quiz #1 - nervous system Flashcards
nervous system function
regulates body activities - by responding rapidly using nerve impulses
endocrine system function
responds by releasing hormones
mass of the nervous system
2kg
3% total body weight
the CNS consists of…
brain & spinal cord
what does the CNS process?
sensory info
source of: thoughts, emotions, memories
signals that stimulate mm to contract & glands to secrete originate where?
CNS
the PNS consists of…
all nervous tissue OUTSIDE the CNS
nerves & sensory receptors
nerve definition
bundle of hundreds to thousands of axons + associated CT & blood vessels that lie outside CNS
how many pairs of spinal & cranial nerves
12 pairs spinal nerves
31 pairs cranial nerves
what is a sensory receptor?
structure of nervous system that monitors changes in external/ internal environment
the PNS is divided into what 2 divisions?
sensory & motor
function of the sensory (afferent) division
conveys input into the CNS from sensory receptors
somatic (pain) & special senses (smell)
function of the motor (efferent) division
conveys output from the CNS effectors (mm & glands)
the motor (efferent) is divided into what 2 divisions?
somatic (SNS) & autonomic (ANS)
function of the somatic nervous system (ANS)
conveys output from CNS to skeletal mm ONLY
= VOLUNTARY
function of the automatic nervous system (ANS)
conveys output from the CNS to smooth mm, cardiac mm, & glands
= INVOLUNTARY
the ANS is comprised of 2 main branches…
sympathetic & parasympathetic
sympathetic nervous system
“fight or flight”
parasympathetic nervous system
“rest & digest”
3rd branch of the ANS
enteric nervous system (ENS)
regulates smooth mm & glands of GI tract
3 functions of the nervous system
- sensory function: detect internal & external stimuli
- integrative function: process sensory info (integration)
- motor function: activate effectors (mm & glands)
neuron function
possess electrical excitability - respond to a stimulus & convert it into an action potential
what is an action potential?
electrical signal that propagates (travels) along surface of the membrane of a neuron
3 parts of a neuron
cell body, dendrites, axon
a collection of neuron cell bodies outside the CNS is called…
ganglion
site of communication between two neurons/ between neuron & effector cell
synapse
slow axonal transport (direction)
ONE direction only
fast axonal transport (direction)
BOTH directions
anterograde = forward
retrograde = backward
structural classification of a neuron
number of processes extending from the cell body
functional classification of neurons
direction nerve impulse is conveyed with respect to the CNS
3 structural classifications of neurons (polar)
- multipolar: several dendrites, one axon
- bipolar: one main dendrite & one axon
- unipolar: dendrites & one axon fused together (sensory receptors)
3 functional classifications of neurons
- sensory: afferent, sensory receptors, unipolar
- motor: efferent, action potential away from CNS to effectors, multipolar
- interneurons: within CNS between sensory & motor, multipolar
neuroglia
“glue” that holds nervous system together
-smaller than neurons & more numerous
-do not generate action potentials
-can multiply & divide
4 types of neuroglia in the CNS
astrocytes
oligodendrocytes
microglia
ependymal cells
(distinguished based on size, cytoplasmic processes & intracellular organization)
2 types of neuroglia in the PNS
schwann cells
satellite cells
(completely suround axons & cell bodies of neurons)
what are the gaps in a myelin sheath?
nodes of Ranvier
which type of axons are surrounded by a myeline sheath?
schwann cells (PNS)
oligodendrocytes (CNS)
what does white matter consist of?
myelinated axons of many neurons
what does grey matter consist of?
neuron cell bodies, dendrites, unmyelinated axons, axon terminals, neuroglia
graded vs. action potentials (communication distance)
graded = SHORT distance
action: LONG distance
electrical signals rely on what 4 types of ion channels?
