Nervous System Flashcards
What maintains the Na+ & K+ gradients in a neurone?
the Na+/K+ ATPase
What happens when a neurone is stimulated?
- the gated ion channels open
- this causes a change in membrane potential producing a graded potential
- once the threshold potential is reached, an action potential is fired up
Where is org- found?
Inside of the cell. They never leave.
Neurones are very _______
excitable or responsive to stimulit
What determines the permeability of the cell membrane to ions?
- ion channels = ions diffuse through them down their concentration gradient.
What are the important ions that contribute to the electrical properties of a neurone?
Na+, K+, Ca2+, Cl- & large negatively charged organic ions
What types ion channels are found on the cell membrane?
- Gated ion channels
- Non-gated ion channels (leakage channels)
Explain the importance of the higher amount of K+ non-gated ion channels in a neurone.
- this means that the cell is more permeable to K+ which causes them to diffuse out of the cell due to concentration gradient
- As more K+ leave, the inside of the cell because more -ve, causing Na+ to go in due to the opposite charge attraction (But there are not a lot of Na+ non-gated channels, so the inside of the cell won’t become too positive)
- This movement happens until the cell reaches -70mv, where Ka+ going out = Na+ going in
Where is a neurone usually stimulated and what happens when it is stimulated?
- cell body or the dendrites
- when stimulated, an electrical impulse may be generated and passed on through the axon (nerve impulse)
What causes the electrical properties of cells?
- the ionic concentration differences (gradient) across membrane
- permeability of cell membrane to ions
What are the different types of gated ion channels and what are they responsible for?
- voltage gates = deals with membrane voltage changes
- chemical gates = deals with chemicals eg. binding of hormones/neurotransmitter
- thermal gates = deals with temperature
- mechanical gates = deals with mechanical deformation
what is the voltage of threshold
-55mv
What is a Resting Membrane Potential (RMP)?
- when the neurone is at rest or not stimulated, there’s a charge difference (potential difference) that exists across the cell membrane called membrane potential
What is the role of a non-gated channel or leakage channel in a neurone?
- they are always open
- they are very important in establishing Resting Membrane Potential
- They are more permeable to K+ at rest, therefore higher concentration of K+ is found inside of the cell rather than Na+
Cl- is repelled by what? What does this mean
Org- ions. It means that the Cl- concentration is higher outside of the cell
Explain the role of the Na+/K+ ATPase further.
- The ATPase is not a channel.
- it breaks down 1 ATP and uses the energy to pump out 3 Na+ and 2 K+ in.
- as a result, it maintains the concentration gradient of Na+ and K+. and contributes little +ve inside the cell (only 2 K+ go in and 3 Na+ go out)
What is the role of gated ion channels in a neurone?
- they are only active during stimulation.
- they open their gates in response to stimuli
What is the voltage of an RMP?
- about -70 mV
Is the Na+/K+ ATPase a channel?
no
What is the net movement of charge in a RMP?
0
What factors determined the rate of propagation and explain why.
1) Fibre (axon) diameter = the larger the diameter, the faster the propagation because there is less resistance to the ion flow or current
2) myelination = in unmyelinated axons, the AP travels all throughout the axon (Na+ ion channels are adjacent to each other), making it a continuos conduction, therefore it’s slower
- in a myelinated axon, the AP travels at the nodes of ranvier (the ion channels are only present here), making it a leaping/saltatory conduction, meaning faster
What determines the RMP?
- Na+/K+ ATPase
- the negatively charged organic ions trapped inside the cell
- the higher amount of K+ non-gated channels than Na+ channels
What is a Graded Potential (GP) and what are the possible results?
- when stimulation causes small changes in RMP
- stimulation usually occurs on the dendrites or cell body which causes gated ion channels to open?
- depolarization & hyperpolarization
Does the Na+/K+ ATPase pump both down or against their concentration gradient?
against because this is active transport
What is a relative refractory period and why does this happen?
- when an AP cannot be generated after it has been fired BUT can be fired with a larger than normal stimulus. This happens during phase d or hyperpolarization. If the stimulus can reach the threshold, an AP can be fired up again.
What is the voltage of hypepolarization?
Less than -55 mV
What is depolarization?
when the cell because less -ve or more positive +ve
What happens after a GP?
- repolarization = the return to RMP after depolarization or hyperpolarization
What is hyperpolarization?
When the cell becomes more -ve
List the characteristics of GP?
- Graded Potentials move passively
- they can summate (eg. 2 GP’s can occur together which overall create the resulting GP)
- GP’s are short distance signals meaning they die away quickly
- the magnitude and distance travelled by the GP is determined DIRECTLY by the strength of the stimulus (eg. larger stimulus, larger GP)
What is the role of a GP?
