physiology topic 1 Flashcards
neural system
What does the central nervous system (CNS) consist of?
the brain and spinal cord (vertebrates)
what takes place in the CNS?
integration (processing)
What system carries information in and out of the CNS?
peripheral nervous system (PNS)
What does the PNS consist of?
nerves (neurons) and ganglia
more specifically, cranial nerves, ganglia outside CNS and spinal nerves.
What supporting cells do the neurons of both the PNS and CNS require?
glial cells or glia
Is ganglion=glia?
no
(ganglion is any bulging part in the spinal cord)
what does the ganglion consist of?
cell bodies
What do the brain and spinal cord contain?
gray matter and white matter
What does gray matter consist of?
neuron cell bodies, dendrites and unmyelinated axons
What does white matter consist of?
bundles of myelinated axons which do not conduct electricity (made of fat)
what is neuron?
nerve cells that transfer information within the body
what are the two types of signals used by neurons to communicate?
electrical signals (long distance) and chemical signals aka neurotransmitter (short distance)
Name the components and functions of the neuron structure
- neuron cell body - most neuron’s organelles are located there
- dendrites - highly branched extensions that receive signals from other neurons
- axon - a longer extension that transmits signals to other cells
- axon hillock - joining of an axon and cell body
- synapse
- a junction between an axon of the presynaptic cell and postsynaptic cell
- synaptic terminal of one axon passes information across the synapse in the form of neurotransmitter.
What is the function of the myelin sheath?
to enclose axons, form cellular insulation and speed up signal transmission
How is information transmitted?
from a presynaptic cell (neuron) to a postsynaptic cell (neuron, muscle, gland cell)
What does glia do?
to nourish, support, regulate and insulate neurons
List out the types of glia and its function found in CNS
HINT: EMORA
EMORA
1. ependymal cells (promote circulation of cerebrospinal fluid in ventricles)
2 microglia (protect the nervous system from microorganisms)
3. Oligodendrocytes (form myelin sheaths around axons in CNS)
4. Radial glia (has a role in embryonic development of the nervous system & can hardly be seen)
5. Astrocytes (must be in middle of neuron and blood vessel)
- provide structural supports for neurons
- regulate extracellular ions and neurotransmitters
- induce the formation of a blood-brain barrier tht regulates the chemical environment of CNS
List out the types of glia and its function in PNS
HINT: ss
Shock Sendiri
1. satellite cells
- surround neuron cell bodies in the ganglia
- regulate O2, CO2, nutrient and neurotransmitter level around neurons in ganglia
2. Schwann cells
- surround all axons in PNS
- responsible for myelination of peripheral axons
- participate in repair process after injury
Does the transmission of information depend on the path of neurons along which a signal travels?
yes
What are the 3 stages at which the nervous systems transmits and processes information?
sensory input -> integration -> motor output
List out the types of neurons and its functions
- sensory neurons (has a cell body in the middle of axon)
- transmit information about external stimuli (e.g. light, touch) - interneurons (no cell body)
- integrate the information - motor neurons
- transmit signals to muscle cells
describe how the 3 types of neuron work together
- sensory receptors detect external stimuli and transmit information along sensory neurons
- sensory input is sent to the brain (CNS) / ganglia (PNS)
- interneurons integrate the information
- motor output leaves the brain/ ganglia via motor neurons
- motor neuron sends signals to the effector, which trigger muscle or gland activity = response.
Describe how the 3 types of neurons work together IN ANSWERING A QUESTION verbally, after being asked by a lecturer.
- sensory receptors of the ears detect the stimulus/ sound
- Sensory input is sent by the sensory neuron to the brain
- interneurons integrate the information
- motor output leaves the brain via motor neuron
- motor neuron sends signal to the effector tissues which are muscles in the tongue, lips, jaws, and pharynx to vibrate the vocal cord.
define reflex
- the body’s automatic response to a stimulus
- signal is transmitted via spinal cord and independently of the brain
- e.g. knee-jerk reflex
describe knee-jerk reflex
- when the knee is tapped, a sensory receptor detects a stretch in the muscle
- a sensory neuron conveys this information (sensory input) into the CNS (spinal cord)
- In CNS (spinal cord, no brain), the information (motor output) goes to a motor neuron and to one or more interneurons
- One set of muscles (quadriceps) responds to motor signals conveyed by a motor neuron by contracting. jerking the lower leg forward
List out examples of reflex arcs
- knee-jerk reaction
- pupil dilation
- sneeze reflex
- reflexes maintain homeostasis
- automatic actions of swallowing, coughing
- maintain balance and posture
- brain reflexes involve reflex center in brainstem
What are the 4 basic functions that sensory pathways have in common?
sensory reception, transduction, transmission => involve sensory neuron
integration/ perception => involve interneuron / response => involve motor neuron
what do all stimuli represent?
forms of energy
what do sensory receptors convert stimulus energy into?
a change in the membrane potential
where do sensations and perceptions begin?
with sensory reception detection of stimuli by sensory receptors)
where does a stimulus start being sensed?
