Nervous system Flashcards
(204 cards)
1
Q
How do afferent and efferent neurons function?
A
Afferent neurons report changes to the CNS, and efferent neurons tell organs/body parts what is needed in response.
2
Q
What is the basic structure of a neuron?
A
Cell body, myelinated/unmyelinated axon, dendrites, synaptic terminals.
3
Q
What types of synaptic transmission exist?
A
Chemical or electric.
4
Q
How does neuron morphology relate to function?
A
Neurons vary in size/shape, myelination, number of synaptic terminals, and type of synaptic transmission. Their structure directly reflects their function
5
Q
What are the characteristic features of interneurons?
A
Connect two neurons, found in vertebrate and invertebrate nervous systems, increase synapses and complexity.
6
Q
Give examples of invertebrate nervous systems.
A
- Hydra: bidirectional nerve transmission, simple nerve net
- Coral/anemones: more nerves around tentacles and oral disc
- Jellyfish: coordinated contractions for propulsion, rhythmic activity
- Starfish: modified nerve net, radial nerves for limb movement.
7
Q
What is cephalisation?
A
The centralisation of ganglia in an anterior ‘head’.
8
Q
Describe the invertebrate nervous systems of molluscs using octopi as an example.
A
Organised into ganglia (some in the brain, some in the body), allowing for complex behaviours such as playing, thinking, foresight, planning, use of tools, memory, affection.
9
Q
How does the vertebrate CNS develop from the neural tube?
A
- 3 primary vesicles –> 5 secondary vesicles
- Prosencephalon –> telencephalon + diencephalon
- Mesencephalon –> mesencephalon (midbrain)
- Rhombencephalon –> metencephalon + myelencephalon
- The resulting 5 secondary vesicles then develop into different parts of the brain due to the specialisation of the neuroblasts within
10
Q
What are some similarities and differences between higher and lower vertebrate brains?
A
- Lower vertebrate brains tend to lack gyri and sulci, e.g. rabbit
- Lower vertebrates tend to have larger olfactory regions
- Higher vertebrates (mainly primates) have a cerebral cortex and a smaller olfactory region
11
Q
What is white matter?
A
Myelinated axons in the CNS
12
Q
What is grey matter?
A
Collections of cell bodies, dendrites and synapses in the CNS
13
Q
What is a cortical layer (laminae)? How many are there?
A
- Cellular layers in the grey matter of the cerebral cortex
- There are 6 layers
- Characterised by the types of neurons they contain and by their different connections (afferent, efferent, and intracortical)
14
Q
Describe how CNS has evolved for swimming in fish
A
- Central Pattern Generators (CPGs) on both sides of the spinal cord generate rhythmic cordinated movement
- CPGs are controlled by locomotor control centres in the brainstem - these are in turn controlled by the basal ganglia in the cerebral hemisphere
- M-neurons facilitate the styartle response, allowing for unilateral muscle contraction
15
Q
How has the CNS evolved for walking on land?
A
- Spinal circuits work without the control of the brain
inhibition / stimulation of the flexors and extensors (antagonistic muscle groups) - Coordination of movement in more than one joint
- Sensory feedback controls the rate of stepping
- Supraspinal control (ascending and descending pathways to the brain)
16
Q
How has the CNS evolved for birdsong?
A
Learnt behaviour
Bird brain has complex interconnection of nuclei and tracts that control the syrinx, enabling the production of song
17
Q
What are the subdivisions of the PNS? What do they do?
A
- Somatic nervous system: controls skeletal muscle and voluntary movements
- Autonomic nervous system (ANS): controls the cardiac and smooth muscle, and the involuntary actions of the body
18
Q
What are the subdivisions of the ANS?
A
- Sympathetic nervous system: controls the fight or flight response
- Parasympathetic nervous system: controls the ‘rest and digest’ action of the nervous system, maintains homeostasis
19
Q
Describe the structural organisation of the spinal cord (dorsally to ventrally)
A
- Segmented into repeating units
- Dorsal root ganglia > white matter > grey matter > ventral root ganglia (dorsal to ventral)
- Dorsal horn is sensory, and the ventral horn is motor
20
Q
What are the ascending pathways we need to know?
