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Musculoskeletal Module > lecture 26 > Flashcards

lecture 26 Flashcards

1
Q

What do spinal reflexes refer to?

A

also reflexes engaging the brain stem and cranial nerves

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2
Q

What can Alpha motor neurons be referred to ask?

A

Final Common Path
- as only 3x outputs
-motor neurons compose majority of outputs
-final common path for motor commands
Motor commands are coming mainly from the Forebrain
Synaptic inputs from:
1. Descending tracts (corticospinal/pyramidal tract. or Reticulospinal tract from reticular formation of brain stem)
-form synapses with motor neurons
2. Spinal Interneurons - either in spinal cords or brain stem. (Local) Excitatory(glutamate) or inhibitory(GABA)
3. Proppriospinal neurons -located in spinal cords brachio or lumbar enlargements. Long axons up or down. assist in synchronization/coordination of motor neurons controlling upper and lower limbs- movements arent completely independant (e.g. esp in locamotion)
4. Afferent fibres -(Type Ia) from muscle spindles
-this final common path integrating number of things. have to make decision to respond or not to respond to all these inputs, and whether to fire or not to fire an AP- will spread down axon and cause ACh release and contraction of all muscles of motor unit being activated

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3
Q

What are the 4x main groups of synaptic inputs?

A
  1. Descending tracts
  2. Spinal Interneurons
  3. Proppriospinal neurons
  4. Afferent fibres
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4
Q

What are 2x examples of Descending tracts of synaptic inputs?

A 
Cortico spinal (pyramidal) tract
Reticulospinal tract-from reticular formation of brain stem
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5
Q

What are the key features of motor neurons?

A

axon
proximal dendrites
cell body densly covered with presynaptic terminals (ball like) 1000s
-some synaptic terminals are excitatory or inhibitory
–synaptic intergration

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6
Q

How does the motor system control movements?

A

the motor system controls movements together/in synchrony with SENSORY systems

  • cannot just send a command to muscles to do movement.
  • also important to receive feedback information from muscles or sensory structures
  • how much progress occurred (bucket too heavy to lift)
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7
Q

What is the direction of flow of sensory commands?

A

from muscles/tendons/joints(proprioceptors) –> back to CNS
-inform them about what has happened
–as Motor system controls movements together/in coordination with the sensory systems (feedback)
5x External sensory receptors e.g.
1. Retina (see what is going on)
2. Vestibular (info about vestibular position)
3. Auditory (hear what is going on)
4. Olfactory (smell influences movement-bacon and eggs facilitate movement)
5. Skin receptors (touch important signalling/tactile
“interaction of motor commands with sensory information coming from propriorecpetors and external receptors is key”
-movement disorders are the most frequent symptoms seen in neurological patients
- most movement disorders can occurs either a disruption of motor pathways. Or also as a result of disruption of sensory pathways
–if any one of these 2x systems fail, the movement will suffer

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8
Q

What are 5x examples of External sensory receptors?

A
  1. retina
  2. vestibular
  3. auditory
  4. olfacory
  5. skin receptors
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9
Q

What is the relationship between neurological disorders, movement disorders and motor and sensory system interaction and disruption?

A

“interaction of motor commands with sensory information coming from propriorecpetors and external receptors is key”

  • movement disorders are the most frequent symptoms seen in neurological patients
  • most movement disorders can occurs either a disruption of motor pathways. Or also as a result of disruption of sensory pathways
  • -if any one of these 2x systems fail, the movement will suffer
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10
Q

What are the main receptors which control movement?

A
  1. Muscles spindles (monitor muscle length (L) and Speed of length changes: (dL/dt))
    - can detect vibration easily, or tiny stretches (micron)
  2. Golgi tendon organs (monitor changes in muscle tension)
  3. Pain receptors in the skin (can induce movement)–initiated e.g. withdrawal reflex
  4. Joint receptors (monitor position, signal hyperextension or hypoflexion at the joint to the CNS as not usual)-position of limbs
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11
Q

What are the 3x types of reflexes which are induced?

