MD137 Skeletal Muscle Reflex Responses

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Questions and Answers

What is the primary function of muscle spindles during rapid shortening contractions?

To increase muscle contraction speed

To decrease muscle tone

To provide sensory information about muscle length (correct)

To promote muscle fatigue

Which type of sensory endings report both velocity and length of muscle stretch?

Alpha motor neurons

Type II endings

Golgi tendon organs

Type Ia endings (correct)

What is the characteristic of a monosynaptic stretch reflex?

It only occurs in smooth muscle

It is the simplest reflex arc (correct)

It involves multiple synapses

It does not involve sensory neurons

What occurs during the knee-jerk reflex when the patellar ligament is struck?

Stretch on spindle fibers is activated Signup and view all the answers

What role do Golgi tendon organs (GTOs) serve in the muscle system?

Monitor tension in tendons Signup and view all the answers

What occurs during disinhibition related to Golgi tendon organs?

Reduction of GTO influence Signup and view all the answers

How do muscle spindles help protect the body from injury?

By providing feedback on overstretching Signup and view all the answers

Which sequence of events correctly outlines the process of a monosynaptic stretch reflex?

Stretch on spindle → Sensory neuron activation → Alpha motor neuron activation Signup and view all the answers

What type of muscle fibers are contained within the muscle spindle apparatus?

Intrafusal fibers Signup and view all the answers

Which sensory nerve cell type is primarily responsible for detecting signals from both nuclear bag and nuclear chain fibers in the muscle spindle?

Type Ia afferent nerves Signup and view all the answers

What function does the gamma motor neuron serve in the muscle spindle apparatus?

Adjusts the sensitivity of muscle spindles Signup and view all the answers

Which muscle group is likely to have a higher density of muscle spindles?

Extraocular muscles Signup and view all the answers

What is the primary function of the Golgi tendon organs?

Monitoring muscle tension Signup and view all the answers

Which statement about muscle fibers is correct?

Alpha motor neurons activate extrafusal fibers. Signup and view all the answers

During a slow contraction of a muscle, which nerve activity is present?

Coactivation of alpha and gamma motor neurons Signup and view all the answers

What aspect of voluntary muscle control is primarily achieved through the local control systems?

Adjusting movements based on sensory feedback Signup and view all the answers

Study Notes

Skeletal Muscle Reflex Responses

Skeletal muscles are typically voluntary, controlled by higher brain regions.
They can also contract unconsciously in response to stimuli.
Reflex responses involve muscle spindle apparatus and Golgi tendon organs.

Principles of Physiology

MD137 course discusses skeletal muscle reflex responses.
Lecturer is Dr. K.McCullagh

Nervous System Control of Movement

See Chapter 5 in Medical Physiology, Rhoades & Bell, 4th Edition, for further details.

Skeletal Muscle Reflexes

Skeletal muscles are usually voluntary and controlled by higher brain regions.
They can also contract unconsciously in response to stimuli.

Classification of Muscle Types;

Muscles are categorized by control mode (voluntary/involuntary), anatomical type (skeletal, cardiac, visceral), and histological structure (striated, smooth).
Voluntary muscles, like skeletal muscles, are categorized as either involuntary reflex or voluntary.

Motor Control System

The motor control system includes: cerebral cortex, basal ganglia, thalamus, brainstem, cerebellum, spinal cord, and motor neurons, working together to control skeletal muscle movement.

Local Control of Motor Neurons

Local control systems receive instructions from higher brain centers.
They make adjustments based on sensory receptor information from muscles, tendons, and joints.

Muscle Sensory Organs

Muscle spindle apparatus responds to muscle length, and the Golgi tendon organs respond to muscle tension on tendons.
Muscles requiring precise control (extraocular, e.g.) have more spindles. Stretching a muscle causes spindles to stretch.
Golgi tendon organs sense tension a muscle applies to a tendon.

Muscle Spindle Apparatus

Contains intrafusal fibers.
Two fiber types: nuclear bag fibers and nuclear chain fibers.
Two types of sensory nerve cells (afferent nerves) surround the fibers: primary (type Ia) and secondary (type II).

