9 - The Muscle Unit Flashcards
What does the peripheral nervous system consist of?
cranial nerves (12 pairs) spinal nerves (31 pairs)
What does the central nervous system consist of?
brain, spinal cord
What does the autonomic nervous system consist of?
sympathetic
parasympathetic
What is a nerve?
a bundle of fibres within a connective tissue sheath
What forms the neuromuscular system?
the neuron and muscle fibre represent nervous and motor systems combined
What is the functional unit of the neuromuscular system?
the motor unit
Explain the neural organisation
- motor neurons (efferent) = exit the spinal cord via the ventral root
- sensory neurons (afferent) = enter the spinal cord via the dorsal root
What are the components of the motor neuron?
cell body, dendrites, axon, myelin sheaths, terminal branches, node of ranvier
Describe the cell body
information arrives and is processed
Describe the axon
travels to the muscle cell
Describe the terminal branches
the region where the axon branches out and connects to the muscle cell
Describe the dendrites
makes connections with other neurons
Describe the myelin sheaths
insulation points, the electrical signals jump from one myelin sheath to the next to get to the next destination quicker
Describe the node of Ranvier
the action potential jumps from one node to the next
Why do myelinated nerves have faster conduction velocities?
because the impulses can jump from one node of Ranvier to the next due to the myelin sheath
Explain the neuromuscular synapse
- synapse transmit the impulses from the neuron to the effector cell
- signal transmission at the neuromuscular synapse is chemical
What is a neuron?
a single nerve cell
What are the three types of neurons?
1 - motor neuron (efferent) - signals exciting the spinal cord
2 - sensory neurons (afferent) - signals coming into the spinal cord
3 - connection neuron (interneuron) - can elicit excitatory and inhibitory responses in other neurons
What is a muscle unit?
single motor neuron and all the muscle fibres it innervates
What is the force created by he muscle unit dependent upon?
- motor unit recruitment
- motor unit firing rate
Example of type 1 muscle fibre?
soleus, erector spinae
Example of type 2a muscle fibre?
deltoid
What determines the motor unit type?
nerve fibre
What are the two ways to increase the force of muscle contraction?
- number of MUs that are recruited
- firing rate
Explain the size principles of motor unit recruitment
- motor unit recruitment starts from smaller MUs
- followed by progressively larger MUs as more force is required
What the difference between high and low firing frequency?
high (no relaxation) - maximal contraction
low - muscle fibres can partially relax
Describe the gradation of contraction
all MUs and high frequency = maximal force
What is electromyography?
measurement of muscle activation
What is the principle behind electromyography?
- signal from brain to MU = innervation of associated muscle fibres
- action potential in muscle fibres initiates excitation contraction coupling
What can you measure with electromyography?
- when a muscle is turned on and off
- the magnitude of activation
- timing of activation
What determines the electromyography signal?
- the number of motor units activated
- motor unit action potential firing rate
- the type of motor units activated
What is perception?
processes of obtaining information about the internal and/or external environment form sensory stimulation
What is sensation?
conscious feeling relating to a sensation
What are sensory receptors?
- respond to different types of stimuli
- absorb energy and convert it into neural signals
What are exteroceptors?
- near a body surface
- respond to signals coming from the environment including the five senses
What are the interoceptors?
respond to signals from within the body
What are the two types of interoceptors?
1 - visceroreceptors = stimulated by excessive contraction or distention
2 - proprioceptors = responds to position and movement
How do the stimuli and receptor interact in sensory receptors?
mechanical (mechanoreceptor) visual (photoreceptor) chemical (chemoreceptor) heat (thermorceptor) (nocioreceptor)
How do sensory neurons/receptors adapt?
- stronger stimulus = high firing rate in affect axon
- response decrease over time if stimulus stays constant
- slowing adapting = decline is slow
- fast adapting = decline is fast
What are the proprioceptors?
