Reflexes and muscles Flashcards
What is a reflex arc?
neural pathway causing involuntary and immediate reactions to stimuli e.g for protection
What is an example of a reflex arc?
when you touch a sharp object a reflex arc is responsible for the rapid withdrawal of the hand preventing injury
What are the 7 key stages of a reflex arc?
1) stimulus = e.g hot object
2) receptor = speacalised cells, e.g temperature cells in skin that detect stimuli generating nerve impulses
3) sensory neuron = transmits the nerve impulse to relay neurons
4) relay neuron = connect sensory neurons to motor neurons
5) motor neuron = transfers nerve impulses from the relay neuron to effectors
6) effector = muscle or gland that receives the signal and carries out a response
7) response = final action taken such as muscle contraction
What are spinal reflexes and give 2 examples?
spinal reflexes = involve the spinal cord only
example:
- withdrawal reflex = removes the hand rapidly from sharp/hot object
- knee-jerk reflex = causes leg to kick when tapped just below the kneecap to help maintain posture and balance
What are cranial reflexes and give an example?
cranial reflexes = involves the brain only
example:
- blinking reflex = triggers involuntary blinking of the eyelids when cornea is stimulated
What are the key features of a reflex arc and what do they do?
involuntary = allow brain to concentrate on complex tasks
rapid = ensure swift response
protective = safeguard body from potential injuries
innate = intrinsic mechanisms from birth eliminating need for learning
What are skeletal muscles?
forms majority of the body’s muscle, attaches to bones too move parts of the body
What are cardiac muscles?
unique to the heart and functions to circulate blood
What are smooth muscles?
located in the walls of hollow organs like blood vessels and the intestines and function to move substances through these organs
What are the features of skeletal muscle?
- tubular striated fibre structure
- multiple nuclei per fibre
- regular parallel bundles of myofibrils
- voluntary control
- neurogenic stimulation
- fast contraction speed
- short contraction duration
What are the features of cardiac muscle?
- branched striated fibres
- single nuclei per fibre
- branching network of myofibrils
- involuntary control
- myogenic stimulation
- intermediate contraction speed
- intermediate contraction duration
What are features of smooth muscle?
- spindle-shaped non-striated
- single nuclei per fibre
- unorganised no myofibrils
- involuntary control
- neurogenic stimulation
- slow contraction speed
- long lasting contraction duration
What is the structure of skeletal muscle fibres?
numerous bundles of long cylindrical muscle fibres
individual cells fuse forming muscle fibres to avoid weakness at junctions between cells and increasing overall muscle strength
What are the key components of muscle fibres and their roles?
- sarcolemma = cell surface membrane
- sarcoplasm = cytoplasm
- t-tubules = extensions of sarcolemma transmitting electrical signals to ensure the entire muscle receives the impulse simultaneously
- sarcoplasmic reticulum = speacalised endoplasmic reticulum responsible for storing and releasing CA+ ions
- myofibrils = subcellular structures designed for contraction
- multiple nuclei = several merge to form 1 muscle fibre
- mitochondria = release energy in the form of ATP muscle contractions
What are the structure of myofibrils?
core unit of muscle fibres containing organised bundles of protein filaments
filaments slide past each other to enable muscle contractions
made up of repeating units called sarcomeres
What are the 2 main filaments making up a sarcomere and their structure?
myosin = thick filaments composed of long rod-shapes with bulbous heads
actin = thin filaments composed of 2 strands twisted round each other
What are the key sections of the sarcomere?
A band = myosin and overlapping actin filaments
I band = only actin filaments
Z lines = boundaries of each sarcomere unit
M line = central line of sarcomere
H zone = only myosin filaments
What is the structure of myosin?
has globular head regions that connect with binding sites to the actin filaments
2 regulatory proteins tropomyosin and troponin modulate binding
What do myosin heads have?
- hinge enabling movements
- 1 site for binding to actin
- another site for ATP binding providing energy
What do actin filaments have?
- sites for myosin head attachment (actin-myosin binding sites)
- tropomyosin and troponin proteins attached playing a regulatory role
What are the changes to the sarcomere during muscular contractions?
- I band and H zone in sarcomeres shorten due to increased overlapping of actin and myosin filaments
- A band remains constant in length
What are the main steps in the sliding filament theory?
1) CA2+ ions bind to troponin altering their shape
2) this change moves tropomyosin away from actins binding site making them available for myosin
3) myosin heads attach to exposed actin filaments forming actin-myosin cross-bridges
4) myosin heads execute a power stroke, pulling the actin filaments along and releasing ADP
5) ATP molecule binds to myosin head leading to it’s detachment from actin
6) CA2+ activates myosin’s ATPase activity, breaking down ATP to ADP and P releasing energy
7) energy resets the myosin head to it’s original position
8) myosin head reattaches to a new actin site further along the filament
How can ATP be generated for muscular contractions through different pathways?
aerobic respiration = suitable for prolonged low intensity exercise
anaerobic respiration = used during short high intensity exercise
ATP-creatine phosphate system = used for short bursts of vigorous exercise
What is a neuromuscular junction?
where a motor neuron meets a skeletal muscle fibre
What is a motor unit?
muscle fibres supplied by a single motor neuron
How do motor units determine the force of muscular contractions?
strong force = to exert a large number of motor units are stimulated
small force = requires stimulation of only a few motor units
What are the stages in neuromuscular transmission?
1) action potential arrives at the end of the neuron
2) triggers the opening of CA2+ ion channels and CA2+ enters the neuron
3) causes acetylcholine vesicles to release their contents into the synaptic cleft
4) acetylcholine diffuses across the synaptic cleft
5) acetylcholine binds to receptors on the sarcolemma leading to the opening of NA+ ion channels
6) this results in the depolarisation of the sarcolemma
How is acetylcholine broken down and why is this process important?
Acetylcholinesterase enzyme breaks down acetylcholine into choline and ethanoic acid
crucial to prevent excessive stimulation of the muscle fibre
How is acetylcholine recycled?
choline and ethanoic acid returns to the synaptic knob where they’re reassembled into acetylcholine for future use
mitochondria in the neuron provide energy for acetylcholine reformation
What is the role of the sarcoplasmic reticulum in muscle contractions?
depolarisation extends into the muscle fibres through t-tubules which interact with the sarcoplasmic reticulum (storage site for CA2+)
when stimulated by the arrival of an action potential CA2+ channels open in the sarcoplasmic reticulum membrane, this release a flood of CA2+ into the sarcoplasm causing a surge triggering muscular contractions
