Physiology of Skeletal Muscle Contraction Flashcards

Question

_Troponin: how it works_ * ... Ca2+ bind to troponin C (C = calcium binding), * *In heart TnC only binds to ... Ca2+ ions* * TnC changes ... * ... change in TnC “shuts off” TnI * tropomyosin-troponin leaves F-actin groove * unmasks the myosin binding site on actin * next myosin heads make cross bridges (cycling) to actin * Myosin breaks down ATP * Myosin pulls thin filaments

Answer 1

* **4** Ca2+ bind to troponin C (C = calcium binding), * *In heart TnC only binds to **3** Ca2+ ions* * TnC changes **conformation** * **conformational** change in TnC “shuts off” TnI * tropomyosin-troponin leaves F-actin groove * unmasks the myosin binding site on actin * next myosin heads make cross bridges (cycling) to actin * Myosin breaks down ATP * Myosin pulls thin filaments

Answer 2

* 4 Ca2+ bind to troponin C (C = calcium binding), * *In heart TnC only binds to 3 Ca2+ ions* * TnC changes conformation * conformational change in TnC “shuts off” **TnI** * tropomyosin-troponin leaves **F**-actin groove * unmasks the myosin **binding** site on actin * next myosin heads make cross bridges (cycling) to actin * Myosin breaks down ATP * Myosin pulls thin filaments

Answer 3

* 4 Ca2+ bind to troponin C (C = calcium binding), * *In heart TnC only binds to 3 Ca2+ ions* * TnC changes conformation * conformational change in TnC “shuts off” TnI * tropomyosin-troponin leaves **F**-actin groove * unmasks the myosin binding site on actin * next myosin heads make **cross** bridges (cycling) to actin * Myosin breaks down ATP * Myosin pulls thin filaments

Answer 4

* **4** Ca2+ bind to troponin C (C = calcium binding), * *In heart TnC only binds to 3 Ca2+ ions* * TnC changes conformation * conformational change in TnC “shuts off” TnI * tropomyosin-troponin leaves F-actin groove * unmasks the myosin binding site on actin * next myosin heads make cross bridges (cycling) to actin * Myosin breaks down **ATP** * Myosin pulls **thin** filaments

Answer 5

Total TnI = marker for total muscle **breakdown**

Answer 6

Cardiac TnI = marker for **myocardial infarct**

Answer 7

Cardiac **TnI** = marker for myocardial infarct

Answer 8

* Molecular cycle of actin-myosin interaction * Mechanism of Contraction at **Molecular** level * Contraction depends on binding of **myosin** heads to **thin** filaments (actin) at specific binding sites * In resting state of sarcomere, myosin heads are blocked from binding to actin by tropomyosin, which occupies the specific binding sites (in F-actin double helical groove)

Answer 9

* Molecular cycle of actin-myosin interaction * Mechanism of Contraction at Molecular level * Contraction depends on binding of myosin heads to thin filaments (actin) at specific binding sites * In **resting** state of sarcomere, myosin heads are **blocked** from binding to actin by **tropomyosin**, which occupies the specific binding sites (in F-actin double helical groove)

Answer 10

* *Between A & B: the degree of filament overlap is directly proportional to force muscle can generate.* * *When the effect of small shortening of one sarcomere is multiplied by many sarcomeres in a myofibril and the shortening of many myofibrils together is summed, the whole muscle fibre shortens.* * *Shortening of many muscle fibres is manifest as contraction of the entire muscle with change in muscle length*

Answer 11

* REACTIONS * 1.Myosin releases actin * 2.Myosin head **cleaves** ATP * 3.Myosin binds actin * 4.**Power stroke** ## Footnote *Tropomyosin: The important thing to notice in the animation (you can animate this by running this powerpoint in slide show mode (shift-F5) is that the tropomyosin (long blue string) rolls up and down. It turns out that myosin (top and left) can only interact with specific bits of the actin molecule. In the absence of calcium, this active site of actin is covered by tropomyosin. In the presence of calcium (yellow balls that fly in to cartoon), tropomyosin is rolled away from actin’s active site because the calcium causes troponin (3 purple beads connected to one another, one of which is connected to the blue tropomyosin) to drag tropomyosin down (i.e. away from the active site of actin). This allows myosin to interact with actin at its active site.*

