Physiology of Nervous System Flashcards
How is the metabolism of nervous tissue unique from other body tissues?
- Constant, very high, metabolic rate
- Depend entirely on glucose
- Limited or no anaerobic capabilities
- Don’t store an energy source (glycogen)
Effects of low glucose on neurons
- Neurons malfunction and if prolonged may die
- Primarily effects higher cortical levels
- patient “spaced out”, irritable, diaphoretic, blurred vision, coma, seizure
Effects of low oxygen on neurons
- More dramatic than low glucose
- rapidly induces confusion and coma
- Neuronal death in 3-4 min
3 major embryologic divisions of the brain
- forebrain (cerebral cortex, thalamus, hypothalamus, basal ganglia)
- midbrain
- hindbrain (cerebellum, pons, medulla)
What is the largest portion of the brain and what does it consist of?
cerebrum, consisting of cerebral cortex and basal ganglia
grey matter vs white matter in cerebrum
grey matter - cell bodies and dendrites
white matter - myelinated nerve fibers beneath cortex
reticular formation
Large network of nuclei (grey matter) in brainstem that regulate CV, respiratory rate, and wakefulness/consciousness
reticular formation + cerebral cortex = reticular activating system
General functions of the limbic system
emotions (rage, fear), feeding behaviors, bio rhythms, smell
eg. music/smell makes you think of particular memory
General functions of the frontal lobe
thought and judgement
Neuroglia
cells that support neurons of CNS
50% of brain and spinal cord volume
astrocytes
- Most abundant glial cells
- Surround BV of CNS and fill space between neurons
- Provide rapid transport of nutrient and metabolites
- Essential components of blood brain barrier
- “scar forming” cells (foci for seizures)
myelinated vs unmyelinated
myelinated have myelin sheath and use saltatory conduction
unmyelinated do not have and use continuous conduction
salutatory conduction
allows for faster conduction of a nerve impulse because impulses jump from node to node (gaps in myelin)
inhibitory vs excitatory neurotransmitters
inhibitory: hyperpolarize; make harder for neuron to reach threshold (GABA)
excitatory: depolarize; make neuron less negative; easier to reach threshold (glutamate)
What produces myelin?
Schwann cells in PNS
Oligodendrocytes in CNS
What type cells are damaged by Guillain-Barre? Effects?
Antibodies destroys Schwann cells and axonal myelin
prevents nerves from transmitting signals to brain, causing weakness, numbness, or paralysis
GABA
- most common inhibitory neurotransmitter in brain
- used to treat seizures
- GABA release is blocked in tetanus
IPSP vs EPSP
IPSP: passage of hyperpolarizing ions into cell (chloride)
EPSP: passage of depolarizing ions into cell (Na/K)
ependymal cells
neuroglia that line the ventricles and are involved in CSF production
microglia
neuroglia that remove debris via phagocytosis in CNS
plasticity
CNS capability of changing what a region of the brain does
Capability in children high, but declines with age
substantia gelatinosa
part of posterior horn with sensory axons involved in pain transmission
spinothalamic tract
pain and temp
crosses at spinal level
medial lemniscus tract
touch, pressure, vibration, proprioception
crosses at medulla
tracts that run through anterior horn?
MOTOR pathways - corticospinal tract and corticobulbar tract
Where do motor axons cross midline?
medullary pyramid
corticobulbar tract specifically controls what?
- muscles of head and face
- motor component of cranial nerves 5, 7, 9-12
spinal reflexes
reflexes contained within the spinal cord
afferent neuron (sensory) -> interneuron -> efferent neuron (motor) -> effector muscle or gland
_______ influence and modify reflex spinal arcs.
upper motor neurons
What nerves make up the PNS?
cranial nerves and spinal nerves
______ pathways carry SENORY impulses _____ the CNS.
_______ pathways carry MOTOR impulses _____ the CNS.
afferent; towards
efferent; away from
What do motor impulses target?
effector organs - skeletal, cardiac, smooth muscle; glands
What are the divisions of PNS?
somatic: motor/sensory of voluntary motor control of skeletal muscle
autonomic: motor/sensory of involuntary muscles (sympathetic & parasympathetic)
Wallerian degeneration
Degeneration of peripheral nerve fiber (axon and myelin) that has been severed from its cell body (nutrition center)
Occurs at DISTAL portion of severed axon
Wallerian regeneration
PROXIMAL end of injury site sprouts new terminal 1-2 wks after injury, hopefully connecting with Schwann cell pathway and grow approx 1 mm/day
Where is Wallerian regeneration restricted to in nervous system? Why?
