deck_2789705 Flashcards
Define an upper motor neurone
- Motor efferent fibres- Cell body in the motor region of the cerebral cortex or brainstem- Axons remain in the CNS and synapse with lower motor neurones
Define a lower motor neurone
- Somatic motor efferent neurone- Cell body is found in Lamina IX of the spinal cord or in the cranial nerve motor nucleus- Axons directly supply skeletal muscles
What are the two types of lower motor neurones?
Alpha and gamma
Define a motor unit
Made up of:- an alpha motor neurone- all the muscle fibres that is suppliesThis is the minimum functional unit of the motor system
What is a motoneurone?
A somatic efferent nerve which supplies skeletal muscles
What do motoneurones do?
- Bring about movements2. Set muscle tone
Where do you find the two different subtypes of motoneurones?
UMN - CNS to LMNLMN - UMN to muscle
Describe what alpha-motoneurones innervate and initiate
Innervate the extrafusal muscle fibres of skeletal muscle. It is directly responsible for initiating skeletal muscle contraction
Describe what gamma-motoneurones innervate and initiate
Innervate intrafusal muscle fibres of muscle spindles and keep muscle spindles taut
Define a muscle spindle
Connective tissue capsules that contain intrafusal muscle fubres
How are the muscle spindles innervated?
Middle portion = afferent sensory neuronesEnd portion = efferent gamma-lower motoneurones
Define a spinal reflex
A reflex is an involuntary, unlearned, repeatable autonomic reaction to a specific stimulus that does not require the brain.
What are the components that make up the reflex arc?
A receptorAn afferent fibreAn integration centreAn efferent fibreAn effector
How does stretching affect the action of the afferent sensory neurones in muscle spindles?
Stretching the muscle fibres increase the firing of the afferent sensory neurones. Therefore, shortening the muscle fibres causes a decrease in the firing rate.
Why do gamma motoneurones innervate the intrafusal muscle fibres?
They prevent the muscle spindle from becoming slack when extrafusal fibres contract. The contraction of extrafusal muscles removes feedback from the sensory neurones, therefore there is no information provided to the motor centre regarding muscle length.
Where do you find golgi tendon organs?
At the junction between the muscle and the tendon. They are innervated by sensory neurones.
Define a reflex arc
The neuronal pathway that describes a relex
What are golgi tendon organs composed of?
Network of collagen fibres inside a connective tissue capsule with a sensory axon that winds around the collagen
What does the stretch reflex circuit connect?
A lower motor neurone with the afferents of the muscle-length sense organs.
What happens when a tendon is stretched?
The firing rate of the sensory neurone increases.
What happens to golgi organs when muscles contract?
The tension throughout the golgi tendon organ increases which leads to an increased inhibition on the alpha-lower motoneurones. This reduced firing of the sensory afferents and therefore decreasing the muscle contraction.
Describe the golgi tendon organ reflex?
Acts as a protective mechanism, by controlling the tension of an active muscle. it does this by causing relaxation before the tendon tension becomes high enough to do any damage.
Describe the process of the golgi tendon organ reflex
- Contracting muscle stretches golgi tendon organ- Afferent sensory neurone fires, synapsing with inhibitory interneurones in the spinal cord- Inhibitory interneurones redude alpha-LMN firing, reducing muscle contraction, preventing damage from over-contraction
Where does the golgi tendon organ reflex act?
On the antagonising muscle, to allow for a reflex to occur and to prevent damage due to over contraction.
