Transcript Central Nervous System

Central Nervous System
Chapter 13
CNS Coverings
• Bone
• Meninges
– Dura Mater: white fibrous tissue
– Arachnoid membrane: cobweb-like layer
– Pia Mater: adheres to outer surface of brain & cord;
contains blood vessels
• Spaces surrounding meninges
– Epidural space: (“on the dura”) btwn dura mater and
bone coverings
– Subdural space: (“under the dura”) btwn dura mater
and arachnoid space
– Subarachnoid space: under arachnoid; outside pia
mater
http://faculty.irsc.edu/FACULTY/TFischer/AP1/meninges.jpg
Cerebral Spinal Fluid (CSF)
• Protective cushion of fluid
• Brain monitors CSF to help maintain
homeostasis
– Ex: CO2 levels
• Fluid spaces
– Subarachnoid space
– Spinal cord
– Ventricles (4)
Formation of CSF
• Fluid separated from blood in choroid
plexuses
– Choroid plexus: network of capillaries that
project into ventricles
– Lined with ependymal cells
• Circulation:
– Separation in choroid plexuses  ventricles
 central canal of spinal cord & subarachnoid
spaces  blood
Diagnostic Study – Lumbar Puncture
• Removal of CSF from subarachnoid space in
lumbar region of spinal cord
• Above/below L4, locate iliac crest
• Side-lying, knees to chest
• Sterile technique
• CSF tested for abnormalities
– Blood counts, bacteria, pressure
• Administer diagnostic agents or medications
http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/19078.jpg
Hydrocephalus
• Internal hydrocephalus
– Obstruction blocks drainage of CSF from ventricles
(1-3)
• Ex: tumor
• External hydrocephalus
– Obstruction in subarachnoid space causes build up of
CSF in subarachoid space
• Hemorrhage  blood clots
• Treatment
– Infants
• Unfused sutures  cranium swells
• Shunt placement btwn lateral and 4th ventricles
– Adults
• Pressure compresses brain  coma, death
http://bryanking.net/wp-content/uploads/2009/02/national_hydrocephalus_foundation.jpg
http://www.choa.org/images/graphics/hydrocephalus.jpg
http://www.articleslounge.com/wp-content/uploads/2009/06/Hydrocephalus.jpg
Spinal Cord - Structure
• Extends from foramen magnum to L1
• Fissures
– Anterior median fissure (larger)
– posterior median sulcus
• Nerve Roots – Project from each side of spinal cord
– Dorsal nerve root: carry sensory information to spinal cord
• Unipolar neurons
• Cell bodies make up dorsal root ganglion
– Ventral nerve root: carry motor information that exits spinal cord
– Dorsal + ventral nerve roots = spinal nerve
• Gray matter (“H” in the center of the spinal cord)
– Anterior, posterior, lateral horns (or columns)
– Contains interneurons and cell bodies of motor neurons
• White matter (surrounds gray matter)
– Anterior, posterior, lateral columns
– Contains bundles of axons (tracts)
Spinal Cord - Functions
Two main functions:
1. Conduction routes to/from brain
2. Integration or reflex center for all spinal
reflexes
Spinal Cord – Conduction Routes
• Ascending tracts – conduct sensory impulses up
to the brain
– Lateral spinothalamic: pain, temperature, crude touch
opposite side
– Anterior spinothalamic: crude touch and pressure
– Fasciculi gracilis and cuneatus: discriminating touch &
pressure sensations (vibrations, stereognosis, twopoint discrimination), conscious kinesthesia
– Anterior & posterior spinocerebellar: unconscious
kinesthesia
– Spinotectal: touch that triggers visual reflexes
Spinal Cord – Conduction Routes
• Descending tracts – conduct motor impulses
down from the brain
– Lateral corticospinal: voluntary movement, contraction
of small muscle groups (hands, fingers, feet, toes of
opposite side)
– Anterior corticospinal: same as above but affect
muscles on same side
– Reticulospinal: maintain posture during movement
– Rubrospinal: coordination of body movement &
posture
– Tectospinal: head and neck movement during visual
reflexes
– Vestibulospinal: coordination of posture & balance
Spinal Cord – Reflex Centers
• Center of reflex arc
• Switching from afferent to efferent
– 3 neuron arc  interneuron
– 2 neuron arc  synapse btwn afferent &
efferent
• Located in gray matter (“H”)
Brain
• Consists of:
– 100 billion neurons
– 900 billion glial cells
• Weighs approx 3 lbs in an adult
• Mature neurons are incapable of cell
division
– Only during prenatal and beginning months of
life
– Malnutrition hinders neuron
growth/development
Brain - Divisions
• Brainstem
– Medulla oblongata
– Pons
– Midbrain
• Cerebellum
• Diencephalon
– Thalamus
– Pineal body
– hypothalamus
• Cerebrum
– Cortex
– Corpus callosum
Brainstem
• Medulla Oblongata
– Enlarged extension of the spinal cord
– Located just above the foramen magnum