Sensory receptors of sensory organ
What are the 5 categories of sensory receptors?
- *mechanoreceptors (pressure or movement, e.g. skin & muscles)
- *chemoreceptors (chemical, e.g. in the tongue)
- electromagnetic receptors (light, elec, magnetism, e.g. eyes)
- thermoreceptors (temperature, e.g. skin)
- pain receptors (tissue damage, e.g. skin)
compare mechanoreceptors and chemoreceptors
mechanoreceptors:
-found in dendrites of sensory neurons
- sense physical deformation caused by stimuli (pressure)
- E.g. stretching causes gated ion channels of dendrites to open and allow positive ions to enter stretch
- They typically consist of ion channels linked to structures that end outside the cell, such as “hairs”
Chemoreceptors:
- Found in dendrites of sensory neurons
- Transmit information about the concentration of a solute
- E.g binding of a stimulus molecule to a ligand gated ion channel causes the chemoreceptor to become more or less permeable to ions
- The antennae of the male silkworm moth have very sensitive specific chemoreceptors
what is sensory transduction?
is the conversion of stimulus energy into a change in the membrane potential (electrical energy) of a sensory receptor.
what is the conversion of stimulus energy into the change in membrane potential called?
receptor potential
what are graded potentials?
receptor potentials
Explain why receptor potential is known as ‘graded potentials’
Their magnitude varies with the strength of the stimulus. The stronger the stimulus, the higher the value/ the more ion channels will open
where does a stimulus start being transduced?
dendrites
what happens after energy has been transduced into a receptor potential?
some sensory cells generate the transmission of action potentials to the CNS
the size of the receptor potential increase means tht the?
the intensity of the strength increases
where does a stimulus start being transmitted?
axon hillock
what are perceptions?
the brain’s construction of stimuli
what happens when an action potential reaches the brain?
Action potential reaches brain. Brain processes this
input and generate perception of this input.
how does the brain distinguish stimuli?
The brain distinguishes stimuli from different
receptors by the area in the brain where the action
potentials arrive.
what is the use of intracellular recording?
to monitor the changes in membrane potential
define membrane potential
the voltage (difference in electrical charge) across the plasma membrane that every cell has
define resting potential
is the membrane potential of a
neuron not sending signals.
define action potential
Changes in membrane potential or the membrane potential of a neuron that sends signals
or
a strong stimulus results in a massive change in membrane voltage (signals that carry information along axons)
what is the value of resting potential?
-70mV
why is resting potential -70mV
- distribution of ion
outside cell [Na+] increases, [K+] decreases - the difference in numbers of K+ & Na+ non-gated channels (passive transport)
- Na+/K+ pump
- net movement of 1 cation out of the cell
how is resting potential maintained?
- Inside the cell is negative, outside the cell is positve
- resting potential is -70mV
- Anions and negatively charged proteins contribute to the negative charge with the neuron
- inside the cell has greater K+, outside the cell has greater Na+
- More non-gated K+ channel and fewer non-gated Na+ channel
- K+ diffuses out of the cell while Na+ diffuses into the cell
- sodium-potassium pumps use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane (3 Na out, 2K in)
- the opening of ion channels in the plasma membrane converts chemical potential to electrical potential
Question: Inside cell is relatively more negative mainly due to?
Note: There is no net movement of K+
Anions and negatively charged proteins
How many kinds of Na
and K channels are there?
2 kinds. Non-gated ion channels (open all the time) and voltage-gated ion channels
State the value of the membrane
potential of a resting neuron.
Describe how the neuron
maintains the resting potential.
Value?
70mV
Charges? Due to?
negatively charged, due to presence of
anions and negatively charged proteins that
contribute to the negatively charge of the
inside neuron
Distribution & concentration of ions?
More sodium outside and more
potassium inside
Type of channels?
There is more non-gated potassium
channels as compared to non-gated
sodium channels
Movement of ions?
efflux of potassium ions,
influx of sodium ions
ATP?
sodium-potassium pump uses ATP to pump
out 3 Na from the neuron and 2 K
into the neuron
what channels in the neuron open or close in response to stimuli?
