Physiology Flashcards
Where on the neurone decides whether to initiate an all or nothing action potential?
Axon Hillock
Unipolar neurones occur where?
Peripheral autonomic
Pseudounipolar neurones occur where?
Dorsal root ganglion
Bipolar neurones occur where?
Retinal bipolar neurone
Multipolar neurones occur where?
Lower motor neurones
What triggers the upstroke within a neuronal AP?
Na + influx
Voltage gated Na+ channels
What triggers the downstroke within a neuronal AP?
K+ efflux
Voltage gated K+ channels
Why if signalling was passive would the AP diminish as it travels along the neurone?
The membrane is leaky allowing ions to exit the axon and reducing the concentration gradient reducing speed of transmission.
Saltatory Conduction is enabled by what?
The nodes of Ranvier formed between myelin sheath.
Why does myelination increase the speed of conduction?
As it insulates the axons preventing leakage of ions and maintaining the concentration gradient.
Ion channels only located at nodes thus conduction jumps from one node to the next.
How would you increase the passive conduction speed of a neurone?
Decrease Ri - Increase axon diameter
Increase Rm - Add insulating material
Influx of what ion causes the exocytosis of vesicles containing the neurotransmitter?
Ca 2+
What types of synapse are there?
Axodendritic
Axosomatic
Axoaxonic
Axodendritic
Synapse between axon and dendrite
Axosomatic
Synapse between axon and Soma ( cell body )
Axoaxonic
Synapse between axon and axon
What is the main excitatory neurotransmitter?
Glutamate
How does Glutamate cause an increased +ve AP?
Activates postsynaptic Cation selective channels
What is the main inhibitory neurotransmitter?
GABA
How does GABA cause an increased -ve AP?
Activates postsynaptic anion selective channels
Influx of Cl- ion
What are the two main forms of synaptic summation?
Spatial and Temporal Summation
What is the purpose behind summation?
Calculation of excitatory and inhibitory AP that responds too many stimuli from the surroundings allowing a proportionate response.
Spatial Summation
Convergence of many inputs upon a neurone to determine its output.
Determined by the axon hillock whether the sum of the AP input is enough to surpass the threshold to trigger an all or nothing response.
Temporal Summation
If a single input fires frequently enough it can trigger an all or nothing response.
Direct postsynaptic membrane potential is activated by…
Ionotropic receptors
Why do inotropic receptors result in rapid opening of the ion channels?
Ionotropic receptors are integral to the ion gates
Indirect postsynaptic membrane potential is mediated by
Metabotropic receptors
Metabotropic receptors result in rapid opening of ion channels? T/F
False - Activation results in slow opening of ion channels
Why does metabotropic receptors cause a slow opening of ion channels?
G - protein coupled receptor
Receptor is separate to the ion channel
Muscarinic receptors are usually
Metabotropic
Nicotinic receptors are usually
Ionotropic
How are ionotropic receptors classified?
Via lab induced responce to foreign agonist
What are the two types of Ionotropic receptor
non NMDA
NMDA
Non-NMDA channels
Ionotropic
Permeable to Na+ and K+
Fast brief AP
What do Non-NMDA channels react to?
AMPA and Kianic acid
NMDA channels
Ionotropic
Permeable to Na+ Ca 2+ K+
Slow long AP
What do NMDA channels react to?
NMDA
What is a motor unit?
An alpha MN and all the skeletal muscle fibres it innervates.
What is a motor neurone pool?
The collection of alpha MN that supply a whole muscle.
What determines the force of contraction?
Frequency of AP discharge
Recruitment of additional synergistic motor units
What three things regulate alpha motor neurones
Central terminals of dorsal root ganglion
UMN
Spinal Interneurones
Why do twitches occur?
A isolated Alpha MN neurone firing
What is the difference between a twitch and a contraction?
A twitch is an isolated alpha motor neurone firing, a contraction is the summation of many alpha MN firing.
The motor units that control fine movements are large. T/F
False small motor units allow refined smaller muscle movements
What differentiates skeletal muscle fibres?
How quickly myosin ATPase splits ATP to provide energy.
Different myosin heavy chains
ATP - Type 1 muscle fibres
Slow Oxidative
ATP mostly from oxidative phosphorylation
Describe Type 1 Slow Oxidative fibres
Slow Contraction and relaxation
Fatigue resistant
Red fibres due to high myoglobin
ATP - Type 2a muscle fibres
ATP from oxidative phosphorylation
Describe Type 2a muscle fibres
Fast contraction and relaxation
Fatigue resistance
Red and reasonably well vascularised
ATP - Type 2b and 2x muscle fibres
ATP from glycolysis
Describe Type 2b and 2x muscle fibres
Fastest contraction but not fatigue resistant
Pale in colour and poorly vascularised
Type 2B muscle fibres are present in all mammals.