Answer 12

*Tropomyosin: The important thing to notice in the animation (you can animate this by running this powerpoint in slide show mode (shift-F5) is that the tropomyosin (long blue string) rolls up and down. It turns out that myosin (top and left) can only interact with specific bits of the actin molecule. In the absence of calcium, this active site of actin is covered by tropomyosin. In the presence of calcium (yellow balls that fly in to cartoon), tropomyosin is rolled away from actin’s active site because the calcium causes troponin (3 purple beads connected to one another, one of which is connected to the blue tropomyosin) to drag tropomyosin down (i.e. away from the active site of actin). This allows myosin to interact with actin at its active site.*

Answer 13

* After death, **respiration** ceases to occur, depleting the corpse of oxygen used in the making of Adenosine triphosphate (ATP). * ATP depleted after death * Muscle cell does not resequester Ca2+ into **SR** * Increase in **Cytosolic** Ca2+ * Ca2+ allows crossbridge cycle contraction * Until ATP & creatine-P run out * W/o ATP -\> myosin stops just after power stroke * With myosin still bound to actin * Rigor mortis ends when muscle tissue degrades after 3 days

Answer 14

* After death, respiration ceases to occur, depleting the corpse of oxygen used in the making of Adenosine triphosphate (ATP). * ATP depleted after death * Muscle cell does not resequester Ca2+ into SR * Increase in Cytosolic Ca2+ * Ca2+ allows **crossbridge** cycle contraction * Until **ATP** & **creatine**-P run out * W/o ATP -\> myosin stops just after power stroke * With myosin still bound to actin * Rigor mortis ends when muscle tissue degrades after 3 days

Answer 15

* After death, respiration ceases to occur, depleting the corpse of oxygen used in the making of Adenosine triphosphate (ATP). * ATP depleted after death * Muscle cell does not resequester Ca2+ into SR * Increase in Cytosolic Ca2+ * Ca2+ allows crossbridge cycle contraction * Until ATP & creatine-P run out * W/o ATP -\> myosin stops just after **power stroke** * With myosin still bound to **actin** * Rigor mortis ends when muscle tissue degrades after 3 days

Answer 16

* After death, respiration ceases to occur, depleting the corpse of oxygen used in the making of Adenosine triphosphate (ATP). * ATP depleted after death * Muscle cell does not resequester Ca2+ into SR * Increase in Cytosolic Ca2+ * Ca2+ allows crossbridge cycle contraction * Until ATP & creatine-P run out * W/o ATP -\> myosin stops just after power stroke * With myosin still bound to actin * Rigor mortis ends when muscle tissue degrades after **3** days

Answer 17

* Creatine found in muscle **fibres** * Phosphorylated to creatine **phosphate** * This is how energy is stored in muscle * When cross bridge cycling hydrolyses ATP to ADP + Pi, creatine phosphate donates a high energy phosphate to ADP restoring it to ATP * ATP levels must be kept stable – buffering & regeneration * The reaction is catalysed in both directions by the enzyme creatine phosphokinase (a/k/a CK, CPK)

Answer 18

* Creatine found in muscle fibres * Phosphorylated to creatine phosphate * This is how energy is stored in muscle * When cross bridge cycling **hydrolyses** ATP to ADP + Pi, creatine phosphate donates a high energy phosphate to ADP restoring it to **ATP** * ATP levels must be kept stable – buffering & regeneration * The reaction is catalysed in both directions by the enzyme creatine **phosphokinase** (a/k/a CK, CPK)

Answer 19

* Creatine is a small molecule that can accept high energy phosphate bonds from **ATP** * Creatine-phosphate is the above molecule after phosphate has been added to it * Creatine-**phosphokinase** (CPK) is the enzyme the adds phosphate to creatine * This is a plasma marker of muscle destruction * It is a large molecule detected by antibodies * Creatine-kinase (CK) is just another name for creatine phosphokinase (above). They are the same thing. * Creatinine is a diagnostic marker of kidney function. It is a breakdown product of creatine.

Answer 20

* Creatine is a small molecule that can accept high energy phosphate bonds from **ATP** * Creatine-phosphate is the above molecule after phosphate has been added to it * Creatine-phosphokinase (CPK) is the enzyme the adds phosphate to creatine * This is a plasma marker of muscle **destruction** * It is a large molecule detected by **antibodies** * Creatine-kinase (CK) is just another name for creatine phosphokinase (above). They are the same thing. * Creatinine is a diagnostic marker of kidney function. It is a breakdown product of creatine.

