Nervous SystemNervous System

B. Supporting cells of the CNSB. Supporting cells of the CNS

OligodendrocytesOligodendrocytesAstrocytes:Astrocytes: protoplasmic protoplasmic fibrousfibrousMicrogliaMicrogliaEpendymal cellsEpendymal cells

① ① oligodendrocytesoligodendrocytes

One oligodendrocyte may myelinate one axon or several nearby axons

② ② AstrocytesAstrocytes

Protoplasmic astrocyteProtoplasmic astrocyte Fibrous astrocyteFibrous astrocyte

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③ ③ Ependymal cellsEpendymal cells

Line the brain ventricles and central canal of the spinal cordLine the brain ventricles and central canal of the spinal cordSome are ciliated to facilitate the movement of cerebrospinal fluidSome are ciliated to facilitate the movement of cerebrospinal fluid

④ ④ MicrogliaMicroglia

Derived from bone marrow, phagocyte in nerve tissueDerived from bone marrow, phagocyte in nerve tissueInvolved with inflammation and repair in the CNSInvolved with inflammation and repair in the CNS

Summary 2Summary 2

Supporting cells in the PNSSupporting cells in the PNS Myelin sheathMyelin sheath neuroglianeuroglia

I. The peripheral nervous systemI. The peripheral nervous system

Nerve fibersNerve fibers

GangliaGanglia

Nerve endingNerve ending

1. Nerve fibers1. Nerve fibers

A peripheral A peripheral nerve is a nerve is a bundle of bundle of nerve nerve fibers fibers held held together together by by connectivconnective tissuee tissue

Unmyelinated nerve fiberUnmyelinated nerve fiber

2. Ganglia2. Ganglia Ovoid structures containing neuronal ceOvoid structures containing neuronal ce

ll bodies and glial cells supported by conll bodies and glial cells supported by connective tissuenective tissue

The direction of the nerve impulse deterThe direction of the nerve impulse determines whether sensory or autonomic gamines whether sensory or autonomic ganglia.nglia.

Sensory ganglia:Sensory ganglia: receive afferent impulses th receive afferent impulses that go to the CNSat go to the CNS

Cranial ganglia: Cranial ganglia: cranial nervescranial nervesSpinal ganglia: Spinal ganglia: dorsal root of spinal nervesdorsal root of spinal nerves

Autonomic ganglia:Autonomic ganglia:Sympathetic: Sympathetic: paravertebrate, preveterbrateparavertebrate, preveterbrateParasympathetic: Parasympathetic: close to organs or in organsclose to organs or in organs

3. Nerve ending3. Nerve ending

Sensory nerve endingSensory nerve endingFree: pain, temperatureFree: pain, temperature

encapsulateencapsulate

Motor nerve endingMotor nerve endingMotor end plateMotor end plate

Visceral motorVisceral motor

Tactile corpuscle: sense of touch

Lamellar corpuscle: pressure, vibration

Muscle spindle: limbs position

Muscle spindleMotor end plateMotor end plate

Tactile corpuscle Lamellar corpuscle

Autonomic nervous systemAutonomic nervous system

The ANS consists of motor neurons that: Innervate smooth and cardiac muscle and glands (most of the effectors are viscera)

Three major differences in the ANS and SNSThree major differences in the ANS and SNS

EffectorsEffectors

Efferent pathwaysEfferent pathways

Target organ responsesTarget organ responses

EffectorsEffectors

The effectors of the SNS are skeletal muscles

The effectors of the ANS are cardiac muscle, smooth muscle, and glands

Efferent PathwaysEfferent Pathways

Myelinated axons of the somatic motor neurons extend from the CNS to the effector (lacks ganglia)

Pathways in the ANS are a two-neuron chain

The preganglionic (first) neuron has a lightly myelinated axon. The ganglionic (second) unmyelinated neuron extends to an effector organ via the postganglionic axon

Neurotransmitter EffectsNeurotransmitter Effects

In the ANS:

Preganglionic fibers release ACh

Postganglionic fibers release norepinephrine (most s.) or ACh (p.) and the effect is either stimulatory or inhibitory

All somatic motor neurons release Acetylcholine at their synapses, Ach always has an excitatory effect

The nuclei of the Sym. are located in the thoracic and lumbar segments of the spinal cord.

The 2nd neuron is located in sensory ganglia.

The nuclei of the Para. are located in the medulla and midbrain and in the sacral portion of the spinal cord.

The 2nd neuron is in ganglia located near or within the effector organs

II. The central nervous systemII. The central nervous system

CerebrumCerebrum CerebellumCerebellum Spinal cordSpinal cord

CNS has almost no connective tissue,CNS has almost no connective tissue,

A relatively soft gel-like tissue.A relatively soft gel-like tissue.

White matterWhite matterMyelinated nervous fibers and oligodendrocytes Myelinated nervous fibers and oligodendrocytes

Gray matterGray matterNeuronal cell bodiesNeuronal cell bodiesdendritesdendritesInitial segmentInitial segmentGlial cellsGlial cells

1. Cerebrum 1. Cerebrum

The gray matter forms cortex, the The gray matter forms cortex, the white matter forms medulla.white matter forms medulla.

Cerebral cortex has six layers of cellsCerebral cortex has six layers of cells

Sensory inputs first Sensory inputs first activate neurons in layer activate neurons in layer 4, which propagate the 4, which propagate the excitement up to layer excitement up to layer 2,3, and down to layer 5,62,3, and down to layer 5,6

Out molecular layerOut molecular layer

Purkinje cells layerPurkinje cells layer

Inner granular layerInner granular layer

2. Cerebellar cortex has 3 layers2. Cerebellar cortex has 3 layers

Purkinje cells are the efferent neurons

Mossy and climbing fibers are afferent fibers

3. Spinal cord3. Spinal cord

DH: sensory fibers form dorsal root

VH: motor neurons

4. Connective tissue of the CNS4. Connective tissue of the CNS

MeningesMeningesConnective tissue encConnective tissue encase the skull and the vase the skull and the vertebral columnertebral column

Dura materDura materArachnoidArachnoidPia materPia mater

The region between thThe region between the arachnoid and pia me arachnoid and pia mater is filled with CSFater is filled with CSF

5. Blood-brain barrier (BBB)5. Blood-brain barrier (BBB)

Prevents the passage of some substances, such as chemical and bacterial toxin matter, from the blood to nerve tissue

Response of neurons to injuryResponse of neurons to injury

SummarySummary

The PNSThe PNSNerve fibers, ganglia, nerve endingNerve fibers, ganglia, nerve endingAutonomic nerve systemAutonomic nerve system The CNSThe CNSSpinal cordSpinal cordCerebrumCerebrumCerebellumCerebellumMeninges Meninges

QuestionsQuestions List differences between the Central List differences between the Central

and Peripheral nervous systems.and Peripheral nervous systems. List difference between the somatic List difference between the somatic

and autonomic nervous systems  and autonomic nervous systems