A
  1. Stretch reflex
  2. Revers/Inverse myotatic reflex
  3. Flexion/Withdrawl reflex, and the cross-extension reflex
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12
Q

Why are reflexes explored?

A
  1. learn how reflexes induce movement
  2. Clinical relevance in neurological disorders, when dealing with movement deficits, there are changes in reflexes
    - need to examine reflexes
    - some will be abolished, exaggerated and/or unstable
    - testing will give a clue as to what is happening
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13
Q

What are the 5x elements of Spinal reflex Pathways?

A

Somatic

  1. Receptors (that are engaged)
  2. Afferent (sensory) fibres
  3. Central synaptic relay(s)/connections
  4. Efferent (motor) fibres - coming out of brain
  5. Effectors (skeletal muscles)-target group of muscles. therefore not heart
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14
Q

Stretch reflex

A

myotatic reflex = tendon reflex = monosynaptic reflex (one synapse engaged)

  • only stretch reflex is monosynaptic- al other reflexes are polysynaptic (involve more than one synapse in CNS)
    1. Receptors (IN muscle spindles) detect : change L and dL/dt
    2. Afferent fibres: 1a
    3. Synaptic Relays: Ia afferents to a alpha MNs motor nurons (also 2nd synapse from MN to muscle)
  • even though “mono”synaptic - is referring to synapses in the Central nervous system
    4. Afferent fibres: Axons of a alpha MNs motor neurons
    5. Effectors muscles (extrafusal)
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15
Q

What are the 3x other names for stretch reflex?

A

Myotatic reflex
Tendon reflex
Monosynaptic reflex
-Knee Jerk

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16
Q

What are the components of the stretch reflex example of Knee Jerk?

A

Quadriceps

  • muscle spindle embedded within. receives motor innervation from gamma motor neurons. also has sensory fibre connection from central part of muscle spindle
  • afferent fibre= myelinated and fast conducting
  • information sent via AP action potentials
  • Dorsal Root ganglion contains cell bodies of all sensory neurons (from muscle spindles, temperature, pain, touch)
  • Peripheral axons outside of root of spinal cord
  • Central axon within root of spinal cord. synapse with alpha motor neurons
  • Alpha motor nuerons sends its axon to make synaptic end plate/contact with extrafusal muscle fibres

Examination hammer strikes tendon of quadriceps which goes around the kneecap

  • hit tendon as want to induce a tiny stretch of the muscle
  • this is enough to activate many of these muscle spindles in synchrony
  • and induce action potentials in Ia afferents. and evoke postsynaptic potentials in a Alpha motor neurons. will reach threshold, will trigger AP. cycle continues. Contraction of whole muscle/extrafusal muscle fibres
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17
Q

What are the properties of an afferent fibres?

A

Myelinated
fast conducting
Type 1A Afferent fibres = fastest conducting nerve fibres in body = 100ms (1 metre in 10 ms)

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18
Q

Can you resist a knee jerk?

A

no
is Involuntary
-exaggerated because of adrenlain

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19
Q

Stretch Reflex and Reciprocal Inhibition

A

Isn’t just contraction of Extrafusal muscles of stretching muscle
is also Parallel engagement of separate mechanism (Reciprocal inhibition of other muscles -are inhibited)
Additional synaptic relay : 1a afferents to 1a interneurons which Inhibits MNs innervating antagonists muscle

20
Q

What is the additional synaptic relay elements of the Stretch reflex and Reciprocal Inhibition relationship?

A

1a afferents to –> 1a (inhibitory) interneurons –> which INHIBITS MNNs motor neurons which innervated Antagonist muscles
-knee jerk /biceps
Biceps and antagonistic triceps
-Hit tendon of biceps, biceps will contract, and at same time triceps relaxes
-make sense because if you have movement in one direction, something has to give up (reciprocal inhibition)
-Reciprocal inhibition is a standard feature of all Flexor reflexes in the upper limbs and lower limbs
Note: One more “collateral” branch of 1a afferents, which contacts group of cells, and activate/excite neurons of the spinocerebellar tract. Sends signal to /activates CNS to the cerebellum and further
-sensory feedback, telling brain what is going on at Spinal cord level

21
Q

How does Reciprocal inhibition occur?

