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anatomy of neurons
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section 1, chapter 10
Nervous System IBasic Structure and Function
ivyanatomy.com
The nervous system is divided into 2 subdivisions
The Central Nervous System (CNS) consists of the brain and spinal cord.
The Peripheral Nervous System (PNS)• Consists of 12 pairs of cranial
nerves and 31 pairs of spinal nerves
• Nerves may be motor (efferent), sensory (afferent), or both (mixed)
Divisions of the PNS
The Somatic Nervous System is under voluntary control
Somatic motor controls skeletal muscles
Somatic sensory relays info regarding touch, pressure, and pain to the brain
The Autonomic Nervous System is under involuntary control
autonomic motor controls smooth muscles, cardiac muscles, and glands
autonomic sensory relays visceral info regarding pH, blood gasses, etc. to the brain
Figure 10.2. (a) overview of nervous system. CNS is grey, PNS is yellow. (b) CNS receives sensory input from PNS, and sends motor output to PNS. Somatic division of PNS is under voluntary control, while the autonomic division is under involuntary control.
The Autonomic Nervous System (ANS) is further divided into two branches.
The Sympathetic branch • prepares the body to respond to a stressful situation.• “Fight or Flight” Response
The Parasympathetic branch • Maintains normal body activities at rest• “Resting and Digesting”
Cells of the Nervous SystemNeurons• Integrate, regulate, and coordinate body functions
• Functions• Receive information - sensory • Conduct impulses - motor• Connect neurons - integrative
Neuroglia (glia = “glue”)• Neuroglia provide neurons with
nutritional, structural, and functional support
Neurons
Neurons vary in shape and size
3 Components of a neuron1. Dendrites receive impulse
2. Call body (soma)
3. Axon – transmits the impulse away from the cell body
Dendrites conduct information to the soma.
A cell may have a few dendrites, many dendrites, or no dendrites.
Dendritic Spines are additional contact points on some dendrites that increase the number of synapses possible by a neuron
Cell Body – SomaContains organelles such as the nucleus Mitochondria, Golgi Apparatus, etc.
The rough ER is often called chromatophilic substance (Nissl Bodies)
Dendrites
Axon
Axon Hillock is a specialized part of the soma that connects to the axon.
The axon hillock is often called the Trigger Zone because action potentials begin here.
Each neuron has only 1 axon, but it may divide into several branches, called collaterals
The end of the axon is called the axon terminal and it enlarges into a synaptic knob (bouton)
Microtubules called neurofibrils support long axons and aid in axonal transport (transport of biochemicals between the soma and the axon terminal)
Axon
Schwann Cells form the myelin sheath in the PNS. They wrap around the axons in a jelly-roll fashion to form a thick layer of fatty insulation.
The cytoplasm and the nucleus are pushed to the outermost layer, forming the neurolemma
Schwann cells are separated by gaps, called Nodes of Ranvier.
Myelination of axons occurs differently in the PNS than in the CNS.
Myelination of Axons
The myelin sheath is a thick fatty coating of insulation surrounding the axon that greatly enhances the speed of impulses.
Myelination of axons in the PNS.
Schwann cells still surround the axons of unmyelinated neurons, but they do not form the myelin sheath.
Unmyelinated axons with a Schwann cell.
A myelinated axon with a Schwann Cell.
Myelination of Axons in CNS
end of section 1, chapter 10
Within the CNS the myelin sheath is formed by Oligodendrocytes.
1 Oligodendrocyte may form the myelin sheath of several axons.
A mass of myelinated axons in the CNS forms the white matter.
A mass of cell bodies (which are unmyelinated) along with unmyelinated axons form the gray matter.
Gray and White Matter
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