Skeletal Muscle, Cardiac Muscle and Movement - Topic 1 Flashcards
Motor Unit
One alpha motor neuron and all muscle fibres/ cells associated with it.
What do neurotransmitters do and how are they transmitted?
Initiate nerve impulses and they are transmitted by electrical signal.
Skeletal Muscle
Muscle type activated by motor neurons.
What way are skeletal muscles arrnged and what direction do they contract?
They are arranged lengthwise and contract horizontally.
Neuromuscular Junction
Synapse between motor neuron and muscle fibre where electrical signal is relayed into mechanical action by the muscle
Princliples of muscle contraction
- Alpha motor neurons activates bundle of muscle cells (motor unit)
- Each muscle cell produces an equal amount of force
- The no. alpha neurons activated contribute to the force produced by motor units
- So the relative force gained by muscle contraction is dependent on the number of motor units activated.
Gap between motor neuron post synapse and muscle cell
Neuromuscular junction
Why do muscle cells produce an equal amount of force?
Because they are very thin and long and approx. the same length so the overlapping of actin and myosin is equal on each one (equal contraction).
Muscle Twitch
Single muscle contraction followed by relaxation.
What is needed for another muscle contraction or even a twitch to occur?
The previous contraction must relax. (Repolarisation - action potential must not be reached so Voltage needs to be below threshold)
What controls fine movement, e.g. eye?
Many motor neurons associated with the same mucle cells
Summation
Increased force from multiple muscle twitches in short enough intervals.
Tetanus
Sustained muscle contraction from very rapid/continual stimuli.
How can one motor nueron cause tetanus?
It can release Ca2+ multiple times, causing repeated stimulation required for tetanus to occur.
What happens when the intervals between stimuli are short? How does it gettig shorter change the contraction of muscle?
The action potential generated in the previous contraction (e.g a twitch) cannot go below the threshold so the next contraction is stronger (summation). This eventually creates incomplete tetanus and then tetanus when stimuli is continuous and at maximal strength.
What is the difference between summation and tetanus?
Summation = series of stimuli added produce a stronger contraction because the muslc eis stimulated before it has fully relaxed from a previous twitch. The second twitch is stronger
Ttanus = contractions fuse, producing continuous contraction without relaxation in between. When stimuli are repeated so frequently that there is no noticeable relaxation phase between twitches.
Alpha Motor Neuron
Neuron that stimulates skeletal muscle contraction.
Graded Response
Variable muscle force based on motor unit activation.
Muscle Fatigue
Decreased muscle performance after prolonged activity.
Electrical Impulse
Signal from the brain to initiate muscle contraction.
Stimulus Intensity
Magnitude of signal affecting muscle tension.
Twitch Force
Force generated by a single muscle twitch.
Skeletal Muscle Activation
Process of stimulating muscle fibers to contract.
Muscle Cell Arrangement
Skeletal muscle cells are horizontally bundled.
Force Production
Dependent on number of activated motor units.
Threshold Level
Minimum force required for muscle contraction.
Twin Pulse Interval
Time between two stimuli affecting muscle response.
Short Intervals
Time gaps between stimuli impacting contraction strength.
Incomplete Tetanus
Partial relaxation between rapid stimuli.
Muscle Response
Reaction of muscle fibers to stimulation.
Force Doubling
Increased contraction force with closely spaced stimuli.
Electrical Stimulation Frequency
Rate of stimuli affecting muscle contraction dynamics.
Muscle Contraction Decision
Brain determines number of activated muscle cells.
Muscle Fiber Innervation
Each fiber receives input from one motor neuron, causing it to contract.
Twitch
Single muscle contraction followed by relaxation.
Recruitment
Activation of multiple motor units for greater force.
Motor Units
Alpha motor neuron and its innervated muscle fibers.
What are the two modes of skeletal muscle activation?
Recruitment of multiple motor units (TENSION) and Frequency of stimuli (STIMULUS VOLTAGE)
Recruitment of multiple motor units
The amount of force generated when skeletal muscle contracts is dependent on the number of activated motor neurons collaorated.
Number of motor units for muscles for delicate movement vs muscles for strength
Delicate movement have less motor units (less muscles less per motor neuron)
Frequency of Stimulation
Sustained skeletal muscle contraction by the same motor neuron
Fast Twitch Units
Muscle fibers that contract quickly and powerfully.
Slow Twitch Units
Muscle fibers that contract slowly and endurance-focused.
Cardiac Muscle
Muscle tissue that makes up the heart.
Arrangement of Cardiac Muscle Cells
Tandemly (not horizontally) arranged - they contract independently in sequence.
Intercalated Discs
Separation wall between two neighbouring cardiac muscle cells with holes that allow communication between cardiac cells (signalling molecules). They insulate a signal so it doesn’t get lost between the cells.
Sino Atrial (SA) Node
Pacemaker of the heart initiating contraction signals.
Autorhythmic Cells
Cells generating spontaneous action potentials in heart.
Contractile Cells
Cells responsible for heart muscle contraction. They contract when a signal from the neighbouring cell is transported through the insulated wall of intercalated disc.
Difference between cardiac and skeletal muscle activation.
Skeletal muscle is only activated by a motor neuron and contractile cardiac muscle cell is activated by neighbouring cell through an intercalated disc AND internal pacemaker.
Action Potentials
Electrical signals triggering muscle cell contraction - rapid change in the voltage across a cell membrane, caused by a shift in the balance of ions inside and outside the cell
Gap Junctions
Connections allowing electrical signals between cells.
Horizontal Contraction
Skeletal muscle cells contract in a coordinated manner.
Sequential Contraction
Cardiac muscle cells contract one after another and pulled to the direction the signal travels from.
Unidirectional Signal Travel
Signal flows in one direction through cardiac cells.
Autorythmic Muscle Cells
Muscle cells that function independently of nervous input.
Muscle Relaxation
Return of muscle fibers to resting state.
Maximum Force in Tetanus
Peak tension achieved during sustained contraction.