Answer 21

Creatinine is a diagnostic marker of ***kidney*** function. It is a breakdown product of creatine.

Answer 22

Creatine-kinase (CK) is just another name for creatine **phosphokinase** - They are the same thing.

Answer 23

* There are **two** Ca2+ gradients * **Extracellular** vs. **cytosolic** free Ca2+ * **SR** vs. **cytosolic** free Ca2+ * Efflux of Ca2+ from sarcoplasmic reticulum to cytoplasm provides most of calcium * Calcium entering cell from outside provides only small fraction of calcium needed for contraction

Answer 24

* There are two Ca2+ gradients * Extracellular vs. cytosolic free Ca2+ * SR vs. cytosolic free Ca2+ * **Efflux** of Ca2+ from **sarcoplasmic** **reticulum** to cytoplasm provides most of calcium * Calcium entering cell from outside provides only small fraction of calcium needed for contraction

Answer 25

* **ACh** -\> Depolarisation * Active Nicotinic **AChR** -\> net inward current * depolarisation spread via **T**-Tubules * Local action potentials trigger Ca2+ efflux from terminal cisternae * Across membrane of sarcoplasmic reticulum * Into the fibre cytoplasm

Answer 26

* ACh -\> Depolarisation * Active **Nicotinic** AChR -\> net inward current * depolarisation spread via T-**Tubules** * Local action potentials trigger Ca2+ efflux from **terminal cisternae** * Across membrane of sarcoplasmic reticulum * Into the fibre cytoplasm

Answer 27

* Excitation-contraction coupling = the molecular mechanism for how the **depolarisation** of the plasma membrane leads to the release of **Ca2**+ into the cytoplasm followed by **contraction**. * Ryanodine Receptor (RyR) * In SR membrane * Releases Ca2+ * From SR * Triggered by voltage sensor on Ca2+ channel * SERCA * In SR membrane * Pumps Ca2+ Back into SR * Needs ATP

Answer 28

* Excitation-contraction coupling = the molecular mechanism for how the depolarisation of the plasma membrane leads to the release of Ca2+ into the cytoplasm followed by contraction. * **Ryanodine** Receptor (RyR) * In SR membrane * Releases Ca2+ * From SR * Triggered by voltage sensor on Ca2+ channel * **SERCA** * In SR membrane * Pumps Ca2+ Back into SR * Needs ATP

Answer 29

* Excitation-contraction coupling = the molecular mechanism for how the depolarisation of the plasma membrane leads to the release of Ca2+ into the cytoplasm followed by contraction. * Ryanodine Receptor (RyR) * In SR membrane * **Releases** Ca2+ * **From** SR * Triggered by voltage sensor on Ca2+ channel * SERCA * In SR membrane * **Pumps** Ca2+ **Back** into SR * Needs **ATP**

Answer 30

* Excitation-contraction coupling = the molecular mechanism for how the depolarisation of the plasma membrane leads to the release of Ca2+ into the cytoplasm followed by contraction. * Ryanodine Receptor (RyR) * In SR membrane * Releases Ca2+ * From SR * Triggered by **voltage** sensor on Ca2+ channel * **SERCA** * In SR membrane * Pumps Ca2+ Back into SR * Needs ATP

Answer 31

SERCA = Smooth endoplasmic Reticulum Calcium ATPase = a **calcium** pump in the sarcoplasmic reticulum (smooth endoplasmic reticulum) membrane of a muscle cell. It **pumps** free cytosolic calcium back into the SR; thus it **resequesters** calcium and requires **ATP** to do so.