A

-Biceps and Triceps example
Muscle spindle in biceps –>
1a afferent of muscle spindle –> dorsal root ganglion contains neuron cell body –> excitatory synapse of alpha motor neurons
–> alpha motor neuron axon going to extrafusal muscle fibres

1a afferent has small colateral branch which makes synaptic contact with 1 a inhibitory interneuron cell.
1a inhibitory interneuron send inhibitory synapse (GABA/glysene) to a group of motor neurons that innervate triceps (antagonist)

-2x loops: contraction of biceps. and very soon/almost simultaneously, via the inhibitory interneuron, there is inhibition of alpha motor neuron activity (hyperpolorised if was firing action potential before (baseline tone)).
AP would stop. there would be no more muscle tone. relaxation of triceps muscle

22
Q

What are the Commonly tested stretch reflexes and their segments?

A
  1. Jaw jerk (5th cranial nerve)
  2. Biceps jerk (C5,6)
  3. Triceps jerk (C7)
  4. Finger-flexion reflex (C8)
  5. Knee jerk (L3,4)
  6. Ankle jerk (S1)
23
Q

Why is it often not enough to test just one reflex?

A

Test several as each reflex closes/has its reflex pass through different segments of spinal cord or brain stem
-segments = where reflex closes
Test multiple to very quickly conclude about the integrity of the reflex pathway
-if most reflexes are interacting and one isnt, then there may be an interruption of transmission at a particular level

24
Q

Why do you use simple examination tools for testing reflexes/jerks, and not advanced technology?

A

doctors are irreplaceable
most important examination and diagnostic tool are our eyes, hands and our brains
Clinical contact with patient, when we look, touch,hearing, manipulate patient is extremely important first step of diagnosis process
-Technology provides sophisticate imaging tools (where spinal cord lesion occurs) but are expensive, and it takes time to get results
-during first doctor- patient you need to have a plan of action and human features allows you to over technology

25
Q

What are the roles of Gamma (y) motor neurons?

A

Extrafusal muscle fibres , innervated by alpha motor neurons.
The single element= muscle spindle
muscle spindles are in PARRALLEL to extrafusal muscle fibres. are also smaller and embedded in the muscle
-when whole muscle extends/is stretched, the muscle spindles will be stretched.
-When whole muscle contracts, the muscle spindles will become flaccid/relax, and assume a different tragectory
Sensory parts of muscle spindle is located in the Cetnre of the muscle spindle. –> you Have Anular spinal spiral like endings of 1a afferent
-when muscles are stretched, because the muscle spindles are mechanoreceptors (sensitive to stretch), there will be a burst of AP action potentials to be innervated
-the Axon of gamma motor neurons activate the contractile elements in the muscle spindles located only in the periphery.
–activation via ACh. will be contraction of peripheral parts of the muscle spindles

26
Q

Where are the sensory part of muscle spindles located?

A

in the centre of the muscle spindle

Anular spinal spiral like endings of 1a afferent in the Centre of the muscle spindle

27
Q

Where are the contractile elements of the muscle spindles?

A

in the Periphery
the Contractile elements of muscle spindles are ONLY located in the Periphery
-they’re activated bia ACh release
–> these peripheral parts(of the muscle spindle) will then contract

28
Q

What happens when you have the contraction of a muscle?

A

Commands from Forebrain and sent to Alpha motor neurons
muscle contracts- if load isnt to big
Muscle contraction= isotonic= muscle shortens
Peripheral contractile parts of the muscle spindle becomes flaccid/completely relaxed
and the action potentials which are normally initiated (from the centre) have seized
-as there is no longer any stretch of the muscle spindle

WithOUT Gamma Motor neurons:
As a result of activation of alpha motor neuron, through AP entering through the Alph motor neuron, and contracting extrafusal muscle fibres. Muscle spindles become silent, and stops sending any information to the CNS (including spinalcerebro tract cells to the forebrain)
-the CNS wouldnt know what is happening to the muscle during contraction, as there is no longer any sensory feedback loop

WITH Gamma motor neurons:
contraction of extrafusal muscle fibres, causing shortening of the whole muscle. Simultaneously there are excitatory commands(ACh)/AP action potential coming from Gamma (y) motor neurons MNs. This leads to contraction of Intrafusal msucle fibres, which restore the stretch of the central part of the muscle spindle- theyre still generating action potentials in the 1a afferents
-Interplay between activity of alpha MN and gamma MN. Interplay allows information to be fed to the brain via 1a afferents, even if the muscle contracts as a whole.

