The Nervous System Flashcards
How many pairs of cranial nerves are there?
12
How can you divide the nervous system at the gross level?
Brain, spinal cord and nerves.
How many pairs of spinal nerves are there?
31
What are the two types of cell in the nervous system, and in what proportion are they present?
Neurons (10%)
Glia (90%)
What glia are present in the CNS, and what are their functions?
Oligodendrocytes - myelination of the axons
Astrocytes - physical support of neurons, phagocytosis, constitute blood brain barrier, assist in transfer of nutrients and waste products between neuron and blood stream, break down glucose to lactate for neuronal nourishment.
Microglia - inflammatory response, phagocytes.
Ependyma - ciliated cells lining ventricles and central canal of spinal cord, promote circulation of spinal cord.
What are the glia of the PNS, and what are their functions?
Schwann cells - myelination of axons.
Microglia - immunity and inflammation, phagocytosis.
Satellite cells - physical support of neurones.
What does the cell body contain?
Nucleus
Nissl substance - RER
Golgi
Some cell bodies have dendrites.
What is the diameter of a cell body?
4-120um diameter
What is a collection of cell bodies?
Grey matter
What is a collection of axons?
White matter
What is grey matter in the CNS?
Nerve nuclei
What is grey matter in the PNS?
Ganglia
What is the membrane surrounding the axon called?
Axonal membrane
Where are the nodes of ranvier found, and what is their function?
Between the Schwann cells wrapped around the axon.
Speeds up nerve impulse as it causes saltatory conduction of the impulse.
What is the end of the axon called?
Axonal terminal
What is the axonal membrane that is covered in a Schwann cell called?
Internodal membrane
What is the first part of the axon called?
Initial segment.
What is the axonal hillock?
Part of the cell body that connects to the axon.
How is the speed of nervous impulse related to the level of myelination?
Directly proportional - CV=6FD
How thick is the myelin in a thin axon?
0.5um
How thick is the myelin in a thick axon?
2.5um
How does a Schwann cell myelinate an axon?
Wraps around the axon roughly 100 times.
Which axons conduct faster when unmyelinated?
Those with a diameter less than 1um
Which axons conduct faster when myelinated?
Those with a diameter greater than 1um
How long is an average node of ranvier?
1um
How long is the stretch of axon myelinated by one Schwann cell?
100um
What can be used to stain myelin?
Sudan black.
What makes up white matter in the PNS?
Peripheral nerves
What appearance do nerves have, and why?
Shiny white appearance due to myelin sheath
What are the connective tissues in a nerve, and where are they found?
Endoneurium surrounds each axon.
Perineurium surrounds each fascicle
Epineurium surrounds the whole nerve, including fascicles and blood vessels.
How does a nerve react to its axon being severed?
The proximal segment seals to prevent leakage of the cell contents and forms a nerve stump.
The distal segment is cut off from the cell body, loses nutritional support and dies, undergoes wallerian degeneration.
Chromatolysis occurs - cell body puffs up with increased content, and nucleus is displaced.
How is the autonomic nervous system divided?
Parasympathetic nervous system - rest and digest
Sympathetic - fight or flight
What marks the boundary between CNS and PNS?
Pia mater
How are the neurones arranged in the autonomic nervous system?
Pre-ganglionic neurone and post ganglionic neurone connected in series.
What neurotransmitters are involved in the ANS?
Acetylcholine and noradrenaline.
Describe the structure of the parasympathetic arm of the ANS:
Longer pre-ganglionic neurone, shorter post-ganglionic neurone.
Both neurones are myelinated.
What neurotransmitter is used in the ganglion in the parasympathetic arm of the ANS?
What receptors are present?
Acetylcholine
Nicotinic
Describe the structure of the sympathetic arm of the ANS:
Shorter pre-ganglionic neurone, longer post-ganglionic neurone.
Pre-ganglionic is myelinated. Post-ganglionic membrane is unmyelinated.
What neurotransmitter is used in the ganglion in the sympathetic arm of the ANS?
What receptors are present?
Acetylcholine
Nicotinic
What neurotransmitter is used at the neuro-effector junction in the parasympathetic nervous system? What receptors are present?
Acetylcholine
Muscarinic
What neurotransmitter is used at the neuro-effector junction in the sympathetic nervous system? What receptors are present?
Noradrenaline
Adrenoreceptors - alpha and beta
Except for perspiration and ejaculation.
What physiological responses does activity of the sympathetic nervous system create?
Increase in heart rate Increase in blood pressure Diversion of blood to muscles and heart Expenditure of energy Reduced blood flow to GI tract and skin
Which segments of the spinal cord does the sympathetic nervous system have cell bodies in?
All the thoracic segments (T1-T12)
The first two lumbar segments (L1 & L2)
Where can the lateral horn be observed?
T1-L2
What is the paravertebral chain?
Chain of ganglionic neurones running from the base of the skill to the sacrum, bilaterally and parallel to the spine.
What are the three possible modes of termination of a sympathetic nerve?
Does not synapse in paravertebral chain (splanchnic nerve)
Synapses at the same level as its origin
Synapse at a different level to its origin.
What are the classes of adrenoreceptors?
Alpha receptors, which exhibit alpha 1 or alpha 2 behaviour
Beta receptors which can exhibit beta 1 or beta 2 behaviour
Where are the cell bodies in the autonomic nervous system?
Presynaptic cell body in the central nervous system.
Postsynaptic cell body in the peripheral nervous system.
What are the effects of the parasympathetic nervous system?
Lowers heart rate and blood pressure.
Promotes bodily functions such as passing urine.
Promotes sleep
Promotes digestion
Which nerves are involved in the parasympathetic nervous system?
Cranial nerves (oculomotor (3) facial (7) glossopharangeal (9) vagus (10)) Sacral spinal cord levels S2-S4
