Somatosensory System Part 2 SN Flashcards
What is a Motor Unit?
A single motor neuron and all the muscle fibres it innervates
What is an Alpha Motor Neuron?
- Located in ventral (anterior) horn of gray matter in spinal cord.
- Innervates extrafusal muscle fibres
- Force generating muscle fibres
What is a Gamma Motor Neuron?
Smaller and less numerous than alpha motor neurons
Innervates intramural muscle
What is a Muscle Spindle?
Long Thin Fibres surrounded by extrafusal muscle fibers
Where are muscle spindles the greatest concentration in?
In the Hand and Neck
Why are Muscle Spindles the greatest concentration in hands and neck?
The most position (and velocity) sensitive areas.
How many muscle spindles in the human body?
25,000 to 30,000
How many muscles spindles in each arm and leg?
Average of about 4,000 in each arm and 7,000 in each leg
What is the Number for the Rough Guess of Muscle Spindles?
38*(Muscle Mass)^1/3
What is the function of muscle spindles?
Detect how fast a musle changes or lengtens (stretch receptors)
What are Group Ia Afferent?
Reference to sensory muscle (not skin)
- Sensory, large, myelinated, fast
What is Extrafusal Muscle Fibres?
Outside Muscle Spindles
- Force Generating Muscle Fibres
- Innervated by alpha motor neurons
What are Intrafusal Muscle Fibres?
Located inside the Muscle Spindles
- Controlled by gamma motor neurons
What does Stimulation of Intrafusal Fiber Lead to?
Elongation of Muscle Spindle (maintains sensitivity to stretch) due to equitorial region lengthening
What are Nuclear Bag Fibers?
Thick and contain nuclei within central region
Contains Group Ia and II afferents
What are Dynamic Nuclear Bag Fibers?
High frequency impulses relayed to CNS during muscle stretching (responsive during a dynamic muscle activity)
What are Static Nuclear Bag Fibers?
Stopped (holding it in place) impulses that are transmitted when a muscle has shortened and held at a new length
What are nuclear chain fibers?
Thin and Contain nuclei throughout
- Contains group II afferents (sensory) …static (responsive when muscle is held at a new length)
What happens with y-motor (intrafusal) neuron activation?
Equatorial region gets longer and the polar region gets shorter
What is Alpha-Gamma Co activation?
Stimulation of the ventral horn of grey matter of spinal cord.
What is Low Threshold?
Discharges first
What is High Threshold?
Needs a stronger stimulus
What happens in alpha motor activation?
Muscle fibre shortens (physical change)
What happens in gamma motor activation?
Muscle spindle lengthens
What is the function of spinal reflexes?
Detect and regulate changes in muscle length and rate of muscle length change
How does the muscle lengthen in spinal reflexes?
Stretches intra-and extrafusal muscle fibres (components will lengthen)
How is the parallel muscle spindle lengthened?
The equatorial region of intramural muscle fibres is stretched
Ia afferent impulses when disturbed causes an action potential in the spinal cord
What do synapses with alpha motor neurons cause?
Motor Unit Activation
What is a Monosynaptic Reflex?
One chemical synapse activated by action potentials of alpha motor neurons
Where are Golgi Tendon Organs situated?
At the junction between muscle tendons and where that tissue merges into active muscle; called musculotendinous junction.
What is the function of the Golgi Tendon Organs?
- Monitors Muscle Tension (Force)
- Inhibitory effect to the same muscle and excitatory to the antagonist muscle
- Protective function under high loads
- “Fine Tunes” muscle force production for smooth movements
- Works with other sensory inputs
What is Active Muscle Force?
- Due to Cross-Bridge cycling (contractile proteins will form reversible chemical bonds)
- Force Transfer.. Tendon lengthening (information generating through Ib afferent)
What do linear regression lines demonstrate?
- Cat Soleus Muscle
- Positive Relationship
What is the relationship between force and discharge rate?
As more force is produced, discharge increases due to Action Potentials from Force Transduces
