Case 1 - intro to the nervous system Flashcards
what is perception
constructive process in the brain that depends upon both information about stimuli (sensations) and the mental structure of the perceiver.
what is pain derived from
is a perception derived from sensory input between nociceptors
what is nociception
is the sensory nervous systems process of encoding noxious stimuli. it deals with a series of events and processes required for an organism to receive a painful stimulus, convert it to a molecular signal, and recognise and characterise the signal in order to trigger an appropriate defence response
what are neurones
cells which integrate information and pass it on
what are glia
‘support cells’, maintaining the environment and ‘moping up’
how much of the cardiac output is directed to the brain
25-30% of cardiac output is directed to the brain
what two substances from blood can the brain only use
glucose and O2
what is there no build up of in the brain
lactate buildup from anaerobic metabolism
what is excitotoxicity
over exposure to glutamate with actions on NMDA receptors which allow Ca influx and can cause swelling and rupture
morphological features of a neurone
what are the three types of synaptic connection
- axodendritic
- axosomatic
- axoaxonic
diagram explaining the simple circuits of synapse connection
what do dendrites do
they ‘collect’ information from synaptic outputs, potentially from relatively long distances away, with the membrane at the soma summing all of the dendritic EPSPs and IPSPs both across time and location
what is an EPSP
excitatory postsynaptic potential
what is an IPSP
Inhibitory postsynaptic potential
what happens if the membrane depolarisation at the exon hillock reaches threshold
an action potential is initiated, which travels down the axon to the axon terminal which releases a neurotransmitter
what is the neurone used in this
an analoge-to-digital converter (D2A etc)
what does continuously varying changes in the cell soma membrane potential do
gives rise to discrete ‘all or none’ action potential events
how many synapses can there be onto any single Nerone
can be hundreds to thousands
what are the 4 reflex types
- stretch reflex
- inhibitory reflex
- flexor reflex
- crossed extensor reflex
what do ligaments bind
ligaments bind bone to bone
what do tendons bind
tendons bind muscle to bone
what is flexion
the closing of a joint e.g contraction of the biceps (flexor muscle) - cases the joint at the elbow
what extension
the opening of a joint e.g contraction of the triceps (an extensor muscle) opens the joint at the elbow
what would contraction of both extensor and flexor cause
results in stiffness at the joint with no movement
what has to happen in order to get movement
the antagonist muscle must relax during agonist contraction - this is an important concept to understand
what happens during flexion of the elbow joint
- the biceps are the agonist
- the triceps are the antagonist
what happens during extension of the elbow Joint
- the triceps are the agonist
- the biceps are the antagonist
what is a reflex
uses existing neural circuits In the spinal cord - reflexes do not require learning
the sensor, integrator and effect model
stretch reflex
taping the tendon connecting a muscle to a bone causes that muscle to stretch slightly. this stretch is deterred by a sensor which through a reflex circuit causes the muscle to contract
why does the muscle contract
to counteract the imposed stretch
describe the ‘knee jerk’ reflex
stretch of the patellar tendons stretches the quadriceps. the induces reflex quadriceps contraction. as the quadriceps is an extensor muscle, contraction ‘opens’ the knee joint and straightens the leg
what does the knee jerk reflex protect from
protects the muscle from damage due to over-stretching.
what is this reflex also called
the myotatic reflex
what are the two main types of muscle fibres
- extrafusal: main body of the muscle
- intrafusual: lie within the extrafusal and forms the muscle spindle
diagram of knee jerk reflex
what is the spindle response
a mechanoreceptor
relationship between the main muscle fibres and the spindles
parallel
what happens when muscle fibres stretch
the spindle also stretches increasing the sensory signal in its Group 1a afferents. these project to the spinal cord via the dorsal horn
diagram showing spindle strech
what happens when muscle fibres contract
the muscle length shortens, making the spindle fibres go slack, loose and stop signalling stretch
what counteracts this
the gamma motor neurone excites the spindles intrafusal fibres to maintain spindle muscle tone during contraction
spindle being slack explanation and compensation
when the spindle is slack, there is not information about muscle length being transmitted to the spinal cord. this is bad as the position of the joint and related muscle state of contraction are vital in order to effect controlled movement. contracting the intrafusal fibres compensates for this state by restoring spindle output. in such a case the brain can calibrate the ‘new’ value of spindle output against the amount of activity in the gamma motor neurones to estimate true length of the main muscle
what produces muscle contraction
motor units are small in order to deliver fine control of movement. motor units air large for muscles involved in large powerful movements where u need a small range of simple powerful movements
diagram of muscle contraction
arrangement of motor neurones in the spinal cord diagram
what are the steps underlying monosynaptic stretch reflex
- stretching of muscle stimulates muscle spindles
- activation of sensory neurone
- information processing at motor neurone
- activation of motor neurone
- contraction of the muscle
how is the flexor muscle inhibited
via synapse at 2 and inhibitory interneurone
what can abnormal oscillation of flexion and extension around the joint be often seen in
spasticity
how does the Golgi tendon organ lie in relation to tendons and muscles
it lies in series with muscle fibres (spindles are parallel)
what does Golgi tendon organ do
responds to tension developed by muscle during isometric contraction. prevents heavy loading of muscle causing damage.
ow does the Golgi tendon organ work
works by activating inhibitory interneurones to relax the muscle immediately
diagram showing lay out of Golgi tendon organ and spindle
what is the inverse of a stretch reflex
when the agonist muscle is excited and aids in extension of the joint. at the same time the antagonist muscle is relaxed, so therefore inverse of a stretch reflex
diagram of the flexor reflex
what is the crossed extensor reflex
flexors in the withdrawing limb contract and the extensors reflex, while in the other limb the opposite happens.
signals travelling via the spinal cord contract the contralateral muscles of the hips and abdomen. this shifts the body centre f gravity over the extended leg
summary: please please work.
Neurones combine to form simple and highly complex circuits.
simplest neuronal circuit organisation can be seen in the 4 reflex types.