A
Dorsal column and the spinothalamic pathway
21
Q
Describe the dorsal pathway
A
Primary sensory neurones with cell bodies in the dorsal root ganglia (ipsilateral) receive info - begins ipsilateral
2nd: neurones decussate at the medulla oblongata (now contralateral), pass through to the thalamus
3rd: passes through to the somatosensory cortex
I.E: dorsal root ganglia, dessucate at medulla, thalamus, somatosensory cortex
Ipsilateral then contralateral
22
Q
Describe the spinothalamic pathway - from the spine up to the thalamus
A
1st order neuron: cell body in the dorsal root ganglia
Neuron immediately decussates (contralateral) at point of entry L5
Synapses with another neurone to create contralateral pathway
Goes to thalamus
I.E: dorsal root, immediate dessucation, synapse, thalamus
Always contralateral
23
Q
What is a lower motor neurone?
A
Neurons that directly innervate muscles, cell bodies in the CNS
Descending pathways provide output info to the LMNs
Not involved in the ascending tracts as they do not provide sensory output, they only receive motor input
24
Q
What is the descending pathway we need to know? Describe it
A
The pyramidal / corticospinal tract (2 names)
Tract passes through the pyramidal structures of the medulla and decussates there
- Controls the LMNs and skeletal muscles
- Controls non-stereotyped (purposeful) movements
I.E: immediate dessucation at medulla
25
What are the consequences of interruptions to the 3 required ascending and descending pathways?
- Dorsal tract: affects fine touch and proprioception
- Spinothalamic: affects pain and temperature perception
- Pyramidal/corticospinal (efferent): affects movement, can cause paralysis
26
How can the location of the interruption to the pathway affect how the damage presents?
- Whether the interruption has occurred before or after the pathway decussates will affect the side of the body that the injury has occurred on
- If it hasn't decussated, the damage will affect the same side (ipsilateral), and if it has decussated, the the damage will affect the contralateral side
27
What key principles apply to all mammalian brains?
- Brains have topographic maps representing anatomical organisation
- Specific parts of the brain have specialised functions
- A greater number of neurons = more integration
- Neural circuits are plastic
- Neurogenesis is confined to specific areas
28
What does the cerebellum control?
Extrapyramidal system for stereotyped (repetitive) movements
- Coordinates motor output
- Involved in initiating, timing, and terminating movements
29
What does the basal ganglia control?
A collection of nuclei that produce regulated movements
- Extrapyramidal motor control, receiving inputs and outputs from the cerebral cortex, thalamus, and brainstem
Regulate voluntary movement, smooth it out, etc. So has implications in PD, HD
30
What does the thalamus do?
- Relays sensory pathways to the cerebral cortex
- Activating the cerebral cortex - sleep and consciousness
- Emotional effects generating autonomic activity
- Coordination of visual and motor activity
31
What does the hypothalamus do?
- Responds to physiological, environmental, and emotional changes that affect the autonomic nervous system
- Part of the limbic system
- Involved in thirst, hunger, and appetite
- Reproduction and associated behaviour
- Maintenance of homeostasis
- Neuroendocrine control via the pituitary gland
32
What does the brainstem do?
Connects the brain top the spinal cord, composed of the midbrain, the pons, and the medulla oblongata from top to bottom
Composition of some cranial nerves
Conveying and relaying info to and from the cortex
Cerebellar connections to the main brain
Regulation of the autonomic nervous system
Visual and auditory reflexes
Alertness and consciousness
Breathing
LIFE AND DEATH
33
What are the main areas of the brain involved in movement?
Basal ganglia - enhances desired movement, inhibits unwanted
Cerebral cortex - planning of movement
Thalamus - relays sensory info to cortex
Cerebellum - coordinates motor output and required force
Brainstem - relay sensory info to cortex, carry motor output to LMNs
34
What are the main ascending pathways? What information do they carry?
