Describe the structure of peripheral nerves
- bundle of nerve fibres
- entire nerve ensheathed by the epineurium
- nerve fascicle (smaller bundle of nerve fibres within whole nerve) ensheathed by perineurium
- single cell axon ensheathed by endoneurium
How is an action potential generated?
- Action potentials are formed when a stimulus causes the cell membrane to depolarize past the threshold of excitation, causing all sodium ion channels to open.
- When the potassium ion channels are opened and sodium ion channels are closed, the cell membrane becomes hyperpolarized as potassium ions leave the cell; the cell cannot fire during this refractory period.
- The action potential travels down the axon as the membrane of the axon depolarizes and repolarizes.
- Potassium channels close.
How is resting potential maintained?
Sodium/Potassium transporter proteins restore resting potential (3 sodium out/2 potassium in)
What is the consequence of demyelination?
- further travelling distance, no nodes of ranvier so no saltatory conduction,
- Multiple sclerosis- destruction of myelin sheath and replacement with scar tissue
What are nodes of ranvier and what is their function?
Schwann cells don’t conduct electricity due to high lipid content. Nodes of ranvier are gaps in myelin sheath that allow for saltatory conduction. Peripheral nerve cells are surrounded by schwann cells (neurolemma)
What is the term for several layers of schwann cells wrapped around an axon
Plasmolemma
Why is a special fixative required to see schwann cells?
High lipid content. Fixative could be osium tetroxide
How is the myelin sheath maintained in the CNS?
Oligodendrocytes produce and maintain the sheath
What is the distribution of myelinated and unmyelinated axons, with regards to the ANS and somatic nervous system?
ANS- myelinated in CNS and unmyelinated in PNS
Somatic- Myelinated
What is a ganglion?
Collection of cell bodies in the PNS. 1 cell has its cell body in the CNS, one has its cell body in the PNS.
How do neurones exert action?
- via smooth muscle
- viscera
- secretory glands
What is the function of glial cells and what are the 5 kinds?
Glial cells support neurones, help maintain homeostasis and form myelin/insulate neurones
- astrocytes
- oligodendrocytes
- microglia
- schwann cells
- satellite cells
What is the function of astrocytes?
- Found in CNS
- blood/brain barrier
- assist in transfer of nutrients and waste
What is the function of oligodendrocytes?
- Found in CNS
- myelination (up to 250 axons/cell)
What is the function of microglia?
-Found in CNS and PNS
immune and inflammatory functions
What is the function of schwann cells?
- Found in PNS
- myelination (1 axon/cell)
What is the function of satellite cells?
-Physical support of peripheral neurones
Describe the synapses in the sympathetic nervous system
- Pre-ganglionic neurones are cholinergenic
- Post-ganglionic neurones express nicotinic receptors
- Post-ganglionic neurones are noradregenic with the exception of some perspiration and ejaculation pathways which are cholinergenic
Describe the synapses in the parasympathetic nervous system
- Pre-ganglionic neurones are cholinergic
- Post-ganglionic neurones express nicotinic receptors
- Post-ganglionic neurones are cholinergic
What is the difference between the afferent and efferent pathways?
Afferent-leads towards the CNS
Efferent-away from the CNS
Describe the sympathetic nervous system
- Fight/Flight/Fright response
- Diversion of blood to muscles (vasodilation) and heart
- Increase in heart rate
- Increase in blood pressure
- Reduced blood flow to GIT and skin
- Hyperventilation
- Skin blood vessels- vasoconstriction
Describe the parasympathetic nervous system
- Relaxation
- Reduced heart rate and force of contraction
- Promotes digestion
- Promotes bodily functions such as bladder emptying
- Promotes sleep
Outline the difference in excitatory and inhibitory synaptic neurotransmitters
- Excitatory neurones release glutamate/aspartate neurotransmitter
- Inhibitory neurones release glycine/GABA[-amino butyric acid] neurotransmitter
What are the three layers of the meninges and what is their function?
from outermost to innermost, three layers of protective tissue:
- dura mater
- arachnoid mater
- pia mater that surround the neuraxis.
The meninges of the brain and spinal cord are continuous, being linked through the magnum foramen.
