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HUBS191 > HUBS Progress Test 2 > Flashcards

HUBS Progress Test 2 Flashcards

1
Q

Two types of errors in Biostatistics

A
  1. Errors that make our answers more uncertain eg variability
  2. Errors that move us away from the truth eg bias (can be avoidable by taking a random sample from the whole population)
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2
Q

Terminologies for Continuous Variables

A

(Terminologies describe the centre and spread)
Population - Described by (population) mean and standard deviation
Sample - Described by (sample) mean and standard deviation.
Sampling Distribution - Centred on population mean (when there is no bias) and described by standard error (SD of sampling distribution).

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3
Q

Terminologies for Binary Variables

A

(Terminologies describe the centre and spread)
Population - Described by (population) proportion
Sample - Described by (sample) proportion
Sampling Distribution - Centred on population proportion (when no bias) and described by standard error = variability / SD of sampling distribution

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4
Q

Sampling Distribution

A

Sampling distribution follows the normal distribution where it is a symmetrical bell-shaped curve. Its shape depends on the mean and SD. 95% of the sample means lie within +/- 1.96 SD of the mean.
Sampling distribution will get narrower as the sample size increases (less variability)

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5
Q

Regression Lines

A

Regression lines can be determined by the equation

y = a + b x X, where a is the intercept and b is the slope. Height = a + b x variable.

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6
Q

Standard Error

A

(The approximate standard deviation of a statistical sample population. ie measures the difference between the sample mean and the actual mean.)
Can be estimated from the sample by using the formula
SE=s/√n

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7
Q

95% confidence Intervals

A

General formula = Estimate ± 1.96 × SE
This formula means that if repeated sampling was carried out, 95% of the intervals would contain the true population mean.
For means = x̄ ± 1.96 × s/√n

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8
Q

Interpretation of confidence intervals

A

We’re 95% confident that the true population mean lies between the upper and lower limit.

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9
Q

Population Mean and SD

A 
Mean = a measure of the centre of the distribution.
SD = Measures the spread or variability of the data around the mean.
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10
Q

Nervous system 2 structural divisions

A
  1. Central Nervous System (CNS)

2. Peripheral Nervous System (PNS)

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11
Q

CNS Structure

A

Consists of Brain and Spinal Cord.

Cellular structure = neurons and glia.

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12
Q

PNS Structure

A

Consists of peripheral nerves (everything other than the spinal cord and brain).
Cellular structure = neurons and glia.

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13
Q

Neurons

A

(Nerve Cells) Specialised for transmission of information.
Four types:
- Multipolar (multiple process emanate from the cell body ie normal type)
- Bipolar (two processes emanate from the cell body)
- Unipolar ( one process emanates from the cell body)
- Anaxonic (no distinct axon, all processes look alike)

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14
Q

Glia

A

(Glue) Support for neurons
Five basic types (each has a specific function)
4 in CNS and 1 in PNS

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15
Q

Neuron Generic structure

A
  1. Dendrites – receive input and send it to the cell body
  2. Cell body – Contains the nucleus/ organelles and aggregates inputs form the dendrites
  3. Axon – transmits electrical impulses, can be myelinated
  4. Axon Terminal – releases neurotransmitters
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16
Q

4 zones of the neuron

A
  1. Input zone - Consists of dendrites and cell body.
    Receives chemical signals from other neurons
  2. Summation zone - Consists of axon hillock (start of the axon). Summates inputs.
  3. Conduction zone - Consists of axon.
    Transmits electrical signals between brain and spinal cord, from peripheral sensory receptors as well as to effector cells.
  4. Output zone - Consists of axon terminals.
    Synapses on input zone of other neurons or effector cells and releases neurotransmitters.
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17
Q

Organisation of the CNS

A

Group of cell bodies = Nucleus (not same nucleus as in cells)
Group of cell bodies in cerebral cortex or spinal cord = Grey Matter
Bundle of axons = Tract
Bundle of axons in cerebral cortex or spinal cord = White matter

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18
Q

Organisation of the PNS

A

Group of cell bodies = Ganglion

Bundle of axons = Nerve

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19
Q

Glia Types and Functions

A

4 types in CNS:

  1. Ependymal - Line fluid-filled spaces in CNS. Have cilia to circulate cerebrospinal fluid.
  2. Microglia - Immune cells of the CNS. Engulf microorganisms and debris.
  3. Astrocytes - Supply nutrients to neurons. Ensheath blood capillaries.
  4. Oligodendrocytes - Support nerve fibres (axons). Ensheath them with myelin.