Answer 32

* A **single** AP -\> Ca2+ release from SR -\> **twitch** * Ca2+ ions are rapidly pumped back into SR -\> end of **twitch** * Frequent APs -\> insufficient Ca2+ resequestration -\> summation of contraction

Answer 33

* A single AP -\> Ca2+ release from SR -\> twitch * Ca2+ ions are rapidly pumped back into SR -\> end of twitch * **Frequent** APs -\> insufficient Ca2+ **resequestration** -\> **summation** of contraction

Answer 34

* muscle fibres are divided into 2 main types: * **slow** twitch (type I – ‘red’ – oxidative, small diam.) * High myoglobin, many mitochondria * **fast** twitch (type II – ‘white’ – nonoxidative, wide diam.) * Lower myoglobin, increased energy from glycolysis * fibre types differ in: * aerobic (slow) vs anaerobic * faster calcium re-uptake (fast) * maximum tension produced (fast) * fatigue resistance (slow)

Answer 35

* muscle fibres are divided into 2 main types: * slow twitch (type I – ‘**red**’ – oxidative, small diam.) * High myoglobin, many mitochondria * fast twitch (type II – ‘**white**’ – nonoxidative, wide diam.) * Lower myoglobin, increased energy from glycolysis * fibre types differ in: * aerobic (which are **slow**) vs anaerobic * faster calcium re-uptake (**fast**) * maximum tension produced (fast) * fatigue resistance (slow)

Answer 36

* muscle fibres are divided into 2 main types: * slow twitch (type I – ‘red’ – oxidative, small diam.) * **High** myoglobin, many mitochondria * fast twitch (type II – ‘white’ – nonoxidative, wide diam.) * **Lower** myoglobin, increased energy from glycolysis * fibre types differ in: * aerobic (slow) vs anaerobic * faster calcium re-uptake (fast) * maximum tension produced (**fast fibres**) * fatigue resistance (**slow fibres**)

Answer 37

* Type **I** – ‘**red**’ – oxidative, small diam * High myoglobin, many mitochondria * **Aerobic** * Fatigue resistant

Answer 38

* Type I – ‘red’ – oxidative, small diam * **High** myoglobin, many mitochondria * Aerobic * **Fatigue** resistant

Answer 39

* Type II – ‘white’ – nonoxidative, wide diam * Lower myoglobin, increased energy from glycolysis * Anaerobic * **Faster** calcium re-uptake * **Maximum** tension produced

Answer 40

* Type **II** – ‘**white**’ – nonoxidative, wide diam * Lower myoglobin, increased energy from glycolysis * Anaerobic * Faster calcium re-uptake * Maximum tension produced

Answer 41

* Type II – ‘white’ – nonoxidative, wide diam * **Lower** myoglobin, increased energy from **glycolysis** * **Anaerobic** * Faster calcium re-uptake * Maximum tension produced

Answer 42

* Muscles contain mixtures of fibre types, composition depends on muscle action: * **soleus** = 80% type I (slow), 20% type IIA * vastus lateralis = mixture of type I, IIA, IIX * Proportions depend on **physical** **fitness**: * Inactive * Moderately active * Endurance athlete * Anaerobic athlete

Answer 43

* Muscles contain mixtures of fibre types, composition depends on muscle action: * soleus = **80% type I (slow), 20% type IIA** * vastus **lateralis** = mixture of type I, IIA, IIX * Proportions depend on physical fitness: * Inactive * Moderately active * Endurance athlete * Anaerobic athlete

Answer 44

* Muscles contain mixtures of fibre types, composition depends on muscle action: * soleus = 80% type I (**slow**), 20% type IIA * vastus lateralis = mixture of type I, IIA, IIX * Proportions depend on physical fitness: * Inactive * Moderately active * Endurance athlete * Anaerobic athlete

Answer 45

* Muscles contain mixtures of fibre types, composition depends on muscle action: * soleus = 80% type I (slow), 20% type IIA * vastus lateralis = mixture of type I, IIA, IIX * **Proportions** depend on physical fitness: * Inactive * Moderately active * Endurance athlete * Anaerobic athlete

Answer 46

* Normal gastrocnemius - T1 and T2 Fibres mixed together, some dark (T1) some light (T2) * **Sprint** runner - Very little T1 (slow) most T2 (fast) * **Long Distance** runner - Very little T2 (fast) a lot more T1 (slow)

Answer 47

* Normal gastrocnemius - T1 and T2 Fibres mixed together, some dark (T1) some light (T2) * Sprint runner - Very little T1 (**slow**) most T2 (**fast**) * Long Distance runner - Very little T2 (**fast**) a lot more T1 (**slow**)

Answer 48

* 3 types of co-ordination * **Motor** Units * Recruitment & size principle * **Tetany** * Fusion of myocytes into long myofibres

Answer 49

* 3 types of co-ordination * Motor Units * **Recruitment** & size principle * Tetany * **Fusion** of **myocytes** into long myofibres

Answer 50

* Definition: A **single** alpha motor **neuron** and all muscle fibres it **innervates**. * Functions as a single **contractile** unit of skeletal muscle * all muscle fibres in a single motor unit are of the same type * (e.g. slow oxidative, fast oxidative, fast glycolytic).

