Chapter 5

The Central Nervous System

V edit. Pg. 133-183

VI edit. Pg. 131-179

VII edit. Pg. 133-181

The endocrine system and the nervous

system are the main regulatory

systems of the body

Nervous System

(wired & specific)

Endocrine System

(wireless & diffuse)

Coordinate rapid,

precise responses

Control body activities

over long periods

Generate signals that

propagate rapidly

(action potentials)

Generate slowly acting

signals (hormones)

Target organs:

skeletal muscles,

heart, glands

Target organs: visceral

organs, heart, smooth

muscles, glands

Organization of the Nervous System

Nervous TissueNervous tissues are found in the brain, spinal cord,

and nerves

Main components:

Nerve cells (conduct nerve impulses)

Neuroglia (glial cells, support and nourish the

neurons)

Functional Classification of Neurons

Sensory neurons

(afferent)

Interneurons

Motor neurons

(efferent)

The spinal cord circuit as an example of

a neuronal networkCell body of

efferent neuron

Cell body of

afferent neuron

Efferent fiber

From receptors

To effectors

Spinal nerve

White matter Gray matter

Interneuron

Dorsal root

Dorsal root

ganglion

Ventral root

Classification of Glial Cells(Provide protection and nourishment to nerve cells)

Astrocytes

Oligodendrocytes

Microglia

Ependymal cells

Function of Neuroglia (Glial Cells)Astrocytes: Star-like glial cells, found between neurons and blood

vessels.

Function: nourishment of neurons, support neurons and isolate group of

neurons into nuclei, buffer potassium ions and neurotransmitter from

the extracellular space, scaffold for brain development, synapse

formation and maintenance

Oligodendrocytes (Schwann cells in PNS): small glial cells with fewer

processes.

Function: insulation of axon with myelin sheath, guide the outgrowth of

axons

Function of Neuroglia (Glial Cells)

Microglia: Small glial cells, immune defense cells in CNS.

Function: removal of debris after injury

Ependymal cells: Ciliated cuboidal or elongated cells usually connected

through gap junctions. Found in the inner lining of the central canal of

the spinal cord, the lining of the brain ventricles and the choroid

plexus.

Function: form part of the blood-brain barrier (BBB), control transport of

substances into the cerebrospinal fluid, stem cells

Defense Mechanisms of Nerve Tissue

1) Skull and vertebral column

2) Meninges

3) Cerebrospinal fluid

4) Blood-brain barrier

The Meninges

Three layers of connective tissue that surround

and protect nerve tissue

Dura: toughest layer, consist of

connective tissue and

collagen fibers. Loosely

surrounds the brain and

spinal cord

Arachnoid: richly vascularized

layer

Subarachnoid space: contains

the cerebrospinal fluid (CSF)

Pia: closely adheres to brain and

spinal cord tissue, richly

vascularized

The cerebrospinal fluid (CSF)

surrounds and cushion the brain and

spinal cord

The cerebrospinal fluid is formed in the

choroid plexus and flow through the

ventricular system

The cerebrospinal fluid is reabsorbed in

the arachnoid villi

The CSF contains a higher

concentration of Na+ ions and less K+

than blood plasma

The Brain Ventricles

Aqueduct of

Sylvius

The Blood-Brain BarrierConsist of tightly packed endothelial cells that prevent

the unregulated flow of substances into the CSF and

the brain

Organization of the CNS

Cerebrum

Cerebellum

Diencephalon

Brain Stem

Spinal Cord

Structure and Function of Brain

Components

The Cerebral

Cortex

Central Sulcus

Convolutions

The Cerebral Cortex

Spinal Cord Cross Section

Grey matter White matter

The Cerebral Cortex

Layers of the Cerebral Cortex

© Brooks/Cole - Thomson Learning

Functional Areas of the Cerebral

Cortex: Cortical Lobes

Functional Organization of the Cerebral

Cortex

Somatotopic MapsCortical areas that process information from specific areas of the

body

Left

hemisphere

Cross•-•sectional view

Temporal lobe

Sensory homunculus

Somatotopic Maps

Front

Left

hemisphere

Primary

motor

cortex

Top

view

Somato•-

sensory

cortex

Right

hemisphere

Frontal

lobe

Centralsulcus

Parietal

Occipital lobe

Back

Somatotopic MapsDifferent areas of the body are represented differently in the brain-

somatotopic maps

The area of representation is determined by the amount of

sensory/motor innervation on contralateral side of the body

Lefthemisphere

Cross•-•sectional view

Temporal lobe

Motor homunculus

Somatotopic Maps

Use-dependent competition

Plasticity (remodeling ability of the brain in response to changes in demand)

Lefthemisphere

Cross•-•sectional view

Temporal lobe

Motor homunculus

Control of Language

Control of Language

Association AreasBrain areas responsible for integration and processing of complex

information

Association AreasFunctional linking of various brain areas

Sensory input

Primary sensory areas

(somatosensory, visual,

auditory cortices)

Higher sensory areas

Association areas

Higher motor areas

Primary motor areas

Motor output

Basal Nuclei

Thalamus & Hypothalamus

Basal Nuclei(inhibit muscular tone, control of motor activity, control of slow

movements)

© Brooks/Cole - Thomson Learning

Hypothalamus & Pituitary GlandCoordinate homeostatic functions in the body

© Brooks/Cole - Thomson Learning

Hypothalamus & Pituitary Gland

Function:

