nerve cells & connections Flashcards
name the 2 nervous systems
CNS, PNS
name the separate components of the CNS
brain and spinal cord
name the separate components of the PNS
autonomic and somatic nervous system
name the components of the autonomic nervous systems
sympathetic, parasympathetic, enteric nervous system
what is the smooth section of the brain
sulcus
what is the ridges of the brain
gyrus
name the sections of the brain
cerebellum, cerebrum, diencephalon, brainstem
what is the meninges
connective tissue that covers the brain to suspend the brain
name the 4 lobes of the cerebrum
- Frontal lobe
- Temporal lobe
- Parietal lobe
- Occipital lobe
name the 2 components of the diencephalon
- Thalamus
- Hypothalamus
name the 3 components of the brainstem
- Midbrain
- Pons
- Medulla oblongata
what different types of spinal nerves does the spinal cord contain and how many pairs are there
31 pairs of spinal nerves
cervical, thoracic, lumbar, sacral, coccygeal
how many lumbar and sacral in the spinal word, provide where they are located
5 lumbar : hips and legs
5 sacral: Genitalia and gastrointestinal tract
how many cervical, coccygeal & thoracic in the spinal word, provide where they are located
12 thoracic : chest & abdomen
1 coccygeal
8 cervical : neck, shoulders and arms
determine the difference between dorsal and ventral
ventral refers to the front of the body, and dorsal refers to the back
describe the pathway of a stimulus using the spinal cord cross section, include grey/white matter
afferent –> dorsal root ganglion –> grey matter (interneuron) –> ventral root –> efferent
(need to go through which matter go get to grey both in and out)
what and where is the axon hillock in a neuron
initial segment of axon that triggers A.P, located in end of cell body and start of the axon
what is the soma of a neuron
cell body, contains nucleus
name 3 different types of neurosn
afferent, interneurons and efferent neurons
describe the pathway of an electrical impulse using the different types of the neurons
stimulus–>afferent sensory receptor –> interneurons –> efferent motor neuron –> muscle/gland/neuron
provide the different types of morphologies of the afferent sensory neuron and describe what they look like
bipolar and pseudo unipolar, 1 dendrites and 1 axons on either side
provide the different types of morphologies of the interneuron and describe what they look like
multipolar and anaxonic, cell bodies are in the middle of neuron, which more than 2 dendrites and axons
provide the different types of morphologies of the efferent motor neuron and describe what they look like
multipolar, cell body is at the end of the neuron
what are the 4 types of glia in CNS
Astrocytes, Oligodendrocytes, Microglia, Ependymal cells
what is the function of astrocytes (glia type)
Maintain external environment for the neurons
Surround blood vessels and form blood brain barrier
what is the function of oligodendrocytes (glia type)
form myelin Ssheath
what is the function of microglia (glia type)
macrophages of the CNS, hoover up infection
what is the function of ependymal cells (glia type)
produce cerebrospinal fluid
what are the 2 types of glia in PNS
Schwann cells and satelitte cells
what is the role of Schwann cells and satellite cells
Schwann: forms myelin sheath
Satellite: support neuron cell bodies
what is a graded & action potentials
A.P : Transmit signals over long distances
G.P : Decide when an action potential should be fired
what is the role of the Resting membrane potentials
Keeps cell ready to respond
why is the K channels know as leaky in the membrane
K+ leaks out down its concentration
gradient
* This builds up an electrical gradient
how does the conc. gradient and electrical gradient help maintain the resting membrane potential, regarding K+ ions
CG: K+ being pulled out cells
EG: K+ being pulled into cell
what does the the Nernst equation tell us
predicts the equilibrium potential for a single ion species
what is the Gold-Hodgkin-Katz equation measure
Predicts the equilibrium potential generated by several ions
how does the fact that the Na+/K+ pump is electrogenic mean
producing a change in the electrical potential of a cell
why is the leaky K+ channels needed
Without leaky K+ channels, only a small membrane potential would be generated
what happens if too much K+ is ingested
reduces K+ conc. grad. –> smaller electrical gradient at equilibrium –> resting membrane potential reduces –> cell depolarises –> neurons to fire A.P –> seizures
e.g. -70 to -50 mV
how does the B.B.B protect the brain
prevents changes in plasma as capillaries of the brain are especially “tight”
K+ (other polar substances) cannot cross through/or/between, the endothelial cells
provide examples of graded potential
Generator potentials
Postsynaptic potentials
End plate potentials
Pacemaker potentials
where are the graded potentials located
Generator potentials
* At sensory receptors
Postsynaptic potentials
