Module 3 Flashcards
1
Q
Major subdivisions of the nervous system
A
Central Nervous System (CNS)
Peripheral Nervous System (PNS)
2
Q
Location of CNS and PNS
A
CNS - skull and spinal cord
PNS - nerves outside skull and spinal cord
3
Q
Anatomical divisions of the nervous system
A
Diencephalon
Brain stem
Cerebellum
Spinal cord
4
Q
Brain stem
A
Connection between spinal cord and brain
Is comprised of the midbrain, pons, and medulla oblongata
In charge of involuntary actions including breathing, consciousness, blood pressure, heart rate, and sleep
5
Q
Diencephalon
A
Thalamus
Hypothalamus
Epithalamus
6
Q
Cerebellum
A
Balance and coordination
7
Q
Spinal cord
A
Two distinct zones:
Outer zone - white/light in colour because it has a lot of myelinated nerve tracks
Central zone - a lot of nuclei, giving it a darker colour
Two distinct ends:
Dorsal end
Ventral end
8
Q
Dorsal end of spinal cord
A
Sensory as this is where information travels to from the PNS
- a receptor has been stimulated and the information is carried to the spinal cord via the dorsal roots
9
Q
Ventral end of spinal cord
A
Motor as it carries information from the spinal cord to an effector organ to command a response
10
Q
Dorsal root ganglion
A
Modification that connects with the autonomic nervous system and induces reflex reactions to certain stimuli
11
Q
Central Nervous System
A
Sensory activities
Memory
Emotions
12
Q
Peripheral nervous system
A
Autonomic nervous system and somatic nervous system
13
Q
Autonomic nervous system
A
Involuntary movements
Divided into:
- parasympathetic division
- sympathetic division
- enteric division
14
Q
Somatic nervous system
A
Voluntary movements
15
Q
Parasympathetic division (PANS)
A
rest and relax state
- constricts pupils
- stimulates saliva flow
- slows heart rate
- constricts bronchi
- stimulates stomach, pancreas, and intestines
- stimulates bile release
- contracts bladder
16
Q
Sympathetic division (SANS)
A
fight or flight state
- dilates pupils
- inhibits saliva flow
- accelerates heart rate
- dilates bronchi
- stimulates stomach, pancreas, and intestines
- converts glycogen to glucose
- secretes adrenaline
- inhibits bladder contractions.
17
Q
Cerebrospinal fluid
A
ultra filtrate of plasma fluid (secreted by the choroid plexus) contained within the ventricles of the brain and the subarachnoid spaces of the cranium and spine
- provides nourishment (contains glucose)
- waste removal
- cushions the brain
18
Q
Functional lobes of the brain
A
Frontal lobe
Parietal lobe
Temporal lobe
Occipital lobe
Cerebellum
Brain stem
19
Q
Frontal lobe
A
Motor control in the premotor cortex
Problem solving in the prefrontal cortex
Speech production in Broca’s area
20
Q
Parietal lobe
A
Sensory cortex
Touch perception
Body orientation and sensory discrimination
21
Q
Temporal lobe
A
Wernicke’s area for language comprehension
Auditory processing
Memory and information retrieval
22
Q
Occipital lobe
A
Sight in the visual cortex
Visual reception and interpretation
23
Q
Broca’s area
A
Speech production
Broca’s aphasia: affects the use of spontaneous speech and motor speech control
- words may be uttered slowly and poorly articulated
- severe impairment in writing
24
Q
Wernicke’s area
A
Speech comprehension
Wernicke’s aphasia: speech is devoid of meaning
25
Typical spinal nerve structures
Axons: extensions from soma
Fascicle: when multiple axons come together
Perineurium: encloses the fascicle as a connective tissue sheet
Endoneurium: covers individual axons
Blood vessels
Epineurium: bundle of fascicles
Spinal nerve
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Cellular elements of the CNS
Glial cells
- microglia and microglia
Neurons
Oligodendrocytes
Astrocytes
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Glial cells
Microglia - scavengers as they eliminate damaged or inefficient areas
Macroglia - oligodendrocytes, astrocytes, and ependymal cells
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Oligodendrocytes
Produce the myelin sheath for axons
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Astrocytes
Maintain the blood-brain barrier
Immune system of the brain
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Schwann cells
myelinate the PNS
