The Nervous System Flashcards
What are the components of the Peripheral Nervous System?
- Nerves
(connects the CNS to the other tissues in the body)
What does a bundle of neurones together in the PNS make?
a nerve
What are examples of neurotransmitters?
- Dopamine
- Serotonin
- Acetylcholine
- Substance P
- Glutamate
- GABA
- Histamine
- Endorphins
- Adrenaline
Give (5) examples of uses of the nervous system
- movement
- sensation
- memory
- balance
- language
- behaviour
- aging
- sleep
- sweating
- hormone control
- healing and immune system
What is the purpose of the somatic nervous system?
guides your voluntary movements.
What is the purpose of the autonomic nervous system?
regulates the activities you do without thinking about them (involuntary movements).
What is the name of the specialist receptor that connects the nervous system to the muscles?
motor end plate
What is Neuropraxia?
Local myelin damage with the nerve still intact
What is Axonotmesis?
- Continuity of axons is lost.
- Endoneurium, perineurium, and epineurium can remain intact.
- Loss of continuity of axons with Wallerian degeneration due to disruption of axoplasmic flow.
What is Neurotmesis?
Complete physiological disruption of entire nerve trunk.
Ganglion.
Collection of cell bodies
Fasciculus.
Cluster of axons forming a recognisable bundle
Funiculus.
Bundle of axons forming a raised bump on the surface of the CNS (especially in the spinal cord)
Tract.
Cluster of axons with similar functions
Nucleus.
Cluster of cell bodies with similar functions
What is the meninges made up of?
- Dura mater (dural sheath)
- Arachnoid mater
- Pia mater
Hemianopia
loss of half the visual field
Cell body.
Contains nucleus and all the things needed to sustain the metabolic activity of the neuron
Dendrites.
- Processes of cell membrane radiating from cell body in various directions
- Predominantly receive information and send it to the cell body
Axons
- Long tubular extension of the cell membrane and cytoplasm
- Extends towards atarget
- Sends information away from the cell body
Plasmalemma.
Semipermeable membrane of the neuron
Neurons.
Convey information by conducting electrical signals (action potentials)
– but use chemical information to pass messages from one neuron to the next (synapse)
Nerve fibre.
the axon + surrounding Schwann cell
Nodes of Ranvier.
junctions between Schwann cells
Oligodendrocytes.
specialist cells that perform myelination in the CNS
Schwann cells.
specialist cells that perform myelination in the PNS
Myelin.
lipid (fatty) sheath that wraps around axons
Unipolar
Autonomic nervous system:
- one single process
- axon emerges from cell body and branches into dendrites.
Bipolar.
Functionally specialised sensory cells.
- Two processes form from the cell body, one an axon that carries information to CNS, dendrites that convey information from periphery.
Psuedounipolar.
Certain sensory cells (i.e. touch or stretch).
- Bi-polar which fuses to form one axon from cell body
- One branch goes to periphery (to sensory receptors)
- Other to spinal cord
Multipolar.
Predominate form in our nervous system.
- Single axon, and typically many dendrites around cell body.
- Number dendrites correlates with number of synaptic connections
What does the distribution of Na+ and K+ lead to (in a neuron)?
an electrical gradient across the plasmalemma (greater +ve charge outside)
Depolarisation (at the post synaptic plasmalemma).
more +ve ions cross into the neuron (making the inside more +ve)
Excitatory postsynaptic potential (EPSP)
Hyperpolarisation (at the post synaptic plasmalemma).
less +ve ions to cross into the neuron (inside more -ve)
Inhibitory postsynaptic potential (IPSP)
Excitatory postsynaptic potential (EPSP).
More +ve ions tocross into the neuron (making the inside more +ve)
– Depolarisation
Inhibitory postsynaptic potential (IPSP).
Less +ve ions to cross into the neuron (making theinside more-ve)
– Hyperpolarisation
Temporal Summation.
if lots ofExcitatory postsynaptic potentials (EPSPs) arriveone after the other in quick successionthis increases the neteffect
Spatial Summation.
multipleExcitatory postsynaptic potentials (EPSPs) arriveat different locations on the dendriteincreases the net effect
When are action potentials able to occur?
