Study your flashcards anywhere!

Download the official Cram app for free >

  • Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off

How to study your flashcards.

Right/Left arrow keys: Navigate between flashcards.right arrow keyleft arrow key

Up/Down arrow keys: Flip the card between the front and back.down keyup key

H key: Show hint (3rd side).h key

A key: Read text to speech.a key


Play button


Play button




Click to flip

57 Cards in this Set

  • Front
  • Back
What is a Reflex?
An involuntary stereotyped motor response to a sensory input.
2 Functions of Reflexes:
1. Fast-acting safety reactions to avoid hazardous situations
2. Automatically adapt motor patterns to achieve a behavioral goal
Are spinal reflexes entirely limited to only involve the spinal cord and peripheral nerves?
No; descending pathways from the brainstem and motor cortex modulate spinal reflexes.
Complete loss of a reflex
Reduced strength of a reflex
Overactive reflex
What are the 2 general components of information in a reflex?
1. Sensation of muscle status
2. Effect caused on muscle
What 2 muscle receptor types sense muscle status?
-Muscle spindles
-Golgi tendon organs
What do the muscle receptors monitor ABOUT the muscle?
Where are the cell bodies of the muscle sensory neurons located?
In the DRG
What are the efferent neurons for spinal reflexes?
Lower motor neurons in the spinal cord ventral horn.
What MODIFIES information between the sensing and effect?
-Interneurons locally in SC
-Descending neurons from cortex and brainstem.
What can interneurons and descending neurons be?
2 Types of muscle efferents:
1. Alpha motor neurons
2. Gamma motor neurons
What do alpha motor neurons innervate?
Extrafusal - work muscle fibers
What do gamma motor neurons regulate??
Sensitivity of muscle spindle intrafusal fibers
What about the muscle do Muscle Spindle receptors sense?
What about the muscle do Golgi tendon organ receptors sense?
What does length of muscle tell?
The angle of a joint
What 2 structures do the muscle Spindle receptors work with to sense position of limbs wrt body?
-Joint afferents
-Cutaneous afferents
When do Spindle receptors discharge best?
When muscle is stretched.
What happens to Spindle receptors when the muscle shortens?
They fall silent.
What are muscle spindle receptors composed of?
Intrafusal fibers
Where are intrafusal fibers located within muscle?
Parallel to extrafusal fibers.
2 General types of intrafusal fibers:
1. Dynamic nuclear bag fibers
2. Static nuclear bag fibers
What is the response of Dynamic nuclear bag fibers to lengthening muscle?
It adapts over time
What is the response of static nuclear bag fibers to lengthening muscle?
Steady over time - so it senses at all muscle lengths.
How are muscle spindle afferents associated with the intrafusal fibers?
They wrap and spiral around them.
What type of afferents innervate the dynamic nuclear and static nuclear muscle spindles?
Ia afferents - innervate both dynamic and static nuclear bag fibers.
What do Ia afferents sense?
Info about:
-Muscle length
-Rate of change of length
What does each afferent convey?
-Ia conveys fast phasic dynamic responses of muscle fibers
-II conveys slow tonic static responses
So when are Type Ia afferents responsive?
During small changes of muscle
When are Type II afferents responsive?
When the muscle length is static
What happens to the spindle afferents when intrafusal fibers are stretched?
Sensory endings are stretched and increase their firing rate.
What happens to spindle afferents when intrafusal fibers are unloaded?
Sensory endings stop firing.
What are the Muscle Spindle Efferents and what do they innervate?
Gamma motor neurons that innervate both static and dynamic nuclear bag fibers.
2 things that happen when gamma motor neurons fire:
-Intrafusal fibers shorten
-Central region of intrafusal fibers stretch
What is achieved by gamma efferents firing?
It increases the firing of afferent fibers from spindles.
What is the role of gamma motor efferents for spinal reflexes?
To adjust the dynamic and static sensitivity of the muscle spindle and their afferents.
How is it that by shortening the ends of intrafusal fibers it causes their central regions to stretch?
Their central regions are not contractile.
Why do we need dynamic and static intrafusal fibers in muscle spindles?
To sense two things:
1. When muscle length changes
2. What the muscle is doing when not changing - new stable length
What process occurs in muscle efferents during voluntary movements?
Alpha-gamma co-activation
Why are both alpha and gamma efferents coactivated?
To keep the spindles sensitive as the contracting muscle shortens, preventing them from falling silent.
Response of a Ia afferent fiber to sustained tension:
Steady firing
Response of a Ia afferent fiber to stimulation of only an alpha motor neuron:
Ongoing discharge pauses because muscle shortens as it contracts.
Response of a Ia afferent fiber to stimulation of an alpha AND a gamma motor neuron:
Spindle won't be unloaded by contraction so it keeps on firing.
What do Golgi tendon organ muscle receptors detect?
Tension of the muscle
Where are Golgi tendon organ receptors located?
At junction between muscle fibers and tendon.
Are Golgi tendon organ receptors free?
No, they're encapsulated.
What innervates a Golgi tendon organ receptor?
A single Ib afferent
What stimulates the Golgi tendon organ receptor?
How does stretch stimulate the Golgi tendon organ receptor
By straightening the collagen fibers and compressing the nerve fibers underlying them.
How are Golgi tendon organ receptors associated with the rest of muscle?
In series with 15-20 extrafusal fibers.
When do Golgi tendon organ receptors discharge BEST?
When muscle contracts
What do Golgi tendon organ receptors measure?
Force in contracting muscle
Why do we need Golgi tendon organ receptors?
To protect against too much muscle tension and damage.
Other than protecting against muscle damage what do Golgi tendon organ receptors do?
Signal very minute changes in muscle tension to precisely inform CNS about the state of a muscle contraction.