INTEGRATIVE PHYSIOLOGY EXAM 2 : MUSCLE AND MOVEMENT

Skeletal Muscle

Voluntary, striated, attached to the bone → Attached to the bone, contains sacromeres, T-tubules. Main Calcium source is sacroreticulum. fastcontraction with Troponin +Tropomyosin

Cardiac Muscle

Striated, involuntary, heart muscle with sacromeres and T-tubules which Main Calcium source is sacroreticulum/extracellular fluid. Moderate contraction with Troponin +Tropomyosin, moderate fatigue, limited regeneration

Smooth Muscle

Not striated, involuntary, hollow organs with no sacromeres with Calcium source being sacroreticulum and extracellular fluid. Typically has slow contraction with Calcmodulin + MLCK being regulatory proteins so less fatigue, and considerable regeneration

myosin/actin → filaments → Sacromere → Myofibril → Muscle Fiber → Muscle Fascicle → Whole skeletal muscle

How is the skeletal muscle organized?

Muscle

Made up of many muscle cells/gibers

Muscle Cell

Packed full of long fiber-like contractile organelles known as myofibrils

Myofibrils

Made up of contractile proteins known as myosin and actin and act as long fiber-like contractile organelles

Sacromere

A muscle unit in overlapping stripes with myosin and actin that forms light and dark striations

T-tubules

carry action potentials into the interior of the muscle fiber

Myosin

Thick filaments within a myofibril

Actin

Thin filaments within a myofibril

Z-line

Boundary of sarcomere where actin attaches to adjoining sacromeres

A-band

Stretches end to end of myosin which contains both actin and myosin filaments

I-band

Space between myosin and contains only actin

H-band

Non=overlapped regions of myosin only with no actin

M-line

Center of sacromere holding adjacent myosin together with supporting proteins

The myosin ATPase site

What can activate the myosin head?

Titin

provides elasticity and stabilizes myosin.

Nebulin

helps align actin.

Thin Filaments

When multiple actin molecules form together, they will form a double helix known as this.

Tropomyosin

Binds to actin to block the myosin binding sites on actin

Troponin

Binds to tropomyosin and can move it out of the way

1) Action potential

2) Calcium Release

3) Troponin activated where Calcium binds

4) Release of Tropomyosin for Troponin to pull off

5) Cross bridge between myosin and actin forms

6) Power Stroke when myosin heads pull actin inwards

7) reset

What are the quick muscle contraction steps?

Through a motor neuron that contacts the muscle at the neuromuscular junction acetylcholine is released which binds to a ligand ion receptor to depolarize the muscle membrane

How is an action potential released from the muscle cell membrane?

Sarcoplasmic Reticulum stores and releases Calcium into the cytosol of the muscle cell once an action potential occurs (depolarization will spread down T-tubes)

How is calcium released in the muscle cell?

Due to the release of Calcium, Troponin releases from Tropomyosin, making actin active

How does Tropomyosin get off of the muscle cell membrane

Cross-Bridge

When myosin binds to actin

Power stroke

A methoid requiring ATP to move actin inwards towards the M-line

Sarcoplasmic Reticulum

Where is calcium sent to after power stroke?

DHP receptor

Opens RyR Ca2+ release channels in sarcoplasmic reticulum and Ca2+ enters cytoplasm.

twitch

a single contraction-relaxation cycle

Creatine kinase

helps rapidly regenerate ATP using phosphocreatine.

phosphocreatine

This provides a rapid source of ATP during intense muscle activity.

Fatigue

reversible condition in which a muscle is no longer able to generate or sustain the expected output.

Slow oxidative

Have a high resistance to fatigue due to having low creatine kinase

Fast oxidative-glycolytic

Have a low resistance to fatigue due to having intermediate creatine kinase

Fast glycolytic

Lowest resistance to fatigue (i.e., easily fatigued) high creatine kinase

Isotonic contractions

create force and move load → because elastic elements are already stretched, the entire muscle must shorten.

