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Cranial Nerves, source: training.seer.cancer.gov
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Nervous System Overview
BIOL241 - Lecture 12a
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Topics Divisions of the NS: CNS and PNS Structure and types of neurons
Synapses Structure and function of glia in the CNS and PNS
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The Nervous System Includes all neural tissue in the body
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General Overview
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Neural Tissue Contains 2 kinds of cells: neurons:
cells that send and receive signals neuroglia (glial cells): cells that support and protect neurons
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Organs of the Nervous System
Brain and spinal cord Sensory receptors of sense organs (eyes, ears, etc.) Nerves connect nervous system with other systems INTERCONNECTEDNESS
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Anatomical Divisions of the Nervous System
Central nervous system (CNS) Peripheral nervous system (PNS)
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Nervous System CNS PNS Somatic NS Autonomic NS Sympathetic
Parasympathetic
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The Central Nervous System (CNS)
Consists of the spinal cord and brain Contain neural tissue, connective tissues, and blood vessels INTERCONNECTEDNESS
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Functions of the CNS Are to process and coordinate: sensory data:
from inside and outside body (“inputs”) motor commands: control activities of peripheral organs (e.g., skeletal muscles) [“controls’] higher functions of brain: intelligence, memory, learning, emotion (“outputs”)
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The Peripheral Nervous System (PNS)
Includes all neural tissue outside the CNS (nerves that control muscles and glands)
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Functions of the PNS Deliver sensory information to the CNS
Carry motor commands to peripheral tissues and systems
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Nerves Also called peripheral nerves:
bundles of axons with connective tissues and blood vessels carry sensory information and motor commands in PNS: cranial nerves—connect to brain spinal nerves—attach to spinal cord
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Functional Divisions of the PNS
Afferent division: carries sensory information from PNS sensory receptors to CNS Efferent division: carries motor commands from CNS to PNS muscles and glands SAME: Sensory is Afferent, Motor is Efferent
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PNS divisions Somatic nervous system (SNS)
Autonomic nervous system (ANS) More “layers”
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The Somatic Nervous System (SNS)
Controls skeletal muscle contractions: voluntary muscle contractions involuntary muscle contractions (reflexes)
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The Autonomic Nervous System (ANS)
Controls subconscious actions: contractions of smooth muscle and cardiac muscle glandular secretions
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Divisions of the ANS Sympathetic division: Parasympathetic division:
has a stimulating effect Parasympathetic division: has a relaxing effect
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Nervous System CNS PNS Somatic NS Autonomic NS Sympathetic
Parasympathetic
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Neurons The basic functional units of the nervous system
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The Structure of Neurons
Figure 12–1
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Major Organelles of the Cell Body
Large nucleus and nucleolus Cytoplasm (perikaryon) Mitochondria (produce energy) RER and ribosomes (produce neurotransmitters) Cytoskeleton Nissl Bodies: RER and ribosomes
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Dendrites Highly branched Dendritic spines: many fine processes
receive information from other neurons 80–90% of neuron surface area
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The Axon Are long Carries electrical signal (action potential) to target Axon structure is critical to function
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Structures of the Axon Axon hillock: Initial segment: Collaterals:
thick section of cell body attaches to initial segment Initial segment: attaches to axon hillock Collaterals: branches of a single axon Synaptic terminals with knobs: tips of axon (knobs at ends)
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Movie Neurophysiology: Neuron Structure
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The Synapse Figure 12–2
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Synapse Synapse: Area where a neuron communicates with another cell
Presynaptic cell: neuron that sends message Postsynaptic cell: cell that receives message Synaptic cleft The small gap that separates the presynaptic membrane and the postsynaptic membrane Area of terminal containing synaptic vesicles filled with neurotransmitters
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Neurotransmitters Chemical messengers (like ACh)
Released at presynaptic membrane Affect receptors of postsynaptic membrane Broken down by enzymes and, or, taken up into presynaptic cell Are reassembled at synaptic knob
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Soma What does soma mean?
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Major Structural Classifications of Neurons
Unipolar neurons: found in sensory neurons of PNS Multipolar neurons: common in the CNS include all skeletal muscle motor neurons cell body (soma) short, branched dendrites long, single axon
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Unipolar Neurons Have very long axons Dendrites fused to axon
Cell body to 1 side Figure 12–3 (3 of 4)
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Multipolar Neurons Often have long axons Multiple dendrites, 1 axon
Figure 12–3 (4 of 4)
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3 Functional Classifications of Neurons
Sensory neurons: afferent neurons of PNS Motor neurons: efferent neurons of PNS Interneurons: association neurons
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Sensory (Afferent) Neurons
Monitor internal environment (visceral sensory neurons) Monitor effects of external environment (somatic sensory neurons)
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Motor (Efferent) Neurons
Signals from CNS motor neurons to visceral effectors pass synapses at autonomic ganglia dividing axons into: preganglionic fibers postganglionic fibers
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Interneurons Most are located in brain, spinal cord, and autonomic ganglia: between sensory and motor neurons Are responsible for: distribution of sensory information coordination of motor activity Are involved in higher functions: memory, planning, learning
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Neuroglia are supporting cells
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Neuroglia Half the volume of the nervous system
Many types of neuroglia in CNS and PNS
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Volume What is volume?
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Neuroglia of the Central Nervous System
Figure 12–4
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4 Types of Neuroglia in the CNS
Ependymal cells Astrocytes Microglia Oligodendrocytes
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1. Ependymal Cells Form epithelium called ependyma
Line central canal of spinal cord and ventricles of brain: secrete cerebrospinal fluid (CSF) have cilia or microvilli that circulate CSF monitor CSF contain stem cells for repair
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Blood-Brain Barrier What is this?
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2. Astrocytes Maintain blood–brain barrier (isolates CNS)
Create 3-dimensional framework for CNS Repair damaged neural tissue Guide neuron development Control interstitial environment
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3. Microglia Migrate through neural tissue
Clean up cellular debris, waste products, and pathogens Not of neural origin; related to macrophages (like osteoclasts)
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4. Oligodendrocytes Processes contact other neuron cell bodies
Wrap around axons to form myelin sheaths
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Myelination Increases speed of action potentials
Myelin insulates myelinated axons Makes nerves appear white
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Nodes and Internodes Internodes: Nodes: myelinated segments of axon
also called nodes of Ranvier gaps between internodes where axons may branch
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White Matter and Gray Matter
regions of CNS with many myelinated nerves Gray matter: unmyelinated areas of CNS
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2 Neuroglia of the Peripheral Nervous System
Satellite cells (amphicytes) Schwann cells (neurilemmacytes)
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1. Satellite Cells Surround ganglia Regulate environment around neuron
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Ganglia vs Nuclei Masses of neuron cell bodies
Called ganglia in the PNS and are surrounded by satellite cells Called nuclei in the CNS
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1. Schwann Cells Form myelin sheath around peripheral axons (nerves)
1 Schwann cell sheaths 1 segment of axon: many Schwann cells sheath entire axon
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Schwann Cells Figure 12–5a
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Schwann Cells Figure 12–5b
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“Summary” Divisions of the NS: CNS and PNS
Structure and types of neurons Synapses Structure and function of glia in the CNS and PNS
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