concept 3a Flashcards
neurons
specialized cells capable of transmitting electrical impulses and then translating those electrical impulses into chemical signals
anatomy of the neuron
have a nuclei located in the cell body (soma)
dendrites branching off of the soma
axon hillock is the narrowing of the soma as it enters the axon, signal is integrated
axon is long appendage that terminates near target cell, carries the action potential
myelin sheath and Schwann cells surround the axon to help transmit the action potential
action potential jumps between the myelin sheath to areas called nodes of Ranvier
nerve terminal at the end of the axon to transmit signal to next cell
cell body
location of the nuclei, endoplasmic reticulum, and the ribosomes
dendrites
appendages of the soma
receive incoming messages from other cells
this info is transmitted to the cell body before reaching the axon hillock where the signal is integrated
myelin sheath
insulation around the axon
prvent signal loss or crossing of signals
increase the speed of conduction in the axon
myelin is produced by oligodendrocytes in the CNA and Schwann cells in the PNS
nodes of Ranvier
small breaks in the myelin sheath with exposed areas of axon membrane
critical for rapid signal conduction
action potentials jump from one break to the next for conduction of signal
nerve terminal
synaptic bouton (knob)
end of the axon
enlarged and flattened to maximize neurotransmission to the next neuron and proper release of neurotransmitters
these are the chemicals that transmit info b/w neurons
synaptic cleft
space b/w neurons where terminal portion of the axon releases neurotransmitters which bind to the dendrites of the postsynaptic neuron
synapse
the nerve terminal, synaptic cleft, and postsynaptic membrane
neurotransmitters released from the axon terminal traverse the synaptic cleft and bind to receptors on the postsynaptic neuron
nerve
multiple neurons bundled together in the peripheral nervous system
nerves may be sensory, motor, or mixed and these are related to the type of info they carry
cell bodies are clustered into ganglia
tracts
axons bundled together in the central nervous system
only carry one type of information
cell bodies are grouped into nuclei
neuroglia
glial cells
support cells for neurons
responsible for function such as holding neurons in place, supplying neurons w/ oxygen and nutrients, insulating neurons from other neurons, destroying pathogens, and removing dead neurons
astrocytes
nourish neurons and form the blood-brain barrier, which controls the transmission of solutes form the bloodstream into nervous tissue
ependymal cells
line the ventricles of the brain and produce cerebrospinal fluid, which physically supports the brain and serves as a shock absorber
microglia
phagocytic cells that ingest and break down waste products and pathogens in the central nervous system
oligodendrocytes
in the CNS
produce myelin around the axons
Schwann cells
in the PNS
produce myelin around the axons
action potential
an abrupt change in the membrane potential of a nerve or muscle cause by changes in the membrane ionic permeability
results in conduction of an impulse in nerves or contraction in muscle
all-or-nothing
relay electrical impulses down the axon to the axon terminal
ultimately release neurotransmitters into the synaptic cleft
resting membrane potential
exhibited by all neurons
there is an electric potential difference b;/w the inside of the neuron and the extracellular space
about -70 mV
inside of neuron being negative relative to outside
inside has more K+ and outside has more Na+
Na+/K+ ATPase
neurons have selective permeability to Na+ and K+ ions
this structure is used to maintain the negative internal environment
important for restoring gradient after action potential has been fired–> it transports 3 Na+ out of the cell for every 2 K+ into the cell using 1 ATP
depolarization
raising the membrane potential from its resting potential
makes neuron more likely to fire an action potential
happens when neuron receives excitatory input
hyperpolarization
lowering the membrane potential from its resting potential
makes neuron less likely to fire an action potential
happens when neuron receives inhibitory input
threshold
the lowest magnitude of stimulus strength that will induce a response
usually around -55 to -40 mV
when axon hillock receives enough excitatory input to be depolarized
once this is reached an action potential will be triggered
summation
additive effects of multiple signals that can reach threshold and create and action potential
2 types: temporal and spatial
temporal summation
multiple signals are integrated during a relatively short period of time
a number of small excitatory signals firing at nearly the same moment could bring cell to threshold
spatial summation
multiple signals are integrated from a number of different locations on one neuron
action potential generation
cell reaches threshold and voltage-gated Na+ channels open and permit passage of Na+ into the membrane bc of electrochemical gradient
as Na+ moves into cell it becomes more positive and rapidly depolarizes
when cell reaches +35 mV Na+ channels are inactivated
positive potential opens voltage-gated K+ channels and gradient moves K+ out of cell
this restores the negative potential of the cell as it is repolarized
efflux of K+ is overshot and causes hyperpolarization this the the refractory period
voltage-gated sodium channels
can exist in 3 states
closed- before cell reaches threshold and after inactivation has been reversed
open- from threshold to approximately +35 mV
inactive- from approximately +35 mV to the resting potential where it is deinactivated and returns to closed state
repolarization
when K+ is driven out of the cell restoring the negative potential
refractory period
when efflux of K+ is overshot and potential goes below -70 mV (hyperpolarization)
this is a period when an action potential can not be fired
resting period for the membrane
2 types: absolute and relative
absolute refractory period
no amount of stimulus can cause another action potential to occur
relative refractory period
there must be a greater than normal stimulate not cause an action potential because the membrane is starting from a potential that is more negative than the resting value