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Neuron cell structure
Soma - body
Dendrites
Axons
- axon hillock
- initial segment
- presynaptic terminal
- synaptic knobs
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Types of neurons
Unipolar neurons
Bipolar neurons
Pseudounipolar neurons
Multipolar neurons
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Unipolar neurons
Different segments serve as receptive surfaces and releasing terminals
One main axon
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Bipolar neurons
Two specialised processes with two axons
- a dendrite that carries information to the cell
- an axon that transmits information from the cell
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Pseudounipolar cells
One single axon which divides into two along its length
Subclass of bipolar cells
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Multipolar cells
Have one axon and many dendrites found in the cerebellum
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Retrograde transport
Occurs from the axon terminal to the cell body
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Excitation and conduction
Nerve cells respond to electrical, chemical, or mechanical stimuli
Two types of physiochemical disturbances are produced:
- local, non-propagated potentials (synaptic, generator, or electronic potentials)
- propagated potentials
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Resetting membrane potential
The result of the movement of several different ion species through various ion channels and transporters in the plasma membrane
- These movements result in different electrostatic charges across the cell membrane
- For RMP to occur, there must be an unequal distribution of ions of one or more types across the membrane (concentration gradient)
- The membrane also must be permeable to these ions
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Channel types
Ligand-gated ion channels
Voltage-gated ion channels
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Ligand-gated ion channels
Open when a ligand binds to them
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Voltage gated ion channels
Open when there is a change in the voltage gradient across the membrane
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Action potential and ionic flux
Action potential is a change in the membrane conductance of NA+ and K+
- Sodium (K+) rushes inside the cell
- Membrane potential becomes positive
In response to a depolarising stimulus, some of the voltage-gated NA+ channels open and NA+ enters the cell and the membrane is brought to its threshold potential
- The nerve cell fires when it reaches the threshold potential
- Sodium opens lots of channels – positive feedback – and the membrane potential overshoots
- When it reaches +30mV, sodium channels starts to close
- Potassium channels open and re-enter the cell
P- umps pump out the remaining sodium ions
The entry of NA+ causes the opening of more voltage-gated NA+ channels and further depolarisation
- Positive feedback loop
- The membrane potential moves toward the equilibrium potential for NA+ but does not reach it during the action potential
T- he NA+ channels rapidly enter a closed state called the inactive state and remain in this state for a few milliseconds before returning to the resting state
Overshoot reverses the direction of the electrical gradient for NA+ which limits NA+ influx
- Voltage-gated ion channels open
- Repolarization occurs
- The opening of voltage-gated K+ channels is slower and more prolonged than the opening of the NA+ channels
- The net movement of positive charge out of the cell due to K+ efflux at this time helps complete the process of repolarisation
- The slow return of the K+ channels to the closed state also explains the after-hyperpolarization
- Voltage gated K+ channels bring the action potential to an end and cause closure of their gates through a negative feedback process
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Feedback control of voltage-gated ion channels
Positive feedback: occurs to increase the change or output; the result of a reaction is amplified to make it occur more quickly.
--> Change in one cell membrane opens other channel membranes.