Dorsal: vibration, proprioception, fine touch
Spinothalamic: pain, temp, pressure
35
What are the main descending pathways? What information do they carry?
Pyramidal / corticospinal: non-stereotyped movement of muscles
Extrapyramidal pathway: stereotyped movement of muscles
36
How does a reflex arc work?
- Sense organ / receptors send APs in afferent neuron in dorsal root ganglia
- Interneuron releases inhibitory mediator
- AP passes onto the efferent motor neuron (EPSPs and IPSP)
- This travels out of the ventral root ganglia
- Neurotransmitter is released at the neuromuscular junction, causing muscular contraction
- Responses are not dependent on conscious perception
37
What is the knee jerk somatic reflex used to test?
Whether the LMNs of the legs are functional
38
What is the sequence of events of the knee-jerk reaction?
Stimulate patellar tendon
Activates stretch receptors or muscle spindles within the extensor muscle
Activates the sensory nerve
Extensor Muscle contracts
Flexor muscle relaxes
39
What is reciprocal inhibition of a reflex action?
Muscle opposed to the one being activated is inhibited, or relaxed (occurs in the spinal cord)
40
What is the crossed extensor reflex?
e.g. when stepping on something painful:
- Foot is removed from painful stimulus (flexor contracts and extensor relaxes)
- Other side of the body stabilises (flexor relaxes and extensor contracts)
41
What is the general function of the ANS?
- Functions without you being aware of it
- Responds principally to physiological demands, but also to environmental and emotional demands
- It innervates and controls the organs (viscera) of the body
42
How is an ANS reflex arc different to a somatic reflex arc?
ANS reflex arcs have TWO efferent motor neurons: the autonomic preganglionic neuron, and the autonomic postganglionic neuron
43
Compare the effects of the sympathetic and parasympathetic nervous systems
- They often have antagonistic effects on eachother
- Many organs are innervated by both the sympathetic and parasympathetic nervous systems
44
Compare sympathetic and parasympathetic nervous system efferent neurone structure
- Sympathetic: postganglionic neuron is longer, and the neurotransmitter released is either NA *OR* ACh
- Parasympathetic: preganglionic neuron is longer, and the neurotransmitter is ACh *ONLY*
45
What do ALL preganglionic neurones release?
- All preganglionic neurons release ACh at the ganglionic synapse regardless of whether theyre in the sympathetic or parasympathetic nervous systems
46
What does the ACh produced by preganglionic neurons act on?
Nicotinic ACh receptors
47
What is the other thing that SOME postganglionic neurons release?
some release a peptide
48
What controls ALL preganglionic neurons?
ALL preganglionic neurons are under the direct control of the descending pathways
49
Compare and contrast the distribution of sympathetic and parasympathetic outflows from the CNS
- Sympathetic oputflows from the CNS are relatively unrestricted
- Parasympathetic outflows from the CNS are relatively restricted
50
What is the pupillary response? How does it work?
- The contriction of pupils when light is shone directly into one eye
- Short postganglionic fibres travel to the muscles of the iris, causing them to contract, narrowing the pupils
51
What is the autonomic response to increased temp?
- Central thermoreceptors in the hypothalamus detect the increased temp
- Reflex causes increased sympathetic discharge to sweat glands causing sweating
- Reflex decreases sympathetic discharge to the cutaneous blood vessels causing vasodilation
52
What is the enteric nervous system?
The enteric nervous system is the innervation of the GI tract, and its intrinsic control by the parasympathetic nervous system
53
What is exteroception?
Detection of external stimuli via exteroceptors
If there is a higher receptor density, each receptor has a smaller receptive field the have to gather info from, leading to greater acuity
54
What is proprioception?
- The body’s sense of its own position and movement within space
- Receptors monitor muscle spindles, golgi tendon organs, and joint receptors
55
How does proprioception work in muscle spindles?
