Biological Foundations of Behaviour Flashcards
action potential
an electrochemical impulse that consists of localized areas of depolarization of the plasma membrane that travels in a wave-like manner along an axon
synaptic transmission
when an action potential reaches the end of an axon at a synapse, the signal is transformed into a chemical signal with the release of neurotransmitter into the synaptic cleft
bipolar
neurons with one dendrite
multipolar
multipolar
how many axons do all neurons have?
only one
synaptic knobs
the terminal end of the axons that form connections with target cells
synaptic cleft
the small gap between the synaptic knob and the target cell
what is a neuron’s resting membrane potential?
-70mV
what are the two primary membrane proteins that determine the resting membrane potential?
sodium potassium pump and potassium leak channels
how does the sodium potassium pump work?
for every ATP, three sodium ions are pumped out of the cell and two potassium ions pumped into the cell
in which direction does potassium flow through potassium leak channels?
out of the cell
polarized
difference in charge across membrane of neuron, negative on the inside and positive on the outside
depolarization
change in membrane potential from resting -70mV to +35mV
repolarization
returns the membrane potential to normal
what causes the change in membrane potential during the passage of an action potential?
movement of ions in and out of neurons through ion channels
voltage-gated sodium channels
opens at -50mV and close at +35mV, allows sodium ions to flow into cell
threshold potential
-50mV, must reach this potential for voltage-gated sodium channels to open
what allows for repolarization
1) voltage-gated sodium channels inactivate at +35mV
2) voltage-gated potassium channels open at +35mV and stay open until -90mV
3) potassium leak channels contribute to repolarization
myelin
an insulating sheath wrapped around some neurons, no ions can exit or enter axonal membranes covered in myelin
what cells create the myelin sheath?
Schwann cells
nodes of Ranvier
gaps in the myelin sheath where voltage-gated sodium and potassium channels and concentrated
saltatory conduction
the rapid jumping conduction in myelinated axons at Nodes of Ranvier
glial cells
specialized non-neuronal cells that typically provide structural and metabolic support to neurons, do not generate action potentials
what are the five types of glial cells?
Schwann cells, oligodendrocytes, astrocytes, microglia, ependymal cells
Schwann cells
PNS glial cell, forms myelin to increase speed of conduction of action potentials along axon
oligodendrocytes
CNS glial cell, forms myelin to increase speed of conduction of action potentials along axon
astrocytes
CNS glial cell, guides neuronal development, regulates synaptic communication via regulation of neurotransmitter levels
microglia
CNS glial cell, remove dead cells and debris
ependymal cells
CNS glial cell, produce and circulate cerebrospinal fluid
equilibrium potential
the membrane potential at which the gradient does not exist and there is no net movement of ions across the membrane, specific to each particular ion
what is the equilibrium potential for Na+?
+50mV
what is the equilibrium potential for K+?
-90mV
refractory
the state of a neuron after passage of an action potential in which it is unresponsive to membrane depolarization and unable to transmit another action potential
absolute refractory period
a neuron will not fire action action potential no matter how strong a membrane depolarization is induced: VOLTAGE-GATED SODIUM CHANNELS HAVE BEEN INACTIVATED (+35mV to -70mV)
relative refractory period
neuron can be induced to transmit an action potential but the depolarization required is greater than normal because the membrane is hyperpolarized: VOLTAGE-GATED POTASSIUM CHANNELS HAVE NOT CLOSED YET (-70mV to -90mV)
synapse
junction between the axon terminum of a neuron and the dendrites, soma, or axon of a second neuron or an organ
electrical synapse
when the cytoplasms of two cells are joined by gap junctions, allows an action potential to spread directly from one cell to another (ex. smooth and cardiac muscle)
chemical synapse
found at the ends of axons where they meet their target cell, action potential is converted into a chemical signal
what is the neurotransmitter released at a neuromuscular junction?
acetylcholine (ACh)
excitatory neurotransmitter
opens a channel that depolarizes the postsynaptic membrane
inhibitory neurotransmitter
makes the membrane potential more negative than the resting potential (hyperpolarized)
what determines the effect of the neurotransmitter on the postsynaptic cell?
the receptor for the neurotransmitter and its associated ion channel
what kind of event is an action potential?