-voltage-gated ion channels
-opening or closing of these channels changes the permeability of ions across membranes
-membrane potential (-70mV) changes with an increase or reduction in the magnitude
changes in membrane potential result in graded potential
what are the types of graded potential?
graded hyperpolarization and graded depolarization
explain hyperpolarization
HINT: further from the threshold
- when voltage-gated K+ channels open, K+ diffuses out, making the inside of the cell more negative
- leading to an increase in magnitude of the membrane potential (farther from threshold) = threshold value is -55mv therefore an increase in magnitude means -50 -> -60
- graded hyperpolarizations produced by 2 stimuli that increase membrane permeability to K+
explain depolarization
HINT: nearer to the threshold
- when voltage-gated Na+ channels open, Na+ diffuses in, making the inside of the cell more positive
- a reduction in the magnitude of the membrane potential
- graded depolarizations produced by two stimuli that increase membrane permeability to Na+
what effects does graded potential have?
on the generation of nerve signals in dendrites of neuron
what happens to the graded potential if the stimuli are weak?
fade away
How does action potential occur?
if a stimulus causes the membrane voltage to cross a particular threshold
explain why action potential is an “all or none” event
action potentials always have the same amplitude of depolarization and can only be generated if a threshold is achieved.
it is independent, regardless of the strength of the stimulus
- it is actively propagated or regenerative
how can action potential be initiated?
if stimulus is strong enough, enough number of ions travel from dendrites to axon hillock
explain the production of action potential
- at resting potential, most voltage-gated Na+ and K+ channels are closed, but some K+ channels (not voltage-gated) are open
- In depolarization, a stimulus opens some voltage-gated Na+ channels; Na+ influx. If threshold is reached, an action potential is triggered later
3a. During the rising phase, the threshold is crossed and the membrane potential increases
3b. More voltage-gated Na+ channels open and more Na+ influx
4a. During the falling phase, voltage-gated Na+ channels become inactivated
4b. Voltage-gated K+ channels open and K+ efflux - During the undershoot, membrane permeability to K+ is at first higher than at rest (voltage-gated K+ channels more slowly)
- voltage-gated K+ channels close and resting potential is restored
what is refractory period?
add info: During the refractory period after an action potential, a second action potential cannot be initiated
- action potential travels in one direction
Temporary inactivation of Na channels behind the zone of
depolarization prevent the action potential from traveling
backwards
explain the conduction of action potential
- when a region of the axon has its sodium channels open, sodium rushes inward and an action potential is generated
- soon, the potassium channels in the same region will open, allowing potassium to diffuse out of the axon; at this time, its sodium channels closes and inactivated
- A short time later, we would see no signs of action potential at this spot because the axon membrane here has returned to its resting potential.
Which type of stimulus (i.e., weaker? stronger?) opens more ion channels of the dendrites of a sensory neuron?
stronger stimulus
- The frequency of action potentials can reflect the strength of a
stimulus
how can the speed of an action potential increase?
- with the axon’s diameter and presence of myelin sheath
- broad axons provide less resistance and action potential moves faster
contrast continuous conduction with saltatory conduction
continuous conduction:
- via unmyelinated axons
- nerve impulses travel along the entire length of the axon.
- slower
- uses more energy
saltatory conduction:
-via myelinated axons’
- nerve impulses travel between nodes of Ranvier
- faster
- uses less energy
why do undershoot happen?
it occurs because of the slow closing of the voltage-gated potassium channel
action potentials are formed where?
- Action potentials are formed only at nodes of Ranvier, gaps in the myelin sheath where voltage-gated Na+ channels are found.
- Action potentials in myelinated axons occurs between the nodes
of Ranvier in a process called saltatory conduction - This is because ions at one node flow through cytosol to the next node , where they depolarizes the membrane and generate
action potential.
list out the types of channel protein
- VG channel
- open channel
- mechanically-gated channel
- ligand-gated channel
How is a message from one neuron transmitted to another?
condition: at electrical synapses
the electrical current flows from one neuron to another through gap junctions
How is a message from one neuron transmitted to another?
condition: at chemical synapses
a chemical neurotransmitter carries information between neurons
how are neurotransmitters synthesised?
the presynaptic neuron synthesize and packages the neurotransmitter in synaptic vesicles located in the synaptic terminal
how is neurotransmitter released?
action potential causes neurotransmitter to release
what happens when a neurotransmitter is released?
the neurotransmitter diffuses across the synaptic cleft and is received by the postsynaptic cell
