ANSWER THE ESSAYS AND THE BULLET (-) QUESTIONS

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APLECTURE20CentralNervousSystem-PartI.ppt

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Central Nervous System- Part I

Central Nervous System

overview of the brain

meninges, ventricles,
cerebrospinal fluid and
blood supply

hindbrain and midbrain

forebrain

integrative functions

the cranial nerves

Frontal lobe

Occipital lobe

Central sulcus

Longitudinal fissure

Parietal lobe

(a) Superior view

Cerebral

hemispheres

Directional Terms and Landmarks

rostral - toward the forehead

caudal - toward the spinal cord

brain weighs about 3.5 lb

three major portions of the brain -
Cerebrum- 83% of brain volume; cerebral hemispheres, gyri and sulci, longitudinal fissure, corpus callosum

Cerebellum-50% of the neurons; second largest brain region, located in posterior cranial fossa

Brainstem- diencephalon, midbrain, pons, and medulla oblongata

Brainstem

Cerebellum

Cerebrum

Spinal cord

Rostral

Caudal

Central sulcus

Lateral sulcus

Gyri

(b) Lateral view

Temporal lobe

Cerebrum

longitudinal fissure – deep groove that separates cerebral hemispheres

gyri - thick folds

sulci - shallow grooves

corpus callosum – thick

nerve bundle at bottom

of longitudinal fissure

that connects hemispheres

Frontal lobe

Occipital lobe

Central sulcus

Longitudinal fissure

Parietal lobe

(a) Superior view

Cerebral

hemispheres

Cerebellum

occupies posterior cranial fossa

marked by gyri, sulci, and fissures

about 10% of brain volume

contains over 50% of brain neurons

Brainstem

Cerebellum

Cerebrum

Spinal cord

Rostral

Caudal

Central sulcus

Lateral sulcus

Gyri

(b) Lateral view

Temporal lobe

Brainstem

brainstem – what remains of the brain if the cerebrum and cerebellum are removed

major components

diencephalon

midbrain

pons

medulla oblongata

Brainstem

Cerebellum

Cerebrum

Spinal cord

Rostral

Caudal

Central sulcus

Lateral sulcus

Gyri

(b) Lateral view

Temporal lobe

Median Section of the Brain

leaves

Thalamus

Hypothalamus

Frontal lobe

Corpus callosum

Cingulate gyrus

Optic chiasm

Pituitary gland

Mammillary body

Midbrain

Pons

Central sulcus

Parietal lobe

Parieto–occipital sulcus

Occipital lobe

Pineal gland

Habenula

Posterior commissure

Cerebral aqueduct

Fourth ventricle

Cerebellum

(a)

Epithalamus

commissure

Temporal lobe

Medulla

oblongata

gray matter – seat of neuron cell bodies, dendrites, & synapses
dull white color when fresh, due to little myelin
forms surface layer, cortex, over cerebrum & cerebellum
forms nuclei deep within brain

white matter - bundles of axons
lies deep to cortical gray matter, opposite relationship in the spinal cord
pearly white color from myelin around nerve fibers
composed of tracts, bundles of axons; connect brain parts, & spinal cord

Gray and White Matter

Meninges

meninges – 3 connective tissue membranes that envelop brain
lies between the nervous tissue and bone
dura mater, arachnoid mater, and pia mater
protect brain & provide structure for its arteries & veins

dura mater
in cranial cavity - 2 layers
outer periosteal- similar to periosteum cranial bones
inner meningeal – forms dural sac around spinal cord
cranial dura mater is pressed closely against cranial bones
folds inward to extend between parts of the brain

Meninges- continued

arachnoid mater and pia mater are similar to those in the spinal cord

arachnoid mater
transparent membrane over brain surface
subarachnoid space separates it from pia mater below
subdural space separates it from dura mater above

pia mater
very thin membrane that follows contours of brain
not usually visible without a microscope

Meninges of the Brain

Subdural space

Skull

Pia mater

Blood vessel

Dura mater:

Periosteal layer

Meningeal layer

Arachnoid mater

Brain:

Gray matter

White matter

Arachnoid villus

Subarachnoid

space

Superior sagittal

sinus

Falx cerebri

(in longitudinal

fissure only)

