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Bio Chapter 4

Terms in this set (32)

what are neurons
specialized cells that transmit electrical impulses and then translate the impulses into chemical signals

a neurons shape matches its function
neuron shape

where is the nucleus

what is in the soma

what are dendrites and their function

what is an axon
the nucleus of the neuron is located in the cell body which is also called the soma


in the soma is also the ER and the ribosomes


dendrites radiate from the soma and receive msgs from other cells

information received by dendrites goes through cell body before reaching the axon hillock that integrates the incoming signal


axon is a long appendage that terminates in close proximity to a target structure (a muscle, gland or another neuron)
what is the important function of the axon hillock?
it plays an important role in action potentials or the transmission of electrical impulses down the axon

signals that arrive from the dendrites can be excitatory or inhibitory and the axon hillock sums up these signals

if the signal is excitatory enough (reaches the threshold) it will initiate an action potential
what is the function of myelin and myelin sheath

where is it produced
prevents signal loss or crossing of signals and increases the speed of conduction in the axon

myelin sheath will maintain the electrical signal within one neuron


produced by oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system
What are the nodes of Ranvier?
small breaks in the myelin sheath with exposed areas of axon membrane

critical for rapid signal conduction
end of the neuron structure

what is at the end of an axon

what is the synaptic cleft

what is the synapse
the nerve terminal or synaptic bouton (knob) is at the end of the axon

it is flattened to maximize the transmission of the signal to the next neuron and to ensure proper release of neurotransmitters


the synaptic cleft is a small space into which the terminal portion of the axon releases neurotransmitters that bind to the dendrites of the adjacent neuron


nerve terminal, synaptic cleft and the post synaptic membrane are called a synapse

neurotransmitters that are released from the axon terminal traverse the synaptic cleft and bind to receptors on the post synaptic neuron
what is a nerve

what are the 3 types of nerves

what is a ganglia

what are tracts
bundle of neurons


sensory, motor or mixed

named based on the information they carry (mixed carry both sensory and motor information)


cell bodies of neurons of the same type clustered together


in the central NS, axons can bundle to form tracts but unlike nerves the tracts only carry one type of information
what are glial cells or neuroglia
neurons are not the only cells in the NS and need support and myelination from these cells

they have a structural and supportive role
NS cells (only need to know these on a basic level)

what are astrocytes

what are ependymal cells

what are microglia

what are oligodendrocytes (CNS) and Schwann cells (PNS)
nourish neurons and form the blood-brain barrier, which controls the transmission of solutes from the bloodstream into nervous tissue

line the ventricles of the brain and produce cerebrospinal fluid, which physically supports the brain and serves as a shock absorber

phagocytic cells that ingest and break down waste products and pathogens in the CNS

produce myelin around axons
Neuron Signalling

what are action potentials
neurons use these all or nothing msgs to carry electrical impulses down the axon to the synaptic bouton and ultimately cause the release of neurotransmitters into the synaptic cleft
what is resting membrane potential and now is it generated or maintained?
resting membrane potential is the net electrical potential differences that exists across the cell membrane due to the movement of charged mlcs across the membrane

for neurons this potential is -70 mV and the inside is neg relative to the outside

resting membrane potential is generated and maintained by Na+ and K+
resting potential

Explain the isolation of K+ ions
K+ [ ] in the cell is around 140 mM and 4 mM outside the cell

so K+ wants to move outside the cell and potassium leak channels in the cell membrane facilitate this outward movement

this slow leak of K+ out of the cell causes the cell to lose a small amount of pos charge and leave behind a small amount of negative charge and now outside is slightly positive

the building neg charge inside the cell causes K+ to be brought back into the cell bcuz the pos K are attracted to the neg charge inside

at some point each K+ that is leaked out due to [ ] gradient will be matched by another K+ ion that will be pulled back in due to electric potential (so no net movement of ions now)

this pot difference that presents this potassium equilibrium is called the equilibrium potential of potassium which is around -90 mB (neg sign is because the pos K ion is leaving the cell)
resting potential