1 Type in the PNS:
1. Schwann Cells - Support peripheral nerve fibres. Ensheath them with myelin.

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20
Q

Myelin Sheath

A

Myelin sheath is a layer of lipids that wraps around the axon, it increases conduction velocity via Nodes of Ranvier- the gaps between myelin.
The myelin sheath in the PNS consists of multiple Schwann cells in a line.

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21
Q

Communication between Neurons at Synapse

A

When an AP travels down pre-synaptic neuron, it will stimulate synaptic vesicles waiting in the axon terminals to fuse with the membranes in the output zone and undergo exocytosis to release neurotransmitter (chemical signal) into the synaptic cleft. The neurotransmitter travels across the synaptic cleft to receptors in the membrane of the input zone in the post-synaptic neuron.

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22
Q

Flow of information

A

(Information only travels in 1 direction within a nerve)
Information going into the brain = Afferent (also called ascending)
Information coming out of the brain = Efferent (also called descending)

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23
Q

Types of Information Transmitted

A

Somatic = The information that we are aware of and have control over. Examples:
Motor - somatic efferent = voluntary muscle control
Sensory - somatic afferent = Sensory information we are aware of such as touch or sight.

Autonomic = The information we’re unaware of and cannot control. Examples:
Motor - autonomic afferent = involuntary muscle control such as heartbeat
Sensory - autonomic efferent = sensory information we’re unaware of like information regarding blood pressure.

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24
Q

Somatic Efferent System

A

Consists of 2 myelinated neurons:
1. Upper motor neuron - cell body in brain, axon in spinal cord.
2. Lower motor neuron - cell body in spinal cord, axon in peripheral nerve (PNS)
Lower motor neuron is the pre-synaptic cell which synapses onto the effector skeletal muscle (post-synaptic cell) at the neuromuscular junction. Pre-synaptic cell relases neurotransmitter acetylcholine (Ach).

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25
Q

Autonomic Efferent System

A

Consists of 3 neurons:
1. Neuron 1 - cell body in brain, axon in brain or spinal cord.
2. Neuron 2 is myelinated - cell body in brain or spinal cord, axon in PNS. Synapses onto neuron 3 in autonomic ganglion.
3. Neuron 3 is unmyelinated - cell body in PNS (autonomic ganglion), axon in PNS. Synapse onto effector organ. Neurotransmitter released is Ach or norepinephrine (NE)
Effectors include smooth muscle, cardiac muscle, glands and adipose tissue.

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26
Q

2 subdivisions for Autonomic Nervous System

A
  1. Sympathetic

2. Parasympathetic

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27
Q

Sympathetic division of Autonomic NS

A

Prepares the body for acute or stress response. The ‘fight or flight’ system.

Effects:
Increased heart rate, pupil size, sweating and blood flow to muscles (by constricting blood vessels to skin and viscera).
Decreased gastric motility, salivation.

Neurotransmitter:
From Neuron 2 -> 3 = Ach
From Neuron 3 -> Effector = NE

Structural differences in neurons:
Neuron 2 = has short axon. Cell body in thoracolumbar level of spinal cord.
Neuron 3 = long axon. Cell body close to CNS in sympathetic ganglion.

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28
Q

Parasympathetic division of the Autonomic NS

A

Prepares the body for restful situations. The ‘rest and digest system’.

Effects:
Decreased heart rate and pupil size
Increased gastric motility and salivation

Neurotransmitter:
From neuron 2 -> 3 and from neuron 3 -> effector = Ach

Structural Differences:
Neuron 2 = long axon. Cell body in cranial (brainstem) and sacral (spinal cord) levels.
Neuron 3 = Short axon. Cell body distant from CNS in parasympathetic ganglion near effector.

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29
Q

Sympathetic chain ganglia

A

The site where the pre-ganglionic neurons synapse onto input zone of the post-ganglionic neuron. It is found on each side of the vertebral column and has 21 pairs.

