BIOL 319 Lab Practical 2

what prefixes refer to muscle?

myo, mys, sarco

excitability

ability to respond to stimuli, all muscle cells are this

contractibility

ability to shorten, all muscle cells

extensibility

all muscle cells can be stretched

elasticity

all muscle cells, can go back to their normal size after being stretched

what is in skeletal muscle with the muscle fibers

nerves, blood vessels, and connective tissues

epimysium, perimysium, endomysium

3 connective layers that make up muscle, the epimysium is around the muscle, the perimysium is around the muscle fascicle, and the endomysium is around the muscle cell/fiber

is skeletal muscle autorhythmic?

no

tendons

attach muscle to bone

what determines the insertion of a muscle?

the insertion is the muscle is the bone or structure that is being moved by the muscle

what determines the origin of a muscle?

the origin of the muscle is the structure or bone that mostly doesn't move

thick filament anatomy

-made of myosin

-runs the length of the A band

-golf club shaped, stacked on top of each other in alternating directions, each is two golf clubs that form a double helix and the two heads join together

-connected by the M-line

-each thick filament contains over 300 myosin molecules

thin filament anatomy

-made of actin

-connect at the Z-line

-have a helix of two actin chains

-also have tropomyosin and troponin

-the troponin has 3 globular polypeptides

-one binds actin, one binds tropomyosin, and the other binds calcium ions

what is z-line made of mostly

alpha-actinin

cross section anatomy

3 thick filaments surround each thin filament, and six thin filaments surround each thick filament

T tubules

Also called transverse tubules, these are deep invaginations of the plasma membrane found in skeletal and cardiac muscle cells. These invaginations allow depolarization of the membrane to quickly penetrate to the interior of the cell.

-when a muscle contracts the nerve travels down the T tubule to penetrate deep in the muscle

sliding filament model

when sarcomeres shorten, thick and thin filaments slide past one another

- H zones and I bands narrow

- Z lines move closer together

A-band

where thin and thick filaments overlap in a relaxed muscle

-dark band on sarcomere

-these never change size in muscle contractions, they become closer together

muscle contraction steps

a motor nerve will stimulate a electrical action potential that will go to the sarcolemma. this will briefly allow calcium to be released in the cell, resulting in excitation-contraction coupling. somatic (voluntary) motor neurons activate skeletal muscles.

where are somatic (voluntary) motor neurons?

in the brain and spinal cords. the axons are bundled together and form a nerve that then runs to the muscle they innervate.

what happens to a nerve once it enters the muslce?

the axon enters the muscle, it divides into several axon branches which serve muscle fibers (cells)

How many neuromuscular junctions (motor end plate) does each muscle fiber have?

only one, it is used to communicate with the muscle

space between end of axon and the axon and the muscle fiber

the end of the axon is the synaptic cleft, and the space between that and the muscle fiber is called the synaptic cleft and it is filled with extracellular fluid with collagen fibers and glycoproteins. there are "mounds" called the axon terminals have ACh (acetylcholine). there are folds to increase surface space for more ACh receptors.

muscle contraction explained

motor neurons release action potentials to the muscle fibers. when the action potential go through the cell it causes calcium/sodium? to temporarily be released. this then causes ACh to be released and the chemicals diffuse across the membrane and out of the NaK channels. it is then depolarized and stoped by acetylcholinervse at the neuromuscular junction (NMJ)

Myasthenia gravis

immune system attacks the ACh receptors causing the muscles to not be able to contract. symptoms are difficulty swallowing, drooping eyelids, and generalized muscle weakness

initiation and propagation of a muscle action potential

1. acetylcholine binds to its receptors opening the chemical ligand-gated ion channels for sodium and potassium. sodium enters the cell due to diffusion and having a higher concentration outside of the cell. this makes the inner surface of the sarcolemma less negative, aka depolarized. this is called the end plate potential

