Flashcards
Neuromotor 1
Cards in this deck (21)
- 1Describe neuromuscular synaptic transmissionNM synaptic transmission is the synapse that connects motor nerve cells to skeletal muscles. Governs all movement.
In the motor cortex there are Betz cells (UMNs) that send axons down the spinal cord and make direct or indirect connects with the MNs in the ventral horns of the spinal cord.
Acetylcholine receptors are in ion channels in the membrane of the muscle that gets activated, and allows the muscle to contract - 2functions of skeletal muscleSkeletal muscle is the effector organ
- Movement (including vocalisation adn respiration): maintains posture, stabilises joits, generates heat and helps with venous return
- lymphatic drainage
- vision
- reproduction
- digestion
- excretion - 3organisation of muscle structure- The whole muscle is made up of muscle fibres which are composed of myofibrils.
- the protein components of myofibrils are the thick myosin and thin actin filaments
- thick and thin filaments slide over eachother - cross bridge action for muscle contraction - 4features of the neuromuscular synapse (Junction) NMJ- biggest chemical synapse in the body
- excitable
- simple
- can undergo re innervation if damaged - 5connections of the NMJ- axons of cell bodies (alpha motor neurons/UMNs) in the ventral horn of the spinal cord make connections with skeletal muscle fibres. These axons are myelinated to facilitate propagation of APs. Nerve endings have vesicles containing NT (acetylcholine) which gets released into the synaptic cleft and binds to receptors on the post synaptic membrane (muscle). These are ligand gated channels, and when opened allow entry of Na+. Membrane reaches threshold and opens calcium channels, which initiate an AP.
- 6excitation contraction coupling of skeletal muscle1. Alpha MN AP to motor nerve terminal
2. Ca++ enters the nerve terminal and synaptic vesicles release acetylcholine
3. Acetylcholine binds to receptors and initiates a muscle AP
4. Muscle AP is propagated across the surface of the of the muscle and down the T tubules
5. muscle AP triggers Ca++ release from SR
6. Ca++ in the cytoplasm is free to interact with troponin on actin filaments. Set in motion the cross bridge cycle to bring about muscle contraction powered by ATP
7. Ca++ actively taken back up by SR by carrier Ca++ATPase pump in SR when local AP is no longer present
8. Contraction ends, actin slides back to original resting position - 7time delay in muscle action potential and contractionMuscle APs last for only 1-2ms, where as the muscle contraction that results can last ~ 50ms. The time delay between stimulation and contraction is called the latent period
- 8what is rate modulationincreasing the firing rate of motor units (AP frequency)
each motor unit increases its force contribution as frequency increases - 9lambert eaton syndromeAuto immune self antibodies to the pre synaptic voltage gated calcium channels, Poor pre synaptic release of NT leads to NT block.
- 10Botulinum (botox)targets snap25 vesicles, so they can't release NT into the synaptic cleft
- 11what is a motor unita motor unit = 1 motor neuron and the number of muscle fibres it innervates,
small motor units have fine control but weaker muscle contraction
larger units have less control but larger contraction - 12what happens if one motor neuron diesUsually larger neurons die first (type 2 fibres). When one dies, the muscle fibres it innervates become deinnervated. The muscle pumps out growth factors and the small motor neuro will branch and make new connections with the dead connections. All fibres will become type 1, this is called fibre type conversion. Fibre type is dictated by the MN.
- 13Fibre type groupingchronic denervation re-innervation events lead to type 1 fibre predominance. Best seen in MND where fast MNs die first. Also seen in ageing where fast MNs may be more vulnerable with age. The total muscle contraction becomes type 1, slow type muscle fibres.
- 14Henneman's Size PrincipalFor a given synaptic input motor neurons with the smallest cell bodies are activated first, and large are activated last. Smaller neurons have higher membrane resistance and require lower depolarising current to reach spike threshold.
- 15small medium and large motor neuron fibre typesSmall MNs to slow type muscle fibres (smallest tension but non fatigable - used to maintain posture etc)
Medium MNs to fast fatigable resistant type muscle fibres IIA
Large MNs to fast fatigable type muscle fibres IIX (IIB) - 16Motor unit recruitmentSmall MNs, then with increasing synaptic current input larger MNs are activated
this increases whole muscle tension - 17control of motor activity(control of motor neuron output)
3 levels of input control motor neuron output
1. input of afferent (sensory) reflexes
2. priimary motor cortex (direct - hierarchial)
3. multi-neuronal motor system (indirect - parallec) - 18Muscle sensory receptors- Muscle spindles and golgi tendon organs
- Joint receptors information on spatial position of joints
I) muscle spindles - 2 types of intafusal muscle fibres
- nuclear bag: muscle length and velocity
- Nuclear chain: muscle length
Muscle spindles (chain and bag) receive motor innervation via gamma motor neurons
Muscle spindles are activated by stretch e.g. tap the patella tendon will cause the muscle spindle to lengthen and thus activate it - 19Gamma MNsAct on muscle spindles to keep in register with the changing length of extra-fusal muscle fibres
Gamma MNs maintain muscle spindle sensitivity during muscle contraction - 20Golgi tendon organs- located in the tendinous insertions of muscle
- encapsulated structure with afferent type IB nerve endings
- intertwined amongst collagen fibres
- detects changes in muscle tension - 21activation of golgi tendon organsGolgi tendon organs are activated by increases in muscle tension and thus measure the degree of tension/load that the muscle is under. E.g. as the muscle contracts, it is trying to shorten. This puts increased stretch-tension on the tendons at each end of the muscle, as these tendons dig into the bone. This causes the collagen fibres to close up and pinch in on the inter winding sensory nerve endings.
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- 2065 Flashcards on Neuromotor 1, created by Soph B on 27/10/2019.
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