Negative feedback: reduce the change or output. The results of a reaction is to bring a system back to its stable state
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Receptors
Autoreceptor
Heteroreceptor
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Autoreceptor
Presynaptic receptor that often inhibits further release of the transmitter, providing feedback control
- the neurotransmitter that comes from the proximal part and activates the receptor on the distal part of the nerve will generate some negative feedback
- this lets the body know that no more needs to be secreted
Example: Norepinephrine acts on presynaptic receptors to inhibit additional norepinephrine release
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Heteroreceptor
Presynaptic receptor whose ligand is a chemical other than the transmitter released by the nerve ending on which the receptor is located
Example: Norepinephrine acts on a heteroreceptor on a cholinergic nerve terminal to inhibit the release of acetylcholine
48
Receptors are grouped into two families based on structure and function
Ligand-gated channels - inotropic receptors
- allows the flux of ions across the membrane
Metabotrobic receptors - G-protein coupled receptors
- associated with metabolic pathways which have to be activated by G-protein coupled receptors
Example: steroid hormones bring about a change in the membrane protein structure and thus require ATP, so it activates G-protein coupled receptors
49
Re-uptake of neurotransmitters
Transporter proteins: specialised proteins called neurotransmitter transporters are embedded in the presynaptic membrane
- These transporters actively pump neurotransmitters back into the presynaptic neuron
Repackaging and degradation
- Once inside the presynaptic neuron, neurotransmitters can be repackaged into synaptic vesicles for further release
- Alternatively, neurotransmitters can be broken down by enzymes within the neuron
Example - the enzyme monoamine oxidase (MAO) degrades monoamines like serotonin, dopamine, and norepinephrine
50
Types of transporters for neurotransmitters
Different neurotransmitters have specific transporters, such as the serotonin transporter (SERT), dopamine transporter (DAT), and norepinephrine transporter (NET)
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Neurotransmission process
Release of neurotransmitters to transmit an impulse or action potential
Binding to receptors
Re-uptake process
Repackaging and degradation
Termination of signal
Recycling of neurotransmitters
Regulation of synaptic activity
52
Selective serotonin rey-take inhibitors
Block the reuptake of serotonin, increasing its availability in the synaptic cleft and enhancing its mood-lifting effects
53
Biochemical events at cholinergic synapse
An arriving action potential depolarises the synaptic knob
- Activates calcium channels
- Calcium ions enter the cytoplasm, and after a brief delay, ACh is released through exocytosis of synaptic vesicles
- ACh binds to the sodium channel receptors on the postsynaptic membrane, producing a graded depolarisation
- Depolarisation ends as AC is broken down into acetate and choline by AChE
- The synaptic knob reabsorbs choline from the synaptic cleft and uses it to synthesise new molecules of ACh
54
Nerve and increased temperature
Faster conduction velocity
- As temperature increases, the conduction velocity of nerves generally increases → nerves start to fire more rapidly
- The kinetic energy of ions involved in generating and propagating action potentials is higher, leading to faster opening and closing of ion channels
- Enhanced enzyme activity in neurotransmitter synthesis and degradation
- Also enhances the functioning of sodium-potassium pumps, which helps maintain the resting membrane potential
- Reduced threshold for activation
Potential for hyperexcitability
- Excessively high temperatures can lead to hyperexcitability and abnormal firing patterns
- Potentially cause issues such as seizures
55
Nerve and decreased temperature
Slower conduction velocity
- Lower temperatures result in slower nerve conduction velocities
- Ion channel kinetics slow down, resulting in delayed opening and closing of channels, and thus slower propagation of action potentials
- Increased threshold for activation
Potential for conduction block
- At very low temperatures, conduction velocity can decrease so much that action potentials may fail to propagate
- This leads to conduction block
- This can cause numbness or loss of function in affected nerves
- Impaired enzyme activity
- Enzyme activities involved in neurotransmitter metabolism and ion pump functions are also reduced at lower temperatures, which can impair overall nerve function
56
Compound action potentials and temperature
Changes in temperature affect the rate at which channels open, close, and inactivate, and consequently the speed at which the ionic conductances turn on and off
These rates are described by the rate constants in the Hodgkin-Huxley equations
- These rate constants increase 3-fold for each 10 degree increase in temperature
- The durations of the conductances determine the durations of the currents underlying the action potential and in turn the duration of the action potential itself
- The duration of the action potential changes with temperature by about the same factor as do the rate constants of the Hodgkin-Huxley quotations → 3 fold for each 10 degree increase
57
Action potential
The event of a nerve or an excitable tissue becoming activated
58
The electrogenesis of an action potential
Resting level (-70mV) → Threshold (-55mV) → Rising Phase → Overshoot (+25) → Peak → Spike potential → Repolarisation →After hyperpolarisation → Resting level
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All or none law
