P: Reflexes

Question 1

What is a reflex

Answer 1

An involuntary stereotyped but coordinated response to specific stimulus

Question 2

What is a muscle spindle

Answer 2

Stretch receptor

Question 3

What are golgi tendon organs

Answer 3

They are located at junction between tendon and muscle; sensitive to muscle force/tension

Question 4

Two classifications of reflexes

Answer 4

Somatic - voluntary
Autonomic - involuntary

Question 5

What root do afferent nerves enter the spinal cord (sensory nerve)

Answer 5

Dorsal root

Question 6

Name the 6 essential components of a reflex

Answer 6

Stimulus
Sensory receptor
Afferent nerve fibre
Synapse
Motor fibres
Effector organ

Question 7

What are spindle fibres made of

Answer 7

Intrafusal muscle fibres

Question 8

What is the orientation of intrafusal muscle fibres and what does this allow

Answer 8

Lie parallel to extrafusal fibres (main contracting fibres in muscle)
Therefore responds to length changes in the muscle

Question 9

What two types of tissue do intrafusal fibres have and where

Answer 9

Non contractile at centre
Contractile at the poles (ends)

Question 10

What are the two types of intrafusal fibres

Answer 10

Nuclear bag
Nuclear chain

Question 11

What do the primary (annulospiral) nerve endings do in the spindle

Answer 11

Type 1A afferents
Detect amount of muscle stretch and rate of stretching (dynamic response)

Question 12

What are primary nerve endings

Answer 12

Type 1A afferents
Myelinated , rapidly conducting neurons
Faster and larger than type 2
Detect muscle stretch + rate of change of stretching

Question 13

What do the secondary flower spray endings do

Answer 13

static response

Question 14

Secondary flower spray endings properties

Answer 14

Type 2 afferents
Myelinated
Slower conduction than type 1
Respond to maintained stretch

Question 15

What do primary sensory nerve endings innervate

Answer 15

Both nuclear bag and chain fibres

Question 16

What do the secondary flower spray endings innervate

Answer 16

mainly nuclear chain fibres

Question 17

What is the motor innervation of spindle and where

Answer 17

Gamma motor neurons
Innervate contractile fibres at the poles

Question 18

What is meant by the spindle being unloaded or slack

Answer 18

Occurs after reflex contraction
Over relaxed /under stretched

Question 19

How is a slack spindle reloaded

Answer 19

Gamma motor neurons cause contraction of intrafusal(spindle) fibres
Tightens the spindle
Allows it to continue to respond

Question 20

What’s the inverse myotonic reflex

Answer 20

Golgi tendon reflex

Question 21

What innervate the collagen of tendon

Answer 21

nerve terminals

Question 22

What happens if there’s excessive tension in contraction

Answer 22

GTO sends info to spinal cord via 1b afferents
Synapses with interneurons
Inhibition of contraction muscle
Reflex relaxation occurs

Question 23

Where are muscle spindle and stretch reflexes especially prominent

Answer 23

In anti gravity muscles
Neck muscles
Where fine control is required eg finger

Question 24

What does the GTO reflex prevent

Answer 24

Excessive force generation in a muscle

Question 25

What have a dampening/smoothing effect on jerky muscle movements

Answer 25

GTO and spindle fibres Important in feedback control of muscle length in response to a load and prevent jerky movement

Question 26

What's the most powerful reflex

Answer 26

Flexion (withdrawal) reflex

Question 27

What is the flexion reflex also called

Answer 27

Crossed-extensor reflex

Question 28

What information do dorsal columns carry

Answer 28

- Proprioception - Discriminative touch - Pressure + vibration sense.

Question 29

Spinothalamic tracts transmit information regarding:

Answer 29

- Pain - Temperature - Crude touch - Itch + tickle

Question 30

Difference between monosynaptic + polysynaptic reflexes

Answer 30

Monosynaptic - single synapse, no interneuron Polysynaptic - many interneurones connect afferent and efferent motor signals.

Question 31

Stretch reflex:

Answer 31

Sensory receptor --> muscle spindle Afferent nerve fibre --> IA afferents Synapse --> spinal cord Motor neuron --> alpha motor neuron Effector organ --> skeletal muscle contracts

Question 32

Tonic receptors vs Phasic receptors

Answer 32

1. Tonic receptors do not adapt to stimuli. Tonic receptors fire action potentials constantly. (pain) 2. Phasic receptors adapt to stimuli rapidly; eventually the individual no longer senses the stimulus. Phasic receptors fire action potentials when the stimulus is initiated and when the stimulus is removed. (seeing your nose, feeling clothes on skin)

Question 33

What are dorsal columns made of

Answer 33

Large myelinated axons

Question 34

Where do the dorsal columns enter the spinal cord and where do they go

Answer 34

Enter spinal cord at different levels via dorsal route Travel up the cord in a highly organised fashion

Question 35

What is somatotopic organization?

Answer 35

Correspondence of a specific point in the body to a specific point in the primary motor and sensory cortexes

Question 36

Where do dorsal columns synapse

Answer 36

In the medulla on either side of the dorsal column nuclei

Question 37

What are second order neurons also known as

Answer 37

Medial lemniscus

Question 38

Where do second order neurones synapse and become third order neurones

Answer 38

In the thalamus and travel up to the somatosensory cortex

Question 39

Definition of receptive field

Answer 39

The receptive field of a sensory neuron is an area of skin that, once stimulated, produces a response for that neuron. Receptive fields vary inversely with numbers of receptors in the area (bigger the area, smaller the number of receptors)

Question 40

What are the different types of sensory receptors and their modalities?

Answer 40

- Chemoreceptors --> chemical changes - Thermoreceptors --> warm and cold - Photoreceptors --> light - Mechanoreceptors --> pressure - Nocioreceptors --> noxious stimuli (generate pain) - Propioreceptors --> info about body and limb position

Question 41

How do sensory receptors transmit sensory information?

Answer 41

Action potentials are generated when generator potentials reach threshold for depolarization. Bigger the stimulus, greater number of APs generated. Generator potentials = local graded changes in membrane potential

Question 42

What order neurons are dorsal columns?

Answer 42

First order neurons

Question 43

Damage to lower motor neurone?

Answer 43

Reduced stretch reflexes & flaccid paralysis

Question 44

Physiological benefit of stretch reflex

Answer 44

Muscle tension, posture maintenance

Question 45

Name the sensory receptor for stretch reflex + what stimulates it?

Answer 45

Mechanoreceptors - length changes in muscle

Question 46

Define gamma motor neuron

Answer 46

Innervates intrafusal fibres of muscle spindle

Question 47

What stimulates GTO receptors

Answer 47

Proprioceptors detect muscle contraction