Reflexes lab + briefing

Question 1

what is a reflex?

Answer 1

an involuntary stereotyped response to a stimulus

Question 2

what is a tendon jerk reflex?

Answer 2

reflex muscle contractions produced by muscle stretch

Question 3

describe the monosynaptic circuit for the knee jerk reflex

Answer 3

stimulus: tendon tap
This stretches muscle
activates muscle spindle receptors (important u get this right)
conduction along 1a sensory fibres
transmission occurs at synapse between 1a afferent and motor neuron
conduction along efferent motor fibre
neuromuscular transmission occurs (release of ACh)
contraction of muscle

Question 4

what are two aspects of PNS which if affected can lead to PNS disorders?

Answer 4

peripheral nerve conduction

neuromuscular junction

Question 5

what does a unilateral difference suggest in neurology?

Answer 5

mononeuropathy

Question 6

what does it suggest if there is reduced ankle jerk bilaterally but normal knee jerk?

Answer 6

polyneuropathy

Question 7

what is polyneuropathy?

Answer 7

damage or disease affecting peripheral nerves in roughly the same areas on both sides of the body,

Question 8

how does the jendrassik manoeuvre (of reinforcement) increase tendon reflex?

Answer 8

it makes the reflex response larger by activating more motor neurons and getting them to fire off and contribute to an action potential. (increases excitability to reach an AP)

Question 9

what does the stretch reflex act to maintain?

Answer 9

a constant muscle length and controls muscle tone

Question 10

what clinical effect do disorders in descending pathways cause in a patient?

Answer 10

spasticity and Hyperreflexia

Question 11

list 4 tendon jerk reflex tests

Answer 11

biceps, triceps, ankle and jaw jerk

Question 12

what is the normal plantar response and how does this differ in a positive babinski sign?

Answer 12

normal/babinski negative: toes down (flexion)

babinski sign: withdrawal of foot and fanning of toes

Question 13

what is a sensory homunculus?

Answer 13

a somatotopic map in the sensory cortex which represents the degree of sensitivity in different body parts

Question 14

how does two point discrimination differ over body surface?

Answer 14

when you touch two body areas that are further apart, you can tell them apart more distinctly. whereas if you touch two body areas that are closer together, it’s harder to tell them apart

Question 15

what is a receptive field?

Answer 15

this is the specific area which a sensory receptor branches to form and its peripheral endings monitor this area.

Question 16

what must 2 stimuli do to be perceived as separate?

Answer 16

they must activate different receptors in separate receptive fields

Question 17

list the segmental nerve root levels of:
jaw jerk 
biceps
trcieps
brachioradialis/supinator
knee jerk
ankle jerk

Answer 17

jaw = 5th cranial nerve
biceps: C5, 6
triceps: C6, 7, 8
brachioradialis/supinator: C5, 6
knee: L3, 4
ankle: S1, 2

Question 18

how do you elicit the plantar reflex?

Answer 18

firm stroke to the outer edge of the sole of the foot, stroking from heel forwards

Question 19

who is a positive babinski sign found in?

Answer 19

in neonates and adult with a lesion of the corticospinal tract

Question 20

what muscles contract in the ankle and knee reflex ?

Answer 20

ankle: gastrocnemius
knee: quadriceps femoris

Question 21

what is a sensory unit?

Answer 21

a single afferent nerve fibre with all the receptor endings to which it is connected