Once a threshold stimulus is reached, a neuron or muscle fibre will fire an action potential in its entirety or not at all
- Threshold stimulus: for a neuron or muscle fibre to fire, the stimulus must be strong enough to reach a certain threshold
- Action potential: once the threshold is reached, an action potential is generated and propagated along the entire length of the neuron or muscle fibre without diminishing its strength
- Binary response: the response is “all” if the stimulus reaches the threshold, meaning the full action potential occurs. It is “none” if the stimulus does not reach the threshold, meaning no action potential occurs
60
Electronic potentials
Electronic potentials are graded potentials: changes in the membrane potential of excitable cells that occur in response to a stimulus
- variable in magnitude and duration
- they can be depolarising or hyperpolarising, depending on the nature of the stimulus
Graded response: the magnitude of an electronic potential is proportional to the strength of the stimulus
Local and passive: electrotonic potentials occur locally around the site of the stimulus and decrease in amplitude as they spread away from the source, diminishing over time and distance
Summation: multiple electrotonic potentials can summate or combine to produce a larger change in membrane potential
Summation can be spatial (inputs from multiple locations) or temporal (multiple inputs in rapid succession)
Depolarising or hyperpolarising: depending on the ions involved and their movement across the membrane electrotonic potentials can cause depolarisation (making the membrane potential more positive) or hyperpolarisation (more negative)
Electrotonic potentials are generated by the opening of ion channels in the cell membrane in response to a stimulus
61
Graded response
The magnitude of an electronic potential is proportional to the strength of the stimulus
62
Mechanicaly gated channels
Open in response to mechanical stimuli
63
Thermally gated channels
Open in response to temperature changes
64
Depolarisation
The influx of positively charged ions or efflux of negatively charged ions makes the inside of the cell more positive
65
Hyperpolarisation
The efflux of positively charged ions or influx of negatively charged ions makes the inside of the cell less negative
66
Excitatory postsynaptic potentials
The event that will excite the neuron to the threshold value so that it can fire
- Aiming to make the membrane less negative for the threshold potential to be reached
Depolarisation: EPSPs are depolarising events, meaning they make the inside of the postsynaptic cell more positive
Ion movement: typically, EPSPs result from the influx of positively charged ions (sodium Na+) into the postsynaptic neuron
Effect: EPSPs increase the likelihood that the postsynaptic neuron will reach the threshold potential and generate an action potential
Multiple ESPSs can summate to bring the membrane potential closer to the threshold
67
Effect of EPSP
EPSPs increase the likelihood that the postsynaptic neuron will reach the threshold potential and generate an action potential
Multiple ESPSs can summate to bring the membrane potential closer to the threshold
68
Common excitatory neurotransmitters
To transmit an impulse from the neuron the postsynaptic cell, the neurotransmitter is the medium that transports the impulse
Glutamate and acetylcholine → allow for an EPSP to occur
69
Inhibitory postsynaptic potentials
Aiming to make the membrane more negative to ensure that we do to over activate our muscles
Hyperpolarisation: IPSPs are hyperpolarising events, meaning they make the inside of the postsynaptic cell more negative
Ion movement: IPSPs typically results from the influx of negatively charged ions or the efflux of positively charged ions out of the postsynaptic neuron
Flux of potassium and chloride (Cl) that keeps the membrane more towards the negative side
70
Common IPSP neurotransmitters
gamma-aminobutyric acid and glycine
71
Effect of IPSP
IPSPs decrease the likelihood that the postsynaptic neuron will reach the threshold potential and generate an action potential. They counteract the effects of EPSPs and can make it more difficult for the postsynaptic neuron to fire an action potential
72
Temporal summation
One neuron and one effector
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Spatial summation
More than one neurone would be connected to other neurone
74
Local anaesthetics
Reversibly inhibit neurotransmission by binding to voltage gated sodium channels in the nerve plasma membrane
- Injection usually given is called Lignocaine
- The binding of Lignocaine blocks the entry of sodium into the cell
- Prevents the feeling of pain
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Saltatory conduction
Action potentials jump from one node of Ranvier to the next along a myelinated axon
- This type of conduction is much faster than the continuous conduction seen in unmyelinated axons
- When an action potential is generated at the axon hillock, the local depolarisation at a node of Ranvier causes the adjacent node to reach the threshold and generate its own action potential
- The myelin sheath prevents ion leakage, allowing the depolarisation to travel quickly and efficiently along the axon to the next node
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Myelin sheath
The insulating layer around the axon produced by glial cells (oligodendrocytes in CNS and Schwann cells in PNS)
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Orthodromic conduction
The propagation of an action potential in the natural, forward direction, from the soma down the axon to the axon terminals
- ensures that signals are transmitted from the presynaptic neuron to the postsynaptic neuron or target cell