- it is important in initiating an Action Potential
- if the GP causes depolarization and if it’s large enough (due to a critical stimulus or multiple GP’s added together) to reach threshold, then an AP will be fired up
What are electrically excitable cells?
- nerve or muscle cells
- they are capable of producing departures from RMP due to stimulation
What is an Action Potential?
It is a large change in membrane potential that propagates along an axon with a consistent intensity?
What is the voltage of an action potential?
+30 mV
What happens during depolarization?
- More voltage-gated Na+ channels open making the membrane more permeable
- This causes more Na+ to diffuse into the cell and at the same time open more voltage-gated Na+ channels (positive feedback mechanism)
- This continues to happen until the cell becomes +30 mV
How many Action Potentials are needed to cause measurable change in ion in the cell?
- 10,000
What type of gates are operating in an AP
ONLY voltage gates
What is an absolute refractory period?
- A time when an AP cannot be summated or generated despite the how strong the stimulus is.
What are the steps to achieving action potential?
critical stimulus –> reaching threshold –> AP
Why can’t another AP be summated or generated during an absolute refractory period?
Because all voltage-gated Na+ channels are activated or open (region b or depolarization) OR all the Na+ channels are deactivated or closed (region c or repolarization)
What is an IPSP and what types of nT activate this?
- Inhibitory Postsynaptic Potential
- In which graded potential becomes hyperpolarization due to the opening of K+ ion channels or Cl- ion channels
- this prevents the cell from achieving an AP
- glycine or GABBA
Explain the propagation of an Action Potential
once the action potential is fired up in a cell, the +ve ions travel through the the axon to the terminal ends and reaches the adjacent membrane. the previous +ve ions depolarizes the adjacent membrane reaching the threshold and an AP occurs. Then
What is an EPSP? And what nTs usually activate this?
- Excitatory Postsynaptic Potential
- in which, a graded potential becomes depolarization due to the opening of Na+ or Ca2+ ion channels, or the closing of K+ ion channels
- acetylcholine or glutamate
What are the types of gates operating in a graded potential?
- thermal, mechanical and chemical
What is a synapse?
a junction where a presynaptic neurone and a postsynaptic neurone connect for transmission
Do the Na+/K+ ATPase work continuously? why or why not?
Yes, to maintain the concentration gradients
Explain the procedure of a PSP
- many neurones can synapse into one neurone –> if a lot of EPSP’s are generated –> summation occurs –> large are of membrane is the depolarized –> spreads to the axon hillock –> If EPSP’s reach the threshold, an AP will be fired
- BUT the neurone can get IPSP’s too –> the sum of the IPSP’s and the EPSP’s will determine wether an AP can be achieved
When does the cell return to RMP?
once the K+ gated channels close
What happens during repolarization?
- voltage-gated Na+ channels begin to close making the membrane less permeable to Na+ = as a result, the Na+ movement returns to resting levels
- voltage-gated K+ channels begin to open, diffusing out K+ from the cell which causes the cell to become more -ve
Explain the synaptic transmission at neuromuscular junction?
- this takes place at the junction between an axon terminal of a neurone and an individual muscle fibre
- the nT is released from the neurone (always ACh)
- the Na+ gated ion channels open on the muscle motor end plate which is called the sarcolemma
- GP is generated which causes an End Plate Potential or EPP
- EPP triggers AP on sarcolemma
- lots of ACh is released in, therefore AP is always guaranteed to happen
Describe a Type A axon/fibre.
- large diameter,
- myelinated
- propagates AP at about 130m/s
- usually found in sensory & motor neurons, and skeletal muscles
Explain the steps of a synaptic transmission.
1) AP reaches the axon terminal (at the synaptic end bulb)
2) Ca2+ gated ion channels open due to the AP, allowing Ca2+ from the outside to diffuse in.
3) The rise of Ca2+ inside the membrane, triggers exocytosis of neurotransmitter in vesicles
4) the Nts cross the synapse and bind to the designated receptors on the postsynaptic membrane
5) gated ion channels open, allowing movement of ions in our out of the cell
6) this causes a graded potential called Postsynaptic Potential or PSP
Describe a Type C axon/fibre
- small diameter
- unmyelinated
- propagates AP at about 0.5 m/s
- found in autonomic nervous system and some pain fibres
What direction do AP’s move to?
They move in one direction because the previous membrane is in refractory period
Where do APs travel faster, a myelinated or an unmyelinated axon?
myelinated
What is the all-or-none phenomenon?