all or nothing: speed and magnitude of depolarization do not vary from one action potential to another
summation
the addition of stimuli
excitatory postsynaptic potentials (EPSP’s)
excitatory neurotransmitters that cause postsynaptic depolarization
inhibitory postsynaptic potentials (IPSPs)
inhibitory neurotransmitters that cause postsynaptic hyperpolarization
temporal summation
a single presynaptic neuron fires action potentials so rapidly that EPSPs or IPSPs pile up on top of each other
spatial summation
EPSPs and IPSPs from all the synapses on the postsynaptic membrane are summed at a given moment in time
what is the sensory function of the nervous system
receiving information (PNS)
what is the integrative function of the nervous system
processing the information (CNS)
what is the motor function of the nervous system
acting on the integrative processes (PNS)
motor neurons
carry information from the nervous system toward organs which can act upon that information
effectors
organs that act upon the information carried by motor neurons
efferent neurons
motor neurons that carry information away from the CNS and innervate effectors
afferent neurons
sensory neurons which carry information toward the central nervous system
reflex
the simplest form of nervous system activity, in which a direct motor response to sensory input occurs without conscious thought
monosynaptic reflex arc
a reflex that involves only two neurons and one synapse (spinal cord) ex. muscle stretch reflex
inhibitory interneuron
a short neuron which forms an inhibitory synapse with a motor neuron, example of the integrative role of the nervous system, ex. reciprocal inhibition of muscles
nuclei
bunches of neuronal cell bodies in the CNS
ganglia
bunches of neuronal cell bodies located outside of the CNS
what does the CNS consist of?
spinal cord and brain
another word for hindbrain
rhombencephalon
another word for midbrain
mesencephalon
another word for forebrain
prosencephalon
how many cranial and spinal nerves are there?
12 pairs of cranial and 31 pairs of spinal nerves
vagus nerve
a cranial nerve that decreases heart rate and increases GI tract activity, part of the parasympathetic division of the autonomic nervous system
what is the organization of the somatic PNS?
all somatic motor neurons innervate skeletal muscle cells, use ACh as their neurotransmitter, have their cell bodies in the brainstem or the ventral portion of the spinal cord, have a long dendrite extending from a sensory receptor toward the soma (located just outside the CNS in a dorsal root ganglion)
dorsal root ganglion
bunch of somatic (and autonomic) sensory neuron cell bodies located dorsal to the spinal cord. outside the meninges but within the vertebral column, considered outside of the CNS
meninges
protective sheath of the brain and cord
where is the first synapse of somatic sensory neurons?
in the CNS
preganglionic neuron
cell body in the brainstem or spinal cord, sends an axon to an autonomic ganglion located outside the spinal column
postganglionic neuron
synapses with preganglionic neuron, sends an axon to an effector (smooth muscle or gland)
what does the organization of autonomic PNS consist of?
preganglionic and postganglionic neurons
what is the neurotransmitter released by autonomic preganglionic neurons?
acetylcholine
what is the neurotransmitter released by autonomic parasympathetic postganglionic neurons?
acetylcholine
what is the neurotransmitter released by autonomic sympathetic postganglionic neurons?
norepinephrine (NE)
where is the cell bodies of sympathetic preganglionic efferent neurons located?
thoracic (chest) or lumbar (lower back) regions of spinal cord
where is the cell bodies of parasympathetic preganglionic efferent neurons located?
craniosacral (in the head/cranium or lower back/sacral portion)
length of the preganglionic axon in the sympathetic system:
short, few but large ganglia, very long post-ganglionic cell
length of the preganglionic axon in the parasympathetic system
long, small ganglion close to effector, short post-ganglionic cell
how are autonomic afferent (sensory) neurons different to somatic afferent neurons?
they can synapse in the PNS (at the autonomic ganglia) with autonomic efferent neurons to form a “short reflex”
adrenal gland
located above each kidney, consists of the inner medulla and outer cortex
what hormones does the adrenal cortex secrete?
glucocorticoids, mineralocorticoids, and some sex hormones
what system is the adrenal medulla part of?
the sympathetic nervous system, it is directly innervated by sympathetic preganglionic neurons
what does the adrenal gland release when the sympathetic system is activated?
epinephrine (adrenaline), acts like a neurotransmitter because of rapid but short effects
