CELLS OF THE NERVOUS SYSTEM

CELLS OF THE NERVOUS SYSTEMCHAPTER 12Nervous system3 main parts: brain, spinal cord, nervesFunction: To detect changes in the internal and external environment, evaluate the information and possibly respond by initiating changes in muscles or glands.Endocrine system works very closely with nervous system. Nervous system: immediate responsesEndocrine: slower uses hormones.DivisionsCentral Nervous System (CNS)= Brain and spinal cordPeripheral Nervous System (PNS)= nerves outside of SC

Afferent division- incoming sensory information. Toward the SCEfferent division- outgoing pathways. Motor neurons.

Divisions contSomatic Nervous System: 12 pairs of cranial nerves31 pairs of spinal nervesBundles of neuron axons bound together by connective tissue. Cell bodies are in the spinal column.Relay to skeletal muscleReflexes

Autonomic Nervous SystemCarries impulses from the CNS to internal organs. Involuntary responses-Sympathetic Nervous System: Stress fight or flight.-Parasympathetic Nervous System: Rest and repair functions (digestion)Cells in the nervous system30 billion cells in the NS with over 100 trillion connections that are electrical in nature and generate a great deal of heat. Heat loss is primarily through head.Neuron-basic unit of the nervous systemMany support cells as well.Glial- satellite cells of the nervous system 4 types1. Microglial2. fibrous astroglial3. protoplasmic astroglial4. oligodendroglial

Also known as ASTROCYTES

Support CellsMicroglial- small. Immune function. Act like white blood cells in the CNS. Fight bacteria, breakdown worn out organelles.Epedemal Cells surround spinal cord and make cerebrospinal fluid. This bathes the brain and spinal cord.

Fibrous Astroglia- white matter.Protoplasmic Astroglia-white matter.Both work to form the blood brain barrier.Blood Brain BarrierYou do not get the same free exchange of nutrients and gases through the capillaries into nervous tissue of the brain. Astroglia form a protoplasmic foot that guards the capillary to prevent material from coming through.

Astroglia- forms scar tissue in the brain

4. OligodendrogliaCreates the myelin that surrounds the axon by wrapping several times around the axon. Myelin insulates the nerve and speeds nerve transmission.

Schwann CellsFound in the peripheral nervous system (PNS) and have the same function as oligodenrdriocytes.Gaps between these cells create NODES OF RANVIER. These gaps are important for proper nerve conduction as an impulse jumps from node to node. Schwann Cells form the NEURILEMMAForms WHITE MATTER or myelinated fibersNeuron.Cell body = somaDendrites= several ways into cell bodyAxon = 3-4 inches in length. Axon endingsNucleus

DendriteAxonMyelin sheathCell bodyStructural classification of neuronsClassified by their number of extensions from the cell body.Multipolar- most neurons of brain and spinal cord. Have one axon but several dendritesBipolar-One axon and one highly branched dendrite. Only found in the retina of the eye inner ear, and in the olfactory pathway (nose).Unipolar-single extending process from the cell body. Branches to form one way into the CNS, the second toward the PNS. Always sensory conducting information to the CNS.

3 types of neurons:Sensory- impulses from spine to brain (AFFERENT NERVES)Motor- carry response brain to organ or muscle that was stimulated to respond. (EFFERENT NERVES)Interneurons- within the spinal cord

Nerves and TractsTracts are bundles of peripheral nerves that are held together by several layers of connective tissues. Surrounding each nerve fiver is an delicate layer of fibrous connective tissue: Endoneurium, perineurium, epineurium (sound familiar?)

Repair of Nerve Fibers1. Injury or cut nerve2. Distal portion of axon degenerates3. Remaining neurolemma forms a tunnel from effector to nerve body.4. Axons sprout on form within the tunnel.5. Neruons connection is re-established

Can grow from 3-5mm per day.Page 352 Figure 12-10

Electrical Function of a NeuronVolt= difference in electrical potential.Energy flows from the point of higher voltage to an area of low voltage.

Depolarization occurs when a stimulus hits the nerve and Na++ flows into the axon in a wave pattern. As the stimulus travels it is called an ACTION POTENTIAL.

Na++ is High outside the cell (4:1)K++ is High inside the cell (30:1)

Na++ flows into the area of lower potential and is pumped out by Active transport (requiring ATP) after the impulse passes. This is called REPOLARIZATION

The difference between the inside and outside of the cell is called the RESTING POTENTIAL. High K+ concentration in tissue increases the resting potential making it harder to stimulate. If K+ concentration gets too high you can go into cardiac arrest.

Neurons are high energy users.ThresholdThreshold is the minimum amount of stimulus required to produce a response. (elicit an action potential)

All or none law- If you stimulate a nerve below the threshold you will get NO response.At threshold you get a maximum response.

The strength of a stimulus or action potential remains constant from the time it is generated until it is complete. The impulse does not weaken in transit.Refractory period.For a few milliseconds after a threshold potential has been reached the nerve will not respond to a stimuli no matter how strong. This is called the refractory period.

Neurotransmitters- how nerves communicateMore than 30 kinds of transmittersClassified by function and structure

AcetylcholineVarious locations. Excitatory in muscles, inhibitory in the heart.AminesFrom amino acids. In brain, learning, emotions, motor control

Amino AcidMost common NTs in the Central Nervous SystemIn PNS- stored in synaptic vesiclesNeuropeptidesCo- transmitter used to regulate the effects of other NTs when they are released.

Neurotransmitters released through the blood stream are called HORMONES.SYNAPSE

CNSBrain Anatomy:Brain: control system of entire nervous system. 3 main parts.

CerebrumSkullMedulla oblongataCerebellum

Section 36.1 Summary pages 943 - 950

Motor areaSensory areaLanguage areaVision areaGeneral interpretation areaCerebrumSpeech areaTaste areaIntellect, learning, and personalityHearing areaBrain stemCerebellumBalance areaAnatomy of the brain

Cerebrum2 hemispheres connected by bundles of nervesConscious activity

Lobes of the brainParietal lobeSensory association areas- impulses from skin such as pain and temp. Estimates distancesFrontal lobeMotor cortex, controls skeletal musclesBrocas speech area- forming wordsPersonalityTemporal lobeAuditory, memory and speechOccipital lobevision

CerebellumBack of your brainBalancePostureCoordination

Brain stem: 3 main partsMedulla oblongata- Involuntary activity- breathing and heart ratePons-Connect various parts of the brain togetherMidbrain- similar function to the Pons

MidbrainCerebellumMedulla oblongataPons