Muscle Tissue Lecture 3 Flashcards
1
Q
NMJ Definition
A
- Area where somatic motor neuron terminal and skeletal muscle synapse/connect.
- Site for transmitting action potential from nerve to muscle.
1
Q
Ca2+ Influx and AP
A
- Ca2+ influx into muscle fiber due to AP.
- AP causes membrane changes, opening/closing ion channels, releasing Ca2+.
2
Q
Somatic Motor Neurons
A
- Extend from brain & spinal cord, responsible for somatic movements.
- Terminate at muscle fiber sarcolemma, forming NMJ.
3
Q
Synaptic Cleft
A
- Gap between somatic neuron terminal and muscle.
- Allows communication between nerves.
4
Q
Neurotransmitters
A
- NTs propagate signals across cleft.
- Excitatory/inhibitory effects depending on synapse.
- Acetylcholine (ACh) is primary neurotransmitter at NMJ.
5
Q
ACh and Motor End Plate
A
- ACh stored in vesicles in pre-synaptic terminal.
- Motor end plate: Post-synaptic membrane with ACh receptors.
- ACh binding triggers ion channel opening.
6
Q
Presynaptic vs. Postsynaptic
A
- Presynaptic membrane: Motor neuron terminal.
- Postsynaptic membrane: Muscle fiber (motor endplate).
7
Q
Steps of AP Generation:
A
- Release of ACh
- Activation of ACh receptors
- Production of the Action Potential
- Termination of the Action Potential
8
Q
Release of ACh
A
- Nervous impulse reaches axon terminal.
- Voltage-gated Ca2+ channels open.
- Ca2+ triggers exocytosis of ACh into cleft.
9
Q
Activation of ACh Receptors
A
- ACh binds to ligand-gated Na+ channels at motor endplate.
- Opens channels, allowing Na+ influx into sarcoplasm.
10
Q
Production of Action Potential
A
- Na+ influx causes cell depolarization.
- Opens more voltage-gated Na+ channels, generating AP.
- AP propagates along sarcolemma, triggering Ca2+ release from SR for muscle contraction.
11
Q
Termination of Action Potential
A
- ACh must be removed once nerve signal stops.
- ACh removed by diffusion or broken down by acetylcholinesterase (AChE).
- End products recycled for new ACh synthesis.
- Some NTs removed via reuptake, but not ACh.
12
Q
Characteristics of Cardiac Muscle
A
- Heart is hardest working muscle.
- Beats over 100,000 times daily.
- Average 75 beats per minute.
- Striated and involuntary.
- Uses Ca2+ ions from SR and interstitial fluid.
- Allows prolonged contraction (10-15x longer than skeletal muscle).
13
Q
Auto-Rhythmicity of Cardiac Muscle
A
- Contracts in response to self-generated action potentials.
- Does not rely on nerve supply.
- Some cells are “self-excitable” (pacemaker cells).
- Generate rhythmic contractions to adjacent cells.
14
Q
Pacemaker Cells
A
- Sinoatrial (SA) node
- Atrioventricular (AV) node
- Responsible for automatic rhythmic contractions of upper and lower heart portions.
15
Q
Characteristics of Smooth Muscle
A
- Non-striated and involuntary.
- Can be autorhythmic, influenced by nervous system.
- Action potential in one fiber spreads to neighboring fibers, causing synchronized contraction.
16
Q
Structural Features of Smooth Muscle
A
- Thin filaments attached to dense bodies (similar to Z-discs).
- Intermediate filaments also attach to dense bodies, transmitting tension from muscle contraction.
17
Q
Caveolae in Smooth Muscle
A
- Pouchlike invaginations containing extracellular Ca2+.
- Less sarcoplasmic reticulum (SR) and no transverse tubules.
- Contraction relies more on extracellular calcium.
18
Q
Role of Calmodulin
A
- Protein binding to Ca2+ in smooth muscle.
- Acts as regulatory protein like troponin in skeletal muscle.
- Activates myosin heads for contraction.
- Contraction involves pulling of actin and myosin on dense bodies, intermediate fibers, causing cell contraction.
19
Q
Biological Energy Systems:
A
Anaerobic Processes:
* Occur without oxygen.
* Short bursts of high-intensity movements.
Aerobic Processes:
* Require oxygen.
* Long-duration, low-intensity exercises.
20
Q
Types of Exercises
A
Anaerobic:
* Weight training, sprinting, interval training.
Aerobic:
* Running, walking, swimming, biking.
21
Q
Anaerobic Glycolysis
A
- Breaks down glucose to yield ATP.
- Produces lactic acid in absence of oxygen.
- Provides ATP for moderate to high-intensity, short-term exercise.
22
Q
Aerobic Respiration
A
- Occurs in presence of oxygen.
- Utilizes pyruvic acid from glycolysis to produce ATP.
- Primary source of ATP at rest and during low-intensity activities.
23
Q
Muscle Fatigue
A
- Inability to maintain forceful contraction.
- Reasons include lack of oxygen, calcium, ATP, or buildup of waste products.
24
Oxygen Replenishment
* Postexercise oxygen uptake termed Oxygen Debt or EPOC.
* Used for resynthesis of ATP and creatine phosphate, glycogen, and tissue oxygenation.
25
Motor Unit
* Includes somatic motor neuron & all innervated muscle fibers.
* Can range from 1 fiber per neuron to over 3000 fibers per neuron.
26
Muscle Twitch
* Brief contraction of all fibers in response to a single action potential (AP).
* Lasts about 20-200 msec, longer than muscle AP.
27
Fasciculations
* Involuntary visible contractions of motor units.
* Can be benign or indicative of underlying pathologies.
28
Stages of Contraction
**Latent Period:** AP sweeps sarcolemma, no tension.
**Contraction Period:** Ca²⁺ binds, crossbridges form, contraction.
**Relaxation Period:** Crossbridges break, Ca²⁺ restored.
**Refractory Period:** Subsequent AP can't generate contraction.
29
Frequency of Stimulation
* Peak tension depends on stimulation frequency.
* Myograms show effects like wave summation, unfused tetanus, fused tetanus.
30
Un-Fused Tetanus
* Sustained, wavering contraction at 20-30 stimuli/sec.
* Shows partial relaxation between stimuli.
30
Wave Summation
* Second stimulus before relaxation causes stronger contraction.
* Results in contractions up to 5x greater than single twitch.
31
Fused (Complete) Tetanus
* Sustained contraction at 80-100 stimuli/sec.
* No time for relaxation, sustains powerful contractions.
32
Motor Unit Recruitment
* Increases number of active motor units for smooth movement.
* Smaller fibers recruited first, larger fibers as force requirement increases.
33
Muscle Tone:
Amount of tension in a muscle at rest due to weak, involuntary contractions.
Caused by constant innervation from spinal cord and higher brain centers.
34
Flaccid Paralysis
* Loss of muscle tone.
* Reduced reflexes, muscle atrophy.
* Associated with lower motor neuron injuries like trauma, ALS, Guillain-Barre Syndrome, Polio, nerve compression, and Myasthenia gravis (MG).
35
Spastic Paralysis
* Increased muscle tone, hyperreflexia.
* Associated with upper motor neuron injuries like stroke, multiple sclerosis, traumatic brain injury, spinal cord injury, and cerebral palsy.
36
Rigidity
* Increase in muscle tone with no reflex effect, inability to relax.
* Can occur with tetanus (Clostridium tetani infection).
* Tetanus may also cause tetany.
