Flashcards in Physiology Review Deck (175)
What are cells in the motor cortex organized into?
What does each vertical column of cell in the motor cortex stimulate?
A group of synergistic muscles or even a single muscle.
What is each vertical column of cells in the motor cortex divided into?
6 distinct layers
In the motor cortex, which layer is pyramidal cells in?
What layers does input signals enter in the motor cortex?
What do neurons arising in the 6th layer of the motor cortex communicate with?
With other regions of the cerebral cortex.
What are the groups of neurons in the spinal cord?
> sensory (afferent)
> anterior motor neurons (efferents)
What type of fibers do alpha motor neurons give rise to?
A alpha fibers
What are interneurons responsible for most of in the spinal cord?
spinal cord integrative function
What are the characteristics of interneurons?
> 30X as numerous as anterior motor neurons
> small and highly excitable
> capable of spontaneous activity
> responsible for most of spinal cord integrative function
Where are Renshaw cells located?
anterior horns of spinal cord
What are Renshaw cells?
inhibitory interneurons in the anterior horns of the spinal cord
What do Renshaw cells do?
Transmit inhibitory signals to surrounding motor neurons.
- results in lateral inhibition
- enhance fluidity of limb movement
Transmit inhibitory signals to same motor neuron.
- results in recurrent inhibition
Where do Renshaw cells receive collateral branches from?
alpha motor neurons
What type of cell innervates muscle spindles?
small gamma motor neurons (group II afferents)
What are the two types of intrafusal fibers that make up muscle spindles?
> Nuclear bag fibers
> Nuclear chain fibers
What do nuclear bag fibers detect in the muscle spindle?
Rate of change (dynamic change) in muscle length.
What do nuclear chain fibers detect in the muscle spindle?
Static change in muscle length.
What are nuclear bag fibers innervated by?
group Ia afferents and dynamic gamma efferents
What are nuclear chain fibers innervated by?
group II afferent and static gamma efferents
Which are more numerous, nuclear chains fibers or nuclear bag fibers?
nuclear chain fibers more numerous
How are nuclei arranged in nuclear bag fibers?
multiple nuclei located in a central "bag-like" configuration
How are nuclei arranged in nuclear chain fibers?
multiple nuclei arranged in a single row
In muscle spindles, what transmits dynamic stretch reflex signals?
signals transmitted from primary nerve endings
What action of the muscle elicits a dynamic stretch reflex?
elicited by rapid stretch or unstretch
What is the purpose of the dynamic stretch reflex?
opposes sudden changes to muscle length
What is the purpose of the static reflex?
causes degree of muscle contraction to remain relatively constant
In muscle spindles, what transmits static reflex signals?
signals transmitted by both primary and secondary endings
You know muscle spindles have both a dynamic stretch reflex and a static reflex, but what is the main function of these two components combined?
prevents jerkiness of body movements (damping)