Reflexes lab + briefing Flashcards
what is a reflex?
an involuntary stereotyped response to a stimulus
what is a tendon jerk reflex?
reflex muscle contractions produced by muscle stretch
describe the monosynaptic circuit for the knee jerk reflex
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
what are two aspects of PNS which if affected can lead to PNS disorders?
peripheral nerve conduction
neuromuscular junction
what does a unilateral difference suggest in neurology?
mononeuropathy
what does it suggest if there is reduced ankle jerk bilaterally but normal knee jerk?
polyneuropathy
what is polyneuropathy?
damage or disease affecting peripheral nerves in roughly the same areas on both sides of the body,
how does the jendrassik manoeuvre (of reinforcement) increase tendon reflex?
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)
what does the stretch reflex act to maintain?
a constant muscle length and controls muscle tone
what clinical effect do disorders in descending pathways cause in a patient?
spasticity and Hyperreflexia
list 4 tendon jerk reflex tests
biceps, triceps, ankle and jaw jerk
what is the normal plantar response and how does this differ in a positive babinski sign?
normal/babinski negative: toes down (flexion)
babinski sign: withdrawal of foot and fanning of toes
what is a sensory homunculus?
a somatotopic map in the sensory cortex which represents the degree of sensitivity in different body parts
how does two point discrimination differ over body surface?
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
what is a receptive field?
this is the specific area which a sensory receptor branches to form and its peripheral endings monitor this area.
what must 2 stimuli do to be perceived as separate?
they must activate different receptors in separate receptive fields
list the segmental nerve root levels of: jaw jerk biceps trcieps brachioradialis/supinator knee jerk ankle jerk
jaw = 5th cranial nerve biceps: C5, 6 triceps: C6, 7, 8 brachioradialis/supinator: C5, 6 knee: L3, 4 ankle: S1, 2
how do you elicit the plantar reflex?
firm stroke to the outer edge of the sole of the foot, stroking from heel forwards
who is a positive babinski sign found in?
in neonates and adult with a lesion of the corticospinal tract
what muscles contract in the ankle and knee reflex ?
ankle: gastrocnemius
knee: quadriceps femoris
what is a sensory unit?
a single afferent nerve fibre with all the receptor endings to which it is connected
