Lower Motor Neurons

Question 1

Neuromuscular transmittion

Answer 1

AP arrives -> Ca2+ channels open -> Ca2+ entry triggers release of ACh -> ACh binding to nAChRm opening ligand-gated channel on muscle -> Na+ influx into muscle generates EPP -> EPP initiates AP spreads via Na+ channels -> transmittion terminated by AChEase -> Choline reuptake via transporter

Question 2

Disease affecting Presynaptic terminal

Answer 2

botulism & Eaton-Lambert syndrome -> impaired release of ACh

Question 3

Disease affecting the synapse

Answer 3

Cholinergic drugs & nerve gases -> block transmittion by ACh breakdown w/in synapse

Question 4

Disease affecting the receptors

Answer 4

mysthenia gravis

Question 5

Force generation in whole muscles

Answer 5

Frequency of stim, Recruitment, Size principle, muscle fibre type

Question 6

Patella Tendon

Answer 6

hammer tap stretches tendon -> sensory neuron synapses w/ & excites motor neuron in the spinal cord & sensory neuron -> motor neuron conducts AP to synapse on extensor m. causing contraction, flexor relaxes -> leg extends

Question 7

Withdrawal reflex

Answer 7

postsynap. reflex to noxious stim. used to localise lesions, reflex functions even if spinal cord seg have been isolated but consciousness of the pain will not occur

Question 8

Withdrawal & Crossed Extensor reflex

Answer 8

afferent neurons activate excitatory and inhbitory interneurons that stim. flexors and relax extensors causing ipsilateral leg to withdraw and contralat. leg to extend to take the weight

Question 9

Muscle spindles

Answer 9

intrafusual fibres, do not contribute force but act as measures for muscle length, innervated by gamma motor neurons, muscle fibres innervated by alpha motor neurons (generally from same spinal seg)
Dynamic gamma motor neurons (GMN) innervate contractile zone of dynamic bag fibres (act for fast and unpredictable change in length
Static (GMN) innervate contractile zone of chain and static bag fibres (act for slow and predictable change in length)
Primary Type Ia detect changes in length (all fibres)
Secondary Type II detect the length alone (chain and static bag fibres)

Question 10

Golgi Tendon Organs

Answer 10

changes in muscle tension,
afferent nerve endings located at junction of muscle and tendon
innervated by Type Ib sensory neurons
-ve feedback loop to prevent excessive tension

Question 11

LMN Disease

Answer 11

Signs: weakness/paralysis, neurogenic atrophy, flaccidity/hypotonia

Question 12

Reflexes

Answer 12

Biceps tendon reflex: musculocutaneous, C6-8
Triceps reflex: radial, C7-T1
Patellar reflex: femoral, L4-L6