2. voltage-gated sodium channels on the surrounding sarcolemma respond to the charge change and open to allow positive charged sodium to enter. once threshold is met, then it can spread and open more channels called a muscle action potential

3. once the voltage becomes sufficiently less negative , the voltage-gated sodium channels close and the voltage-gated potassium channels open. potassium exits the cell and it is polar again. these channels close once it is negative enough

what happens when a muscle contraction starts before the other is finished?

the second contraction will be stronger and/or more sustained due to intracellular calcium still being present in the cell from the first contraction

what is a motor unit?

a motor unit is the motor neuron with all the individual muscle fibers it innervates

-they vary in size, a small motor unit only has a few muscle fibers, where a large motor unit has thousands of muscle fibers

-each only contains one motor neuron regardless of size

-not in bundles in the muscle fiber, are spread out to have control of whole muscle and not just little parts of it

-small motor units may only go in a few fibers, while large motor units go to more fibers

small motor unit

for fine motor control (hand, fingers, eye)

large motor unit

occur in weight-bearing muscles, limb muscles

isometric contraction

muscles contract but joints do not move and muscle fibers maintain a constant length

-muscle tension increases but muscle length remains constant

-performed against a immovable constant

-help maintain posture and stabilize joints

isotonic contraction

body part is moved and the muscle fibers shorten and lengthen. muscle tension remains constant and muscle length changes

-concentric= muscle length decreases, bicep curl

-eccentric= muscle length increases, calf mucles when walking

isometric twitch graph

latent period, period of contraction, period of relaxation

hoe many motor axons control a whole muscle?

up to hundreds, use recruitment (adjusting the number of motor axons firing to control the number of twitching muscle fibers

when does a threshold stimulus occur?

when the stimulus is just strong enough to generate an observable contraction

the strenth of the stimulus...

affects the strength of the muscle contraction

-low threshold, easily excitable motor neurons control small motor units

-high threshold, least excitable motor neurons control large motor units

summation

when stimulation levels between 200 and 75ms are still active when another contraction starts. the next contraction will be stronger than normal

tetanic contraction

continuous, forceful muscular contraction without relaxation

complete tetanic contraction

when the resulting forceful, sustained contraction lacks even partial relaxation

antagonistically

two or more muscles where contraction of one muscle stretches/elongates the other

Electromyography (EMG)

recording the strength of muscle contraction as a result of electrical stimulation

-provides depiction of the timing and pattern of muscle activity during complex movements

co-activation of muscles

when a contraction of one muscle leads to some minor contractile activity in the antagonist muscle

-helps stabilize joints and generate smooth contractions and relaxations against the load on the muscle

learned reflexes result from

repetition

an inborn reflex is

a rapid, predictable, involuntary, and unlearned reflex as a result of a stimulus

visceral reflex

regulated my more primitive regions of the central nervous system, pupil

myotatic reflex

A fundamental spinal reflex that is generated by the motor response to afferent sensory information arising from muscle spindles. The knee jerk reaction is a common example. Also called a "stretch" or "deep tendon" reflex.

5 parts of reflex arc

1. receptor- senses the stimulus, initiates signal

2. sensory neuron- carries afferent nerve impulses to the CNS

3. integration center- where signal is processed, mostly in the CNS

-one single synapse between a motor and sensory neuron is this in simple monosynaptic

-polysynaptic reflexes have a few synapses and interneurons

4. motor neuron- carries efferent signals to effector from integration center

5. effector- muscle or gland where the response to the signal is generated

somatic reflex

contraction of skeletal muscles

autonomic reflex

regulate the activity of smooth muscles, the heart, and glands

what do the muscle spindles do in skeletal muscle?

convey information about muscle length or the amount of stretch

what do the golgi tendon organs do?

the golgi tendon organs convey information about tendon tension to inform the central nervous system for the regulation of these reflexes