An AP can either fire up or not. It is always the same intensity when fired (+30 mv)
What happens after hyperpolarization?
- voltage-gated K+ channels stay open longer than necessary
- voltage-gated Na+ opens or becomes reactivated to allow the cell for future stimulation
What is the voltage of depolarization?
-55 mV and above
What makes up the central nervous system?
The brain and the spinal cord
What is the afferent nervous system
nerves responsible for sensing a stimulus and sending signals/info about the stimulus to the central nervous system
In afferent nervous system, the stimulus is detected by
a receptor
Receptors can be?
- dendrites of a unipolar neurone
- an individual cell which synapses on a neurone
Give an example of an individual cell synapsed on a neurone?
Hair cell
What happens when a receptor is stimulated
- gated ion channels open, mostly Na+
- generator potential occurs
What happens when dendrite on a unipolar neurone is stimulated?
- It directly generates an AP
- Generator Potential/Receptor Potential —> Action Potential
What happens when an individual cell synapsed to a neurone is stimulated?
receptor potential on the individual cell –> nT is released to the associated neurone —> generator potential occurs on the neurone —> Action potential
What are some types or receptors?
Phasic Receptors & Tonic Receptors
What is a Phasic Receptor?
- they respond to stimulation change
- in the presence of constant stimulation, they show adaptation (less sensitivity to stimulation = decreased frequency of AP to the CNS)
What is a Tonic Receptor?
- no Adaptation = frequency of AP to the CNS is constant
- they give continuous info to the CNS, eg. pain and posture for protection
- they monitor presence and intensity of stimulus
How does the brain perceive different types of stimuli?
- mainly by the type of receptor stimulated
- the axon activated by the receptor synapses to part of the CNS concerned with that sense
What type of receptor is the Meissner’s Corpuscle?
Touch Receptor
What happens when the Meissner’s corpuscle in the right index finger is stimulated?
It impulses to the postcentral gyrus region for right index finger
The mechanical pressure on an eyeball is perceived as ________
Light
How does the brain perceive stimuli of different strengths?
- by the frequency of the AP (#/time)
- the stronger the stimulus = the higher the frequency
More receptors are activated when the stimulus is ________
stronger
What is the ascending pathway for touch?
- Meissner’s corpuscle –> medulla –> thalamus -> postcentral gyrus
What does the postcentral gyrus do?
- It processes the information regarding the stimulus, it identifies it and localizes it.
What is the ascending pathway for vision?
light enters the pupil –> image focused in the retina (reduced and inverted) –> light stimulates chemical reaction on rods and cons (receptor potential) –> nt released –> bipolar neurones (graded potential) –> nt –> ganglion cell (generator potential, get AP) –> optic nerve (axons of ganglion cells) –> optic tracts –> visual cortex of occipital lobe
What is the ascending pathway for hearing?
hair cells on the cochlear ducts gets stimulated (receptor potential, no AP) –> nt –> associated neurone (generator potential, get AP) –> neurone of cochlear branch of cranial nerve VIII –> auditory cortex of temporal lobe
What is the ascending pathway for equilibrium
Check answer from notes, Topic 4, page 4
What is the afferent division of the NS?
responsible for sending info to the brain + spinal cord (CNS)
What is the efferent division of the NS
- It sends info away from the CNS aka the output
What is a reflex?
it is a rapid, automatic response to a stimuli
for reflexes, stimulus always causes the _______
same motor response
Reflex is not for protection. True or False
False
How many neurones are involved in a reflex?
2 or more
Indicate the basic procedure of a reflex arc
stimulus —> Reflex —> CNS –> Effector
Reflexes are categorized into what?
Effector, which side of the body the motor+sensory neurones are located & the number of synapse + neurones in an arc
what is a somatic reflex
When the effector is skeletal muscle
What is a visceral reflex?
When the effector is smooth muscle, cardiac muscle or glands
When the motor + sensory neurones are on the same side, what type of reflex is it?
ipsilateral reflex
When the motor + sensory neurones are on opposite sides, what type of reflex is it?
contralateral reflex
Describe a monosynaptic reflex
when there is one synapse between a sensory neurone and a motor neurone
When there is 2 synapses between 3 neurones, what type of reflex is this?
polysynaptic reflex
Give examples of a somatic reflex?
- stretch reflex
- flexor (withdrawal) reflex
- crossed extensor reflex
What is a stretch reflex, what is it’s stimulus, receptor and effector, what is categorized into and give an example?
