Nervous System – Ch 7Nervous System – Ch 7

IntroductionIntroduction Neurons – nerve cellsNeurons – nerve cells Transmit information in the form of electrochemical Transmit information in the form of electrochemical

changes (nerve impulses)changes (nerve impulses) Neuron structureNeuron structure

Cell bodyCell body Dendrites – numerous; receive messagesDendrites – numerous; receive messages Axons – send information; usually one per neuronAxons – send information; usually one per neuron

Nerves – bundles of axonsNerves – bundles of axons Neuroglial cells – supporting cells that provide neurons Neuroglial cells – supporting cells that provide neurons

with physiological requirements and functionwith physiological requirements and function Two groups of nervous system:Two groups of nervous system:

Central nervous system (CNS) – brain and spinal cordCentral nervous system (CNS) – brain and spinal cord Peripheral Nervous System (PNS) – nerves and other body Peripheral Nervous System (PNS) – nerves and other body

partsparts

General Functions of Nervous General Functions of Nervous SystemSystem

Sensory FunctionSensory Function Sensory receptors gather information by detecting changes Sensory receptors gather information by detecting changes

inside and outside the body (light, sound, temp, O2 inside and outside the body (light, sound, temp, O2 concentration)concentration)

• Convert information into nerve impulses that are integrated, added Convert information into nerve impulses that are integrated, added to memory, or translate to sensationsto memory, or translate to sensations

Integrative FunctionIntegrative Function Conscious or subconscious decisionsConscious or subconscious decisions

Motor FunctionsMotor Functions Use peripheral neurons to carry impulses to effectors Use peripheral neurons to carry impulses to effectors

(responsive structure)(responsive structure) Two categoriesTwo categories

• Somatic nervous system – consciously controlled; skeletal muscleSomatic nervous system – consciously controlled; skeletal muscle• Autonomic nervous System – involuntary; heart muscle Autonomic nervous System – involuntary; heart muscle

Neuroglial CellsNeuroglial Cells NeurogliaNeuroglia FunctionsFunctions::

Fill spacesFill spaces provide structural frameworkprovide structural framework produce myelinproduce myelin carry on phagocytosiscarry on phagocytosis

Types of Neuroglial Cells:Types of Neuroglial Cells: Microglial cellsMicroglial cells: scattered through CNS; support neurons and : scattered through CNS; support neurons and

phagocytize bacterial cells and cell debrisphagocytize bacterial cells and cell debris OligodendrocytesOligodendrocytes: occur in nerve fibers; provide myelin around : occur in nerve fibers; provide myelin around

axons in brain and spinal cordaxons in brain and spinal cord AstrocytesAstrocytes: found between neurons and blood vessels; provide : found between neurons and blood vessels; provide

structural support, join parts, regulate nutrient and ion concentration structural support, join parts, regulate nutrient and ion concentration in tissues, form scar tissuein tissues, form scar tissue

Ependymal cellsEpendymal cells: form epithelial-like membrane to cover specialized : form epithelial-like membrane to cover specialized brain parts (choroid plexuses) and form inner linings that enclose brain parts (choroid plexuses) and form inner linings that enclose brain spaces (ventricles) and spinal cord (central canal)brain spaces (ventricles) and spinal cord (central canal)

The PNS contains neuroglial called Schwann cells that form the The PNS contains neuroglial called Schwann cells that form the myelin sheath around axons.myelin sheath around axons.

Neuron StructureNeuron Structure

Vary in size and shapeVary in size and shape Structure:Structure:

Neuron cell bodyNeuron cell body Consist of cytoplasm, cell membrane, and organellesConsist of cytoplasm, cell membrane, and organelles Chromatophilic substance (Nissl bodies) similar to rough ER Chromatophilic substance (Nissl bodies) similar to rough ER

also contain ribosomesalso contain ribosomes Contain a nucleus and nucleolusContain a nucleus and nucleolus Do not divideDo not divide

DendritesDendrites Short, highly branchedShort, highly branched Main receptive surfaceMain receptive surface

