Neuromuscular Junction + Spinal Chord

Question 1

What is EPSP?

Answer 1

It is an exitatory post synaptic potential

–> potential that makes membrane less negative (lower threshold for fiering)

Question 2

What is IPSP?

Answer 2

It is an inhibitory post synaptic potential

–> potential that makes membrane more negative (higher threshold for fiering)

Question 3

How do you call process of graded effects that occur at a post-synaptical membrane that determine the response?

Answer 3

Summation

Question 4

What is an alpha-motorneuron?

Answer 4

The lower motor neuron of the brainstem and spinal chord

Question 5

What/where does an alpha-motor neuron innervate?

What is the consequence?

Answer 5

They innervate the extrafusal (outside a muscle fibre) skeletal muscle

–> cause muscle contraction

Question 6

What is the motor neuron pool?

Answer 6

It contains all motor neurons that innervate one single, specific muslce

Question 7

How are the alpha motor neuron pools organised in the ventral horn of a spinal chord?

Answer 7

Question 8

Where are extensor and flexor motor neuron pools located in the ventral horn of the spinal chord?

Answer 8

Flexors are located more dorsally

Extensors are located more ventrally

Question 9

What is a motor unit?

Answer 9

The unit of a single motor neuron and all muslce fibres it innervates

Question 10

What is the smallest functional unit to produce force?

Answer 10

It is the motor unit

Question 11

How many muscle fibres does an average motor neuron innervate in a motor unit?

Answer 11

About 600

Question 12

Name the three types of muscle units

Answer 12

1. S (Type I), slow
2. FR (Type IIA), Fast, Fatigue resistant
3. FF (Type IIB), Fast, Fatiguable

Question 13

What are the propoerties of a Type I Motor unit?

Answer 13

It has slow conduction due to

• low diameter in cell body, axon
• small dendritic trees

–> slow twith, low tension but fatigue resistant

Question 14

What are the properties of a Type IIA muscle unit?

Answer 14

FR –> Fast, Fatigue resistant

1. larger cell body diameter, axonal diameter
2. larger dendritic trees

–> Fast twitch, moderate tension, resistance to fatigue

Question 15

What are the propoerties of a Type IIB motor unit?

Answer 15

FF –> Fast, fatigueable

1. Larger diameter, larger dentritic trees

–> Fast twitch, high force, high fatigue

Question 16

What are the two mechanisms by which force of muscle contraction it regulated?

Answer 16

1. Recruitement
   
   • targeted selection of motor neurons needed
2. Rate coding
   
   • the rate of AP fiering –> the higher the rate, the higher the force

Question 17

Explain the concept of muscle unit recruitment

Answer 17

Done via the “size principle”

• smaller units are requruited first (normalls T1 units)
• As more force is required, more units are recruited

–> Allows fine tuning for low-force movements (e.g. writing)

Question 18

Explain the concept of Rate coding in muscle force regulation

Answer 18

As the firing rate increases, the force produced by the unit increases

–> higher fiering rate= higher force

Question 19

Which changes do muslce fibres undergo during training?

Answer 19

There is a shift from TIIB to TIIA –> Fatiguable to Fatigue resistant

Question 20

What are the associated changes in muscle fibres with ageing?

Answer 20

Ageing is associated with both: loss of TI+II but more commonly TII

–> leading to slower muscle contraciton

Question 21

The corticospinal tracts in the spinal chord controll voluntary movement. What is collective name of tractrs that modulate/controll involuntary movements ?

Answer 21

They are collectively known as extrapyramidal tracts e.g.

1. Rubrospinal tracts
2. Vestibulospinal tract etc. for balance reflex, maintaining posture etc.

Question 22

What is the function of the extrapyramidal tracts?

Answer 22

Modulate involuntary movement via:

Automatic movements in responst to posture, balance changes, painful stimmuli etc.

Question 23

What is a reflex?

Answer 23

An automatic response to an external stimulus without involvement of conciousness (no brain involved)

An involuntary coordinated pattern of muscle contraction and relaxation elicited by peripheral stimuli.

Question 24

What are the componenets of a reflex?

Answer 24

Question 25

What is a monosynaptic reflex?

Answer 25

A simple relex response with a single synapse between afferent and efferent pathways --\> Simple stretch responses: e.g. knee jerk etc.

Question 26

What is a polysynaptic reflex?

Answer 26

A reflex that involved two or more synapses in the spinal chord, involves more muscles at different levels --\> Complex reflexes e.g. withdraw from sharp objects--\> also involves balance, weight change onto other leg to maintain balance etc.

Question 27

What is supraspinal control of reflexes?

Answer 27

Reflexes can be controlled by higher centres of the CNS 1. Normally inhibitory Rigidity and spasticity can result from brain damage giving over-active or tonic stretch reflex

Question 28

Through which ways can supraspinal reflex control be achieved?

Answer 28

Higher centres influence reflexes by: 1. Activating alpha motor neurons 2. Activating inhibitory interneurons 3. Activating propriospinal neurons 4. Activating gamma motor neurons 5. Activating terminals of afferent fibres

Question 29

What is intrafusal innervation of muscle fibres?

Answer 29

Innervation within the muslce cells consisting of 1. Gamma motor neurons 2. sensory axons

Question 30

What are the characteristics and function of gamma motor neurons?

Answer 30

They innervate the muscle intrafusally --\> respond intracellularly to muscle movement

Question 31

Name examples of centres that are involved in higher controll of reflexes

Answer 31

1. Cortex – **corticospinal** (fine control of limb movements, body adjustments) 2. Red nucleus – **rubrospinal** (automatic movements of arm in response to posture/balance changes) 3. Vestibular nuclei – **vestibulospinal** (altering posture to maintain balance) 4. Tectum – **tectospinal** (head movements in response to visual information).

Question 32

What is the difference between an intrafusal and extrafusal muscle fibre?

Answer 32

**Intrafusal** = skeletal muscle fibres that serve as sensory organs/proprioceptors which detect the amount and rate of change of the length of a muscle **Extrafusal =** standard skeletal muscle fibres which are innervated by alpha motor neurones

Question 33

What are signs and symptoms for a upper motor neuron lesion?

Answer 33

* HYPERREFLEXIA * CLONUS * BABINSKI’S SIGN

Question 34

Explain the structure of a NMJ

Answer 34

It is just a specialised Synapse 1. AP arrives 2. Ca2+ influx 3. Vesicle exocitosis 4. Release of Ach 5. Binds to recetors on Motor end plate 6. Cause Ion channel opening an Ca2+ influx 7. AP in mucle fibres

Question 35

What are neurotrophic factors?

Answer 35

Are a type of growth factor * Prevent neuronal death * Promote growth of neurons after injury

Question 36

What are the effects of neurotrophic factors on a motorunit?

Answer 36

They affect the function of the muscle fibres (by changing the innerveating nerve)

Question 37

What are pyramidal tracts?

Answer 37

Connection of the motor cortex with the periphery (spinal chord) --\> * corticospinal tracts (lateral and anterior) * Fine, precise movements

Question 38

What are the extra-pyramidal tracts?

Answer 38

Connecting different parts of the CNS (includieg Cortex but also Cerebellum etc.) to periphery * Mainly involved in gross, movement of proyimal muscles *

Question 39

What is the exact order in which different motor fibres are recruited?

Answer 39

Slow, fast fatigue resistant, fast fatigable