“Gamma (y) motor neurons MNs keep muscle spindles at appropriate lengths so that they REMAIN ACTIVE during muscle shortening, which is evoked by alpha motor neurons”
-This implies that there is a co-activation of alpha and gamma motor neurons by descending pathways (these 2x systems of the brain are almost simultaneously activated by descending pathways)

29
Q

What happens if the load placed upon a muscle is too large?

A

Isometric contraction

-actually not much change of the Length, but only a change in the Tension

30
Q

What type of contraction is muscle contraction with a sufficient load?

A

Isotonic contraction

  • Load is not too large
  • muscle shortens
31
Q

What is the relationship between Alpha and Gamma motor neurons and activation?

A

There is Co-activation of alpha MN and gamma MN (the 2x systems) via Descending pathways
-these 2x systems of the brain are almost simultaneously activated b descending pathways

32
Q

Golgi tendon Organ

A

-involved in Reverse Myotatic Reflex
Sensory receptors located in the TENDON (not the muscle itself)
-receptors located in all tendons
-parallel to belly of muscle
-mechanoreceptors (activated due to stretch)
When activated leads to activation/AP action potentials conducted in Sensory afferents (1b), travels via dorsal root ganglion cell, and there is a release of Glutamate at the synapse of 1b Inhibitory Interneurons.
Ib interneurons are activated, and the GABA/glycene release with Hyperpolorise cell bodies of alpha motor neurons, causing the APs to stop. The muscle will relax.

-Revers myotatic reflex is when you have a stretch of a muscle, which may lead to a relaxation of a muscle (Reverse myotatic reflex is Reverse to tendon/myotatic reflex)

33
Q

What is the relative speed of conduction between Afferents 1a and 1b?

A

Sensory afferents 1b conduct action potentials Slower

34
Q

What reflexes occur in a Golgi tendon organ?

A

Revers Myotatic reflexes

35
Q

What is the Reverse Moyotatic/Tendon reflex?

A

Stretch of a muscle, which may lead to a relaxation of a muscle (Reverse myotatic reflex is Reverse to tendon/myotatic reflex)
Receptors: Golgi tendon organs (in series/parallel to muscle)
Afferens: 1b fibres
Synaptic relays: 2x synapses = disynaptic reflex
1b afferents to 1b INTERneurons which INhibits a alpha motorneurons MNs
Efferents: axons of a alpha MN motor neurons
Effectors: muscles
Under extreme conditions this reflex Protects muscle from overload
-if there is too much stretch of muscle, muscle could tear. This Reverse myotatic reflex kicks in, and inhibits the contraction of muscle to avoid tear/damage.
- at a certain point the muscle gives up. despite will to activate, the muscle reflex takes over and relaxes the muscle
Physiological role of preventing muscle from excessive tension and possibly damage

Normal function: to maintain muscle tension in optimal range

  • threshold for activation was lower than believed. Receptors can be engaged during physiological contractions
  • when tension is too high, they try to reduce the tension
  • when the tension drops too low then it removes inhibitory inhibition and the tension comes back
36
Q

What type of reflex is the Reverse myotatic reflex in relation to its synapses?

A

Disynaptic reflex

-has 2x synapses in CNS

37
Q

What is the physiological role of Reverse Myotatic Reflexes under extreme conditions?

A

Under extreme conditions this reflex Protects muscle from overload
-if there is too much stretch of muscle, muscle could tear. This Reverse myotatic reflex kicks in, and inhibits the contraction of muscle to avoid tear/damage.
- at a certain point the muscle gives up. despite will to activate, the muscle reflex takes over and relaxes the muscle
Physiological role of preventing muscle from excessive tension and possibly damage

38
Q

What is the normal function of Reverse myotatic reflexes?

