P: Reflexes Flashcards
What is a reflex
An involuntary stereotyped but coordinated response to specific stimulus
What is a muscle spindle
Stretch receptor
What are golgi tendon organs
They are located at junction between tendon and muscle; sensitive to muscle force/tension
Two classifications of reflexes
Somatic - voluntary
Autonomic - involuntary
What root do afferent nerves enter the spinal cord (sensory nerve)
Dorsal root
Name the 6 essential components of a reflex
Stimulus
Sensory receptor
Afferent nerve fibre
Synapse
Motor fibres
Effector organ
What are spindle fibres made of
Intrafusal muscle fibres
What is the orientation of intrafusal muscle fibres and what does this allow
Lie parallel to extrafusal fibres (main contracting fibres in muscle)
Therefore responds to length changes in the muscle
What two types of tissue do intrafusal fibres have and where
Non contractile at centre
Contractile at the poles (ends)
What are the two types of intrafusal fibres
Nuclear bag
Nuclear chain
What do the primary (annulospiral) nerve endings do in the spindle
Type 1A afferents
Detect amount of muscle stretch and rate of stretching (dynamic response)
What are primary nerve endings
Type 1A afferents
Myelinated , rapidly conducting neurons
Faster and larger than type 2
Detect muscle stretch + rate of change of stretching
What do the secondary flower spray endings do
static response
Secondary flower spray endings properties
Type 2 afferents
Myelinated
Slower conduction than type 1
Respond to maintained stretch
What do primary sensory nerve endings innervate
Both nuclear bag and chain fibres
What do the secondary flower spray endings innervate
mainly nuclear chain fibres
What is the motor innervation of spindle and where
Gamma motor neurons
Innervate contractile fibres at the poles
What is meant by the spindle being unloaded or slack
Occurs after reflex contraction
Over relaxed /under stretched
How is a slack spindle reloaded
Gamma motor neurons cause contraction of intrafusal(spindle) fibres
Tightens the spindle
Allows it to continue to respond
What’s the inverse myotonic reflex
Golgi tendon reflex
What innervate the collagen of tendon
nerve terminals
What happens if there’s excessive tension in contraction
GTO sends info to spinal cord via 1b afferents
Synapses with interneurons
Inhibition of contraction muscle
Reflex relaxation occurs
Where are muscle spindle and stretch reflexes especially prominent
In anti gravity muscles
Neck muscles
Where fine control is required eg finger
What does the GTO reflex prevent
Excessive force generation in a muscle
What have a dampening/smoothing effect on jerky muscle movements
GTO and spindle fibres
Important in feedback control of muscle length in response to a load and prevent jerky movement
What’s the most powerful reflex
Flexion (withdrawal) reflex
What is the flexion reflex also called
Crossed-extensor reflex
What information do dorsal columns carry
- Proprioception
- Discriminative touch
- Pressure + vibration sense.
Spinothalamic tracts transmit information regarding:
- Pain
- Temperature
- Crude touch
- Itch + tickle
Difference between monosynaptic + polysynaptic reflexes
Monosynaptic - single synapse, no interneuron
Polysynaptic - many interneurones connect afferent and efferent motor signals.
Stretch reflex:
Sensory receptor –> muscle spindle
Afferent nerve fibre –> IA afferents
Synapse –> spinal cord
Motor neuron –> alpha motor neuron
Effector organ –> skeletal muscle contracts
Tonic receptors vs Phasic receptors
- Tonic receptors do not adapt to stimuli. Tonic receptors fire action potentials constantly. (pain)
- Phasic receptors adapt to stimuli rapidly; eventually the individual no longer senses the stimulus. Phasic receptors fire action potentials when the stimulus is initiated and when the stimulus is removed. (seeing your nose, feeling clothes on skin)
What are dorsal columns made of
Large myelinated axons
Where do the dorsal columns enter the spinal cord and where do they go
Enter spinal cord at different levels via dorsal route
Travel up the cord in a highly organised fashion
What is somatotopic organization?
Correspondence of a specific point in the body to a specific point in the primary motor and sensory cortexes
Where do dorsal columns synapse
In the medulla on either side of the dorsal column nuclei
What are second order neurons also known as
Medial lemniscus
Where do second order neurones synapse and become third order neurones
In the thalamus and travel up to the somatosensory cortex
Definition of receptive field
The receptive field of a sensory neuron is an area of skin that, once stimulated, produces a response for that neuron.
Receptive fields vary inversely with numbers of receptors in the area (bigger the area, smaller the number of receptors)
What are the different types of sensory receptors and their modalities?
- Chemoreceptors –> chemical changes
- Thermoreceptors –> warm and cold
- Photoreceptors –> light
- Mechanoreceptors –> pressure
- Nocioreceptors –> noxious stimuli (generate pain)
- Propioreceptors –> info about body and limb position
How do sensory receptors transmit sensory information?
Action potentials are generated when generator potentials reach threshold for depolarization. Bigger the stimulus, greater number of APs generated.
Generator potentials = local graded changes in membrane potential
What order neurons are dorsal columns?
First order neurons
Damage to lower motor neurone?
Reduced stretch reflexes & flaccid paralysis
Physiological benefit of stretch reflex
Muscle tension, posture maintenance
Name the sensory receptor for stretch reflex + what stimulates it?
Mechanoreceptors - length changes in muscle
Define gamma motor neuron
Innervates intrafusal fibres of muscle spindle
What stimulates GTO receptors
Proprioceptors detect muscle contraction