impulse propagation
movement of an action potential down an axon
resulting in neurotransmitter release at the synaptic bouton and transmission of the impulse to the target neuron or organ
depolarization of one segment of the axon will bring subsequent segments to threshold which will result in an action potential
speed of impulse
depends on length and cross-sectional area of the axon
longer axon results in higher resistance and slower conduction
greater cross sectional area results in after propagation and decrease resistance
effects of area are more significant than length
myelin insulates axon and increases the speed of conduction
saltatory conduction
process by which an electric single jumps across the nodes of Ranvier to travel down the axon
presynaptic neuron
the neuron preceding the synaptic cleft
release neurotransmitters into the synaptic cleft
postsynaptic neuron
neuron after the synaptic cleft
neuron that the neurotransmitters bind to
effector
neuron signals to a gland or muscle (target organ) rather than another neuron the postsynaptic cells is called effector
neurotransmitters in nerve terminal
before release they are stored in membrane-bound vesicles in nerve terminal
when action potential reaches this area voltage-gated calcium ions open allowing calcium to flow into cell
this triggers fusion of vesicles with membrane at synapse causing exocytosis of neurotransmitter
neurotransmitter in synapse
neurotransmitters are exocytized from the nerve terminal into the synapse
they diffuse accrues the cleft and bind to receptors on the postsynaptic membrane
this allows message to be passed from one neuron the the next
neurotransmitter regulation
neurotransmitters must be removed from the synapse after they transmit the signal
3 mechanisms to remove them: breakdown, reuptake, or diffuse out of cleft
breakdown of neurotransmitters
neurotransmitters are broken down by enzymatic reactions
break down of acetylcholine (ACh) by acetylcholinesterase (AChE)
reuptake of neurotransmitters
neurotransmitters are brought back into the presynaptic neuron using reuptake carriers
reuptake carriers for serotonin, dopamine, and norepinephrine
diffusion of neurotransmitters
neurotransmitters diffuse out of the synaptic cleft
nitric oxide is a gaseous signaling molecule that diffuse out of cleft
nervous system
collection of cells that govern involuntary and voluntary behavior
role in maintaining homeostasis
many different functions
over 100 billion cells that communicate, coordinate, and regulate signals for the body
actions occur when body reacts to stimuli using the nervous system
functions of the nervous system
sensation and perception motor function cognition (thinking) and problem-solving executive functioning and planning language comprehension and creation memory emotion and emotional expression balance and coordination regulation of endocrine organs regulation of heart rate, breathing rate, vascular resistance, temperature, and exocrine glands
3 types of nerve cells
sensory neurons
motor neurons
interneurons
sensory neurons
afferent neurons
transmit sensory information from receptors to he spinal cord and brain
ascend in the spinal cord toward the brain
motor neurons
efferent neurons
transmit motor information form the brain and spinal cord to muscles and glands (target organs)
exit the spinal cord on way to rest of the body
interneurons
found b/w the neurons
most numerous of the 3 types
located predominantly in the brain and spinal cord
often linked to reflexive behavior
divisions of the nervous system
Central nervous system and Peripheral nervous system
CNS consists of the brain and spinal cord
PNS is divided into somatic NS and autonomic NS
Autonomic NS is divided into sympathetic NS and parasympathetic NS
central nervous system
consists of the brain and spinal cord
brain in CNS
white matter- consists of axons encased in myelin sheaths, lies deeper than grey matter
grey matter- consists of unmyelinated cell bodies and dendrites
spinal cord in CNS
extends downward from the brainstem
divided into 4 divisions: cervical, thoracic, lumbar, and sacral
protected by the vertebral column
like brain has white and grey matter but white is on the outside and grey is deep within it
axons of motor and sensory neurons are in the spinal cord
dorsal root ganglia
contains cell bodies of sensory neurons
sensory info enters the spinal cord here where it can be synapsed with motor neurons in the grey matter of the spinal cord
ventral root
motor root
on the side closest of the front of the body
where motor neurons exit the spinal cord where they can then transmit info to the rest of the body
peripheral nervous system
made up of nerve tissue and fibers outside the brain and spinal cord
12 pairs of cranial nerves and 31 pairs of spinal nerves
connects the CNS to the rest of the body
subdivided into the somatic and autonomic NS
somatic NS
consists of sensory and motor neurons distributed throughout the skin, joints, and muscles
governs all voluntary actions
autonomic NS
regulates heartbeat, respiration, digestion, and glandular secretions–> manages involuntary muscles of internal organs and glands
helps regulate body temp but activating sweating or piloerection
automatic function
differences b/w somatic and autonomic
motor neuron in somatic goes directly from spinal cord to muscle w/out synapsing
in autonomic 2 neurons work in series to transmit messages from spinal cord
2 neurons of the autonomic NS
first is the preganglionic neuron
seconds is the postganglionic neuron
soma of the preganglionic neuron is in the CNS and its axon travels to a ganglion in the PNS
this is where it synapses on the soma of the postganglionic neuron which affects the target organ
divisions of the autonomic NS
sympathetic NS- fight or flight
parasympathetic NS- rest and digest (feed or breed)
act in opposition to each other, antagonistic
parasympathetic NS
rest and digest (or feed or breed)
main role is conserve energy
associated w/ resting and sleeping states
act to reduce heart rate and constrict bronchi
manage digestion by increasing peristalsis and exocrine secretions
neurotransmitter is acetylcholine-released by pre and post ganglionic neurons
innervated by the vagus nerve (cranial nerve X)