Summary of the IB SEHS Unit 4.1 (neuromuscular function). You will find detailed yet summarized information on the topic, organized according to the IB syllabus (contains all necessary information to achieve a 7).
Label a diagram of a motor unit
[ Motor unit = muscle + motor neuron ]
Afferent neurons: information from the receptors (sensors) to the CNS
Efferent neurons: motor neurons that carry informations from the CNS to the muscle
Interneurons: connect afferent and efferent neurons. Inhibitory/excitatory effect
Number of muscle fibers per motor neuron:
Small: great precision but small force
Large: large forces
Diagram of motor unit
Cell body: where organelles are located. most of the cytoplasm is located there and the nucleus is also
there (contains genetic information)
Dendrites: link neurons to other neurons and transmits info to the cell body
Axon: cylindrical elongated fiber that carries the nerve impulse. can be 20cm long.
Myelin sheath: covers the axon and increases nerve impulse
Motor end plate: joint between neuron and muscle/other neurons.
Synapse: small junction across where a nerve impulse passes from one cell to another (they don’t touch
eachother)
Skeletal muscles are formed by a group of muscle cells (muscle fiber) that are packed into bundles
(fascicle). Muscle fibers are formed by overlapping proteins (actin and myosin) in a structure called
myofibril.
Basic structure of myofibril: sacromere
Thin filament: actin
Thick filament: myosin
Actin attaches to the Z-line at one end and
myosin is in the middle.
sacromere
H-zone: region of myosin only (lightest one)
Z-line: perpendicular stripe of t-tubules where
actin attaches
*sacromere is what whe find between two Z-
lines
A-band: total lenght of myosin
I-band: region of actin only
M-line: perpendicular line of proteins in the middle
During muscle contraction
actin filaments run along myosin filaments towards M-line and shortens muscle fiber
4.1: Neuromuscular function 2
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