Chapter 12

The Central Nervous System:The Brain and Spinal Cord

J.F. Thompson, Ph.D. & J.R. Schiller, Ph.D. & G. Pitts, Ph.D..

The Brain General

100 billion neurons

about 1.6 kg in males/1.45 kg in females proportional to body size

divided into hemispheres and lobes

its size is not representative of intelligence

complexity dictates processing power

Major Subdivisions of the Brain

Cerebral hemispheres

Diencephalon thalamus hypothalamus epithalamus

Brain stem midbrain pons medulla oblongata

Cerebellum

Distribution of Gray and White Matter

Gray matter: mostly unmyelinated processes and neuron cell bodies

White matter: myelinated fiber tracts cerebrum & cerebellum

gray matter mostly superficial (cortex)

white matter deep brain stem

variable spinal cord

white matter superficial gray matter deep

Brain Ventricles

Fluid filled spaces in brain 2 lateral ventricles

C-shaped chambers located deep in cerebral hemispheres

connected to 3rd ventricle

3rd ventricle a slit between and inferior to the

right and left halves of thalamus connects to lateral ventricles connects to 4th ventricle

4th ventricle lies between brain stem and

cerebellum connects to central canal of

spinal cord

Cerebral Hemispheres of Brain ~80% of the brain’s

mass During development,

gray matter grows faster than white matter gyrus - elevated ridges sulcus - shallow grooves fissure - deep grooves that

separate major regions Longitudinal fissure -

separates R and L hemispheres

Transverse fissure - separates cortex from cerebellum

Cerebral Lobes (5/hemisphere) Frontal, parietal,

temporal, occipital lobes Central sulcus separates

frontal from parietal lobe precentral gyrus postcentral gyrus

Lateral sulcus separates frontal from temporal lobe

Parieto-occipital sulcus separates parietal from occipital lobe

Insula: deep to portions of the temporal, parietal, and frontal lobes

Cerebral Cortex ~40% of brain’s mass Only 2-4 mm thick Center of

consciousness Contains neuron cell

bodies, dendrites, unmyelinated axons, glial cells

Folds greatly increase its surface area

A rich capillary blood supply is nearby

Cortex: General Functional OrganizationThree types of activity (areas)

motor sensory association

Each hemisphere primarily controls the opposite side of the body

Although roughly equal in structure, the hemispheres are not equal in function

No functional area of the brain works alone

Consciousness involves all areas of the brain

Primary motor cortex (4*) [* Brodmann areas] precentral gyrus of frontal lobe primarily involved in voluntary motor control with more

area devoted to skilled muscles (e.g., controls fingers, face)

Motor Areas of the Cerebral Cortex

Map of the Primary Motor Cortex Motor homunculus – shows

the locations on the precentral gyrus which control the skeletal muscles of each body region

The “size” of the illustrated body part indicates the number of neurons dedicated to that region

Control is contralateral

Note: areas of specialization for communication (large size of tongue, face) and manipulation (hands)

Motor Areas of the Cerebral Cortex

Premotor cortex Anterior to the

primary motor cortex

Involved in learned repetitious or patterned movements, e.g., playing a piano, typing

Also important in planning movements

Homeostatic Imbalance of Motor Cortex

Damage to the primary motor cortex effects the opposite side of body, e.g., stroke, trauma only voluntary control of skeletal muscle is lost reflexes remain -- controlled by the spinal cord

Damage to the premotor cortex loss of programmed motor skills muscle strength and the ability to perform

tasks remain one can still make finger movements to type, etc. not automatic

need to re-learn fine motor control

Motor Areas of the Cerebral Cortex

Language areas (Broca's area, 44, 45) only found in one hemisphere - left? a motor center for speech, controlling the muscles of the

tongue, throat, and lips also involved in planning some voluntary motor activities

Frontal eye field (8) - voluntary movements of eyes

Broca's areaBroca's area

Sensory Areas of the Cerebral Cortex

Primary somatosensory area Receives inputs directly from peripheral somatic sensory

receptors Localizes points of the body where sensations originate

primary areas are directly wired to the peripheral sensory receptors or motor effectorssecondary areas receive input from primary areas

