Topic 5 - Peripheral nervous system

Question 1

What are the 3 major divisions of the PNS?

Answer 1

• Sensory = relaying info. to CNS about internal/external environment (afferent neurons)
• Somatic = control of skeletal muscle via action of motor neurons (voluntary). S.Muscle X contract w/o neuronal activation (efferent neurons)
• Autonomic = regulates smooth muscle & gland function (efferent neurons) - heart, blood vessels etc. are involuntary.

Question 2

What is the motor end plate?

Answer 2

It’s a region on skeletal muscle fibre containing high numbers of receptors

Question 3

What is the receptor called on a skeletal muscle?

Answer 3

Cholinergic nicotinic receptors (acetylcholine (ACh) is the neurotransmitter that activates them)

*Binding of ACh opens ion channel &Na+ flows into muscle fibre (&K+) - overall response = excitatory (muscle contraction)

Question 4

What is the sympathetic (autonomic) nervous system and what activates it?

Answer 4

• Preps body for emergency intense physical activity
• Often responds to provoking situations (e.g fright, fight or flight response)
• Stress also (acute/chronic)

Question 5

What is the parasympathetic (autonomic) nervous system

Answer 5

• when body responds to basic metabolic demands, undergoing maintenance & reinstating homeostasis (often more dominant)
• called “rest & digest” functions
• e.g eating meal = activated

Question 6

What does a sympathetic neuron have?

Answer 6

• has short preganglionic neuron and long postganglionic neuron.

*results in sympathetic ganglia often occur in chain near spinal column.

Question 7

How does sympathetic neurons activate and cause muscle movement?

Answer 7

1. Preganglionic neuron releases ACh
2. ACh binds & activates cholinergic nicotinic receptors on the sympathetic post-ganglionic neuron. This allows Na+ & K+ to move across neuronal membrane
3. The strong movement of NA+ ions into neuron results in depolarisation/excitatory event
4. The S.postGN release noradrenaline
5. Noradrenaline binds & activates alpha/beta adrenergic receptors (many types) expressed on target cell (e.g smooth muscle cell)
6. After activation of Adrenergic receptors (which are G protein-coupled receptors), initiation of 2nd messenger activity.
7. Effects are triggered (like change in ion entry into cell/change in DNA transcription) & result in biological effect e.g muscle contraction/muscle relaxation

Question 8

What does the Parasympathetic neurons have?

Answer 8

• a long preganglionic neuron & a short postganglionic neuron

*often occur close/in organ they’re innervating (effector organ)

Question 9

How does parasympathetic neurons activate?

Answer 9

1. Preganglionic neuron releases ACh
2. ACh binds & activates cholinergic nicotinic receptors on the parasympathetic post-ganglionic neuron. This allows Na+ & K+ to move across neuronal membrane
3. The strong movement of NA+ ions into neuron results in depolarisation/excitatory event
4. P.postGN releases ACh
5. ACh binds & activates muscarinic cholinergic receptors on target cell
6. After activation of Muscarinic receptors (which are G protein-coupled receptors), initiation of 2nd messenger activity.
7. Effects are triggered (like change in ion entry into cell/change in DNA transcription) & result in biological effect e.g muscle contraction/muscle relaxation

Question 10

What are the 5 main types of muscarinic receptors?

Answer 10

• M1
• M2
• M3
• M4
• M5