major - slip that separates and acquires own attachments on scapula.
- Other dorsal humeral muscles are: teres minor, subscapularis and deltoideus and the triceps group, although those are extensors of the forearm and not the arm.
- dorsal muscles of the forearm are most of the extensors and straighten the digits via tendons.
- Located along the ventral wall of the chest; include: Pectoralis and its derivatives, including pectoantebranchialis and deeper pectoralis major, pectoralis minor and xiphihumeralis.
- Supracoracoideus - coracoid to humerus in reptiles.
- In mammals, originates dorsally, from the lateral scapular face - divided into supra and infraspinatus muscles that insert on the humerus.
- The coracobrachialis arise from the coracoid that runs along the underside of the humerus.
- In mammals, the biceps branchii has two heads, and represents the fusion of two muscles with their insertions on the forearm. They are flexors in early tetrapods.
- Forearm flexors act on digits through tendons.
- lacks muscular sling of pectoral girdle - dircet attachment and therefore few extrinsic muscles control the position of the limb with respect to the body Psoas minor is extrinsic and the exception.
- Most pelvic limb musculature from dorsal or ventral groups.
- Dorsal - puboischiofermralis internus of tetrapods - lumbar region to pelvic girdle and femur - serves as limb rotator.
- In mammals becomes psoas major, iliacus and pectineus muscles.
- Iliofemoralis in tetrapods - ilium to femur and extends limb.
- In mammals becomes tensor fascia lata, pyriformis and gluteus complex.
- collective name for rectus femoris, and three heads of vastus; i.e., lateralis, medialis and intermedius.
- These surround anterior, medial and lateral aspects of femur, extend leg and insert on patella.
- two-joint muscle crosses hip and knee and inserts on tibia.
- The ambiens (reptiles) and iliotibialis (amphibians) probably=homologous to sartorius.
In mammals the gastrocnemius has two heads from fusion of two phylogenetic predecessors
- Castrocnemius (medial head) and flexor hallucis longus are derived from the reptilian gastrocnemius internus.
- Gastrocnemius (lateral head), soleus and plantaris arise form reptilian gastrocnemius externus.
Anuran locomotion is saltatorial
- Hindlimbs act simultaneously to propel animal initiating leap.
- Forelimbs and girdles absorb shock of landing.
- This locomotor specialization explains the relatively complex musculature of frogs when compared to salamanders.
Anatomical changes for cursorial locomotion in many forms, not only mammals.
- Limb muscle bellies moved proximally to reduce distal bulk and weight of limb.
- Limb movements controlled by distal tendons.
Bird appendicular muscles increase
- Axial muscles decrease.
- Synsacral fusion for stability allows lumbar region axial musculature reduction.
- Appendicular muscles increase in complexity with specializations for flight and landing.
- Cervical muscles and long vertebral chains allow great head control precision and neck flexibility.
- Long tendons to toes give precise toe positioning and control for landing and gripping supports.
- Tibialis anterior (and other lower leg muscles from dorsal group) dorsiflex ankle vial long tendons.
- The muscle is the tibialis cranialis in birds.
- both wing depressor and elevator are centrally located in birds for better weight and balance distribution.
- Patagialis muscle inside leading edge of skin of wing.
- Arises from clavicle and extends to wrist metacarpals.
- Maintains aerodynamic shape of leading edge of wing and can be modified to enhance flight capabilities.
- Similarly tensile patagium occurs in bat wings and probably in pterosaurs.
- Gliding squirrels have similarly structured patagial reinforcements as well.
Pectoral muslces specialized for flight
- Pectoralis large and muscle belly near midline to control position of center of mass.
- Supracoracoideus deep to pectoralis; also lifts wing in birds.
- Modified by tendon running through foreamen triosseum in shoulder - alters line of action.
- Supracoracoideus=limb adductor in reptiles.
- both branchiomeric and hypobranchial jaw muscles arose form paraxial mesoderm.
- Branchiomeric muscles from cranial paraxial mesoderm (somitomeres)
- Hypobranchial muslces from trunk paraxial mesoderm (somites)
- Cranial nerves supply the branchial arches.
