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Reflexes
Karten in diesem Stapel (69)
- 1what is a reflex?have a sensory component and an effector component
- does not involve conscious thought = autonomic - 2what are motorneurons?neutrons that cause muscles to move
- 3monosynaptic reflexone synapse
- sensory nerve fibre synapses in the spinal cord
- onto a motorneuron that travels to the effector muscle - 4what are the peripheral differences in axons?- diameter
- myelination - 5what is the fastest nerve fibre?A alpha then beta then gamma
- 6what do somatic nerve fibres supple?skeletal muscles
- 7what type of nerve fibres are somatic nerves?alpha
- 8what neurotransmitter is released at the somatic nerve fibre NMJ?Ach
- 9what do somatic nerve fibres always lead to?muscle excitation
- inhibition take solace due to interneurons - 10classification based on conduction velocityAalpha - 70 -120 m/s
A beta - 30-70 m/s
A gamma - 15-30 m/s
A Delta - 12-30 m/s
B - 3-15 m/s
C - 0.5-2 m/s - 11classification based on diameterAalpha - 12-20 μm
A beta - 5-12 μm
A gamma - 3-6 μm
A Delta - 2-5 μm
B - 1-3 μm
C - 0.1-2 μm - 12function of fibre typesA alpha - proprioception, somatic motor
A beta - touch, pressure
A gamma - motor to muscle spindles
A delta - pain, temperature
B - preganglionic autonomic
C - postganglionic sympathetic, pain and possibly heat, cold and pressure - 13classification based on sensory function1a - muscle spindles
1b - golgi tendon organs
2 - muscle spindles, touch and pressure receptors
3 - pain and temperature receptors
4- pain and other receptors - 14which section of the spinal cord controls muscles?a pool of MNs on the anterior horn
- flexors are more dorsal then extensors
- distal muscle are more lateral than axial ones - 15UMN and LMNUMNs are contained entirely within the CNS but LMN project outside the CNS to the muscle
- 16what control do small motor units give?highly precise
- 17what does the annual spectrum of motor unit sizes within a given muscle depend on?1. The precision of control required (small motor units gives highly precise i.e. fingers, eyes)
2. The force of contraction required or a low precision (large motor units ie postural muscles or calf muscles) - 18what is the intensity of a particular muscle's contraction is graded by?1. Alterations in the frequency with which any single motor neuron fires action potentials
2. Recruitment of α-motor neurons - 19how many motor neurones can innervate one muscle fibre??one
one muscle can be innervated by several motor neurons
Neighbouring fibres may be innervated by different neurons - 20how easy to excite are the small and large alpha MNs?Motor neurons at the smaller end of the (12-20micrometres and 70-120m/s) form smaller motor units and are more readily excited
Motor neurons at the larger end form larger motor units and are harder to activate - 21what fibres do small MNs innervate?slow oxidative muscle fibres (small motor units) so can give low power but sustained effort
- 22what fibres do large MNs innervate?fast glycolytic muscle fibres (large motor units) give high power but fatigue quickly
- 23why are large MNs harder to recruit?- the smaller MN resting membrane potential is closer to the AP threshold than a large MN
- more EPSPs are needed to reach the large alpha MN AP threshkoth - 24what is a polysynpatic reflex?- more than one synapse
- these reflexes can be ipsilateral or contralateral or both - 25what are the two ways reflexes can be classified?1. Intrasegmental – the reflex arc is restricted to one or two spinal cord segments
2. Intersegmental – the reflex arc involves a number of spinal cord segments - 26why is the brain bypassed?the reflex is then achieved at maximum speed
- 27muscle reflex time components?1. Activation of sensory receptors (start the clock)
2. Conduction to CNS along nerve fibres from receptors
3. Transmission across neuron/neuron synapses in CNS (1-2ms)
4. Conduction from CNS along nerve fibres to muscle
5. Activation of muscle contractile machinery (5ms) - 28what are muscle stretch reflexes used for?These reflexes enable muscle to oppose external forces that tend to elongate them
- 29what are muscle stretch reflexes mediated by?- sense organs within muscles known as
muscle spindles - 30what are muscle spindles mounted in parallel to ?the extrafusal muscle fibres
- 31what innervates extrafusal muscle fibres?alpha MNs
- 32what are intrafusual muscle fibres innervated by?A gamma MNs
- innervate the contractile part of the spindle (end parts) - 33what are the afferent neurones of muscle spindlesgroup 1a and 2
- form the less elastic/contractile, sensory portion (middle) - 34how many intarfusal fibres are there per spindle?8 - 10
- 35what are the two types of intrafusal fibresbag and chain
- depending on where the nuclei are - 36function of the central portion of the spindle- provides the sensory output for muscle length
- however it is sensitive only over a relatively small change in length - 37when is the spindle at its least sensitive?When the muscle is almost completely contracted, the spindle sensitivity is at the most compressed part of its range
- 38how is low sensitivity of the spindle prevented?the length of the spindle is adjusted to keep it within its most sensitive range by extending or shortening the contractile spindle ends depending on the state of the whole muscle.