- the extensor muscle contracts
- stimulus - tapping the patellar ligament which stretches the quadriceps femoris muscle
- receptor - muscle spindle in quads
- effector - skeletal muscle in quads it contracts
- ipsilateral, monosynaptic
- knee jerk reflex
What is a Flexor (Withdrawal) Reflex (stimulus, receptor, effector), and what is it categorized into and give an example
- stimulus = stepping on a nail
- receptor = touch, pressure, pain
- effector = hamstrings (flexor) contracts
- ipsilateral and polysynaptic
- in leg
What is a crossed extensor reflex (stimulus, receptor and effector), What is it categorized into and give an example
- stimulus = stepping on a nail
- receptor = touch, pressure, pain
- effector = quadriceps femoris in the opposite leg (extensor) contracts
- contralateral and polysynaptic
What is a reciprocal inhibition?
when an agonist contracts and the antagonist is inhibiting from contracting (inhibitory interneurones firing)
in reciprocal inhibition during a stretch reflex, what is the agonist and what is the antagonist?
agonist = quadriceps femoris antagonist = hamstrings
What is the effector of an autonomic spinal reflex?
- smooth muscle, cardiac muscle or gland
What is an example of an autonomic spinal reflex and what is its stimulus, receptor, CNS and effector
- Micturition reflex in the urinary bladder
- stimulus = the stretch of bladder
- receptor = stretch receptors on the bladder wall
- CNS = sacral segment of the spinal cord (PSNS)
- effector = detrusor muscle of urinary bladder contracts & the internal urethral sphincter opens (both are smooth muscle)
What is the cerebrum?
- It interprets sensory information from general and special senses
- it deals with memory and intellect
- it relays info to different areas of the brain and spinal cord (association, commissural and projection tracts)
- it initiates and controls skeletal muscle movements (motor areas and basal nuclei)
What is the brainstem?
- ## it controls life-sustaining processes such as breathing and circulation
If the brain stem is functioning but higher centres are damaged, what happens?
- a human will be still be alive but not aware, no conscious control
What are the different parts of the brainstem
- midbrain, pons and medulla
What does the midbrain do and where does it belong to?
- it controls auditory and visual reflexes (eye movement, head and neck movement in response to auditory/visual stimuli)
- brain stem
What part of the brain stem works with the medulla to regulate breathing
- pons
due to the pons’ role in breathing regulation, it is considered to be a part of
pontine respiratory centres
What are the function regions of the medulla?
1) decussation or crossing of the sensor + motor tracts
eg. left brain controls the right skel. muscles, and receives sensory input from the right side
2) autonomic vital reflex centres
- Respiratory area = drives breathing rate
- Cardiovascular Centre =
- cardiac area = modifies heart rate
- vasomotor area = controls the blood vessel diamater
3) other areas for non-vital centres = controls swallowing, coughing, sneezing, vomiting etc.
What are the major functions of the hypothalamus?
- regulates the Autonomic Nervous System (smooth + cardiac muscles, glands)
- regulates parts of the endocrine system
- regulates temperature via “thermostat cells”
- regulates food and water intake, body fluid concentration
- part of the limbic system (composed of cerebrum, thalamus and hypothalamus)
- this is the emotional brain where basic emotions are regulated
- co-ordinates reticular activating system
- in reticular formation (functional area of the brain stem) = alerts rest of brain
- receives sensory input for awakening = sets daily rhythm (sleep/awake)
What happens when the hypothalamus is damaged
- loss of homeostasis since it controls major homeostatic functions
What is the basic pathway of the efferent nervous system?
CNS –> smooth, cardiac muscle or gland
How many and what neurones are involved in the efferent nervous system
2 neurones called preganglionic and postganglionic
neurones in ANS of the efferent NS can be distinguished by type of nt released. What are they?
- cholinergic = Ach
- adrenergic = norepinephrine (NE)
The Autonomic Nervous System is dived into two parts, what are they?
- Sympathetic & Parasympathetic NS
What is the Sympathetic NS in charge of?
- preparing the body for activity
- flight or fight response
- activated during exercise
What is the pathway of the Sympathetic NS?
CNS (cell bodies in spinal cord) [Axon exits via spinal nerves T1 - L2] —> preganglionic neurone -> nT = ACh –> postganglionic neurone –> nT = NE except sweat glands, its ACH –> Effector
In Autonomic NS of efferent neurones, how is chemical stimulation stopped? Give examples.
- nT is removed
- ACh is broken down by Acetylcholinesterase (AChE) by the postsynaptic membrane
- NE is broken down by Monoamine Oxidase (MAO) in the synaptic end bulbs of the neurone that released it
What is the parasympathetic NS responsible for?
for resting and digesting
What is the pathway of the parasympathetic NS?