Concentric action

a shortening action

Eccentric action

a lengthening action

Isometric contractions

create force without moving a load → sarcomeres shorten while elastic elements stretch resulting in little change in overall length

elastic elements

stretch resulting in little change in overall length

IP3-receptor channel

is the primary calcium channel in smooth muscle

calmodulin (CaM)

In smooth muscle, Calcium binds to this where it activated myosin light chain kinase (MLCK).

myosin light chain kinase (MLCK)

phosphorylates light chains in myosin heads and increases myosin ATPase activity

Myosin phosphatase

removes phosphate from myosin, which decreases myosin ATPase activity

myogenic contraction

Smooth muscle cells contain stretch-activated calcium channels → Open when pressure or other force distorts cell membrane

Proprioceptors

Located in skeletal muscle, joint capsules, and ligaments → carry input sensory neurons to CNS

monosynaptic reflex

has a single synapse between the afferent and efferent neurons.

Polysynaptic reflexes

have two or more synapses.

Autonomic Reflexes

Some visceral reflexes are spinal reflexes

Stretch reflex

Propriopretors that is in the position of muscle spindle → will cause a contraction of the skeletal muscle in response to the stretching of a muscle, which occurs monosynaptically

Tendon reflex

Propriopretors that is in the position of Golgi tendon organ → operates as a feedback mechanism to control muscle tension by cuasing muscle relaxation before muscle force becomes so great that tendons must be torn

Joint receptors

Are found in capsules and ligaments around joints

Muscle Spindles

monitor muscle length and prevent overstretching

Alpha-Gamma Coactivation

Stretch on centers of intrafusal fibers unchanged. Firing rate of afferent neuron remains constant. (without it, there would be: Less stretch on center of intrafusal fibers)

Alpha

actual muscle contraction in skeletal muscle fibers

Gamma

keeps the spindle "tuned" during contraction

Crossed Extensor Reflex

a polysynaptic reflex that helps maintain balance when you withdraw from a painful stimulus.

Somatic Reflex

Seen in skeletal muscles, and could be voluntary but not too often (withdrawal reflex)

Autonomic Reflex

Smooth muscles and glands that is under the control of autonomic nervous system but not voluntary

Somatic is seen as voluntary and only using two neurons with post and preganglionic neurons

Compared to autonomic and somatic motor rflexes, what can make both of them unique?

CNS

What type of integrating center can autonomic reflexes use?

1) Alpha motor neuron fires and gamma motor neuron fires

2) muscle begins to contract

3) Stretch on centers of intrafusal fibers unchanged where firing rate of afferent neuron remains constant

Steps of Alpha Gamma Coactivation

There is less stretch on the center

What would happen if gamma neurons weren’t in the alpha-gamma coactivation?

golgi tendon organ

Sensory reflexes of tendon reflexes which lies near its junction with a muscle (response to muscle tension is to relax)

1) Stretching of muscle stimulates snesory receptors in the muscle known as muscle spindles

2) muscle spindle can generate a receptor potential, which could become an action potential when threshold is reached

3) sensory neurons can make an excitatory synapse to activate a motor neuron

4) when excitation is strong enough, one or more action potentails arise int eh motor neuron and propagate along its axon, which extends from the spinal cord to the ventral root

5) Acetylcholine released by action potentials triggers action potnetials int he stretched muscles ot cause contraction

stretch reflex steps

1) As tension is applied to a tendon, tendon organ is stimulated

2) action potentials arise and propagate into spinal cord along in a senosry neuron

3) within the spinal cord, sensory neuron activates inhibitory itnerneuront aht synapes with motor neuron

4) inhibitory neurotransmitter

Tendon reflex steps

Flexor (withdrawal) reflex

Causes flexion of a limb in order to withdraw from a painful stimulus

1) Stimulus is stepping on a tack to send a siganlt ot a sensory neuron

2) Sensory neuron generates action potentials to propagate into spinal cord

3) Wtihin the spinal cord, sensory neurons activates interneurons to extend to several spinal cord segments

4) interneurons activate motor neurons in several spinal cord segments which causes motor neurons to generate action potnetials to propagate towards axon terminals

5) AcH in motor neurons can cuase flexor muscles to contract, causing withdrawal

Withdrawal reflex steps

1) stepping on tack stimulates sensory receptor of a pain sensitive neuron int he right foot

2) Sensory neuron will generate action potentials which can propagate into spinal cord

3) sensory neuron activates several interneurons that synapse with motor neurons ont he self side of the spinal cord

4) interneurons excite motor neurons in several spinal cord segements that innervate extensor muscles to generate more action ptoentials

5) AcH caues extensor muscles of the unstimulated left limb to contract and extends at left foot

Cross Extensor Reflex Steps