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30
Q

Action Potentials

A

Action Potentials are information travelling along a nerve (or muscle) cell associated with the generation of electrical impulses.

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31
Q

Resting Membrane Potential

A

In living cells, resting membrane potential is about -70mV. This is due to the distribution of cations across the membrane.
ECF = High Na+, Low K+. ICF = High K+, Low Na+.
These concentrations are caused by a sodium- potassium exchange pump which tosses out 3 Na+ ions and brings in 2 K+ ions.
RMP is negative because K+ ions can leave the cell much easier than Na+ ions can enter the cell.

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32
Q

K+ and Na+ gradients

A 
K+:
Chemical gradient = Out
Electrical gradient = In
Electrochemical (overall) gradient = Out 
Na+
Chemical gradient = In
Electrical gradient = In
Electrochemical (overall) gradient = In
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33
Q

Sending Information via AP

A

AP much reach a threshold (around -60mV) at the axon hillock. If this is met, AP will travel down the axon. Propagation occurs when voltage-gated Na+ channels open at the axon initial segment.

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34
Q

Voltage-gated Na+ Channels

A

These will open when there is a change in the membrane potential (activation gate - outer membrane surface). This allows Na+ ions to enter the cell and further depolarise the membrane. There has to be a strong enough depolarisation to open enough Na channels and generate an output. The channels can close when the membrane potential is too high (inactivation gate - inner membrane surface).

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35
Q

Stages of AP

A
  1. Depolarisation to threshold (-60mV):
    - Change in MP is sufficient enough to depolarise cell, voltage-gated Na+ channels will open.
  2. Activation of Na+ channels and rapid depolarisation (+10mV):
    - Na+ channels are open and Na+ ions flowing into cell.
  3. Inactivation of Na+ ion channels and activation of K+ channels (+30mV):
    - Membrane is fully depolarised, inactivation Na+ gate has stopped Na+ entering the cell.
    - Voltage-gated K+ channels open. (They repsond to same change in MP as Na+ channels but at a much slower rate.) K+ ions leave the cell, beginning to repolarise the membrane.
  4. K+ ion channels close
    - Because they are slow to do so, hyperpolarisation occurs.
    - Membrane repolarises to RMP as K+ and Na+ channels are both closed.
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36
Q

Absolute refractory period

A

(Stages 2 and 3)
A period where a second action potential cannot be generated. Sodium channels will not reactive (open) until hyperpolarisation occurs.

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37
Q

Relative refractory period

A

(Stage 4)
A period where a second action potential cannot be generated unless there is sufficient stimulus. Na+ channels begin to reactivate to return to RMP.

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38
Q

AP Propagation (Unmyelinated axons)

A

Once AP at initial segment causes the MP to depolarise to +30mV, Na+ ions entering the cell will spread away from the channel along the inside of the membrane, graded depolarisation brings the segment 2 to threshold. AP will develop in segment 2 as initial segment begins repolarisation and is refractory. Na+ ions entering the cell in segment 2 will spread to segment 3 causing a graded depolarisation, bringing this segment to threshold. Initial segment will still be in refractory period.
This pattern continues along the full length of the axon, resulting in a continuous propagation of AP.

39
Q

AP Propagation in Myelinated axons

A

Myelinated axons increase AP conduction velocity. This is because Na+ channels are restricted to nodes and between the nodes the axon behaves like an excellent conductor. The current cannot escape the sheath because it does not have access to the ECF. Therefore the AP will develop in the initial segment and then jump from node to node.

40
Q

Synaptic Transmission Steps

A
  1. AP arriving down the axon of the presynaptic neuron triggers the opening of voltage-cated Ca2+ channels.
  2. Ca2+ ions diffuse into the axon terminal triggering synaptic vesicles to release ACh by exocytosis.
  3. ACh diffuses across synaptic cleft and binds to ACh-gated sodium ion channels, as Na+ ions enters postsynaptic neuron, a graded depolarisation is generated - ESPS.
  4. Depolarisation ends as ACh is broken down into acetal and choline by AChE.
  5. The Axon terminal reabsorbs choline and uses it to synthesise new ACh molecules.
41
Q

Graded Depolarisations - EPSP and IPSP

A

EPSP (excitatory postsynaptic potential) is a minor depolarisation. Chemical stimulus opens sodium ion channels, stimulus is removed and excess Na+ ions are transported out of the cytosol.
IPSP (inhibitory postsynaptic potential) is a minor hyperpolarisation. Chemical stimulus opens K+ ion channels, stimulus is removed and excess K is transported out of the cytosol.
If EPSP and IPSP occur at the same time, they cancel out, therefore there is no change in MP. If multiple EPSP occur at once, an AP is generated.

