Neuromuscular Physiology Flashcards
What are dendrites
Tree-like structures that receive information from other neurons
What is the soma
Cell body of neurone that contains the nucleus and structures which support chemical processing of the neuron e.g. neurotransmitter production
What is the axon
The nerve fibre that carries nerve impulses away from the cell body to other tissues
What is the myelin sheath
Insulates axons and enhances transmission speed along axons
What is the myelin sheath
Insulates axons and enhances transmission speed along axons
What is the resting membrane potential
-70mV
What is meant by the membrane is polarised
More negative charge on the inside compared to extracellular fluid
What maintains the resting membrane potential
Na+K+ pump
What has the greatest effect of the resting membrane
The movement of K+ through potassium leak channels (membrane is more permeable to potassium) as k+ wants to move down it’s concentration gradient but also does not want to move to area where it is already more positive
What are ligand gated ion channels
Ion channels which open in response to neurotransmitters binding
What are voltage gated ion channels
Ion channels which open in response to a change in membrane potential
What are mechanically gated ion channels
Ion channels that open in response to mechanical stimulation
What is an action potential
A rapid sequence of changes in voltage across a membrane brought about by the opening and closing of various ion channels
What does a stimulus arriving/ binding to the post synaptic membrane receptor cause
Na+ voltage gated ion channels open causing an influx of Na+ into the neuron, (crossing threshold) in an all or nothing fashion
What happens when the cell interior becomes positively charged
Na+ gates close, depolarisation ends and voltage gated k+ channels open causing the k+ to leave the cell (repolarisation)
What is the refractory period
The period where some k+ channels remain open after resting potential has been reached causing hyperpolarisation and therefore no other action potential can be initiated at this time
How does the wave of depolarisation spread along the axon
Via the uncovered nodes of ranvier
What is the difference between an excitatory and inhibitory neurotransmitter
Excitatory causes influx of positive ions ( depolarisation) and inhibitory causes influx of negatively charged ions (hyperpolarisation)
What is the central nervous system
Brain and spinal cord
What is the peripheral nervous system
All nerves and sensory structures despite brain and spinal cord
What is the somatic nervous system
Voluntary control of skeletal muscle
What is the autonomic nervous system
Involuntary control of glands and smooth muscles (consists of parasympathetic and sympathetic nervous systems which are involved in fight/flight)
What is the motor cortex
Area of the brain which moving command signals are initiated
What is the corticospinal tract
Primary descending pathway controlling voluntary movement of contra lateral limb muscles
How is muscle contraction initiated from the motor cortex
Nerve signals are sent from the motor cortex down the corticospinal tract which travels down the spinal cord
What are the 2 components of the spinal cord
White matter and grey matter
What is white matter
Part of spinal cord that consists of long axons of neurons that transmit impulses
What is the grey matter
Part of spinal cord that consists of neuronal cell bodies and their dendrites
Describe how corticospinal tract neurons travel through the spinal cord
Move through the white matter before entering the grey matter where cell bodies for alpha-motonerons are located
What shape is the grey matter
H shape
What are the two limbs of the grey matter
Dorsal and ventral limbs
What are the three types of neurons in the spinal cord
Motoneurons (efferent), sensory neurons (afferent) and interneurons
Where are motoneurons located in the spinal cord
In the ventral horn
Where do motoneurons exit the spinal cord
Through the ventral roots to muscle
Where do sensory neurons enter the spinal cord
Through the dorsal horn from the peripheral
What are alpha motoneurons
Moto neurons within the spinal cord that receive and subsequently send never signals to the muscle fibres they innervate to produce voluntary movement
What is a motor unit
The motoneuron and the muscle fibres they innervate (up to 6000 muscle fibres)
What are the three motor unit types
Slow twitch (S), fast twitch fatigue resistant (FR) and fast twitch fatiguable (FF)
What are slow twitch motor units
Motor units that recruit a smaller number of type 1 muscle fibres and are recruited first at low forces
What are fast twitch fatigue resistant muscle fibres
Motor units that recruit a larger number of type IIa muscle fibres and are recruited second at moderate forces
What are fast twitch fatigable motor units
Motor units that recruit a larger number number of type IIx muscle fibres last at high forces
Which type of motor unit has the largest axon diameter and cell body size
Type FF
Which type of motor unit has the highest excitability
Type S
Which type of motor unit has the highest maximal discharge frequency
Type FF
Which type of motor unit has the highest number of muscle fibres per motor unit
Type FF
Which type of motor unit has the fastest axon conduction velocity
Type FF
What is the effect of body temperature on conduction velocity
High temperature= high conduction velocity
What are mechanisms of force gradation
Mechanisms that increase force of muscle contraction
What are the two main mechanism of force gradation
Increase in motor unit recruitment (spatial summation) and increase in dishcharge frequency/rate coding (temporal summation)
What 3 main types of afferent nerve fibres/ sensory neurones innervate muscles
Proprioreceptors (location, moment and tension detection), mechanoreceeptors and noiciceptors (detection of chemical alterations/chemoreceptors)