Muscle Spindle (Diagram)

Contains intrafusal muscle fibers.
Sensory endings (primary and secondary) are connected to extrafusal fibers via efferent and afferent nerves.

Muscle Spindle Apparatus (during slow contractions)

Passive stretch of muscle fibers from resting length.
Alpha nerve stimulation causes la response to cease.
Alpha and gamma nerve coactivation maintains la responsiveness.

Muscle Spindle Apparatus (continued)

Gamma motor neurons adjust muscle spindle sensitivity to respond appropriately as extrafusal fibers contract and shorten.
Maintaining spindle tautness prevents slackening.
Slackening would reduce sensory information during rapid shortening.
Alpha-gamma coactivation prevents this loss of information.

Muscle Spindle Apparatus (rapid stretch)

During rapid stretches, type I a endings significantly increase firing rate. Type II show a modest increase.
Upon release of stretch type I a ceases firing and type II slows down.
Type la endings report both velocity and muscle length. Type II endings only report muscle length.

Monosynaptic Stretch Reflex

The simplest reflex, involves a sensory neuron synapsing on a motor neuron in the spinal cord.
Maintains optimal resting length of skeletal muscles.
Stimulated by striking the patellar ligament (knee-jerk reflex).

Knee-Jerk Reflex (Diagram)

Sensory neuron activated by spindle stretch, which stimulates motor neuron.
Motor neuron stimulates extrafusal muscle fibers to contract.
Striking patellar ligament stretches tendon and quadriceps femoris muscle.

Stretch Reflex (protects from damage)

Load added to a muscle, stretches muscle and spindles.
Muscle spindle afferents increase firing rate.
Reflex contraction restores position and prevents damage from overstretching.

Monosynaptic Stretch Reflex (continued)

Stretch on muscle stretches spindle fibres.
Activates sensory neuron.
Sensory neuron activates alpha motor neuron.
Motor neuron stimulates extrafusal muscle fibres to contract.
Stretch on spindle is reduced.
Main purpose of muscle spindle and stretch reflex is injury prevention and muscle tone maintenance.

Golgi Tendon Organs

Constantly monitor tension in tendons.
Sensory neuron activates interneuron in spinal cord.
Interneuron inhibits motor neuron, lowering tension in tendons.
Disynaptic reflex (involving two synapses).

Golgi Tendon Organ (Diagram)

Located at the junction of muscle and tendon.
Connected to sensory neurons.
Sensing tension in the tendon.

Golgi Tendon Organs (continued)

Tension on tendon activates sensory neuron.
Sensory neuron stimulates interneuron in spinal cord.
Interneuron inhibits motor neuron.
Tension in tendon is reduced.

Golgi Tendon Organs (ultimate protection role)

GTOs protect muscle and surrounding connective tissue from injury due to sudden, unaccustomed movement or excessive load.

Golgi Tendon Organs (in athletic training)

Minimizing GTO influence is called disinhibition. It's part of athletic training.
Allows pushing performance to the limits of tissue capacity.
Risks include muscle/tendon rupture and broken bones.

Flexor Withdrawal Reflex (Diagram)

Painful skin stimulation triggers it.
Flexor muscles on the same side (ipsilateral) contract, while they relax on the other side.
The limb moves away from the harmful stimulus and is a withdrawal reflex.
Contra lateral leg maintains stance by reciprocal inhibition (flexors on contralateral leg inhibited, while extensors stimulated).

Flexor Withdrawal Reflex (continued)

Painful skin stimulation activates flexor muscles and inhibits contralateral leg's extensor muscles.
This reflex moves the affected limb away from the harmful stimulus, to avoid injury.
The same stimulus elicits the opposite response (reciprocal inhibition) on the contralateral leg (opposite side) so the body can maintain its balance while the affected leg withdraws.

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Description

Explore the fascinating world of skeletal muscle reflex responses in this MD137 course quiz. Understand the distinction between voluntary and involuntary muscle actions, and learn about the mechanisms like the muscle spindle apparatus and Golgi tendon organs. Dive into Chapter 5 of Medical Physiology for deeper insights.