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BIOL1040! > Module 3 > Flashcards

Module 3 Flashcards

1
Q

Major subdivisions of the nervous system

A

Central Nervous System (CNS)
Peripheral Nervous System (PNS)

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2
Q

Location of CNS and PNS

A

CNS - skull and spinal cord
PNS - nerves outside skull and spinal cord

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3
Q

Anatomical divisions of the nervous system

A

Diencephalon
Brain stem
Cerebellum
Spinal cord

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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

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5
Q

Diencephalon

A

Thalamus
Hypothalamus
Epithalamus

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6
Q

Cerebellum

A

Balance and coordination

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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

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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

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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

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10
Q

Dorsal root ganglion

A

Modification that connects with the autonomic nervous system and induces reflex reactions to certain stimuli

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11
Q

Central Nervous System

A

Sensory activities
Memory
Emotions

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12
Q

Peripheral nervous system

A

Autonomic nervous system and somatic nervous system

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13
Q

Autonomic nervous system

A

Involuntary movements

Divided into:
- parasympathetic division
- sympathetic division
- enteric division

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14
Q

Somatic nervous system

A

Voluntary movements

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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

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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.

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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
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18
Q

Functional lobes of the brain

A

Frontal lobe
Parietal lobe
Temporal lobe
Occipital lobe
Cerebellum
Brain stem

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19
Q

Frontal lobe

A

Motor control in the premotor cortex
Problem solving in the prefrontal cortex
Speech production in Broca’s area

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20
Q

Parietal lobe

A

Sensory cortex
Touch perception
Body orientation and sensory discrimination

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21
Q

Temporal lobe

A

Wernicke’s area for language comprehension
Auditory processing
Memory and information retrieval

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22
Q

Occipital lobe

A

Sight in the visual cortex
Visual reception and interpretation

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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

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24
Q

Wernicke’s area

A

Speech comprehension
Wernicke’s aphasia: speech is devoid of meaning

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25
Q

Typical spinal nerve structures

A

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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26
Q

Cellular elements of the CNS

A

Glial cells
- microglia and microglia
Neurons
Oligodendrocytes
Astrocytes

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27
Q

Glial cells

A

Microglia - scavengers as they eliminate damaged or inefficient areas
Macroglia - oligodendrocytes, astrocytes, and ependymal cells

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28
Q

Oligodendrocytes

A

Produce the myelin sheath for axons

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29
Q

Astrocytes

A

Maintain the blood-brain barrier
Immune system of the brain

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30
Q

Schwann cells

A

myelinate the PNS

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31
Q

Neuron cell structure

A

Soma - body
Dendrites
Axons
- axon hillock
- initial segment
- presynaptic terminal
- synaptic knobs

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32
Q

Types of neurons

A

Unipolar neurons
Bipolar neurons
Pseudounipolar neurons
Multipolar neurons

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33
Q

Unipolar neurons

A

Different segments serve as receptive surfaces and releasing terminals
One main axon

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34
Q

Bipolar neurons

A

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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35
Q

Pseudounipolar cells

A

One single axon which divides into two along its length
Subclass of bipolar cells

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36
Q

Multipolar cells

A

Have one axon and many dendrites found in the cerebellum

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37
Q

Retrograde transport

A

Occurs from the axon terminal to the cell body

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38
Q

Excitation and conduction

A

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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39
Q

Resetting membrane potential

A

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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40
Q

Channel types

A

Ligand-gated ion channels
Voltage-gated ion channels

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41
Q

Ligand-gated ion channels

A

Open when a ligand binds to them

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42
Q

Voltage gated ion channels

A

Open when there is a change in the voltage gradient across the membrane

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43
Q

Action potential and ionic flux

A

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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44
Q

Feedback control of voltage-gated ion channels

A

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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45
Q

Receptors

A

Autoreceptor
Heteroreceptor

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46
Q

Autoreceptor

A

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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47
Q

Heteroreceptor

A

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
Q

Receptors are grouped into two families based on structure and function

A

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
Q

Re-uptake of neurotransmitters

A

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
Q

Types of transporters for neurotransmitters

A

Different neurotransmitters have specific transporters, such as the serotonin transporter (SERT), dopamine transporter (DAT), and norepinephrine transporter (NET)

51
Q

Neurotransmission process

A

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
Q

Selective serotonin rey-take inhibitors

A

Block the reuptake of serotonin, increasing its availability in the synaptic cleft and enhancing its mood-lifting effects