Answer 51

* Definition: A single **alpha** motor neuron and all muscle fibres it innervates. * Functions as a single contractile unit of skeletal muscle * all muscle fibres in a single motor unit are of the **same** **type** * (e.g. slow oxidative, fast oxidative, fast glycolytic).

Answer 52

* In **large** muscles responsible for powerful gross contractions, a single motor neuron may synapse on 1000 fibres * In **small** muscles mediating precision movement a single motor neuron may synapse with as few as 2 – 3 muscle fibres * Type and function of the lower motor neuron determines the muscle fibre, * There are different sorts of motor units in a single muscle

Answer 53

* In large muscles responsible for powerful gross contractions, a single motor neuron may synapse on 1000 fibres * In small muscles mediating precision movement a single motor neuron may synapse with as few as 2 – 3 muscle fibres * Type and function of the **lower** motor neuron determines the muscle fibre, * There are different sorts of motor units in a single muscle

Answer 54

* In large muscles responsible for powerful gross contractions, a single motor neuron may synapse on 1000 fibres * In small muscles mediating precision movement a single motor neuron may synapse with as few as 2 – 3 muscle fibres * Type and **function** of the lower motor neuron determines the muscle **fibre**, * There are different sorts of motor units in a single muscle

Answer 55

* **Isometric** – generates a variable force while length of muscle remains unchanged. * “Iso” = same, “metric” = length * **Isotonic** – generates a constant force while the length of the muscle changes * “tonic” = tone = tension/force

Answer 56

* Isometric – generates a **variable** force while length of muscle remains **unchanged**. * “Iso” = same, “metric” = length * Isotonic – generates a **constant** force while the length of the muscle **changes** * “tonic” = tone = tension/force

Answer 57

* Using example: picking up a drinking glass * Stage 1: **isometric** – force increases, joint does not move * Muscle Force \< force of gravity –\> force increases * biceps and brachioradialis generate force by **isometric** contraction as muscles have not yet shortened * Stage 2: **isotonic** – force remains the same, arm moves * Glass moves upward in response to force * An **isotonic** contraction starts as the force generated by the muscles overcomes gravitational and inertial forces keeping glass on the table * Glass starts to rise as the muscles shorten and the elbow bends and force generated by the muscle is constant as the glass is moving

Answer 58

* Using example: picking up a drinking glass * Stage 1: isometric – force **increases**, joint does **not move** * Muscle Force \< force of gravity –\> force increases * biceps and brachioradialis generate force by isometric contraction as muscles have not yet shortened * Stage 2: isotonic – force remains the **same**, arm **moves** * Glass moves upward in response to force * An isotonic contraction starts as the force generated by the muscles overcomes gravitational and inertial forces keeping glass on the table * Glass starts to rise as the muscles shorten and the elbow bends and force generated by the muscle is constant as the glass is moving

Answer 59

* Using example: picking up a drinking glass * Stage 1: isometric – force increases, joint does not move * Muscle Force \< force of gravity –\> force increases * biceps and brachioradialis generate force by isometric contraction as muscles have not yet shortened * Stage 2: isotonic – force remains the same, arm moves * Glass moves upward in response to force * An isotonic contraction starts as the force generated by the muscles overcomes gravitational and inertial forces keeping glass on the table * Glass starts to rise as the muscles **shorten** and the elbow bends and force generated by the muscle is **constant** as the glass is moving

Answer 60

* Muscle contraction ≠ (necessarily) muscle **shortening** * **Concentric** – force during contraction – tossing a ball into air * **Eccentric** (negatives) – force during muscle elongation * e.g. when “braking” or when the weight of the object is overwhelming – catching a ball * Both types of force generation can occur in one behaviour * Proprioception controls force gen. based on length and stretch

Answer 61

* Muscle contraction ≠ (necessarily) muscle shortening * Concentric – force during **contraction** – tossing a ball into air * Eccentric (negatives) – force during muscle **elongation** * e.g. when “braking” or when the weight of the object is overwhelming – catching a ball * Both types of force generation can occur in one behaviour * **Proprioception** controls force gen. based on length and stretch

Answer 62

A **concentric** contraction is a type of muscle activation that causes tension on your muscle as it shortens

Answer 63

**Eccentric** contraction occurs when the total length of the muscle increases as tension is produced. (For example, the lowering phase of a biceps curl constitutes an eccentric contraction.)

