Lesson 4: PNS Flashcards
Where do somatic nerve axons extend? What do they do there?
Into the spinal cord to synapse on a motor/inter/sensory neuron
What is a monosynaptic reflex?
One sensory neuron synapses directly on one motor neuron - a simple reflex
What is areflexia?
Absence of reflex
What are central pattern generators? What do they do?
Constantly active neurons at the spinal cord. They produce basic motor patterns without voluntary action
What is the viscera?
The internal organs of the body
What is the role of the autonomic nervous system, in term of information?
Carries info to and from the viscera
What is the covering of a peripheral nerve? 4 layers
Each axon: schwann cell sheath, then endoneurium. Axons bungled together by perineurium = fascicles. Epineurium layer over fascicles
What does a peripheral nerve consist of?
A bundle of fascicles
Which senses are the ‘special senses’? What’s different about them
Smell, vision, hearing, taste
They have specialized receptors - little sensory organs
What is the most common receptor type? What information does it conduct?
Bare nerve ending. It processes tissue damage or stretch as pain
What are muscle spindles? (Label). What are muscle spindles made of?
Mechanoreceptors. Small sensory organs, with a sensory area at its equator and small intrafusal fibres at each pole
What are the three roles of muscle spindles?
Spasticity following injury to the nervous system, monitoring the muscle length, monitoring rate of change in muscle length
What is the role of alpha-motor neurons?
Innervate the extrafusal fibers of the skeletal muscles
What is the primary role of gamma-motor neurons? (2)
To regulate the length of spindle fibers and modulate the excitability of the annulospiral primary endings
How do gamma-motor neurons differ from alpha-motor neurons in terms of structure?
There are fewer and smaller axonal processes
What happens when the ventral nerve root receives information to contract?
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
What is the static role of the muscle spindle?
Modulate the length of a muscle
What is the dynamic role of the muscle spindle?
Modulate the rate of change in a muscle length
Why must gamma motor neurons reset?
So that the centre is constantly sensitive
Which tracks do gamma motor neurons receive input from?
The reticulospinal and vestibulospinal tracts
What occurs during a monosynaptic stretch reflex?
Impulses along the afferent fibers –> dorsal horn –> alpha motor neuron
What is reciprocal innervation?
When the contraction of one muscle is paired with the antagonist being relaxed
What is co-contraction? What is the result?
Simultaneous contraction fo opposing muscles due to abnormal reflex activity. Results in no movement of the body part
What is a motor unit?
A single alpha motor neuron and all the muscle fibres it innervates
What is the difference between a sign and a symptom?
A symptom is reported by the patient, whereas a sign can be observed and measured
What is neuropraxia? What is its outlook?
Light compression of the nerve - reversible
What is axonotmesis? How is it healed?
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
What is neurotmesis? What are its consequences?
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
How quickly does a severed axon grow back?
1 mm/day
What is the stapedius?
A small muscle that responds to loud sounds by contracting, to reduce the ossicle vibration
What nerve innervates the stapedius?
The facial nerve
What may cause innapropriate contraction of facial muscles in response to loud noises?
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
What are the four symptoms of lower motor neuron lesions?
Areflexia, rapid muscle atrophy, flaccid paralysis, and abscence of muscle tone
What are the two main causes for sensory neuron damage?
Damage to the disc protrusion at the root, or nutritional damage at the root
What are the causes of damage to alpha motor neurons?
Poliomyelitis, nutritional damage, and autoimmune disease
What is wallerian degeneration
Degeneration from the point of injury distally
What is the treatment for a severed sheath? Why?
Surgical repairment of the nerve, as the sheath must remain aligned
How does Polio affect the body?
It infects the alpha motor neuron cell body of the voluntary motor nerve (lower motor neuron)
What has occurred in Myasthenia Gravis?
Receptors on the postsynpatic membrane of the muscle are destroyed by the immune system, resulting in a limited number of receptors
What happens when there is damage to either the parasympathetic or sympathetic system?
Over-action of the unopposed function
Where is acetylcholine?
In parasympathetic nerve endings of neuromuscular junctions
Where is norepinephrine located?
In the sympathetic nerve endings
Where does dopamine go, and what transports it there?
Into the basal nuclei, via the substantia nigra cells
What disease is involved in irregular dopamine amounts?
Parkinson’s disease
Where is GABA?
Basal nuclei
What disease is associated with less GABA?
Huntington’s Chorea
What is the role of enkephalins and endorphins?
Pain modulation
What is the role of substance P?
Pain
