DOC PREVIEW
UT Arlington BIOL 2457 - Muscle Tissues

This preview shows page 1 out of 3 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 3 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 3 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

BIOL 2457 1st Edition Lecture 19Outline of Last Lecture The skeletal system: joints Outline of Current LectureMuscle tissues Contraction and Relaxation of Skeletal Muscle The Contraction Cycle The onset of contraction begins with the SR releasing calcium ions into the muscle cell The calcium ions bind to actin opening the myosin binding sites The contraction cycle consists of 4 steps ATP hydrolysis Reorients and energizes the myosin head Formation of cross-bridges Myosin head attaches to the myosin-binding site on actin Power stroke During the power stroke the crossbridge rotates, sliding the filaments Detachment of myosin from actin As the next ATP binds to the myosin head, the myosin head detaches from actin The contraction cycle repeats as long as ATP is available and the Ca2+ level is sufficiently high Continuing cycles apply the force that shortens the sarcomere Excitation–Contraction Coupling An increase in Ca2+ concentration in the muscle starts contraction A decrease in Ca2+ stops it Action potentials causes Ca2+ to be released from the SR into the muscle cell Ca2+ moves tropomyosin away from the myosin-binding sites on actin allowing cross-bridges to form The muscle cell membrane contains Ca2+ pumps to return Ca2+ back to the SR quickly Decreasing calcium ion levels As the Ca2+ level in the cell drops, myosin-binding sites are covered and the muscle relaxes Length–Tension Relationship The forcefulness of muscle contraction depends on the length of the sarcomeres When a muscle fiber is stretched there is less overlap between the thick and thin filaments and tension (forcefulness) is diminished When a muscle fiber is shortened the filaments are compressed and fewer myosin heads make contact with thin filaments and tension is diminished The Neuromuscular Junction Motor neurons have a threadlike axon that extends from the brain or spinal cord to a group of muscle fibers Action potentials arise at the interface of the motor neuron and muscle fiber Synapse Where communication occurs between a somatic motor neuron and a muscle fiber Synaptic cleft Gap that separates the two cells Neurotransmitter Chemical released by the initial cell communicating with the second cell Synaptic vesicles Sacs suspended within the synaptic end bulb containing molecules of the neurotransmitter acetylcholine (Ach)  Motor end plate The region of the muscle cell membrane opposite the synaptic end bulbs Contains acetylcholine receptors Nerve impulses elicit a muscle action potential in the following way (1) Release of acetylcholine Nerve impulse arriving at the synaptic end bulbs causes many synaptic vesicles to release ACh into the synaptic cleft (2) Activation of ACh receptors Binding of ACh to the receptor on the motor end plate opens anion channel Allows flow of Na+ to the inside of the muscle cell (3) Production of muscle action potential The inflow of Na+ makes the inside of the muscle fiber more positively charged, triggering a muscle action potential The muscle action potential then propagates to the SR to release its stored Ca2+ (4) Termination of ACh activity Ach effects last only briefly because it is rapidly broken down by acetylcholinesterase (AChE) Botulinum toxin Blocks release of ACh from synaptic vesicles May be found in improperly canned foods A tiny amount can cause death by paralyzing respiratory muscles Used as a medicine (Botox®) Strabismus (crossed eyes) Blepharospasm (uncontrollable blinking) Spasms of the vocal cords that interfere with speech Cosmetic treatment to relax muscles that cause facial wrinkles Alleviate chronic back pain due to muscle spasms in the


View Full Document

UT Arlington BIOL 2457 - Muscle Tissues

Documents in this Course
Load more
Download Muscle Tissues
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Muscle Tissues and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Muscle Tissues 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?