42
Q

Synaptic Transmission at NMJ (presynaptic neuron synapses onto muscle fibre)

A

The synaptic transmission at the NMJ is excitatory and absolute. There is no axon hillock and no EPSP / IPSP summation. This is because post-synaptic event does not depend on amount of input. There is enough Ca2+ and neurotransmitter release at NMJ.

43
Q

Temporal Summation

A

Temporal - in time. One stimulus will not depolarise the membrane enough to reach threshold, however, a second (or multiple) stimulus coming from the same place will be sufficient to depolarise the membrane to threshold. The closer together they are in time, the stronger the response.

44
Q

Spatial Summation

A

Spatial - space. Two stimuli occur at the same time at different places of the neuron, individually, these stimuli would not be sufficient to reach threshold, when added together they can reach threshold. However they must be close enough to each other for this to occur.

45
Q

External Anatomy of the spinal cord

A

Spinal cord starts at the foramen magnum (the opening at the base of the skull) and ends at the inferior boarder of the 1st lumbar vertebra.
The spinal cord is contained within a meningeal sac which fits inside of the spinal cavity within the vertebra. The meningeal sac is filled with cerebrospinal fluid (CSF) to help with cushioning.
The end of the spinal cord tapers into a cone called Conus medulairs. (made up of non-neural tissue and is for the attachment of the filum terminal). There is an extension from here to the the bottom of the spinal cavity called the filum terminal (non-neural tissue which anchors the spinal cord).

46
Q

Spinal nerves

A

The spinal cord has 31 segments. 1 pair of spinal nerves are associated with each segment. The names of the spinal nerves are determined by the vertebra which they exit inferiorly. (except C1 which exits above first cervical vertebra).
Because the vertebrae extend further down than the spinal cord, there is a bundle of long nerves inferior to the conus medularis, forming the cauda equina.

47
Q

Internal anatomy of the spinal cord

A 
The spinal cord is 1 long continuous structure with pairs of nerves at every segment.
(Best to look at diagram at notes)
Sulcus = small indentation 
Fissure = a deep sulcus
White matter = bundle of myelinated axons
Grey matter = cell bodies 
CNS = white matter and grey matter.
PNS = (dorsal root) ganglion and nerve roots (ventral and dorsal)
Dorsal (back) half controls afferent / sensory information.
Sensory neurons are unipolar with their cell body in the dorsal root ganglion.
The ventral (front) half controls efferent / motor information. Motor neuron cell bodies are found in the ventral horn. Autonomic cell bodies are found in the lateral horn.
48
Q

Spinal Nerves structure to allow information travelling in both directions

A

(Best to look at diagram in notes)
Information only travels in one direction in the dorsal and ventral nerve roots but can travel in both directions in the spinal nerves.
Dorsal Ramus - Efferent to back, afferent from back
Ventral Ramus - Efferent to front, afferent from front
Rami communicans - Sympathetic branch, only in T1 - L1
(contains sympathetic chain ganglion)

49
Q

Peripheral Nerve

A

(Bundles of axons in the PNS = a nerve)
Individual axons (either myelinated or unmyelinated) are covered with endoneurium.
These are bundled together to form a fascicle.
Fascicles are covered with perineurium.
Fascicles are bundled together to form a nerve. A nerve will also contain blood vessels.
Nerves are covered with epineurium.

50
Q

Meninges

A 
Meninges encase the brain and spinal cord.
3 layers under the cranium:
- Dura Mater
- Arachnoid Mater
- Pia Mater
51
Q

Dura Mater

A

Outer most layer.
Dense and fibrous = tough.
Two layers = outer and inner which can seperate to form venous sinuses.
These are collecting veins which collect venous blood from the brain and old CSF that has cycled through the ventricular system.
The inner layer can fold on itself, forming the dural folds which separate major divisions of the brain and provide stability. There are 3 dural folds:
- Falx cerebri, separating cerebral hemispheres in the median plane
-Falx cerebelli, separating cerebellar hemispheres in the median plane
-Tentorium cerebelli, separating the cerebrum and cerebellum in the horizontal (transverse) plane.