- leak channels
- ligand-gated
- mechanically-gated
- voltage-gated
which type of ion channel randomly alternates between open & closed?
leak channels
which type of ion channel opens & closes in response to binding of a chemical stimulus?
ligand-gated channels
which type of ion channel opens/ closes in response to mechanical stimulation in the form of vibration?
mechanically-gated channels
which type of ion channel opens in response to a change in membrane potential?
voltage-gated channel
what is the resting membrane potential?
electrical potential difference (voltage) that exists across the PM of an excitable cell under resting conditions
resting membrane potential typical value
-70 mV
= polarized
3 factors that contribute to RMP
- unequal distribution of ions in ECF & cytosol
- inability of most ions to leave cell
- electrogenic nature of Na+, -K+, ATPase (pumps)
what is it called when the membrane potential inside is more polarized (more negative) than resting level?
hyperpolarizing graded potential
what is it called when the membrane potential inside is less polarized (less negative) than resting level?
depolarizing graded potential
what is summation?
process by which graded potentials add together
a graded potential forms in response to which two gated channels opening?
mechanically-gated or ligand-gated
phases of an action potential
depolarizing phase & repolarizing phase, may be followed by an after-hyperpolarizing phase
what is happening at the after-hyperpolarizing phase?
following repolarizing phase, membrane potential temporarily becomes MORE negative than resting level (voltage-gated K+ channels remain open) = after-hyperpolarizing
when will an action potential occur?
once the membrane potential reaches THRESHOLD
depolarizing phase - ion flow
*Na+ channels open, Na+ rushes in
*inside of membrane = more positive
*more gates open, Na+ inflow increases
*positive feedback mechanism
repolarizing phase - ion flow
*after Na+ channels open, depolarization opens voltage-gated K+ channels
*slow K+ channel opening & open Na+ channels = repolarizing
*revert to resting state
period of time after an action potential begins during which an excitable cell cannot regenerate another action potential in response to a normal threshold stimulus
refractory period
what are the 2 types of propagation?
continuous & saltatory conduction
where does continuous conduction occur?
unmyelinated axons & mm fibers
where does saltatory conduction occur?
myelinated axons (nodes of Ranvier)
saltatory = “leaping”
factors that affect the speed of propagation
- amount of myelination: myelinated = faster
- axon diameter: larger diameter = faster
- temperature: warmer = faster
A fibers (classification of nerve fibers)
-fastest
-largest diameter
-myelinated
-motor neurons
B fibers (classification of nerve fibers)
-slower speed
-middle sized diameter
-partly myelinated
-saltatory conduction
C fibers (classification of nerve fibers)
-slow
-smallest diameter
-unmyelinated
-longest absolute refractory period
where do neurons communicate with other neurons?
SYNAPSE
-junctions between one neruron & a second or an effector cell
2 electrical synapse advantages
- faster communication: faster than chemical
- synchronization: coordinated contraction
at a chemical synapse, a presynaptic neuron converts an electrical signal (nerve impulse) into a…
chemical signal (neurotransmitter)
a postsynaptic neuron converts a chemical signal back into an…
electrical signal (postsynaptic potential)
type of neurotransmitter receptor that contains a neurotransmitter binding site & an ion channel
ionotropic receptor
type of neurotransmitter receptor that contains a neurotransmitter binding site & is coupled to a separate ion channel by a G protein
metabotropic receptor
3 ways to remove a neurotransmitter
- diffusion
- enzymatic degradation
- uptake by cells
a neurotransmitter that causes depolarization of the post-synaptic membrane
EXCITATORY (EPSP)
(bring membrane closer to threshold)
a neurotransmitter that causes hyperpolarization of a post-synaptic membrane
INHIBITORY (IPSP)
(farther from threshold)
2 types of summation - spatial & temporal
- spatial: stimuli occur at different locations on membrane at same time
- temporal: stimuli occur at same location on membrane at different times
chemical substances that neurons use to communicate with other neurons, mm fibers & glands
neurotransmitters
small molecule neurotransmitters
acetycholine (ACh), amino acids (GABA, inhibitory)
biogenic amines
norepinephrine, epinephrine, dopmine, seratonin
cause excitation or inhibition
what is a neural circuit?
functional group of neurons that processes a specific kind of information
4 types of neuronal circuits
- diverging
- converging
- reverberating
- parallel after-discharge
the capability to change based on experience
plasticity
most common type of neurotransmitter
acetylcholine
