Lecture 4: Neurological System Flashcards
Afferent/Sensory neurons
Carry signals to spinal cord
Sensory info from environment/body to CNS for interpretation
Efferent/motor neurons
Carry signals to muscle
Impulses from CNS to PNS to allow for movement/action
Interneurons
Interpretive neurons between afferent and efferent nerves in CNS
Dorsal horns
Cells transmit sensory info
Ventral horns
Contains alpha motor neurons with axons terminating in skeletal muscle
Motor units
All-or-none
All fibers in a motor unit are the same type
Motor unit types: activation
Type I activated first, then Type IIa, then Type IIB
Asynchronous activation
Activation is temporally spaced but summed with preceding motor unit activity
Synchronous activation
Large and small motor units activated together
E.g. ballistic movements, adaptation from weight training
Frequency coding
Also called rate coding
High frequency can induce high tension production
Monosynaptic reflex arc
When sensory neuron is stimulated, it facilitates stimulation of a spinal motor neuron
Myotactic reflex
Also called stretch reflex
Causes contraction of a muscle being stretched
Flexor reflex
Initiated by painful stimulus
Causes quick withdrawal/flexion of limb
Cutaneous reflex
Causes relaxation of muscle with heat or massage
Proprioceptive receptors
- Sensory receptors in musculoskeletal system
- transform mechanical distortion in muscles or joints
- carry input to CNS to change joint position, muscle length & tension, stimulate motor response
Examples of proprioceptive receptors
Muscle spindle
Golgi tendon organ
Joint receptors
Muscle spindle
- Monitors muscle stretch
- Lies parallel to muscle fibers (mostly found in muscle belly)
- Connect into fascicles via connective tissue
Intrafusal fibers
Contained within a capsule, forming a muscle spindle
Nuclear bag fibers, nuclear chain fibers
Gamma motor neuron
Innervated contractile ends of muscle spindle
Gamma bias
Readjustment of muscle spindle length by contracting ends of intrafusal fibers
Gamma loop
Reflex arc that works with stretch reflex
Includes afferent, gamma, and alpha pathways
Primary afferent
Type Ia, respond to stretch by initiating stretch reflex
Secondary afferent
Type II, facilitate flexors and inhibit extensor activity
Stretch reflex
Facilitates contraction (via muscle spindle) of a muscle being stretched
Autogenic facilitation
Internally generated excitation of alpha motor neurons through stretch or other input
Reciprocal inhibition
Relaxation of antagonist while agonists produce joint action
Golgi tendon organs
Monitors muscle force/tension
Connected directly to extrafusal fibers
Inverse stretch reflex (initiated by high tension in muscle, inhibits contraction and causes relaxation)
Joint sensory receptors: Ruffini ending
Sensory receptor in capsule that responds to change in joint positioning
Joint sensory receptors: pacinian corpuscle
Sensory receptor in skin stimulated by pressure
Cutaneous receptors
Found in dermis or epidermis
Sense pressure, vibration, heating, cooling, tissue damage
Exteroception
Perception of environment (pressure, skin deformation)
Force coordination during precision grip
Kinesthesia
Sense of movement/motion
Mechanoreceptors
Merkel receptors/discs
Slowly adapting receptors
Pressure, position, deep static touch (shapes, edges)
Meissner corpuscles
Rapidly adapting receptors
Light touch sensitivity
Ruffini cylinders
Slowly adapting receptors
Gross pressure changes and vibrations
Electromyography (EMG)
- technique for evaluating and recording electrical activity produced by skeletal muscles
- can learn time course of muscle contraction, contraction force, coordination of several muscles in movement sequence, ergonomics
EMG instrumentation
Correct placement of electrodes = parallel to muscle fibers
Prepare skin by shaving, abrading, cleaning with alcohol
Inserted/intra-muscular/needle EMGs
Extremely sensitive, access to deep musculature, little cross-talk
BUT: requires cert, cant reposition, painful
Surface electrode EMGs
Quick and easy, no medical supervision, minimal discomfort
BUT: superficial only, may affect movement patterns, cross-talk concern, limitations in dynamic activity
Electrical noise
- Inherent in electronic equipment
- frequency range: 0-thousands of Hz
- cannot be eliminated
- reduced by using high quality components
Ambient noise
- electromagnetic radiation sources
- impossible to avoid
- dominant frequency: 60Hz
- 1-3x amplitude of EMG signal
Motion artifact
- Two main sources: electrode/skin interface and electrode cable
- Frequency range: 0-20
- Reducible by proper circuitry and set up
