Simple Reflexes Flashcards
what is a reflex?
Neural reflexes are STEREOTYPED INVOLUNTARY reactions of the CNS to specific sensory input
Stereotyped – predictable and reproducible (if we activated a reflex we could accurately predict the response as it will always be the same)
Involuntary – happens without conscious thought, just happens rapidly
what is used instead of voluntary/involuntary in the context of reflexes?
SOMATIC and AUTONOMIC are the contexts of a reflex and not voluntary or involuntary
Somatic – activating skeletal muscle
Autonomic – activating smooth or cardiac muscle
So i.e. the somatic nervous system through neural reflexes may exhibit an involuntary response.
what is the clinical relevance of reflexes?
give examples
If reflexes are predictable (as they’re stereotyped) it allows a clinician to test a reflex
If the response is abnormal there is a problem with a specific part of the nervous system
E.g. the pupillary reflex – constriction of pupil in response to bright light, caused by smooth muscle contraction so under control of autonomic nervous system.
E.g. deep tendon reflexes – contraction of the skeletal muscle – under control of somatic nervous system.
what are the 3 general functions of reflexes?
Protective
Postural control
Maintaining homeostasis
give examples of when reflexes are used for the purpose of protection
e.g. limb withdrawal (removing hand from hot surface)
e.g cough reflex (stops food entering the lungs –> cause damage and infection)
e.g. prevent skeletal muscle damage (example further along)
May use the somatic and autonomic NS
give an example of when reflexes are used for the purpose of postural control
e.g. when walking you do not have to think about what muscle to contract (involuntary)
so you don’t have to take up conscious thinking activity
Mainly somatic as it uses skeletal muscles
give an example of when reflexes are used for the purpose of maintaining homeostasis
e.g. blood pressure
if blood pressure falls, reflexes will bring it back to the right level.
Mainly autonomic, involved smooth and cardiac muscle
what are the neural components of a reflex arc?
Sensory receptors
Afferents (sensory neurones)
Integration centre (CNS)
Efferent neurones
Effectors
what do sensory receptors do?
Detect stimuli
Generate action potentials
what do afferent (sensory neurones) do?
they allow the AP to flow from the receptor to the CNS
what does the integration centre (CNS) do?
Once the impulse reaches the CNS they pass along interneurons.
Interneurons – where the information from a sensory neurone is passed on to a motor neurone. They can be excitatory or inhibitory.
Interneurons are found in the spinal cord, brain stem nuclei and in the enteric NS (controls the gut).
how does the integration centre integrate info?
They produce outputs depending on the inputs they receive (modulation)
The Reflex arc doesn’t work in isolation but it interacts with the rest of the nervous system (NS -Brian)
e.g. as impulse are sent to your muscles to remove your hand from a hot surface, impulses are also sent to the brain which causes you to feel the pain due to the heat. (what the arrow pointing to NS means)
you can also override reflexes e.g. you know a surface is hot but you are making a conscious decision to hold your hand there. Therefore, impulse from the brain are being sent to the integration centre causing the reflex to be overridden (what the arrow pointing away from NS means)
If there is damage to neurones that take information to or from the (NS-Brian) we will see different activity.
E.g. individuals with Cerebral Palsy have exaggerated contractions as information coming down from the brain to influence reflex arc is being disrupted. So reflex arc works without check – hyperreflexia
where in the body does the somatic and autonomic NS operate via?
most somatic reflexes operate via spinal cord whereas most autonomic reflexes operate via the brain stem nuclei
what do efferent neurones do?
Called “Motor neurones” - somatic reflexes
Called just efferent neurones - autonomic reflexes
Innervate effectors by passing on the AP from interneurons or sensory neurones.
what do effectors do?
E.g. Glands, muscle (all types)