NBSS (neuroscience) - spinal cord and reflexes Flashcards
What is the definition of a reflex?
- It is involuntary.
- It is a response to stimulus.
- It is not subject to conscious control.
What do the autonomic reflexes activate and how are they mediated?
- Mediated by the autonomic nervous system
- Activates:
- Smooth muscle
- Cardiac muscle
- Glands
What do the somatic reflexes activate and how are they mediated?
- Mediated by the somatic nervous system.
- Stimulates skeletal muscle.
What are the 3 steps of a reflex?
- Sensory input
- Information processing
- Motor output
What are the 5 components of reflexes?
- Receptor
- Sensory neurone
- afferent pathway to CNS
- Interpretation centre
- one or more synapse in CNS
- Motor neurone
- efferent pathway from CNS
- Effector
- e.g. muscle contracts / gland secretes
What are the 5 components of a monosynaptic reflex?
- Receptor - A. muscle spindle
- Sensory neurone:
- B. mylenated, large diameter, 1A (alpha) afferent axon.
- C. peripheral nerve
- D. dorsal root ganglion - Interpretation centre
- E. spinal cord - Alpha motor neurone - myelinated large diameter
- Effector
- F. Muscle extrafusal fibres - neuromuscular junction
What are most reflexes?
Most reflexes are polysynaptic - they include interneurones.
why are polysnapses slower?
- As there are more synapses - there is a greater synaptic delay.
- One synapse = 0.5msec.
- Interneurones can be either excitatory or inhibitory and pass this message on, on the second synapse.
What are the proprioreceptors?
- Proprioceptors carry input from the sensory neurons to CNS
- CNS integrates input signal
- Somatic motor neurons carry output signal – Alpha motor neurons
- Effectors - contractile skeletal muscle fibers
Where are proprioreceptors located?
skeletal muscle, tendons, joint capsules, and ligaments
where are muscle spindles and Golgi tendon organs found?
sensory muscle receptors
how can muscle spindle be described?
- muscle spindle in parallel to muscle fibres
- poles of intrafusal fibres have contractile filaments
- tonically active - continuously giving information to CNS
- muscle spindle contracts in parallel to main muscle fibres
how can golgi tendon organ be described?
- golgi tendon organ at muscular-tension junction in series with main muscle fibres
- sensory receptor intertwined with collagen fibres
- only afferent neurone
what do muscle spindles do?
- monitor muscle length
- monitor rate change of length
- prevent overstretching
- healthy muscles are never fully relaxed, always tone as sensory neuron is tonically active
why do we need reflexes?
prevent muscular damage
whats the difference in reaction to a heavy load in the muscle spindle and golgi tendon reflex?
In the muscle spindle reflex - the addition of a load stretches the muscle and spindles, creating a reflex contraction.
- Add load to muscle.
- Muscle and muscle spindle stretch as the arm falls
- Reflex contraction is initiated by muscle spindle which restores the arms position.
In the golgi tendon reflex - an inhibitory interneurone is added. This blocks the muscle from firing.
- Add load to muscle.
- Muscle contraction stretches Golgi tendon organ.
- Neuron from golgi tendon organ fires.
- Motor neuron is inhibited.
- Muscle relaxes.
- If the excessive load is placed on the muscle, golgi tendon reflex causes relaxation, thereby protecting muscle.
what is a total flexor pattern?
withdrawal reflex of finger, wrist, elbow and shoulder
What is reciprocal innervation?
excitation of one muscle group and inhibition of their antagonists around a joint
what are cross cord reflexes?
more than one limb, opposite limb affected and effects reversed
- same side/ipsilateral : excitation of flexor and inhibition of extensors
- opposite side/contralateral: inhibition of flexor and excitation of extensor
difference between ipsilateral and contralateral
- Ipsi for withdrawal - flex to remove
- Contra for stability - straight leg for support
what are intersegmental reflexes ?
reflexes travelling different levels of spinal cord to enable different muscles to be affected - enables full withdrawal
What is the building block for walking?
Crossed extensor reflex.
What are central pattern generators?
They control rhythmic movements
What is descending control?
Change motor neurone pool excitability
can be pyramidal (from motor cortex) and extra pyramidal (vestibular nuclei)
how is descending control seen clinically?
patients overriding knee-jerk reflex, can be determined whether they are overriding or if there is a neural issue via Jendrassik manoeuvre (patient holds hands together before them and squeezes simultaneously as knee-jerk happens)
What is the function of Renshaw cells?
you dont want continuous excitation to motor neurone so Renshaw cells act as inhibitory interneurons that inhibits itself (feedback mechanism of control) regulating spinal motor neruones
Essentially act as a negative feed back loop to stop excessive excitation.
what is in the pyramidal pathway?
- corticospinal - from cortex to spine; descending = motor pathway
- coritcobulbar - from cortex to pons/brain stem
what is in the extrapyramidal pathway?
- vestibulospinal - vestibular nucleus to spinal cord
- tectospinal - from superior colliculus - midbrain to spinal cord
- reticulospinal - from reticulum in brainstem; MRST-pons or LRST-medulla to spinal cord
- rubrospinal - from red nucleus to midbrain
What is the function of vestibulospinal control?
control balance and posture innervating antigravity muscles
what is the tectospinal extrapyramidal pathway for?
coordination of head movements in relation to visual/auditory stimuli; ringing bells behind baby heads
what is the reticulospinal extrapyramidal pathway for?
MRST pons: increase muscle tone - exciting vol
LSRT medulla: inhibit muscle tone - inhibit vol
what is the rubrospinal extrapyramidal pathway for?
fine movements
what are the supra spinal reflexes?
- postural reflexes (whole body - center of gravity remains )
- vestibular reflexes
- brain stem reflexes
what is the labyrinthine righting reflex
labyrinthine righting reflex (vestibular) - FALL PREVENTION
- lean off balance
- stimulates semicircular canals
- motor response of neck and limbs
- maintenance of upright posture
where do we detect labyrinthine righting reflex?
labyrinth in inner ear - vestibular apparatus detecting movement and position
Inner ear → vestibular nuclei → spinal motor neurones
Postural reflex body movements
where is the reflex centre?
cerebellum
what does reflex centre in cerebellum do?
- integrate sensory information
- position of the body
- coordinates complex movements
- maintains posture
what does possible nerve damages outside spinal cord indicate
peripheral neuropathy
what does damage to motor neruons indicate
motor neruon disease
what does damage to neuromuscular junction indicate
myasthenia gravis
what is a muscle disease
myopathy
what does an excessive response suggest?
- spinal cord damage ABOVE level controlling hyperactive response
- higher CNS damage
- disinhibition
what does an asymmetric response suggest?
- early progressive disease onset
- localised nerve damage : trauma
What is the Babinski reflex?
- Stroke the lateral aspect of the sole of the foot
- The reaction = extension in the first two toes in hemiplegic and paraparetic patients and neonates.
how is cerebral palsy related to developmental issues?
- children unable to make transition to inhibit survival patterns - disinhibition
- movement random and uncontrolled
- failed development higher control
- spectra of disorders retaining prmitive reflexes affecting sensory perception of movement
- limbs, eyes, balance and hearing uncontrolled via disinhibit due to no descending control