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Antidromic conduction
The propagation of an action potential in the reverse direction, from the axon terminals back towards the soma
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Biphasic action potentials
Action potential that exhibits two distinct phases of voltage change when recorded extracellularly
- these two phases are negative and positive
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A nerve fibre types
Usually myelinated
- fast conduction
- carry basic information that helps you locate yourself in time and space
- touch and pressure
- motor to muscle spindles
- pain and temperature
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B nerve fibre types
Preganglionic autonomic
82
C nerve fibre types
Unmyelinated
Postganglionic sympathetic
Pain and temperature
Good for carrying information from your viscera
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Neurotrophins
Family of proteins that play crucial roles in the development, survival, and plasticity in neurons in both the CNS and PNS
84
Receptor concentration
Strong concentrations of receptors in certain parts of the body can generate or elicit a very strong response
85
Recruitment of sensory units
The process by which additional sensory receptors or sensory neurons are activated in response to increasing intensity of a stimulus
86
Generator potentials
Type of receptor that occurs specifically in the sensory nerve endings of the first-order neuron itself
- occurs where the receptor and the neuron are the same structure
87
Receptor potential
The graded, local change in the membrane potential of a sensory receptor cell in response to a stimulus
- magnitude varies with the strength of the stimulus
88
Laws of specific nerve energies and projection
Specificity of nerves
- Each type of sensory nerve is dedicated to transmitting a particular kind of sensory information
Perception of stimulus
- Regardless of how sensory nerve is stimulated, the perception corresponds to the modality associated with that neervee
Implications
- The laws of specific nerve energies and projection implicates the brain’s role in interpreting the signals from nerves
- This type of sensation experienced is linked to the type of nerve stimulated, not the nature of the stimulus itself
The law of projection
- Regardless of where a sensory pathway is stimulated along its course, the sensation is projected to the location of the original sensory receptor
Nerve sensitivity
Phantom limb sensation: amputees may feel sensations in the limb that is no longer there
89
Axodendritic
Axon of one nerve comes into contact with the dendrites of another nerve
90
Axosomatic
Axon of one nerve comes into contact with the nerve cell body of another nerve
91
Axoaxonic
Axon of one nerve comes into contact with the axon of another nerve
92
Synapse
One nerve communicates with another
93
Presynaptic nerve terminals
Neurotransmitters start to move into vesicles as soon as they are generated
- Translocation: once the neurotransmitter has been filled up within the vesicle it needs to be moved to the site where acetylcholine is required
- When it reaches the site, it docks → attaching to it by the snare protein
- Energy requiring process → remains docked on the membrane where ATP is used
Calcium is required
- Calcium brings about a change in the membrane
- Causes microtubules to pull the vesicles closer to the membrane
- Calcium can combine or attach to the vesicles making them exocytose the neurotransmitter in the synaptic junction
The action potential has been transmitted to the effector
- The vesicles is released from the membrane and goes back towards the cytoplasm of the nerve where it is grabbed by the endosome and recycled to be used again
94
Endosomes
Responsible for the generation of vesicles within the nerve cell body
95
Proteins involved in synaptic vesicle docking and fusion
N-ethylmaleimide-sensitive fusion protein
SNAPs - soluble NSF attachment proteins
SNAREs - snap receptors
→ Synaptobrevin in the vesicle membrane links with syntaxin and SNAPs in the cell membrane
→ GTPases regulate a multiprotein complex that includes Rab and Sec1/Munc18-like proteins
96
Tetanus
Synapses can be infected by a bacteria called C.tetani
Toxin retrogradely traveled and abolishes the inhibitory pathways
Excitatory pathways have nothing inhibiting them from continuously exciting cells
Body is in a perpetual stage of contraction
97
Bell Magendie law
The anterior spinal nerve roots → contain only motor fibres
Posterior roots → contain only sensory fibers
Nerve impulses are conducted in only one direction in each case
98
Reflexes
Has to be a sense organ and effector and pathways in between these structures
- These are activated by generator potentials which most are excitatory
- These are carried by afferent/sensory nerves towards the synapses (spinal cord)
- The center processes it and uses motor nerves/efferent to carry the information to the effector organs
99
Receptors
Structures which communicate with the external environment
100
Muscle spindle
Sensory receptor located within muscles that plays a crucial role in detecting changes in muscle length
Also maintains muscle tone and posture
Specialised fibres that control how much your muscles are able to contract
101
Reciprocal innervation
If one muscle is activated, the other must relax
102
Inverse stretch reflex
Whenever muscles contract, it is because the muscle spindles are stretched
103
Muscle tone
Refers to the continuous and passive partial contraction of muscles or the muscle's resistance too passive stretch during its resting state
- essential for posture, readiness for action, and overall muscle health
104
How is muscle tone maintained?