Detects muscle stretch and length changes
56
What do proprioception receptors monitor in tendons?
Golgi tendon organs detect tension
57
What do proprioception receptors monitor in joints?
Detect joint angle and position
58
What are the 6 different nerve endings involved in exteroception, and what do they detect?
No hats may make pie rings
- Naked nerve endings = pain and temperature
- Hair follicle endings = hair position/movement
- Merkel's endings = sense sustained pressure
- Meissner's corpuscle = sense transient touch/pressure
- Pacinian corpuscle = vibration
- Ruffini's endings = shear stress
59
How does exteroception occur in invertebrates?
- Mechanosensory hairs detect touch, axon terminals travel to the brain
- Somatotopy - the brain has different regions for processing touch from different regions of the body
60
What 3 organs do insect have for proprioception? What do they do?
Hair plates: as the hair plate is hit, it indicates that the limb can travel no further (same as vertebrate joint receptors)
- Campaniform sensilla: depressions in cuticle that monitor exoskeleton distortion
- Chordotonal organs: detect the position and speed of movements
61
What is electroreception? Give examples of what invertebrates use it for
- Sharks and rays can detect the electric fields of muscle activity in prey
- Some fish stun their prey with high voltages
- Some fish constantly emit electricity for navigation in murky water and communication
62
What is magnetic sensation? How does it work?
- Birds use magnetic fields for navigation
- Seems to be linked to vision - theory is that magnetic field alters the spin of high energy electrons in the eyes that allow vision
63
What is the primary function of photoreceptors in invertebrates?
Light depolarises the photoreceptors
## Footnote
Invertebrate photoreceptors include rhabdomeres formed by microvilli and retinula cells.
64
What is the primary function of photoreceptors in vertebrates?
Light hyperpolarises the photoreceptors
## Footnote
Vertebrate photoreceptors include rods and cones with stacked discs of opsin molecules.
65
How does phototransduction differ between vertebrates and invertebrates?
Vertebrates:
* In light, cGMP → GMP; channels close, hyperpolarising cell
* In dark: Na+ and Ca2+ channels are kept open by cGMP, photoreceptor is deposlarised, and glutamine is released
Invertebrates:
* In light, phospholipase C activates, causing depolarisation, histamine is released
## Footnote
Vertebrates release glutamine; invertebrates release histamine.
66
What are the key characteristics of rods in the vertebrate retina?
More discs, more opsin-containing membrane, active at low light levels, more sensitive
## Footnote
Rods do not provide color perception.
67
What are the key characteristics of cones in the vertebrate retina?
Less sensitive, work in higher light levels, allow for trichromatic vision (in humans)
## Footnote
Cones are responsible for color vision.
68
Where does visual processing occur in lower vertebrates such as frogs or fish?
Midbrain (optic tectum)
## Footnote
In mammals, the midbrain is involved in visual reflexes.
69
What is significant about the adaptations of avian vision?
Some birds have 2 foveae: lateral for forward vision, medial for side vision
## Footnote
The medial fovea provides better visual acuity.
70
What is the structure and function of the insect ommatidium? Why are they advantageous?
* Compound eyes made of photoreceptor units with their own lens, providing a wider field of vision
* Aids in navigation as they can detect polarised light
* Some insects' rhabdomeres are sensitive to UV light, and can guide them to pollen sources
## Footnote
Microvilli detect light polarized parallel, aiding navigation.
71
What are ocelli and what role do ocelli play in invertebrates?
- Ocelli are smaller than compound eyes, with may receptors under a single lens
- Ocelli provide a wide field of view and are used as horizon detectors
## Footnote
In insects, they are often arranged in a triangle pattern.
72
How has cephalopod vision adapted?
Eyes similar to vertebrates; change skin pattern and texture for camouflage and signaling
## Footnote
Example: Male cuttlefish adopts female markings on half of body to avoid threats.
73
How does infrared vision work in snakes?