Meningitis-inflammation of the meninges

serious disease of infancy & childhood

caused by bacterial and virus invasion of the CNS

pia mater and arachnoid are most often affected

bacterial meningitis can cause swelling the brain, enlarging the ventricles, & hemorrhage

signs- high fever, stiff neck, drowsiness, & intense headache

diagnosed by examining the CSF for bacteria
lumbar puncture (spinal tap) draws fluid from subarachnoid space between two lumbar vertebrae

Brain Ventricles

Lateral ventricles

Central canal

Lateral aperture

Fourth ventricle

Third ventricle

Median aperture

(a) Lateral view

Caudal

Interventricular

foramen

Cerebral

aqueduct

Rostral

Lateral ventricle

Third ventricle

Cerebrum

Lateral aperture

Fourth ventricle

Median aperture

(b) Anterior view

Interventricular

foramen

Cerebral

aqueduct

two lateral ventricles – one in each cerebral hemisphere
third ventricle- narrow medial space beneath corpus callosum
fourth ventricle – small triangular chamber between pons &

cerebellum

choroid plexus – spongy mass of blood capillaries on the floor of each ventricle

ependyma – neuroglia lines the ventricles & covers choroid plexus
produces cerebrospinal fluid

Ventricles-four internal chambers within the brain

clear, colorless liquid filling CNS ventricles & canals
bathes its external surface

brain produces and absorbs 500 mL/day

production begins with the filtration of blood plasma through the capillaries of the brain
ependymal cells modify ionic content of CSF filtrate

Cerebrospinal Fluid (CSF)

buoyancy
allows brain to attain considerable size without being impaired by its own weight
if it rested heavily on floor of cranium, the pressure would kill the nervous tissue

protection
protects the brain from striking the cranium when head is jolted
shaken child syndrome & concussions do occur from severe jolting

chemical stability
flow of CSF removes metabolic wastes from nervous tissue & homeostatically regulates its chemical environment

Functions of CSF

Blood Supply to the Brain

brain is only 2% of adult body weight & receives 15% of blood
750 mL/min

Neurons- high demand for ATP, oxygen and glucose

10 s interruption of blood flow may cause loss of consciousness

1 – 2 minute interruption can cause significant impairment of neural function

4 minutes with out blood causes irreversible brain damage

Brain Barrier System- protects blood capillaries
throughout brain tissue

tight junctions form between endothelial cells of capillary walls

two points of entry must be guarded:
blood capillaries throughout the brain tissue
capillaries of the choroid plexus

highly permeable to water, glucose, & lipid-soluble substances

(O2, CO2, caffeine, & anesthetics)

slightly permeable to sodium, potassium, chloride, and the waste products urea and creatinine

obstacle for delivering medications (antibiotics & cancer drugs)

Hindbrain - Medulla Oblongata

begins at foramen magnum of skull

extends for about 3 cm rostrally and ends at a groove between the medulla and pons

slightly wider than spinal cord

leaves

Thalamus

Hypothalamus

Frontal lobe

Corpus callosum

Cingulate gyrus

Optic chiasm

Pituitary gland

Mammillary body

Midbrain

Pons

Central sulcus

Parietal lobe

Parieto–occipital sulcus

Occipital lobe

Pineal gland

Habenula

Posterior commissure

Cerebral aqueduct

Fourth ventricle

Cerebellum

(a)

Epithalamus

commissure

Temporal lobe

Medulla

oblongata

Posterolateral View of Brainstem

Diencephalon:

Midbrain:

Spinal cord

Pons

Optic tract

Fourth ventricle

(b) Posterolateral view

Regions of the brainstem

Midbrain

Diencephalon

Pons

Medulla oblongata

Medulla

oblongata

Hindbrain - Medulla Oblongata

cardiac center- adjusts rate and force of heart

vasomotor center-adjusts blood vessel diameter

respiratory centers- control rate & depth of breathing

reflex centers (for coughing, sneezing, gagging, swallowing, vomiting, salivation, sweating, movements of tongue and head)

all nerve fibers connecting the brain to the spinal cord pass through the medulla

four pairs of cranial nerves begin or end in medulla

Pons

ascending sensory tracts

descending motor tracts

pathways in and out of cerebellum

cranial nerves V, VI, VII, and VIII
sensory roles – hearing, equilibrium, taste, facial sensations
motor roles – eye movement, facial expressions, chewing, swallowing, urination, and secretion of saliva and tears

reticular formation in pons contains additional nuclei concerned with: sleep, respiration, and posture