* At synapses
End plate potentials
* At neuromuscular junction
Pacemaker potentials
* In pacemaker tissues
why are graded potentials called local potentials
as they only useful over a short distance
graded potentials are decremental- become smaller as they travel along the membrane
do graded potentials excite or inhibit a cell
both as it depends on magic firing threshold
the Neurotransmitters can open channels that depolarise the cell, or different channels that hyperpolarise the cell
what does the phrase ‘graded potentials can summate’ mean
A single neuron has lots of synapses, evoking their own postsynaptic potential
* If two occur at the same time, they can add to together
* This is important for synaptic integration
provide a summary of the properties of the graded potentials
decremental, depolarising/hyperpolarising, summate
provide the summary of the an ionic basis of graded potentials (EPSP and IPSPs)
EPSPs generated by opening NA+/K+ channels or closing leaky K+ channels
IPSPs generated by opening CL- channels or opening K+ channels
describe ionic basis of AP using voltage
-70mV= resting potential, K+ in
40mV = K+ out and Na+ mV
-90mV = hyperpolarisation, K+ out
what type of threshold do AP potentials have
all or nothing
whats is a refractory period and where is it found
refractory period is is the time in which a nerve cell is unable to fire an action potential (nerve impulse)
in an AP
do ionic, pacemaker APs travel fast/slow and why
slowly as no fast Na + channels , slower action potentials in SA node in terms of how rapidly they depolarize. Therefore, pacemaker AP are slow
how is the stimulus encoded in the APs
through intensity of firing freq., not amplitude
how to speed up an action potential in axon
large axon diameter, reduces axial resistance
&
myelination
what’s the difference of channels between the postsynaptic & action potentials
action potentials : all mediated by voltage gated channels
postsynaptic: ligand gated channels
describe what a larger axon diameter does
Electric current flows more easily down a large axon than a small axon (axial resistance is lower)
* Allows the Na+ channels to be more spaced out along the membrane
provide examples of animals with large axons
squid/ fish/ earthworms
define saltatory conduction
A.P spreads passively from node to node and still reach threshold
what do the demyelinating diseases do to an axon
diseases attack the myelin sheath,
decreased membrane resistance –> more current leaks out of membrane
increased membrane capacitance more current wasted changing up the membrane
conduction fails
nerve fibre type
Aα , Aβ, Aγ, Aδ, C
describe Aα (a nerve fibre type)
anatomy? velocity? function?
largest
myelinated
70-120 m/sec Proprioception,
motor neurons
describe Aβ (a nerve fibre type) anatomy? velocity? function?
Large
myelinated
30-70 m/sec
Touch, pressure
describe Aγ (a nerve fibre type) anatomy? velocity? function?
Small
myelinated
15-30 m/sec
Motor neurons of muscle spindles
describe Aδ (a nerve fibre type) anatomy? velocity? function?
Smallest
myelinated
12-30 m/sec
Touch, cold, “fast” pain
what generates a compound action potential
different nerve fibre types/axons all conduct different velocities therefore
extracellular recordings from a nerve (bundle of axons)
what’s A.P and compound A.P
type of recording ?
where?
AP: intracellular recording
microelectrode through membrane
relative to outside the cell
C A.P: extracellular recording
electrodes outside axons
each A.P very small but add up to large waves
what is the neuromuscular junction
synapse between the motor neuron and skeletal muscles
what is the first step in triggering muscle contraction
it is to evoke an action potential in the skeletal muscle membrane (the sarcolemma)
name the 3 sections of the neuromuscular junction
- Presynaptic terminal filled with vesicles containing acetylcholine(ACh)
- Synaptic cleft
- Postsynaptic end plate of the skeletal muscle fibre
Note the folds of the end plate
descrie the processes within the neuromuscular junction
- Action potential in motor neuron
- Fusion of vesicles (Ca2+-dependent exocytosis)
3 ACh diffuses across synaptic cleft - ACh binds to ACh (nicotinic) receptors
- Opens ligand-gated Na+/K+ channels
- Evokes end plate potential (graded potential)
- (Always) depolarises membrane to threshold
- Opens voltage- gated Na+ channels
- Evokes action potential
- Muscle contracts
- Acetylcholine cleared up
by acetylcholinesterase
the neuromuscular junction: key characteristics: what evokes end plate potentials
Ligand-gated Na+/K+ channels
evoke the end plate potentials
the neuromuscular junction: key characteristics: describe the graded potential and also its relation to threshold
Very large graded potential,
always big enough to reach
threshold
the neuromuscular junction: key characteristics: describe the function of post junctional folds
increase number of voltage-gated Na+ channels close to where it is evoked
