Module 3: reflexes Flashcards
what is a reflex?
an inborn, involuntary or hardwired rapid response to a stimulus
what do reflexes do?
- maintain posture
- control visceral organs/autonomic activities (heart beat, breathing)
- safety mechanism
can you change reflexes?
yes, by learning them and by concious effort
do reflexes go to the brain?
no
How would you describe the control of a reflex?
limited, top down voluntary control, lowest activity in flow of reactions
what are the 2 types of reflexes?
- somatic: skeletal muscle
- autonomic (visceral): cardiac muscles
what are the 5 components of the reflex arc?
- receptor
- sensory neuron
- integration centre
- motor neuron
- effector neuron
what does the receptor do?
senses change in their environment and change their properties in response to the stimuli
what does the sensory neuron do?
arises from receptors and synapses either directly or indirectly (interneurons) to the motor neuron in the spinal cord
what does the integration center do?
takes in sensory in the CNS and relays to motor, it can be either monosynaptic or polysynaptic (interneurons)
what does a motor neuron do?
conducts efferent impulses from integration centre to effector organ
what does an effector do?
the axons of the alphs motor neuraons form connections with the extrafusal muscle fibers via the neuromuscular junction to cause a rection
what does polysynaptic mean, give example
there are interneurons in the spinal cord combined to create the reaction, can be slower than monosynaptic.
e.g. withdrawl reflex
what does monosynaptic mean, give example
there is a direct synapse between the sensory neuron and motor neuron, it’s a very fast reaction
e.g. knee jerk
describe a receptor
- a very specialised structure adapted to their purpose
- come in a diversity of form due to specialisation
- do not perceive, they sense
what are the 5 different senses that receptors sense?
- mechanical: touch, vibration, stretch
- termperature: thermoreceptor
- light ( photoreceptor)
- chemical (chemoreceptor)
- painful (Nociceceptors)
describe a muscle spindle
- long (elongated) structure aligned in parrallel to skeletal muscle fiber
- embedded within the extrafusal muscle fiber
- has own muscle fibers called intrafusal muscle fibers
- has efferent and afferent neurons s attached to keep it sensitive to the extrafusal muscles.
- is encased in a capsule made from connective tissue
describe the Golgi tendon organ
- located within the tendon, near the junction
- aligned in a series
- responds to muscle tension by doing the opposite
how is the muscle spindle innervated?
by the gamma motor neuron
how are the extrafusal muscles innervated?
by the alpha neurons
how are sensory neurons classified?
by their diamter
which nerve groups are important for somatic reflexes?
group 1A
group 1B
group 2
which group is the fastest in somatic reflexes?
group 1A
which group is the slowest in somatic reflexes?
group 4
why is the size of the somatic nerve important?
the bigger it is the more myelinated sheets it has, so faster responses
what are the properties of interneurons
they are either excitory or inhibitory
what are the 2 types of motor neuron?
- alpha motor neuron: receives input from the sensory and interneurons
- gamma motor neuron: innervates intrafusal muscle fibers
what happens to the extrafual muscle fibers when the motor neuron is activated?
shortens
what is happening to a muscle spindle at rest?
the action potentials are generated at a constant rate in the sensory fibers
what is happening to a muscle spindle at stretch?
the action potentials are increased, which activates the muscle spindle to stretch, keeping it sensitive to the extrafusal muscles
what is happening to the muscle spindle in contraction?
both the alpha and gamma neurons are activated and contract so tension is maintaned, the EFM and IFM move at the same time and the ICF stays sensitive to the ECF
which reflexes are normally assessed?
- stretch and tendon
- flexor/crossed- extensor
- ocular
- superficial
what is does a stretch and tendon reflex do?
- gives smooth coordination of the body
- proprioception (awareness of self in the world)
what are the 2 types of information the stretch and tendon reflexes use?