Pit organ detects heat, not light; visual processing occurs in midbrain (optic tectum), image from eyes is overlayed with the heatmap
## Footnote
The receptor in the pit organ is similar to the one for sensing heat.
74
What are the basic elements of the vertebrate ear?
External ear: pinna
Middle ear: tympanic membrane (ear drum), ossicles, oval window
Inner ear: organ of Corti, nerves to the brain
75
How is sound detected in the vertebrate ear?
Sound sets up vibrations in the eardrum and is amplified by the movement of the ear ossicles in the middle ear
76
What are hair cells in the ear?
Sound sensitive cells with tufts called stereocilia that send signals to the auditory nerves
77
Where are hair cells embedded?
In supporting cells, sandwiched between the tectorial membrane and the basilar membrane
78
What triggers an electrical signal in hair cells?
The movement of stereocilia against the tectorial membrane
79
What is tonotopy?
The brain can tell what frequency the noise is by which part of the brain the signal travels to
80
How does invertebrate hearing work?
The tympanum vibrates, passing the vibration to the acoustic membrane, converting it into an electrical signal into the auditory nerve
81
What is the role of the prothoracic ganglion in invertebrate hearing?
Processes the electrical signal with tonotopy for different frequency sounds
82
What is the primary use of auditory information in insects?
To attract mates at a certain frequency
83
How do bats use sound?
For echolocating calls for navigation and catching prey
84
What role do moths' auditory systems serve?
To detect predators and take evasive action
85
How do male mosquitos use hearing?
To detect the humming of female wingbeats
86
What structure in male mosquitos detects vibrations?
Johnston’s organ at the base of the antenna
87
What is a key difference in complexity between insect and vertebrate ears?
Insects have simpler nervous systems; vertebrates have more complex central processing in the brain
88
Where is sound detected in insects compared to vertebrates?
Insect: leg/antenna; Vertebrate: tympanic membrane
89
How is sound **amplified** in insects versus vertebrates?
Insect: minimal amplification by sensory dendrites; Vertebrate: external ear, ossicles, cochlear amplifier
90
Where does tonotopy occur in insects and vertebrates?
Insect: normally in the ganglion; Vertebrate: in the CNS
91
What are the five types of human taste?
* Sweet
* Salt
* Bitter
* Sour
* Umami
92
What channels do taste cells for salt and acid have?
Channels for Na+ and H+ ions
93
What do taste cells for bitter, sweet, and umami have?
G-protein coupled receptors that bind to food molecules
94
Why do we need olfaction?
* To smell if food is rancid/rotten
* Social signaling (pheromones)
* Environmental information (presence of predators, sources of food)
95
What happens when odour molecules bind in mammalian olfaction?
A G protein subunit stimulates adenylyl cyclase, increasing cAMP levels, opening ion channels, causing depolarization, and generating an AP
96
Where do invertebrates have taste receptors?
All over the body, e.g. flies have them on their feet
97
What is the pathway for olfaction in mammals?
Olfactory epithelium > olfactory bulb (glomeruli) > olfactory cortex
98
What is the pathway for olfaction in insects?
Antenna maxillary palp > antennal lobe (glomeruli) > mushroom body
99
What are the 3 brain divisions of a 3-4 week old embryo?
Prosencephalon
Mesencephalon
Rhombencephalon
100
What are the 5 brain divisions of a 5 week old embryo?
Telencephalon
Diencephalon
Mesencephalon
Mesencephalon
Myelencephalon
Ten dicks might melt me
101
What does the telencephalon become?
Cerebrum
102
What does the diencephalon become?
Thalamus
Hypothalamus
Epithalamus
103
What does the mesencephalon become?
Midbrain
104
What does the metencephalon become?
Pons
Cerebellum
105
What does the myelencephalon become?
Medulla oblongata
106
What are some key features of lower vertebrate brains?
Large areas devoted to olfaction.
Importance of the optic lobes in fish and amphibians.
Increasing size of cerebrum. Cerebral cortex = 3 layers
107
What are some key features of higher vertebrate brains?
