lecture 26 Flashcards

Question

What are the roles of Gamma (y) motor neurons?

Answer 1

Extrafusal muscle fibres , innervated by alpha motor neurons. The single element= muscle spindle muscle spindles are in PARRALLEL to extrafusal muscle fibres. are also smaller and embedded in the muscle -when whole muscle extends/is stretched, the muscle spindles will be stretched. -When whole muscle contracts, the muscle spindles will become flaccid/relax, and assume a different tragectory Sensory parts of muscle spindle is located in the Cetnre of the muscle spindle. --> you Have Anular spinal spiral like endings of 1a afferent -when muscles are stretched, because the muscle spindles are mechanoreceptors (sensitive to stretch), there will be a burst of AP action potentials to be innervated -the Axon of gamma motor neurons activate the contractile elements in the muscle spindles located only in the periphery. --activation via ACh. will be contraction of peripheral parts of the muscle spindles

Answer 2

in the centre of the muscle spindle | Anular spinal spiral like endings of 1a afferent in the Centre of the muscle spindle

Answer 3

in the Periphery the Contractile elements of muscle spindles are ONLY located in the Periphery -they're activated bia ACh release --> these peripheral parts(of the muscle spindle) will then contract

Answer 4

Commands from Forebrain and sent to Alpha motor neurons muscle contracts- if load isnt to big Muscle contraction= isotonic= muscle shortens Peripheral contractile parts of the muscle spindle becomes flaccid/completely relaxed and the action potentials which are normally initiated (from the centre) have seized -as there is no longer any stretch of the muscle spindle WithOUT Gamma Motor neurons: As a result of activation of alpha motor neuron, through AP entering through the Alph motor neuron, and contracting extrafusal muscle fibres. Muscle spindles become silent, and stops sending any information to the CNS (including spinalcerebro tract cells to the forebrain) -the CNS wouldnt know what is happening to the muscle during contraction, as there is no longer any sensory feedback loop WITH Gamma motor neurons: contraction of extrafusal muscle fibres, causing shortening of the whole muscle. Simultaneously there are excitatory commands(ACh)/AP action potential coming from Gamma (y) motor neurons MNs. This leads to contraction of Intrafusal msucle fibres, which restore the stretch of the central part of the muscle spindle- theyre still generating action potentials in the 1a afferents -Interplay between activity of alpha MN and gamma MN. Interplay allows information to be fed to the brain via 1a afferents, even if the muscle contracts as a whole. "Gamma (y) motor neurons MNs keep muscle spindles at appropriate lengths so that they REMAIN ACTIVE during muscle shortening, which is evoked by alpha motor neurons" -This implies that there is a co-activation of alpha and gamma motor neurons by descending pathways (these 2x systems of the brain are almost simultaneously activated by descending pathways)

Answer 5

Isometric contraction | -actually not much change of the Length, but only a change in the Tension

Answer 6

Isotonic contraction - Load is not too large - muscle shortens

Answer 7

There is Co-activation of alpha MN and gamma MN (the 2x systems) via Descending pathways -these 2x systems of the brain are almost simultaneously activated b descending pathways

Answer 8

-involved in Reverse Myotatic Reflex Sensory receptors located in the TENDON (not the muscle itself) -receptors located in all tendons -parallel to belly of muscle -mechanoreceptors (activated due to stretch) When activated leads to activation/AP action potentials conducted in Sensory afferents (1b), travels via dorsal root ganglion cell, and there is a release of Glutamate at the synapse of 1b Inhibitory Interneurons. Ib interneurons are activated, and the GABA/glycene release with Hyperpolorise cell bodies of alpha motor neurons, causing the APs to stop. The muscle will relax. -Revers myotatic reflex is when you have a stretch of a muscle, which may lead to a relaxation of a muscle (Reverse myotatic reflex is Reverse to tendon/myotatic reflex)

Answer 9

Sensory afferents 1b conduct action potentials Slower

Answer 10

Revers Myotatic reflexes

Answer 11

Stretch of a muscle, which may lead to a relaxation of a muscle (Reverse myotatic reflex is Reverse to tendon/myotatic reflex) Receptors: Golgi tendon organs (in series/parallel to muscle) Afferens: 1b fibres Synaptic relays: 2x synapses = disynaptic reflex 1b afferents to 1b INTERneurons which INhibits a alpha motorneurons MNs Efferents: axons of a alpha MN motor neurons Effectors: muscles Under extreme conditions this reflex Protects muscle from overload -if there is too much stretch of muscle, muscle could tear. This Reverse myotatic reflex kicks in, and inhibits the contraction of muscle to avoid tear/damage. - at a certain point the muscle gives up. despite will to activate, the muscle reflex takes over and relaxes the muscle Physiological role of preventing muscle from excessive tension and possibly damage Normal function: to maintain muscle tension in optimal range - threshold for activation was lower than believed. Receptors can be engaged during physiological contractions - when tension is too high, they try to reduce the tension - when the tension drops too low then it removes inhibitory inhibition and the tension comes back

