Introduction to CNSIntroduction to CNS

The nervous system consists of The nervous system consists of

• CNS made up of brain and spinal CNS made up of brain and spinal cordcord

• PNS consisting of peripheral nerves PNS consisting of peripheral nerves and gangliaand ganglia

Brain DescriptionBrain Description

• Brain weighs 3 to 3.5 poundsBrain weighs 3 to 3.5 pounds

• Major portions of the brain--brainstem, Major portions of the brain--brainstem, cerebrum, and cerebellumcerebrum, and cerebellum– cerebrum is 83% of brain volume; cerebellum cerebrum is 83% of brain volume; cerebellum

contains 50% of the neuronscontains 50% of the neurons

Longitudinal fissure separates 2 cerebral hemispheres.Longitudinal fissure separates 2 cerebral hemispheres.

Central sulcus separates frontal and parietal lobe.Central sulcus separates frontal and parietal lobe.

Cranial Meninges Cranial Meninges

Meninges of Vertebra & Meninges of Vertebra & Spinal CordSpinal Cord

•The massive cerebral hemispheres hide the other parts of the brain from view,

•Diencephalon: The largest part of the diencephalon is the thalamus; in fact, this is a paired structure.

•Basal ganglia: These large neuronal areas are found within the brain; its three parts are shown

•— the caudate nucleus (head and tail), the putamen, and the globus pallidus.

Brain VentriclesBrain Ventricles

Ventricles and Ventricles and Cerebrospinal FluidCerebrospinal Fluid• Internal chambers within the CNSInternal chambers within the CNS

– lateral ventricles found inside cerebral lateral ventricles found inside cerebral hemisphereshemispheres

– third ventricle is single vertical third ventricle is single vertical – cerebral aqueduct runs through midbraincerebral aqueduct runs through midbrain– fourth ventricle is small chamber between pons fourth ventricle is small chamber between pons

& cerebellum& cerebellum– central canal runs down through spinal cordcentral canal runs down through spinal cord

• Lined with ependymal cells and containing Lined with ependymal cells and containing choroid plexus of capillaries that produce CSFchoroid plexus of capillaries that produce CSF

Cerebrospinal FluidCerebrospinal Fluid• Clear liquid fills ventricles and canals & Clear liquid fills ventricles and canals &

bathes its external surface (in subarachnoid bathes its external surface (in subarachnoid space)space)

• Brain produces & absorbs about 500 ml/dayBrain produces & absorbs about 500 ml/day– filtration of blood through choroid plexusfiltration of blood through choroid plexus

• FunctionsFunctions– buoyancy -- floats brain so it neutrally buoyancy -- floats brain so it neutrally

buoyantbuoyant– protection -- cushions from hitting inside protection -- cushions from hitting inside

of skullof skull– chemical stability -- rinses away wasteschemical stability -- rinses away wastes

Flow of Cerebrospinal FluidFlow of Cerebrospinal Fluid

MidbrainMidbrain

• MesencephalonMesencephalon

• Central aqueductCentral aqueduct

• CN III and IVCN III and IV– eye movementeye movement

Medulla OblongataMedulla Oblongata

• Ascending & descending nerve tractsAscending & descending nerve tracts

• Nuclei of sensory & motor cranial Nuclei of sensory & motor cranial nerves (IX, X, XI, and XII)nerves (IX, X, XI, and XII)

• Cardiac center adjusts rate & force of heart beatCardiac center adjusts rate & force of heart beat

• Vasomotor center adjusts blood vessel diameterVasomotor center adjusts blood vessel diameter

• Respiratory centers control rate & depth of Respiratory centers control rate & depth of breathingbreathing

• Reflex centers for coughing, sneezing, gagging, Reflex centers for coughing, sneezing, gagging, swallowing, vomiting, salivation, sweating, swallowing, vomiting, salivation, sweating, movements of tongue & headmovements of tongue & head

Medulla and PonsMedulla and Pons

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PonsPons• Bulge in the brainstem, rostral to Bulge in the brainstem, rostral to

the medullathe medulla

• Ascending sensory tractsAscending sensory tracts

• Descending motor tractsDescending motor tracts

• Pathways in & out of cerebellumPathways in & out of cerebellum

• Nuclei concerned with sleep, hearing, Nuclei concerned with sleep, hearing, balance, taste, eye movements, facial balance, taste, eye movements, facial expression, facial sensation, respiration, expression, facial sensation, respiration, swallowing, bladder control & postureswallowing, bladder control & posture– cranial nerves V, VI, VII, and VIIIcranial nerves V, VI, VII, and VIII

CerebellumCerebellum

• Connected to brainstem by cerebellar pedunclesConnected to brainstem by cerebellar peduncles

• White matter (arbor vitae) visible in sagittal sectionWhite matter (arbor vitae) visible in sagittal section

• Sits atop the 4th ventricleSits atop the 4th ventricle

The Peripheral Nervous The Peripheral Nervous SystemSystem

• Nervous structures outside the brain Nervous structures outside the brain and spinal cordand spinal cord

• Nerves allow the CNS to receive Nerves allow the CNS to receive information and take actioninformation and take action

Functional Organization of Functional Organization of the PNSthe PNS

Figure 14.1

Basic Structural Basic Structural Components of the PNSComponents of the PNS• Sensory receptors – pick up stimuli from Sensory receptors – pick up stimuli from

inside or outside the bodyinside or outside the body

• Motor endings – axon terminals of motor Motor endings – axon terminals of motor neuronsneurons– Innervate effectors (muscle fibers and glands)Innervate effectors (muscle fibers and glands)

• Nerves and ganglia Nerves and ganglia – Nerves – bundles of peripheral axonsNerves – bundles of peripheral axons– Ganglia – clusters of peripheral neuronal cell Ganglia – clusters of peripheral neuronal cell

bodiesbodies

• On Old Olympic Towering Top On Old Olympic Towering Top  A Famous Vocal German A Famous Vocal German  Viewed Some HopsViewed Some Hops

Structural Organization of Structural Organization of PNS in Region of a Spinal PNS in Region of a Spinal NerveNerve

Figure 14.2