spinal reflexes Flashcards

1
Q

what is a reflex?

A

any response that occurs automatically without conscious effort

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2
Q

what is an example of an everyday reflex?

A

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

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3
Q

what is a monosynaptic reflex?

A

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

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4
Q

what is a polysynaptic reflex?

A

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

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5
Q

what are the components of a reflex arc?

A

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

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6
Q

what are 3 examples of sensory receptors?

A

-exteroceptors
-proprioceptors
-interoceptors

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7
Q

describe exteroceptors

A

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

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7
Q

describe proprioceptors

A

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

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8
Q

describe interoceptors

A

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

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9
Q

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

A

-muscle spindles
-golgi tendon organs

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10
Q

what do muscle spindles carry info about?

A

length / rate of change in length of muscle

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11
Q

what do Golgi tendon organs carry info about?

A

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

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12
Q

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

A

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

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13
Q

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

A

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

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14
Q

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

A

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

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15
Q

what are the effectors in the reflex arc?

A

-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

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15
Q

what are interneurons responsible for?

A

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

16
Q

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

A

-stretch (myotatic) reflexes

17
Q

why are muscles always slightly contracting?

A
  • 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
18
Q

what is a stretch reflex ?

A

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

19
Q

describe how a stretch reflex works

A
  • 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
20
Q

what are the 2 types of motor neurons?

A

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

21
Q

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

A

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

22
Q

how does the knee jerk reflex work?

A
  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
23
Q

what sensory receptor is the primary regulator of muscle tone?

A

the muscle spindle

24
Q

what does testing stretch reflex responses provide information about?

A

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

25
Q

how are the stretch reflex responses graded?

A

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

26
Q

what is hyporeflexia?

A

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

27
Q

what are examines of conditions associated with hyporeflexia?

A

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

27
Q

what is areflexia?

A

apparent loss of stretch reflexes

28
Q

what are the causes of areflexia?

A

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

29
Q

what is hyperreflexia?

A

results following damage to motor pathways from brain to spinal cord

30
Q

what are examples of causes of hyperreflexia?

A

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

31
Q

what is a Golgi tendon organ?

A

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

32
Q

describe the Golgi tendon organ pathway

A
  • 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
33
Q

what is reciprocal innervation

A

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.

34
Q

what are flexor withdrawal reflexes?

A

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

35
Q

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

A

-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

36
Q

what is a crossed extensor reflex?

A

-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

37
Q

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

A

-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

38
Q

what are examples of learned/ acquired reflex?

A

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