52
Q

Arachnoid Mater

A

Beneath the dura mater.
Contains subarachnoid space. This is filled with CSF and contains blood vessels on top of the pia mater. Arrachnoid granulations perforate the inner layer of the dura mater, which drain old CSF from subarachnoid space into the venous sinus.

53
Q

Pia Mater

A

Beneath the arachnoid mater.
Most inner layer, which is transparent and delicate.
Adheres to brain and follows gyri and extends into the sulci.

54
Q

Ventricular System

A

A network of interconnected spaces within the brain, filled with CSF which supplies nutrients to and protects the brain. These spaces are lined with ependymal cells which have cilia and that wave to circulate the CSF.

55
Q

Ventricles

A

Lateral ventricle - 2 in each cerebral hemisphere.
Third ventricle - Located in the diencephalon
Cerebral aqueduct - connects the third and fourth ventricles and is located in the midbrain.
Fourth ventricle - Located at the cerebellum level.

56
Q

Cerebrospinal fluid

A

Surrounds the CNS with subarachnoid space.
Provides support and cushioning.
Transports food and waste.
Produced by choroid plexus within the ventricles.

CSF Circulation path:
Starts at the Lateral ventricles
-> Third ventricle
-> Cerebral aqueduct
-> Fourth ventricle
-> Subarachnoid space flowing around the brain and spinal cord
-> Exits through arachnoid granulations into venous sinus.

57
Q

External anatomy of the brain.

A

Look at diagram.
Sulcus = furrow / valley
Gyrus = Hill

58
Q

Functions associated with each lobe

A

Frontal - Personality, language and motor control.
Parietal - Somatosensory
Occipital - Vision
Temporal - Memory, hearing

59
Q

Diencephalon and Brainstem

A

Diencephalon is made up of the thalamus and hypothalamus

Brainstem is made up of the midbrain, pons and medulla oblongata.

60
Q

3 types of white matter in the brain

A
  1. Commisural Tissue - Axons cross from side to side in both directions. eg Corpus collasum
  2. Projection Tracts - Axons extend between cortex and CNS areas outside cerebrum.
  3. Association Tracts - Axons on same side of cerebral cortex. Enable communication between brain areas.
61
Q

Major cortical areas

A

Primary motor cortex / Pre-central gyrus = Efferent / outgoing information.
Somatosensory cortex / Post-central gyrus = Afferent / incoming information.
Specific regions of each cortex correlate to specific regions of the body on the opposite side.

62
Q

Corticospinal Pathway (Efferent information)

A

Consists of 2 neurons - upper and lower motor neuron.
Upper motor neuron - Cell body in primary motor cortex. Axon extends down to spinal cord, crossing at the medulla oblongata. Synapses onto lower motor neuron.
Lower motor neuron - Cell body in ventral horn of spinal cord. Axon extends out of spinal cord (ventral nerve root) into body. Synapses on skeletal muscle.

63
Q

Dorsal / Posterior Column Pathway (Afferent)

A

Consists of 3 neurons.
Neuron #1 (unipolar) - Cell body in dorsal root ganglion.
Peripheral fibre (input zone) from sensory receptor. Central fibre (output zone) ascends towards brain in dorsal columns. Synapses onto neuron 2 in medulla oblongata.
Neuron #2 - Cell body in medulla oblongata. Axon crosses medulla oblongata and ascends. Synapses onto neuron 3 in thalamus.
Neuron #3 - Cell body in thalamus. Axon ascends to somatosensory cortex. Synapses onto somatosensory cortex neuron.

64
Q

Reflex movement

A

A reproducible and automatic response to a certain stimulus. It is an organised neural circuit contained within the spinal cord. Example = stretch and withdrawal reflex.

