Physiology Flashcards
Explain what a motor unit is
A single alpha motor neuron and the muscle fibres that it innervates
What is a muscle fibre?
How big is it?
1 muscle cell
Typically the full length of the muscle
What is the neurotransmitter at the neuromuscular junction?
ACh
What 2 things are needed for muscle contraction?
Ca2+
ATP
Where does skeletal muscle get its Ca2+ from?
SR only
Ca2+ is released from lateral sacs as action potential spreads down transverse (T)-tubules
(look at diagram in notes)
Explain how rigor mortis takes place?
Muscles need ATP in order to contract and RELAX
Without ATP muscles continually seize
What is the smallest functional unit in skeletal muscle?
Sacromere
Functional unit = ability to carry out full function of cell
Draw and label a sacromere: A band H zone M line I band
A band - area of actin and myosin that overlaps
H zone - central area of myosin with no overlap of actin
I band - peripheral areas of actin with no myosin underneath
M line - central part of myosin
What has more muscle fibres per motor unit - intricate muscles or large powerful muscles?
Intricate muscles - fine movement requires more motor units per muscle fibres
What 2 things is the gradation of muscle contraction dependant on?
- No of motor units stimulated (motor unit recruitment)
- Summation of contractions + length of fibre
Explain how tetanus can become a thing in skeletal muscle
In skeletal muscle action potentials are much smaller than contractions
Hence multiple action potentials can occur and enable constant contraction of muscle
What prevents cardiac muscle from becoming tetanised?
Long refractory period
What is optimum length of muscle?
The optimum overlap of actin and myosin that allows for maximum tetanic tension
What are the 2 types of skeletal muscle contraction - describe them both?
Isotonic - length changes and tension stays the same
Isometric - length stays same and tension changes
Met = police = rising tension
How is muscle contraction in sarcomeres communicated to the bones of the body?
Via the elastic component of muscle e.g. tendons/connective tissue
What impact does increased load have on velocity of muscle contraction?
Increased load decreases velocity of contraction
think if holding something v heavy on fingers it would take more time to scrunch up hand
Describe how each of the following types of fibres get their energy:
Type I
Type IIa
Type IIx
Type I - slow twitch - aerobic
Type IIa - intermediate-twitch - aerobic and anaerobic
Type IIx - fast twitch - anaerobic
What pathways are involved in providing immediate energy to muscle cells and energy in oxygenated and deoxygenated situations
Immediate - transfer of creatine phosphate to ADP = ATP
Oxygenated - oxidative phosphorylation
Deoxygenated - glycolysis
What is a stretch reflex?
Sterotyped response to a specific stimulus
Stretching of the muscle results in firing of what kind of neurons
Afferent neurons
What are muscle spindles also known as and what are the sensory nerve endings found within them called?
Where are they found?
Intrafusal fibres - in the belly of the muscle
Annulospiral fibres
What motor neurons supply the intrafusal fibres (muscle spindles)?
What is the role?
Gamma motor neurons
Maintain sensitivity of intrafusal muscle fibres to stretch
What are nociceptors?
What are noxious stimuli?
1st order neurons
Afferent neurons activated NORMALLY by noxious stimuli
Thermal, mechanical and chemical
What are the 2 types of nociceptors and compare them based on:
- Speed of transmission
- Response to what kind of stimuli
- Myelination
A𝛿-fibres
- Fast/1st
- Thinly myelinated
- Mechanical/thermal
C-fibres
- 2nd/slow
- no myelination
- ALL noxious stimuli (polymodal)
Describe the pathway of a 1st order neuron
From site of noxious stimuli
Travels to soma (cell body) in dorsal root ganglion
Terminates in dorsal horn of spinal cord
What neurotransmitters are found between afferent 1st and 2nd order neurons? (in dorsal horn of spinal cord)
Peptides and glutamate
What are the 2 tracts of 2nd order neurons and what is each responsible for?
Where do they travel?
Spinothalamic tract (STT) - Perception of pain (intensity and location)
Spinoreticulothalamic tract (SRT) - autonomic response to pain, arousal, fear etc.
Anterolateral system
Where do 2nd order neurons terminate?
Thalamus
How is pain classified?
Time course Severity Source of pain (visceral/somatic) Mechanisms - Nociceptive - Inflammatory - Pathological
What mechanisms of pain are adaptive? What are maladaptive?
Adaptive
- Nociceptive
- Infammatory
Maladaptive
- Pathological
In terms of inflammatory pain what is hyperalgesia and what is allodynia?
What causes inflammatory pain?
Hyperalgesia - increased sensitivity to noxious stimuli
Allodynia - increased sensitivity to innocuous (harmless) stimuli
Activation of immune system - increased cytokine production and local inflam
What are the 2 types of pathological mechanism, describe them
What analgesics can be used?
Neuropathic - damage to neural tissue
Dysfunctional - no identifiable damage/inflam e.g. IBS
Normal analgesics don’t work - ~use anti-depressants
What gives skeletal muscle it’s striated appearance?
Dark areas = A zone (where myosin and actin overlap)
Light zones = I zone (where actin is without myosin)
How does the rapid termination of muscle contraction occur?.
ACh is broken down by AChE (acetylcholinesterase) at the end plate membrane
How does Ca+ release from the SR lead to muscle contraction?
Ca+ binds to troponin on actin which causes tropomyosin to move out of the way and thencross-bridge binding sites are avaliable for myosin to bind to actin and contract