Folding of the cortex (gyri & sulci - cerebral cortex only found in higher vertebrates)
Development of six layered neocortex
Enlargement of the cerebellum
Reduction of the olfactory system (especially in primates)
108
What are layers in the brain called?
Laminae
109
What are CPGs?
Central pattern generators - networks of
neurons which produce rhythmic behaviours
110
Describe the use of CPGs in lampreys
CPGs on each side of each spinal cord segment in lamprey.
Each half of the spinal cord can generate the basic rhythmic drive for locomotion.
Connections between left and right sides ensure co-ordination
111
What are CPGs controlled by in lampreys?
Locomotor command centres in the brainstem
112
What are locomotor command centres controlled by?
The basal ganglia in the cerebral hemisphere
113
What is the fast escape/startle response mediated by in fish?
Mauthner neurones (M-neurones)
114
Where are the M-neurones located? Describe their response
Either side of the brainstem
Detect vibration by sensory input.
Axon of the m-neurone crosses the midline and extends throughout spinal cord.
Collaterals contact interneurones and motor neurones at all spinal levels.
Unilateral muscle contraction
115
In the evolution of walking on land, what part of the cerebellum evolved for balance?
Vestibulocerebellum
116
In the evolution of walking on land, what part of the cerebellum evolved for raising the body off the ground?
Spinocerebellum
117
In the evolution of walking on land, what part of the cerebellum evolved and connected to the cerebral cortex for motor coordination?
Neocerebellum
118
What are the 4 phases of the walking cycle?
Flexion (F)
First Extension (E1)
Second extension (E2)
Third extension (E3)
119
What is the basic pattern of walking on land?
Flexors and extensors inhibit each other reciprocally, giving rise to alternating stepping movements.
120
Where in the bird is birdsong controlled?
There is a complex interconnection of nuclei and tracts in the bird brain which control the syrinx enabling the production of song
121
Name the 3 types of interneurones
Relay neurones, association neurones, and connector neurones
122
Describe the nervous system of hydra
A simple nerve net with no central nervous system
AP conduction is bidirectional
Permits movement of body through water
123
Describe the nervous system of sea anemone and coral
Slow but co-ordinated movements of polyps.
Tentacles /oral disc 4000x more sensitive than the ‘column’.
No CNS or ganglia
Used for feeding and defense
124
Describe the jellyfish nervous system
More complex nerve nets
Spontaneous rhythmic activity (slow state and startle)
Contractions of the margin of the ‘bell’ produce a propulsive force forwards
125
Describe the nervous system of a starfish
A modified nerve net with control of limb movements coordinated by the neural ring.
The radial nerves can control the movements of each limb individually.
Basically a neural ring and radial nerves
126
What are the 7 evolutionary trends that result as a consequence of cephalisation?
1. Increase in number of nerve cells.
2. Concentration of nerve cells into ganglia; ganglia into brains, nerves into nerve cords.
3. Development of functional speciality:
AFFERENT neurons – towards the CNS.
EFFERENT neurons – away from CNS.
4. Localisation of specific functions in different parts of the nervous system.
5. Development of interneurones and more complex synaptic contacts.
6. Development of head bearing sense organs.
7. Development of a ventral nerve cord
127
What are the 2 consequences of sementation?
1. Development of segmental ganglia with sufficiently complex neural circuitry to control locomotion in individual segments
2. Coordination of movement (and/or limb movement) between adjacent segments
128
Describe the arthropod nervous system
Arthropods have connectives = ganglia joined by connecting nerves
Arthropods also have an autonomic nervous system (ANS) which innervates the viscera of the body
129
Give the 6 different parts of the molluscan nervous system
Organised into ganglia
* Buccal – feeding
* Cerebral - coordination
* Pleural – respiration
* Pedal – movement
* Parietal – ‘peripheral’
* Visceral - organs
130
Define ipsilateral
The same side
131
Define contralateral
The other side
132
Which part of the nervous system is divided into sympathetic and parasympathetic?
