Neuromuscular and spinal cord final

Question 1

Synapses between

Answer 1

Neurones and neurones

Neurones and muscle

Question 2

Contact ratio for which N-N N-M:

1000: 1
1: 1

Answer 2

1: 1 N-M
1000: 1 M-M

Question 3

Presynaptic terminal is also known as

Answer 3

bouton

Question 4

Synaptic cleft length

Answer 4

10-50nm

Question 5

How can the membrane potential of the post synaptic neurone be altered

Answer 5

It can be made less negative – i.e. be brought closer to threshold for firing; this is an excitatory post synaptic potential (EPSP)

OR

It can be made more negative – i.e. be brought further away from threshold for firing; this is an inhibitory post synaptic potentials (IPSP)

EPSPs and IPSPs can also summate

Question 6

NMJ

Answer 6

A specialised synapse between the motor neuron and the motor end plate, the muscle fibre cell membrane

Question 7

Activation of the neuromuscular junction

What happens at rest

Answer 7

When an action potential arrives at the MNJ, Ca2+ influx causes ACh release. ACh binds to receptors on motor end plate.
Ion channel opens – Na+ influx causes action potential in muscle fibre.

At rest, individual vesicles release ACh at a very low rate causing miniature end-plate potentials (mEPP)

Question 8

Alpha motor neuron-innervate? from ?

Activation causes

Answer 8

lower motor neurons of the brainstem and the spinal cord

They innervate the (extrafusal) muscle fibres of the skeletal muscles

muscle contraction

Question 9

Alpha motor neuron in anterior ventral horn where are flexors, extensors, proximal, distal in

Answer 9

Flexors are found more dorsally
Extensors found more anteriorly
Proximal musculture, alpha motor neurones found medially
Distal musculuture, alpha motor neurones found laterally

Question 10

Motor unit consists of

Answer 10

Motor neuron and muscle fibres it innervates

Question 11

Types of motor unit

Answer 11

Type 1:S-Slow, Low tension
Type 2A: FR- Fast, Fatigue resistant, moderate tension
Type 2B: FF- Fast, fatiguable, High tension

Question 12

Dendritic trees of each

Answer 12

Slow type:
 Small dendritic tree
Fast, fatigue resistant: Larger dendritic tree
Fast, fatiguable: 
Larger dendritic trees

Question 13

Two ways in which brain regulates the force a single muscle can produce

Answer 13

Recruitment

Rate coding

Question 14

What is size principle in recruitment

What does this allow

Answer 14

Smaller units are recruited first (these are generally the slow twitch units). S->FR->FF
As more force is required, more units are recruited.
This allows fine control (e.g. when writing), under which low force levels are required.

Question 15

Rate coding

Summation in rate coding occurs when to allow

Answer 15

As the firing rate increases, the force produced by the unit increases.
Summation occurs when units fire at frequency too fast to allow the muscle to relax between arriving action potentials.

Question 16

Neutrophic factors are

Function

Answer 16

Type of growth factor

Prevent neuronal death and promote growth of neurons after injury

Question 17

Does motor neurone have an effect on the properties of the muscle which it innervates

Answer 17

yes. If a fast twitch muscle and a slow muscle are cross innervated, the soleus becomes fast and the FDL becomes slow.

Question 18

Reflex

Answer 18

a nerve impulse passing inward from a receptor to a nerve centre and then outward to an effector (as a muscle or gland) without reaching the level of consciousness

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

Question 19

Components of a reflex arc

Answer 19

1. SENSORY RECEPTOR
2. SENSORY NEURON– dorsal root ganglion =cell body of sensory neuron And into dorsal horn of Spinal cord
3. INTEGRATING CENTER-One or more regions within the CNS that relay impulses from sensory to motor neurons
4. MOTOR NEURON from ventral horn, ventral root
5. EFFECTOR