65
Q

Muscle Spindle

A

Muscle spindles monitor the length of the muscle. It is made up of modified muscle fibres (intrafusal fibres) innervated (supplied with) gamma motor neurons and sensory neurons that have dendrites spiraling around the centre of the intrafusal fibres.
They’re important for maintaining posture.

66
Q

Stretch Reflex

A

Stimulation of the receptor - muscle spindle stretches. Activation of a sensory neuron (stretch stimulates ion channels to open, depolarising the sensory neuron.)
Information processing in the CNS
Activation of the motor unit
Response of a peripheral effector (skeletal muscle fibre)

67
Q

Withdrawal Reflex

A

The withdrawal reflex consists of the sensing of a painful stimulus which travels via a sensory neuron to the spinal cord.
Reciprocal inhibition occurs, in which flexors are stimulated and extensors are inhibited (AP in motor neuron inhibited by inhibitory interneuron). This information also travels to other sections of the spinal cord and the brain.

68
Q

Control of muscle tension

A

Can be achieved by 2 mechanisms:
1. Motor unit recruitment - more motor units are recruited, thus more muscle fibres activated and therefore more tension.

  1. Stimulation frequency - If APs are more frequent, maximum tension is reached faster and a smoother tension is also developed.
69
Q

Preparing for movement

A

Decision to perform voluntary movement arises in the frontal lobe. It then travels to the premotor cortex. Information then travels to the cerebellum.

70
Q

Cerebellum

A

Involved in preparing and performing a movement.
It coordinates muscles, guided by sensory feedback.
Compares intended movement with the actual result.
Helps maintain posture and gaze.
Deficits of the cerebellum can cause ataxia – characteristic ‘drunken gait.’

71
Q

Performing movement - voluntary motor control loop

A

The planning of voluntary muscle control occurs in the cerebellum, sending information to the motor cortex, which activates lower motor neurons in the spinal cord to produce a movement. Muscle spindles monitor muscle movement and body positioning and provides sensory feedback to the brain (alongside other sensory feedback systems). Cerebellum compares intended and actual result and relays this to the motor cortex, correcting movements carried out.

72
Q

Sensory Neurons

A

Most sensory neurons are pseudo unipolar as they have one axon which splits into two branches, centrally and peripherally.

73
Q

4 types of CNS inputs

A
  1. Special senses - Vision, hearing, taste, smell and vestibular (balance)
  2. Somatic and visceral (felt internally) sensations - Touch, pain, temperature and body position
  3. Direct - temperature sensing by the hypothalamus
  4. Endocrine or hormonal - eg food intake regulation
74
Q

Sensory receptors

A

Sensory receptors are highly sensitive to particular stimuli, different stimuli will activate different sensory receptors. Sensory receptors can be the sensory endings of an afferent neuron or specialised receptor cells ( as for the special senses).

75
Q

4 types of information which describe a sensory stimulis

A
  1. Modality - Type of sensory receptor activated.
    Proprioception - via muscle spindle, detects muscle length, body position, movement and posture.
    Touch - Variety of forms, functions and receptive fields.
  2. Intensity - Frequency
    If stimulus intensity increases, the frequency of action potentials will increase. If stimulus is not very intense, there may be no AP if the threshold was not reached.
    Intense stimulus may also activate a higher number of receptors, resulting in more action potentials in sensory neurons.
  3. Duration - Duration of an action potential firing in a sensory neuron.
    Sensory receptors can be most sensitive to change. They often adapt to the stimulus so a continuous stimulus will decrease output (reception) over time. Eg thermoreceptors mostly only sense changes in temperature. However tonic receptors like muscle spindles will not adapt.
  4. Location - Location of your sensory receptors which were activated.
    The region of space in which a receptor can detect a stimulus is known as the receptive field. When these fields are small and dense, the stimuli can be easily discriminated. Fields can also overlap and so multiple receptors may detect a single stimulus.
76
Q

Conscious Sensations

A

When a sensation is consciously detected by a sensory receptor, the sensory stimulus is converted into an AP. This is known as transduction. Receptors than synapse onto afferent neurons which carry the AP down the their peripheral fibre via a sensory tract / pathway. This is then integrated in the somatosensory cortex. Identification of sensation type and location occurs in the primary somatonsensory cortex (postcentral gyrus) whilst the perception and interpretation of the information occurs in the somatosensory association cortex (parietal lobe).
Areas of the somatosensory cortex are associated with specific areas of the body.
Large regions of the cortex are associated with densely innovated areas of the body with small receptive fields such as the hands.