CNS (brain stem or sacral spinal cord –> preganglionic neurone –> nT = ACh –> postganglionic neurone –> nt = ACh –> Effector
What does the Autonomic nervous system do?
controls the non-consciously directed bodily functions like breathing, digesting and heart beat
Most organs innervated by ANS only have either SNS or PSNS, never together. True or False
False, most organs have both SNS and PSNS and work opposite actions
Recite the “Effects of ANS Table” From topic 6, page 2
did you get it right?
What are the higher control areas of the ANS?
medulla –> hypothalamus (the boss)–> cerebrum for emotions
What is the pathway of the Somatic NS for the efferent NS
CNS (brain) –> upper motor neurone –> CNS (spinal cord) –> lower motor neurone –> E = skeletal muscle
What are the three types of movement, the somatic NS is responsible for?
1) Reflex
= spinal reflex - least complex, requires sensory input
= postural reflex - for balance and posture, requires input from proprioceptors (muscle spindle), eyes, inner ear
2) Voluntary - most complex, no external stimuli required (act of will)
3) Rhythmic - combinations of reflex and voluntary
- walking, running, etc
Explain the pathway of motor control.
Check the diagram from page 3 of Topic 6.
What happens during Level 1 of motor control?
- Planning
- it asks the question, “do you want to move?” if yes, “what movement is needed and which muscles need to contract?”
- it plans muscle contractions sequence
- it signals primary motor cortex
- works with input from cerebellum
What happens in level 2 of motor control?
it signals directly to lower motor neurones via corticospinal tract for fine skilled movements only
What happens in Level 3 of Motor control?
Brain stem nuclei –> descending motor tracts –> lower motor neurones (therefore it travels in indirect tracts)
- its involved in co-ordinating large muscle groups
- its important in maintaining posture and locomotion
Where does the brain stem nuclei get its input from?
The cortex, basal nuclei & cerebellym
In Level 4, What does the Spinal cord contain and what are they for?
- cell bodies of lower motor neurones
- networks of neurones like (Central Pattern Generators; CPGs) which set rhythmic, repeated movements like walking and running
what does the spinal cord need to begin or stop movements?
cortical signals
what is the role of the cerebellum in motor control?
- plays a role in planning and initiating movements => sends input to the cortical areas
- it stores planned movements and compares it to the actual by receiving input from proprioreceptors, and corrects the movement if necessary
- it maintains balance, controls eye movements, and plays a role in maintaining muscle tones (low level of contractions)
- coordinates skilled voluntary muscle movements and timing of contractions involving more than 1 joint
What is the role of the basal nuclei in motor control?
- it aids in planning movement
- plays a role in maintaining muscle tones
- suppresses unwanted motions eg. at rest
What is the corticospinal (direct) pathway?
- cortex to skeletal muscle
What are the 2 parts of the direct pathway?
- upper motor neurones = cell bodies in the primary cortex and axons down the spinal cord
- lower motor neurones = cell bodies in the ventral horn of the spinal cord and axons exit via spinal nerves
What happens when the upper motor neurones are destructed?
- reflex arcs will still be present BUT one will get spastic paralysis and exaggerated reflexes
What is a spastic paralysis?
its an increase in muscle tone meaning no muscle atrophy
What are some examples of exaggerated reflexes?
- patellar, achilles and babinkski sign
During a plantar reflex what happens normally?
- once the sole of the foot is scratched, in a normal response, the toes flex or curl under
During a plantar reflex what happens when the upper motor neurones are damaged?
- presence of babinski sign in which the big toe extends but this is normal for babies
What happens when the lower motor neurones are destructed?
- no reflex arcs (no reflex at all)
- flaccid paralysis
What is a flaccid paralysis?
a decrease in muscle tone so there is marked muscle atrophy
Give an example of a Flaccid paralysis.
polio or poliomyelitis = the virus destroys cell bodies in ventral horn of spinal cord
In most people, what ares of the brain plays a role in speech
areas in left cortex
What are the important brain regions in relation to speech?
1) cortex = for concepts and ideas
2) Wernicke’s area, brocca’s area and the basal nuclei = makes up the language implementation system
= analyzes incoming and produces outgoing words sounds and grammatical structures
Explain in general what happens to produce speech
Signals pass from the language areas to the premotor cortex to plan muscle contraction and then passed to the primary cortex to initiate planned contractions
What happens when the Wernicke’s area is damaged?
- one wont be able to understand spoken or written words
- they can speak but words are meaningless or mixed up
What happens when the Brocca’s area is damaged?
- they can understand words but can’t produce sensible speech
