Grey Matter Flashcards
1
Q
What is a neurone?
A
A single cell, each one is a long nerve fibre which carries the nerve impulse
2
Q
What is a nerve
A
Bundles of nerve fibres (neurones)
3
Q
What are the 3 types of neurone?
A
- Sensory
- Motor
- Relay
4
Q
State the role of dendrites and dendron.
A
To receive the impulse and transmit it towards the cell body.
5
Q
State the role of the axon.
A
To transmit the impulse away from the cell body.
6
Q
What is the myelin sheath made of?
A
Schwann cells
7
Q
Describe the role of the myelin sheath.
A
Wraps around the axon or dendron to provide protection from damage. As it is composed of predominantly lipid membrane, it acts as an electrical insulator preventing depolarisation of the neurone in these areas.
8
Q
Name the gaps between the Schwann cells.
A
Nodes of Ranvier
9
Q
Describe the role of the Nodes of Ranvier.
A
They provide an area along the axon or dendron where depolarisation can occur. This enables the impulse to jump from node to node speeding up nervous impulse transmission
10
Q
Which organsims have nodes of Ranvier?
A
Vertebrates only
11
Q
Describe the reflex arc. e.g. for touching something hot
A
- Receptors detect a stimulus and generate a nerve impulse
- Sensory neurones conduct a nerve impulse to the CNS along a sensory pathway
- Sensory neurones enter the spinal cord through the dorsal route
- Sensory neurone forms a synapse with a relay neurone
- Relay neurone forms a synapse with a motor neurone that leaves the spinal cord through the ventral route
- Motor neurone carries impulses to an effector which produces a response. In this example the bicep contracts to raise the arm away from the flame
12
Q
Explain the features of a reflec arc.
A
- Rapid/fast – Only 3 neurones and 2 synapses are involved
- Involuntary – The main impulse pathways does not travel to the brain for processing
13
Q
Name the two muscles in the iris
A
Radial and circular muscles working as antagonistic pairs.
14
Q
Which part of the nervous system controls the muscles in the iris?
A
The autonomic
15
Q
Name the muscle that is ‘told’ to contract by the sympathetic nervous system?
A
Radial
16
Q
Name the muscle that is ‘told’ to contract by the parasympathetic nervous system?
A
Circular
17
Q
Describe the pupil reflex in high light intensity.
A
Light strikes photoreceptors in the retina. Sensory neurons pass nerve impulses along the optic nerve to the CNS. These impulses are sent along parasympathetic motor neurons. Circular muscles contract and radial muscles relax. The pupil constricts, reducing the amount of light entering the eye.
18
Q
What is the resting potential of a neurone?
A
The resting potential has a value of -70mV.
The inside of the axon is more negative than the outside and hence the membrane is polarised.
19
Q
What is the first step in setting up the resting potential?
Describe how the resting potential is set up
A
The Na+/K+ pump pumps Na+ out of the neurone and K+ into the neurone against their concentration gradients using ATP.
20
Q
How does the membrane’s permeability affect resting potential?
Describe how the resting potential is set up
A
The membrane is virtually impermeable to Na+ but permeable to K+, allowing K+ to diffuse out of the neurone.
21
Q
What happens when K+ diffuses out of the neurone?
Describe how the resting potential is set up
A
The outside of the neurone becomes more positive than the inside.
22
Q
What creates the electrical gradient in a neurone?
Describe how the resting potential is set up
A
The decrease in positive ion concentration inside the cell creates an electrical gradient.
23
Q
What occurs when the K+ chemical gradient balances the electrical gradient?
Describe how the resting potential is set up
A
There will be no further net movement of K+ in or out of the neurone, creating an electrochemical equilibrium for K+.
24
Q
What is the result of the electrochemical equilibrium for K+?
Describe how the resting potential is set up
A
The membrane is polarised, and a steady state exists with the potential difference settling at -70mV.
25
What is the resting potential?
The resting potential is the state of a neurone when it is not being stimulated.
26
Describe how the resting potential is set up
1. Sodium ions are pumped out of the axon and potassium ions are pumped into the axon via sodium-potassium pump
2. which uses ATP
3. The potassium ions diffuse down the concentration gradient
4. The sodium ions cannot diffuse back into the axon.
27
What occurs during depolarisation?