If there’s enough Excitatory postsynaptic potentials (EPSPs)
- and outweighs the Inhibitory postsynaptic potentials (IPSPs) to give a net depolarisation
How do Na+ channels closing & K+ channels opening affect membrane potential?
Becomes more -ve
(no further Na+ enters the axon hillock and K+ exits the hillock)
What happens when a cell is hyperpolarised?
K+ channels to close and the cell then reverts to its resting potential
How does hyperpolarisation occur?
moreK+ leaves the hillock than Na+ has entered so thepotential overshoots
Absolute refactory period
immediately after peakNa+ conductance theNa+ channels areinactive
- so noNa+ ions can move in or out and the hillock cannot fire another action potential
Relative refactory period
Immediately after peak K+ conductance as the Na+channelsbecome active and theplasmalemma repolarises.
- to set up an action potential requires more stimulus than when in the resting state
What is the speed of propagation dependent on?
- Diameter of axon (larger = faster conduction)
- Presence of myelin (concentrates K+ and Na+ channels in nodes so increased conduction velocity)
When an action potential arrives at an axon terminal/presynaptic process what happens?
Ca++ channels open
so calcium floods into the bouton
What does an increase in Ca++ lead to?
- Synaptic vesicles dock and fuse with axon terminal membrane
- The vesicles remain fused to the membrane until the Ca++ concentration has increased to a critical point
- At this point the vesicle fuses into the membrane and releases neurotransmitter into the synaptic cleft
- Retrieves new vesicles from a storage area so that the process can be repeated.
What are (3) possible causes of injury to the nervous system?
- Direct injury to neuron(s)
- Disruption to neural function due to indirect effects of injury (decreased blood flow, oedema, cerebral metabolism, CSF)
- Synaptic loss from damaged neuron cascades that cause degeneration of neighbouring neurons (leading to further damage)
Describe Wallerian Degeneration (PNS).
- Trophic degenerationof the neuron at site of lesion and travels distally from cell body
- Swelling andgranulation
- Lasts for3-4 days
- Myelindegenerates too
- Growth factorspromote thegrowth of axonal buds
- Regenerationbegins to occur at7 days
- Growth occurs at1-4mm a day
- Processoccurs alongsiderestoration of the Schwanncells
Describe the affect of Diaschisis & Oedema on the nervous system.
- Temporary disruption of neural function (due to shock of injury or disease)
- This can occur locally to the injury or at some distance (due to altered metabolism and reduction of blood flow)
- Oedema is common around the brain following injury
- Can be local or remote
- Can be significant enough to block neural conduction
- Some function is restored when diaschisis and oedema settle
When does Denervation Supersensitivity occur?
when there’s a loss of input from another area of the brain
Describe Denervation Supersensitivity?
The post synaptic membrane becomes more sensitive to the release of neurotransmitter
Describe the unmasking of silent synapses.
- During recovery previously unused synapses are recruited
- Suggests the existence of structural synapses in the brain that are not normally functional due to competition
How long does Synaptogensis (Regenerative) take following injury?
Occurs within 3-7 days of injury
What happens during Collateral Sprouting (reactive synaptogenesis)?
Neighbouring, uninjured axons sprout to innervate synaptic sites previously activated by the injured neuron
What is short-term potentiation?
- A change in the performance or output of a synapse in the short term
- An increase in synaptic strength due to increase in neurotransmitter production and/or altered post synaptic receptors
What is long-term potential (LTP)?
- Change in the performance or output of a synapse in the long term
- Related to increase in pre-synaptic neurotransmitter release + structural change of the post-synaptic structure
- Related to spatial + temporal summation (LTP occurs with high frequency stimulation or pairing of stimulation)
This is how we learn!
Describe Transneuronal degeneration.
- Axotomy: axon of a neuron is cut.
- Anterograde Degeneration: distal portion of damaged neuron degenerates.
