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The

The nervous system is responsible for all of our behaviors, memories, & movements The Nervous System The nervous system… • Cooperates with endocrine system • Senses environment Chapter 11 • Responds to changes in environment • Maintains homeostasis

Functions of the Nervous System Sensory input 1. Sensory input – Information gathered by sensory receptors about internal and external changes 2. Integration – Interpretation of sensory input 3. Motor output – Activation of effector organs (muscles and glands) Integration produces a response Motor output Works through rapid and specific electrical and chemical signals to produce immediate responses

Organization Organization

• • Peripheral Nervous System – Brain – Afferent (sensory) – Spinal Cord – Efferent (motor) • Somatic • Autonomic – Sympathetic – Parasympathetic

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Central nervous system (CNS) Peripheral nervous system (PNS) Brain and spinal cord Cranial nerves and spinal nerves Integrative and control centers Communication lines between the Major Structures of the Nervous System CNS and the rest of the body

Sensory (afferent) division Motor (efferent) division Somatic and visceral sensory fibers nerve fibers Conducts impulses from the CNS Conducts impulses from to effectors (muscles and glands) receptors to the CNS

Somatic sensory Somatic nervous Autonomic nervous fiber Skin system system (ANS) Somatic motor Visceral motor (voluntary) (involuntary) Conducts impulses Conducts impulses from the CNS to from the CNS to skeletal muscles cardiac muscles, Visceral sensory fiber smooth muscles, Stomach and glands Skeletal muscle Motor fiber of somatic nervous system

Sympathetic division Parasympathetic Mobilizes body division systems during activity Conserves energy Promotes house- keeping functions during rest

Sympathetic motor fiber of ANS Heart Structure Function Sensory (afferent) division of PNS Parasympathetic motor fiber of ANS Bladder Motor (efferent) division of PNS

Copyright 2009 John Wiley & Sons, Inc. 7

Histology of Neurons and Nerves

• Two principal cell types • Neurons 1. Neurons • Excitable cells that transmit electrical signals – Individual nerve cells 2. Accessory cells (neuroglia) • Nerves • Non-excitable supporting cells – Parallel bundles of neurons carrying impulses in the PNS (called tracts in the CNS) • Types – Sensory (afferent) – Motor (efferent) – Association ()

ó Only about 20% empty space!

Nerves Neurons

• Special characteristics of neurons – Long lived – Amitotic – High metabolic rate – Excitable

ó Endo = within ó Peri = next to; around ó Epi = above

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Figure 11.4 Structure of a motor .

The Structure of a Neuron Cell body Neuron cell body (receptive (biosynthetic center regions) and receptive region) • Body • Dendrites

• (only one) Nucleolus

Axon (a) Dendritic (impulse spine Nucleus generating Impulse and conducting direction Nissl bodies region) Axon terminals (secretory Neurilemma (one inter- region) (b) node) Terminal branches

Copyright © 2010 Pearson Education, Inc.

The Structure of a Neuron The Structure of a Neuron

• Unipolar neurons • Pseudounipolar neurons – Found mostly in ANS, although some in CNS – Found chiefly in PNS as sensory neurons

The Structure of a Neuron The Structure of a Neuron

• Bipolar neurons • Multipolar neurons – Rare, but found in the special sense organs (retina, olfactory mucosa) – Most common type in humans (>99%)

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Accessory Cells Accessory Cells • Neuroglia • Neuroglia of the CNS • About 50% of cellular mass in nervous tissue 1. - support • Do not conduct impulses 2. - 3. Microglial cells - defense • Most retain capacity to divide 4. Ependymal cells - CSF • Different types found in PNS and CNS

Accessory Cells Capillary • Astrocytes – Most abundant of CNS neuroglia Neuron – Contact blood vessels – Blood Brain Barrier (BBB) regulates passage of molecules

Astrocytes are the most abundant of CNS neuroglia. Provide most structural support

Figure 11.3a

Accessory Cells

• Oligodendrocytes Myelin sheath – Branched cells Process of – Processes wrap around CNS neurons • Form insulating myelin sheaths Nerve fibers

Oligodendrocytes have processes that form myelin sheaths around CNS nerve fibers.

Figure 11.3d

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Accessory Cells

– Ependymal cells • Vary in shape from squamous to columnar • Many are ciliated • Line the central cavities of the brain and spinal column • Form cerebrospinal fluid • Separate the CNS interstitial fluid from the cerebrospinal fluid in the cavities

Myelin insulates neuronal , much the way insulation protects wires.

Accessory Cells

• Fluid-filled cavity – Small, ovoid cells with thorny processes Ependymal – Migrate toward injured neurons cells – Phagocytize microorganisms and neuronal debris Brain or • Why do you think this would be so important? spinal cord tissue Ependymal cells line cerebrospinal fluid-filled cavities. Add these to your list!

Figure 11.3c

Accessory Cells

• Neuroglia of PNS 1. Satellite cells Neuron • Surround neuron cell bodies in the PNS Microglial 2. Schwann cells cell • Surround peripheral nerve fibers and form myelin sheaths – Axon + myelin = nerve fiber • Vital to regeneration of damaged peripheral nerve fibers (b) Microglial cells are defensive cells in the CNS.

Figure 11.3b

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Accessory Cells

Satellite • Schwann cells cont. Cell body of neuron cells – Myelin sheath Schwann cells Neurilemma (forming myelin sheath) – Nerve fiber – Nodes of Ranvier

Satellite cells and Schwann cells (which form myelin) surround neurons in the PNS.

Figure 11.3e

Schwann cell plasma membrane Schwann cell 1 A Schwann cell cytoplasm envelopes an axon. Axon Schwann cell nucleus

2 The Schwann cell then rotates around the axon, wrapping its plasma membrane loosely around it in successive layers.

Neurilemma 3 The Schwann cell Myelin sheath cytoplasm is forced from between the membranes. The tight membrane wrappings surrounding (a) Myelination of a nerve the axon form the myelin fiber (axon) sheath.

Figure 11.5a

Multiple Sclerosis

• Autoimmune disease of young adults • Variety of clinical signs • No known cure

Antibodies produced in multiple sclerosis attack myelin made by oligodendrocytes, and lead to demyleination in the CNS.

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