Note:

Sensory Areas of the Cerebral Cortex

Primary somatosensory area distribution of input areas for cutaneous sensationscutaneous sensations spatial discriminationspatial discrimination - identifies the areas of the

body being stimulated

Motor Sensory

Compare motor and sensory homunculi:

Somatosensory association area Gets input from primary somatosensory association

area Integrates and analyzes information relative to size,

texture for identification of objects Uses memories and experiences for object

identification without visual input

Sensory Areas of the Cerebral Cortex

Posterior to the primary somatosensory area

Sensory Areas of the Cerebral Cortex

Visual area Medial surface of occipital lobe Impulses from the eyes are routed through the thalamus

Sensory Areas: Visual Cortex Sensory fibers cross over

to the opposite side -- 75%/25% at the optic chiasm lateral geniculate nucleus

(visual area) of the thalamus

occipital lobe primary sensory area association areas

Processing different areas for

different functions monocular vs binocular color, form, movement

Motion Aftereffect

Pinwheel

Stare directly into the center of the pinwheel for 60 seconds. Then immediately look away from the screen and at the back of your hand. Try looking at other things in the immediately vicinity as well!

Color Afterimage

Stare directly at the center of the next screen for 60 seconds.

+

+

What did you see?

Let’s repeat it.

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green red

yellow blue

Reviews of Neural Processing Different levels

Neuron to neuron communication

Specific hardwired pathways route information in predictable directions to specific locations

Association areas permit integration and interpretation of different types of sensory information

Motor areas issue appropriate commands to effector organs

Sensory Cortex: Auditory Area Superior part of the temporal lobe Primary auditory cortex (anterior arrow) for pitch,

rhythm, loudness Auditory association area (posterior arrow)

identifies/perceives sounds using memories as references

Sensory Cortex: Olfactory Cortex

Located above the orbits and in the medial portion of the temporal lobes

Conscious awareness of different smells

Multimodal Association Areas Anterior association area (prefrontal cortex)

anterior frontal lobe intellect, complex learning, recall and personality judgement, & planning matures slowly – influenced by environment

Frontal Lobotomy

sever the frontal lobes from the rest of the brain stops all strong emotional reactions once a popular medical/psychiatric procedure with a

long history obsolete: patients had problems with planning and

performing socially appropriate behaviors despite seeming to know what those behaviors would be

films: Frances and One Flew Over the Cuckoo’s Nest

1500’s

1950’s

Multimodal Association Areas Posterior association area

Temporal, parietal and occipital lobes Pattern recognition, localizing position Receives input from motor and other sensory association areas and

interprets it dropping an acid bottle (sound, sight, touch, smell, memory, learning) many sensory inputs, but the dominant feeling is of danger

Multimodal Association Areas Limbic association area

Cingulate and parahippocampal gyri, & hippocampus Provides emotional impact and sense of danger

Association: Language Areas Wernicke’s area - involved in pronouncing and

interpreting words Broca’s area - speech production lateral prefrontal cortex - language

comprehension, word analysis lateral, ventral temporal lobe - auditory, visual

aspects (naming objects, reading) the right side is more

involved in body language

Brain Lateralization both hemispheres participate in every activity,

but one hemisphere is dominant for most activities

e.g.: the left hemisphere is dominant for language skills in most people (90%)

the left is also dominant for math abilities and logic

the right hemisphere is usually dominant for “creative” skills: visual-spatial skills intuition emotion appreciation of art and music

most left-hemisphere-dominant people are right-handed

Brain Lateralization (or Not)

Hemispheric dominance is reversed or lacking in 10% of people

Most right-hemisphere-dominant people are left-handed and male

Equal hemispheric function may result in ambidexterity and/or dyslexia

Beware of the many “pop psychology” interpretations of the significance and meaning of hemispheric dominance