AxonsAxons Arise from elevation of cell body (Arise from elevation of cell body (axonal hillockaxonal hillock) to ) to conduct nerve conduct nerve

impulses away from the cell bodyimpulses away from the cell body Many mitochondria, microtubules, neurofibrilsMany mitochondria, microtubules, neurofibrils Single structure that may have many branchesSingle structure that may have many branches Large ones are covered by sheaths of Schwann cells (membrane Large ones are covered by sheaths of Schwann cells (membrane

covering). Membrane is composed of myelin (lipoprotein) covering). Membrane is composed of myelin (lipoprotein) Myelin sheath - higher proportion of lipids in cell membraneMyelin sheath - higher proportion of lipids in cell membrane Neurilemmal sheath – surrounds myelin sheath; contains cytoplasm and Neurilemmal sheath – surrounds myelin sheath; contains cytoplasm and

nucleinuclei Nodes of RanvierNodes of Ranvier – gaps between Schwann cells – gaps between Schwann cells

With myelin sheath – myelinatedWith myelin sheath – myelinated Also found in CNSAlso found in CNS Appear white – Appear white – white matterwhite matter Unmyelinated axons and neurons form the Unmyelinated axons and neurons form the gray mattergray matter

When damaged, the PNS regenerate due to neurilemma; the CNS When damaged, the PNS regenerate due to neurilemma; the CNS do not because of lack of neurilemmado not because of lack of neurilemma

Classifying NeuronsClassifying Neurons

Differ in size, structure, shape of cell bodiesDiffer in size, structure, shape of cell bodies Vary in length and size of axons and dendritesVary in length and size of axons and dendrites Vary in functionVary in function

Some carry impulses to brain or spinal cordSome carry impulses to brain or spinal cord Some transmit impulses out of brain or spinal cordSome transmit impulses out of brain or spinal cord Some conduct impulses from neuron to neuronSome conduct impulses from neuron to neuron

Bipolar NeuronsBipolar Neurons

Cell body has two processes, one from Cell body has two processes, one from each endeach end One is axon, one is dendriteOne is axon, one is dendrite

Eyes, nose, ear neuronsEyes, nose, ear neurons

Unipolar NeuronsUnipolar Neurons

Single process from body that Single process from body that branches into two that branches into two that function as a single axonfunction as a single axon Peripheral process – dendrite Peripheral process – dendrite

association near peripheral association near peripheral body partsbody parts

Central process – enters the Central process – enters the brain or spinal cordbrain or spinal cord

In specialized masses called In specialized masses called gangliaganglia

Multipolar NeuronsMultipolar Neurons

Many processes from cell Many processes from cell bodybody One is an axonOne is an axon All the others are dendritesAll the others are dendrites

Most neurons in brain and Most neurons in brain and spinal cord are multipolarspinal cord are multipolar

Sensory NeuronsSensory Neurons

Also called Also called afferent neuronsafferent neurons Carry nerve impulses from peripheral body to Carry nerve impulses from peripheral body to

brain or spinal cordbrain or spinal cord Have specialized receptor ends on dendrites OR Have specialized receptor ends on dendrites OR

dendrites are closely related with receptor cells dendrites are closely related with receptor cells in skin and sensory organsin skin and sensory organs

Changes stimulate receptors, triggering a nerve Changes stimulate receptors, triggering a nerve impulseimpulse

Most are unipolar, some are bipolarMost are unipolar, some are bipolar

InterneuronsInterneurons

Also called Also called associationassociation or or internuncialinternuncial neuronsneurons

Lie within brain or spinal cordLie within brain or spinal cord Multipolar and link other neuronsMultipolar and link other neurons Transmit impulses from one part of brain Transmit impulses from one part of brain

or spinal cord to anotheror spinal cord to another Direct incoming sensory impulsesDirect incoming sensory impulses

Motor NeuronsMotor Neurons

Efferent NeuronsEfferent Neurons MultipolarMultipolar Carry nerve impulses out of the brain or Carry nerve impulses out of the brain or

spinal cord to effectorsspinal cord to effectors Stimulate muscles to contract and glands Stimulate muscles to contract and glands

to release secretionsto release secretions

SynapseSynapse

Nerve impulses travel from neuron to neuron Nerve impulses travel from neuron to neuron along pathways. along pathways.

The junction between communicating The junction between communicating neurons is a synapse.neurons is a synapse.

Gap between neurons is synaptic cleft.Gap between neurons is synaptic cleft.