When a neurone is stimulated, voltage dependent Na+ gated channels open, allowing Na+ to diffuse into the neurone, leading to depolarisation. This triggers all Na+ gates to open until the threshold potential of -55mV is reached, resulting in an action potential with a potential difference of +40mV. There is a refractory period to ensure that impulses only travel one way.
28
What happens during repolarisation?
After 0.5 ms, Na+ gated channels close, and K+ gated channels open, allowing K+ to diffuse out of the neurone, making the inside more negative.
29
What is hyperpolarisation?
Hyperpolarisation occurs when more K+ diffuse out than in, resulting in a membrane potential of -75 to -80mV, causing K+ gated channels to close.
30
What happens after multiple action potentials?
The resting potential is re-established if multiple action potentials have occurred.
31
Describe synaptic transmission.
1. An action potential arrives at the pre-synapse.
2. The membrane depolarised and Ca2+ channels open.
3. Ca2+ causes synaptic vesicles to fuse with the pre-synapse membrane.
4. The neurotransmitter is released into the synaptic cleft via exocytosis and binds with receptors on the post-synaptic membrane.
5. Cation channels open and Na+ ions flow through. The membrane depolarises and causes an action potential.
6. Neurotransmitter is taken up by the pre-synaptic neuron (re-uptake), broken down by enzymes or diffuses away from the synaptic cleft.
32
What happens if sufficient Na+ enters the neurone?
An excitatory post-synaptic potential (EPSP) is reached, producing and propagating an action potential along the postsynaptic neurone.
33
What must happen to the neurotransmitter after the impulse has moved on?
It must be removed by one of three methods:
a) reuptake across the presynaptic membrane, b) breakdown by enzymes
c) diffusion away from the synapse.
34
What are examples of enzymes that break down neurotransmitters?
Acetylcholinesterase and MAOA.
35
What is a photoreceptor?
A receptor cell that is sensitive to light
36
What are the two forms of photoreceptor in a human and what type of vision do they provide?
* Rods – black & white vision
* Cones – colour vision
37
Where are photoreceptors located?
Within the retina of the eye
38
Name the photochemical pigment present in rod cells.
Rhodopsin
39
Describe where rhodopsin is located.
Within the flattened vesicles of the outer segment of the rod cell
40
Describe what happens to a rod cell in the dark.
1. Na+ is actively pumped out of the inner segment of the rod cell. This requires the hydrolysis of ATP.
2. Na+ in the outer segment diffuses down its concentration gradient into the inner segment.
3. Na+ diffuses into the outer segment through open non-specific cation channels by facilitated diffusion down its concentration gradient. This influx causes a slight depolarisation of -40mV.
4. This slight depolarisation causes the release of the neurotransmitter glutamate from the rod cell. Binding of the glutamate to the bipolar cell hyperpolarises it and prevents it from depolarising (inhibitory synapse). The bipolar cell does not release its neurotransmitter to depolarise the ganglion neurone.
41
Describe what happens to a rod cell in the light:
1. When light (photons) hits the rod, rhodopsin (formed of retinal and opsin) absorbs the light. The retinal (non-protein) converts from its cis form to the trans form and breaks apart from the opsin (protein) - The opsin activates a series of membrane-bound reactions ending in the hydrolysis of a cyclic nucleotide molecule. This hydrolysis results in the closure of the non-specific cation channels in the outer segment. The diffusion of Na+ into the rod cell decreases.
2. Na+ is still pumped out of the inner segment. This results in the hyperpolarisation of the rod cell causing the release of glutamate to stop.
3. The lack of glutamate results in the depolarisation of the bipolar cell. This causes the bipolar cell to release its neurotransmitter and depolarise the ganglion neurone. An action potential is generated and impulses are sent along the optic nerve to the brain.
42
What occurs during dark adaptation?
The trans retinal converts back to cis retinal. The retinal and opsin recombine to form rhodopsin. This requires ATP. The process can take up to 50 minutes.
43
What is the purpose of dark adaptation?
This enables the eye to transition from a high light setting to a low light setting and restore retinal sensitivity i.e. the eye adapts its definition of what is black.
44
Describe the structure of the cortex
Also known as the cerebrum. Highly folded outer layer composed of nerve cell bodies, synapses and dendrites – known as grey matter. Underneath is the white matter composed of millions of myelinated axons connecting neurones in different areas.
