Neurology 9 - Neuromuscular and Spinal Cord Flashcards
1
Q
Describe the transmission across synapses
A
- Can make membrane potential less negatve (excitatory post synaptic potential)
- Can make membrane potential more negative (inhibitory post synaptic potential)
- Added together this is summation
2
Q
Where are the alpha motor neurons found?
A
- Brainstem and ventral horn of the spinal cord
- Innervate the extrafusal muscle fibres of skeletal muscles
- Activation causes voluntary muscle contraction
- Motor neuron pool contains all alpha motor neurons innervating a single muscle
3
Q
What is a motor unit?
A
- Smallest functional unit with which to produce force
- The name given to a single motor neuron together with all the muscle fibres that it innervates.
- Stimulation of one motor unit causes contraction of all of the muscle fibres innervated
4
Q
List the types of motor unit
A
- Slow (S type 1, smallest cell bodies, small dendritic trees, thin axons)
- Fast, fatigue resistant (FR type IIA, large diameter and dendritic trees, thicker axons)
- Fast, fatiguable (FF type IIB, large diameter and dendritic trees and thicker axons).
5
Q
How are the motor unit types classified?
A
- Amount of tension generated
- Speed of contraction
- Fatiguability
6
Q
What are the two mechanisms by which the brain regulates the force produced by a muscle?
A
Recruitment and rate coding
7
Q
What is recruitment?
A
- Motor units are not randomly recruited.
- Governed by the “Size Principle”. 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.
8
Q
What is rate coding?
A
- A motor unit can fire at a range of frequencies. 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.
9
Q
What are neurotrophic factors?
A
- A type of growth factor
- Prevent neuronal death and promote growth of neurons after injury
- Activity of the motor unit can be modified by these factors, to increase speed of contraction of a muscle usually innervated by slow neurones for example.
10
Q
Which fibre types change?
A
- Type IIB to type IIA is the most common
- Type I to II is possible in severe spinal cord injury (and during spaceflight)
- Ageing is associated with loss of type II preferentially as well as some type I, resulting in slower contraction times
- Governed by neurotrophic factors
11
Q
List the extrapyramidal tracts
A
- Extrapyramidal tracts are outside of the pyramids
- Rubrospinal causes automatic movements of the arm in response to posture change
- Reticulospinal tract coordinates automated movements of locomotion and posture
- Vestibulospinal tract maintains balance by regulating posute, and facilitates alpha motorneurones of the postural anti–gravity muscles
12
Q
What is a reflex?
A
- 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.
13
Q
What are the components of a reflex arc?
A
- Sensory receptor
- Sensory neuron
- Integrating center
- Motor neuron
- Effector
14
Q
Describe the pathway of the monosynaptic (stretch) reflex
A
- Sensory receptor stimulated by stretch which triggers contraction of the same muscle via a single synapse
- At the same time, via an interneuron, antagonistic muscles are inhibited so they relax. This takes longer.
15
Q
What is the Hoffman reflex?
A
- Electrical stimulation causing a monosynaptic reflex
- Eg. A precise way of measuring the patellar reflex
- M wave is triggered at higher intensity stimulus, causing a faster response than hitting the patellar
- Used to determine conduction times