Question 20

Monosynpatic (Stretch) reflex

Answer 20

1. Stretching stimulates SENSORY RECEPTOR
2. Within dorsal horn info goes up to brain (but no input from brain) and INTEGRATING CENTER to motor etc. cause contraction

Relax antagonistic muscle
Inhibitory interneuron
Receives input from sensory neuron

Hoffmann (H-) Reflex= electrically stimulated monosympatic reflex

Question 21

3 different conditions in which fibre types can change properties

Answer 21

1) Following training: Type2b to Type 2a
2)severe deconditioning or spinal cord injury. –Type I to II
Microgravity during spaceflight results in shift from slow to fast muscle fibre types
3)Ageing associated with loss of type I and II fibres but also preferential loss of type II fibres. This results in a larger proportion of type I fibres in aged muscle (evidence from slower contraction times).

Question 22

List 3 Extrapyramidal tracts

Answer 22

Rubrospinal tract
Reticulospinal tract
Vestibulospinal tract
Olivospinal tract

Question 23

Rubrospinal tract function

From where to where

Answer 23

Automatic movements of arm in response to posture/balance changes

Red nucleus in midbrain to spinal cord

Question 24

Reticulospinal tract function

Answer 24

Coordinate automated movements of locomotion and posture (e.g to painful stimuli)

Question 25

Vestibulospinal tract function

Answer 25

Regulates posture to maintain balance and facilitates mainly alpha motorneurones of the postural, anti-gravity (extensor) muscles

Question 26

Polysynaptic reflex-Flexion withdrawal

Answer 26

Stimulation of flexor muscle to allow withdrawal of leg
More than one motor unit and involved in innervation of several muscles stimulation
sometimes stimulation occurs above and below level of stimulation of spinal cord to promote contraction of muscle
excitatory innervation

Question 27

Crossed extensor

Answer 27

Inhibition across midline for relaxation of antagonistic muscle to maintain gait – crossed extensor

Question 28

Example of supraspinal reflex

Answer 28

Jendrassik manoeuvre

Clench teeth or making a fist when having patellar tendon tapped will make reflex action stronger

Question 29

Supraspinal reflex acton upon which reflex

What normally dominates in normal conditions

Decerebration results in

Answer 29

Higher centres of CNS exert inhibitory and excitatory regulation upon stretch reflex.

Inhibitory control dominates in normal conditions

Decerebration reveals the excitatory control from supraspinal areas– no inhibitory input

Rigidity and spasticity can result from brain damage giving over-active or tonic stretch reflex

Question 30

Supraspinal reflexes: Higher centres activate what to influence reflexes

Answer 30

Activating alpha motor neurons-ventral horn
inhibitory interneurons
Activating propriospinal neurons-proprioceptive info
Activating gamma motor neurons-interfusal to tense or not– innate from afferent input
Activating terminals of afferent fibres

Question 31

Supraspinal reflexes: Higher centres and pathways involved

Answer 31

Higher centres & pathways involved are:
Cortex – corticospinal (fine control of limb movements, body adjustments)
Red nucleus – rubrospinal (automatic movements of arm in response to posture/balance changes)
Vestibular nuclei – vestibulospinal (altering posture to maintain balance)
Tectum – tectospinal (head movements in response to visual information).

Question 32

Extrafusal muscle fibers

Answer 32

Under control of alpha motor neurones voluntary contraction of muscle
have sensory axons and respond to changes in lengths of muscle fibres and gamma motor neurones supply intrafusal- reacting to activity of muscle itself

Question 33

What if the knee is extended and the muscle goes slack?

Answer 33

The spindle is shortened to maintain its sensitivity

THIS IS THE GAMMA REFLEX LOOP

Question 34

Hypereflexia- inhibition of

Answer 34

stroke
loss of descending pathway inhibition
babinski sign–toes should curl not splayed
clonus

Question 35

Hyporeflexia

associated with what

Answer 35

Below normal or absent reflexes

Mostly associated with lower motor neuron diseases