45
Role of frontal lobe
Decision making, reasoning, planning, emotions, forming associations
46
Role of temporal lobe
Processes auditory info – hearing, sound recognition, speech. Also memory
47
Role of parietal lobe
Orientation, movement, sensation, calculation, recognition & memory
48
Role of occipital lobe
Occipital lobe (visual cortex): Processes info from eyes – vision, colour, shape and perspective
49
Role of motor cortex
Neurones connect directly to spinal cord, brain stem & muscles via motor neurones. Stores info about how to carry out movement
50
Label the diagram
51
What is the role of the corpus callosum?
White matter composed of axons. Allows connections between the two hemispheres and the structures below.
52
What is the role of the medulla oblongata?
Regulates heart rate, breathing rate, and blood pressure.
53
What is the role of the cerebellum?
Responsible for balance and coordinates movement by receiving inputs from the motor cortex, muscles, and joints.
54
What is the role of the hypothalamus?
Controls thermoregulation, thirst, hunger, circadian rhythms, and sleep. Acts as an endocrine gland and stimulates the pituitary gland.
55
What is the role of the thalamus?
Routes all incoming sensory information to the correct regions, e.g., visual inputs to the occipital lobe.
56
What is the role of the basal ganglia?
Selects and initiates stored programmes for movement.
57
What is the role of the hippocampus?
Involved in laying down long-term memory.
58
What is the role of the pituitary gland?
Endocrine gland responsible for secreting hormones controlling growth, blood pressure, energy management, sex organs, thyroid gland, metabolism, pregnancy, childbirth, nursing, water/salt concentration at the kidneys, temperature, and pain relief.
59
What is the role of the midbrain?
Relays information to the cerebral hemispheres, including auditory information to the temporal lobe and visual information to the occipital lobe.
60
What does the pons do?
Relays information from the forebrain to the cerebellum and medulla. Involved in sleep, breathing, respiration, swallowing, bladder control, hearing, taste, eye movement, facial expressions, sensations, and posture.
61
What does MRI stand for?
MRI stands for Magnetic Resonance Imaging.
62
How is an MRI image obtained?
A combination of a magnetic field and radio waves cause the nuclei of hydrogen atoms to change their orientation. When the radio waves are switched off, some hydrogen nuclei change their orientation, releasing energy that can be detected and converted into an image.
63
What can MRI be used for?
Identifying issues with soft tissues – tumour location and size, stroke, brain, spinal cord and joint injuries.
64
What are the advantages of MRI?
Uses magnetic field & radio waves, so no harmful X-rays. Thin slices of image are created which can be combined to produce a 3D image. Better resolution than CT.
65
What are the disadvantages of MRI?
Loud noise. Small imaging space – not good for claustrophobic patients, children or those with special learning needs. Can’t be used on people with metal implants.
66
What does fMRI stand for?
fMRI stands for Functional Magnetic Resonance Imaging.
67
How is an fMRI image obtained?
Increased neural activity results in a greater demand for oxygen and an increased blood flow to that region. Oxyhaemoglobin does not absorb fMRI signals (radio waves). The more oxyhaemoglobin is delivered, the less the radio waves are absorbed, causing those areas to ‘light up’. Must compare brain activity whilst doing the task with relaxation.
68
What can fMRI be used for?
Able to study the brain in action. Study human activities such as memory, emotion, language and consciousness. Able to study psychiatric disorders, epilepsy, Alzheimer’s, tumours, autism, pain, consequences of a stroke.
69
What are the advantages of fMRI?
Uses magnetic field & radio waves, so no harmful X-rays. Has a very high resolution of 1 – 6 mm. Can identify which areas of the brain are being used for particular tasks and which areas are being used together as a network. 4 images produced per second.
70
What are the disadvantages of fMRI?
Expensive. Patient/subject must lie completely still – difficult for children and those with special learning needs. Only measures blood flow and not how individual neurones are behaving.
71
What does CT stand for?
CT stands for Computerised Axial Tomography (CAT).
72
How is a CT image obtained?
Narrow beam X-rays fired at different angles around the patient. The beam is reduced in strength according to the density of the tissue. The X-rays are then detected to create slices of tissue.
73
What can CT be used for?
Investigating the soft tissues i.e. brain, tumour growth.
74
What are the advantages of CT?
More resolution than broad-beam X-ray. Soft tissues can be imaged.
75
What are the disadvantages of CT?
Uses X-rays – not good for pregnant women. Frozen picture. Look at structure rather than function. Limited resolution so small structures can’t be distinguished.
