NERVOUS SYSTEM HONORS ANATOMY PHYSIOLOGY excitable characteristic of

NERVOUS SYSTEM HONORS ANATOMY & PHYSIOLOGY

�excitable characteristic of nervous tissue allows for generation of nerve impulses (action potentials) that provide communication & regulation of most body tissue. �together with endocrine system: responsible for maintaining homeostasis Nervous Tissue & Homeostasis

NERVOUS ENDOCRINE �rapid �slow, responder �action potentials prolonged response �releases hormones Differences in Nervous & Endocrine Control of Homeostasis

�total mass of 2 kg (~3% of total body mass) �Skull �Spinal Cord �Spinal Nerves �Cranial Nerves �Ganglia �Enteric Plexus �Special Senses & other Sensory Receptors Structures of the Nervous System

Major Structures of the Nervous System

� 3 basic functions: 1. Sensory 2. Integrative 3. Motor Functions of the Nervous System

�sensory receptors detect internal & external stimuli �sensory (afferent) neurons carry this sensory information to spinal cord & brain thru cranial & spinal nerves Sensory Function

�integrate: process �nervous system takes information from sensory neurons & processes that information, analyzes it, stores some of it & makes decisions for appropriate responses �served by interneurons (connect 1 neuron to another neuron �Perception: ◦ conscious awareness of sensory stimuli ◦ occurs in brain Integrative Function

�served by motor (efferent) neurons �carry info from brain/spinal cord effectors (muscle or gland) thru cranial or spinal nerves �results in muscles contraction or gland secreting Motor Function

terms are given to neurons that carry input spinal cord & brain? �What terms are given to neurons that carry output of the brain & spinal cord? Quick Quiz

Organization of the Nervous System

� 2 cell types 1. Neurons 2. Neuroglia Histology of the Nerrvous System

�nerve cells that possess electrical excitability: ◦ ability to respond to a stimulus & convert it into an action potential ◦ stimulus: any change in environment that is strong enough to initiate an action potential Neurons

Direction Action Potential Travels

�electrical signal that propagates along surface of neurolema (membrane) ◦ begins & travels due to movement of ions between interstitial fluid & inside of neuron thru specific ion channels ◦ once begun it travels rapidly @ constant strength Action Potential

Parts of a Neuron

�contains nucleus, cytoplasm, typical organelles, �+ Nissl bodies clusters of RER ◦ make materials for: �growth of neuron �regenerate damaged axons in PNS Parts of Neuron: Cell Body

�general term for any neuronal process or extension that emerges from cell body �most neurons have 2: 1. Dendrites 2. Axons Nerve Fiber

�“little trees” �input portion of neuron �usually, short, tapering, highly branched �their cytoplasm contains Nissl bodies, mitochondria Dendrites

�propagates action ◦ another neuron ◦ muscle fiber ◦ gland cell Axon potentials

�joins cell body @ cone-shaped elevation: axon hillock �part of axon closest to hillock = initial segment �jct of axon hillock & initial segment where action potential arises so is called the trigger zone Parts of an Axon

�axoplasm: cytoplasm of an axon �axolemma: plasma membrane of axon �axon collaterals: side branches along length of axon (most @ 90°) �axon terminals: axon divides into many fine processes Parts of an Axon

�site of communication between 2 neurons or between a neuron & effector cell �synaptic end bulbs: tips of some axon terminals swell into bulb-shaped structures �synaptic vesicles: store neurotransmitter ◦ many neurons have >1 neurotransmitter, each with different effects on postsynaptic cell Synapse

� 2 types: ◦ for moving materials from cell body axon terminals slow 1. ◦ ◦ 1 -5 mm/d replenishes new axoplasm to developing or regenerating axons fast 2. ◦ ◦ 200 – 400 mm/d moves materials to/from cell body � organelles or membranes needed in axon terminal Axonal Transport

Functional Classification Structural Classification � use � Sensory � Interneurons � Motor Types of Neurons # processes extending from cell body 1. Multipolar neurons 2. Bipolar neurons 3. Unipolar neurons

�several dendrites with 1 axon �includes most neurons in brain & spinal cord Multipolar Neurons

� 1 main dendrite & 1 axon �retina, inner ear, olfactory area of brain Bipolar Neuron

�are sensory neurons that begin in embryo as bipolar �during development axon & dendrite fuse then divide into 2 branches (both have characteristic structure & function of an axon) � 1 branch ends with dendrites (out of CNS) � 2 nd branch ends in axon terminal (in CNS) �cell bodies of most found in ganglia Unipolar Neuron

Unipolar Neuron

�found in cerebellum Purkinje Cells

�in cerebral cortex of brain Pyramidal Cells

�~50% vol of CNS �“glue” �do not generate or propagate action potentials �multiply & divide in mature nervous systems �glioma: ◦ brain tumors derived from glial cells ◦ very malignant, grow rapidly Neuroglia (Glia)

ASTROCYTES 2. OLIGODENDROCYTES 3. MICROGLIA 4. EPENDYMAL CELLS 1. Glial Cells of the CNS

�star-shaped �largest & most numerous of glial cells �functions: 1. physically support neurons 2. assist in blood-brain-barrier (bbb) 3. in embryo: regulate growth, migration, &interconnections between neurons 4. help maintain appropriate chemical environment for propagation of action potentials Astrocytes

�“few trees” �smaller & fewer branches than astrocytes �Functions: 1. form & maintain myelin sheath on axons in CNS 2. 1 oligo. myelinates many axons Oligodendrocytes

�small cells with slender processes giving off many spine-like projections � function: 1. phagocytes ◦ ◦ remove cellular debris made during normal development remove microbes & damaged nervous tissue Microglia

�single layer of cuboidal to columnar cells �ciliated & have microvilli �function: 1. line ventricles of brain & central canal of spinal cord 2. produce, monitor, & assist in circulation of cerebrospinal fluid (CSF) 3. form bbb Ependymal Cells

�Schwann cells �Satellite cells Neuroglial Cells of the PNS

�functions: myelinate axons in PNS 1. ◦ 2. 1 Schwann cell myelinates 1 axon participate in axon regeneration Schwann Cells

�flat cells that surround cell bodies of neurons in PNS ganglia �functions: 1. structural support 2. regulate exchange of materials between neuronal cell bodies & interstitial fluid Satellite Cells

�myelin sheath: made up of multilayered lipid & protein (plasma membrane) covering �function: 1. electrically insulates axon 2. increases speed of nerve impulses Myelination

Myelinated & Unmyelinated Axons

�gaps in myelin sheath � 1 Schwann cell wraps axon between nodes of Ranvier Nodes of Ranvier

Sheath of Schwann = Neurolemma

�amount increases from birth to maturity �infant‘s responses slower & less coordinated as older child or adult in part because myelination is a work in progress thru infancy Myelin

�loss of myelin sheath �see in disorders: ◦ multiple sclerosis ◦ Tay-Sachs ◦ side effect of radiation therapy & chemotherapy Demyelination

�contains: ◦ neuronal cell bodies ◦ dendrites ◦ unmyelinated axons ◦ axon terminals ◦ neuroglia Gray Matter of the Nervous System

�composed of: ◦ myelinated axons White Matter of the Nervous System