Spinal and neuromuscular.. Flashcards
Describe transmission across synapse
The membrane potential of the post synaptic neurone can be altered in two directions by inputs. It can be made less negative – i.e. be brought closer to threshold for firing; this is an excitatory post synaptic potential (EPSP) OR It can be made more negative – i.e. be brought further away from threshold for firing; this is an inhibitory post synaptic potentials (IPSP) Graded effects = SUMMATION. EPSPs & IPSPs can also SUMMATE. The degree of summation will determine how readily a neuron can reach threshold to produce an action potential.
LO30 What is the neuromuscular junction? How is it activated?
A specialised synapse between the motor neuron and the motor end plate, the muscle fibre cell membrane. When an action potential arrives at the MNJ, Ca2+ influx causes ACh release. ACh binds to receptors on motor end plate. Ion channel opens – Na+ influx causes action potential in muscle fibre. At rest, individual vesicles release ACh at a very low rate causing miniature end-plate potentials (mEPP
LO31 What are alpha motor neurons?
the lower motor neurons of the brainstem and the spinal cord -in ventral horn of spinal cord They innervate the (extrafusal) muscle fibres of the skeletal muscles Their activation causes muscle contraction The motor neuron pool (in ventral horn) contains all alpha motor neurons innervating a single muscle
LO32 What is a motor unit?
Single motor neuron together with all the muscle fibres that it innervates. - It is the smallest functional unit with which to produce force. - Stimulation of one motor unit causes contraction of all muscles fibres in the unit
LO32 Name and describe the 3 types of motor unit.
- Slow (S, type 1) smallest diameter cell bodies small dendritic trees thinnest axons slowest conduction velocity 2. Fast, Fatigue Resistant (FR, Type 2A) largest diameter cell bodies larger dendritic trees thicker axons faster conduction velocity 3. Fast, fatiguable largest diameter cell bodies larger dendritic trees thicker axons faster conduction velocityt
LO32 What are the different motor unit types classified by?
classified by amount of tension generated, speed of contraction and fatiguability of the motor unit photo in slide
Describe the two mechanisms by which the brain regulates the force that a single muscle can produce.
- Recruitment: Smaller units are recruited first (these are generally the slow twitch units). As more force is required, more units are recruited. This allows fine control (e.g. when writing), under which low force levels are required. 2. Rate coding: Slow units fire at a lower frequency. As the firing rate increases, the force produced by the unit increases. Summation occurs when units fire at frequency too fast to allow the muscle to relax between arriving action potentials
Give the order of recruitment and de-recruitment of motor units.
recruitment: slow -> fr -> ff de-recruitment: reverse order
Motor units can be affected by neurotrophic factors. What are they. What is their effect?
Are a type of growth factor Prevent neuronal death Promote growth of neurons after injury effect?
Give 3 examples of motor unit plasticity, ie when fibre types change properties under different conditions. (from one type to another)
1.Type IIB to IIA most common following training 2.Type I to II possible in cases of severe deconditioning or spinal cord injury. Microgravity during spaceflight results in shift from slow to fast muscle fibre types 3.Ageing associated with loss of type I and II fibres but also preferential loss of type II fibres. This results in a larger proportion of type I fibres in aged muscle (evidence from slower contraction times)
LO33 Summarise the functional organisation of the spinal cord (motor tracts)
- 2a: automatic movements of arm in response to posture/balance
- 2b: coordinate automated movements of locomotion and posture (Eg to painful stimuli)
- 2c: regulates posture to maintain balance and facilitates mainly a motorneurons of the postural, anti-gravity (extensor) muscles
LO34 What is a reflex?
An automatic and often inborn response to a stimulus that involves a nerve impulse passing inward from a receptor to a nerve centre and then outward to an effector (as a muscle or gland) without reaching the level of consciousness. An involuntary coordinated pattern of muscle contraction and relaxation elicited by peripheral stimuli
LO 34 Describe the monosynaptic (stretch) reflex.
slide
Describe the polysynaptic reflec
LO 34 Describe the flexion withdrawal (& crossed extensor) reflex.
