How reflexes keep us safe Flashcards
What is a reflex?
A reflex is a simple, stereotyped response that couples sensory input to motor output. It relies on functional connections between a-motor neurons and muscle receptors. Such reflexes are examples of involuntary movements that kirap us safe from harm
What is the spinal reflex
Sensory input detected by sensory receptors
Peripheral nerve Synapse onto alpha-motor (lower motor) neurons in the spinal cord ventral horn
Innervate muscle to cause movement
Avoid damage to muscle to keep us safe
What is divergence spinal cord
Information from the periphery comes into the spinal cord and have segregation of message
message spreads out
Why is divergence of the spinal cord important
amplifies sensory input and coordinates muscle
contractions = movement
What is convergence spinal cord
Different areas of the periphery will come together onto one neuron
Why is convergence of the spinal cord important
interneurons increase flexibility of response
How is stretching of the muscles detected
Sensory neurons in muscle spindle (intrafusal muscle fibre) encode information on muscle length
Specialised muscle cells that detect stretch- 1a and 11 sensory afferents
monitor the extent of stretch and the rate of change of length
Synapse in spinal cord onto a motor neurons
Intrafusal muscle fibres in parallel
- surrounded by extrafusal muscle fibres
-associated with afferent and efferent neurons
How does tapping of the knee activate the stretch monysynaptic reflex?
Sretches Patellar ligament and so the intrafusal muscle
Action poteential across la affernent neurone and synapses to efferent neurone which restores muscle length of same muscle while maintaining muscle tone
What are the lower motor neurons
Alpha motor neurones
Gamma motor neurons
Where are the lower motor neuron cell bodies located
Ventral horn
What is the polysynaptic reflex
Two (or more) synapses Stimulus is muscle stretch Instead of one efferent neuron afferent neuron synapses on Inhibitory interneurons which synapse onto another alpha motor neuron and this acts on antagonistic muscle ANTAGONISTIC muscle relaxes RECIPROCAL INNERVATION Coordination of antagonistic muscles Movement of entire limb
Why is the polysynaptic reflex important
Protective
it relaxes the antagonistic muscle and prevents it from tearing
What is more common polysynaptic or monosynaptic
Polysynaptic as to innervate antagonistic pairs
What is the role of gamma motor neurons
Innervate specialised striated muscle (intrafusal muscle fibres)
Adjust sensitivity of muscle spindles & increase range of function
How do Golgi tendon organs detect stretch?
Sensory neurons in tendon encode information on muscle tension and contraction
1b afferent sensory neurons associated with collagen fibres within the tendon
Located within tendons each end of a muscle
Monitor and maintain muscle tension
Inhibit further muscle contraction
Funnel-like capsule containing collagen fibre bundle and nerve fibres
Arranged in series with extrafusal muscle fibres
What is the golgi tendon reflex also known as ?
Reverse monosynaptic reflex
What is the golgli tendon reflex?
Muscle tension reflex
Golgi tendon body stretch
Disynaptic reflex = TWO synapses
Prevents overstretching of tendon
Muscle contraction stretches tendon
Sensory neurons (lb afferent) activate interneurons
Inhibit a neurons innervating muscle of origin
Opposite to myotatic reflex
Controls muscle tension
Inhibits muscle contraction
Protects muscle from causing damage to tendons
Fine control of tension for grasping fragile objects
What are the different sources inputting in the motor neuron
sensory input form Muscles (reflex)
Descending input form upper motor neurons
Interneurons from neuronal coircuts that produce cooirdinated movement
What lesion would it be if there is weak or absent reflex?
Llwer motor neuron lesion
What lesion would it be if there is exaggerated reflex?
Upper motor neuron lesion
How do you purposefully exagerrate lower limb tendon reflex?
Jendrassick manoeuvre
What happens to purposefully exagerrate lower limb tendon reflex?
Voluntary Upper Motor Neuron innervation
‘overflows to increase the excitability of the lower
motor neuron pool of the lower extremities
Increases fusimotor (y motoneuron) drive Increases amplitude of reflex
Counteracts (removes) descending inhibition of
the reflex arc.
Modulates interneuron excitability Removes inhibitory action on the late component of the stretch reflex (Group II afferents)
What does the flexion withdrawal reflex do?
Rapidly removes limb from harmful (noxious) stimuli
What is the flexion withdrawal reflex
Cutaneous receptors in the skin
Activation of primary afferent neurons (flexor reflex afferents)
Disynaptic reflex — inhibitory interneurons excite flexor motor neurons and inhibit extensor motor neurons
What does the crossed extensors reflex do ?
Maintains balance during flexion withdrawal reflex
Simultaneous extension (strengthening contraction) of contralateral limb
What is the crossed extensor reflex?
PAIN activates sensory neuron that
synapse with spinal cord interneurons
Interneurons activate
CONTRALATERAL extensor motor neurons and inhibit CONTRALATERAL flexor motor neurons
Extensor muscles contract (and flexor muscles relax) and LEG STRENTHENS to support weight
What is the jaw jerk reflex?
Downward tap on jaw stretches muscle
Activation of trigeminal nerve (CNV)
Contraction of masseter muscle
What is jaw unloading reflex
Initiated by sudden unloading of the jaw
Activation of trigeminal nerve (CNV)
Inhibition and activation of jaw muscles
Stops jaw movement, protects teeth
Pupillary light reflex
Pupil constriction (both eyes) in response to bright light
Activation of optic nerve (CNII) 4 constriction via oculomotor nerve (CNIII)
Protective = adaptation to light levels
Accommodation reflex
Adduction of eyes initiated by change in focus
Activation of optic nerve (CNII) 4 change in lens shape (CNIII)
Protective = prevents blurred vision
Corneal (blink reflex)
Closure of both eyes initiated by foreign object touching one eye
Activation of trigeminal nerve (CNV) innervates eyelid by facial nerve (CNVI I)
Protective = protects eyes from foreign bodies
Gag reflex
Initiated by object touching posterior wall of pharynx
Activation of glossopharyngeal nerve (CN IX)
Contraction of soft palate and pharynx
Protects the airway
Swallowing reflex
Initiated by food bolus created by chewing
Causes closure of glottis, elevation of larynx, and transient cessation of respiration
Protects the airway •
Tectospinal and vestibulospinal reflex
Initiated by visual or audio stimuli
Coordinates head and eye movement, maintains posture
Protective = responsive to changes in surrounding environment
