1 - intro to the nervous system lecture Flashcards
what is perception?
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
is pain subjective?
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
what are some morphological features of a neurone?
what are the 4 reflex types?
- stretch aka. monosynaptic
- inhibitory
- flexor
- crossed extensor
what is a joint?
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)
tendons vs. ligaments
tendons — bind muscle to bone
ligaments — bind bone to bone
what does contraction of both flexor and extensor together result in?
stiffness at the joint with movement
flexion vs extension at joints
- flexion — closing of a joint
- extension — opening of a joint
what is the agonist and antagonist at the elbow joint during flexion/extension?
flexion:
- biceps = agonist
- triceps = antagonist
extension:
- biceps = antagonist
- triceps = agonist
for movement to occur, what must happen to the agonist and antagonist?
agonist must contract and antagonist must relax
what does activity in both the agonist and antagonist result in?
rigidity and tremor
what is the basic circuit in spinal cord reflexes?
what are the 2 basic parts of the simplest reflex?
- sensory, afferent neuron
- alpha motor neuron
what is the function of most reflexes?
protection
what is another naem for the stretch reflex?
myotatic reflex
in a stretch reflex, what happens when the tendon is tapped?
tapping the tendon causes that muscle to stretch slightly
what happens when the patellar tendon is tapped? (knee jerk reflex)
- 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)
what are the 2 types of muscle fibre?
- extrafusal fibres — forms the main body of muscle
- intrafusal fibres — forms the muscle spindle
what detects stretch?
sensory muscle spindle = a complex structure within muscles
what is the spindle like when slack?
when slack there is no sensory output from the spindle — therefore no info being sent to the brain about muscle length
what detects stretch?
mechanoreceptor eg. muscle spindle
the spindle is in ____ with the main muscle fibres
parallel
what happens when muscle fibres stretch?
spindle also stretches, increasing the sensory signal in its group 1a afferents
where do the group 1a afferents project?
to the spinal cord via the dorsal horn
what happens when muscle fibres contract?
the muscle length shortens, making the spindle fibres lose ‘tone’ (go slack) and stop signalling stretch
how is the spindle muscle tone maintained during contraction?
gamma motor neurons excite the spindle’s intrafusal fibres
how is measuring the amount of activity in gamma motor neurones useful?
- helps estimate the true length of the main muscle
- help to match the length of the muscle
what is a motor unit?
the number of muscle fibres supplied by a motor neuron
where do spindle 1a afferents synapse?
on alpha motor neurones in spinal cord
small vs large number of motor units
- 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
label
describe the brief 5 steps that lead to muscle contraction in the monosynaptic stretch reflex
- stretching of muscle stimulates muscle spindles
- activation of sensory neuron (1a afferent)
- information processing at motor neuron
- activation of motor neuron (alpha motor neuron - efferent)
- contraction of muscle
how is the stretch reflex protective?
prevents damage due to over-stretching of muscle fibres
why is describing the stretch reflex as monosynaptic only partially correct? use knee jerk reflex as example
- 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)
what is clonus?
a neurological condition that creates involuntary muscle contractions
what can deficitis in the control of the agonist and antagonist muscle by spinal interneurons result in? where is this often seen?
abnormal oscillation of flexion and extension around a joint (clonus) — often seen in spasticity
what is spasticity?
abnormal increase in muscle tone or stiffness
what is a golgi tendon organ? describe them
= 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
why can golgi tendon organ detect loading and a muscle spindle cant?
muscle spindle — in PARALLEL therefore just detects stretch/muscle length
golgi tendon organ — in SERIES
what kind of fibres are golgi tendon organ?
1b afferent
how do golgi tendon organs work?
- neuron from golgi tendon organ fires - 1b afferent
- motor neuron is inhibited
- muscle relaxes
- load is dropped
describe the flexor reflex
describe the crossed extensor reflex
why do people with Parkinson’s disease walk with a wide gate?
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
what happens to motor neurons in spina bifida?
apoptosis of motor neurons — dysfunction of limbs
reflexes sometimes okay day 1 but bad by day 7
surgery in spina bifida?
= 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
