intro to nervous system Flashcards
What is a nerve?
bundle of axons (nerve fibers) wrappe din connective tissue
What is a ganglion?
swelling or bulbous region of a nerve where the cell bodies of neurons are concentrated
What are the functions of the spinal cord?
- walking movements
- reflexes
- postural support
- reflex control of bv, gi movements and urinary excretion
What are the functions of the subcortical (CNS)?
- arterial pressure
- equilibrium
- feeding reflexes
- emotional responses
What are the functions of the cortical (CNS)?
-association and integration of information from lower nervous system levels
What are the information pathways for the somatosensory system?
spinal cord, reticular formation, cerebellum, thalamus, cerebral cortex
Is the motor functional division of the PNS efferent or afferent?
Efferent (CNS to effectors)
What are the properties of neurons?
- excitability (irritability)
- conductivity
- secretion
What is the ability to respond to changes in the body and external environment?
stimuli
What is the difference between somatic sensory and visceral sensory?
somatic carries signals from receptors in the skin, muscles, bones and joints while viscerl carries signals from internal organs
What are interneurons?
association neurons
lie between sensory and motor pathways in CNS
90% of our neurons
-process, store, retrieve information performing an integrative function
What are the two divisions of the autonomic nervous system?
sympathetic and parasympathetic
What do visceral motor neurons do in the ANS?
carry signals to glands, cardiac muscle, and smooth muscle of organs and blood vessels
What do somatic motor neurons do?
carry signals to the skeletal muscle (voluntary and reflexes)
Afferent neurons carry…
signals ot the CNS
Efferent neurons carry…
signals from the CNS to effectors
What are other anmes for the cells body of a neuron?
perikaryan or soma
What is the primary site for receiving signals form other neurons?
dendrites
What is lipofuscin?
material that cannot be digested by lysosomes
What are neurofibrillary tangles?
prominent feature of degeneration neurons in Alzheimer’s, ALS, and down syndrome
What is the axon cytoplasm and its membrane called?
axoplasm
axolemma
Each branch of an axon ends in a synaptic knob. What is this?
little swelling that forms a junction (synapse) with the next cell
What is important in maintianing axonal diameter?
neurofilaments
What are microtubules important for in axons?
important as tracks for fast anterograde and retrograde axonal transport
What is the myelin in the CNS called? In the PNS?
CNS= oligodendrocytes PNS= Schwann cells
In PNS, as many as a hunndred layers wrap around an axon. What are the layers?
outermost coil is Schwann cell
covered by basal lamina and endoneurium
Where do signals begin?
intial segments and axon hillock form trigger zone
When does myelination occur?
begins during fetal development but proceeds most rapidly in infancy
MS is a chronic demyelinationg disease of the CNS. What is ti often characterized by?
remission and relapse
Patients with MS have CNA plaques (scar) formed by ____ in the white matter.
astrocytes
What are the most common symptoms of MS?
unilateral visual impairment, diplopia (double vision), paresthesias (pins and needles), ataxia, vertigo, fatigue, muscle weakness, dysarthria, mental disturbances
What is Tay-Sachs disease?
hereditary disorder of infants of eastern european jewish ancestry
-abnormal accumulation of glycolipid called GM2 in the myelin sheath
What effect would a person homozygous for Tay-Sachs allele be missing?
the lysosomal enzyme that would usually decompose the glycolipid GM2
In Tay-Sachs, accumulation of ganglioside GM2 disrupts cnoduction of nerve signals. What are the symptoms of this disease and to what age do they live?
- blindness, loss of coordination and dementia
- fatal before age 4
What are the three neuronal types?
unipolar, bipolar, multipolar
The multipolar neuron is the most common. What are the characteristics?
many dendrites, one axon
The unipolar neuron is sensory from what?
skin and organs to spinal cord
What is the anaxonic neuron?
many dendrites, no axon
-help in visual processes in retina
What is an electrical synapse?
gap junction allowing ion movement between neurons– this is common in smooth and cardiac muscle
When are electrical synapses found in the CNS?
when groups of interconnected neurons need to be fired synchronously
How do ionotropic post-synaptic neurons work?
on a short time scale
Na+, K+, Ca2+, Cl-
How do metabotropic post synaptic neuron work?
workj through second messanger systems
functions on a long term scale (seconds to possibly months or years)
What are the 4 possible metatropic receptors?