Peripheral autonomic
133
The spinal cord has dorsal and ventral root ganglia protruding from it. Which horn is sensory and which is motor?
Dorsal horn is sensory
Ventral horn is motor
134
What is the gap in the middle of the spinal cord called?
Ventral median fissure
135
Which end of the spinal cord has the ventral median fissure?
Ventral - motor
136
What kind of matter are the horns of the spinal cord?
Grey matter
137
What are the 4 kinds of spinal nerve fibres?
General sensory afferent
General visceral afferent
General visceral efferent
General somatic efferent
138
Define somatotopy
The orderly arrangement of the nervous system in relation to the parts of the body
139
What is the association cortex involved in?
Communication, memory, planning future behaviour, and thought. i.e. complex
processes
140
Give 2 examples of inter-hemispheric commissures
Corpus callosum
Anterior commissure - bundles of nerve fibers that connect the two hemispheres of the brain, facilitating communication and coordination between them
141
What are 3 areas of grey matter deep within the brain hemisphere?
Basal ganglia (nuclei)
Thalamus
Hypothalamus
142
What neurotransmitter excites muscles?
Acetylcholine
143
What is the knee-jerk reflex also called?
Stretch reflex / mono-synaptic reflex
144
What is the parasympathetic outflow in the ANS?
Craniosacral
4 cranial nerves - head secretory glands and eyes
Sacral spinal cord 2, 3, 4 - emptying
145
What is the sympathetic outflow in the ANS?
From the lateral horn of the spinal cord at T1 to L2/3.
Neurones exit the spinal cord and enter a chain of sympathetic ganglia (called the paravertebral ganglia or sympathetic trunk)
146
What set of ganglia is the sympathetic chain?
paravertebral ganglia
147
What are photoreceptors?
Cells that contain opsins (light-sensitive molecules) in their external membranes, allowing them to absorb photons.
148
Why are photoreceptors expanded into discs or finger-like rods?
To increase the efficiency of light trapping by increasing membrane surface area.
149
What are the two evolutionary origins of photoreceptive membranes?
1) Modified cilium (ciliary system – vertebrates); 2) Cell body-derived membranes (rhabdomere – invertebrates).
150
What are the two main types of photoreceptors in the vertebrate eye?
Rods (low light, more opsin) and cones (bright light, color vision).
151
How does vertebrate phototransduction work in the dark?
High cGMP keeps Na+ and Ca2+ channels open, depolarising the cell and increasing neurotransmitter release.
152
How does light affect vertebrate phototransduction?
Light activates transducin, which activates PDE to break down cGMP, causing ion channels to close and the cell to hyperpolarise.
153
What role does cGMP play in vertebrate photoreceptors?
It keeps ion channels open in the dark; breakdown leads to hyperpolarisation in light.
154
How many classes of photoreceptors are there in humans?
Four: rods for low light, and three cones (sensitive to red, green, and blue) for color vision.
155
What is the main site of visual processing in reptiles, amphibians, and fish?
The optic tectum in the midbrain.
156
How does avian visual behaviour demonstrate specialization?
Birds like hawks keep their heads steady in flight while their visual axis remains at an angle to minimize drag.
157
What triggers phototransduction in invertebrates?
Light activates phospholipase C to break down PIP2 into IP3 and DAG, which opens ion channels and depolarizes the cell.
158
What are compound eyes?
Eyes made up of multiple photoreceptor units (ommatidia), each with its own lens, allowing nearly 360° vision.
159
What visual features are insects sensitive to?
Color, polarized light, motion, looming objects, and field slippage.
160
Why are central rhabdomeres important in insect eyes?
Their microvilli detect polarized light in specific directions, aiding navigation.
161
What is UV sensitivity used for in bees?
To detect flower patterns that guide them to nectar, supporting pollination.
162
How does the fly's visual system prioritize?
It focuses on key tasks like detecting movement, danger, and visual flow with only ~250,000 neurons.
163
What is the visual capability of the mantis shrimp?
