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1 Cranial Nerves, source:

2 Nervous System Overview
BIOL241 - Lecture 12a

3 Topics Divisions of the NS: CNS and PNS Structure and types of neurons
Synapses Structure and function of glia in the CNS and PNS

4 The Nervous System Includes all neural tissue in the body

5 General Overview

6 Neural Tissue Contains 2 kinds of cells: neurons:
cells that send and receive signals neuroglia (glial cells): cells that support and protect neurons

7 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

8 Anatomical Divisions of the Nervous System
Central nervous system (CNS) Peripheral nervous system (PNS)

9 Nervous System CNS PNS Somatic NS Autonomic NS Sympathetic

10 The Central Nervous System (CNS)
Consists of the spinal cord and brain Contain neural tissue, connective tissues, and blood vessels INTERCONNECTEDNESS

11 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”)

12 The Peripheral Nervous System (PNS)
Includes all neural tissue outside the CNS (nerves that control muscles and glands)

13 Functions of the PNS Deliver sensory information to the CNS
Carry motor commands to peripheral tissues and systems

14 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

15 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

16 PNS divisions Somatic nervous system (SNS)
Autonomic nervous system (ANS) More “layers”

17 The Somatic Nervous System (SNS)
Controls skeletal muscle contractions: voluntary muscle contractions involuntary muscle contractions (reflexes)

18 The Autonomic Nervous System (ANS)
Controls subconscious actions: contractions of smooth muscle and cardiac muscle glandular secretions

19 Divisions of the ANS Sympathetic division: Parasympathetic division:
has a stimulating effect Parasympathetic division: has a relaxing effect

20 Nervous System CNS PNS Somatic NS Autonomic NS Sympathetic

21 Neurons The basic functional units of the nervous system

22 The Structure of Neurons
Figure 12–1

23 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

24 Dendrites Highly branched Dendritic spines: many fine processes
receive information from other neurons 80–90% of neuron surface area

25 The Axon Are long Carries electrical signal (action potential) to target Axon structure is critical to function

26 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)

27 Movie Neurophysiology: Neuron Structure

28 The Synapse Figure 12–2

29 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

30 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

31 Soma What does soma mean?

32 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

33 Unipolar Neurons Have very long axons Dendrites fused to axon
Cell body to 1 side Figure 12–3 (3 of 4)

34 Multipolar Neurons Often have long axons Multiple dendrites, 1 axon
Figure 12–3 (4 of 4)

35 3 Functional Classifications of Neurons
Sensory neurons: afferent neurons of PNS Motor neurons: efferent neurons of PNS Interneurons: association neurons

36 Sensory (Afferent) Neurons
Monitor internal environment (visceral sensory neurons) Monitor effects of external environment (somatic sensory neurons)

37 Motor (Efferent) Neurons
Signals from CNS motor neurons to visceral effectors pass synapses at autonomic ganglia dividing axons into: preganglionic fibers postganglionic fibers

38 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

39 Neuroglia are supporting cells

40 Neuroglia Half the volume of the nervous system
Many types of neuroglia in CNS and PNS

41 Volume What is volume?

42 Neuroglia of the Central Nervous System
Figure 12–4

43 4 Types of Neuroglia in the CNS
Ependymal cells Astrocytes Microglia Oligodendrocytes

44 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

45 Blood-Brain Barrier What is this?

46 2. Astrocytes Maintain blood–brain barrier (isolates CNS)
Create 3-dimensional framework for CNS Repair damaged neural tissue Guide neuron development Control interstitial environment

47 3. Microglia Migrate through neural tissue
Clean up cellular debris, waste products, and pathogens Not of neural origin; related to macrophages (like osteoclasts)

48 4. Oligodendrocytes Processes contact other neuron cell bodies
Wrap around axons to form myelin sheaths

49 Myelination Increases speed of action potentials
Myelin insulates myelinated axons Makes nerves appear white

50 Nodes and Internodes Internodes: Nodes: myelinated segments of axon
also called nodes of Ranvier gaps between internodes where axons may branch

51 White Matter and Gray Matter
regions of CNS with many myelinated nerves Gray matter: unmyelinated areas of CNS

52 2 Neuroglia of the Peripheral Nervous System
Satellite cells (amphicytes) Schwann cells (neurilemmacytes)

53 1. Satellite Cells Surround ganglia Regulate environment around neuron

54 Ganglia vs Nuclei Masses of neuron cell bodies
Called ganglia in the PNS and are surrounded by satellite cells Called nuclei in the CNS

55 1. Schwann Cells Form myelin sheath around peripheral axons (nerves)
1 Schwann cell sheaths 1 segment of axon: many Schwann cells sheath entire axon

56 Schwann Cells Figure 12–5a

57 Schwann Cells Figure 12–5b

58 “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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