Cerebral White Matter

Myelinated fibers provide 3 types of connections within the CNS: commissural fibers

connect the hemispheres (right left)

ex: corpus callosum association fibers –

connect neurons within one hemisphere

projection fibers connect cerebral

hemispheres to other parts of the CNS

ex: internal capsule

Deep Cerebral Gray Matter: Basal Nuclei

Diffuse masses of gray matter deep within the cerebral hemispheres

Involved in regulating slow, sustained motor movements – ex: arm swinging

Also inhibit unnecessary movements (stabilize and smooth primary movements)

this area is affected in Parkinson’s disease

results in tremors and slow, unsteady movements

Brain Regions: Diencephalon

Composed of the thalamus, hypothalamus, and epithalamus

Surrounded by the cerebral hemispheres

Encloses the third ventricle

An egg shaped collection of nuclei serving as major “switching station” as impulses transfer from one neuron to the next

Forms the lateral walls of the third ventricle

Receives input from: all ascending pathways afferent impulses from all

senses except smell

Processes sensory information

crude recognition of sensation (cerebral processing required for precise localization and conscious awareness)

Thalamus (“Gateway” to the Cortex)

Hypothalamus (below Thalamus)

Forms the bottom of the third ventricle many nuclei infundibulum – the

stalk connecting the hypothalamus and pituitary gland

Pituitary gland endocrine gland – “the

master gland” releases its several

hormones in response to chemical regulation factors from the hypothalamus

Functions of the Hypothalamus

1. Autonomic Nervous System (visceral) control center – important in homeostasis

2. a center for emotional responses and behaviors

3. body temperature regulation4. regulation of food intake5. regulation of water balance and thirst6. regulation of sleep-wake cycles7. controls many endocrine system functions

neuroendocrine feedback control

Epithalamus (upon the Thalamus)

Dorsal portion of the diencephalon

Pineal gland (body) melatonin involved in sleep-

wake cycles Location of one of

the choroid plexus sites for production of cerebrospinal fluid (CSF)

Brain Regions: Brain Stem

midbrain

pons

medulla

Composed of the midbrain, pons and medulla

Involved in automatic, unconscious behaviors needed for survival

Provides pathways (fiber tracts) for neurons which are communicating up or down

Brain Stem: Midbrain Pons to the lower

portion of the diencephalon with the cerebral aqueduct passing through it

Main connecting routes for all parts of the brain and spinal cord

Connections between the cerebellum and the brainstem (cerebellar peduncles)

Brain Stem: Pons

above the medulla and anterior to the cerebellum

contains both gray matter nuclei and white fibers tracts

primarily conduction pathways

site of origin for several cranial nerves

cerebral peduncles

Brain Stem: Medulla Oblongata most inferior part of the

brain; merges into the spinal cord inferiorly

involved in maintaining internal homeostasis cardiovascular center respiratory center other centers for:

vomiting hiccuping swallowing coughing sneezing

Brain Regions: Cerebellum Second-largest brain

region (cerebellum = “small brain”)

Separated from the cerebrum by the transverse fissure

Its surface is the cerebellar cortex (gray matter) with folds (folia)folia); its white matter fiber tracts are located in the interior (arbor arbor vitaevitae = “tree of life”)

Cerebellar Structure and Function

Shaped like a butterfly central vermis (“worm”) cerebellar hemispheres

Functions to compare an intended movement (directed from the cortex) with what movement is actually happening

Constantly receiving sensory input from muscle, tendon, and joint proprioceptors, and visual and equilibrium receptors

Homunculi: maps of the functional areas

arbor vitae

Cerebellar Structure and Function

Purkinje neurons play a major role in control over the refinement of motor activities initiated by the frontal motor cortex

Functional Systems of the Brain Limbic System

encircles the brain stem the “emotional” center different regions of gray matter, including part

of the hypothalamus and the olfactory bulbs

Limbic System (cont.) Functions in emotional aspects of behavior

related to survival Also functions with the cerebrum in memory

olfactory centers are near the limbic system individuals, objects and experiences which initiate

strong emotional responses or are associated with smells are committed to memory more easily