- Retrograde Degeneration: proximal portion of damaged neuron may degenerate.
- Transneuronal Degeneration: neurons that synapsed on the damaged neuron may degenerate.
What are the (4) main types of Glial Cells?
- Oligodendrocytes
- Microglia
- Ependymal cells
- Astrocytes
Where are Glial Cells?
between the nerve cells
What is the purpose of Glial Cells?
Hold the neurons of the CNS in place
What are the Meninges?
3 layers of fibrous material that surrounds the brain & spinal cord to prevent it from injury + infection
The Meninges and Cerebrospinal Fluid (CSF) work together to do what?
Cushion the brain + prevent too much movement within the skull
What is Pia Mater?
Very thin, translucent, mesh-like meningeal envelop that lies directly on the surface of the brain
Where is the Arachnoid Mater?
Lies between the Dura + Pia Mater
What is contained in the Arachnoid space?
- Cerebrospinal Fluid (CSF)
- Arterial blood supply (that goes to outside the brain)
Where is the Arachnoid space?
the space between the Arachnoid + Pia Mater
How does the Arachnoid layer attach to the Pia Mater?
via fibrous strands
What is Dura Mater?
a tough outer layer of the meninges
Where is Dura Mater?
directly attached to the skull (except where it allows space for the venous supply)
How much Cerebrospinal Fluid (CSF) is produced per day?
500ml
How much Cerebrospinal Fluid (CSF) circulates at any time?
125-150ml
What is Cerebrospinal Fluid (CSF)?
Straw colouredviscous fluid
Where is Cerebrospinal Fluid (CSF) produced?
the lateral ventricles
Where does Cerebrospinal Fluid (CSF) circulate?
around the brain & spinal cord in thesubarachnoid space
What is the Circle of Willis?
a circular vascular anatomy the brain has evolved to limit the possibility of loss of blood supply
What is the name of the tough outer layer of the meninges that adheres to the skull?
Dura mater
Are cranial nerves part of the CNS or PNS?
PNS
What are interneurones?
Small nerves linking to other nerves
What is the conus medullaris?
the terminal end of the spinal cord
Where does the conus medullaris typically occur in the average adult?
L1 vertebral level
What is Gray Matter?
Areas of the CNS that are a large collection of cell bodies
What is White Matter?
Areas of the CNS that are a large collection of neuron processes
(As they can be wrapped in insulating layers that are white)
What is the route for pain & temperature info?
Sensory receptors:
- Thermoreceptors in the skin stimulated by heat or cold
- Nociceptors in skin, muscle, joints and viscera stimulated by noxious stimuli
Ascend via peripheral nerves to dorsal horn of spinal cord
Ascend spinal cord via:
- Spinothalamic tract
- Spinoreticular tract
What are the (5) nuclei that make up the basal ganglia?
- Caudate Nucleus (Striatum)
- Putamen (Striatum)
- Globus Pallidus-internal and external segments
- Subthalamic nucleus
- Substantia Nigra
What are the (3) different dopamine pathways?
- Mesocortical
- Nigrostriatal
- Mesolimbic
What does the mesocortical dopaminergic pathway effect?
-Cognition
- Memory
- Attention
- Emotion
- Behaviour
- Learning
What does the nigrostriatal dopaminergic pathway effect?
Movement Control
What does the mesolimbic dopaminergic pathway effect?
- Pleasure
- Reward seeking behaviours
- Addiction
- Emotion
Describe the circuitry of the Basal Ganglia.
- Provides a feedback circuit.
- It receives informationfrom several sources including the cerebral cortex (sensory and motor areas).
-The input information enters via the striatum and leaves via the globus pallidus. - Itfeeds this information to the cortexvia the thalamus.
Information enters via the ____ and leaves via the ___ to then be sent to the cerebral cortex.
- Striatum
- Globus pallidus
True or False…
The substantia nigra is not part of the basal ganglia.
False
What are the components of the Central Nervous System?
- Brain
- Spinal Cord
(within the skull and vertebral column)
