Lesson 4: PNS

Question 1

Where do somatic nerve axons extend? What do they do there?

Answer 1

Into the spinal cord to synapse on a motor/inter/sensory neuron

Question 2

What is a monosynaptic reflex?

Answer 2

One sensory neuron synapses directly on one motor neuron - a simple reflex

Question 3

What is areflexia?

Answer 3

Absence of reflex

Question 4

What are central pattern generators? What do they do?

Answer 4

Constantly active neurons at the spinal cord. They produce basic motor patterns without voluntary action

Question 5

What is the viscera?

Answer 5

The internal organs of the body

Question 6

What is the role of the autonomic nervous system, in term of information?

Answer 6

Carries info to and from the viscera

Question 7

What is the covering of a peripheral nerve? 4 layers

Answer 7

Each axon: schwann cell sheath, then endoneurium. Axons bungled together by perineurium = fascicles. Epineurium layer over fascicles

Question 8

What does a peripheral nerve consist of?

Answer 8

A bundle of fascicles

Question 9

Which senses are the ‘special senses’? What’s different about them

Answer 9

Smell, vision, hearing, taste

They have specialized receptors - little sensory organs

Question 10

What is the most common receptor type? What information does it conduct?

Answer 10

Bare nerve ending. It processes tissue damage or stretch as pain

Question 11

What are muscle spindles? (Label). What are muscle spindles made of?

Answer 11

Mechanoreceptors. Small sensory organs, with a sensory area at its equator and small intrafusal fibres at each pole

Question 12

What are the three roles of muscle spindles?

Answer 12

Spasticity following injury to the nervous system, monitoring the muscle length, monitoring rate of change in muscle length

Question 13

What is the role of alpha-motor neurons?

Answer 13

Innervate the extrafusal fibers of the skeletal muscles

Question 14

What is the primary role of gamma-motor neurons? (2)

Answer 14

To regulate the length of spindle fibers and modulate the excitability of the annulospiral primary endings

Question 15

How do gamma-motor neurons differ from alpha-motor neurons in terms of structure?

Answer 15

There are fewer and smaller axonal processes

Question 16

What happens when the ventral nerve root receives information to contract?

Answer 16

This information travels along the gamma-motor neurons –> Portions of the intrafusal muscle fibers contract, which stretches the central part of the muscle spindles –> afferent projections to spinal cord –> alpha-motor neurons to extrafusal muscles –> reflexive contraction of the extrafusal fibers of the muscle

Question 17

What is the static role of the muscle spindle?

Answer 17

Modulate the length of a muscle

Question 18

What is the dynamic role of the muscle spindle?

Answer 18

Modulate the rate of change in a muscle length

Question 19

Why must gamma motor neurons reset?

Answer 19

So that the centre is constantly sensitive

Question 20

Which tracks do gamma motor neurons receive input from?

Answer 20

The reticulospinal and vestibulospinal tracts

Question 21

What occurs during a monosynaptic stretch reflex?

Answer 21

Impulses along the afferent fibers –> dorsal horn –> alpha motor neuron

Question 22

What is reciprocal innervation?

Answer 22

When the contraction of one muscle is paired with the antagonist being relaxed

Question 23

What is co-contraction? What is the result?

Answer 23

Simultaneous contraction fo opposing muscles due to abnormal reflex activity. Results in no movement of the body part

Question 24

What is a motor unit?

Answer 24

A single alpha motor neuron and all the muscle fibres it innervates

Question 25

What is the difference between a sign and a symptom?

Answer 25

A symptom is reported by the patient, whereas a sign can be observed and measured

Question 26

What is neuropraxia? What is its outlook?

Answer 26

Light compression of the nerve - reversible

Question 27

What is axonotmesis? How is it healed?

Answer 27

Heavier compression - the axon is severed, but the Schwann cell sheath and fibrous coverings are intact. The axon regenerates from the point of the lesion

Question 28

What is neurotmesis? What are its consequences?

Answer 28

Severance of the axon and disruption or misalignment of the Schwann cell sheath = action potential can't conduct, and degeneration of the axon distally from the lesion

Question 29

How quickly does a severed axon grow back?

Answer 29

1 mm/day

Question 30

What is the stapedius?

Answer 30

A small muscle that responds to loud sounds by contracting, to reduce the ossicle vibration

Question 31

What nerve innervates the stapedius?

Answer 31

The facial nerve

Question 32

What may cause innapropriate contraction of facial muscles in response to loud noises?

Answer 32

If the lesion to the facial nerve is before the branch that innervates the stapedius breaks off, the axon may regenerate in the wrong sheath

Question 33

What are the four symptoms of lower motor neuron lesions?

Answer 33

Areflexia, rapid muscle atrophy, flaccid paralysis, and abscence of muscle tone

Question 34

What are the two main causes for sensory neuron damage?

Answer 34

Damage to the disc protrusion at the root, or nutritional damage at the root

Question 35

What are the causes of damage to alpha motor neurons?

Answer 35

Poliomyelitis, nutritional damage, and autoimmune disease

Question 36

What is wallerian degeneration

Answer 36

Degeneration from the point of injury distally

Question 37

What is the treatment for a severed sheath? Why?

Answer 37

Surgical repairment of the nerve, as the sheath must remain aligned

Question 38

How does Polio affect the body?

Answer 38

It infects the alpha motor neuron cell body of the voluntary motor nerve (lower motor neuron)

Question 39

What has occurred in Myasthenia Gravis?

Answer 39

Receptors on the postsynpatic membrane of the muscle are destroyed by the immune system, resulting in a limited number of receptors

Question 40

What happens when there is damage to either the parasympathetic or sympathetic system?

Answer 40

Over-action of the unopposed function

Question 41

Where is acetylcholine?

Answer 41

In parasympathetic nerve endings of neuromuscular junctions

Question 42

Where is norepinephrine located?

Answer 42

In the sympathetic nerve endings

Question 43

Where does dopamine go, and what transports it there?

Answer 43

Into the basal nuclei, via the substantia nigra cells

Question 44

What disease is involved in irregular dopamine amounts?

Answer 44

Parkinson's disease

Question 45

Where is GABA?

Answer 45

Basal nuclei

Question 46

What disease is associated with less GABA?

Answer 46

Huntington's Chorea

Question 47

What is the role of enkephalins and endorphins?

Answer 47

Pain modulation

Question 48

What is the role of substance P?

Answer 48

Pain