NeurotransmittersNeurotransmitters Chemical that reacts with specific Chemical that reacts with specific

receptors to create a nerve impulsereceptors to create a nerve impulse Acetylcholine – controls skeletal muscle actionsAcetylcholine – controls skeletal muscle actions Norepinephrine – “good” feeling, low levels may Norepinephrine – “good” feeling, low levels may

lead to depressionlead to depression Dopamine – “good” feelingDopamine – “good” feeling Serotonin – sleepSerotonin – sleep Histamine – alertnessHistamine – alertness Endorphins – reduce painEndorphins – reduce pain Nitric oxide – vasodilation, memoryNitric oxide – vasodilation, memory pg. 218 chart of neurotransmitterspg. 218 chart of neurotransmitters

Types of NervesTypes of Nerves

Nerves are cordlike bundles of nerve Nerves are cordlike bundles of nerve fibersfibers held together by connective tissue held together by connective tissue layers that conduct impulses layers that conduct impulses

Sensory nerves – impulses into the brain Sensory nerves – impulses into the brain or spinal cordor spinal cord

Motor nerves – carry impulses to Motor nerves – carry impulses to muscles or glandsmuscles or glands

Mixed nerves – include both of the aboveMixed nerves – include both of the above

Nerve PathwaysNerve Pathways

Routes that nerve impulses follow in the nervous Routes that nerve impulses follow in the nervous systemsystem

Reflex arcs are the simplest pathways that constitute Reflex arcs are the simplest pathways that constitute reflexes.reflexes.

Reflexes are subconscious responses to stimuliReflexes are subconscious responses to stimuli within within or outside the body. or outside the body. Help maintain involuntary actions Help maintain involuntary actions such as heart rate, breathing rate, blood pressure and such as heart rate, breathing rate, blood pressure and digestiondigestion

Knee-jerk reflex – simple, only using two Knee-jerk reflex – simple, only using two neurons; helps maintain upright postureneurons; helps maintain upright posture

Withdrawal reflex – unexpected touch to Withdrawal reflex – unexpected touch to something painful; protective by limiting tissue something painful; protective by limiting tissue damagedamage

MeningesMeninges Membranes beneath the bony coverings of the skull and Membranes beneath the bony coverings of the skull and

vertebral column for protectionvertebral column for protection Three layersThree layers

Dura materDura mater – – outermost layeroutermost layer of connective tissue, of connective tissue, blood vessels, and nerves; interior periosteum of blood vessels, and nerves; interior periosteum of skull bones and between lobes of brain; surround skull bones and between lobes of brain; surround spinal cord for protection.spinal cord for protection.

Arachnoid materArachnoid mater – thin membrane lacking blood – thin membrane lacking blood vessels in the middlevessels in the middle

Pia MaterPia Mater – thin layer of nerves and blood vessels – thin layer of nerves and blood vessels that nourish the cells of the brain and spinal cord; that nourish the cells of the brain and spinal cord; hugs surfaces of organshugs surfaces of organs

Cerebrospinal fluid (CSF)Cerebrospinal fluid (CSF) – in between arachnoid – in between arachnoid and pia maters.and pia maters.

Spinal CordSpinal Cord

Nerve column passing from brain into Nerve column passing from brain into vertebral canalvertebral canal

Begins at the foramen magnum and Begins at the foramen magnum and terminates at the first and second lumbar terminates at the first and second lumbar vertebrae.vertebrae.

Structure of Spinal CordStructure of Spinal Cord Consists of 31 segments that give rise to spinal Consists of 31 segments that give rise to spinal

nerves which branch to various body partsnerves which branch to various body parts Cervical enlargement is the thickening of the Cervical enlargement is the thickening of the

spinal cord in the neck region that supplies nerves spinal cord in the neck region that supplies nerves to upper limbsto upper limbs

The lumbar enlargement is in the lower back The lumbar enlargement is in the lower back giving nerves to lower limbs.giving nerves to lower limbs.

Divided into right and left halves by the anterior Divided into right and left halves by the anterior median fissure and posterior median sulcus median fissure and posterior median sulcus grooves.grooves.

Functions of Spinal CordFunctions of Spinal Cord

Two major functions: conducting nerve impulses Two major functions: conducting nerve impulses and center for spinal reflexesand center for spinal reflexes

Axons of the spinal cord provide two way Axons of the spinal cord provide two way communication between the brain and the body communication between the brain and the body partsparts

Ascending tracts carry sensory information to the Ascending tracts carry sensory information to the brainbrain

Descending tracts conduct motor impulses from Descending tracts conduct motor impulses from the brain to the musclesthe brain to the muscles

Knee-jerk and withdrawal reflexes are spinal Knee-jerk and withdrawal reflexes are spinal reflexes because they pass through the spinal reflexes because they pass through the spinal cordcord