Lecture 13: General Muscle Anatomy

 Define what a muscle fiber is 

One muscle consists of many muscle fibers (cells) bundled together by connective tissue. 

Muscle fiber = muscle cell.

whats the hierarchy for muscle fibers/muscle cell, muscle, myofibrils. from smallest unit to largest

myofibrils

muscle fibers/muscle cell

muscle

myofibrils are primarily composed of two kinds of proteins filaments ___ and __.

actin and myosin

actin is thick/thin and myosin is thick/thin.

thin;thick

Define sarcomeres 

Myofibrils are made of smaller, repeating units called sarcomeres 

sarcomere contraction looks like overlapping ___>

fingers

what are the 3 parts of a neural network

1. Afferent neurons (send information from sensory organs to CNS) 

2. Interneurons (the CNS - processes info and send signals to efferent) 

3. Efferent (receive signals and then sends info to muscles)

Where do motor neurons (efferent neurons) and muscular cells meet? 

Neuromuscular junction 

tell me the process of action potential from motor neuron to muscle contraction

1. Action potential reaches ends of motor neuron synapse

1. this action potential travels through muscle cell via t tubule

2. T tubules descend into cytoplasm 

3. T tubules runs close to the sarcoplasmic reticulum

4. Action potential reaches SR and depolarization occurs in SR which causes it to released  Ca2+ ions

steps for myosin filament to actin contraction

1. Myosin filament cant grab on actin bc tropomyosin is blocking myosin filament from grabbing actin 

2. Ca2+ from SR interacts with troponin, and troponin moves tropomyosin out of the way

3. Now myosin grabs actin, then triggers myosin to bend backwards 

4. ATP is required for myosis to let go, then resets 

   1. If Ca2+ is still present, myosin keeps grabbing and pulling

 list 3 types of muscle and what the control (Vertebrate specific)

1. Skeletal

   1. Voluntary movement and breathing 

2. Cardiac 

   1. Beating of heart 

3. Smooth 

   1. Involuntary movement of internal organs 

All of these muscle use same sliding myosin filament mechanism to contract 

skeletal, cardiac, smooth muscles. describe them all

Skeletal muscles
a. striated (meaning have repeating pattern of actin and myosin). 
b. Multinucleate 

Cardiac muscles
a.Striated 
b. Uninucleate 
c. Connect to each other via gap junctions 
d. Heartbeat is myogenic - not under direct neural control but generated by the heart muscle itself (muscle creates electrical signal, not outward stimulus)

Smooth muscle (blood vessels)
a. Uninucleate 
b. found internal organs 
c. Not striated, but actin and myosin are still theres 
d. involuntary - Stretch cells depolarize first which fire action potentials and start contraction (Ex. swallow food, food stretches cells, then causes esophagus to move food down due to contractions)

difference between a twitch, treppe, tetany

1. One action potential = one contraction = twitch 
   a. Twitch how long myosin filament can pull actin until Ca2+ is removed by SR

2. Two action potentials close together in time = treppe 

3. Maximum level of contraction = tetany 
   a. Actin and myosin are as interlocked as possible (Ex. lock jaw)
   b. Sustaining a muscle contraction for a long time requires ATP to be present **does Ca2+ also have to be present?. Answer: ca2+ still needs to be present.

what are slow twitch cells. what are characteristics of these cells

Slow twitch cells (our endurance muscle cells, can keep going and being active for sustained period of time)

a. Maximum tensions develops slowly 

b. Highly resistant to fatigue 

c. Aerobic respiration occurs: lots of mitochondria, myoglobin (slow cell meat tends to be darker because of high myoglobin), O2, fule reserves 

what are fast twitch cells. what are characteristics of these cells

Fast twitch cells 

a. Develop greater maximum tension faster 

b. Fatigue more quickly 

c. Primarily anaerobic glycolysis, cannot replenish ATP for prolonged contraction

Define skeletal systems

The rigid supports to which muscles attach and pull on

Define hydrostatic skeletons

Don't have permanently rigid parts, but use body fluids to temporarily create them (ex. Is worm moving)

Define exoskeleton. share a drawback

Consists of a hardened outer surface to which muscles attach

Drawback: for growth to occur, the animal must molt. When molt you're vulnerable to predation.

Define endoskeleton

Internal scaffold for muscle attachment 

Made of cartilage (collagen) and/or bone (calcium phosphate crystals) 

whats the diff between osteoblasts and osteoclasts

a. Osteoblasts make new bone matrix 

b. Osteoclasts are cells that reabsorb bone. 

 Define joints

Where bones come together. Different types of joints allow different types of motion. 

Define tendons

Connective tissue straps that join muscle to bone 

Define ligaments

Bands of connective tissue that hold bones together at joints