1 - intro to the nervous system lecture

Question 1

what is perception?

Answer 1

a constructive process in the brian that depends upon information about stimuli (sensations) and the mental structure of the perceiver
- derived from sensory input from nocicpetors

Question 2

is pain subjective?

Answer 2

yes — it is a perception ie. a product of the brain
- the brains interpretation of sensory input means pain is subjective, therefore allowing different pain thresholds

Question 3

what are some morphological features of a neurone?

Answer 3

Question 4

what are the 4 reflex types?

Answer 4

• stretch aka. monosynaptic
• inhibitory
• flexor
• crossed extensor

Question 5

what is a joint?

Answer 5

where 2 bones (or other hard surfaces) connect in the body:
- some joints allow movement (eg. hip, elbow)
- others lack movement (eg. sutures between skull bones)

Question 6

tendons vs. ligaments

Answer 6

tendons — bind muscle to bone
ligaments — bind bone to bone

Question 7

what does contraction of both flexor and extensor together result in?

Answer 7

stiffness at the joint with movement

Question 8

flexion vs extension at joints

Answer 8

• flexion — closing of a joint
• extension — opening of a joint

Question 9

what is the agonist and antagonist at the elbow joint during flexion/extension?

Answer 9

flexion:
- biceps = agonist
- triceps = antagonist

extension:
- biceps = antagonist
- triceps = agonist

Question 10

for movement to occur, what must happen to the agonist and antagonist?

Answer 10

agonist must contract and antagonist must relax

Question 11

what does activity in both the agonist and antagonist result in?

Answer 11

rigidity and tremor

Question 12

what is the basic circuit in spinal cord reflexes?

Answer 12

Question 13

what are the 2 basic parts of the simplest reflex?

Answer 13

1. sensory, afferent neuron
2. alpha motor neuron

Question 14

what is the function of most reflexes?

Answer 14

protection

Question 15

what is another naem for the stretch reflex?

Answer 15

myotatic reflex

Question 16

in a stretch reflex, what happens when the tendon is tapped?

Answer 16

tapping the tendon causes that muscle to stretch slightly

Question 17

what happens when the patellar tendon is tapped? (knee jerk reflex)

Answer 17

• stretch of patellar tendon stretches the quadriceps
• induces reflex quadriceps contraction
• quadriceps is an extensor muscle, therefore contraction ‘opens’ the knee joint (straightens the leg)

Question 18

what are the 2 types of muscle fibre?

Answer 18

1. extrafusal fibres — forms the main body of muscle
2. intrafusal fibres — forms the muscle spindle

Question 19

what detects stretch?

Answer 19

sensory muscle spindle = a complex structure within muscles

Question 20

what is the spindle like when slack?

Answer 20

when slack there is no sensory output from the spindle — therefore no info being sent to the brain about muscle length

Question 21

what detects stretch?

Answer 21

mechanoreceptor eg. muscle spindle

Question 22

the spindle is in ____ with the main muscle fibres

Answer 22

parallel

Question 23

what happens when muscle fibres stretch?

Answer 23

spindle also stretches, increasing the sensory signal in its group 1a afferents

Question 24

where do the group 1a afferents project?

Answer 24

to the spinal cord via the dorsal horn

Question 25

what happens when muscle fibres contract?

Answer 25

the muscle length shortens, making the spindle fibres lose ‘tone’ (go slack) and stop signalling stretch

Question 26

how is the spindle muscle tone maintained during contraction?

Answer 26

gamma motor neurons excite the spindle’s intrafusal fibres

Question 27

how is measuring the amount of activity in gamma motor neurones useful?

Answer 27

- helps estimate the true length of the main muscle - help to match the length of the muscle

Question 28

what is a motor unit?

Answer 28

the number of muscle fibres supplied by a motor neuron

Question 29

where do spindle 1a afferents synapse?

Answer 29

on alpha motor neurones in spinal cord

Question 30

small vs large number of motor units

Answer 30

- motor units are small (low number of muscle fibres per motor unit) in order to deliver fine control of movements. - motor units are large (high number of muscle fibres per motor unit) for muscles involved in large, powerful movements where you need a small range of simple, powerful movements

Question 31

label

Answer 31

Question 32

describe the brief 5 steps that lead to muscle contraction in the monosynaptic stretch reflex

Answer 32

1. stretching of muscle stimulates muscle spindles 2. activation of sensory neuron (1a afferent) 3. information processing at motor neuron 4. activation of motor neuron (alpha motor neuron - efferent) 5. contraction of muscle

Question 33

how is the stretch reflex protective?

Answer 33

prevents damage due to over-stretching of muscle fibres

Question 34

why is describing the stretch reflex as monosynaptic only partially correct? use knee jerk reflex as example

Answer 34

- patellar tendon stretch causes reflex contraction of the quadriceps muscle (agonist) to extend the knee joint (via synapse at 1) - for this to occur the flexor (hamstrings; antagonist) must be inhibited (via synapse at 2 and inhibitory interneuron)

Question 35

what is clonus?

Answer 35

a neurological condition that creates involuntary muscle contractions

Question 36

what can deficitis in the control of the agonist and antagonist muscle by spinal interneurons result in? where is this often seen?

Answer 36

abnormal oscillation of flexion and extension around a joint (clonus) — often seen in spasticity

Question 37

what is spasticity?

Answer 37

abnormal increase in muscle tone or stiffness

Question 38

what is a golgi tendon organ? describe them

Answer 38

= another muscle proprioceptor at the junction of tendons and muscle fibres - lie in SERIES with muscle fibres (spindles are in parallel) - respond to tension developed by muscle during isometric contractions - prevent heavy loading of msucle causing damage - work by activating INHIBITORY INTERNEURONS to relax the muscle immediately - 1b afferent

Question 39

why can golgi tendon organ detect loading and a muscle spindle cant?

Answer 39

muscle spindle — in PARALLEL therefore just detects stretch/muscle length golgi tendon organ — in SERIES

Question 40

what kind of fibres are golgi tendon organ?

Answer 40

1b afferent

Question 41

how do golgi tendon organs work?

Answer 41

- neuron from golgi tendon organ fires - 1b afferent - motor neuron is inhibited - muscle relaxes - load is dropped

Question 42

describe the flexor reflex

Answer 42

Question 43

describe the crossed extensor reflex

Answer 43

Question 44

why do people with Parkinson’s disease walk with a wide gate?

Answer 44

cant control movements very well so centre of gravity is not central and moves around a lot — therefore walk with wide gate to try and keep centre of gravity central

Question 45

what happens to motor neurons in spina bifida?

Answer 45

apoptosis of motor neurons — dysfunction of limbs reflexes sometimes okay day 1 but bad by day 7

Question 46

surgery in spina bifida?

Answer 46

= prevents further damage — cannot repair damage already made in terms of motor neurons — prenatal repair offers very good chance of maintaining spinal (lower) motor function — postnatal surgery stabilises but doesn’t repair