Answer 64

* as the initial **isometric** contraction occurs: * more and more motor units are recruited starting with **smaller** ones and progressively adding **larger** ones * Allows fine gradation of force for **small** movements * In drinking glass example: * more and bigger motor units recruited until the glass starts moving and the contraction becomes isotonic

Answer 65

* as the initial **isometric** contraction occurs: * more and more motor units are recruited starting with smaller ones and progressively adding larger ones * Allows fine gradation of force for small movements * In drinking glass example: * more and bigger motor units recruited until the glass starts moving and the contraction becomes **isotonic**

Answer 66

* Lower motor neuron disease * **Weakness** * Muscle **atrophy** * Upper motor neurone disease * Spasticity, hypertonia

Answer 67

* Lower motor neuron disease * Weakness * Muscle atrophy * Upper motor neurone disease * **Spasticity, hypertonia**

Answer 68

**Hypertonia** = muscle is over-contracted when at rest (IN UPPER MOTOR NEURONE DISEASE)

Answer 69

**Spasticity** = muscle has involuntary spasms of activity that resist relaxation. They are VELOCITY-dependent, and often one-way (ie there is resistance to flexion but no resistance to extension) (IN UPPER MOTOR NEURONE DISEASE)

Answer 70

**Upper** motor neuron = signal starts (dendrites) in the brain (especially the motor cortex) and extends to (axon) the spinal cord, where it forms a synapse with a **lower** motor neuron.

Answer 71

**Atrophy** = muscle wasting, muscle becomes smaller (and weaker) due to disuse. Often caused by loss of neural input to the muscle fibre. (IN LOWER MOTOR NEURON DISEASE)

Answer 72

* Controls Muscle Length * **Increases** Muscle Force * Lack of patellar reflex = **Westphal’s** sign

Answer 73

Stretch Reflex controls muscle **length** and increases muscle **force** (lack of patellar reflex - westphal's sign)

Answer 74

* Sensory spindle fibre = Muscle Spindle Fibre * Detects **Stretch**, i.e. Length * Proprioception * Spindle is **Parallel** to other muscle fibres * Ipsilateral Spinal reflex * Monosynaptic

Answer 75

* Sensory spindle fibre = Muscle Spindle Fibre * Detects Stretch, i.e. Length * **Proprioception** * Spindle is Parallel to other muscle fibres * Ipsilateral **Spinal** reflex * Monosynaptic

Answer 76

The patellar reflex is a clinical and classic example of the **monosynaptic** reflex arc.

Answer 77

* A monosynaptic reflex, such as the knee jerk reflex, is a simple reflex involving only one synapse between the sensory and motor neurone. * The pathway starts when the muscle spindle is **stretched** (caused by the tap stimulus in the knee jerk reflex). The muscle spindles are responsible for detecting the **length** of the muscles fibres. * When a **stretch** is detected it causes action potentials to be fired by Ia afferent fibres. These then synapse within the spinal cord with α-motoneurones which innervate **extrafusal** fibres. The antagonistic muscle is inhibited and the agonist muscle contracts i.e. in the knee jerk reflex the quadriceps contract and the hamstrings relax.

Answer 78

* A spindle consists of 3-12 **intrafusal** fibres * Gamma motor neurons increase **sensitivity** * Drive contraction of edge of intrafusal fibres * Sensors from muscle spindle are: * Called Type 1a and Type 2 * Wrap around the intrafusal fibres * Detect stretch (ie length) of central non-contracting region using stretch receptors * Spindle is like a thermostat that regulates the relationship between muscle length and muscle contractility * ie the relationship between neural drive and force generation