- ion channel opening
- cAMP or cGMP activation
- intracellular enzyme activation (MAPK, PKC)
- direct changes in gene transcription
What are the characteristics of small molecule chemical neurotransmitters?
short lasting effect
1000’s per vesicle
produced in synaptic terminal
ex: ACh, glycine, nitrous oxide
What are the characterisitics of the neuropeptide chemical neurotransmitters?
long lasting effect
100’s per vesicle
produced in soma within Golgi
ex: prolactin, carnosine, enkephalins, substance P, gastrin
What are the differences in speed of nerve signal depending on size and myelination?
small, unmyelintaed- 0.5-2 m/sec
small, myelinated- 3-15.0 m/sec
large, myelinated- up to 120 m/sec
What do slow signals supply?
stomach and dilate pupil
What do fast signals supply?
skeletal muscle and transport sensory signals for vision and balance
What effects excitatory neurotransmission?
- sodium channel opening
- decrease in Cl- or K+ channels
- change in # of channels via changes in gene expression
What effects inhibitory neurotransmission?
- Cl- channel opening
- increased K+ conductance
- inhibition of excitatory channels
- decreased # of excitation channels
Describe neuronal excitation.
excitatory neurotransmitter–> increased sodium permeability results in EPSP (excitatory post-synaptic potential)
- need 40-80 vesicles to cause action potential
- summation of EPSPs can cause depolarization sufficient to initiate action potential
Describe neuronal inhibition.
inhibitory neurotransmitters are release form presynaptic neuron–> opening of Cl- and/or K+ channels
- increased Cl- or K+ permeability results in hyperpolarization of the cell
- IPSP (inhibitory post-synaptic potential)
NO action potentials in dendrites, ONLY ____ ____.
electrotonic conduction
Describe dendrites channels.
low numbers of sodium channels, high numbers of K+ and Cl- leaky channels (decremental conduction)
What does resting membrane potential (RMP) result from?
- ions diffuse down their concentration gradient through the membrane
- plasma membrane is selectively permeable and allows some ions to pass easier than others
- electrical attraction of cations and anions to each other
What provides the greatest contribution to the resting membrane potential?
leaking of potassium ions
During RMP, what is the membrane much less permeable to?
high concentration of sodium found outside the cell
What accounts for 70% of the energy required for the nervous system?
Na+/K+ pump
- pumps out 2 sodium for every 2 potassium it brings in
- requires a lot of ATP
What is an action potential and when does it occur?
- dramatic change produced by voltage-regulated ion gates in the plasma membrane
- only occur where there is high enough density of voltage-regulated gates
Where is the action potantial generated?
trigger zone (350-500 gates per micrometer squared)
Where can an actional potential NOT be generated?
soma (only 50-75 gates per micrometer squared)
How does an action potential work?
- a rapid up and down shift in the membrane voltage
- sodium arrives at the axon hillock
- depolarize the membrane at that point
- threshold must be reached, neuron fires and produces an action potential
What is a threshold and what is the value to create an action potential?
critical voltage to which local potentials must rise to open the voltage-regulated gates
-55 mV
What is the spike of an action potential?
when more and more sodium channles open in the trigger zone in a positive feedback cycle creating a rapid rise in membrane voltage
What are the characteristics of action potential?
- all or none law
- nondecremental- do not get weaker with distance
- irreversible- once started goes to completion and cannot be stopped
What is the refractory period in an action potential?
period of resistance to stimulation
What are the two phases of the refractory period?
- absolute refractory- no stimulus od any strength will trigger AP
- relative refractory period- only especially strong stimulus will trigger new AP
What are 4 ways that receptors can be activated?
- mechanical deformation of the receptor
- chemical
- change in temp
- effect of EM radiation
What is the labeled-line theory?
each sensory receptor is tied to a specific nerve in the central nervous system
Pacinian corpuscle activation
- deformation of the nerve fiber induces Na+ channel opening (receptor potential)
- receptor potential induces local current whihc travels to 1st Node of Ranvier
- if the local current is high enough it will generate an action potential
increase strength of stimulus to the pacinian corpuscle=
increase in amplitude of receptor potential which leads to increase in action potential frequency
increase in membrane potential will cause an increase in….