Body temperature

Urine output

Food intake

Uterine contractions

Milk production

Smooth and

cardiac muscles

CerebellumInvolved in balance maintenance, planning of voluntary

movements, motor skills learning

© Brooks/Cole - Thomson Learning

CerebellumInvolved in balance maintenance and planning of voluntary

movements

Unfolded

Regulation of

muscle tone,

coordination of

skilled voluntary

movement

Planning and

initiation of

voluntary activity

Maintenance of

balance, control

of eye movements

Vestibulocerebellum

Spinocerebellum

Cerebrocerebelum

Organization of the CNS: Brain Stem

Cerebrum

Cerebellum

Diencephalon

Brain Stem

Spinal Cord

Brain Stem

Brain Stem

Function:

1) Origin of 12 cranial nerves

innervating head, neck and

portions of the thoracic cavity http://www.wisc-online.com/objects/index.asp?objID=AP11504

2) Control of visceral functions

(vegetative): heart rate,

respiration, digestive activity

3) Control of arousal states via

the reticular formation

4) Basic reflexes: pupillary,

tympanic, oculocephalic

reflexes http://library.med.utah.edu/kw/animations/hyperbrain/oculo_reflex/oculocephalic2.html

Brain Stem and Neuronal Pathways

Somatosensory

area

of cerebral

cortex

Thalamus

Cerebral

cortex

Midbrain

Cerebellum

PonsVentral

spinocerebellar

tract

Primary

motor

cortex

Medulla

Fasciculus

cuneatus

Ventral

corticospinal

tract

Lateral

corticospinal

tract

Pressure receptor in skin

Muscle

stretch

receptor

Spinal cord

Spinal cord

Spinal cord

•1

•2•3

•4

•5

•6

Ascending tracts Descending tracts

Organization of the CNS: Spinal cord

Cerebrum

Cerebellum

Diencephalon

Brain Stem

Spinal Cord

The Spinal Cord

The Meninges

The Meninges

Functional Organization of the Spinal

Cord

Gray Matter Regions

Spinal Nerves: Mixed nerves

Function of the Spinal Cord

Conduct information to and from the brain

Control of motor functions

Spinal reflex

Spinal Cord Pathways

Somatosensory

area

of cerebral

cortex

Thalamus

Cerebral

cortex

Midbrain

Cerebellum

PonsVentral

spinocerebellar

tract

Primary

motor

cortex

Medulla

Fasciculus

cuneatus

Ventral

corticospinal

tract

Lateral

corticospinal

tract

Pressure receptor in skin

Muscle

stretch

receptor

Spinal cord

Spinal cord

Spinal cord

•1

•2•3

•4

•5

•6

Ascending tracts Descending tracts

Ascending Tracts

Fasciculus gracilis

and fasciculus

cuneatus

Spinothalamic

tract

Spinocerebellar

tract

Ascending axons leave

spinal cord at dorsal

funiculi

Ascending axons

leave spinal cord at

lateral and dorsal

funiculi

Ascending axons

leave spinal cord at

lateral funiculi

Axons cross to

contralateral site at the

medulla oblongata

Axons cross to

contralateral site at

the spinal cord

Dorsal tract: no

crossing of

ascending axons.

Ventral tract: cross at

the level of the

medulla

Conduct sensory

information about: touch

(vibration), pressure and

body movements

Conduct sensory

information about:

pain, temperature

and touch (crude)

Involve in motor

coordination

Descending Tracts

Corticospinal tract

(or Pyramidal tract)

Reticulospinal

tract

Rubrospinal tract

Axons cross to

contralateral site at the

medulla oblongata

Some axons cross

to contralateral site

but other remain

uncrossed

Axons cross to

contralateral site at

the cortex

Descending axons

enter spinal cord

segment at lateral and

ventral funiculi

Descending axons

enter spinal cord

segment at lateral

and ventral funiculi

Descending axons

enter spinal cord

segment at lateral

funiculi

Control of`

voluntary movements

Regulate muscle

tone and sweat

gland activity

Muscle coordination

and posture control

Neuronal Circuit and Spinal ReflexA reflex is an automatic response to an external stimuli that occurs

without any conscious effort

Central

nervous system

(spinal cord)

Peripheral

nervous system

Axon

terminals

Cell

bodyAfferent neuron

Central

axonPeripheral axon

(afferent fiber) Receptor

Interneuron

Efferent neuron*

Effector organ

(muscle or gland)Axon

(efferent fiber)

Axon

terminals

* Efferent autonomic nerve pathways consist of a two •-•neuron chain between

the CNS and the effector organ.

Cell

body

Muscle

spindles

Muscle SpindleSensory receptors inside skeletal muscles that sense changes in

length

Reflex Arc

Receptor

Afferent neuron

Interneuron

Efferent neuron

Effector muscle

Centralnervous system(spinal cord)

Peripheralnervous system

Axonterminals

Cellbody

Afferent neuron

Centralaxon

Peripheral axon(afferent fiber) Receptor

Interneuron

Efferent neuron*

Effector organ(muscle or gland)

Axon(efferent fiber)

Axonterminals

* Efferent autonomic nerve pathways consist of a two•-•neuron chain betweenthe CNS and the effector organ.

Cellbody

http://www.brainviews.com/abFiles/AniPatellar.htm

Patellar tendon

Extensor muscle of knee(quadriceps femoris)

Musclespindle

Alpha motorneuron

Monosynaptic Reflex:

The Knee-Jerk Reflex

Polysynaptic Reflex:

The Withdrawal Reflex

The Crossed Withdrawal Reflex