-proprioceptive feedback

muscle spindles

made up of 3-10 modified skeletal small muscle fibers called intrafusal muscle fibers

what makes a fiber contractable?

presence of myofilaments

anulospiral endings

endings of large axons that wrap around the spindle center, stimulated by both rate and degree of stretch

flower spray endings

smaller axons, supply the ends of the muscle spindles and are the only stimulated in response to amount of stretch

gamma efferent fibers

-from small motor neurons of the spinal cord ventral horn, stimulates the contraction of intrafusal fibers when rest of muscle contracts.

what maintains tension in the intrafusal fibers and why?

the gamma efferent fibers, makes sure they do not slack as the muscle contracts to not loose sensitivity.

Alpha efferent fibers

Stimulate the extrafusal muscle fibers to contract

alpha-gamma coactivation

When the muscle is stimulated to contract by the alpha motor neuron, the gamma motor neuron is simultaneously stimulated

why does the brain stimulate gamma neurons?

to cause the spindle to stretch and become more sensitive or to make them loose and insensitive. increases sensitivity during difficult or fast movements

Ipsilateral

involve motor activity on the same side of the body

all stretch reflexes are

ipsilateral and monosynaptic

-on one side of the body and one synapse

-includes the myostatic reflex (knee cap hit)

the total stretch reflex arc is

polysynaptic

a absent reflex could indicate

damage of peripheral nerves such as from neurosyphilis or chronic diabetes mellitus

what prevents tendons and muscles from tearing?

the stretch reflex stimulates a contraction when the muscle is stretched but the tendon reflex has the opposite response

reciprocal activation

contracting muscle relaxes, antagonist contracts

-relieves tension on the tendon

what causes a longer delay between stimulus reception in more complicated reflexes?

they have interneurons and more than one population of motor neurons

-pupillary reflex is an example

consensual light reflex

shining a light into one eye causes the pupil of the other eye to contract

Miosis

constricted pupils

mydriasis

dilation of the pupil

flexion reflex

A polysynaptic spinal reflex that produces withdrawal of a limb from a painful stimulus

-ipsilateral

nociceptive pain

pain from a normal process that results in noxious stimuli being perceived as painful

frontalis action

elevates eyebrows, creases skin of forehead, move scalp forward

frontalis origin

epicranial aponeurosis

Frontalis Insertion

skin of eyebrows and forehead

occipitalis action

moves scalp backwards (as part of epicranius muscle-elevation of eyebrows, creases forehead)

occipitalis origin

occipital bone (superior nuchal line)

occipitalis insertion

epicranial aponeurosis

temporalis action

elevation and retraction of mandible

temporalis origin

temporal fossa

temporalis insertion

coronoid process and ramus of mandible

masseter action

elevation and protraction of mandible

masseter origin

zygomatic arch

masseter insertion

mandible (external surface of angle and ramus)

medial pterygoid action

elevation, protrusion and side-to-side movement of mandible

medial pterygoid origin

sphenoid bone (pterygoid process)

medial pterygoid insertion

mandible (medial surface of angle and ramus)

lateral pterygoid action

protraction and side-to-side movement of mandible

lateral pterygoid origin

sphenoid bone (greater wing and lateral pterygoid process)

lateral pterygoid insertion

mandible (neck); articular disk of temporomandibular (TM) joint

zygomaticus action

elevation of corner of mouth and upper lip

zygomaticus origin

zygomatic bone

zygomaticus insertion

muscle at angle of mouth and orbicularis oris muscle

buccinator action

compresses cheek

buccinator origin

pterygoidmandibular raphe, maxilla (lateral), mandible (lateral body)

buccinator insertion

muscles at angle of mouth

platysma action

elevates and creases skin of neck; depression of lower lip and angle of mouth

platysma origin

fascia of upper thorax and lower neck

platysma insertion

mandible (lower border); skin and fascia of lower face; muscles of lower lip and angle of mouth

orbicularis oculi action

closes eyelids