• Reflex centers: cardiac, vasomotor, respiratory
• Pons
– White matter & reticular formation
– Reflex centers for CN 5-8
• Midbrain
– White matter & reticular formation
– Reflex centers for CN 3-4
Cerebellum
• Structure
–
–
–
–
Lower posterior portion of brain
Outer region  cortex  gray matter
Internal areas  white matter
Grooves  sulci; raised areas  gyri
• Function
– Produce skilled movements by coordinating muscle
groups
– Posture (unconscious)
– Maintains balance
Cerebellar Disease
• Diseases of the cerebellum (tumor,
abscess, trauma, hemorrhage) produce
abnormalities in muscle coordination
• Most common – ataxia (muscle
incoordination)
• Signs/symptoms:
– Hypotonia
– Tremors
– Disturbances in gait & balance
Diencephalon
• Thalamus
– Dumbbell-shaped mass of gray matter
– Forms walls of third ventricle
– Functions:
• Processes auditory & visual input
• Conscious recognition of pain, temperature &
touch
• Emotional responses (associates sensory
impulses with pleasantness vs unpleasantness)
Diencephalon
• Hypothalamus
– Lie beneath thalamus and forms the floor of
the 3rd ventricle
– Functions:
• Controls responses made by autonomic effectors
• Maintains water balance
• Endocrine function – release hormones that
regulate actions of the anterior pituitary gland
• Waking state (alert and arousal)
• Regulating appetite
• Maintaining normal body temperature
Diencephalon
• Pineal Body
– Located just
above the
midbrain
– Functions:
• Regulates
biological
clock
• Produces
melatonin
Cerebrum
• Largest, upper division of the brain
• Two halves – right & left hemispheres
– Communicate via corpus callosum
• Cerebral cortex – surface of the cerebrum;
gray matter
– Gyri & sulci (shallow) or fissures (deep)
– Frontal lobe, parietal lobe, temporal lobe,
occipital lobe
Functional Areas of the Cerebral
Cortex (fig 13-16)
Functions of the Cerebral Cortex
• Postcentral
gyrus –
termination
area for
sensory
pathways
– Touch,
pressure,
temperature,
body
position
• Precentral
gyrus –
primary
motor area
– Neurons in
this area
control
individual
muscles
Functions of the Cerebral Cortex Language
• Speech centers are located in frontal,
parietal & temporal lobes
• In 90% of the population these areas are
found in the left hemisphere
• Aphasia = language defects
• Broca’s area – unable to articulate words;
able to make vocal sounds
• Wernicke’s area – deficit in language
comprehension
Functions of the Cerebral Cortex - Emotions
• Experiencing and expressing emotions involves the
function of the limbic system
– Area of the brain that surrounds the corpus callosum
– For proper expression the limbic system functions with the
cerebral cortex
Functions of the Cerebral Cortex Memory
• Temporal, parietal and occipital lobes
• Limbic system also plays a role
– Removal of hippocampus inhibits a person
from recalling new information
Disorders of the Central
Nervous System
Cerebrovascular Accident (CVA)
• Aka Stroke
• Hemorrhage or cessation of
blood flow through cerebral
blood vessels
• Lack of oxygen to neurons
causes cell damage or death
• If motor areas are affected,
patient loses function on
opposite side of the body
– (motor neurons cross over from
side to side in the brainstem)
• Hemiplegia – paralysis (loss
of voluntary muscle control)
on one whole side of the body
http://www.strokegenomics.org/img/stroke_hem_web.jpg
Cerebral Palsy
• Permanent, non-progressive damage to motor
control areas of the brain
• Damage present at birth or shortly after birth;
remains throughout life
• Possible causes:
– Prenatal infection, trauma to head before/during/after
birth, reduced oxygen supply to brain
• Results in impairment to voluntary muscles
• Most common  spastic paralysis: involuntary
contractions of affected muslcles
Dementia
• Dementia: degeneration of neurons that
affect memory, attention span, intellectual
capacity, personality & motor control
Alzheimer’s Disease (AD)
• Lesions develop in
the cortex of the
brain
• Result is dementia
• No known cause; no
effective treatment
• Genetic basis
http://www.crystalinks.com/alzheimersbrain.jpg
Seizures
• Sudden bursts of abnormal neuron activity that
cause temporary changes in brain function
• Mild seizures
– Small changes in level of consciousness, motor
control & sensory preception
• Severe seizures
– Convulsions (jerky, involuntary movements) &
sometimes unconsciousness
• Treatment
– Drugs (phenobarbital, valproic acid) block
neurotransmitter activity in affect areas  inhibits
bursts of explosive neuron activity
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