Reflexes Flashcards
Describe the reflex arc
Stimuli - detectable change in internal/external environment Receptor - detects the change Integrating centre - Signal received Effector Response - sometimes neg feedback
List the compounants of a monosynaptic reflex
Sensory receptor, sensory nerve fibre, motoneuron and muscle
Draw the motor reflex
What are the principle differences between axons?
The diameter and myelination
Describe some of the features of alpha motor neurons
They have a very large diameter with a very fast conduction velocity (70-120m/s).
They are classes as Aα type fibres and innervate skeletal muscle
What is the entery root for sensory signals and what occurs after they have entered the grey matter
Entery point is the from the dorsal roots. Once enterd, the signal branches into two; one terminates immediatly in the grey matter and one signal is sent to higher levels in the NS
Anterior motor neurons give rise to what fibres?
Alpha motor fibres and Gamma motor fibres
Describe some of the features of alpha motor neurons
- Give rise to a large Type A alpha (Aα) motor neuron fibres which are very thick.
- These fibres innervate the large skeletal muscle fibres
- Stimulation of a single alpha nerve fiber innervates many fibres
Describe some of the features of Gamma motor neurons
- Far fewer Gamma than Alpha motor neurons
- Transmit signals via much smaller Type A gamme motor nerve fibres
- Innervate special small skeletal muscle fibres called intrafusal fibres (help control muscle tone as they make up the middle part of muscle spindles)
What are the other type of neurons in the spinal cord?
Interneurons
Sensory information from muscles to the spinal cord is provided by what?
- Muscle spindles throughout the belly of a muscle (send info about muscle length or rate of change of length)
- Golgi tendon organs located in muscle tendons ( Sends info about tendon tension or rate of change of tension)
Muscle spindal receptor excitation can be via?…
Lengthening of the whole muscle or contraction of end portions of the spindle’s intrafusal fibres (both streching the midportion of the spindle where sensory fibres originate from)
What are the two types of sensory endings in the central muscle spindle receptor area?
Primary afferent (Type 1a) - big
Secondary afferent (Type 2) - small
Name the different fibre types
Aα
Aβ
Aγ
Aδ (delta)
B
C
For each fibre type (
Aα
Aβ
Aγ
Aδ (delta)
B
C) name their conduction velocity(m/s), diameter (µm) and function
Aα - 70-120m/s, 12-20µm and their function is proprioception and somatic motor
Aβ - 30/40m/s, 5-12µm and their function is for touch and pressure
Aγ - 15-30m/s, 3-9µm and their function is motor to muscle spindles
Aδ (delta) - 12-30m/s, 2-5µm and their function is pain and temperature
B - 3-15m/s, 1-3µm and their function is preganglionic autonomic
C - 0.5-2m/s, 0.1-2µm and their function is postganglionic sympathetic, pain, temp and pressure
For each fibre (
Aα
Aβ
Aγ
Aδ (delta)
B
C) Name their other name
Aα - IA, IB (one A and B)
Aβ - II (two)
Aγ - II (two)
Aδ (delta) - III (three)
B - ?
C - IV (four)
What are the two types of muscle spindle intrafusal fibres?
Nuclear bag and Nuclear chain intrafusal fibres
What are some of the features of nuclear bag and nuclear chain fibres
Nuclear bag - 1-3 per muscle spindle and several nuclei gathered in ‘bags’
Nuclear chain - 3-9 per muscle spindle, 1/2 diameter and length of nuclear bags
Primary sensory nerve endings are excited by what?
Both nuclear bag and nuclear chain intrafusal fibres
Secondary sensory nerve endings are excited by what?
Only nuclear chain fibres
Gamma Dynamic motor neurons excite what? and gives what response?
Gamma-d excite mainly the nuclear bag intrafusal fibres and so the dynamic response of the muscle spindles is enhances but static response is not.
Gamma-static motor neurons excite what? and what response do they give?
Gamma-s excites mainly the nuclear chain intrafusal fibres and so enhanse static response but not on the dynamic response
What are the static and dynamic responses?
Static Response - Its a response from both primary and seconday endings to a change in length or the deceptor
Dynamic Response - This is a response that arises from stimulation of the primary endngs to a rate of change of receptor
Describe the basics of a muscle spindle strech reflex
Type 1a nerve fibre.
Branch of fibre goes directly to ventral horn of grey matter of spinal cord where it synapses with an anterior motor neuron and sends motor nerve fibres back to the same muscle where the muscle spindle fibre originated from.
Explain what a dynamic response is elicted by and and what occurs after it is elicited.
Elicited from dynamic signals from primary sensory endings of the muscle spindle caused by rapid stretch/unstretch. It opposes sudden changes in muscle length.
This is a fast response and means if a muscle is stretch/unstreched then a signal is transmitted to the spinal cord and a strong reflex contraction/decrease in contraction occurs (preventing muscle from ripping)
What is a static response elicited by and what does it involve?
It is elicited by continuous static receptor signals transmitted by primary and secondary endings.
It causes a degree of muscle contraction to remain constant and produces a slow gradual change.
What does reciprocal innervation mean?
It is innervation of a mucle(s) that is accompanied by the simultaneus inhibition of antagonist muscle(s)
(for example if quads are innervated then hamstrings are inhibited)
What is the function of a Golgi tendon organ receptor?
When is it stimulated?
It helps control muscle tension and is stimulated when the receptor is tensed by the contracting or stetching of the muscle
How does the Golgi tendon organ reflex prevent excessive tension
GTO stimulated by increased tension in the muscle, the signals are transmitted to the spinal cord to cause an inhibitory reflex thus preventing the development of too much tension. If the tension becomes extreme the inhibitory effect of the GTO causes instantaneous relaxation of the muscle.
Other than skeletal muscle, where else will you find reflexes?
In glands, heart, eyes, gut, vestibular system and capillary system
Give examples of reflexes involving special senses?
Rotatory Nystagmus - Eye movement driven by movement of visual images
Post Rotatory Nystagmus - Eye movement driven by the movement of fluid in the semi-circular canals of the inner ear
Interpretation of movement within images on the retina - used to make postural adjustments to preserve balance.