the neuromuscular junction: key characteristics: synaptic integration and define it
No synaptic integration occurs here, it acts more like a switch
SI: where multiple inputs combined from multiple neurons to generate AP
describe the range of postsynaptic potentials
- Fast EPSPs (ionotropic)
- Slow EPSPs (metabotropic)
- Fast IPSPs (ionotropic)
- Slow IPSPs (metabotropic)
These are generally small (~1 mV)
What does the range of post synaptic potentials enable
- Enables complex synaptic integration
name the 3 anatomical arrangements of CNS synapses
Axo-dendritic
Axo-somatic
Axo-axonal
synaptic connectivity: describe the difference between divergence and convergence
divergence: from one to many
convergence: many to one
feedback inhibition: what activates the inhibitory interneuron
When action potential fired,
collateral (branch) activates an inhibitory interneuron
feedback inhibition: what are the effects of the activation of inhibitory interneuron
Inhibitory neurotransmitter
released
* Blue neuron hyperpolarises
Prevents repeated firing
describe the different pathways between monosynaptic reflexes & polysynaptic reflexes
Monosynaptic reflexes involve:
* Sensory (afferent) neurons
* Motor (efferent) neurons
Polysynaptic reflexes
involve:
* Sensory (afferent) neurons
* Interneurons
* Motor (efferent) neurons
synaptic plasticity: what is it dependent on
Can be activity-dependent
synaptic plasticity definition
changes in strength of synapses
name a few examples of synaptic plasticity
Long-term potentiation
Long-term depression
name the steps of a muscle spindle reflex
- extrafusal muscle fibres at resting length
- sensory neurons is tonically active
- spinal cord integrates function
- alpha motor neurons to extrafusal fibres receive tonic input from muscle spindles
- extrafusal fibres maintain a certain level of tension even at rest
what does the addition of a load to do the muscle spindle reflex
muscle spindle stretch as arm falls and contraction is initiated by muscle spindle restores arm position
how does the stretch reflex acts as a negative feedback system
the stretch reflex acts as a negative feedback system by detecting stretch of the muscle and making it contract accordingly
what is the problem with muscle spindle reflex if the muscle is already partly contracted and how is this solved?
There is no tension on the
muscle spindle and it cannot
respond to stretch, solved with α-γ coactivation
muscle spindle reflex; describe the orientation of extrafusal fibres compared to intrafusal fibres
how much of muscle do they form? innervated by? where to they lie in comparison to sensory muscle spindle ?
Extrafusal fibres
* Form the main bulk of the muscle
* Are innervated by α motor neurons
* Lie in parallel with the sensory muscle spindle
* Intrafusal fibres
* Form a very minor part of the muscle
* Are innervated by γ motor neurons
* Lie in series with the sensory muscle spindle
Muscle spindle (stretch) reflex: what does the α-γ co-activation of extrafusal and intrafusal fibres allow for
α-γ co-activation of extrafusal and intrafusal fibres allows muscle spindle to respond to stretch whatever the length of the muscle
enables the muscle spindle to act as a stretch receptor, even if the muscle is part contracted
what is the function of muscle spindle reflex
A mechanism to keep muscle at a constant length,
Stretch of the muscle is detected by muscle spindle receptors
what is the function for Golgi tendon organ reflex
A mechanism to ensure that excessive tension does not damage the muscle
name the processes of the golgi tendon organ reflex
- neuron from golgi tendon organ fires
- motor neuron is inhibited
- muscle relaxes
- load is dropped
which reflex is muscle spindle/ Golgi tendon monosynaptic/polysynaptic reflex and provide an example for each
muscle spindle: monosynaptic reflex
patellar tendon (knee-jerk) reflex
Golgi tendon: A polysynaptic reflex
the clasp-knife reflex
what activates the golgi tendon organ reflex
excessive tensions
describe the process during golgi tendon organ reflex
- Afferent fibres activate inhibitory interneurons in the spinal cord
- Inhibits motor neurons supplying the muscle
- Muscle relaxes to prevent damage
what is THE FUNCTION flexion reflex
a mechanism to remove a limb from a damaging/potentially damaging stimulus, and not fall over
describe how the Flexion (withdrawal) reflex occurs
activates interneurons that activate motor neurons supplying ipsilateral flexors, and inhibit motor neurons supplying ipsilateral extensors = Flexion (withdrawal) reflex
how is the flexion reflex detected
by nociceptors
describe how the crossed extensor reflex occurs
activates interneurons that inhibit motor neurons supplying
contralateral flexors, and activate motor neurons supplying contralateral
extensors
what can over-ride the reflexes
Motor neurons are also under the influence of descending controls that can over-ride the reflex