T/F
False only present in small mammals it is not found in humans.
What are the three types of motor unit?
Fast Contraction + Fatiguing + Very high tension
Fatigue resistant + High tension
Slow Contraction + Fatigue Resistant + Low tension
Fast Contracting, Fatiguing, Very High Tension
Describe
Large alpha MN
Type 2x
Burst power
Fatigue resistant + High tension
Describe
Intermediate alpha MN
Type 2a
Sustained Locomotion
Slow Contraction + Fatigue Resistant + Low tension
Describe
Small alphaMN
Type 1 fibres
Antigravity muscle
Why do smaller alpha MN have a lower activation threshold?
Allows fine control of muscle force as they activate prior to the larger stronger motor units.
Appropriate force for the task
What is the Myotatic (myotonic) reflex?
Muscle spindle within the muscle registers and reacts to a change in the length of the muscle.
What forms a spindle fibre?
Fibrous capsule
Intrafusal muscle
Sensory afferents
Gamma Motor neurone
What class is the sensory afferent found in the spindle fibre?
Type 1a
Myelinated and very fast conduction
What does the sensory afferent innervate in the spindle?
The intrafusal muscle which reports on the tension within the muscle.
What motor neurone innervates the intrafusal muscle fibre?
Gamma MN
What neurotransmitter regulates the myotatic reflex?
Glutamate
What is the function of the Gamma MN?
To accurately record an inform on the tension within the whole muscle the intrafusal muscle fibre must be kept at the same tension as the whole muscle.
This achieved by the gamma MN
What kind of reflex is the myotatic ?
Monosynpatic
What are intrafusal nuclear bags?
Sensory muscle fibres that lie in the middle of the Spindle fibres.
What are the two types of Nuclear Bag?
Bag 1 - Gama MN
Bag 2- Static Gamma MN
Static Gamma MN
Sensitive to the absolute length of the muscle
Bag 1 Gamma MN
Very sensitive to the rate of change
How many afferent fibre innervate the intrafusal bag?
Two
1a = A alpha - wraps around all the fibres
2 = A Beta - Slower conducting wraps all fibres except dynamic Bag 1.
From the two afferent fibres which innervate the intrafusal bag which is more sensitive to rate?
1a
In slow and predictable muscle movement which MN are active?
Static Gamma MNs
In rapid and unpredictable muscle movement which MNs are active?
Dynamic Gamma MNs
Where are Golgi tendons organs located?
At the junction between the tendon and the muscle.
What is the purpose of the Golgi tendon organs?
To monitor changes in the extrafusal muscle tension to prevent muscle overload and regulate tension to an optimal range.
What innervates the Golgi tendon organs?
Type 1b sensory
Describe 1b sensory neurones
Myelinated slower than 1a
If type 1b neurones detect too much tension within the Golgi tendon organ what happens?
Synapse onto a inhibitory interneurone
Interneurone synapses onto an alpa MN of homogenous muscle, leading to a reduction in tension.
What two key things help in proprioception?
Threshold
Adaption
What is threshold?
The strength of the stimuli required to initiate an action potential.
What is adaptability?
Slow adapting - AP produced so long as stimuli is present
Fast adapting - AP produced only at the moment stimuli is applied
Describe free nerve endings
High Threshold
Slow Adapting
Nociceptive (Pain)
Describe Golgi type
High Threshold
Slow Adapting
Protective
Describe Paciniform
Low threshold
Fast Adapting
Found within periosteum - detects acceleration
light touch in dermis and fascia etc
Describe Ruffini
Low Threshold
Slow Adapting
Static position and location of the joint
Found in joint capsule
Where do spinal interneurones get input from?
Primary sensory axons
Descending axons
Collaterals
Other interneurones
What is the role of spinal inter neurones?
Intergate incoming information to generate an output, much quicker as no conscious input.
What is the main role of inhibitory interneurones?
Mediate Reciprocal inhibition
Generally for a joint to move the antagonistic muscle needs to be relaxed.
What are two reflexes that the excitatory interneurones control?
Flexor reflex
Crossed extensor reflex
What is the flexor reflex?
Contraction of the flexor
Relaxation of the extensor via excitatory and inhibitory
What is the crossed extensor reflex?
Painful stimuli on one side
Opposite limb contraction of extensor
relaxation of flexor
Enhances postural support during withdrawal of limb from painful stimuli.
