lecture cns
TRANSCRIPT
-
8/10/2019 Lecture Cns
1/44
15
THE NERVOUS
SYSTEM
C H A P T E R F I F T E E N
-
8/10/2019 Lecture Cns
2/44
Divisions of the nervous system
-
8/10/2019 Lecture Cns
3/44
Anatomical Organization of theNervous System
-
8/10/2019 Lecture Cns
4/44
Neuronal Organization: CNS
Found in both
brain and spinalcord:
1. centers= cellbodies
2. gray matter=cell bodies/centers,neuroglia,unmyelinatedaxons, anddendrites of motorneurons
- Clusters of cellbodies = nuclei
Tracts = white matter, bundles of axons For the conduction of nerve impulses
Two types: sensory and motor tracts(ascending anddescending)
Sensory tracts relay sensory information obtained fromreceptors throughout the body to the brain via the spinalcord
Responses to this information is relayed back to effectorsvia motor tracts
-
8/10/2019 Lecture Cns
5/44
Sensory pathway
Ascending
Information from sensory receptors to CNS
Motor pathway
Descending
Information from CNS to skeletal muscle or glands
Direct pathwayscause precise, voluntary movements
I ndir ect pathwaysresult in involuntary movement (from brain
stem)
Pathways
A neural pathway is comprised of centers/cell bodies andtracts
-
8/10/2019 Lecture Cns
6/44
An Introduction to the Organizationof the Brain
-
8/10/2019 Lecture Cns
7/44
Figure 15.1 Major Divisions of
the Brain
Major Regions of the Brain
-
8/10/2019 Lecture Cns
8/44
Major Regions of the Brain
-
8/10/2019 Lecture Cns
9/44
Figure 15.13b Sectional Views of
the Brain
-
8/10/2019 Lecture Cns
10/44
Cerebrum= largest portion-left and right cerebralhemispheresdivided by the longitudinal fi ssure
-connected by the corpus callosum-folded into ridges and grooves: grooves = sulci
-sulci divide the cerebrum into lobes
-ridges = gyri(gyrus)
Major Regions and Landmarks
Central sulcus
Frontal and parietallobes
-
8/10/2019 Lecture Cns
11/44
-cerebrum is comprised of:
1. white matter- neurons with
long, myelinated axons
-organized into tracts
2. basal nuclei or gray matter
-sometimes called the basal
ganglia4 nuclei found
deep within the cerebrum
- links to the midbrain
- receives input from the cortex& provides output to the motor
areas of the cortex via the
thalamus
-integrate motor commands
-regulates the initiation &
termination of muscle mve.-also functions to anticipate
body movements & controls
subconscious contraction of
skeletal muscle
Major Regions and
Landmarks
-
8/10/2019 Lecture Cns
12/44
- basal ganglia:multiple nuclei found deep within the cerebrum-first described by Thomas Wells - 1664
- links to the midbrain
-1. receives input from the cortex & provides output to the motor areas of the cortex via the
thalamus
-2. integrates motor commands-3. regulates the initiation & termination of muscle mve.
