CNS II Bowman Flashcards
What is sensory function in CNS dependent on?
intact afferent cellular circuits
Sensory nerve =
afferent, dorsal root
Motor nerve=
efferent, ventral root
General outlay of dermatomes of body?
What is exteroceptive information?
Interaction of skin with the environment
- Fine discriminatory touch
- Pain and temperature
What is proprioceptive information
Body and limb position informing movement
What is enteroceptive information
Internal status of the body
What are some type of sensory transductions we have?
- Mechnical (mechanoreceptor)
- Chemical (chemoreceptor)
- Thermal (thermoreceptors)
- Pain (nociceptors)
- Electromagnetic (detect photons)
- When dark, gate is open, passing ions
- When light hits, gate closes
What is common thread with all receptors?
Changing permeability of ions in some way (with gate opening, distort membrane to open gate, standard ligand etc)
What are receptor potentials?
Need enough stimulus to get enough ion flow, to get to threshold, get to first node of ranvier, then we get action potential
What are tactible fibers fast (FA)
From onset of stimulus, quick adaptation to stimulus and action potentials stop
(i.,e. shoe on foot)
What are slow adaptation fibers?
From onset of stimulus, continuous action potentials fire (rock in shoe)
What are type I fibers for fine discriminatory touch?
High density= better two point discrimination (tip of finger)
What are type II fibers?
Large receptive field (i.e. back)
What type of receptors are meissner’s corpuscles?
FA1
What type of receptors are pacinian corpuscles?
FA2
What type are merkel’s discs?
SA1
What typeare ruffini receptors?
SA2
What does the amplitud of stimulus intensity look like?
Rapid change in amplitude with stimulus strength increase, levels out at higher levels
What are some coding of action potentials from stimuli?
- Modality
- touch, pressure, flutter
- taste, smell etc
- spatial location
- stimulus intensity
- stimulus frequency
- stimulus duration
What makes up dorsal column- medial lemniscal pathway?
- Highly localized touch
- touch sensation (fine gradation of intensity)
- phasic sensation (vibratory)
- skin contact
- joint position
- pressure sensation
Largers myelinated fibers
More spatial orientation
What is anterolateral pathway?
Type of somatosensory pathway (spinothalamic)
- Pain
- Thermal sensation
- crude touch/pressure
- tickle and itch
- sexual sensation
Composed of smaller myelinated fibers and slower (40m/sec)
Less spatial orientation
Pathway of dorsal column medial lemniscal pathway?
SOMATOSENSORY PATHWAY (more fine, localized touch)
Transmits signal upward toward medulla via dorsal column
- Synpases in dorsal column nuclei (in medulla)
- 2nd order crosses over in medulla and then go thalamus (3rd order)
General pathway of anterolateral system (spinothalamic tract)
- SOMATOSENSORY PATHWAY
- Enters S.C. form dorsal spinal nerve roots, immediately sypases in dorsal horn
- Cross to contralateral cord
- travel up through anterior and lateral white column
- tract terminate at all levels of lower brain
- note, there is flame at the toe. this is major pain pathway
What is spinocerebellar proprioceptive pathway?
PRIOPRIOCEPTIVE PATHWAY
- Perception of position, conscious awareness of body movementa nd local reflexes
- cutaneous and proprioceptive info to cerebellum and cortex
What are the central pain pathways?
Spinothalamic
Spinoreticular
SPinomesencephalic
What is motor function dependent on ?
Intact efferent cellular circuits
Where do motor neurons contorlling somatic musculature form a column of cells?
Ventral horn of spinal cord
Where are interneurons for distal muscles?
Intermediate/lateral ventral horn
WHere are interneurons for proximal muscles?
Medial ventral horn
What is corticospinal tract pathway?
- Major motor tract that controls trunk and proximal limbs
- EXTREMELY FAST motor signals (70m/sec)
- some fibers come down and end up in ventral portion (trunk muscles)
- some cross over and end up in lateral (control limbs)
4 majors vessels supplying blood to brain
2 vertebral arteries
2 carotids
Which area of the spinal cord has poor callateral blood supply?
Anterior portion
What is purpose of CSF?
- CNS “lymphatic” system
- protection from mechanical force
What is volume capacity of brian and spinal cord?
1600-1700 mL
What amount of volume is CSF and CSF in cerebral ventricles?
CSF- 125 mL
About 30 mL in cerebral ventricles
What is rate of CSF production in chroid plexuses?
0.35 mL/min
What reabosrbs CSF?
Arachnoid villi
if fluid flows into arachnoid villi when CSF is 1.5 mmHg>venous pressure
What constiuents appear in CSF at higher level than blood concentration?
- Sodium (148 IN CSF (slightly higher))
- Chloride (120-130 in CSF)
*
What constituents of CSF is found at a lower concentration than blood?