Memory impairment results from damage to the limbic system

Also associated with pleasure and pain electrical stimulation elicits different responses includes defensive posturing (rage); others inspire

timidity

Brain Systems: Reticular Formation

Gray matter (nuclei) distributed within the medulla, pons, and midbrain

Axonal connections to many other areas of the brain

Structural and functional areas sensory, integrative

and motor functions receives input from

higher centers for skeletal muscle actions

Reticular Formation Reticular Activating

System functions to alert the cerebral

cortex to important incoming signals

filters signal “noise” = repetitive stimuli (LSD interferes with this)

e.g., studying in a noisy room maintenance of consciousness

and waking from sleep (sudden stimuli)

sends a constant stream of information to the cortex, maintaining arousal

the RAS is inhibited by sleep centers in the hypothalamus

the RAS is depressed by alcohol, sleep-inducing drugs (hypnotics) and anti-anxiety drugs

LSD

Protection of the Brain Soft tissue which needs to be protected Several different protective mechanisms

scalp hair to prevent sunstroke? bones – the cranium (“brain case”) of the skull meninges

three connective tissue membranes wrapping the CNS

cerebrospinal fluid (CSF) a fluid “shock absorber” which cushions and

nourishes the brain blood-brain barrier

the physical and physiological separation of the CNS from the bloodstream

Functions of the Meninges Covers and protects

brain and spinal cord

Protect blood vessels and enclose venous sinuses

Confine the cerebrospinal fluid in the subarachnoid space

Form major connective tissue partitions for brain regions within skull falx cerebri, falx cerebelli,

tentorium cerebelli

Meninges: Dura Mater Outermost layer Dense, irregular fibrous connective tissue Strong, protective wall around the brain

and spinal cord (dura mater = “tough/hard mother”)

Meninges: Arachnoid Membrane

Loose connective tissue layer deep to the dura mater Subdural space

separates the arachnoid from the dura contains interstitial fluid

Arachnoid villi extend into the subdural space CSF is reabsorbed back into the blood here

Subarachnoid space separates arachnoid from pia mater contains CSF

CSF

Meninges: Pia mater Deepest layer A thin, tight transparent fibrous connective

tissue supporting a network of many tiny blood vessels

Pia mater extends into the sulci and follows the large blood vessels into the brain

Pia mater = “gentle/little mother”

Protection of the Brain: Cerebrospinal Fluid

CSF protects against chemical & physical injury; it serves as a second circulatory system and nourishes the CNS

Found in the four ventricles and subarachnoid space

80-150 ml of CSF is normal for an adult CSF composition differs slightly from plasma Clear, colorless plasma filtrate containing:

H2O, glucose, other nutrients, proteins, lactic acid, urea cations (Na+, K+, Ca2+, Mg2+) anions (Cl-, HCO3

-) some lymphocytes (white blood cells)

Formed by the choroid plexuses; reabsorbed by the arachnoid villi and returned to the plasma

Functions of Cerebrospinal Fluid

Mechanical protection shock absorbing fluid the brain “floats” in this fluid

Chemical protection provides a constant chemical environment the pH of the CSF is important in the control

of breathing CSF composition is important for regulating

cerebral blood flow Circulation for the exchange of nutrients

and waste products between the blood and nervous tissue

Cerebrospinal Fluid: Choroid Plexuses

Special capillary networks in certain places in the ventricular walls

Ependymal cells Fluid from plasma

passes through the ependymal cells at choroid plexuses

cells have ion pumps modify CSF regulate and maintain

the blood-brain barrier Protect the brain from

harmful substances in the blood

Blood-Brain Barrier Penetration of molecules from the blood

into the brain is regulated by: tight junctions between capillary cells thick basal lamina (connective tissue layer) astrocytes pressed against capillaries

