reflexes Flashcards
Descending motor control
VOLUNTARY
Brain
Spinal cord /brainstem
Muscle
Planning
REFLEX coordination
INVOLUNTARY
Spinal cord/ brainstem - muscle and vice versa
Reactionary, unplanned
What is a reflex
Simple, sterotyped response that couples sensory input and motor output
Relies on functional connections between alpha motor neurones and muscel receptors
Examples of reflexes
Myotatic ( stretch) reflex e.g. jaw jerk reflex, knee jerk reflex
Flexor /withdrawal to remove limb from harm
Crossed extensor reflex to maintain postural balance
Cranial nerve reflexes e.g. gag
2 types of neurones in reflex
Peripheral
Lower motor
Peripheral neurones in the reflex
From receptors in periphery to spinal cord/brainstem
Innervate alpha motor neurones and gamma motor nuerones
Lower motor neruones in hte reflex
Brainstem or spinal cord to muscle
Simulate or inhibit muscle contraction via NMJ
Reflex arc
Sensory input detected by sensory receptors
Synapse onto a motor neurones in the spinal cord ventral horn
Innervate muscle to cause movement
Divergence
Amplifies sensory input and coordinates muscle contractions = movement
CONVERGENCE
Messages all come together onto one neurone
On interneurones increases flexibility of response
Inhibition
Reciprocal inhibition; interneurones and renshaw cells
Potentiation
Mild stretching of the muscle
Sensory system
Detects change to enables system to be reactive
Detecting stretch
Muscle spindles PROPRIOCEPTORS
What are proprioceptors made from
La and II sensory afferents
Monitor the extent of stretch and the rate of change of length
Synapse in spinal cord onto a motor neurons
Intrafusal muscle fibers in parallel surrounded by extrafusal
Mytotatic reflex
ONE synapse
Monosynaptic
Stretch reflex
Importance of myotatic reflex
Prevents overstretching of muscle
Tested by tapping tendon
Stretches attached muscle
Controls muscle length, maintains muscle tone and prevents muscular damage
Subsequent contraction of same muscle restores muscle length
Reflex pathway of muscle stretch
Weight added Muscle stretch AP firing in afferent neurone AP firing in efferent neurone alpha motor neurone Muscle shortens
Lower motor neurones
Innervate muscle
Alpha motor neurones
Gamma motor neurones
Cell bodies located in ventral horn
Axons exit in ventral root
Motor unit
alpha motor nuerone + all innervated muscle fibers
Alpha motor neurone
Large multipolar neurones
Terminate at neuromuscular junctions ( end plate)
Innervate skeletal muscle fibers ( extrafusal muscle fibers )
Polysynaptic reflex
2 or more synapses
Stimulus is muscle stretch
inhibitory interneurons syanpse onto another alpha motor nuerone
Anatgonisitic muscle relaxes
recipricol innervation
Enables other muscle to contract
Gamma motor neurones
Smaller neurones
Innervates specialised striated muscle ( intrafusal muscle fibers)
Adjust sensitivity of muscle spindles and increase range of function
Detecting stretch via golgi tendon organs ( another proprioceptor )
Sensory neurones in tendon
Ib afferent sensory neurones associated with coallgen fibers within hte tendon
Located within tendons each end of a muscle
Monitor and maintain muscle tension
Inhibit further muscle contraction
Funnel like capsule containing collagen fiber bundle and nerve fibers
Arranged in series with extrafusal muscle fibers
Function of golgi tendon reflex
Prevents overstretching of tendon
Controls muscle tendon
How does the golgi tendon reflex(disynaptic (2 synapses )) prevent overstretching of tendon
Muscle contraction stretches tendon
Sensory neurones ( 1b afferent) activate interneurones
Inhibit a neurones innervating muscle of origin
Opposite to myotatic reflex
How does the golgi tendon reflex control muscle tension
Inhibits muscle contraction
Protects muscle from causing damage to tendons
Fine control of tension for grasping fragile objects
where do alpha motor neurones receive input from ?
Sensory input from muscles ( reflex)
Descending input from upper motor neurones ( initating and controlling voluntary movement)
Interneurons (excitability of inhibitory) form neuronal circuits that produce coordinated movements
What do gamma motor neurons do in relation to alpha
ADJUST SENSITIVITY OF MUSCLE SPINDLES
Weak or absent reflex
lower motor neurone lesion
Exaggerated reflex
upper motor neurone lesion
Overriding descending control of reflexes
Conditioning the reflex - jendrassick manouvere
EXAGGERATE reflex
2 theories of how we override descending control of reflex ( lower limb)
alpha neurons receive from upper
Voluntary upper motor neurone innervation overflows to increase excitability of the lower motor neuron pool of the lower extremities , increasing drive to gamma motor neurons
Removes descending inhibition of the reflex arc - modulates inter neuron excitability, removes inhibitory action of stretch reflex
Flexion withdrawal reflex
Removing something from harmful stimuli
Cutaneous receptors in the skin
Activation of primary afferent neurones - synapse with spinal cord interneurons- activate flexor motor neurones
Disynaptic reflex - inhibitory interneurones excite flexor motor neurons and inhibit extensor motor neurones
Crossed extensor reflex
Enables balance during flexion withdrawal reflex Simulataneous extension ( strengthening contraction) of contralateral limb
Interneurons from flexion withdrawal activate CONTRALATERAL extensor motor neonres and inhibit contralateral flexor motor neurones, extensor muscles contract adn leg strengthens to support weight
Jaw reflexes
Jaw jerk reflexes
Jaw unloading reflex
jaw jerk reflexes
Downward tap on jaw stretches
Activation of trigemeninal nerve
Contraction of masseter muscle
Jaw unloading reflex
Initiated by Sudden unloading of jaw
Activation of trigeminal nerve
Inhibition and activation of jaw muscles
Stops jaw movement and protects teeth
Visual reflexes
Pupillary light reflex
Accomodation reflex
Corneal ( blink ) reflex
Pupillary light reflex
Pupil constriction(both eyes) in response to light Activation of optic nerve (CNII)- constriction via oculomotor nerve (CNIII) Protective = adaption to light levvels
Accomodation reflex
Adduction of eyes initated by change in focus (CNII)
Activation of optic nerve - change in lens shape (CNIII)
Protective = prevents blurred vision
Corneal blink reflex
Closure of both eyes initated by foreign object touching one eye
Activation of trigeminal nerve ( CNV) - innervates eyelid by facial nerve ( CNVII)
Throat reflexes
Gag
Swallowing
Gag reflex
Object touching posterior wall of pharynx
Activation of glossopharyngeal nerve ( CNIX)
Contraction of sot palate and pharynx
Protects airway
swallowing reflex
Initiated by food bolus
Causes closure of glottis, elevation of larynx and transient cessation of respiration
Protects airway
Postural reflex
Tectospinal and vestibulospinal reflex
Initiated by visual or audio stimuli
Coordinates head and eye movement, maintains posture
Protective - responds to changes in surrounding environments
