Transcript What are the structures of a spinal nerve?

What are the primary structures and functions of
the central nervous system? 11/9 and 11/14
CH 13 and 14
What are landmark structures of the CNS?
What are the structures of a spinal nerve?
What are the structures of the spinal cord?
Blood Brain Barrier: how does it protect us?
Meninges: how do they protect us?
Cerebral Spinal Fluid: Where does it come from?
Central nervous system can be broken down
into two parts: brain and spinal cord
Embryonic Origin: CNS forms as an in-folding of epithelium
-Implications for spina bifida and folic acid
Three Major Regions of the Brain:
• Cerbrum (cerbral hemispheres): the neurons of the “cortex”
controls voluntary thoughts and actions
-Consists of folds (gyri) and grooves (sulchi)
-The corpus callosum connects the two cerebral halves
• Cerebellum: helps coordinate the wishes of the cortex
-It contains half the neurons of the brain!
-It makes an “action” possible
• Brain Stem: coordinates baseline functions: breathing/heart rate
-Medulla Oblongata is the last part of brain
• CNS continues as the “Spinal Cord”
Nerve: cluster of axons/dendrites
located outside of the CNS
Ganglion: cluster of nerve cell
bodies (soma) outside CNS
Neurons Need Constant Oxygen! PERIOD!
• Neurons are specialized for maintaining specific
membrane potentials and forming action potentials at the
“right” moment.
• Neurons are mostly dependent upon glycolysis because
they have very few mitochondria.
• The few mitochondria neurons we “DO” have are in
need of a constant supply of oxygen to maintain the
tenuous balance of ATP production and demand in
neurons.
• Blood supply to capillaries where gas/nutrient exchange
occurs are under low pressure (10-20 mmHg), while the
blood pressure in the aorta is typically 120/80.
How do oxygen and other nutrient molecules reach neurons?
The oxygen and nutrient demands of the brain are met by nutrients that
must first enter capillaries and diffuse out to the surrounding tissues.
The blood vessels are permeable to glucose, Na+, oxygen and CO2.
They extend deep into the neural tissues!
Blockages in cerebral vessels can cause brain injury (ischemia) or a
CerbralVascular Accident/ CVA/stroke (infarct or brain cell death ).
Causes of Blockage: Blood clot or external pressure (tamponade)
Stoppage of the Heart does lead to stoppage of cerebral blood flow!
Three Considerations:
1) What happens to intracranial pressure and capillary flow when a
cerebral artery undergoes an aneurism or a rupture?
2) How do we know that stoppage of blood flow to the brain stops for
more than about 20 seconds, you black out?
3) How do we know that stoppage of 3-5 minutes causes cell infarct?
Blood vessels pass through the nervous tissues of a nerve, however these
blood vessels have a very limited permeability due to the BBB. Note:
Endoneurium surround/support axons with or without Schwann cells.
Spinal nerves exit the spinal cord via the intervertebral notchs
(foramen) of every vertebra. This permits “afferent” nerves to enter
and “efferent” nerves to leave the spinal cord (CNS).
Important Features:
• Ventral Root: MOTOR
• Dorsal Root: SENSORY
D. Root “Ganglia”:
Nerve Plexus Functions:
31 spinal nerves total!
• C1-8+T1-12+L1-5+ S1-5
and 1 coccygeal
• Each with a left/right
branch
After a spinal nerve exits the intervertebral
foramen it splits into three major branches
• 1) Dorsal Ramus: to dorsal region
• 2) Ventral Ramus: to ventral region
• 3) Communicating Rami: to the sympathetic
chain ganglion
• Sometimes a plexus is formed when several
ventral rami merge (cervical, brachial, lumbar,
sacral and coccygeal)
Each spinal nerve is responsible for sensation in a band of skin that
extends around the body in a band roughly adjacent to the nerves origin.
This band of skin is called a dermatome.
Dermatomes overlap by about 50%
Novacaine blocks Na+-voltage gated
channels! When applied to a
spinal nerve it prevent AP
conduction of afferent neurons.