Answer 12

Disynaptic reflex | -has 2x synapses in CNS

Answer 13

Under extreme conditions this reflex Protects muscle from overload -if there is too much stretch of muscle, muscle could tear. This Reverse myotatic reflex kicks in, and inhibits the contraction of muscle to avoid tear/damage. - at a certain point the muscle gives up. despite will to activate, the muscle reflex takes over and relaxes the muscle Physiological role of preventing muscle from excessive tension and possibly damage

Answer 14

to maintain muscle tension in optimal range - threshold for activation was lower than believed. Receptors can be engaged during physiological contractions - when tension is too high, they try to reduce the tension - when the tension drops too low then it removes inhibitory inhibition and the tension comes back

Answer 15

Nociceptor reflex (pain- remove from hot or sharp) Evokes a FAST withdrawl of limb from a nociceptive stimulus Complex pathway: When pain afferents enter spinal cord, dont just go to 1x segment, but harbourise and enter nerve cells in 2-4 segments. =shows is not a response of a single muscle, but of co-ordinated response of a group of muscle -excitatory neurons involved in multisegmental level which activates motor neurons contolling flexors Protecting reflex (remove from pain) Person steps on glass. Nociceptor stimulus/pain receptor stimulus. Activation of Pain afferens, which go through dorsal root ganglion cell, and enter spinal cord. Activation of flexors (physiological muscles are defined(e.g. flexor) by how they respond to the withdrawl reflex). Physiological flexors will always contract, and physiological extensors will often relax. Flexion of knee joint due to contraction of lower limb hamstring muscles and also to leg Gastrocnemius and soleus =foot is withdrawn from nociceptive stimulus

Answer 16

When there is no response to painful stimulus, there is the withdrawl reflex - Pinch animals Tail/Hind limb - see whether there is a withdrawl - No withdrawl if there is an appropriate level of anaethesia Surgery, anaethesiologist. -surgeon piercing skin with scalpel, which is a very painful stimulus. Doesnt want any reflexes/contraction of muscles around. General level of anaethesia has to be high, to prevent this reflex

Answer 17

Complex pathway: When pain afferents enter spinal cord, dont just go to 1x segment, but harbourise and enter nerve cells in 2-4 segments. =shows is not a response of a single muscle, but of co-ordinated response of a group of muscle -excitatory neurons involved in multisegmental level which activates motor neurons contolling flexors

Answer 18

evokes a fast withdrawal of a limb from a Nociceptive stimulus

Answer 19

Receptors:nociceptors Afferents: Type III and IV fibres (slowly conducting and some unmyelinated whilst others are myelinated) belong to type 3 and 4. Pain afferents are slowly conducting -pain may be slow, but it will get you). Most difficult form of pain is CHRONIC continuous pulsing pain, rather than acute pain. doesn't matter about speed of conduction velocity, the brain is still receiving continuous information whether it comes fast or slow- there is still suffering Synaptic relays: to Excitatory INTER neurons which excite flexor alpha MNs motor neurons (afferents project to multiple spinal segments) -excite multiple muscles to flex Efferents: axons of a alpha MN motor neurons Effects: Flexor muscles

Answer 20

Slowly conducting can be either myelinated or unmyelinated afferens belong to either type 3 or 4 fibres (III or IV) -pain may be slow but it will get you -Most difficult form of pain is CHRONIC continuous pulsing pain, rather than acute pain. doesn't matter about speed of conduction velocity, the brain is still receiving continuous information whether it comes fast or slow- there is still suffering

Answer 21

If you lift one leg, unless you have support of other leg, that cut leg would fall down Therefore Flexion withdrawal reflex works in connection/harmony with Crossed-extension reflex -Significance for maintaining balance when nociceptive receptors in a foot are activated

Answer 22

activated after Flexion (flexor/withdrawal) reflex | Maintains balance when nociceptive receptors in a foot are activated