- Potassium (2.5 in CSF)
- Glucose (50-75 in CSF)
- Protein (15-45 in csf MUCH LOWER THAN BLOOD (6.8x10^3 in blood)
Pathway of CSF through brain?
- Fluid from lateral ventricle passes through intraventricular foramina (of Munro)
- goes to 3rd ventricle (additional fluid added there)
- Flow downard toward aqueduct of Sylvius into 4th ventricle
- more fluid added here
- Passes out of 4th ventricle through 3 small openings
- 2 lateral foramina of luschka
- midline foramen of magendie
- Enters cisterna magna (large fluid space behind medulla nd benath cerebellum
- This space is continuous with subarachnoid space surrounding the spinal cord
What is the BBB?
- Large molecules and highly charged ions are excluded from brain and spinal cord requiring active transport mechanisms
- tight junctions between CNS capillary endothelial cells
- fenestrations in brian 1/8th size of fenestrations in other areas
- Astrocytes also restrict movmeent (take up K ions)
Where does BBB exist?
- In tissue capillary membranes in all areas of the brain EXCEPT
- Hypothalamus
- pituitary
- area postrema (involved in vomiting)
What does movement across BBB depend on?
Molecule size (smaller= more likely to ross)
Charge
Lipid solubility
Protein binding
What is permeable across membrane?
H2O, CO2, O2, lipid soluble substances (anesthetics, alcohol)
What is slightly permeable across BBB?
Na, K, Mg, Cl, Ca
What is impermeable across membrane?
Polar molecules, plasma proteins, glucose (FD only), non-lipid soluble large organic molecules (mannitol)
What is ICP normal pressure?
8-12mmHg
What is inside the rigid cranial vauld? percent?
- Brain (cellular and ICF)= 80%
- Blood (arterial and venous)= 12%
- CSF= 8%
CPP?
Cerebral perfusion pressure = MAP- ICP (or CVP, whichever is greater)
Normal 80-100mmHg . In trouble if <50
What is volume compensation
ICP can compesnate for increased volume until a point, and then shoots up very quickly
What is amount of cerebral blood flow?
50mL/100g/min= 750 mL/min
What factors affect CBF?
- Level of arousal/neural metabolism
- temperature
- concnetration of co2 and h ions
- O2 (only when extremely low)
- blood viscosity
- decrease HCT increase CBF but decrease O2 carrying capacity
- Severe polycythemia can reduce CBF
Relationship between neuronal activity and local CBF?
- “Flow metabolism coupling”
- CBF to localized brain regions can change up to 100-150% withins econds in resposne to local neuronal activity changes (sensory input/arousal)
Relationship between CBF and PaCO2?
- co2+ h2o= carbonic acid
- Carbonic acid disassociates into H
- H cause “almost proportional” vasodilation of cerebral vessels
- Each 1 mmHg change in PaCO2
- CBF changes 1-2 mL/100g/min
- CBV changes 0.05 mL/100g brain tissue
- 10 mL change for 15 mmHg change in Paco2
- Effects last about 6 hours and then it will return to normal due to excretion of bicarb
Brains % mass and % total body metabolism?
Brain 2% total body mass
15-20% of total body metabolism and cardiac output
What is normal cerebral metabolic rate in adult, ped?
CMRO2 adults 3-3.8 mL/100g/min= 50mL/min of o2
Ped= 5.2mL/100g/min (2 x as much!)
What is rate of brains glucose consumption?
5.5mg/100g/min
needs constant supply of blood, o2
What is percent used by brain for cellular homeostasis?
60%
What percent energy of brain is required for electrophysiologic activity?
40%
What do anesthetics due to CMRO?
Reduce down to 60%. Removes electrophysiologic activity but cannot remove cellular homeostasis requirement
Relationship between CBF and o2 concentration?
- Except for cases of intense brain activity, o2 utilization by brain remains in narrow range
- 3.5 mLO2/100g brain tissue
- If po2 drops below 30 mmHg, or pAo2 drops below 50-60mmHg, CBF increases
What does CBF like to keep MAP at?
70-150
Adjust to changes after 1-3 minutes
HTN will cause shift in autoregulatory ranges to higher minimum values
Relationship of Sympathetic nervous system and CBF?
- Cerebral circulation strong SNS inntervation (vasoconstrictive)
- especially in larger vessels
- Neither transection of nerves or mild to mod stimulation causes much change- the auto regulation mechanism overrides
- May shift auto regulation curve to the Right
- sns minor role unless EXTREME BP rise (stroke prevention, hemorrphagic shock)
SNS only accounts for acute change to protect brain from high pressure. Not as important as autoregulation
Relationship between temperature and CBF?
- CBF changed 5-7% per 1 degree C change
- hypothermia decreases CBF and CRMO
- only way to decrease cellular function requirement to be <60%
- HYPERTHERMIA IS OPPOSTIE EFFECT
Where is cell body in sensory pathway?
in dorsal root ganglion ( it is a psuedounipolar neuron)
