Lab Seven (Cardiac and Smooth Muscle)

What are some structural similarities between cardiac myocytes and skeletal myocytes?

• possess sarcomeres (therefore myofibirls)

• T-Tubules

• an extensive sarcoplasmic reticulum

• mitochondria

• some glycogen

• myoglobin

The three difference between cardiac and skeletal muscle are?

• presence of gap junction (in cardiac)

• intercalated disk (in cardiac)

• the absence of neuromusclular junction for every cardiac muscle cell

What are Pacemaker cells?

help set both rate of heart contraction and are also controlled by the nervous system to change that rate

What are the two types of cell that make up the cardiac muscle?

• contractile cardiomyocytes (greater than 99% of cardiac muscle is made of contractile cardiomyocytes)

• Pacemaker cells

What are Gap Junction?

are protein pores (similar to ion channels but generally larger) between cardiac cell to pass electrical and chemical signal between them

• as a result cardiac myocytes contract more as a single unit

During each cardiac contraction EVERY cardiac myocyte contractions, while during skeletal muscle contraction, neuron only signal for?

enough skeletal muscle fibers to get the job done

Cardiac pacemaker cells regular?

depolarize which leads to contraction of the contractile cardiomyocytes without the need for motor neuron to tell them to contract

The nervous system only regulates cardiac contraction by sending signal to either?

• slow down (parasympathetic)

• speed up and contract more forcefully (sympathetic)

The rate of cardiac contraction is controlled by?

innervation of the pacemakers cells

Similar to skeletal muscle depoalrization of contractile cardiomyocytes lead to a rise in?

cytosolic Ca2+, removing tropomyosin from actin and promoting the cross-bridge cycle between myosin and actin

One important difference between cardiac and skeletal muscle is?

that a significant amount of Ca2+ crosses the plasma membrane in cardiac muscle

Small amount of Ca2+ influx in cardiac myocytes leads to?

opening of Ca2+ channels on the sarcoplasmic reticulum, thus increasing cardiac cytosolic Ca2+ even further and promoting muscle contractions

• contractile cardiomyocytes

The rise in cytosolic Ca2+ occurs from the sarcoplasmic reticulum in skeletal muscle but from?

outside of the cell and the sarcoplasmic reticulum in cardiac muscle cells

Contractile cardiomyoctes possess a voltage-gated Ca2+ channel in their plasma membrane and T-tubules do they open slowly or quickly?

open slowly and even slower to close, leaving the contractile cardiomyocytes depolarized for a couple of hundred milliseconds

The longer time that a cardiac muscle membrane remains depolarized?

the longer it remains in it absolute refractory period and cannot depolarize again

Depolarization of both skeletal and contractile cardiomyocytes is due to?

Na+ influx through Na+ voltaged-gated channels

When Na+ channels close in skeletal muscle this helps with repolarization phase, but in contractile cardiomyocytes?

Voltage-gated Ca2+ channels are open and keep the membrane depolarized much longer

Repolarization in Contractile cardiomyocytes is due to the opening of?

K+ voltaged-gated channels and closing of Ca channels and inactivation of Na+ channels

What do Pacemaker help set?

the rate of depolarization and contraction of all the contractile cardiomyocytes

Slow depolarization of pacemaker cells involve?

slow opening of Na+ channels and slow closing K+ channels

Once a cell in a pacemaker cell reachs the membrane potential threshold then?

voltage gated Ca2+ channels open and stimulate a rapid depolarization

How does pacemakers repolarize?

are dependent on closing of Ca2+ channels and opening of K+ channels

As the membrane potential starts moving back toward K+ equilibrium potental what happens?

Na+ channels being to open again

Does the membrane potential in a pacemaker truely ever at rest?

no, the cardiomyocytes continue to depolarize and contract and the heart beat goes on

What do smooth muscle not have that cardio and skeletal have?

does not have sacromeres

What does smooth muscle have that cardio and skeletal have?

actin and myosin, but not as highly aligned like skeletal and cardiac

How does the contraction in smooth muscle compare to the ones in skeletal and cardiac?

significantly slower and longer and the force of contraction is generally weaker

What are the two forms of smooth muscle?

• mutli-unit smooth muscle

• unitary or single unit smooth muscle

What is Multi-unit smooth muscle?

makes use of neuronal innervation to promote contraction

• ex. the muscle that promotes the raising of single hairs on your skin (aka goose bumps)

What is Unitary or Single unit smooth muscle?

• acts more like cardiac muscle

• processes gap junction and pacemaker or authorhymic cells to promote peristaltic waves in the digestive tract

Smooth muscle is under what control?

of the parasympatheic and sympatheic system and also endocrine secretions

What are the roles of parasympathetic on cardiac myocyte and smooth muscle of the GI tract?

o   Increase: promote digestion

o   Decrease: turn down bodily functions not essential for rest and digest

• Neurotransmitters: Acetylcholine

What are the roles of Sympathetic on cardiac myocyte and smooth muscle of the GI tract?

o   Increase: heart rate, blood glucose, ventilation rate, and blood pressure to get glucose and O2 to the brain, hear, and skeletal muscle to help you overcome the stress that generated the “flight or fight” response

o   Decrease: digestion, urination, and defecation

• Neurotransmitters: norepinephrine and epinephrine (from adrenal medulla)

What are the receptors used by the cardiac and smooth muscle cells?

• Ionotropic

• Metabotropic

  • Muscarinic

  • Adrenergic

What is Cholinergic?

on skeletal, cardiac, and smooth muscle receive the acetylcholine neurotransmitter

What is Adrenergic?

• for epinephrine and norepinephrine

  • Are also metabotropic

  • Used on Cardiac, Smooth, and Skeletal Muscle

What is Nicotinic?

found on skeletal muscle and in the central nervous system and are ion channels that directly bind to acetylcholine

o   Is a type of cholinergic receptors

What is Muscarinic?

• a G-protein coupled receptor that can indirectly open or close other ion channels

  • Cholinergic receptor on cardiac and smooth muscle

What is Ionotropic?

• found on skeletal, cardiac, and smooth muscle and in the central nervous system and are ion channels that directly bind to acetylcholine

  • Is a type of cholinergic receptors

What is Metabotropic?

• a G-protein coupled receptor that can indirectly open or close other ion channels

  • Cholinergic receptor on cardiac and smooth muscle

How do cholinergic blocker affect heart rate and smooth muscle contraction?

turn down the rest and digest response

How do adrenergic blockers affect heart rate and smooth muscle contraction?

blocking sympathetic stimulation turns down the fight or flight response

What branch of the autonomic nervous is also stimulated by hormone release?

Sympathetic Nervous System

How do hormones from the adrenal medulla affect heart rate and smooth muscle contraction of the GI tract?

It will increase heart rate and blood pressure, while doing that it will decrease smooth muscle contraction in the GI tract

Be able to describe how a cholinesterase inhibitor would affect the acetylcholine levels in a synapse

acetylcholine builds up in the synapse between cells

How will cholinesterase inhibitor effect contractions of skeletal, cardiac, and smooth muscle of the stomach?

o   Skeletal Muscle – fasciculations (twitching leading to muscle weakness

o   Cardiac Muscle – decrease contraction and heat rate

o   Smooth Muscle – cramping, nausea, vomiting, and diarrhea