CAM102 Lecture Notes - Lecture 25: Alpha Motor Neuron, Golgi Tendon Organ, Tendon Reflex
Learning Objectives
• Describe the basic elements of a reflex (input, processing, output)
• Describe simple reflexes such as stretch and tendon - overload reflexes, including their
purpose - why do they happen?
• Describe the properties of complex reflexes and pattern generators
• Complex circuits leading to patterned outputs
• Automation of common movements
• Briefly describe the roles of
• Stretch (la) reflex (Gamma (�) motor neuron sets sensitivity)
• Golgi tendon organ (lb reflex) - inhibits α through interneuron
• Inter- or multi-segmental reflexes
• Spinal cord and brainstem pattern generators
Neural Solutions
• Turn understanding (via senses) into action
• Somatic effectors
• Autonomic control
• Endocrine output
Somatic Motor Neurons
• All somatic motor functions are achieved by influencing α alpha otor euros
Spinal Somatic Motor Neurons
• α alpha otor euros of the spinal cord have their cell bodies in the ventral horn of the
grey matter
• Their axons emerge in the ventral nerve roots and travel along the spinal nerves to their
target muscles
Cranial Somatic Motor Neurons
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Motor Units
• A motor unit is a sigle alpha otor euro αMN ad the uscle fibre it innervates. Fire
the αMN, all fibres contract
• The number of muscle fibres in a motor unit varies greatly
• Innervation ratio (average muscle fibres per neuron) varies 1:3 (eye muscles) to 1:700 (major
limb muscles
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Motor Unit Recruitment
• Each muscle fibre receives an input from only one αMN
• Their activation thresholds vary with the size of motor unit
• Small activation eites ol the ost sesitive αMNs, with the smallest number of fibres
• Stronger stimuli activate more units; tension increases
• This is called recruitment
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Document Summary
Stretch (la) reflex (gamma () motor neuron sets sensitivity: golgi tendon organ (lb reflex) - inhibits through interneuron. Neural solutions: turn understanding (via senses) into action. Somatic motor neurons: all somatic motor functions are achieved by influencing (cid:894)alpha(cid:895) (cid:373)otor (cid:374)euro(cid:374)s. Motor units: a motor unit is a si(cid:374)gle alpha (cid:373)otor (cid:374)euro(cid:374) (cid:894) mn(cid:895) a(cid:374)d the (cid:373)uscle fibre it innervates. Fire the mn, all fibres contract: the number of muscle fibres in a motor unit varies greatly. Innervation ratio (average muscle fibres per neuron) varies 1:3 (eye muscles) to 1:700 (major limb muscles. Motor unit recruitment: each muscle fibre receives an input from only one mn, their activation thresholds vary with the size of motor unit, this is called recruitment. Small activation e(cid:454)(cid:272)ites o(cid:374)l(cid:455) the (cid:373)ost se(cid:374)sitive mns, with the smallest number of fibres. Control of muscle tension: the tension of an active muscle depends on:
