The Nervous SystemIt is comprised of 3 basic componentsBrainSpinal cordNerves

General Functions of the Nervous SystemSensationMonitors changes/events occurring in and outside the body. Such changes are known as stimuli and the cells that monitor them are sensory receptors.IntegrationThe parallel processing and interpretation of sensory information to determine the appropriate response (Conscious or subconscious)ReactionMotor output or the activation of effectors such as muscles or glands (typically via the release of neurotransmitters).

Organization of the Nervous System2 big initial divisions:Central Nervous SystemThe brain + the spinal cordThe center of integration and controlPeripheral Nervous SystemThe nervous system outside of the brain and spinal cordConsists of:31 Spinal nervesCarry info to and from the spinal cord12 Cranial nerves Carry info to and from the brain

What is the basic functional unit of the nervous system?Neuron!What does the neuron do?Carries messages throughout the bodyHow does it carry the messages?By conducting electrical signalsWhat are these signals called?Nerve impulses!

Neuron AnatomyThree parts to a NEURON:Cell body: Large, central portion of the neuron where all organelles are located.What is its job?Interpret incoming signals

Cell Body

Neuron Anatomy2. Dendrites:Short, highly branched fibersWhat is its job?Carries impulses toward the cell bodyReferred to as the afferent processDendrites

Neuron Anatomy3. Axon:Long, slightly branched fiber What is its job?Carry impulses away from the cell bodyReferred to as the efferent process

Neuron AnatomyThree parts of the Axon:Axon hillock: site of initiation of an action potential (point where axon and cell body meet)

B. Axon fiber: the main portion of the axon

C. Axon terminal:branched end of the axon (point of communication with other cells)

The AxonAxon TerminalsAxon Hillockfiber

Neuron AnatomyAdditional Parts of a Neuron

Neuron anatomyWhat do you remember?dendritesnucleusCell bodyaxonNodes of RanvierMyelin sheathAxon terminalsDirection of impulse

3 Types of NeuronsA. Sensory Neurons: Receive incoming stimuliFive types of sensory neurons:Thermo-receptorsMechano-receptorsChemo-receptorsPhoto-receptorsPain-receptors

Thermo-receptorsLocation:SkinHypothalamusBody CoreFunction:Sensation of hot and coldDetects change in body core temp.

Mechano-receptorsLocation:SkinSkeletal muscleInner earFunction:TouchPressureMuscle movementMotionSound

Chemo-receptorsLocation:NoseTongue (taste buds)Blood vesselsFunction:SmellTasteDetects levels of CO2 in blood

Photo-receptorsLocation:EyesFunction:Allow vision thru detection of light

Pain-receptorsLocation:Everywhere, except the brainFunction:Sensation of painDetects chemicals released by damaged cells

Three Types of NeuronsB. Motor Neurons:Carry impulses to muscles and glandsCause a response to some stimuli

C. Interneurons:Connect sensory and motor neuronsAllow for quick response (reflex action)

Three types of neurons

Structural diversity in neuronsMultipolar- many dendrites, one axonMost neurons in CNSBipolar- one dendrite, one axonSensory organsUnipolar- sensoryAxon termini extend into CNS

NeuronsWhat is grey matter?Collective cell bodies and dendrites of all neurons

What is white matter?Myelinated nerve fibersAxons of all neuronsCan be approximately one meter in length

What is a Nerve?Bundle of axons held together by connective tissue.What color is a nerve?White!Why?Because axons are white matter and they compose nerves

How are nerves held together?Connective tissueWhat is this connective tissue called?Neuroglial cells (nerve glue)Approximately half of the volume of the brain is composed of neuroglial cellsMost brain tumors develop in mesoglial cells NOT neurons

What do neuroglial cells do?Support the axonsInsulate the electrical impulsesLike electrical tape insulates electric wires this prevents leaking of electric signals

Four types of neuroglia in CNSOligodendrocytesMyelinating cellsAstrocytesConnects neurons and blood vessels togetherMicrogliaPhagocytes (from bone marrow)Ependymal cellsLine ventricles of brain; produce cerebrospinal fluid (CSF)

Neuroglia of the PNSSchwann cellsMyelinating cellsHelp direct axon regenerationSatellite cellsSupport, protection, regulation of molecular exchangeFilter out other stimuli

The Nerve ImpulseResting potential the charge that exists across a neurons membrane while at rest.-70 mV.This is the starting point for an action potential.

The Nerve ImpulseA nerve signal or action potential is an electrochemical message of neurons.An all-or-none phenomenon either the fiber is conducting an action potential or it is not.Across its plasma membrane, every cell has a voltage called a membrane potential.The inside of a cell is negative relative to the outside.

The Nerve ImpulseNeuron at rest active transport channels in the neurons plasma membrane pump:Sodium ions (Na+) out of the cell.Potassium ions (K+) into the cell.More sodium is moved out; less potassium is moved in.Result is a negative charge inside the cell.Cell membrane is now polarized.

Sodium-Potassium Exchange PumpNa+ flows into the cell during an action potential, it must be pumped out using sodium pumps so that the action potential will continue.

The Nerve ImpulseA nerve impulse starts when pressure or other sensory inputs disturb a neurons plasma membrane, causing sodium channels on a dendrite to open.Sodium ions flood into the neuron and the membrane is depolarized more positive inside than outside.

The Nerve ImpulseThis moving local reversal of voltage is called an action potential.A very rapid and brief depolarization of the cell membrane.Membrane potential changes from -70 mV to +35 mV.After the action potential has passed, the voltage gated channels snap closed and the resting potential is restored.The membrane potential quickly returns to -70 mV during the repolarization phase.An action potential is a brief all-or-none depolarization of a neurons plasma membrane.Carries information along axons. An action potential is self-propagating once started it continues to the end.

Synapses: Junctions Between NervesEventually, the impulse reaches the end of the axon.Neurons do not make direct contact with each other.The junction between the axon of one neuron and the dendrite of the next is called a synapse .

Synaptic PathwaysPresynaptic neurons bring action potentials toward the synapse.Postsynaptic neurons carry action potentials away from the synapse.A synaptic cleft is the small gap between the two neurons.

NeurotransmittersChemical messengers called neurotransmitters carry the message of the nerve impulse across the synapse.

NeurotransmittersNeurotransmitters are released into the synapse and bind with receptors on the postsynaptic cell membrane, which cause ion channels to open in the new cell.

Acetylcholine Example Neurotransmitter

Reflex ArcA simple reflex produces a very fast motor response to a stimulus because the sensory neuron bringing information about the stimulus passes the information directly to the motor neuron.

Reflex ArcUsually, there are interneurons between sensory and motor neurons.An interneuron may connect two neurons on the same side of the spinal cord, or on opposite sides.

The Central Nervous SystemMeninges are membranes that protect the brain and spinal cord Dura mater (outermost layer)Arachnoid membrane ( middle layer)Pia mater (innermost layer)

The Central Nervous SystemCerebrospinal Fluid (CSF)Located between the arachnoid mater and pia mater is an area called the subarachnoid space Continuously secreted from specialized cells (ependymal cells) in the choroid plexus in ventriclesFunctions: Physical and chemical protection of the CNS

*Spinal CordSlender structure that is continuous with the brain Descends into the vertebral canal and ends around the level of the first or second lumbar vertebra.Function of the spinal cord is to carry sensory information to and from the brain 31 spinal segments: 8 cervical segments 12 thoracic segments 5 lumbar segments 5 sacral segments1 coccygeal segment

*Spinal Cord - Ascending and Descending Tracts Ascending tracts - carry sensory information up to the brain Descending tracts - carry motor information down from the brain to muscles and glands

*The Brain Four Parts: Cerebrum Diencephalons Brain stem Cerebellum

*The Brain - CerebrumLargest part of the brain Two halves cerebral hemispheres Thick bundle of nerve fibers called the corpus callosum connect the two hemispheres LobesFrontal Parietal Temporal Occipital CortexVentricles

*The Brain - DiencephalonsThalamus - relay station for sensory information that heads to the cerebral cortex for interpretation Hypothalamus - maintains balance by regulating many vital activities such as heart rate, blood pressure, and breathing rate. Located between the cerebral hemispheres and is superior to the brain stem

*The Brain - Brain stemMidbrain - controls both visual and auditory reflexes Pons - regulates breathing Medulla oblongata - controls many vital activities such as heart rate, blood pressure, and breathing

Connects the cerebrum to the spinal cord

*The Brain - Cerebellum Inferior to the occipital lobes of the cerebrum

Posterior to the pons and medulla oblongata Coordinates complex skeletal muscle contractions that are needed for body movements

Diseases and Disorders of the Nervous SystemCerebrovascular Accident: CVACommonly called a strokeThe result of a ruptured blood vessel supplying (cerebral hemorrhage) a region of the brain or a vessel is obstructed by a clot.Brain tissue supplied with oxygen from that blood source dies, swelling occurs in the brain due to leaking of blood from vessels.Loss of some functions or death may resultThis is due often to elevated blood pressure or hypertension.

Diseases and Disorders of the Nervous SystemEpilepsy: This disease is due to random, mis-firing of neurons within the brain affecting sensory and motor regions of the brain. Ranging in effects from sleep-like state of consciousness (narcolepsy), muscle paralysis and spasms (Petit mal and Grand mal seizures). Still not understood why this disease occurs. However in some cases it can result from brain trauma or injury.

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