Motor Systems: L14

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Questions and Answers

What does the term 'fusa' refer to in the context of muscle spindles?

Sensing organ

Neuronal connection

Muscle fiber type

Spindle (correct)

Which type of afferent fibers are primarily sensitive to the length of muscle fibers?

Gamma efferents

Ib afferents

Ia afferents

II afferents (correct)

What role do gamma efferents play in muscle function?

Provide sensory feedback

Stimulate alpha motor neurons

Control muscle contraction speed

Regulate spindle sensitivity (correct)

Which type of muscle fiber is associated with the phasic response to changes in muscle length?

Nuclear bag fibers Signup and view all the answers

In what scenario would gamma efferents be particularly crucial?

Muscle is actively contracted Signup and view all the answers

What primarily differentiates muscle spindles from Golgi tendon organs?

Type of sensory feedback provided Signup and view all the answers

What occurs when muscle spindles stop signaling during muscle shortening?

Loss of proprioceptive feedback Signup and view all the answers

Which aspect of neuromotor control is not influenced by the brain during certain tasks?

Cyclic repetitive tasks Signup and view all the answers

What is the primary function of inhibitory interneurons in the knee-jerk reflex?

To reduce the activity of opposing flexor motor neurons Signup and view all the answers

Which key sensory structure is involved in the regulation of muscle tension?

Golgi tendon organs Signup and view all the answers

What characterizes the crossed extensor reflex?

It includes excitatory and inhibitory interneurons in its circuitry Signup and view all the answers

What primarily controls the force generated by skeletal muscles?

The number of motor units and their stimulation rate Signup and view all the answers

Which type of reflex involves the pattern generation basics within the spinal cord?

Crossed Extensor Reflex Signup and view all the answers

What determines the properties of stimulated motor units?

The number of fibers and their types within the unit Signup and view all the answers

Which of the following accurately describes the role of alpha motor neurons?

They can be both excited and inhibited synaptically Signup and view all the answers

Which additional sensory structures may drive inhibitory interneurons?

Free-nerve endings Signup and view all the answers

What is the location of alpha motor neurones?

Ventral horn of the spinal cord Signup and view all the answers

What type of muscle fibres are characterized as slow oxidative?

Type1 Signup and view all the answers

Which mechanism leads to increased muscle force during rapid stimulation?

Temporal summation Signup and view all the answers

What is the primary role of proprioceptors like spindles and Golgi tendon organs?

To encode information about muscle length and tension Signup and view all the answers

How are the muscle fibres within a motor unit organized?

They are the same fibre type Signup and view all the answers

What occurs during the spatial summation of motor units?

Simultaneous recruitment of multiple motor units Signup and view all the answers

Which type of motor unit is classified as fast glycolytic?

Type2X Signup and view all the answers

What role do interneurones play in spinal reflexes?

Modulating complex spinal reflexes Signup and view all the answers

What is the defining characteristic of a motor unit?

It includes one alpha motor neurone and all of its innervated muscle fibres Signup and view all the answers

In a reflex circuit, what primarily determines the control strategy?

Structure of the circuit Signup and view all the answers

Study Notes

Motor Systems Lecture Notes

The lecture code is SEATS
The lecturer is Dr Jorn Cheney
The lecture email is [email protected]
The lecture is part of a three-part series on motor systems
A Padlet link is available: https://padlet.com/jcheneySOTON/motor-systems-neuroscience-ico7hjkz3t95kauv
A Blackboard link is also accessible under "Motor systems (Neuroscience)"
The lecture material covers motor units, muscle fibre types and control systems

Alpha Motor Neurones

Alpha motor neurons innervate muscles directly, without intermediate synapses
The soma (cell body) of an alpha motor neuron is located in the ventral horn of the spinal cord
Alpha motor neurons work in pools that control different muscles
Proximal and distal muscles are controlled by different pools
Alpha motor neurons innervate muscles, and each muscle fiber is typically innervated by only one alpha motor neuron

Motor Units

A motor unit consists of one alpha motor neuron and all the muscle fibres it innervates
All muscle fibres in a motor unit are typically the same type of fiber
Motor units are the fundamental building blocks of force generation in the motor system
The force of muscle contraction is determined by the rate of stimulation of the motor units and the number of motor units activated

Muscle Fibre Types

Muscle fibers are categorized into different types based on their properties: Type 1 (slow oxidative), Type 2A (fast oxidative-glycolytic), and Type 2X (fast glycolytic)
These types respond differently to fatigue under different exercise conditions
The type of fiber present in a motor unit determines its capacity for the type of force and endurance it can produce

Muscle Force Control

Muscle force is controlled by the stimulation rate (temporal summation)
It is also controlled by the number of motor units recruited (spatial summation) with progressively larger motor units
Force increases if the rate of stimulation is increased. Different types of muscle fibers also play different roles in force control.
Muscle force increases with the number of motor units activated.
The type of muscle fibers that are activated affects the force and speed of muscle contraction

Neuromotor System

The diagram shows the sensory(inputs to the system), technology/evolution of control systems, and the muscular output from the system components
The neuromotor system refers to the network of neurons and muscles that control movement

Learning Objectives

Understand the location and route of alpha motor neurons to muscles
Understand the role of the ventral horn of the spinal cord in motor control
Understand the principles of force production in different muscles
Know the roles of muscle spindles and Golgi tendon organs (sensors)
Be able to explain how interneurons affect complex spinal reflexes
Discuss why spinal reflexes don't always involve the brain

Muscle Spindles

Muscle spindles are sensory receptors that monitor muscle length
They are sensitive to changes in muscle length (rate of change and length)
Intrafusal and extrafusal fibres are important components of muscle spindles
Gamma motor neurons control the sensitivity of muscle spindles

Golgi Tendon Organs

Golgi tendon organs are sensory receptors in tendons that monitor muscle tension
These are sensitive to changes in muscle tension
The GTOs are sensitive to tension, the force produced by the muscle and are sensitive to the rate of change of tension in the muscles
Inhibiting the alpha motor neuron is the function of the 1b inhibitory neurone, the primary function of the receptors in the GTOs

Spinal Reflexes

Spinal reflexes involve sensory input, integration within the spinal cord, and motor output – without brain intervention
The knee-jerk reflex is a typical example
The crossed-extensor reflex involves two spinal cord segments and is used, for instance, in postural control when a limb is withdrawn

Summary

Muscle force regulation is a combination of factors
All vertebrate muscle control is excitatory to alpha motor neurons
Alpha motor neurons are located in the ventral horn of the spinal cord and are controlled, via synaptic transmission
Different types of fibers in motor units contribute towards muscle action
Different processes like temporal (stimulation rate) and spatial summation (number of units) contribute towards force regulation
Sensors like muscle spindles and Golgi tendon organs aid in the feedback control of reflexes

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Description

Explore the intricacies of motor systems in this comprehensive quiz based on the lecture by Dr. Jorn Cheney. Covering topics like alpha motor neurons and motor units, this quiz is designed to test your understanding of muscle fibre types and control systems. Dive into the fascinating world of neuroscience and enhance your knowledge!