PBL1

Question 1

What are reflexes

Answer 1

Reflexes are involuntary motor actions triggered by sensory input

Question 2

what are the types of reflexes

Answer 2

Monosynaptic or polysynaptic

Question 3

what can reflexes be controlled by

Answer 3

Controlled by descending cortical input

Question 4

what are the neurones that are involved in reflexes

Answer 4

Sensory Neuron

• From the body to the spinal cord (dorsal horn)
• Utilises various different receptors

Motor Neuron

• Upper – brain to spinal cord (ventral horn)
• Lower – spinal cord (ventral horn) to muscle

Interneuron – connect sensory/motor neurons

Question 5

what are the exteroreceptors

Answer 5

• free endings
• meissners
• merkels
• pacinian
• Ruffini

Question 6

what do the exteroreceptros do

Answer 6

Free endings – mechano/chemo/thermos/nociception
Meissner’s – light touch
Merkel – texture (i.e. Braille)
Pacinian – vibration 
Ruffini – deep touch

Question 7

what are the proprioceptors do

Answer 7

Golgi Tendon – senses tendon stretch

Muscle Spindle – senses muscle length

Question 8

describe how a muscle spindle works

Answer 8

Modified muscle fibres sensing muscle stretching

• Activation (stretching) = motor nerve activation
• i.e. tendon reflexes (patellar, biceps, etc…)

Mediates sensitivity of tendon reflex
- Controlled by gamma fibres to muscle spindle

Question 9

describe how a Golgi tendon organ works

Answer 9

Located in tendons of muscles sensing muscle tension

Senses muscle tension

Prevents muscle damage from excess muscle contraction via inhibitory signalling to motor neuron

Question 10

what is the reflex pathway

Answer 10

Sensory Nerve → Dorsal Horn → Motor Nerve → Ventral Horn → Muscle
Polysynaptic has interneuron between s/m nerves

Question 11

which receptor is being testes by

• two point discrimination
• joint position sense
• vibrations sensation

Answer 11

• meissners
• spindle
• pacinian corpuscles

Question 12

describe the biceps reflex

Answer 12

Biceps tendon stretch = biceps contraction

Controlled by C5/6 (musculocutaneous)

Question 13

describe the supinator reflex

Answer 13

Brachioradialis tendon stretch = brachioradialis contraction

Controlled by C6/7 (radial nerve)

Question 14

describe the triceps reflex

Answer 14

Triceps tendon stretch = triceps contraction

Controlled by C7/8 (radial nerve)

Question 15

describe the achilles reflex

Answer 15

Stretch of Achilles = plantarflexor contraction

Controlled by S1/S2 Roots (tibial of sciatic nerve)

Question 16

describe the patellar reflex

Answer 16

Stretch of Patellar tendon = quadriceps contraction

Controlled by L3/L4 Roots (femoral nerve)

Question 17

what is reciprocal inhibition

Answer 17

Afferent neuron synapses with inhibitory interneuron connected to antagonising muscle
i.e. patellar reflex inhibits hamstrings

Question 18

what is an crossed extensor reflex

Answer 18

Flexor reflex causes extension of opposite leg

Sensory neuron innervates stimulates efferent fibres of contralateral side via interneuron

Question 19

what is the difference between extensor and flexor reflexes

Answer 19

Extensor reflexes tend to be faster

Due to extensors preventing falls

Question 20

what does electromyography do

Answer 20

it tests nerve function

Question 21

describe how electromyography works

Answer 21

Can derive compound motor action potentials
- Summation of multiple muscle fibres’ activity

Reduced CMAP indicates motor nerve issues

Question 22

what causes weak or absent reflexes

Answer 22

Issues in the Sensory Nerve
- i.e. GTO issues = NO REFLEX

Issues in the Motor Nerve
- i.e. femoral nerve issues = reduced quadriceps response

Issues in the Spinal Cord
- i.e. transection of spinal cord (i.e. Spinal shock in PBL2

Question 23

what does the lack of biceps and supinator reflexes indicate in the context of normal sensory nerve function

Answer 23

Sensory nerve is not problematic

Motor nerve issues – abnormal EMG

Question 24

what nerve roots are affected

Answer 24

Affects roots C5/C6/C7

Question 25

what could the patient be effected by

Answer 25

Cervical Spondylosis – radiculopathy in C-spine?

Question 26

Name and describe two of the three parameters that can be measured with electrophysiological tests for sensory or motor nerve function

Answer 26

• Action potential latency: Interval between stimulus onset & response onset
• Action potential duration: Time from action potential onset to termination; duration measures the dispersion of all components.
• Action potential amplitude: Proportional to the number & size of nerve fibres that are activated in SNAP. In CMAP shows how many motor units are recruited simultaneously.