It can detect at least 12 different spectral bands, including polarized light.
164
What are simple eyes (ocelli)?
Small eyes with many receptors under a single lens, used by spiders and insects for wide fields of view.
165
What are the visual adaptations of cephalopods?
They have complex eyes and brains, with the ability to change color/texture and perform visual signaling.
166
What is the infrared 'vision' system in pit vipers?
A somatosensory system using pit organs with TRPA1 receptors to detect heat and map infrared input onto the optic tectum.
167
What are simple eyes called?
Ocelli
168
What are the three parts of the vertebrate ear?
External ear, middle ear, and inner ear.
169
What structure detects sound in vertebrates?
The cochlea, specifically the Organ of Corti.
170
How is frequency information encoded in the cochlea?
Tonotopy: different frequencies stimulate different locations along the cochlea.
171
Where is the 'ear' located in insects?
In the legs, with tympanum-like structures and the crista acoustica.
172
What is Johnston’s organ in mosquitoes used for?
Detecting wingbeat frequencies of mates via antennal vibrations.
173
What are the five modalities of human taste?
Sweet, salty, bitter, sour, and umami.
174
How do salt and sour taste receptors work?
Via Na+ and H+ channels causing depolarization and neurotransmitter release.
175
What is the mechanism of olfactory transduction in vertebrates?
Odorants increase cAMP by binding to GPCRs, opening ion channels and generating an action potential.
176
How many odor receptor genes do mammals typically have?
Up to 1000, enabling discrimination of around 10,000 odours.
177
Where do olfactory axons converge in the brain?
Olfactory glomeruli.
178
What structure in insect olfaction is similar to the mammalian olfactory bulb?
The antennal lobes.
179
What is an example of convergent evolution in sensory systems?
Similar olfactory processing in mammals and insects.
180
What is the difference between exteroception and proprioception?
Exteroception senses the external environment; proprioception senses body position and movement.
181
What are receptive fields?
Regions of skin where sensory neurons respond to stimuli; smaller fields mean greater acuity.
182
What are the main proprioceptors in vertebrate muscles?
Muscle spindles and Golgi tendon organs.
183
How do muscle spindles work?
They detect stretch; alpha motor neurons contract muscle; gamma motor neurons restore spindle sensitivity.
184
What do Golgi tendon organs monitor?
Stretch and tension in tendons.
185
What structures mediate exteroception in invertebrates?
Mechanosensory hairs such as trichoid sensilla.
186
What is the chordotonal organ?
A stretch receptor in insects with its own tendon, detecting joint position and movement.
187
What are campaniform sensillae?
Sensory structures at the base of halteres that detect strain during flight.
188
What is the muscle receptor organ (MRO) in crustaceans?
Accessory muscles used to sense stretch, similar to muscle spindles.
189
What are ampullae of Lorenzini?
Electroreceptors in aquatic animals detecting electric fields via conductive gel.
190
What are the two types of electric fish?
High-voltage predators (e.g. electric eels) and weakly electric communicators (e.g. mormyrids).
191
What is the most supported theory of magnetic sense in birds?
A light-dependent mechanism altering electron spin states in photopigments.
192
What kind of photoreceptors do invertebrates have?
Rhabdomere-derived
193
Where in the eye is the sharpest part of the image created?
Fovea
194
How do bitter, sweet, and umami tastes work to initiate a response?
They bind to GCPRs - very similar to olfaction
195
What are palps/proboscis?
Mouthparts
196
What are sensory integration centres called in bees?
Mushroom bodies
197
What detects pain and temperature?
Naked endings
198
What detects sustained pressure?
Merkel's endings
199
What detects fine rapid touch?
Meissner's endings
200
What detects vibration?
Pascinian corpuscle
201
What detects shear stress?
Ruffini endings
202
What are the insect version of joint receptors?
Hair plates
203
What aspect of insect proprioception has its own tendon?
Chordotonal organ
204
What is analogous to the muscle spindle in crustacea?
Muscle receptor organ