A

to maintain muscle tension in optimal range

  • threshold for activation was lower than believed. Receptors can be engaged during physiological contractions
  • when tension is too high, they try to reduce the tension
  • when the tension drops too low then it removes inhibitory inhibition and the tension comes back
39
Q

Flexion (Flexor/Withdrawl) Reflex

A

Nociceptor reflex (pain- remove from hot or sharp)
Evokes a FAST withdrawl of limb from a nociceptive stimulus
Complex pathway: When pain afferents enter spinal cord, dont just go to 1x segment, but harbourise and enter nerve cells in 2-4 segments.
=shows is not a response of a single muscle, but of co-ordinated response of a group of muscle
-excitatory neurons involved in multisegmental level which activates motor neurons contolling flexors
Protecting reflex (remove from pain)
Person steps on glass. Nociceptor stimulus/pain receptor stimulus.
Activation of Pain afferens, which go through dorsal root ganglion cell, and enter spinal cord.
Activation of flexors (physiological muscles are defined(e.g. flexor) by how they respond to the withdrawl reflex). Physiological flexors will always contract, and physiological extensors will often relax.
Flexion of knee joint due to contraction of lower limb hamstring muscles and also to leg Gastrocnemius and soleus
=foot is withdrawn from nociceptive stimulus

40
Q

What is a way of testing the depth of general anaethesia?

A

When there is no response to painful stimulus, there is the withdrawl reflex

  • Pinch animals Tail/Hind limb
  • see whether there is a withdrawl
  • No withdrawl if there is an appropriate level of anaethesia

Surgery, anaethesiologist.
-surgeon piercing skin with scalpel, which is a very painful stimulus. Doesnt want any reflexes/contraction of muscles around. General level of anaethesia has to be high, to prevent this reflex

41
Q

How are the Lower limb hamstring muscles AND the leg gastrocnemius and soleus ALL affected by the Flexion Flexor/Withdrawl Reflex?

A

Complex pathway: When pain afferents enter spinal cord, dont just go to 1x segment, but harbourise and enter nerve cells in 2-4 segments.
=shows is not a response of a single muscle, but of co-ordinated response of a group of muscle
-excitatory neurons involved in multisegmental level which activates motor neurons contolling flexors

42
Q

What does a Flexion Flexor/Withdrawal reflex evoke?

A

evokes a fast withdrawal of a limb from a Nociceptive stimulus

43
Q

What are the 5x elements of Flexion Flexor/Withdrawl reflex?

A

Receptors:nociceptors
Afferents: Type III and IV fibres (slowly conducting and some unmyelinated whilst others are myelinated) belong to type 3 and 4. Pain afferents are slowly conducting -pain may be slow, but it will get you). Most difficult form of pain is CHRONIC continuous pulsing pain, rather than acute pain. doesn’t matter about speed of conduction velocity, the brain is still receiving continuous information whether it comes fast or slow- there is still suffering
Synaptic relays: to Excitatory INTER neurons which excite flexor alpha MNs motor neurons (afferents project to multiple spinal segments) -excite multiple muscles to flex
Efferents: axons of a alpha MN motor neurons
Effects: Flexor muscles

44
Q

What are the features of Pain afferents?

A

Slowly conducting
can be either myelinated or unmyelinated
afferens belong to either type 3 or 4 fibres (III or IV)
-pain may be slow but it will get you
-Most difficult form of pain is CHRONIC continuous pulsing pain, rather than acute pain. doesn’t matter about speed of conduction velocity, the brain is still receiving continuous information whether it comes fast or slow- there is still suffering

45
Q

The flexion withdrawal and Crossed-extension reflex

A

If you lift one leg, unless you have support of other leg, that cut leg would fall down
Therefore Flexion withdrawal reflex works in connection/harmony with Crossed-extension reflex
-Significance for maintaining balance when nociceptive receptors in a foot are activated

46
Q

What is the significance for the Crossed extensor reflex?

A

activated after Flexion (flexor/withdrawal) reflex

Maintains balance when nociceptive receptors in a foot are activated

Musculoskeletal Module (27 decks)

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