Regeneration limited to PNS
Very limited in CNS d/t scar formation after injury and different nature of myelin production by oligodendrocytes
intension vs resting tremor
intension occurs with movement or following commands
resting occurs at rest when not thinking about it
chorea
quick, irregular, involuntary, but relatively coordinated movement face, limbs, trunk
athetosis
distal muscle postural fixation disorder; slower than chorea, writhing, sinuous, abnormal hand posture, slowly fluctuating grimaces
ballism
proximal muscle postural fixation; wild flinging movement of limbs - usually unilateral
agnosia
- inability to recognize and interpret objects, people, sounds, or smells despite intact primary sense organs
- ex: inability to identify a sound despite intact hearing; inability to identify a coin placed in hand; inability to recognize familiar faces
- damage to occipital & parietal lobe
akinesia
paucity of movement
allodynia
condition in which an ordinarily painless stimulus is experienced as being painful (ex. the pant leg touching the thigh is described as uncomfortable)
anosognosia
Lack of self-awareness; unaware they have a problem or disability
Ex: schizophrenic who doesn’t take meds because “there is nothing wrong with me” or hemiplegic who finds excuses (other than paralysis) for not using paralyzed arm
apnea test
part of “brain death exam” where patient taken off the ventilator for a certain amount of time
- Verifies lack of responsiveness to increased carbon dioxide (paCO2 > 60 mm Hg) in the presence of respiratory acidosis (pH < 7.3)
aphasia
inability to formulate or understand language
expressive vs receptive aphasia
expressive: damage to Broca’s; have understanding but can’t produce speech
receptive: damage to Wernicke’s; speak without understanding; “word salad”
apraxia
impaired planning/sequencing of movement that is not due to weakness, incoordination, or sensory loss. Although the movements cannot be performed for a specific situation, they may be performed under other circumstances (e.g., inability to lift feet off the floor when attempting to walk but preserved ability to perform bicycling movements of the legs while lying in bed)
asterixis
sudden palmar flapping movement of the hands at the wrists; indicative of hepatic encephalopathy
ataxia
Lack of coordination of movement usually due to disease of cerebellum or damage to sensory pathways
bradykinesia
slowed movement typically due to dysfunction of the basal ganglia and related structures
Charcot joint
progressive destruction and deformity of bone and soft tissue at weight bearing joints due to severe sensory or autonomic neuropathy.
Chiari malformation
CNS disorder characterized by cerebellar elongation and protrusion through the foramen magnum into cervical spinal cord. Places these individuals at risk with extension of the head on the neck
“clasp knife”
spring-like resistance to passive extension at elbow or flexion at knee that increases up to a certain length and force before suddenly relaxing as the Golgi tendon organ is activated; sign of spasticity
“cogwheeling”
ratchet movement due to superimposition of tremor on rigidity
dysarthria
inability to pronounce or articulate words d/t disorder of vocal apparatus (lips, tongue, larynx)
dysesthesia
pain or discomfort in response to stimuli (e.g. touch) that would not be expected
fasciculation
spontaneous firing of axon resulting in visible twitch of all muscle fibers that it controls; indicates denervation
hemiparesis
weakness on one side of body
hemiplegia
paralysis on one side of body
Horner’s Syndrome
ptosis, miosis, and anhidrosis - ipsilateral to damaged sympathetic nerve fibers
Kernig’s sign
pain in posterior thigh in response to passive flexion of thigh and extension of knee; indicative of meningeal irritation
Long-tract signs
signs referable to impaired functioning of corticospinal tract, spinothalamic tract, and dorsal columns/medial lemniscus
Lower motor neuron lesion
neurons located in brainstem or anterior horn
lesions result in flaccid weakness, reflex loss, atrophy, +/- fasciculations
meiosis
pupillary constriction
neuropathy
disease of axons; manifested by varying combinations of lower motor neuron weakness or peripheral sensory loss that is typically distal > proximal; often with DTR reflex impairment or loss
paresthesia
skin sensation such as burning, prickling, itching, or tingling with no apparent physical cause
rigidity
increased resistance throughout range of motion when passively moving a body part due to co-contraction of agonist and antagonist muscles (“lead pipe”)
Romberg test
inability to maintain upright posture when feet together and eyes closed; assuming intact vestibular system, indicates impaired proprioception or cerebellar disease
simple tic
tic involving a limited number of muscles; simple vocal tics are meaningless noises such as grunting or throat clearing; simple motor tics are focal movements such as eye blinking or facial grimacing
spasticity
abnormal increase in muscle tone and reflexes; indicates upper motor neuron lesion
spondylosis
degenerative disease of vertebral column that results in spinal cord compression. May include osteoarthritis, osteophytes, and disc disease
spondylolisthesis
condition where vertebral body, typically in lumbar or sacral, slips forward and has a “step off”
May cause spinal cord compression
transient ischemic attack
abrupt focal loss of neurologic function caused by reduction in blood flow that persists less than 24 hours and clears without residual disability
2-point discrimination
an increase in distance in which a patient distinguishes two differing points of stimulation.
An increased distance suggests neuropathy (ex. carpal tunnel)
vertigo
subjective sense of imbalance usually noted as “room spinning”
How are nerve fiber sizes and myelination related to function?
Large: myelinated motor fibers
Medium: myelinated sensory (touch, vibrations, proprioception)
Small: thinly myelinated to unmyelinated sensory (pain and temp)
Very small: unmyelinated autonomic fibers (BP, HR, sweating, gut)
Signs of UMN lesion
weakness
spasticity
increased DTRs
+ Babinski
Signs of LMN lesion
weakness
fasciculations
decreased/loss of DTRs
atrophy
Signs of basal ganglia pathology
akinesia resting tremor rigidity athetosis chorea
Signs of cerebellar pathology
errors of rate, range, force, & direction
intension tremor
ataxia
central cord syndrome
- incomplete injury to cervical cord resulting in more extensive motor weakness in UE than LE. - occurs from hyperextension injury with pre-existent osteophytic
Brown-Sequard syndrome
injury to one half of the spinal cord; deficits all on ipsilateral side except pain/temp contralateral
Dermatome of posterior leg and lateral foot
S1
Dermatome of medial foot
L4
Dermatome of bottom and top of foot
L5
Dermatome of sphincter
S3-S5
Rash that follows dermatome
shingles
Examples of primitive rooting reflexes
primitive reflexes exist in infants but should go away in adults
grasp reflex
cheek reflex
Babinski
decorticate
lesion of the cortical spinal tract superior to brainstem