53
Q

Biochemical events at cholinergic synapse

A

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
Q

Nerve and increased temperature

A

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
Q

Nerve and decreased temperature

A

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
Q

Compound action potentials and temperature

A

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
Q

Action potential

A

The event of a nerve or an excitable tissue becoming activated

58
Q

The electrogenesis of an action potential

A

Resting level (-70mV) → Threshold (-55mV) → Rising Phase → Overshoot (+25) → Peak → Spike potential → Repolarisation →After hyperpolarisation → Resting level

59
Q

All or none law

A

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
Q

Electronic potentials

A

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
Q

Graded response

A

The magnitude of an electronic potential is proportional to the strength of the stimulus

62
Q

Mechanicaly gated channels

A

Open in response to mechanical stimuli

63
Q

Thermally gated channels

A

Open in response to temperature changes

64
Q

Depolarisation

A

The influx of positively charged ions or efflux of negatively charged ions makes the inside of the cell more positive

65
Q

Hyperpolarisation

A

The efflux of positively charged ions or influx of negatively charged ions makes the inside of the cell less negative

66
Q

Excitatory postsynaptic potentials

A

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
Q

Effect of EPSP

A

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
Q

Common excitatory neurotransmitters

A

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
Q

Inhibitory postsynaptic potentials

A

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
Q

Common IPSP neurotransmitters

A

gamma-aminobutyric acid and glycine

71
Q

Effect of IPSP

A

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
Q

Temporal summation

A

One neuron and one effector

73
Q

Spatial summation

A

More than one neurone would be connected to other neurone

74
Q

Local anaesthetics

A

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

75
Q

Saltatory conduction

A

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

76
Q

Myelin sheath

A

The insulating layer around the axon produced by glial cells (oligodendrocytes in CNS and Schwann cells in PNS)

77
Q

Orthodromic conduction

A

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

78
Q

Antidromic conduction

A

The propagation of an action potential in the reverse direction, from the axon terminals back towards the soma

79
Q

Biphasic action potentials

A

Action potential that exhibits two distinct phases of voltage change when recorded extracellularly
- these two phases are negative and positive

80
Q

A nerve fibre types

A

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

81
Q

B nerve fibre types

A

Preganglionic autonomic

82
Q

C nerve fibre types

A

Unmyelinated
Postganglionic sympathetic
Pain and temperature
Good for carrying information from your viscera

83
Q

Neurotrophins

A

Family of proteins that play crucial roles in the development, survival, and plasticity in neurons in both the CNS and PNS

84
Q

Receptor concentration

A

Strong concentrations of receptors in certain parts of the body can generate or elicit a very strong response

85
Q

Recruitment of sensory units

A

The process by which additional sensory receptors or sensory neurons are activated in response to increasing intensity of a stimulus

86
Q

Generator potentials

A

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
Q

Receptor potential

A

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
Q

Laws of specific nerve energies and projection

A

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
Q

Axodendritic

A

Axon of one nerve comes into contact with the dendrites of another nerve

90
Q

Axosomatic

A

Axon of one nerve comes into contact with the nerve cell body of another nerve

91
Q

Axoaxonic

A

Axon of one nerve comes into contact with the axon of another nerve

92
Q

Synapse

A

One nerve communicates with another

93
Q

Presynaptic nerve terminals

A

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
Q

Endosomes

A

Responsible for the generation of vesicles within the nerve cell body

95
Q

Proteins involved in synaptic vesicle docking and fusion

A

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
Q

Tetanus

A

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
Q

Bell Magendie law

A

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
Q

Reflexes

A

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
Q

Receptors

A

Structures which communicate with the external environment

100
Q

Muscle spindle

A

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
Q

Reciprocal innervation

A

If one muscle is activated, the other must relax

102
Q

Inverse stretch reflex

A

Whenever muscles contract, it is because the muscle spindles are stretched

103
Q

Muscle tone

A

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
Q

How is muscle tone maintained?

A

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
Q

Mono-synaptic reflex

A

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
Q

Poly-synaptic reflex

A

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
Q

Withdrawal reflex

A

Polysynaptic reflex that protects the body from harmful stimuli

108
Q

Fractionation

A

The process by which the nervous system can selectively activate specific motor units or muscles to produce fine, precise movements

109
Q

Occlusion

A

A phenomenon in neural networks where the activation of on neural circuit can inhibit or reduce the activation of another circuit

110
Q

Crossed extensor reflex

A

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
Q

General properties of reflexes

A

Adequate stimulus – otherwise it would not elicit the reflex
Final common pathway
Central excitatory and inhibitory pathways

112
Q

Neuromuscular junction

A

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
Q

Myasthenia gravis

A

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
Q

Axonal injury

A

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
Q

Neurotransmitters and inhibition or excitation

A

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

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