The barrier is a selective membrane some substances, particularly if lipid-soluble,

pass easily from blood to the brain (water, glucose, O2, CO2, alcohol, caffeine, nicotine, heroin, most anesthetics)

most charged ions do not pass easily proteins and most antibiotics do not pass at

all

Blood-Brain Barrier

Permeability is variable depending on the site choroid plexus – CSF production vomiting center in brain stem - monitors the

blood for toxic molecules and poisons hypothalamus

has no blood-brain barrier monitors blood composition for water balance,

temperature, pH, osmolarity and many other homeostatic metabolic functions

Homeostatic Imbalances of the Brain

Traumatic Brain Injuries concussion

a blow to head the skull stops, but the brain keeps moving the brain bounces off the inside of the skull

possibly, there is no visible external damage a variety of cognitive problems follow

contusion breaks in small vessels, some bleeding, visible

bruising effect depends on the location

laceration tearing of the brain knife and gunshot wounds, other major traumas

Homeostatic Imbalances of the Brain

Traumatic Brain Injuries (cont.) epidural or subdural or subarachnoid hemorrhage

bleeding from ruptured vessels into that space a person is normal immediately after the injury, but

deteriorates as the bleeding continues hemorrhage increases intracranial pressure effects vary with the location of the hematoma surgical intervention

drill holes remove clots install drainage tubes

subarachnoid hemorrhage

Homeostatic Imbalances of the Brain

Cerebrovascular Accidents (CVA’s) Stroke

third leading cause of death in the United States ischemia anemia caused by reduced or blocked blood

flow) hemorrhages and blood clots increase intracranial

pressure brain tissue dies (infarct) risk factors: high blood pressure, high cholesterol,

heart disease, narrowed carotid arteries, diabetes, smoking, obesity, excessive alcohol intake

Transient ischemic attack (TIA/ministroke) may last minutes flow is reduced and brain tissue suffers temporarily blood flow is re-established

Homeostatic Imbalances of the Brain

Degenerative brain diseases Alzheimer’s disease

about 11% of population over age 65, 4 million people suffer, 100,000 die annually; hereditary component

widespread cognitive deficits - (short term) memory loss, shortened attention span and disorientation, loss of language skills

death from secondary causes, e.g., due to being bedridden

diagnosis is difficult since there is no definitive test; only after death can it be confirmed by autopsy:

significant loss of neurons in specific regions abnormal proteins are deposited in brain tissue tangled nerve masses

generally, the damage is limited to the cerebral cortex

Alzheimer’sDisease

Homeostatic Imbalances of Brain

Degenerative brain diseases (cont.) Parkinson’s disease

progressive disorder of the CNS which typically affects victims at age 60 or so

cause(s) unknown; hereditary component sometimes

characterized by degeneration of dopamine-releasing neurons

characterized by tremor (shaking) and rigidity (continuous contraction)

motor performance impaired by bradykinesia (slow motion) and hypokinesia (reduced range of motion)

treatments try to increase dopamine and decrease ACh with therapeutic drugs or by experimental implantation of fetal brain cells

Homeostatic Imbalances of Brain

Traumatic brain diseases Cerebral Palsy

damage to motor areas of brain during fetal life, at birth, or during infancy, usually transient O2

deprivation poor control and coordination of voluntary muscle

activities but usually little impact on intellect irreversible, but not progressive 70% of victims appear to be mentally retarded

often due to their inability to hear or speak well generally, they are more aware and understanding of their

situation and surroundings than they appear

Concussion, Contusion, Sudural or Subarachnoid Hemorrhage, Cerebral Edema, CVAs

Not Everybody is an Einstein!

The Spinal Cord Spinal cord is located within the vertebral

column Passes through the vertebral foramina

Anatomy and Protection of Spinal Cord Bone of vertebral arch CSF Spinal meninges

dura mater, arachnoid, pia mater

meninges cover spinal cord and spinal nerves

epidural space space between the dura

mater and wall of the vertebral canal

filled with adipose and loose connective tissue

nerves exit through intervertebral foramina

External Spinal Cord Anatomy Roughly cylindrical but slightly

flattened dorsi-ventrally

From foramen magnum to second lumbar vertebra (L2)

About 2 cm wide and 42-45 cm long

Cervical enlargementCervical enlargement and lumbar enlargementlumbar enlargement are conspicuous cervical enlargement - nerves

for upper extremities lumbar enlargement - nerves for

lower extremities

External Anatomy (cont.)

