spinal reflexes Flashcards
what is a reflex?
any response that occurs automatically without conscious effort
what is an example of an everyday reflex?
-touching a hot plate
-the person docent know the plate is hot and immediately pulls their hand away
what is a monosynaptic reflex?
a monosynaptic reflex involves only one synapse between sensory and motor neurons.
what is a polysynaptic reflex?
A polysynaptic reflex is a type of reflex arc in which signals travel across multiple synapses (connections between neurons) before producing a response
what are the components of a reflex arc?
-stimulus
-sensory / afferent neuron
-integration centre
-motor / efferent neuron
-effector - muscle
what are 3 examples of sensory receptors?
-exteroceptors
-proprioceptors
-interoceptors
describe exteroceptors
-located on the skin and sense organs
-they respond to external stimuli
-carry info about temp, pressure etc
describe proprioceptors
these receptors are located in muscles eg muscle spindles, tendons and joints
-send information about position of the muscle eg length of muscle, tension
describe interoceptors
-sensory receptors on the internal organs
-send info about pain, stretching of internal organs
what are the 2 main sensory receptors located on muscles and tendons?
-muscle spindles
-golgi tendon organs
what do muscle spindles carry info about?
length / rate of change in length of muscle
what do Golgi tendon organs carry info about?
-tension/ rate of change of tension in muscle / tendon
what id the area for integration in the CNS in a reflex arc?
-brain or spinal cord receives , processes and integrates incoming sensory info and then issues command to effectors
what are the functions of the spinal cord in relation to the reflex arc?
-link for transmission between brain and PNS
-integrates reflex activity between afferent input and efferent output without involving the brain
how do afferent sensory fibres enter the spinal cord & where are their cell bodies located??
through the dorsal root
-CB’s located in the dorsal root ganglion
what are the effectors in the reflex arc?
-the organs which respond by doing something ie executing the response
-in somatic NS - effectors are skeletal muscle and in the ANS the effectors are cardiac, smooth muscle etc
what are interneurons responsible for?
the distribution of sensory information and the co-ordination of commands within the CNS
what are the only monosynaptic reflexes that occur in the body?
-stretch (myotatic) reflexes
why are muscles always slightly contracting?
- if muscles relaxed completely they would over lengthen and too much time would be required to take up slack when a contraction was called for
what is a stretch reflex ?
-type of reflex arc that occurs in response to stretching of a muscle.
-monosynaptic reflex / myotatic reflex
describe how a stretch reflex works
- if a muscle undergoes a stretch, the muscle spindles within the muscle detect the change in length
-they signal this to the CNS through an afferent neuron
-in the spinal cord, the afferent neurons synapse directly with the motor neurons that innervate the muscle
-motor neurons send a signal to the effector muscle causing it to contract
what are the 2 types of motor neurons?
-alpha - innervates extrafusal muscle fibres
-gamma - innervates intrafusal muscle fibres
what is an example of a stretch reflex / monosynaptic reflex?
the knee jerk reflex
-the response to stretch of the quadriceps
how does the knee jerk reflex work?
- quads are briefly stretched by tapping the patellar ligament
- stretched of muscle spindles in quads
- activity in 1a sensory afferent fibres (associated with muscle spindles) increases
- activity in alpha motor neuron supplying the quads increases
-contraction of quads
-knee extends and the leg kicks forwards
what sensory receptor is the primary regulator of muscle tone?
the muscle spindle
what does testing stretch reflex responses provide information about?
the integrity of these reflex responses
- a normal response indicates that all neural and muscular components are functioning normally
how are the stretch reflex responses graded?
0-4
-0 - reflex is absent
-1- minimal
-2- normal
-3- brisk but normal
-4 - very brisk often with clonus (hyporeflexia)
what is hyporeflexia?
-hyporeflexia results if any part of the reflex pathway is damaged (from spinal to spinal cord to muscle)
what are examines of conditions associated with hyporeflexia?
-lower motor lesions
-muscular dystrophy - degenerative disease of skeletal muscle
what is areflexia?
apparent loss of stretch reflexes
what are the causes of areflexia?
-can be due to lack of clinical experience
-any lesion of the reflex arc eg root lesion or peripheral neuropathy
what is hyperreflexia?
results following damage to motor pathways from brain to spinal cord
what are examples of causes of hyperreflexia?
-upper motor lesion
-damage to motor areas of cerebral cortex
-can occur after a stroke or brain tumour
what is a Golgi tendon organ?
encapsulated sensory receptor inside muscle tendon
-detects muscle tension
-10-15 muscle fibres connected
describe the Golgi tendon organ pathway
- if there is an increase in muscle tension
-type Ib sensory nerves transmit signals to spinal cord & brain
-alpha motor neuron is inhibited via inhibitory interneuron
-prevents too much tension on muscle - controls force within muscles and stiffness of particular joints
what is reciprocal innervation
refers to the neural mechanism that coordinates the contraction and relaxation of muscles on opposite sides of a joint during movement
-when one muscle contracts (agonist muscle), its antagonist muscle relaxes to allow smooth and coordinated movement.
what are flexor withdrawal reflexes?
-polysynaptic withdrawal reflexes move a part of the body away from painful stimulation
-protective responses
-eg pulling hand away from hot plate
what happens if you touch a hot plate? - flexor withdrawal reflex
-nociceptors in the hand are stimulated
-sensory pathways synapse first on interneurons
-motor neurons contacted by interneurons
-biceps muscle contracts and the hand is pulled away
-the triceps (antagonist) is inhibited
what is a crossed extensor reflex?
-neurological reflex that occurs in response to a painful stimulus, typically involving withdrawal of a limb from the painful stimulus while simultaneously activating muscles on the opposite side of the body to support balance and posture.
-eg standing on a piece of lego
what is an example of reflexes that are voluntarily influenced and modified by higher brain centres?
-needle insertion during blood draw
-brain sends IPSP via descending paths to bicep motor neurons and EPSP to triceps to keep arm from pulling away - as that is our normal response
what are examples of learned/ acquired reflex?
-eg certain responses in music
-eg sports - catching a ball, somer saults etc
