module 6 neuronal communication Flashcards
Nervous system is composed of 2 types of cells
neurons: generate action potentials
glial cells: supportive
Neurons have 3 parts
cell body
dendrites
axon
dendrites
receive signals and transmit them to the cell body
axons
generate and conduct action potentials
3 types of axons
multipolar
bipolar
unipolar
multipolar axons
have many dendrites and one axon
most common
bipolar axons
have 2 branches off cell body
one for axon one for dendrites
unipolar axons
cell body has one branch off of it that splits to have dendrites on one side and the axon on the other.
Neurons can be
inhibitory or excitatory
4 types of neuroglia
oligodendrocytes
microglia
ependymal cells
astrocytes
oligodendrocytes
form myelin sheath that wraps around nerve axons
microglia
provide phagocytic functions
ependymal cells
produce CSF and maintain CSF-brain barrier
Astrocytes
maintain integrity of the BBB
regulate ionic balance of the interstitial fluid
transfer nutrients from capillaries to neurons
Action potentials in neurons
neurotransmitter binds to receptors on dendrite and cell body
AP are initiated in axon hillock
voltage gated Na channels: depolarization
Voltage gated K channels: repolarization
speed of action potential determined by
axon diameter: inc. diameter = inc speed
myelination: inc. speed
Nodes of Ranvier
allow impulse to hop quickly from node to node: saltatory conduction
Multiple sclerosis
chronic autoimmune inflammatory disease leading to destruction of myelin sheaths in brain and spinal cord
More common in women
S/S depend on location of active lesions
s/s multiple sclerosis
can vary sensory loss muscle weakness incontinence gait imbalance blurry/double vision cognitive difficulties
Dx of multiple sclerosis
MRI: demyelinating lesions of brain and spinal cord
LP: oligoclonal bands of y-globulins in CSF
Guillain-Barre syndrome
acute, progressive, paralytic neuropathy
autoimmune demylination of peripheral nerves
more common in men
ascending and symmetrical progressive muscle weakness without sensory loss
Guillain-Barre syndrome can be in response to
an infection; commonly campylobacter jejuni enteritis
synaptic transmission depolarization causes
voltage gated calcium channels to open
calcium influx
exocytosis of neurotransmitter into synaptic cleft
neurotransmitter in synaptic cleft
acts on receptor of second neuron to excite inhibit, or modify its activity
neurotransmitter after released
either transported back into axon terminals for reuse or destroyed by enzymes.
excitatory neurotransmitters
excitatory postsynaptic potentials
opening of Na channels
example: glutamate
Inhibitory neurotransmitters
inhibitory postsynaptic potentials opening of channels that allow - chloride influx -potassium efflux examples: GABA or glycine
summation
All the EPSP’s and IPSP’s at the axon hillock determines whether an AP will be initiated
spatial summation
multiple presynaptic neurons
temporal summation
one presynaptic neuron fires in rapid succession
myasthenia gravis
autoimmune disease targeting nicotinic acetylcholine receptors in postsynaptic neuromuscular junction.
- impaired muscle contraction
- s/s improve with rest and worsen throughout day
- resp. involvement leads to hypoventilation
- face highly effected
botulism
paralytic neuromuscular disease caused by botulinum toxin produced by clostridium botulinum
infant botulism
72% of cases
ingestion of raw honey
s/s: difficulty feeding, weak cry, irritability and hypotonia
adult botulism
28% of cases
result of home food preservation
s/s: bilateral cranial neuropathies followed by symmetric descending weakness
nervous system divided into 3 units
central (CNS)
peripheral (PNS)
autonomic (ANS)
CNS
brain
spinal cord
primary function of CNS
receive and process sensory info and create appropriate responses
-relayed to muscles and glands
CNS is bathed in
CSF which allows for bouyancy and shock absorbing
CNS and PNS interaction
synapses in spinal cord and cranial nerve ganglia
meninges
composed of 3 layers that suspend and maintain shape and position of nervous tissue during movements
3 layers of meninges
dura mater
arachnoid layer
pia mater
dura mater
protects soft tissue of brain
-outer most layer: thick, tough, collagenous
2 layers
- one contiguous w/ periosteum of skull
- one adherent to first covering of brain
arachnoid layer
beneath and continuous with dura
thin and delicate
semitransparent and weblike
pia mater
connective tissue, trabeculae, extend from arachnoid to pia: subarachnoid space
very thin
attached to brain
leptomeninges
arachnoid and pia mater
CSF
majority produced by choroid plexus in lateral and 3rd ventricals of brain.