Midbrain

short segment of brainstem connecting hindbrain & forebrain

contains cerebral aqueduct, medial lemniscus, reticular formation

contains motor nuclei of cranial nerves controlling eye movements – CN III (oculomotor) and CN IV (trochlear)

tectum – roof-like part of midbrain posterior to cerebral aqueduct
exhibits four bulges, the corpora quadrigemina

cerebral peduncles – two stalks that anchor the cerebrum to the brainstem anterior to the cerebral aqueduct

Midbrain- cerebral peduncles components

tegmentum
dominated by the red nucleus
connections go to and from cerebellum
collaborates with cerebellum for fine motor control

substantia nigra
dark gray to black nucleus pigmented with melanin
motor center that relays inhibitory signals to thalamus & basal nuclei preventing unwanted body movement
neuron degeneration leads to tremors of Parkinson disease

cerebral crus
bundle of nerve fibers that connect the cerebrum to pons
carries corticospinal tracts

Posterolateral View of Brainstem

Diencephalon:

Midbrain:

Superior colliculus

Inferior colliculus

Spinal cord

Pons

Cerebral peduncle

Optic tract

Fourth ventricle

(b) Posterolateral view

Regions of the brainstem

Midbrain

Diencephalon

Pons

Medulla oblongata

Medulla

oblongata

Superior cerebellar

peduncle

Middle cerebellar

peduncle

Inferior cerebellar

peduncle

14-*

Midbrain -- Cross Section

leaves

Tegmentum

Cerebral peduncle:

Cerebral crus

Tectum

Superior colliculus

Cerebral aqueduct

Medial geniculate nucleus

Reticular formation

Central gray matter

Oculomotor nucleus

Medial lemniscus

Red nucleus

Substantia nigra

Oculomotor nerve (III)

Posterior

(a) Midbrain

(b) Pons

Figure 14.9a

Reticular Formation

reticular formation – loosely organized web of gray matter that runs vertically through all levels of the brainstem

has connections with many areas of cerebrum

Visual input

Reticular formation

Thalamus

Radiations to

cerebral cortex

Ascending general

sensory fibers

Descending motor

fibers to spinal cord

Auditory input

Functions of Reticular Formation Networks

somatic motor control
adjust muscle tension to maintain tone, balance, & posture
relays signals from eyes and ears to the cerebellum

cardiovascular control (w/ medulla oblongata)

pain modulation
one route by which pain signals from the lower body reach the cerebral cortex

sleep and consciousness
plays central role in states of consciousness, such as alertness and sleep

habituation

largest part of hindbrain & second largest part of brain as a whole

right & left cerebellar hemispheres connected by vermis

cortex of gray matter w/ folds (folia) & four deep nuclei in each hemisphere

contains more than half of all brain neurons, about 100 billion
granule cells and Purkinje cells synapse on deep nuclei

Cerebellum

leaves

(b) Superior view

Folia

Posterior

Anterior lobe

Vermis

Posterior lobe

Cerebellar

hemisphere

cerebellar peduncles – three pairs of stalks that connect the cerebellum to the brainstem
inferior peduncles – medulla, spinal input
middle peduncles – pons, input from rest of brain
superior peduncles – midbrain, carries cerebellar output

consist of thick bundles of nerve fibers that carry signals to & from the cerebellum

Cerebellum

Superior colliculus

Posterior commissure

Pineal gland

Inferior colliculus

Mammillary body

Midbrain

Cerebral aqueduct

Oculomotor nerve

Pons

Fourth ventricle

Medulla oblongata

Gray matter

(a) Median section

White matter

(arbor vitae)

Cerebellar Functions

monitors muscle contractions and aids in motor coordination

evaluation of sensory input- spatial perception

timekeeping center
predicting movement of objects
helps predict how much the eyes must move in order to compensate for head movements and remain fixed on an object

hearing
distinguish pitch and similar sounding words

planning and scheduling tasks

lesions may result in emotional overreactions & trouble with impulse control