-4. also functions to anticipate body movements & controls subconscious contraction of skeletal
muscle
-
8/10/2019 Lecture Cns
13/44
Basal Ganglia comprised of the:
1. striatum
caudate nucleus:activity occurs prior to eye movements putamen:precedes or anticipates body movements
nucleus accumbens
2. globus pallidus:regulates muscle tone for movements
3. claustrum
4. substantia nigra:high concentration of dopanergic neurons 5. subthalmic nucleus
-
8/10/2019 Lecture Cns
14/44
Medical application: Basal Ganglia
-damage to the basal ganglia:
-results in uncontrollable, abnormal body movements
-muscle rigidity may develop and tremors
-Parkinsonneurons that extend from the substantia nigra
to the caudate nucleus and putamen
degenerate
-loss of dopamine releasing neuronsincrease in
muscle tone and stiffness
-Huntington - hereditary disorder-caudate nucleus and putamen degenerate with loss
of neurons that release GABA or ACh
-spasmatic muscle contractions and loss of mental
status
-
8/10/2019 Lecture Cns
15/44
Major Regions and Landmarks-outer layer = cerebral cortex
-area for specific processing of
sensation, -area of voluntary
movement, speech, all thought
processes
-plus association areasfor integration and
analysis of incoming info & help in
making of decisions
e.g. somatosensory, visual, auditory,
language and common integrative areas
-motor and sensory areas
e.g. pr imary somatosensoryarea (postcentral gyrus):touch,
proprioception, pain, itching,
thermal - forms a map of the
entire body
e.g. primary visual, auditory &gustatory areas
e.g. primary motor area
(precentr al gyrus):controls
voluntary contractions
e.g.Brocas speech area
-
8/10/2019 Lecture Cns
16/44
Major Regions and Landmarks-speech:involves complexactivities that involve sensory,
association & the motor areas ofthe cortex
-97% of the populationthese
language areas are located in the
left hemisphere
-planning and production ofspeechBrocas
-the left frontal lobe
-sends impulses to the premotor
area that controls contractions
of the larynx, pharynx & mouth-plus impulses are sent to the
primary motor area where
they control breathing
-aphasia:injury to language areas of the cortex
-inability to comprehend or use words
-damage to Brocas = nonfluent aphasia
(inability to form words)
-damage to auditory association area =fluent
aphasia(inability to comprehend spoken or
written words)
-
8/10/2019 Lecture Cns
17/44
-Amyotrophic lateral sclerosis:Lou Gehrigs disease
-unknown cause-attacks motor areas of the cortex, axons of motor neurons
in the spinal cord and motor neuron cell bodies
-muscle weakness and atrophy
-begins in regions of the SC that affect hands and arms and
then spreads
-
8/10/2019 Lecture Cns
18/44
Major Regions and Landmarks
Diencephalon
includes the hypothalamus, thalamus,epithalamus and subthalamus
thalamus: 80% of the diencephalon
paired oval masses of gray matter
organized into nuclei, interspersed
with white matter
major relay station for most sensory
impulses from the SC, brain stem
crude perception of pain, heat and
pressure (refined in cerebrum)
transmits motor information from
cerebellum to the cerebrum
relays nerve impulses to and from
different areas of the cerebrum
-
8/10/2019 Lecture Cns
19/44
Major Regions and Landmarkshypothalamus
-Emotions, autonomic
functions, hormone production
-mamillary bodiesserve as
relay stations for reflexes
related to eating
-supraoptic and preoptic
nucleithat in hormone
secretion (ADH) and body
temp
1. control of the ANS
integrates signals from the
ANS (regulated smooth and
cardiac muscle contraction)
major regulator of visceralactivities (heart rate, food
movements, contraction of
bladder)
2. produces hormones&
connects with pituitary to
regulate its activity
3. regulates emotional and behavioral patternsrage,
aggression, pain and pleasure + sexual arousal4. regulates eating & drinkinghypothalamus contains
a thirst center which responds to a rise in osmotic
pressure in the ECF (dehydration)
5. controls body temperaturemonitors temp of blood
flowing through the hypothalamus
-
8/10/2019 Lecture Cns
20/44
epithalamusconsists of the pineal glandand habenular nuclei