action potential frequency
tonic receptors
slow adaptors
keep brain apprised of the status of the body and its relationship to the environment
examples of tonic receptors
golgi tendon organs, muscle spindles, macula receptors in the vestibular apparatus, pain receptors, chemoreceptors
phasic receptors
rapid adaptors
allows prediction of the future location of the body
examples of phasic receptors
pacinian corpuscle- on with pressure–> rapid adaption–> on wiht pressure release
temporal summation
-increased frequency of nerve impulses correlates with in increased strength of stimulus
spatial summation
- A,B,C firing alone cause partial depolarization but not enough for an action potential
- but if they all fire simultaneously their combined effects will cause an action potential
- increased stimulation recruits more nerve endings
In neuronal pools, presynaptic neurons can synapse on multiple postsynaptic neurons. What are the 2 kinds of stimulation?
suprathreshold stimulation
subthreshold stimulation
What is the discharge zone?
if the presynaptic fiber is excitatory then all postsynaptic neurons will generate action potentials
What is the facilitation zone?
if the presynaptic fiber is excitatory then postsynaptic neurons will be more likely to generate action potentials
What is the inhibitory pool?
inhibitory presynaptic fibers will prevent neurons in the center area from generating action potentials
each neuron can have how many presynaptic knobs connecting to dendrites and cell body?
10,000-200,000
How much information is disregarded as irrelevant?
99%
sensory neurons are usually divergent or convergent and why?
usually divergent
allows wide distribution of snesory information
motor neurons are usually divergent or convergent and why?
usually convergent
many presynaptic inputs are required for the activation of a motor neuron
In amplifying divergence, pyrimidal neurons are capapble of activating how many muscle fibers?
10,000
Dorsal column neurons that transmit information tot he cerebellum and the thalamus are an example of what?
multiple source divergence
Why does convergence occur?
because neurons are almost never excited by 1 synaptic input
Parts of spinal cord interneuron convergence
- peripheral neurons entering spinal cord
- propriospinal fibers from on espinal cord region to another
- corticospinal fibers from cerebral cortex
- other pathways including reticulospinal tract fibers
special characteristics of synaptic transmission
fatigue
metabolic disturbances
synaptic delay
What is the mechanism of fatigue in synaptic transmission?
protects against excessive activity
- exhaustion of neurotransmitters
- inactivation of post-synaptic receptors
- abnormal ion concentrations in postsynaptic neuron
the metabolic disturbances of synaptic transmission
alkalosis- increased neuronal excitability, can cause seizure activity
acidosis- decreased neuronal excitability, can lead to coma and death
synaptic delay of synaptic transmission is used to…
estimate number of neurons in series in a circuit
What arteries supply blood to the brain?
carotid and vertebral arteries
What arteries merge to form the Circle of Willis?
carotid and vertebral arteries
supply the brain with blood
What are metabolic factors that regulate cerebral blood flow?
concentrations of CO2, H+, O2
compounds released by astrocytes that regulate local blood flow (NO, arachidonic acid, K+, adenosine)
increase in PCO2 will have what effect on CBF
increase in CBF
CO2+H2O⇔𝐻2𝐶𝑂3⇔𝐻𝐶𝑂3−+𝐻+
anything increasing H+ will increase CBF
Why does a decrease in O2 cause vasodilation?
leads to anaerobic metabolism–> generation of acids
can lead to coma!
How much CSF in CNS?
~150 mL
What produces ~500 mL of CSF each day?
choroid plexus
What regulates CSF pressure by acting as valves?
arachnoid villi
it allows CSF to flow back into venous system
Granulation allow:
free flow of CSF
dissolved protein molecules
RBCs and WBCs back into venous blood
Right side MCA stroke
left hemineglect
left upper motor neuron type muscle wekaness (usually face and arm)
left visual field and somatosensory deficits
Left side MCA stroke
Broca’s aphasia
Wernicke’s aphasia
right upper motor neurons type muscle weakness
right visual field and somatosensory deficits
Coup
initial impact of the brain( frontal)
Contrecoup
when the brain recoils form the initial impact (occipital)
Communicating hydrocephalus
obstruction is in the subarachnoid space
non-communicating hydrocephalus
obstructione is within the ventricular space
Causes of cerebral edema
trauma, cancer, ischemic stroke, inflammation, high-altitude cerebral edema
treatments of cerebral edema
diuretics, corticosteroids, surgical decompression, osmotherapy