- III, VII, IX, and X-XI supply branchial arches 1-3 and 4-7 respectively.
- Each arch has levator and constructor muscles that elevate and close articulated elements.
- Each arch has a constrictor that extends laterally within the gill and may extend laterally onto body under skin.
- The medial part specializes to become adductor.
- Constrictors squeeze water through pharynx and adductors bend gill arch.
- Dorsal and ventral branchial muscles attach to the arch ends and help shape the arch by altering the relationship of individual elements.
- In sharks both adductor and constrictor are near the surface and the jaw is closed by the enlarged adductor mandibulae.
- Preorbitals assists in sharks.
- Bony fishes adducor is composite from many smaller muscles and correlate with skull kinetic elements.
- Adductor mandibulae is strong jaw adductor.
- Mammal temporalis, masseter and pterygoids arise from this muscle.
Ventral parts of constrictor separated by jaws and is the intermandibularis.
- It gives rise to the mylohyoid and digastric.
- The dorsal derivative of the mandibular constrictor in sharks is the levator palatoquadrati.
- In primitive fishes and still chimaeras this arises as a gill arch.
- Then, becomes involved in reinforcing the jaw in other jawed fishes.
- Becomes a separate hyoid apparatus is tetrapods.
- Hyoidean constrictores important in fish where they form water-breathing pump but are reduced or lost in tetrapods.
- In sharks the largest hyoidean constrictor is the levator hyomandibulae.
- The second often fused to the first is the epihyoidean also inserting on the jaw.
- In bony fishes the epihyoidean becomes the levator operculi, inserting on the operculum.
- The depressor mandibular of tetrapods is homologous to levator operculi and epihyoidean.
- In mammals the depressor mandibulae becomes the stapedius, that protects the inner ear from too loud sounds.
Digastric opens jaw and arises form two areas
- Posterior digastric from interhyoideus, which was ventral part of hyoidean constrictor.
- Anterior part of digastric form mandibular arch, intermandibularis muscle.
- This muscle has also a composite innervation, from Cranial nerves V and VII that confirms this evolutionary pathway and homologies.
In tetrapods the interhyoideus becomes
- thin sheets that form the constrictor colli and become facial muscles in mammals.
- The platysma myoides is from the hyoid arch. It is thin and covers the throat superficially.
- Others have become very specialized for controlling the position and function of the special sensory features of the face, eyes, ears, nose and mouth.
Increasing complexity of facial muscles in mammals
to those in which facial expressions are most important in communication.
- In sharks the dorsal branchial arch muscles give rise to the cucullaris running from the dorsal body surface to the last branchial arch and scapula.
- In tetrapods it goes from the axial musculature to the scapula and forms trapezius and mastoid muscle groups.
- Other constrictor muscles contribute to the throat and larynx.
- Arise from cervical somites with ventral ends that migrated to the pharyngeal floor.
- Supplied by spinal nerves.
- Run anteroposteriorly.
- Arise from coracoid region of shoulder girdle in fishes.
- Coracomandibularis and sternohyoideus.
- In sharks the sternohyoideus is divided into anterior coracohyoideus and a posterior coracoarcualis.
- Jaw openers and buccal cavity expanders.
- In tetrapods they accompany branchial arches contributing muscles to the throat, hyoid apparatus, larynx and tongue.
- Other muscles that arise form cervical somites include cervical muscles (epaxial myotomes) that may insert on the neurocranium and lift it during jaw opening in sharks.
- Also, only in sharks cervical somites contribute to interpharyngobranchials which join the branchial arches in the pharynx.
Assorted end-of-chapter (I-don't-know-what-else-to-do-with-them) topics.
- Venom injection from modified salivary glands. Venom gland duct runs to base of fang. Compressor glandulae muscle compresses venom gland to eject venom into duct and to allow venom to enter hollow fang and from there into prey.
- Escape behavior "tail flip" in trout. Fish body form allows for specialization in swimming abilities. Sculpin-undulates against water to produce thrust. Maneuvering-butterfly fish. Pike-quick lunges. Tuna-sustained swimming.