Lecture 7.1: Organisation of the Motor System and Spinal Reflexes Flashcards
What is the role of the motor system?
Control of our muscles
What muscles does the involuntary motor system work on?
Operates more on axial muscles
What is the role of the involuntary motor system? (4)
- Reflexes
- Balance
- Posture
- Locomotion
What muscles does the voluntary motor system work on?
Operates more on distal muscles
What does the motor system comprise of?
Look at image in notability
What are Signs of Upper Motor Neurone Lesions? (5)
- Weakness/Paralysis
- Increased Tone (Spasticity)
- Increased Tendon Reflexes
- Hyperreflexia
- Extensor Plantars (Babinski)
What are Signs of Lower Motor Neurone Lesions? (5)
- Weakness/Paralysis
- Reduced Tone (Flaccidity)
- Loss of Tendon Reflexes
- Wasting
- Fasciculations
What is a Lower Motor Neurone (LMN)?
A neurone whose cell body lies in either the ventral horn of the spinal cord or cranial nerve nuclei of brain stem and directly innervates a muscle with its axon
What is a Motor Unit?
- The number of muscle fibres innervated by a single
axon - Combination of an individual α-motor neurone and
all of the muscle fibres that it innervates
What does a smaller Motor Unit mean?
Finer control
What are the 2 Types of LMNs?
- α-MN: innervate the muscle itself
- γ-MN: innervate the muscle spindle and keep it
taught
What is the Muscle Spindle?
- Encapsulated sensory organ found within the
muscle - Detects muscle contraction
- Is responsible for tendon reflex
- Co-activated with α-motor neurones so tighten as
muscle contracts
What is the role of Muscle Spindles? (3)
- Allow fine motor control and provide limb positional
information to the CNS - Detects extent of muscle tension (contraction/
relaxation) and informs the CNS - Activate LMNs in response to muscle stretch
What are the 3 Main Components of a Muscle Spindle?
- Specialised intrafusal muscle fibres (central part is
non-contractile and contains nuclei) - Large diameter myelinated sensory nerve fibres
- Small diameter gamma motor nerve fibres
What is the role of large diameter myelinated sensory nerve fibres in muscle spindle?
They are wrapped around non-contractile part of muscle, ends are sensitive to stretch of intrafusal fibres
What is the role of small diameter gamma motor nerve fibres in muscle spindle?
- They innervate contractile ends of intrafusal muscle
fibres - Stimulation causes ends to contract
- Stretches central part and stimulates sensory fibres
What are Golgi Tendon Organs?
Sensory receptors found at the myotendinous junction between the muscle and tendon
What is the role of Golgi Tendon Organs? (2)
- Monitors degree of muscle contraction in terms of
force contracted - Prevents over contraction of muscles (when
activated inhibits the muscle and activates its
antagonist)
When we are awake LMN continually activate muscle, what is this called?
Resting Motor Tone
LMN are under inhibition from …..?
descending pathways
What is Muscle Tone?
The amount of tension (or resistance to movement) in muscles
Why is Muscle Tone important?
- Allows body posture
- Rapid responses to environment
What are the 3 Types of Movements?
- Reflexes
- Posture
- Voluntary Movement
What type of movement is facilitated by LMNs & Spinal Cord Circuits?
Reflexes
What type of movement is facilitated by the Brain Stem & Spinal Cord?
Posture
What type of movement is facilitated by the Cortex, Brain Stem & Spinal Cord?
Voluntary Movement
What are Reflexes?
- Automatic, subconscious responses to changes in
the external environment - Does not require the brain!
What are the Roles of Reflexes? (2)
- Reflexes maintain homeostasis (HR, BP, digestion,
balance, posture) - Reflexes are protective
What are the 5 components of a Reflex Arc?
- Receptor: detects the stimulus
- Sensory Neurone: carries the impulse (afferent)
- Integration Centre: processes impulse from sensory
to motor neuron - Motor Neurone: conducts the output to the
periphery (efferent) - Effector: e.g muscle contraction
What is the Integration Centre in a Reflex Arc in a Simple Reflex?
- Some simple reflexes may simply be 2 neurones
and step 3 is a synapse - Or it can be more complex and step 3 is an
interneuron
What are the 2 Types of Reflex Arcs?
- Monosynaptic
- Polysynaptic
What is the Stretch Reflex? Why is it important?
- Resists stretching of muscle and maintains its length
- Importance for posture, balance, holding heavy
objects
The stretch reflex also …1… synergistic muscles and …2… antagonist muscles
1) stimulates
2) inhibits
How does the stretch reflex stimulate synergistic muscles?
Stimulates LMN supplying synergist
How does the stretch reflex inhibit antagonist muscles?
Inhibits LMN supplying antagonist
What is Reciprocal Innervation?
Reciprocal innervation describes skeletal muscles as existing in antagonistic pairs, with contraction of one muscle producing forces opposite to those generated by contraction of the other
What can alter reflexes?
Altered with UMN and LMN lesions
What are some examples of LMN Lesions? (4)
- Carpal Tunnel
- Cauda Equina
- Infection (Polio)
- MND
What are some examples of UMN Lesions? (5)
- Stroke
- MS
- Spinal Trauma
- Traumatic Brain Injury
- CP