Spinal cord tapers, ends in the conus medullarisconus medullaris between L1 and L2

Filum terminaleFilum terminale (pia mater) extends from the conus to attach the spinal cord to the coccyx

Some nerves exit the vertebral column below the level of their exit from the spinal cord

Cauda equinaCauda equina – “horse's tail” at end of the cord are the last few pairs of spinal nerves

Cross-Sectional Anatomy of the Spinal Cord

“H” shaped gray matter – “butterfly” surrounded by white matter

Anterior median fissure Posterior medial sulcus Gray commissure forms

the cross bar of the 'H' Central canal

small space in middle of gray commissure

extends length of spinal cord

at superior end continuous with the 4th ventricle

contains CSF

Cross-Sectional Anatomy of the Spinal Cord

Anterior to the gray commissure is the anterior white commissure

The gray matter of the spinal cord is divided into horns

closer to front are the anterior (ventral) gray horns

closer to back are the posterior (dorsal) gray horns

lateral gray horns between anterior and

posterior horns present only in thoracic, upper

lumbar, and sacral segments gray matter also has some

named nuclei

dorsal

lateral

ventral

Gray Matter Anterior horn – visceral & somatic motor neurons Ventral root - efferent (motor) nerves to skeletal

muscles and to the visceral organs (effectors) Posterior horn – somatic & visceral sensory

neurons Dorsal root - afferent nerves from skin, skeletal

muscles, connective tissues, visceral organs

Gray matter In Chapter 13 we will examine the basic

connections in the spinal cord, such as the reflex arc

The simplest connection is a two cell reflex connecting a sensory neuron directly to a motor neuron

More complicated reflexes have one or more intervening interneurons

White Matter of the Spinal Cord Conduction tracts in the spinal

cord Named by

where each is coming from where each is going to

White Matter of the Spinal Cord Fasciculi cuneatus and gracilis - fine touch and pressure Lateral and anterior spinothalamic tracts - pain,

temperature, deep pressure and coarse touch Two paths for similar functions

The Spinal Cord

In Chapter 13 we will examine the routes and means by which the Central Nervous Connection interacts with and controls the rest of the body.

Those routes form the Peripheral Nervous System.

End Chapter 12

Some slides of specific spinal cord tracts appearafter this slide. You are not responsible for those specific tracts for the exam.

Specific and Posterior Spinocerebellar Tracts

• Specific ascending pathways within the fasciculus gracilis and fasciculus cuneatus tracts, and their continuation in the medial lemniscal tracts

• The posterior spinocerebellar tract

Nonspecific Ascending Pathway

Nonspecific pathway for pain, temperature, and crude touch within the lateral spinothalamic tract

The Direct (Pyramidal) System Direct pathways originate

with the pyramidal neurons in the precentral gyri

Impulses are sent through the corticospinal tracts and synapse in the anterior horn

Stimulation of anterior horn neurons activates skeletal muscles

Parts of the direct pathway, called corticobulbar tracts, innervate cranial nerve nuclei

The direct pathway regulates fast and fine (skilled) movements

Indirect (Extrapyramidal) System Includes the brain stem, motor

nuclei, and all motor pathways not part of the pyramidal system

This system includes the rubrospinal, vestibulospinal, reticulospinal, and tectospinal tracts

These motor pathways are complex and multisynaptic, and regulate: Axial muscles that maintain

balance and posture Muscles controlling coarse

movements of the proximal portions of limbs

Head, neck, and eye movement

Extrapyramidal (Multineuronal) Pathways

Reticulospinal tracts – maintain balance

Rubrospinal tracts – control flexor muscles

Superior colliculi and tectospinal tracts mediate head movements

End Chapter 12