L9 Introduction to the Nervous System Flashcards
What does the brain weigh?
1.5kg
How many neurons does the brain contain?
Approximately 1 billion
How metabolically active is the brain?
Highly metabolically active
- 15% of body’s total blood supply
- 20% of body’s total oxygen supply
Describe the structure of a typical CNS neuron.
- Soma (cell body) containing a nucleus
- Dendrites (branched neuronal processes)
- May have basal and apical dendritic trees
- One axon
- Terminal branching axons with axon terminals
- Synaptic bouton in close contact with post-synaptic dendrite
- Syanptic cleft between bouton and dendrite
What are the 2 categories of synapses?
- Chemical
- Electrical
Describe a chemical synapse.
- Bouton containing synaptic vesicles
- Vesicles contain neurotransmitters which diffues across synaptic cleft and bind to receptors on post-synaptic dendritic membrane
What is the difference between excitatory and inhibitory neurotransmitters?
Excitatory: cause depolarisation of the post synaptic neuron, increasing likelihood of AP firing from post synaptic neuron e.g. acetylcholine and glutamate
Inhibitory: cause hyperpolarisation of the postsynaptic neuron, making it less likely that an AP will be fired from the post synaptic neuron e.g. GABA and glycine
What is grey matter?
- Found closer to the borders of the brain
- Grey matter = nuclei
- Nuclei = a cluster of neuron cell bodies and their dendrites
What is white matter?
- Found closer to the inside of the brain
- White matter = bundles of myelinated axons that form fibre tracts connecting nuclei
Where are grey and white matter found in the spinal cord?
- Gray matter in inner butterfly shaped region (divided into dorsal horn, intermediate zone and ventral horn)
- White matter surrounds grey matter (is the axons of the neurons in the grey matter)
What are the 3 neuron types?
- Motor
- Sensory
- Interneuron
Describe motor neurons.
- Cell body in ventral horn of grey matter
- Single basal axon which passes through ventral root
- Ventral root coalesces with dorsal root to give rise to segmenral spinal nerve
Describe sensory neurons.
- Cell body in the dorsal root ganlgion
- 1 axon projects into segmental spinal nerve makes synaptic connection with target tissue (e.g. skin)
- 1 axon projects centrally into dorsal horn of grey matter where it synapses with motor or interneuron
Describe interneurons.
- Connects neurons
- Relays info between sensory and motor neurons
- Axons project into white matter to make connections with neurons in higher regions of the brain
What are the 2 types of interneuron?
- Local circuit interneurons: short axons which remain in the nucleus and connect with nearby neurons
- Projection interneurons: send their axons along fibre tracts to other nuclei (can be over a metre long)
What is the other major cell type in the nervous system?
Glial cells
What are the 3 types of glial cells?
- Oligodendrocytes
- Astrocytes
- Microglia
Describe oligodendrocytes.
- Myelinating cells
- Form the myelin sheath
- Project processes that wrap around the axon
In the peripheral NS, the equivalent cell type is a Schwann cell.
Describe astrocytes
Large star shaped cells with many processes and roles:
- Regulate extracellular ion concentrations around neurons (essential to maintaining resting potential)
- Processes wrap around synapses to regulate neurotransmitter reuptake and degradation
- Structural support
- Regulate integrity of blood-brain barrier
- Neurotrophic support/nutritive role
Describe microglia.
- Small glial cells
- “Immune system of the brain”, equivalent role in the brain as leukocytes in the periphery
- Release inflammatory cytokines to attack disease organisms and phagocytose damaged cells
- Inappropriately activated microglia play a role in pathological pain and contribute to the onset of some neurogenerative diseases e.g. Alzheimer’s
What are the 2 main neuron types of the peripheral nervous system?
- Peripheral sensory neurons
- Autonomic neurons: neurons of the sympathetic, parasympathetic and enteric nervous systems
Describe the anatomy of the peripheral nervous system.
- 30 segmental spinal nerves which project from either side of the spinal cord
- C1-C8 = cervical nerves
- T1-T12 = thoracic nerves
- L1-L5 = lumbar nerves
- S1-S5 = sacral nerves
How are the segmental spinal nerves formed?
By the coalescence of the ventral and dorsal roots.
What are dermatomes?
The areas of skin suplied by the dorsal root ganlgion neuron associated with each segmental spinal nerve (sensory innervation).
Do not have sharp boundaries.