-pineal glandpart of the endocrine system
-secretes the hormone melatonin
-increased secretion in dark
-promote sleepiness and helps set the circadian
rhythms of the body (awake/sleep period)
subthalamusworks with the cerebrum and cerebellum to control bodymovements
-
8/10/2019 Lecture Cns
21/44
-
8/10/2019 Lecture Cns
22/44
Major Regions and LandmarksBRAIN STEM
Medulla oblongata continuation of the SC
forms the inferior part of the brain stem
relays sensory information and controls
automatic motor functions
white matter contains sensory/ascendingand motor/descending tracts
contains several nuclei also
these regulate autonomic functions - reflex
centersfor regulating heartbeat and BP
(cardiovascular center), respiration
(respiratory center), plus vomiting,
coughing, sneezing, hiccuping and
swallowing
nuclei in the posterior part are associated
with sensations of touch, proprioception,
pressure and vibration
-injury to the medulla: hard blow to the
back of the head or upper neck can be
fatal-damages the medull ary rhythmicity
areaof the respiratory center (disrupts
pattern of breathing)
-non-fatal injury: paralysis and loss of
sensation, irregular breathing and heart
rate
-
8/10/2019 Lecture Cns
23/44
Major Regions and Landmarks
Pons
= bridge
- e.g. connects brain stem to the cerebrumvia bundles of axons
- superior to the medulla and anterior to thecerebellum
consists of nuclei (cell bodies in graymatter) and tracts
somatic and visceral motor responses
Pontine nucleicontrol voluntarymovements that originate in the cerebralcortex and are relayed through the ponsinto the cerebellum
Pneumotaxic areacontrols breathing(with medulla)
Apneustic areacontrols breathing (withmedulla)
BRAIN STEM
M j R i d L d k
-
8/10/2019 Lecture Cns
24/44
Midbrain (Mesencephalon)
relay station between the cerebrum andthe spinal cord
extends from the pons to the
diencephalon
sends motor tracts to the SC, medulla
and pons & conducts sensory tracts tothe thalamus
processes visual and auditory
information - posterior part of the
midbrain
transfers information from the retina tothe eye muscles - tracking & scanning
pupillary reflex, shape of the lens
reflexes that mediate movements of the
eyes, head and neck
relays impulses from hearing receptors
to the thalamus
Major Regions and LandmarksBRAIN STEM
-generates involuntary somatic
motor responsesrelease of dopamine from
substantia nigra(nuclei) - loss of
these neurons = Parkinsons
red nucleiforms synapses with
cerebellum to coordinate muscle
movements
M j R i d L d k
-
8/10/2019 Lecture Cns
25/44
Cerebellum
divided into hemisphere with
lobes - like the cerebrum anterior and posterior lobes
has a superficial layer of gray
matter called the cerebellar cortex
- like the brain
deep to the gray matter are tractsof white matter
adjusts voluntary and involuntary
motor activities
evaluates and coordinates
motor activities initiated by thecerebrum and corrects problems
by sending info back to the
cerebrum
regulate posture & balance
uses sensory data and stored
memories
Major Regions and Landmarks
Th Li bi S
-
8/10/2019 Lecture Cns
26/44
called the emotional brain
group of structures that surround
the brain stem
involved in olfaction and
memory
emotionanger, fear,
happiness
associated with specific
responsesbehavioralpatterns
basic behavioral patterns
preparing for attack,
laughing, crying, blushing
also includes sexualbehaviors for the
continuation of the species
connects with the
hypothalamus to regulate
these behaviors
The Limbic System
olfactory tract
amygdala
hippocampus
anterior thalmic nuclei
fornix
mamillary body
parahippocampal gyrus
corpus
callosum
hypothalmic nuclei
cingulate gyrus
-
8/10/2019 Lecture Cns
27/44
called the emotional brain
involved in olfaction and memory
main components:
1. limbic lobe:rim of cerebral cortex on the medial surface of
each hemispherecomprised of the cingulate and parahippocampal
gyri 2. dentate gyruscontaining the hippocampus
3. amygdala:stimulation - rage
4. olfactory bulbs
5. septal nuclei
6. mammillary bodiesof the hypothalamusmotor nuclei for
reflexes associated with eating (chewing, swallowing, licking
etc...)