- 39how is the spindle length adjusted?the CNS activates the gamma motor efferents to the spindle in concert with the alpha motor neuron activation of the extrafusal muscle fibres
- 40what are the chain spindle fibres innervated by?both 1a and 11 sensory nerve fibres
- chain fibres are most common
- so called because the nuclei are arranged in a chain in the central portion - 41what do 1a fibres give?rate of change
- 42what do type 2 fibres give?total length
- 43what are bag fibres innervated by?type 1a so only give rate of change in length infor
- only one or two per spindle
- so called because of the selling in the equatorial region which house the nuclei - 44how do skeletal muscles respond in a similar way to being stretched?they contract when artificially extended by tapping the tendon
- these reflexes are mediated by the muscle spindles in the muscle - 45how many spindles are there per extrafusal muscle fibres?50 per 100
- 46what is reciprocal innervation?to reach optimum efficiency, contraction of opposing muscles must be inhibited while muscles with the desired action are excited.
This reciprocal innervation occurs so that the contraction of a muscle results in the simultaneous relaxation of its corresponding antagonist.
(flexion of the elbow)
(triceps must be inhibited for biceps to be excited) - 47mechanism of reciprocal innervation1. spindle sensory nerve fibres from one (homonymous) muscle Influence motor neurones projecting to antagonist muscles
2. The effect is opposite to that on their own muscle
3. Relaxes antagonist muscles and facilitates shortening of homonymous muscle - 48how is the inhibition of the antagonist muscle achieved?4. Requires the involvement of a local inhibitory neuron in the reflex onto the antagonist muscles
- 49when a voluntary signal for muscular contraction leave stem spinal cord, what neurones does it make contract?travels to both intrafusal (via Gamma MN’s) and extrafusal muscle fibres (via Alpha MN’s) causing both sets of fibres to contract
- 50what part of the spindle changes length during voluntary contraction?spindle fibre ends contract (shorten) but the centre stays the same
so the anulospiral sensory endings do not detect a change in muscle
length - 51during involuntary stretch which part of the spindle changes length?Intrafusal stretched in center, so output is changed
- 52what do muscle spindles monitor?muscle length, rate of change in length & duration of the change
- 53how is length monitoring achieved?by activation of both principal (group IA) sensory fibres and secondary (group II) sensory fibres on both bag and chain intrafusal fibre types.
- 54what do stretch reflexes act to minimise?unexpected change in muscle length
- 55what causes the contraction of the intrafusal muscle fibres?gamma MNs
they adapt the working range of the fibres to the current muscle length - 56what is the function of Golgi Tendon Organs?They monitor the tension in the muscle because they are in series with the muscle fibres
- regulate the amount of tension that develops in a muscle and, in extreme conditions, to protect the muscle and tendon from damage.
They compliment the information from the muscle spindles in the CNS
- prevent tearing of the muscle - 57how do the GTOs work?as the tendon is put under increasing tendon, the more the collagen fibres lock onto and stretch the 1B sensor fibres
- 58what does the process of increased tension do to the generator potential?increased the GP and speeds signal frequency
- 59how to GTOs function in a reflex arc?provide reflex inhibition to the motor neurons in who's tendon they are located ( their homonymous MNs)
- 60what kind of reflex do GTOs work in?- disynaptic
- 61how do the GTOs regulate tension?The more alpha MN’s that are activated by the CNS, the more the muscles contract and the more tension develops.
As tension develops,
1. the GTO’s increase their rate of firing
2. and so increase the inhibition to the alpha MN’s.
3. This consequently reduces the tension in the muscle. - 62what is skeletal muscle contraction a combination of?1. Alpha MN mediated contraction (under the control of the CNS)
2. Gamma MN mediated spindle fibre contraction enabling accurate feedback
3. GTO mediated inhibitory feedback to the alpha MNs - 63damage to peripheral nerves and effect of reflex?reduction or loss of reflex
- 64damage to pathway from the brain?some reflexes become exaggerated
- 65what is rotatory nystagmus?can be demonstrated when the head is rotating at constant velocity
driven by moving visual images
the eyes flick rapidly in the direction of movement - 66post rotatory nystagmusIf a subject is spun a little faster, if the chair is stopped abruptly after a period of rotation, the eyes of the subject make movements known as post-rotatory nystagmus
In this case, the rapid phase of the eye movements occurs in the opposite direction from the prior rotation.
- eye movements driven by the movement of fluid in the semi circular canals of the inner ear - 67what causes the post rotatory nystagmus?a reflex that is driven by nerve signals from the semi-circular canals of the inner ear.
- 68effect of NS on pupil of the eye (ocular reflexes)when alarmed or exited - sympathetic NS dilates pupil
PSNS constrict the pupil - 69CDV reflexes BPSympathetic NS
1. increases the heart rate as well as the force of contraction
2. Increases the peripheral resistance by constricting small
arterioles
3. Parasympathetic NS reduces the heart rate but has less of
an effect of peripheral resistance than the sympathetic system
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- Neurology Karteikarten am Reflexes, erstellt von hazel wilkie am 06/05/2017.
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- hazel wilkie
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