Knock out any three adjacent Spinal
Nerves and you can do local
surgery on the skin! “Painless ”
Consider the Dentist!
Dermatomes can also be used for:
locating spinal injury sites
accupuntcure
The spinal cord conducts APs to and from the brain, it
controls locomotion, and it mediates reflex actions so that
some APs need not travel all the way to/from the brain.
Parts:
D/V Sulchi
D/V/L Horns
Central Canal
Conus Medullaris
Cauda Equina
Why are spinal cord injuries
less common when you
fracture L3-L5?
There are specialized regions within the spinal cord
called ascending and descending tracts (Lab Review)
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White Matter: axons/dendrites
Grey Matter: somas
Grey Commissure: crossing
Tracts: cluster with similar
source or destination.
Motor vs. Sensory Tracts:
Ascending: Dorsal/Lateral
Descending: Ventral/Lateral
Three layers of protection:
Dura M-Arachnoid M.- Pia M.
Three spaces:
Epidural-Dural-Subarachnoid
The blood brain barrier (BBB) provides critical
protection to the CNS from materials in the blood!
Endothelial cell Tight junctions create the BBB in adults!
What about the BBB neonates?
Why is the blood brain barrier significant?
• Prevents some pathogenic organisms from entering the CSF
• Prevents some toxins from entering the CSF
• Prevents some drugs from entering CSF
• What can happens to BBB function and formation if you have high
blood pressure or a concussion (trauma)?
• Why does the BBB create drug transport problems?
Consider Parkinsons’ Disease, L-DOPA and Michael J. Fox
• Circumventricular organs provide a back door for toxins to reach
the CSF directly from the blood!
• Spinal Tap: provides a way to detect pathogens in CSF!
The CNS is protected by several structures: fluids,
bones and meninges!
• Skull plates/Vertebrae: protection #1
• Three sheaths (meninges) of connective tissue cover the
brain/spinal cord: protection #2
• 2a: Dura mater (Periosteal and Meningeal)- “tough mother”
Tough CT for protection
Falx cerebri and Tentorium cerebelli
“Subdural Space”
• 2b: Archanoid mater- “Spider-like mother”
CSF reabsorption
Some protection
Extends across sulcus
“Subarachnoid Space”
• 2c: Pia mater- “Delicate mother”
Extends into sulcusLast line of defense
Epidural Space: located between dura mater and lumbar vertebrae
Perivascular Space: space filled by blood vessels that penetrate the
pia mater and enter the neural tissue where nutrient exchange occurs
The brain has special fluid filled spaces called ventricles that are
filled with cerebral spinal fluids that protect the brain.
Functions of Cerebrospinal Fluid:
• 1) Brain Buoyancy: Why are plasma membranes fatty acid rich why
does this help achieve neutral buoyancy? Why is this good?
• 2) Shock absorption: When do we receive most concussions?
• 3) Chemical Protection: Why is the brain so sensitive to pH?
Where are the ventricles and what do they do?
• Two Lateral Ventricles: one per cerebral hemisphere
– Interventricular foramen to link lateral ventricles-
• One Third ventricle: one between the two hemispheres
– Mesencephalic aqueduct-
• One Fourth ventricle: one at base of brain stem/cerebellum
Central Canal extends from fourth ventricle into the length of the spinal
Where is the cerebral spinal fluid formed, how much
fluid is produced and where does the fluid go?
• What is CSF composed of relative to blood?
• How much CSF we have/produce?
• CSF is produced at: choroid plexus, subarachnoid plexus
and by ependymal lining
• Excess CSF is removed by arachnoid villi where it enters
the venous blood stream.
• What is Hydroencephally?
• What color is your CSF if you have an infection of the
CNS?
• Why do we perform “Lumbar” Spinal Taps and not
“cervical” taps?
Rarely people create excess CSF and intracranial pressure when they travel
to high altitude causing a potentially fatal condition called HACE.
You could even see this on a ski trip to Colorado! 

The hindbrain consists of two subdivisions:
myelencephalon and metencephalon
• Myelencephalon: This region becomes the medulla oblongata
– Cardiac Center-heart rate
– Vasomotor Center-blood pressure
– Respiratory Centers- PO2 and PCO2
– MO ends at foramen magnum and becomes the spinal cord
– What is life like in an ancephalic neonate? What is needed
for “life”?
