Reflexes

Question 1

what are the three types of movement

Answer 1

involuntary actions
semi automatic actions
voluntary actions

Question 2

what is involved in involuntary actions

Answer 2

these are reflexes that are centred in the spinal cord and brain stem that have no conscious element

Question 3

what is the reflex action centred on

Answer 3

spinal cord for the spinal nerves and cranial nerves are in the brainstem

Question 4

what type of pathway is involved in reflexes

Answer 4

monosynaptic circuit

Question 5

what is the speed of reflexes

Answer 5

they are rapid, and have short latency

Question 6

what is latency

Answer 6

the time between the stimulus and the response

Question 7

what is the common final pathway of a reflex

Answer 7

motor neurons

Question 8

where are somatic motor neuron bodies found

Answer 8

the spinal cord

Question 9

where are cranial nerve cell bodies found

Answer 9

brainstem

Question 10

what activates motor neurons in a reflex

Answer 10

various brain regions and various peripheral receptors

Question 11

what is stimulated in the knee jerk response

Answer 11

group 1a muscle fibres that link the dorsal and ventral roots at spinal level

Question 12

what initiates the reflex response

Answer 12

activation of mechanoreceptors that are muscle spindles in the belly of the muscle that respond to the stretch of the muscle itself

Question 13

what is the muscle afferent in reflexes

Answer 13

1a

Question 14

are mechanoreceptors in the muscle always active

Answer 14

yes - there is always a steady rate of activity from mechanoreceptors to give an indication of the tone of the muscle itself. when they are stretched further than what is normal, there is generation of action potential

Question 15

what spinal afferents alwyas active when muscle is contracting

Answer 15

no

Question 16

describe the knee jerk reflex

Answer 16

• mechanical stimulus applied to the patella tendon in the knee
• tendon pulls on the quadriceps to activate muscle spindles
• generation of action potential that is conducted along the a alpha axon
• into the ventral horn of the spinal cord
• synaptic transmission between the central terminals and the motor neurons they are innervating
• action potential conducted along motor axon as it exist via the ventral roots

Question 17

why are reflex actions so short

Answer 17

the 1a alpha axon is large and has strongly myelination.
only involves one synapse

Question 18

list the components of the stretch reflex pathway in order

Answer 18

• stimulus
• receptor activation
• stimulus transduction
• action potential conduction along sensory axon
• synaptic transmission
• motor neuron recruitment, action potential conduction along motor axon
• synaptic transmission for effector recruitment
• response

Question 19

what is the muscle efferent axon in reflexes

Answer 19

a alpha, same as the sensory afferent

Question 20

describe the reflex pathway for the jaw jerk reflex

Answer 20

• hammer tap to chin
• stretches spindles of jaw elevator muscles
• action potentials conducted along group 1a muscle afferents to brainstem
• monosynaptic activation of motor neurons of jaw elevatory muscles
• axon potentials travel along the motor axon
• jaw elevatory muscles contract
• jaw jerk upward, mouth closes

Question 21

what are the jaw elevator muscles

Answer 21

masseter
temporalis
medial pterygoid

Question 22

describe the reflex pathway of the ankle jerk reflex

Answer 22

• hammer tip to achilles tendon
• stretches spindles within gastrocnemius
• action potentials are conducted along group 1a muscle afferents to the spinal cord
• monosynaptic activation of motor neurons of the gastrocnemius muscle
• axon potentials travel along the motor axon
• gastrocnemius muscle contracts
• foot extends

Question 23

what is plantar extension

Answer 23

the extension of the foot

Question 24

what is the measure of electrical activity within skeletal muscle

Answer 24

bidirection of the electromyogram

Question 25

what are the key features on the myogram to look for when looking at reflexes

Answer 25

latency and amplitude of response

Question 26

why is the latency for the jaw jerk reflex less than that for the ankle jerk reflex

Answer 26

the neural pathway for the jaw jerk reflex is shorter than that for the ankle jerk

Question 27

what is the amplitude of a reflex

Answer 27

the measure of electrical activity in skeletal muscle

Question 28

why is the amplitude for the jaw jerk reflex smaller than in the ankle jerk

Answer 28

the masseter is a small muscle and there are less muscle fibrils that have to be recruited.

Question 29

what is the muscle activated in the ankle jerk reflex

Answer 29

the gastrocnemius

Question 30

which neurons are involved in maintenance of posture and muscle tone

Answer 30

proprioceceptor endings group 1a muscle afferents homonymous motor neurons

Question 31

which receptors are involved in cutaneous reflexes

Answer 31

mechanoreceptor endings and nociceptor endings

Question 32

what are the protection mechanisms of somatic reflexes

Answer 32

- escape mechanism - prevention of muscle overloading - prevention of inadvertent ingestion of a foreign body - digestive aid

Question 33

what kind of pathway is the flexion withdrawal reflex

Answer 33

disynaptic

Question 34

describe the flexion withdrawal reflex

Answer 34

- interneuron is recruited - interneuron axon splits and sends a branch to the higher centres for the perception of pain to reinforce that input via the spinothalamic pathway - input projects directly to the motor neurons to initiate the withdrawal reflex

Question 35

what are golgi tendon organs

Answer 35

a population of nerve endings in the tendon that prevent muscle overloading, that give rise to group 1b muscle afferents

Question 36

how are golgi tendon organs activated

Answer 36

stretching and contraction of the muscle itself, they act to prevent overwork of the muscle by recruiting 1b afferents to inhibit the motor neurons that innervate the muscle group

Question 37

what is the inverse stretch reflex

Answer 37

this is when the golgi tendon organ inhibit the contraction of muscle to prevent it overloading

Question 38

what is another name for the inverse stretch reflex

Answer 38

the inverse myotactic reflex

Question 39

describe how muscle overloading occurs in the rest of the body

Answer 39

there are no golgi tendons in the jaw muscles bit force is instead controlled through the loading of mechanoreceptors in the periodontal ligament the afferents inhibit jaw elevator muscle motor neurons

Question 40

why is it important to consider periodontal ligament when anaesthetising a patient

Answer 40

anaesthetising the sensory afferents in the periodontal ligament can increase the bite force of the patient which can damage their jaw as they are unaware of how hard they are biting down

Question 41

what activates the pharyngeal refledx

Answer 41

mechanoreceptor afferents from the posterior part of the tongue and soft palate there is stimulation of sensory fibres from the glossopharyngeal nerve and trigeminal nerve which terminate in the brain stem

Question 42

where do the IX and V sensory afferents terminate

Answer 42

the brain stem is the SpVn

Question 43

what happens once IX and V terminate in the SpVn

Answer 43

interneurons will project from here to go to the nucleus ambiguus to the vagus nucleus the vagus afferents will terminate and innervate muscles

Question 44

what contracts in the gag reflex

Answer 44

there is mass contraction of both sides of the posterior oral and pharygneal musculature

Question 45

what does SpVn mean

Answer 45

the spinal trigeminal nucleus in the brain stem

Question 46

why is there bilateral contraction in the gag reflex even if stimulus is on one side

Answer 46

to increase the chance of expelling the foreign particle

Question 47

what is the stimulus of the salivary reflex

Answer 47

- gustatory stimuli - visual - olfactory - chewing forces

Question 48

what is the outcome of the salivary reflex

Answer 48

increased salivary flow