spinal reflexes

Question 1

what is a reflex?

Answer 1

any response that occurs automatically without conscious effort

Question 2

what is an example of an everyday reflex?

Answer 2

-touching a hot plate
-the person docent know the plate is hot and immediately pulls their hand away

Question 3

what is a monosynaptic reflex?

Answer 3

a monosynaptic reflex involves only one synapse between sensory and motor neurons.

Question 4

what is a polysynaptic reflex?

Answer 4

A polysynaptic reflex is a type of reflex arc in which signals travel across multiple synapses (connections between neurons) before producing a response

Question 5

what are the components of a reflex arc?

Answer 5

-stimulus
-sensory / afferent neuron
-integration centre
-motor / efferent neuron
-effector - muscle

Question 6

what are 3 examples of sensory receptors?

Answer 6

-exteroceptors
-proprioceptors
-interoceptors

Question 7

describe exteroceptors

Answer 7

-located on the skin and sense organs
-they respond to external stimuli
-carry info about temp, pressure etc

Question 7

describe proprioceptors

Answer 7

these receptors are located in muscles eg muscle spindles, tendons and joints
-send information about position of the muscle eg length of muscle, tension

Question 8

describe interoceptors

Answer 8

-sensory receptors on the internal organs
-send info about pain, stretching of internal organs

Question 9

what are the 2 main sensory receptors located on muscles and tendons?

Answer 9

-muscle spindles
-golgi tendon organs

Question 10

what do muscle spindles carry info about?

Answer 10

length / rate of change in length of muscle

Question 11

what do Golgi tendon organs carry info about?

Answer 11

-tension/ rate of change of tension in muscle / tendon

Question 12

what id the area for integration in the CNS in a reflex arc?

Answer 12

-brain or spinal cord receives , processes and integrates incoming sensory info and then issues command to effectors

Question 13

what are the functions of the spinal cord in relation to the reflex arc?

Answer 13

-link for transmission between brain and PNS
-integrates reflex activity between afferent input and efferent output without involving the brain

Question 14

how do afferent sensory fibres enter the spinal cord & where are their cell bodies located??

Answer 14

through the dorsal root
-CB’s located in the dorsal root ganglion

Question 15

what are the effectors in the reflex arc?

Answer 15

-the organs which respond by doing something ie executing the response
-in somatic NS - effectors are skeletal muscle and in the ANS the effectors are cardiac, smooth muscle etc

Question 15

what are interneurons responsible for?

Answer 15

the distribution of sensory information and the co-ordination of commands within the CNS

Question 16

what are the only monosynaptic reflexes that occur in the body?

Answer 16

-stretch (myotatic) reflexes

Question 17

why are muscles always slightly contracting?

Answer 17

• if muscles relaxed completely they would over lengthen and too much time would be required to take up slack when a contraction was called for

Question 18

what is a stretch reflex ?

Answer 18

-type of reflex arc that occurs in response to stretching of a muscle.
-monosynaptic reflex / myotatic reflex

Question 19

describe how a stretch reflex works

Answer 19

• if a muscle undergoes a stretch, the muscle spindles within the muscle detect the change in length
  -they signal this to the CNS through an afferent neuron
  -in the spinal cord, the afferent neurons synapse directly with the motor neurons that innervate the muscle
  -motor neurons send a signal to the effector muscle causing it to contract

Question 20

what are the 2 types of motor neurons?

Answer 20

-alpha - innervates extrafusal muscle fibres
-gamma - innervates intrafusal muscle fibres

Question 21

what is an example of a stretch reflex / monosynaptic reflex?

Answer 21

the knee jerk reflex
-the response to stretch of the quadriceps

Question 22

how does the knee jerk reflex work?

Answer 22

1. quads are briefly stretched by tapping the patellar ligament
2. stretched of muscle spindles in quads
3. activity in 1a sensory afferent fibres (associated with muscle spindles) increases
4. activity in alpha motor neuron supplying the quads increases
   -contraction of quads
   -knee extends and the leg kicks forwards

Question 23

what sensory receptor is the primary regulator of muscle tone?

Answer 23

the muscle spindle

Question 24

what does testing stretch reflex responses provide information about?

Answer 24

the integrity of these reflex responses - a normal response indicates that all neural and muscular components are functioning normally

Question 25

how are the stretch reflex responses graded?

Answer 25

0-4 -0 - reflex is absent -1- minimal -2- normal -3- brisk but normal -4 - very brisk often with clonus (hyporeflexia)

Question 26

what is hyporeflexia?

Answer 26

-hyporeflexia results if any part of the reflex pathway is damaged (from spinal to spinal cord to muscle)

Question 27

what are examines of conditions associated with hyporeflexia?

Answer 27

-lower motor lesions -muscular dystrophy - degenerative disease of skeletal muscle

Question 27

what is areflexia?

Answer 27

apparent loss of stretch reflexes

Question 28

what are the causes of areflexia?

Answer 28

-can be due to lack of clinical experience -any lesion of the reflex arc eg root lesion or peripheral neuropathy

Question 29

what is hyperreflexia?

Answer 29

results following damage to motor pathways from brain to spinal cord

Question 30

what are examples of causes of hyperreflexia?

Answer 30

-upper motor lesion -damage to motor areas of cerebral cortex -can occur after a stroke or brain tumour

Question 31

what is a Golgi tendon organ?

Answer 31

encapsulated sensory receptor inside muscle tendon -detects muscle tension -10-15 muscle fibres connected

Question 32

describe the Golgi tendon organ pathway

Answer 32

- if there is an increase in muscle tension -type Ib sensory nerves transmit signals to spinal cord & brain -alpha motor neuron is inhibited via inhibitory interneuron -prevents too much tension on muscle - controls force within muscles and stiffness of particular joints

Question 33

what is reciprocal innervation

Answer 33

refers to the neural mechanism that coordinates the contraction and relaxation of muscles on opposite sides of a joint during movement -when one muscle contracts (agonist muscle), its antagonist muscle relaxes to allow smooth and coordinated movement.

Question 34

what are flexor withdrawal reflexes?

Answer 34

-polysynaptic withdrawal reflexes move a part of the body away from painful stimulation -protective responses -eg pulling hand away from hot plate

Question 35

what happens if you touch a hot plate? - flexor withdrawal reflex

Answer 35

-nociceptors in the hand are stimulated -sensory pathways synapse first on interneurons -motor neurons contacted by interneurons -biceps muscle contracts and the hand is pulled away -the triceps (antagonist) is inhibited

Question 36

what is a crossed extensor reflex?

Answer 36

-neurological reflex that occurs in response to a painful stimulus, typically involving withdrawal of a limb from the painful stimulus while simultaneously activating muscles on the opposite side of the body to support balance and posture. -eg standing on a piece of lego

Question 37

what is an example of reflexes that are voluntarily influenced and modified by higher brain centres?

Answer 37

-needle insertion during blood draw -brain sends IPSP via descending paths to bicep motor neurons and EPSP to triceps to keep arm from pulling away - as that is our normal response

Question 38

what are examples of learned/ acquired reflex?

Answer 38

-eg certain responses in music -eg sports - catching a ball, somer saults etc