77
Q

Homeostasis

A

The maintenance of an internal stable environment.
The normal range of a given variable is specific to each individual. The population reference range is based on the variability between individuals and tends to be wider than an individuals range. An individual may move out of their normal range for a variable and may experience symptoms, despite still being in the reference range. Therefore population ranges aren’t always transferable to an individual’s health. Most individuals fall within the population reference range.

78
Q

Synaptic vs Endocrine system

A

Synaptic - AP in neurons and neurotransmitter release at synapse = fast transmission speed and good for brief responses but may need to keep sending signal for a more sustained response. Also limited to specific area and target cells must have appropriate receptors.

Endocrine (hormonal) - Hormones released into bloodstream by endocrine glands. Targeting by presence of specific receptors on target cell. Relatively slow but produces prolonged responses that are widespread.

79
Q

Hormones

A

Hormones are chemical messengers produced in one location and transported via the bloodstream to a second location where they cause a response in those cells.
Receptors are proteins located either on the target cell membrane or within the target cell depending on the solubility of the hormone.

80
Q

Water- soluble hormone

A

Chemical classification - Mostly peptides (75%), Catecholamines (adrenaline, noradrenaline)
Storage - Made and stored until required
Transport - dissolved in blood
Location of hormone receptor - Plasma membrane
Speed - Rapid (milliseconds to minutes)
Action mechanism - Through 2nd messengers:
-Hormone binds to the receptor on target cell membrane, activating an associated G-protein.
-The G protein either activates / inhibits adenylyl cyclase or increases intracellular Ca2+.
-A second messenger is produced or reduced (cyclic AMP, or Ca2+)
-Downstream proteins / pathways are activated or deactivated.

81
Q

Lipid-soluble hormone

A

Chemical classification - Steroid, thyroid hormone
Storage - Steroids are made when required. Thyroid hormones are stored until required.
Transport - Bound to carrier proteins
Location of hormone receptor - Inside of the cell (nucleus or cytoplasm)
Speed - Slow (hours - days)
Action mechanism - Alteration of gene transcription:
- Hormone dissociates from the carrier protein and diffuses across the target cell membrane.
- Hormone binds to an intracellular receptor.
- Hormone-receptor complex acts as a specific transcription factor
- Target gene is activated and transcribed to make mRNA
- mRNA is translated to make a new protein which mediates a cell specific response.

82
Q

Control of hormone secretion

A

Amount of hormone in the blood depends on the rate of hormone secretion and the rate of removal from the blood. Secretion is usually controlled by a negative feedback loop.

83
Q

Pancreas

A

Pancreas is an exocrine gland (pancreatic acini secrete digestive enzyme) as well as an endocrine gland (pancreatic islets which secret insulin and glucagon).
Pancreatic islets contain beta cells which secrete insulin and aplha cells which secret glucagon for blood glucose concentration homeostasis (should be 70 - 110 mg / dL).

84
Q

2 metabolic states

A

Fed state: cellular uptake of nutrients, anabolic metabolism glycogen, fat and protein synthesis.

Fasting state: Mobilisation of nutrients, catabolic matabolism, breakdown of fat, glycogen and protein.
Storing glucose and breaking it down (glycogenolysis) is much faster than synthesising new glucose (glucogeogensis).

85
Q

Insulin

A

Increase fuel storage.
Secreted in response to increases blood glucose concentration by pancreatic islet beta cells.
Effect on liver cells - Glucose output stops, increased net uptake of glucose, glycogen and fat synthesis.
Effect on muscle cells - Increase glucose and amino acid uptake, increase glycogen and protein synthesis.
Effect on adipose (fat) cells - Increase glucose uptake and fat synthesis.
Overall effect = decreased blood glucose concentration.

86
Q

Glucagon

A

Increase fuel release.
Secreted in response to decreased blood glucose concentration by pancreatic islet alpha cells.
Effect on liver cells - Increased breakdown of glycogen,
Increase glucose and ketone synthesis.
Overall Effect - Increased blood glucose and blood ketone concentration.