Answer 79

* A spindle consists of 3-12 intrafusal fibres * **Gamma** motor neurons increase sensitivity * Drive contraction of edge of intrafusal fibres * Sensors from muscle spindle are: * Called Type 1a and Type 2 * Wrap around the intrafusal fibres * Detect **stretch** (ie **length**) of central non-contracting region using **stretch** receptors * Spindle is like a thermostat that regulates the relationship between muscle length and muscle contractility * ie the relationship between neural drive and force generation

Answer 80

* A spindle consists of 3-12 intrafusal fibres * Gamma motor neurons increase sensitivity * Drive contraction of edge of intrafusal fibres * Sensors from muscle spindle are: * Called Type 1a and Type 2 * Wrap around the intrafusal fibres * Detect stretch (ie length) of central non-contracting region using stretch receptors * Spindle is like a thermostat that regulates the relationship between muscle **length** and muscle **contractility** * ie the relationship between neural drive and force generation

Answer 81

* A spindle consists of 3-12 intrafusal fibres * Gamma motor neurons increase sensitivity * Drive contraction of edge of intrafusal fibres * Sensors from muscle spindle are: * Called Type 1a and Type 2 * Wrap around the intrafusal fibres * Detect stretch (ie length) of central non-contracting region using stretch receptors * Spindle is like a thermostat that regulates the relationship between muscle length and muscle contractility * ie the relationship between **neural** drive and **force** generation

Answer 82

* Absence of this reflex = **Westphal’s** Sign * Receptor damage * Femoral nerve damage * Peripheral nerve disease * e.g. Peripheral **Neuropathy** * In upper motor neuron disease * Can lead to hypertonia and spasticity * UMN inhibits normal descending inhibitory input to spinal interneurons * The spindle reflex becomes over-sensitive * Can attempt to contract muscle all the time

Answer 83

* Absence of this reflex = Westphal’s Sign * Receptor damage * Femoral nerve damage * Peripheral nerve disease * e.g. Peripheral Neuropathy * In **upper** motor neuron disease * Can lead to hypertonia and spasticity * **UMN** inhibits normal descending inhibitory input to spinal interneurons * The spindle reflex becomes over-**sensitive** * Can attempt to contract muscle all the time

Answer 84

* Absence of this reflex = Westphal’s Sign * Receptor damage * **Femoral** nerve damage * **Peripheral** nerve disease * e.g. Peripheral Neuropathy * In upper motor neuron disease * Can lead to **hypertonia** and **spasticity** * UMN inhibits normal descending inhibitory input to spinal interneurons * The spindle reflex becomes over-sensitive * Can attempt to contract muscle **all the time**

Answer 85

* Protects from **overloading** * **Decreases** Muscle Force -\> dropping the load * Sensor firing -\> decreased contraction

Answer 86

* Protects from overloading * Decreases Muscle Force -\> dropping the load * Sensor firing -\> **decreased** contraction

Answer 87

* Sensor to Spinal Cord * Interneuron to motor neuron * Motor neuron **inhibited** * Motor neuron to muscle

Answer 88

* Sensor = **Golgi** Tendon Organ * Detects **Tension** * In series with muscle * In tendon * Near border with muscle * Disynaptic * Ipsilateral Spinal reflex

Answer 89

* Sensor = Golgi Tendon Organ * Detects Tension * In **series** with muscle * In tendon * Near **border** with muscle * Disynaptic * Ipsilateral Spinal reflex

Answer 90

* Sensor = Golgi Tendon Organ * Detects Tension * In series with muscle * In tendon * Near border with muscle * **Disynaptic** * Ipsilateral Spinal reflex

Answer 91

* Sensor = Golgi Tendon Organ * Detects Tension * In series with muscle * In tendon * Near border with muscle * Disynaptic * **Ipsilateral** Spinal reflex

Answer 92

Like the stretch reflex, the tendon reflex is **ipsilateral**

Answer 93

The **Golgi tendon** reflex is a response to extensive tension on a tendon.[7] It helps avoid strong muscle contractions which could tear the tendon from either the muscle or bone.

Answer 94

* Fibre types differ in oxidative metabolism * **Slow** red * **Fast** white * **Motor** unit determines fibre type * Balance of force to length * **Size** principle * **Stretch** reflex * Allows for “braking”: eccentric —\> isometric

Answer 95

Muscle contraction is dependent on calcium in the **cytosol** being **raised** - most of this calcium comes from the **sarcoplasmic reticulum (very little from outside the cell)**