7. fornixwhite tracts that connect the hypothalamus to the
hippocampus
fibers end at the mamillary bodies
The Limbic System
-
8/10/2019 Lecture Cns
28/44
Protection and Support of the Brain
Th C i l M i
-
8/10/2019 Lecture Cns
29/44
The Cranial Meninges Cranium is covered with protective membranes
= meninges
Cranial meninges are continuous with spinal
meninges
3 layers: 1. outer, fibrous dura materforms
sheets (falx) that separate the cerebrum and the
cerebellum into the hemispheres and the
cerebellum from the cerebrum
-comprised of an outer endosteal layerand andinner meningeal layer
2. middle arachnoid mater
3. inner, thin pia mater
-there are spaces between these membranes
A. subarachnoid space:between the
arachnoid and pia maters
B. subdural space:between the
arachnoid and the dura mater
C. epidural spacebetween the dura
mater and the vertebral canal in thespinal column
l d i i ( )
-
8/10/2019 Lecture Cns
30/44
Blood-Brain Barrier (BBB) Blood into brain via the internal carotid and vertebral arteries
Blood supply to brain must be continuous Brain stores no glucose Uses about 20% of the oxygen and glucose in the body
The BBB prevents harmful substances in the blood from reachingthe brain tissue
The endothelial cells lining the brain capillaries have very tighttight junctions
BBB allows passage of lipid-soluble substances (gases, alcohol,anesthetic agents), slows the passage of most water-solublesubstances (ions, urea) and PREVENTS the passage of proteinsand most antibiotic drugs (i.e. large molecules)
-
8/10/2019 Lecture Cns
31/44
Ventricles of the Brain & CSF
Ventricles Chambers in centralpassageway of the brain
2 lateral ventricles, 1 third
ventricle, 1 fourth ventricle
connects to the central canalwhich runs into the spinal
canal
These chambers contain
cerebrospinal fluid
-
8/10/2019 Lecture Cns
32/44
CSF:
80 to 150 mLglucose,proteins, lactic acid, urea,ions
made by specialized cellsin the lateral ventricleschoroid plexus
continually circulates -ventricles and central canalto subarachnoid space
Chemical and physicalprotectionprovidesproper ionic environment
for neuronal actionpotentials + shockabsorber
transports nutrients,chemical messengers andwaste products.
Ventricles of the Brain & CSF
-
8/10/2019 Lecture Cns
33/44
CSF is gradually reabsorbed into the
blood through fingerlike projections
into the dural venous sinuses = arachnoid
granulations
large spaces for the circulation
of blood can be found between the
two dural layers = sinuses
e.g. superior sagittal sinus
also large veins run through thesubarachnoid space
e.g. cerebral veins
interfering with the drainage of CSF
into the subarachnoid space can result
in accumulation of CSF in the ventricles
& CSF pressure rises = hydrocephalus
(implantation of a shuntlateral ventricle
into the superior vena cava or abdomen)
-
8/10/2019 Lecture Cns
34/44
Flow of CSF
The blood supply to the brain
-
8/10/2019 Lecture Cns
35/44
The blood supply to the brain
Arterial blood reaches brain viainternal carotid internal carotid arteries give rise to
the Circle of Willis loops around the optic chiasma
the loop is formed from anteriorand posterior communicatingarteries
from this loop branches theanterior and posterior cerebralarteries
the posterior communicating andcerebral unite to form the basilarartery
from the basilar artery branchesnumerous smaller arteriese.g.cerebellar and pontine
the basilar then splits to form thevertebral arteries
Venous blood leaves via internaljugular veins
Th bl d l t th b i
-
8/10/2019 Lecture Cns
36/44
The blood supply to the brain Arterial blood reaches brain via internal carotid, vertebral arteries
Venous blood leaves via internal jugular veins
-transient ischemic attacks (TI A):no permanent neurologic damage-temporary cerebral dysfunction caused by impaired blood
flow to the brain
-dizziness, weakness, blurred vision, slurred speech,
paralysis
-persists from 5 to 50 minutes
-caused by emboli (blood clots), atherosclerosis
-cerebral vascular accident (CVA): stroke
-affects 500,000 people per year
-third leading cause of death