Muscle tone is maintained through a combination of neural and muscular mechanisms via:
- Muscle spindle reflex
- Gamma-motor neurons
- Supraspinal control
- Proprioceptive feedback
- Golgi tendon organs
105
Mono-synaptic reflex
Example of a reflex arc
- The stretch receptor sensory neuron of the quadriceps muscle makes an excitatory connection with the extensor motor neuron of the same muscle and an inhibitory interneuron projecting to flexor motor neurons supplying the antagonistic hamstring muscle
- When the quadricep muscle is tapped, it stretches the muscle spindle
- The muscle spindle was the receptor and carries the information by the afferent neuron to the spinal cord
- Here it is synapsed with a nerve
- Information is carried back to the muscle causing the muscle to contract
106
Poly-synaptic reflex
Type of reflex action that involves one or more interneurons between the sensory (afferent) neuron and the motor (efferent) neuron in the reflex arc
- The motor neurons innervate the hamstrings to elicit movement at the knee joint
- Contrasts with a monosynaptic reflex where there is only a single synapse between the sensory neuron and the motor neuron
- If agonists are contracting, antagonists must relax
107
Withdrawal reflex
Polysynaptic reflex that protects the body from harmful stimuli
108
Fractionation
The process by which the nervous system can selectively activate specific motor units or muscles to produce fine, precise movements
109
Occlusion
A phenomenon in neural networks where the activation of on neural circuit can inhibit or reduce the activation of another circuit
110
Crossed extensor reflex
This reflex occurs in conjunction with the withdrawal reflex
- It helps to maintain balance by coordinating the opposite limb’s response
- When the withdrawal reflex is activated, interneurons in the spinal cord also stimulate motor neurons (becomee extended) on the opposite side of the body
- This causes the muscles in the contralateral limb to extend
- This action helps support the body’s weight and maintain balance while the injured limb is withdrawn
111
General properties of reflexes
Adequate stimulus -- otherwise it would not elicit the reflex
Final common pathway
Central excitatory and inhibitory pathways
112
Neuromuscular junction
Formed by the terminal bit of the neuron (synaptic buttons) and the effector organ
- When action potentials reach the synaptic buttons, they activate the calcium channels
- Calcium channels are voltage gated and opened by the sodium flux
- Vesicles start moving towards the terminals of the synaptic buttons
- Vesicles start exocytosis acetylcholine into the synaptic cleft
- Activation of ligand-gated sodium channels
- The action potential in the neuron can now travel to the muscle
→ the acetylcholine has to be mobilised and sent back
- Acetylcholinesterase breaks down the acetylcholine so that it is taken up into the synaptic buttons
- The vesicles are recycled and filled up with the neurotransmitters
Acetylcholine breaks down into two components → acetyl-CoA and choline
113
Myasthenia gravis
Autoimmune disorder whereby if acetylcholine is damaged or the receptors are damaged there are lots of action potentials but the body is not capable of bringing about any change in the effector organs → muscles
- The resting tone of muscle is challenged
- Droopy eyes and lethargy
- Not enough acetylcholine to produce activities that the body requires
114
Axonal injury
Denervation hypersensitivity/supersensitivity:
- When the motor nerve to skeletal muscle is cut and allowed to degenerate, the muscle gradually becomes extremely sensitive to acetylcholine
A deficiency of a given chemical messenger generally produces:
- Upregulation of its receptors
- Lack of reuptake of secreted neurotransmitters
115
Neurotransmitters and inhibition or excitation
Neurotransmitters can excite or inhibit the postsynaptic target
Neuromodulators: chemicals released by neurons that have little or no direct effects on their own but can modify the effects of neurotransmitters
Negative feedback mechanisms that prevent the further release of the neurotransmitter