87
Q

Pituitary Gland

A

The pituitary gland is found attached to the hypothalamus, inferior to the brain and has anterior and posterior lobes. Each lobe has different cell types and thus a distinctive mechanism for hormone secretion. The hypothalamus controls pituitary secretion of hormones via neural and hormonal input. Pituitary hormones can act on target cells or stimulate secretion of further hormones by other glands.

88
Q

Posterior Lobe of pituitary

A

Connected to the hypothalamus via neurons.
Hormones synthesised in the the neuron cell body in the hypothalamus and then travel down the axon and stored in the axon terminal in the posterior lobe.
Neural communication from the hypothalamus stimulates posterior pituitary hormones to be released into the blood. Peptide hormones released =
- Antidiuretic hormone (kidney water reabsorbtion)
- Oxytocin (uterine contraction, release of breast milk).

89
Q

Anterior Lobe of pituitary

A

Connected to the hypothalamus vis blood vessels.
Hormones synthesised and stored in the pituitary.
Neural input in the hypothalamus will cause the short neurons in the hypothalamus to secret stored releasing hormones into the portal veins. The hormones travel down into the network of blood vessels in the anterior pituitary. They will bind to receptors on specific target cell membranes stimulating the release of specific peptide hormones to be secreted into the bloodstream. Examples of hormones released =
- Growth hormone
- Prolactin
These pituitary hormones will travel to target cells stimulating the release of another hormone

90
Q

Growth Hormone

A

Growth hormone directly acts on muscle, liver and fat cells.
Muscle - stimulates protein synthesis and inhibits cellular uptake of glucose (more glucose in blood for glucose synthesis)
Liver - Stimulates glucose synthesis
Fat - Increase triglyceride breakdown in adipose (fat) tissue. (ie free fatty acids so they can be used in glucose synthesis).
Growth hormone indirectly promotes growth of bones, muscle and other tissue by causing the release of somatomedin C (hormonal growth factor) that promotes cell division.
Growth hormone has a long-term effect on growth and a short-term effect on metabolism.
The concentrations of GH fluctuate throughout the day. Its highest during sleep. GH concentrations are highest during childhood compared to adulthood and spike during puberty.
Growth hormone releasing hormone (GH-RH) secreted by GHRH neurons the hypothalamus stimulates the release of growth hormone from the anterior pituitary gland.
GH release is inhibited by the release of growth hormone inhibiting hormone (GH-IH or somatostatin SS) released by somatostatin neurons in the hypothalamus.

91
Q

Thyroid Gland

A

The thyroid gland is located inferiorly to the larynx and covers the anterior and lateral surfaces of the trachea. It is composed spherical sacs called follicles which are surrounded by follicular cells that function to synthesise thyroid hormones. Clear cells are clustered in the gaps between follicles and function to synthesise calcitonin.

92
Q

Thyroid Hormone

A

A protein called thyroglobulin (TGB) is made in the thyroid follicles. When iodine enters the cells, it reacts with the tyrosine in TGB, forming thyroid hormone. Thyroid hormone then detach from TGB when required (unlike other steroid hormones). Thyroid hormone then travels bound to a carrier protein to the target cell. Two types of thyroid hormone are T3 (active form) and T4 (plentiful form).
Thyroid hormone will detach from the carrier protein to cross the target cell membrane. It will then bind to a T3 receptor (which is already bound to a specific DNA site), specific genes are activated to transcribe mRNA, which is then translated in the cytoplasm synthesising specific proteins. This response time is 45 mins - days.

93
Q

Basal metabolic rate

A

Basal metabolic rate is the body’s energy expenditure when the person is under basal metabolic conditions:

  • Awake
  • At physical and mental rest
  • Comfortable temperature
  • Lying down
  • No muscle movement
  • Fasted (12 -18 hours)
94
Q

Thyroid hormone effects

A

Required for normal growth, alertness and metabolism. It has an arrange of effects on a persons metabolism:

  • Increases body heat production.
  • Stimulates fatty acid oxidation in a variety of tissues.
  • Increases proteolysis mostly from muscle.
  • Stimulates carbohydrate metabolism, enhances insulin-dependent entry of glucose into cells, increases gluconeogenesis and glycogenolysis.

HUBS191 (3 decks)

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