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The Nervous System
Divisions of the Nervous SystemCentral Nervous System [CNS] = Spinal Cord
Brain
Peripheral Nervous System [PNS]= Spinal Nerves [31 pair]
Autonomic Nervous System [ANS]
Sympathetic Division
Parasympathetic Division
Cranial Nerves [12 pair]
Cells of the Nervous System
• Neurons are the functional cell of the system
• Have 3 basic parts to them
Body [soma]
Axon
Dendrites
• Neuroglial [glial] are the supporting cells of the system. They are smaller and more plentiful than neurons. In some areas, there are 10x more neuroglial cells than neurons.
Neuroglial CellsCNS astrocyte oligodendrocyte microglial ependymal
PNS satellite Schwann Myelin Sheath –
fatty covering of axons
80:20Phospholipid
: protein
astrocyte
microglial
oligodendrocyte
Nerve Conduction
• Action Potential – generated by change in membrane’s permeability which causes an exchange of ions – caused by impulse
Resting state of cell – polarized
receiving stimulus – depolarized
returning to resting state - repolarized
At rest, inner environment has a higher concentration of K, the outer environment has a high Na concentration. The neuron’s cell membrane has active Na/K gates. When an impulse comes in contact with the membrane, it turns off the gate.[polarized]
Na rushes in, K leaves and the electrical impulse passes through the cell body. [wave of depolarization]
After the electrical impulse leaves, the gates are turned back on, and Na is pumped out - K reenters the cell
3 Na pumped out for every 2 K pumped in [repolarization]
The Synapse
Gap between two cells
Information can ‘jump’ gap via a chemical [neurotransmitter] or electrical signal.
Electrical synapses cross gap junctions, such as in cardiac and smooth muscle.
Neurotransmitters are used in nervous system synapses. They are released from the axon. Bouton / knobs / presynaptic terminal
Neuromodulators – can influence an action potential
Meninges
• The CNS is covered in a protective membrane
• Dura mater
• Arachnoid mater– Subarachnoid space – Cerebral
Spinal Fluid
• Pia mater
The pia is on the surface of the CNS and forms the filum terminalefilum terminale which anchors the spinal cord onto the sacrum/coccyx
The Spinal Cord
Extends from foramen magnum to the 2nd or 3rd lumbar vertebrae
The uppermost portion is called the medulla oblongatamedulla oblongata
The lowermost portion is called the conus medullarisconus medullaris and gives rise to the cauda equinacauda equina
Spinal Cord Anatomy
• White matter – myelinated axons
• Gray matter – cell bodies
• Anterior – median fissure
• Posterior – median sulcus
• Central canal
• Commissure = connecting nerve fibers from one side to other
• Posterior horn- receives sensory / afferent input
• Anterior horn – transmits motor/efferent response
• Columns – pathways / nerve tracts
Cross Section of Spinal Cord
DermatomesEach spinal nerve, except C1, has a specific cutaneous sensory distribution
Letters and numbers indicate the spinal nerves that innervate a given region
Reflexes
• Protective mechanism• Automatic response to
a stimulus that occurs without conscious input
• Reflex vs reaction
The Brain
The brain can be divided into 4 regions
• Brain Stem– medulla oblongata
– pons
– midbrain
• Cerebellum• Diencephalon
- thalamus
- hypothalamus
- pituitary/pineal glands
•Cerebrum
-lobes -> frontal, occipital, temporal, parietal, prefrontal
-corpus callosum -> main commissure
-ventricles - spaces where CSF is produced/flows
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