Metencephalon=Pons+Cerebellum
Pons: next after medulla
• Helps Medulla Regulate Breathing: pneumotaxic/apneustic areas
• Coordinates passage of APs between cerebrum-cerebellum
Cerebellum: coordinates higher motor neuron output before APs sent
into the spinal cord
• Maintains muscle tone• Control limb proprioceptionStructures of the Cerebellum:
• L/R hemispheres
• Vermis and Folia
• Abundant dendrite rich Purkinji cells
Cerebellum helps turn ideas of cerebrum into action potentials sent to
muscles for action!
The reticular formation is in three different parts
of the brain: medulla, pons and midbrain
RF has special nuclei
that:
• Control arousal
• Moderate pain
• Control autonomic
functions
• Help control somatic
motor activity
Anesthetics work here!
Mesencephalon:
Midbrain sits between
hypothalmus, reticular
formation, and pons
Forebrain1-front, middle and back Diencephalon
• Hypothalmus: front
Hunger and satiety centers
Thermostat: losing or gaining
Heart rate modification
Osmoreceptors/thirst detection
Releasing hormones to Ant.
Pituitary
Post. Pituitary: is an extension of the
hypothalamusoxytocin + ADH
Time keeping and secretions
Centers for emotions/pleasure
• Thalamus: middle
Info gateway to cerebral cortex
• Epithalamus: back
Pineal gland and diurnal
secretions
Forebrain: The cerebral cortex (telencephalon) associates sensory
input APs to create/implement thoughts, value sensory strengths/
weaknesses, create reason and generate voluntary motor functions.
• Grey mater: 2-3mm,4 lobesX2sides
• Gyri/Sulchi increase SA X3 times!
• Frontal Lobe: Voluntary motor
actions, foresight/planning, and
social judgments
• Parietal Lobe: central sulcus to
parietoccipital sulcus
– Sensory Integration
• Occipital Lobe: visual interpreting
• Temporal Lobe: visual recognition,
hearing, learning, memory, smell
• Pete was hit by a baseball and lost
the ability to name people by their
face, but could name people by
their voice. What lobe may have
been effected?
Cerebral white (cortex) matter consists of inter
communicating axons and dendrites allowing
billions of cells to modify each others membrane
potentials and ability to make action potentials!!
THIS IS AMAZING!!
• Lies underneath the Grey Matter!
• Projection Tracts: higher (cortex) to lower brain function
• Commissural Tracts: hemisphere to hemisphere
• Association Tracts: area-to-area in one hemisphere
• Short-term and Long-term potentiation: changing the
resting membrane potential of the right cellmemory
• Learning occurs with repetitive action potentials being
sent along these synapses and tracts.
Cognition is the sum of our awareness, knowledge, and
memory. Its function is dependent upon the integrative
functions of association areas in the cortex.
• Sensory Association Areas:
primarily behind the central
sulchi. Information enters
the cortex via the thalamus!
• Where are the Areas?
• V.I.P. for lab test:
– Primary Somato-Sensory
Area:
– Primary Visual Area:
– Primary Auditory Area:
– Primary Gustatory Area:
– Primary Olfactory Area:
Where are the motor areas?
• Reference Points:
– Central Sulchus– Precentral Gyrus-
Two Main Motor Regions in Cortex:
• 1) Premotor/Motor Association area:
Coordinated or learned muscle sequences
originate here!
• How do you step from here to there?
• What muscles will be used in what sequence?
• 2) Precentral Gyrus is the Primary Motor Area:
• Action potentials from motor association area
arrive here. This is where action potentials are
integrated and leave the cortex
• Next Step: Brainstem
Humunculi for sense and motor functions line up on the precentral or
postcentral gyri. How can this be used to characterize the location of a
injury/stroke? Why is it important to know where the injury occurred?
Hearing involves several different association areas in the cortex.
Interneurons are critical for processing of visual information between
the visual association areas of the brain.