- length of muscle - sent from spindles (mono)
- tension - sent from Golgi tendon organs (poly)
what are the steps of muscular reflexes?
stimulus happens - sensory sends signals to spinal cord - synapses relay to motor neuron either directly or indirectly - leaves spinal cord through motor neuron and either excites (agonist) or inhibits effector (antagonist)
what does it indicate if someone has a large reflex?
they have spinal cord injury or a stroke a while ago because the spinal cord doesn’t have as much interaction with the brain as it used to
what does it indicate if someone doesn’t have a reflex?
there is damage to the lower alpha motor neurons
what is a H reflex?
- Hofman reflex
- controlled way to measure reflex using electrical impluse
- short, low intensity electrical stimulus
how does the H-reflex change over time?
it decreases with age due to motor neurons being less excitable
what would happen if the motor neurons died?
muscle wastage - sarcopenia
what is the purpose of a tendon reflex?
to prevent muscles tearing due to over stretching
how are tendon reflexes iniated?
through the Golgi tendon organ
is a tendon reflex poly or monosynaptic?
polysynaptic
what is the cycle of a tendon reflex?
opposite of muscle reflex
stimulus happens - sensory sends signals to spinal cord - synapses relay to motor neuron indirectly - leaves spinal cord through motor neuron and either excites (antagonist) or inhibits effector (agonist)
what does the tendon reflex do when it senses tension in the muscle?
is forces the muscle to relax (lengthen)
what does a stretch reflex do?
it activates the agonist and inhibits the antagonist
what does a tendon reflex do?
it activates the antagonist and inhibits the agonist
why does the cross extensor work together?
to maintain balance when reacting to a stimulus, e.g. not falling over when stepping on glass
what is a flexor reflex?
the reflex that withdraws the body part from the painful stimulus automatically
is the flexor and cross-extensor reflex poly or monosynaptic?
polysynaptic
what is the cross extensor reflex?
occurs to weight bearing limbs to maintain balance when reacting to a noiciceptor
is the flexor reflex ipsi or contralateral to the stimulus?
ipsilateral
is the cross-extensor reflex ipsi or contra lateral to the reflex?
contralateral
do the interneurons cross the spinal cord in the flexor/cross-extensor reflex?
yes, to activate the contralateral cross-extensor reflex
does the flexor/cross-extensor reflex happen simultaneously?
yes
what are the 2 ocular reflexes?
- pupillary reflex
- vestibulo-ocular reflex
what does the pupillary reflex do?
it controls the diameter of the pupil in response to light on the retina
why is the pupillary reflex important?
to adjust eyes to different levels of light
what does the vestibulo-ocular reflex do?
- controls eye movement when the head moves
- fastest reflex in the human body
- involuntary eye movements equal and opposite to the head so that images can be contrinuously centered on the visual field (maintaining eye contact whilst nodding)
describe the process of pupillary reflex
- light shone into eye
- both precetal nucleus at the very back of the head receives action potentials from light. interneurons send Action potentionals to the Edinger-Westphal nucleus (EWN)
- the EWN is stimulated by the prectal nucleus through the interneurons
- action potentials are generated by EWN and both ocular nerves constrict the pupils
list the components of the pupilary reflex
- eyes
- prectal nucleus
- interneurons
- Edinger-Westphal nucleus
- ocular motor nerves 1 and 2
- ocular motor nerve 3
- ciliary ganglion
what is the purpose of the cilary ganglion in pupillary reflex?
parasympathetic, restricts pupil dialation
describe the vestibulo-ocular reflex
similar process to flexor/cross-extensor reflex, one side of the muscle on both eyes either excites or inhibts the muscles to maintain both eyes moving at the same time
what is the plantar reflex?
the response of your toes flexing downwards in response to a stimulus
what part of the spinal cord tests for integrity in the planter reflex?
L4 to S2
what is Babinski’s sign?
when, upon a stimulus to the side of the plantar the toes move upwards, in a dorsal flex, instead of downwards in a plantar flex
what does it mean if you test positive to Babinski’s sign?
there is potentially damage to the motor cortex or corticospinal tract, or you’re under 1 year old.