76
What does PET stand for?
PET stands for Positron Emission Tomography.
77
How is a PET image obtained?
Radiotracers are created - Isotopes with short half-lives are incorporated into compounds. The radiotracer is injected into the bloodstream. More active areas of the body have increased blood flow. The radiotracer decays and emits positrons which collide with electrons, emitting gamma rays that are detected to create an image.
78
What can PET be used for?
The diagnosis and monitoring of heart disease, cancer and brain disorders such as Alzheimer’s.
79
What are the advantages of PET?
Can follow changes in disease progression or treatment over time if video images are played in succession.
80
What are the disadvantages of PET?
Very expensive. Use of radioactive isotopes. Can only be carried out once or twice a year per patient for safety reasons. After the scan, patient cannot travel by public transport due to potentially coming into contact with mothers in early pregnancy.
81
Define critical period.
Period of time during early development when the nervous system must obtain specific experiences to develop properly so that synapses are strengthened.
82
Describe monocular deprivation.
Depriving vision from one eye.
Monocular deprivation as an infant leads to permanently impaired vision.
Removal of cataracts when older can return vision.
83
Where do the axons leaving the retina arrive?
The axons leaving the retina arrive at the Thalamus.
84
What do the axons connect with in the visual cortex?
The axons connect with a specific column cell (ocular dominance cell) in the visual cortex in the occipital lobe.
85
How do the territories of axons and synapses differ between a newborn mammal and an adult?
At birth, there is a lot of overlap between the territories of the axons and synapses in the visual cortex. In an adult, there is no overlap; each axon is associated with one specific column cell.
86
What is the difference in width of column cells between a normal adult and an adult who has been light deprived in one eye?
The column cells associated with the light deprived eye are narrower than those for the eye receiving more light stimulation.
87
What happens to the column cells associated with the non-light deprived eye?
The column cells associated with the non-light deprived eye are wider and take up more space in the visual cortex.
88
When do changes in the visual cortex take place?
During the critical period (window).
89
What are ocular dominance columns?
Ocular dominance columns (column cells) are located in the visual cortex.
90
What happens every time an impulse travels down a neurone to a column cell?
The connection to that column cell is strengthened.
91
What happens if impulses do not arrive at a column cell?
The connections become weaker.
92
What is needed during the critical period for proper visual cortex development?
Stimulation during the critical period is needed to form effective connections in the visual cortex.
93
What did medical observations reveal about visual development?
A baby with a bandaged eye for two weeks was left with permanently impaired vision. People born with cataracts if not removed by age 10 will develop permanent impairment of perceiving shape or form.
94
What difficulties did newborn monkeys raised in the dark face?
They had difficulty with object discrimination and pattern recognition.
95
What did Hubel & Wiesel's experiments reveal about monocular deprivation?
Newborn monkeys exposed to monocular deprivation for different lengths of time during their critical period did not respond to light in the deprived eye.
96
What is perception?
It involves knowledge and experience to interpret sensory information from the retina to create our virtual experience of the world.
97
Describe depth perception.
* Stereoscopic vision is used for objects less than 30 m away, allowing the brain to compare views from both eyes.
* For objects greater than 30 m away, visual clues and past experiences are used to interpret the image.
* Cross-culturally, depth perception is different. The Carpented World Hypothesis shows that Western cultures perceive depth differently, in accordance to the Müller-Lyer illusion, than those in circular cultures. Babies encouraged to crawl across a glass table where a cliff ledge was pictured underneath proves that depth perception is not innate.
98
Define habituation
99
Describe the process of habituation.
1. With repeated stimulation, the calcium ion channels in the presynaptic membrane become less responsive.
2. With fewer calcium ion channels open, fewer calcium ions move into the pre-synaptic neurone when the presynaptic membrane is depolarised by an action potential.
3. Fewer vesicles move to and fuse with the presynaptic membrane. Less neurotransmitter is released into the synaptic cleft by exocytosis.
4. With less neurotransmitter available to bind to the receptors in the postsynaptic membrane, fewer cation channels open and fewer sodium ions enter the postsynaptic neurone. With less depolarisation, the post-synaptic excitatory potential is not high enough to trigger an action potential – there is no response.
100
Why is habituation important to an animal?
Allows animals to ignore and prevent wasting energy on unimportant stimuli so that they can concentrate on more threatening or rewarding stimuli. It is a crucial part of the learning process.