What is muscle spindle
Dynamic and static stretch receptors
What is the Golgi tendon organ
Tension receptor
What are free nerve endings
Stretch, pressure and metabolic perturbation/disturbance receptor
What is the myotatic reflex arc
Reflex pathway that induces the knee jerk reflex with reciprocal inhibition to prevent excessive stretch
What type of afferents are muscle spindle receptors coupled with
Ia and II
What type of afferent are Golgi tendon organs coupled with
Ib
What type of afferents are free nerve endings coupled with
III and IV
Describe the myotatic reflex arc
1) muscle spindles detect dynamic stretch via percussion of the tendon
2) 1a afferents that innervate muscle spindles are activated
3) In afferents synapse with homologous a-motoneuron monosynpatically activating the quadriceps motoneuron, inducing shortening of the quadriceps to prevent excessive stretch
4) 1a afferents simultaneously synapses with an inhibitory interneuron which synapses with the antagonist muscle so the hamstring relaxes (reciprocal inhibition)
6) the afferent signal is concurrently sent to the brain where it is perceived
What three neurons make up the sensory pathway
1st order, second order and 3rd order neuron
Where is the 1st order neuron located
Extends from periphery to the dorsal horn of spinal cord and synapses with 2order neuron
Where is the 2nd order neuron located
Passes up the spinal cord to the thalamus where it synapse with the 3rd order neuron
Where is the 3rd order neuron located
Passes to sensory regions of the cerebral cortex
How does the nervous system code information
Through frequency of AP and number of AP
What are the functions of skeletal muscle
Produce movement, maintain posture, stabilise joints, generate heat and store nutrient reserves
Describe the gross structure of the skeletal muscle
Wrappings of fibrous connective tissue that can be described in terms of 4 levels of organisation
What are the 4 layers of connective tissue in skeletal muscle
Epimysium, perimysium, endomysium and sarcolemma
What is the epimysium
Fibrous tissue surrounding skeletal muscle that contains a layer of dense, irregular connective tissue which encases the entire muscle and protects it from, friction against other muscles
What is the perimysium
Connective tissue that groups muscle fibres into bundles called fascicles (contain 10-150 muscle fibres)
What is the endomysium
A layer of loose connective tissue that enseaths each individual muscle fibre
What is the sacrolemma
Beneath the endomysium surrounding each muscle fibre containing plasma membrane and basement membrane. The plasma membrane conducts the electrochemical waves of depolarisation over the surface of the muscle fibre
What forms tendons
The epimysium blended/joined to intramuscular tissue sheaths to form tense connective tissue
What is the function of tendons
Connect both ends of the muscle to the periosteum (bones outer cover( to transmit force generated from muscle fibres to pull on the bone
What is the muscles origin
The location where the tendon joins a stable skeletal part (proximal end) of the lever system
What is the insertion
The point of distal attachment to the moving bone
What are myofibrils
Smaller functional units within muscle fibres that lie parallel to the fibres long axis
What are sarcomeres
Smaller subunits in myofibrils that lie parallel to the long axis of the myofibril
What are the 2 contractile proteins in sarcomeres
Actin and myosin
What are the z lines
The lines that represent the separation of successive sarcomeres
What are M bands
Band that bisects the central portion of the sarcomere
What is the H zone
Central portion of sarcomere that contains the protein structures that contain myosin filaments
How are actin and myosin arranged in myofibrils
Hexagonal arrangement
What is myosin
Filaments consisting of bundles or molecules with polypeptide tails and globular heads that enable binding to actin/pulling actin towards the M band
What ion regulates muscle contraction and relaxation
Calcium
Where is calcium secreted from in muscle fibres
The sarcoplasmic reticulum
What are the two accessory proteins involved in muscle contraction
Tropomyosin and troponin
What happens when calcium ions are released from the SR in response to muscle activation
Calcium ions bind to troponin which shifts tropomysoin away from the actin binding sites, enabling the formation of cross bridges and muscle contraction
What are T-tubules
Complex tubule system perpendicular to the myofibril with the lateral end of each tubule terminating in a saclike vesicle (SR) that stores ca2+
What is a triad
The repeating pattern of two vesicles and a T-tubule in each z line region
What is the function of the T-tubule/ triad
T-tubule opens externally from inside the muscle cell and functions are a micro transportation net weak by spreading action potentials from the fibres outer membrane to the inner cell to stimulate ca2+ release
Where does acetylcholine bind to in muscle cells when released from a motoneuron
Sarcolemma
What does binding of acetylcholine to the sarcolemma initiate
An influx of Na+ which spreads into the T-tubules are causes the release of ca2+ from the SR
Why is ATP required for muscle contraction
Bound to the myosin head and hydrolysed to form the cross bridge, for cross bridge reattachment and recycling of the head
What is crossbridge cycling
The hydrolysis of ATP when the crossbridge forms causes the release of Pi from the myosin head to form a stronger bond between actin and myosin and the release of ADP which induces the power stroke
After contraction ATP rebinds to the myosin and the crossbridge reattaches, ATP is hydrolysed again to recock the head
What is the sliding filament theory
Muscle shortens and lengthens because of thick myosin and thin actin filaments that slide past each other without changing length using energy from ATP