- approx. 500mL/day
- only 150-175 mL in circulation
BBB
maintain in part by CNS cells: astrocytes
-specialized glial cells with foot processess that contact brain capillaries and help regulate transport across the endothelium
BBB in infancy
less effective
BBB can be compromised by
ischemia and chemical injury
cerebrum
divided into left and right hemispheres
largest part of brain
cerbral cortex
outmost layer of cerebrum composed of gray matter characterized by - gyri -sulci -fissures
gyri
convoluted exterior with ridges
sulci
grooves
fissures
deeper depression
landmarks that divide brain into lobes
sulci and fissures
diencephalon
deep in brain, forming connective structure between upper brainstem and cerebral hemispheres
principle structures of diencephalon
thalamus hypothalmus pineal gland epithalamus ventral thalmus
cerebellum
coordinates and smoothes movements maintain posture and balance compares desired movement with execution - makes adjustments folia: cortical ridges on surface medullary center: white matter beneath
brainstem
stalk of neuronal tissue between upper spinal cord and diencephalon
3 parts of brainstem
midbrain
pons
medulla oblongata
brainstem and cranial nerves
10 of 12 cranial nerves originate from brainstem
spinal cord
conveys nerve impulses from brain to 31 pairs of spinal nerves
posture, protective respones to pain, muscle tone
gray matter of spinal cord
integration and processing
on inside
white matter of spinal cord
bundles of mylinated axons forming tracts up and down cord.
- on outside
spinal cord extends from
base of skull to first or second lumbar vertebra
dorsal root
carry sensory afferent neurons
ventral root
carry motor efferent neurons
ventral horn of gray matter
where motor neurons exit
dorsal horn of gray matter
where sensory neurons enter spinal cord
lateral horn of gray matter
sympathetic
PNS
31 pairs of spinal nerves and 12 pairs of cranial nerves
-myelinated with schwann cells opposed to oligodendrocytes in CNS
ganglia
groups of cell bodies
PNS does not have
CSF, meninges, or bony coverings
PNS covered by
sheath of connective tissue
ANS
neurons in CNS and PNS that mediate automatic/involuntary functions
branches of ANS
sympathetic and parasympathetic
preganglionic neurotransmitter in ANS
Ach for both PSNS and SNS
postganglionic neurotransmitter in ANS
PSNS: Ach: acts at muscarinic receptors
SNS: norepi: acts at a and B adrenergic receptors
location of ganglia in PSNS
in or adjacent to target organs
location of ganglia in SNS
paravertebral and prevertebral
ionotropic receptor
receptor on postsynaptic membrane that doubles as ion channel; Na influx
metabotropic receptor
works through secondary messenger cascade
neurotransmitters: amines
dopamine norepinephrine: SNS epinephrine serotonin histamine
neurotransmitters: amino acids
excitatory:
- glutamate
- asparate
inhibitory
- Glycine
-GABA
neurotransmitters: pruines
adenosine
ATP
neurotransmitters: gases
nitric oxide
carbon monoxide
PNS breaks down into 2 parts
autonomic
somatic
autonomic NS
sympathetic
parasympathetic
Somatic NS
sensory
motor
Primary sensory function
specialized dendritic processes activated and the signal is transmitted to the spinal cord
- receptor to spinal cord
secondary sensory neurons
in the cord are activated and carry signal up the cord to thalamus
- cord to thalamus
Tertiary sensory neurons
from thalamus relay signals to various brain areas
- somatosensory cortex
ipsilateral side
same side of spinal cord
-touch, pressure, vibration
contralateral side
opposite side of spinal cord
- pain, itch, temperature
sensory pathways 2 major tracts
dorsal column-medial lemniscal tract
anterolateral tract
dorsal column-medial lemniscal tract
fine touch, vibration, proprioception
remains ipsipateral until the medulla then crosses
anterolateral tract
pain, itch, temperature
crosses cord near entry level and travels to brain on contralateral side
upper motor neurons
form descending motor tracts that control
- fine motor movement: corticospinal tract
- controls distal muscles of the upper and lower limbs - posture and balance: vestibulospinal, reticulospinal, and tectospinal tracts
- large proximal muscle groups and axial muscles
lower motor neurons
travel from anterior horn through ventral root, within the spinal and peripheral nerves to innervate target muscles
- alpha motor neurons release Ach to contract all fibers in muscle unit
- gamma motor neurons contract muscle fibers within the muscle spindle
motor unit
single motor neuron and all muscle fibers under its control
muscle spindles:
sensory receptors that sense the length or stretch within the muscle and relay info to spinal cord
somatosensory cortex
organized in columns of gray matter that correspond to specific body locations
-stimulation at specific body points results in discrete sensation in the contralateral side.
dysautonomia
combinations of both parasympathetic and sympathetic dysfunction
can be acute or chronic
-central or peripheral
etiologies of dysautonomia
autoimmunity paraneoplastic disorders toxins diabetes guillian-barre syndrome parkinsons spinal cord disorders
S/S of dysautonomia
faintness/dizzy when arising diarrhea or constipation autonomic instability incontinence orthostatic hypotension impotance
pheochromocytoma
tumors of the adrenal medulla that secrete epinephrine and norepinephrine
- s/s: increased sympathetic activity
- uncontrolled catecholamine release reults in malignant HTN, CVA, MI
pheochromocytoma and clonidine
clonidine can be used to suppress catecholamines, but does not work with pheochromocytoma due to its peripheral excretion not central.
pheochromocytoma treatment
surgical resection of tumor and Rx for HTN.
