Chapter 10, Section 1
Nervous System I Basic Structure and Function
Organization of Nervous System Central Nervous System (CNS)
Peripheral Nervous System (PNS)
• Brain & Spinal Cord
• 12 Pairs of Cranial Nerves • 31 Pairs of spinal nerves
Divisions of Peripheral Nervous System Sensory Division = afferent • Delivers information from periphery to CNS
Motor Division = efferent • Carries impulses to muscles or glands (effectors)
Subdivisions of the Motor Division Somatic Nervous System
Autonomic nervous System
• carries information to skeletal muscle • Voluntary Control
• carries information to smooth muscle, cardiac muscle, and glands • Involuntary Control
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.
Subdivision of autonomic nervous system Sympathetic Division • Increases response to a stressful situation • “Fight or Flight”
Parasympathetic Division • Maintains normal body functions at rest
Components of Nervous System Neurons • Integrate, regulate, and coordinate body functions • Functions • Receive information - sensory • Conduct impulses - motor • Connect neurons - integrative
Neuroglia (neuro “glue”)
• Provide neurons with nutritional, structural, and functional support
Neurons
Neurons vary in shape and size 3 Components of a neuron 1. Dendrites receive impulse 2. Call body (soma) 3. Axon – transmits impulse away from the cell body
Components of a neuron Dendrites – a cell may have one or many • Conducts information to cell body • Dendritic Spines •Additional contact points on some dendrites for other neurons • Increase the number of synapses possible by a neuron
Cell Body – Soma • Cytoplasm, Mitochondria, Golgi Apparatus • Nissl Bodies (rough ER) • Nucleus with nucleolus
Components of a neuron Axon – each neuron has only 1 axon • Axon Hillock • Extension of soma into axon • Trigger Zone – initiates nerve impulse (Action Potential) • Collaterals – Branches of an axon • Axon terminal + Synaptic Knob – Specialized ending of axon • Synaptic Cleft - gap at synapse •Neurofibrils • Microtubules that support long axons • Aid in axonal transport (transport of biochemicals from soma to axon terminal)
Myelination of Axons in PNS Myelin Sheaths greatly enhance the speed of impulses • Schwann Cells wrap around the axons in a jelly-roll fashion to form myelin • Myelin Sheath • thick fatty coating of insulation, • formed from layers of Schwann cell’s membrane • Myelination greatly increases the speed of a nerve impulse • Neurolemma • outermost layer of Schwann cell that contains the nucleus and cytoplasm. • Nodes of Ranvier • Gaps between Schwann Cells - Site of impulse conduction
Myelination of Axons in PNS
Figure 5. TEM micrograph of a myelinated and unmyelinated axon.
Figure 10.4 a myelinated axon.
Myelination of Axons in CNS • Oligodendrocyts • Myelinate neurons in Central Nervous System • 1 Oligodendrocyte may myelinate several axons • White Matter • Myelinated axons in the CNS • Grey Matter • Unmyelinated tissue in the CNS • Includes dendrites, somas, and unmyelinated axons
End of Chapter 10, Section 1