- located in muscles, tendons, joints
- stimulated by motion = depends of magnitude, direction and change of body movement
What are the proprioceptors classified as?
1 - muscle proprioceptors = muscle spindle and Golgi tendon organ
2 - joint and skin proprioceptors = ruffini endings and paccinian corpuscles
3 - labyrinthe and neck proprioceptors
Explain the cutaneous receptors
- each receptor to a difference type of stimuli
- the receptors all involve different places within the body
What are the types of cutaneous receptors and explain them
- merkel disc = edges, corners, points
- Meissner corpuscle = skin motion
- Ruffini ending = skin stretch
- Pacinian corpuscle = vibration
Describe the neck proprioceptors
- maintain equilibrium of the head is due to join receptors in c1-c3
- sensitive to the angle between body and head
Explain the labyrinthine proprioceptors
- labyrinthine recognise orientation and the movements in the head
- consists of cochlea, 3 semicircular canals, utricle and saccule
- 3 semicircular cancals at 90 degrees to each other
What are the two types of joint proprioceptors?
- paccinian corpuscles
- ruffini endings
Describe the paccinian corpuscles
- located around joint capsules, ligaments and tendon sheaths
- activated by rapid joint angle changes and by changes in intra-articular pressure
- phasic and rapid adapting
Describe the ruffini endings
- activated by joint angle change but also recognise constant pressure
- slow/ very little adaptation
- deep layers of the skin
What are the muscle proprioceptors?
- muscle spindles
- Golgi tendon organs
Describe the muscle spindles
lie parallel and between muscle fibres sensitive to length change
How do muscle spindles produce movement?
- when stretched they trigger on impulse in sensory neuron to CNS
- this activates the motor neuron of that muscle via a reflex action to increase force production
- stimulate muscle to produce more force to resist stretching
Describe the Golgi tendon organ
- located at the musclo-tendinous junction
- sensitive to tension
- when stretched muscle relaxes
When sensory fibres connects to the muscle spindle and Golgi tendon organ?
muscle spindle = type 1a
Golgi tendon organ = type 1b
What do the muscle spindle and Golgi tendon organs function together to do?
protect the muscles for excessive stretch and excessive tension
The stretch reflex: receptor, effector agonist, effect on antagonist
- receptor = muscle spindle
- effect on agonist = (positive or negative) more force
- effect on antagonist = (negative or inhibitory) less force
What is the effect of muscle spindles?
when stimulated cause muscles to contract to generate force to resist stretch
The tendon stretch: receptor, effector agonist, effect on antagonist
- receptor = Golgi tendon organ
- effect on agonist = (negative or inhibitory) less force
- effector on antagonist = (positive or excitatory) more force
What is the effect of Golgi tendon organ?
when stimulated cause muscle to relax and produce less force to reduce tension
Withdraw reflex: receptor, effect and how?
- reflex = pain and tactile
- effect = withdraw leg
- how = positive or excitatory effect on hamstring
Cross-extensor reflex: receptor, effect and how?
- receptor = pain and tactile
- effector = weight support on contralateral limbs
- how = positive or negative effect on quadriceps
What is the stretch-shortening cycle?
if a concentric contraction is preceded by active stretching, more force is produced during the concentric phase
Why does the stretch-shortening cycle happen?
- energy storage
- more time to develop
- stretch reflex
- muscle potentiation
Energy storage: the stretch- shortening cycle
- series elastic elements of the muscle stretched during the stretching period
- elastic energy storage in these elements
- this energy is released during concentric phase
More time to develop: stretch shortening cycle
the muscle is activated during the eccentric phase therefore does not have to wait for activation to build up at beginning of concentric phase
Stretch reflex: stretch shortening cycle
when a muscle is stretched muscle spindles feedback to the CNS and the motor neuron stimulation is increased resulting in an increase in force in the muscle to resist the stretch
Muscle potentiation: stretch shortening cycle
- the stretch results in more force being produced by the cross bridges