-permanent cerebral dysfunction caused by impaired blood
flow to the brain
-sudden onset of symptoms
-caused by cerebral hemorrhage (anuerysm), blood clot, atherosclerosis
-treatmentrapid administration of clot-dissolving drugs (e.g. tPA) if stroke
is caused by a clot
Al h i Di
-
8/10/2019 Lecture Cns
37/44
Alzheimers Disease
-loss or reasoning, memory
-11% of population over 65 (4 million people)
-unknown causethought to be genetic factors + environmental &lifestyle
-mutations in 3 genes coding for: prenisil in-1, -2and amyloid precursor
proteinlead to early onset forms (less the 1% of all cases)
-also mutations in gene coding for apolipoprotein E (ApoE)
a protein that helps transport cholesterol in the blood
-brain abnormalities:
1. loss of ACh releasing neurons from the nucleus basalis(below
the basal ganglia subtypeglobus pallidus
2.beta-amyloid plaques
deposited outside of neurons3. neurofibr il lary tanglesabnormal bundles of protein filaments
in affected brain regions
-treatments:drugs that inhibit acetylcholinesterase improve alertness e.g. Tacrine
& Donepezil
-
8/10/2019 Lecture Cns
38/44
THE NERVOUS SYSTEM: THE
SPINAL CORD AND SPINAL
NERVES
S i l C d
-
8/10/2019 Lecture Cns
39/44
Spinal Cord length in adults = 16 to 18 inches
Cervical and lumbar
enlargements
cervical = C4 to T1, nerves to and
from upper limbs
lumbar = T9 to T12, nerves to and
from lower limbs Tapers to conus medullaris
fi li um terminalearises from the
CM - extension of the pia mater that
anchors the SC to the coccyx 31 segments each with
Dorsal root ganglia
Sensory neuron cell bodies
Pair of dorsal roots
Pair of ventral roots
-
8/10/2019 Lecture Cns
40/44
Inferior End of
Spinal Cord
Conus medullaris
cone-shaped end of spinal cord
Filum terminale
thread-like extension of pia mater
stabilizes spinal cord in canal
Caudae equinae (horses tail)
dorsal & ventral roots of lowestspinal nerves
Spinal segment
area of cord from which each pair of
spinal nerves arises
-
8/10/2019 Lecture Cns
41/44
External Anatomy of Spinal Cord
Some nerves to know
-phrenic
-ulnar
-radial
-medial
-musculocutaneous
-femoral
-obturator
-sciatic
-ilioinguinal
-thoracic (intercostals)
i l h i l d
-
8/10/2019 Lecture Cns
42/44
Histology of the Spinal Cord Central gray matter
Contains cell bodies of neurons and
glial cells + unmyelinated axons Gray matter projections are horns
Peripheral whi te matter
Myelinated and unmyelinated axons
Organized as tracts or columns
Organization of Gray Matter 1. Poster ior gray horns
Somatic and visceral sensory nuclei
2. Anter ior gray horns
Somatic motor control
3. Lateral gray horns Visceral motor neurons
Gray commissures
Axons of interneurons crossingcordated and unmyelinated axons
Organization of White Matter
-
8/10/2019 Lecture Cns
43/44
Organization of White Matter Six columns (funiculi )
Anter ior , lateral and poster ior
whi te columns
Contain tracts of myelinatedneurons
Ascending tractsrelay
information from spinal cord
to brain
Descending tractscarry
information in the oppositedirection
Spinothalamic tract
pain, temperature, deep pressure &
crude touch
Posterior columns
proprioception, discriminative touch,
two-point discrimination, pressure andvibration
Direct pathways (corticospinal)
precise, voluntary movements
Indirect pathways (rubrospinal,
vestibulospinal)
programming automatic movements,
posture & muscle tone, equilibrium &
coordination of visual reflexes
rubrospinalmidbrain to spinal cord
corticospinalcortex to spinal cord
reticulospinalRAS (brain stem) to spinal cord
vestibulospinalinner ear to spinal cord
spinocerebellarspinal cord to cerebellum
spinothalmicspinal cord to thalamus
-
8/10/2019 Lecture Cns
44/44
Motor tracts:
lateral corticospinal: cortex to spinal cord
anterior corticospinal
recticulospinal tracts (lateral & medial): RAS (brainstem) to spinal cord
rubrospinal tract: midbrain to spinal cord
vestibulospinal tract: inner ear to spinal cord
tectospinal tract: tectum to spinal cord Sensory tracts:
spinocerebellar (posterior & anterior): spinal cord tocerebellum
posterior column
spinothalmic (Anterior & lateral): spinal cord tothalamus