Neuromuscular Basis Of Human Movement Flashcards
Nerve impulse (action potential)
The signal that passes from one neuron to the next and finally the end organ (muscle fibers)
Pathway of Nerve Impulse
Travels from cell body to axon to terminal
Resting membrane potential
Dynamic equilibrium at -70mV
Potassium inside, sodium outside
Polarized membrane
Depolarization
Nerves transmit information by changing the potential across the membrane
RMP moves closer to 0mV
Threshold
Before a nerve can be depolarized and an AP started, there must be sufficient stimulation
Typical nerve threshold = -55mV
No threshold = no AP
Afférent Pathways
Afférent neurons send sensory information to the CNS
Efferent Pathways
Efferent neurons send executing information to periphery
CNS
Brain, spinal cord, human movement initiated, controlled, and monitored
PNS
Branching nerves outside of spinal cord
Neuron
Functional unit of the nervous system
Motor neurons
Carry signals to muscle
Afferent neurons
Ascending into to spinal cord and brain
Efferent neurons
Descending info from CNS/spinal cord to muscles
Interneurons
Afférent to efférent
Efférent to efferent
Higher centers to spinal cords
Soma
Body of cell
Ganglia
Bundles or cell bodies just outside the spinal cord
Dendrites
Projections on the cell body that serve as receivers
Axon
Large nerve fiber that branches out from spinal cord
Alpha motor neuron
Large, rapidly transmitting neuron
Myelinated
Covered with an insulated shell
Schwann cells
Insulation enveloping specific section of axon
Node of Ranvier
Gap in between Schwann cells
Synapse
Small gap between terminal branch of neuron and muscle
Motor unit
Composed of a motor neuron and all of the muscle fibers it innervates
Motor unit fibers
of fibers depends on the precision of movement required of that muscle
# of motor units decreases with age
All or none principle
When motor units receive sufficient stimulation, all fibers of a motor unit produce tension together
Recruitment
Increasing the # of stimulated motor units
Rate coding
Increasing the stimulation rate of the active motor units
Rate coding - twitch
The effect of a single stimulus
Rate coding - summation
The overall effect of added stimuli
Rate coding - tetanus
Sustained maximal tension due to high frequency stimulation
Type I fibers
Slow contraction time
Generates little tension
Highly fatigue resistant
Maintaining posture
Distance runner
Type IIa
Fast contraction time
More fatigue resistance than type IIb
Swimming and bicycling
Type IIx fibers
Rapid contraction time
Innervated by alpha motor units
Large neuron to fiber ratios
Sprinting, jumping, weightlifting
Tension generation
Determined by size and number of motor units recruited
Order of motor unit activation
Type I
Type IIa
Type IIb
Asynchronous activation
Activation is temporarily spaced but summed with all preceding motor unit activity
Synchronous activation
Large and small motor units activated together
Ballistic movements, adaptation from weight training
Frequency coding
High frequency can induce high tension production (rate coding)
Sensory neurons
Neurons that carry impulses to CNS
Reflex
Involuntary response to stimuli
Monosynaptic reflex arc
When sensory neuron is stimulated, it facilitates the stimulation of a spinal motor neuron
Myotatic reflex
Causes contraction of a muscle being stretched
Also called stretch reflex
Flexor reflex
Initiated by painful stimulus
Causes quick withdrawal/flexion of the limb
Cutaneous reflex
Causes relaxation of muscle with heat or massage
Priopriospinal reflexes
Reflexes processed on both sides and at different levels of the spinal cord
Crossed extensor reflex
Causes extension of flexed limb when contralateral limb rapidly flexes
Tonic neck reflex
Causes flexion or extension of the limbs when head flexes or extends, respectively
Supraspinal reflexes
Reflexes brought into the spinal cord but processed by brain
Labyrinthine righting reflex
Causes body to return head to neutral position when body is tilted or spun
Proprioceptors
Main sensory receptors for muscle
Sense change in joint position muscle length, or muscle tension
Muscle spindle
Monitors muscle stretch
Intrafusal fibers
Fibers inside the muscle spindle
Nuclear bag fibers
Intrafusal fibers with a large clustering of nuclei in the center
Type Ia afferent neurons exit from middle portion of this fiber
Auto-excitatory
Contractile capability of the spindles
Gamma motor neuron
Innervates contractile ends of muscle spindle
Indirectly enhance alpha motor neuron excitation
Gamma bias
Readjustment of muscle spindle length by contracting ends of Intrafusal fiber
Gamma loop
Reflex arc that works with stretch reflex
Include afferent, gamma, and alpha pathways
Nuclear chain
Primary afferent
Type Ia
Respond to stretch by initiating stretch reflex
Secondary afferent
Type II
Facilitate flexors and inhibit extensor activity
Nuclear chain fiber
Intrafusal fiber with nuclei arranged in rows
Stretch reflex
Facilitates contraction of a muscle being stretched
Autogenic facilitation
Internally generated excitation of the alpha motor neurons through stretch or other input
Reciprocal inhibition
Relaxation of antagonist while agonists produce joint action
Golgi Tendon Organ (GTO)
Monitors muscle tension
Extrafusal fibers (GTO)
Fibers outside of the muscle spindle
Inverse stretch reflex (GTO)
Initiated by high tension in muscle
Inhibits contraction of muscle via GTO
Causes relaxation of a vigorously contracting muscle
Myotendinous junction
Attached to muscle fibers, thus more sensitive to contraction than stretch
Ballistic
Activate muscle spindles which elicits a stretch reflex
Static
If static position achieved slowly then can minimize muscle spindle response
Is static or ballistic better?
Static is better than ballistic
Ruffini ending
Sensory receptor in joint capsule that responds to change in joint position and velocity
Pacinian corpuscle
Sensory receptor in skin stimulated by pressure and pain
Active ROM
Degree I’d motion occurring at joint due to voluntary contraction of agonist
Passive ROM
Degree of motion occurring at joint due to external ,manipulation
Gravity, manual resistance
Restrictions to ROM
Soft tissue surrounding joint
Connective tissue surrounding muscle
Ligaments
Bony structures
Stretch reflex
Inverse stretch reflex
Neuromuscular Facilitation (PNF)
Incorporates combination sequences of contraction and relaxation
Often used in rehabilitation settings
Takes advantage of the response of the proprioceptors
Polymetric Training
Purpose is to improve velocity of performance
Rapid stretching through limited ROM immediately followed by rapid contraction of the same muscle