Damage to the brain comes in different forms,
degrees of severity, and permanence.
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Brain concussionBrain lacerationMeningitisEncephalitis-
• What does trauma do to the BloodBrainBarrier?
Consequences of BBB damage?
• “Cerebral vascular accident”/ “Stroke”Blood flow changes and Hypoxia
• Transient ischemic attackHypoxia/Ischemia/Cell Death (Necrosis or Infarct):
• Dementia and Alzheimer Disease
Damage to one side of the brain often appears as a loss of
function/sensation in the contralateral side! The corpus callosum
lets action potentials cross along commissural tracts (decussation)
between the two hemispheres!
Some classic brain injury stories: Phineus Gage, Red Barron,
auto/motorcycle injury victims. Remember: brain/body may live on,
but the personality may never be the same!
Memory entails the modification of nerve cell membrane potentials,
neurotransmitter release and excitability. How do we create
memories that last a few seconds, minutes, days, years or decades?
• Hippocampus organizes input and determines what/if info
goes to long-term locations in the cerebral cortex.
• Long-term potentiation means neurons permanently change
their resting membrane potential. This means memory has
occurred. How this creates “memory” is poorly understood.
• Amnesia can be of two types:
1) Retrograde Amnesia: you cannot remember your past
Example: music you forgot from your past (Ozzy?)
2) Anterograde Amnesia: you cannot remember new things
Example: music today that you forgot (Miley Cyrus?)
Remember: With regards to neuronal function ones amnesia can
be temporary (sometimes due to hypoxia) or permanent
(sometimes due to infarct).
Why doesn’t the pre-frontal cortex always have the capacity
to prevent our emotions from getting the best of us?
• Sob sessions, violent anger, revenge, love, pleasure, passion,
involuntary manslaughter……these are our emotions!
• The farther we go from the cortex, the less control we have over
the brain function!
• Pre-frontal cortex: Judgments, Intent, Premeditation, and SelfControl
• The amygdala and hypothalmus (Limbic System) are inferior to
the cortex and work together to mitigate emotions!
– Because these structures sit below the cortex, they can override the cortex!
– Hypothalmus: mitigates the senses of reward and punishment!
– Hypothamlus: mitigates sleep and circadian rhythms
Review of action potentials moving into (sensory info)/out of (motor
info) the brain. Most control is exerted in a contra-lateral fashion!
Review For Lab Exam: There are 12 (I-XII) cranial nerves
numbered by sequence of exit starting at the rostral end of
the brain and can have motor, sensory or mixed function.
• I-Olfactory: Mostly sensory, cribiform plate
• II-Optic: Mostly sensory, retina
• III-Oculomotor: Mostly motor
Constrict pupils
Control Rectus and inf. Obliques
• IV-Trochlear: Mostly motor-Superior obliques
• V-Trigeminals: Massive and Mixed: Three branches
*Often cut by accident or injury
*Sensation from the face!
*Important for chewing!
NOTE: almost every time a facial nerve innervates a muscle, there
are also sensory fibers (from spindles) running back along the same
nerve that indicate the degree of stretch (proprioception) in the
muscle to prevent overstretch of the target muscle!
VI-Abducens: Mostly motor to the lateral rectus muscles of the eye
VII-Facial: Mixed Nerve Function
Taste or gustation comes from tongue!
Proprioception comes from the scalp!
*Motor activity to facial muscles…huge nerve
*Motor activity to lacrimal glands: please don’t cry!
VIII-Cranial/ Vestibulocochlear/or/Auditory Nerve
Mainly sensory!
@Semicircular canals and equilibrium info sent here!
@Inner ear and hearing info sent here!
*Motor functions adjust sensitivity of haircells!
IX-Glossopharyngeal: Mixed Nerve
Afferent: Taste, touch, temperature
on the tongue. Efferent: muscles for
swallowing in the throat
XI-Spinal Accessory
• Motor: throat, trapezius
sternocleidomastoid
• Sensory: proprioceptor
throat/voice box
XII-Hypoglossal: mixed
• Tongue proprioceptors
• Motor functions help
control: speech and
swallowing