The Nervous System (rest look at Callum ESA 1) Flashcards
What are the function of astrocytes?
- Part of the blood brain barrier
- Found in the CNS
- Assist in transfer of nutrients and waste between the neurone and blood
- Phagocytic functions
- Physical support for neurones
What is the function of the CNS neuroglial cell, Epndyma?
Line ventricles and central canal of spinal cord for circulation of CSF
What are the only cells in the CNS which fullfill an immune function if the blood-brain barrier is overcome?
Microglia
Where is the cell nucleus of neurones found?
Centrally. Displaced nuclei to periphery of cell body can be due to injury
What makes up the grey matter of the nervous system?
Collections of cell bodies
What are collections of cell bodies in the peritheral nervous system called?
ganglia
Where is the internodal membrane found?
Between nodes of Ranvier under the myelin sheath
What is the difference between thin and thick myelinated axons?
Their degree of myelination
Which myelinated axons are affected in MS?
CNS - brain and spinal chord
Under what diameter, do axons conduct faster unmyelinated?
Under 1um
A node of ranvier is a gap between which two cells?
Two Schwann cells
What is a nerve fascicle?
A collection of axons of neurones with a common origin and destination
What is the neurolemma?
The outermost nucleated cytoplasmic layer of Schwann cells that surrounds the axon of the neuron. It forms the outermost layer of the nerve fiber in the peripheral nervous system.
What make up the white matter of the nervous system?
Collections of axons
What is the role of interfasicular epineurium?
Connective tissue which attaches adjacent nerve fascicles
What is the name of membranous envelopes of fibre tracts in the CNS?
Meninges, which are continuous with the coverings of the brain and spinal cord
Name the three membranes that make up the meninges from deep to superficial
Pia mater
Arachnoid mater
Dura mater
How does a neurone react to it axon being severed?
- Proximal segment seal up -> nerve stump
2. Distal segment cut off from nutritional support->dies (Wallerian degeneration)
What happens to the proximal segment when an axon is severed?
- Proximal segment seals up the damage to prevent leakage of cell contents
- Its cell body puffs up with increased contents
- Nucleus is displaced from central to peritheral postion (chromatolysis)
- Axon usually regrows but doesn’t necessarily reinnervate the same target (Wallerian regeneration)
What is the name of the structure that carries impulses away from the neurone cell body?
Axon
What is the name of the structure that carries impulses towards the neurone cell body?
Dendrite
Define an afferent neurone
Neurone that carries signals from periphery to the CNS (sensory neurone)
Define an efferent neurone
Neurone that carries signals from the brain or spinal chord to the periphery (motor neurone) or autonomic neurone
Define a pre-ganglionic neurone
Neurone immediately proximal to the ganglion
Define a post-ganglionic neurone
Neurone immediately distal to the ganglion
Define effector
Target organ through which the nervous system exerts its actions
What relation does the CNS and PNS have to each other?
They are a continuation of the same cell and therefore are dependent on each other.
Locked-in syndrom occurs when the CNS is functional but the PNS is not
What are some characteristics of the CNS?
Encasement by cranium and vertebral column
Suspended in cerebrospinal fluid and mening
Responsible for the sophisticated functions of the nervous system
How many pairs of cranial nerves are there?
12 pairs
How many pairs of spinal nerve axons are there?
31 pairs
How many pairs of autonomic ganglia are there?
25 pairs
How many pairs of sensory ganglia are there?
31 pairs
What is the PNS?
The nervous system outside the central nervous system which connects it to its target organs or sensory organs. It relies on the integrity of the central nervous system
Describe two anatomical categories of the CNS
CNS and PNS
Describe two categories of the NS based on signal direction
afferent and efferent
Describe two functional categories of the NS
autonomic and somatic
How many neurones carry the output in the somatic NS?
1 neurone from brain/spine -> effector organ
What are the two opposing systems in the ANS which maintain a constant internal environment by a changing continuous output?
Parasympathetic and sympathetic NS
In the ANS there is always two neurones in a series. Where are the cell bodies of each neurone located?
Preganglion neurone - CNS cell body
Postganglion neurone - PNS (in ganglion)
Predominant ANS tone is determined by what?
The balance of SNS and PNS outputs
Give an example of an effector which receives only sympathetic innervation from the ANS?
Sweat glands
If the ANS tone is imbalanced to the bladder what can happen?
Retention - if sympathetic output predominant
Constant trickling - if parasympathetic output predominant
What is a clinical implication of overactivity of the PNS e.g. by infection?
Over-activity -> dilated blood vessels over time which can lead to shortage of substrate to the brain -> faint/collapse
What can be the clinical consequences of overactivity of the SNS?
Over-activity -> constriction of blood vessels -> shortage of substrates to tissues of the body -> frostbite etc…
Which sympathetic nerves do not synapse in the paravertebral chain?
Splanchnic nerves that supply the gut
Where are parasympathetic post-ganglionic neurones located?
In the walls of the effector organs (long preganglion neurones and short post-ganglionic ones)
Why do spinal patients end up with autonomic dysfunction?
Damage to the thoraco-lumbar outflow or cranio-sacral outflow disrupts sympathetic or parasympathetic function, disturbing the balance between these two opposing systems and causing autonomic dysfunction