Explain the isolation of Na+ ions
Na+ [ ] inside the cell is 12 mM and outside the cell is 145 mM so Na+ wants to go inside the cell

sodium leak channels allow this slow movement of Na+ inside the cell and this causes the build up of electric potential like for K+

equilibrium potential of sodium is around 60 mV and is pos cause Na+ is moving into the cell
resting potential

in living system how are Na+ and K+ moving and how does this affect the equilibrium membrane potential?
they are moving at the same time, so K+ moves out and Na+ moves in

K+ movement pulled the cell pot towards -90 mV and Na+'s movement pulls the cell pot the opposite way towards 60 mV

its a tug of war but neither ion wins and instead the balance of these 2 effects is around -70 mV

this balance or the net effect of sodium and potassium's equilibrium potential is called the equilibrium membrane potential

its closer to K+ equilibrium because the membrane is more permeable to K+
what is the purpose of Na+/K+ ATPase
due to the continual leak of Na and K ions, this pump will help maintain the resting potential by pumping Na and K back against their [ ] gradient

to rmr the direction of the pump think pumpKin ("pump K in") and then Na is pumped out of cell

the pump is using ATP to help
axon hillock

what happens if axon hillock receives an excitatory input?

what happens if axon hillock receives an inhibitory input?
excitatory input causes a depolarization (raises membrane pot from resting pot) and makes neuron more likely to fire the action potential

need to be depolarized to the threahold value (around -55 to -40 mV) for action pot to be triggered

so not every stimulus causes an action pot


inhibitory input causes hyper polarization (lower membrane pot from resting pot) and makes the neuron less likely to fire an action potential
axon hillock

what is summation

what is a temporal summation

what is a spatial summation
this happens when the axon hillock receives multiple signals that can be mix of excitatory or inhibitory from different neurons


temporal summation is multiple signals are integrated during a short period of time

so a number of small excitatory signals firing at the same moment can bring cell to threshold


for spatial summation the additive effects depend on the number and location of the incoming signals

a large number of inhibitory signals firing directly on the soma will cause a more profound hyper polarization of the axon hillock than the depolarization caused by a few excitatory signals firing on the dendrites of a neuron
ion channels and membrane potential

what happens once the cell membrane reaches the threshold
voltage gated Na channels open in the membrane so Na+ ions can pass, strong electrochemical gradient causes Na ions to migrate into the cell

electrically, inside of cell is more negative so pos ion wants to move in and chemically, there is a greater [ ] of Na+ outside the cell so it moves in

Na+ movement causes the membrane to be more depolarized

when Vm reaches +35 mV, Na channels are inactivated and the voltage-gated K+ channels open

as pos K+ leaves the cell the negative membrane potential is restored and this is called repolarization

the K+ moving can overshoot the resting membrane potential and this is called hyperpolarization (this makes the neuron refractory to further action potentials)

there are 2 refractory periods, during the absolute refractory period no amount of stimulation can cause another action potential to occur

during relative refractory potential, there must be greater than normal stimulation to cause an action potential because the membrane is starting from a potential that is more negative than its resting value

refractory period prevents signals from flowing backwards and it can only go in one direction
what are the 3 states of Na+ channels
closed (before the cell reaches threshold and after inactivation if reversed)

open (from threshold to +35 mV)

inactive ( from +35 mV to the resting potential)

the membrane has to return to resting potential for the channel to be deinactivated
what is impulse propagation?
action potential travels down axon to trigger neurotransmitter release

as Na rushes into one part of the axon it causes depolarization in nearby regions and brings them to their threshold and they open Na channels

this continues until action potential reaches axon terminal
how does axon length affect signal conduction

what is saltatory conduction
longer axon= greater resistance and slower conduction

insulation from myelin is so effective that the membrane is only permeable to ion movement at the nodes of Ranvier, so signal hopes from node to node and that is saltatory conduction
the synapse

what is a presynaptic neuron

what is a postsynaptic neuron

what is an effector
the neuron preceding the synaptic cleft

the neuron after the synaptic cleft

a neuron that signals to gland or muscle rather than another neuron
neurotransmitters

how are neurotransmitters released
stored in membrane-bound vesicles in the nerve terminal

the action potential causes voltage-gated Ca channels to open so Ca2+ flows into the cell

this causes membrane-bound vesicles to fuse with the cell membrane and cause exocytosis of neurotransmitters into the synapse

