Unit 7: The Peripheral Nervous System (Efferent Division)

Question 1

What are the 2 Efferent Pathway’s of the PNS?

Answer 1

The Autonomic system (involuntary) and the Somatic System (voluntary)

Question 2

Describe the Autonomic Nervous Pathway

Answer 2

• Each autonomic nerve pathway is made out of a 2 chain neuron (pre synpatic and post synaptic).
• > The postsynpatic neuron innervates the effector organ.

Question 3

What are the 2 divisions of the Autonomic Nervous System?

Answer 3

The Sympathetic nervous system (fight or flight) and
Parasympathetic systems (rest and digest)

Question 4

What are the features of the Parasympathetic system ?

Answer 4

• Preganglionic fibres arise from the cranial and sacral areas of the CNS
• LONG postganglionic fibres- end on effector organs

Question 5

What are the features of the Sympathetic system?

Answer 5

• Sympathetic nerve fibres originate in the thoracic and lumbar regions of the spinal cord.
• Preganglionic fibres are short, and synapse with cell bodies of postganglionic cells within the sympathetic ganglion chain.
• ->Some preganglionic cells bipass synapsing
• ->Instead, they end up in sympathetic collateral ganglia, with postganglionic cells going the rest of the distance to effector organs.

Question 6

What neurotransmitter do the preganglionic Sympathetic and Parasympathetic release?

Answer 6

Acetylcholine (ACh)

Question 7

What neurotransmitter do the postganglionic Parasympathetic cells release?

Answer 7

Release Acelylcholine, known as Cholinergic fibres.

Question 8

What neurotransmitter do the postganglionic Sympathetic cells release?

Answer 8

Release Noradrenaline (Norepinepherine), called Adrenergic fibres.

Question 9

What are the swellings of terminal branches on autonomic nerve fibres called?

Answer 9

–>Varicosities

Question 10

What is Parasympathetic/ Sympathetic tone (tonic activity) ?

Answer 10

–>Both systems working together

Question 11

What is the Adrenal Medulla?

Answer 11

• Lie above the kidneys
• ENDOCRINE GLANDS
• Secretes hormones into the blood on preganglionic fibre stimulation

Question 12

What is the ratio of medulla hormones?

Answer 12

1:5 Norepinepherine (20%) to Acetylcholine (80%)

Question 13

What are the two types of Acetylcholine receptors?

Answer 13

1. Nictonic -activated by Nictoine

2. Muscarnic- activated by Muscarine.

Question 14

What are the two types of Adrenergic receptors?

Answer 14

1. Alpha receptors
2. Beta receptors
   * Influence secondary messengers which influence metabolic processes.

Question 15

What is an Agonist?

Answer 15

-Bind the same receptor as the neurotransmitter and mimics the effect of it.

Question 16

What is an Antagonist?

Answer 16

-Bind with the receptor and block neurotransmitter response.

Question 17

Where in the brain is Autonomic response governed?

Answer 17

• The brain stem contains the medulla, where the autonomic nervous system is controlled.
• The hypothalamus integrates emotional and behavioral states
• ->The prefrontal cortex can affect personality and expression

Question 18

The Somatic Nervous System mechanisms

Answer 18

• Innervate skeletal muscle by motor neurons

- The axon of motor neurons are continuous from its origin in the CNS to their ending.

Question 19

What neurotransmitter do motor neurons release?

Answer 19

Acetylcholine, which brings about excitation and contraction of skeletal muscle cells.
*Only way to activate skeletal muscles.

Question 20

What is a neuromusclar junction?

Answer 20

• An action potential in a motor neuron rapidly propagates along the cell body within the CNS to skeletal muscle along a large myelinated axon.
• ->As the axon approaches a muscle, it divides into terminal branches and looses its myelin sheath–> this forms a neuromuscular junction.

Question 21

Where does the Specialized End Plate sit?

Answer 21

Below the terminal button

Question 22

Events of a neuromuscular junction

Answer 22

1. Action potential is sent to the terminal button (TB)
2. Triggers the opening of Ca2+ into the TB
3. Ca2+ leads to the release of ACh
4. ACh binds receptor sites on the motor end plate
5. This binding leads to an influx of Na+ and not alot of K+
6. Results in an End Plate Potential (EPP). Local current flows between the depolarized end plate & membrane
7. Local flow opens Na+ channels
8. Local Na+ reduces the potential to threshold, initiating an action potential through the muscle fibre
9. Acetylcholine is broken down by aceytlcholinesterase, terminating muscular response