Fundamentals of the Nervous System HONORS ANATOMY & PHYSIOLOGY CHAPTER 11

Functions of the Nervous System 3 overlapping functions: Sensory input monitor changes in & outside of body information gathered called sensory input which is carried to #2 on afferent nerves Integration processing & interpreting sensory input Motor output activation of effector organs (muscles or glands) to cause a response called motor output which is carried on efferent nerrves

Divisions of the Nervous System Central Nervous System(CNS) Brain Spinal Cord Peripheral Nervous System (PNS) Sensory neurons: specialized endings to detect a particular sense Motor neurons: Somatic: CNS  skeletal muscle (voluntary) Autonomic: Sympathetic Parasympatheric

Organization of the Nervous System

Histology of Nervous Tissue very cellular, ~20% extracellular material 2 cell types: Neurons excitable (respond to stimuli) able to transmit electrical impulses (action potentials) Neuroglia: supporting cells

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

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

Axon another neuron muscle fiber gland cell propagates action potentials  another neuron muscle fiber gland cell

Parts of an Axon 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

Synapse 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

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

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

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

Unipolar 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) 2nd branch ends in axon terminal (in CNS) cell bodies of most found in ganglia

Unipolar Neuron

Purkinje Cells found in cerebellum

Pyramidal Cells in cerebral cortex of brain

Neuroglia (Glia) ~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

Glial Cells of the CNS ASTROCYTES OLIGODENDROCYTES MICROGLIA EPENDYMAL CELLS

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

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

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

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

Neuroglial Cells of the PNS Schwann cells Satellite cells

Schwann Cells functions: myelinate axons in PNS 1 Schwann cell myelinates 1 axon participate in axon regeneration

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

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

Myelinated & Unmyelinated Axons

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

Myelin 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

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

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

White Matter of the Nervous System composed of: myelinated axons