NT diffuse across the cleft and bind to receptors on the post-synaptic membrane
neurotransmitters

what are 3 mechanisms that allow remove neurotransmitters from the synaptic cleft so we can regulate them
NT can be broken down by enzymatic reactions

NT can be brought back to the presynaptic neuron via reuptake carriers (ex. Dopamine)

NT can diffuse out of the synaptic cleft
organization of human nervous system

what are 10 functions of the NS
sensation and perception

motor functions

cognition (thinking) and problem solving

executive function 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
central and peripheral nervous system

what are sensory neurons

what are motor neurons

what are interneurons
also called affluent neurons, transmit sensory information from sensory receptors to the spinal cord and brain

also called efferent neurons, transmit motor information from bran and spinal cord to muscles and glands

these are found b/t other neurons, located in brain and spinal cord
central and peripheral nervous system

what is the CNS comprised of?

explain the matter in the brain?

explain the structure of the spinal cord?
brain and spinal cord


brain has white matter (axons encased in myelin sheath) and grey matter (unmyelinated cell bodies and dendrites)

base of brain is the brain stem


spinal cord extends down from brain stem and has 4 regions: cervical, thoracic, lumbar and sacral

spinal cord has white matter (lies on the outside of the cord) and grey matter (deep within the cord)

axons of motor and sensory neurons are in the spinal cord

sensory neurons bring information from PNS and enter on the dorsal (back) side of the spinal cord

motor neurons enter the spinal cord ventrally or the side closes to the front of the body
central and peripheral nervous system

what makes up the PNS

what is the SNS

what is the ANS
made up of nerve tissue and fibers outside the brain and spinal cord

PNS connect to CNS and the rest of the body

PNS is divided into the somatic nervous system and autonomic nervous system


SNS has sensory and motor neurons distributed throughout the skin, joints and muscles

transmits info through afferent fibers


ANS regulates heartbeat, respiration, digestion, temperature control and glandular secretions

manages involuntarily muscles associated w. internal organs and glands

basically controls things that are automatic and not consciously controlled
what is one primary difference b/t the SNS and ANS
peripheral component of the ANS has 2 neurons

motor neuron of SNS goes from spinal cord to muscles w/o synapsing

ANS has 2 neurons that work together, one is the preganglionic neuron and second is the postganglionic neuron
what are then the 2 divisions of the autonomic nervous system

what does each one do
sympathetic nervous system and parasympathetic nervous system

these branches work against one another meaning for example the sym may increase heart rate while the para will decelerate heart rate


parasympathetic will conserve energy. associated w. the resting and sleeping state, reduces heart rate, and constricts the bronchi, manages digestion


sympathetic is activated by stress, associated w/ rage and fear reactions aka fight or flight reactions

increases heart rate, redistributes blood to muscles of locomotion, increases blood glucose [ ], increases blood glucose [ ], relaxes the bronchi, decreases digestion and peristalsis, dilates the eyes to maximize light intake
reflexes

what are reflex arcs
neural circuits that control reflexive behaviour

2 types are monosynaptic and polysynaptic

basically say you step on a nail, the foot receptors will transmit a pain signal to via sensory neurons to your spinal cord, sensory neuron will connect w/ interneurons to relay pain impulses to the brain

but rather than waiting for the brain to send out a signal, interneurons in SC can also send signals to the muscles of both legs causing the individual to withdraw their foot in pain while supporting the other foot
What is a monosynaptic reflex arc?

What is a polysynaptic reflex arc?
single synapse b/t the sensory neuron that receives the stimulus and the motor neuron that responds to it

ex is the knee-jerk reflect


there is at least one interneuron b/t the sensory and motor neurons

ex. withdrawal reflex
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