Nervous system Flashcards
1
Q
What is a nervous system?
A
A nervous system responds to environmental stimuli that can either be internal or external.
2
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.
3
Q
What is the basic structure of a neuron?
A
Cell body, myelinated/unmyelinated axon, dendrites, synaptic terminals.
4
Q
What types of synaptic transmission exist?
A
Chemical or electric.
5
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
6
Q
What are the characteristic features of interneurons?
A
Connect two neurons, found in vertebrate and invertebrate nervous systems, increase synapses and complexity.
7
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.
8
Q
What is cephalisation?
A
The centralisation of ganglia in an anterior ‘head’.
9
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.
10
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
11
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
12
Q
What is white matter?
A
Myelinated axons in the CNS
13
Q
What is grey matter?
A
Collections of cell bodies, dendrites and synapses in the CNS
14
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)
15
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
16
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)
17
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
18
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
19
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
20
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
21
Q
What are the ascending pathways we need to know?
A
Dorsal column and the spinothalamic pathway
22
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
23
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
24
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
25
What is the descending pathway we need to know? Describe it
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
26
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
27
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
28
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
29
What does the cerebellum control?
Extrapyramidal system for stereotyped (repetitive) movements
- Coordinates motor output
- Involved in initiating, timing, and terminating movements
30
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
31
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
32
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
33
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
34
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
35
What are the main ascending pathways? What information do they carry?
Dorsal: vibration, proprioception, fine touch
Spinothalamic: pain, temp, pressure
36
What are the main descending pathways? What information do they carry?
Pyramidal / corticospinal: non-stereotyped movement of muscles
Extrapyramidal pathway: stereotyped movement of muscles
37
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
38
What is the knee jerk somatic reflex used to test?
Whether the LMNs of the legs are functional
39
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
40
What is reciprocal inhibition of a reflex action?
Muscle opposed to the one being activated is inhibited, or relaxed (occurs in the spinal cord)
41
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)
42
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
43
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
44
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
45
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*
46
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
47
What does the ACh produced by preganglionic neurons act on?
Nicotinic ACh receptors
48
What is the other thing that SOME postganglionic neurons release?
some release a peptide
49
What controls ALL preganglionic neurons?
ALL preganglionic neurons are under the direct control of the descending pathways
50
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
51
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
52
What is the autonomic response to increased temp?
- Central thermoreceptors in the hypothalamus setect the increased temp
- Reflex causes increased sympathetic discharge to sweat glands causing sweating
- Reflex decreases sympathetic discharge to the cutaneous blood vessels causing vasodilation
53
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
54
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
55
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
56
How does proprioception work in muscle spindles?
Detects muscle stretch and length changes
57
What do proprioception receptors monitor is tendons?
Golgi tendon organs detect tension
58
What do proprioception receptors monitor in joints?
Detect joint angle and position
59
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
60
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
61
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
62
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
63
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
64
What is the primary function of photoreceptors in invertebrates?
Light depolarises the photoreceptors
## Footnote
Invertebrate photoreceptors include rhabdomeres formed by microvilli and retinula cells.
65
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.
66
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.
67
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.
68
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.
69
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.
70
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.
71
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.
72
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.
73
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.
74
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.
75
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
76
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
77
What are hair cells in the ear?
Sound sensitive cells with tufts called stereocilia that send signals to the auditory nerves
78
Where are hair cells embedded?
In supporting cells, sandwiched between the tectorial membrane and the basilar membrane
79
What triggers an electrical signal in hair cells?
The movement of stereocilia against the tectorial membrane
80
What is tonotopy?
The brain can tell what frequency the noise is by which part of the brain the signal travels to
81
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
82
What is the role of the prothoracic ganglion in invertebrate hearing?
Processes the electrical signal with tonotopy for different frequency sounds
83
What is the primary use of auditory information in insects?
To attract mates at a certain frequency
84
How do bats use sound?
For echolocating calls for navigation and catching prey
85
What role do moths' auditory systems serve?
To detect predators and take evasive action
86
How do male mosquitos use hearing?
To detect the humming of female wingbeats
87
What structure in male mosquitos detects vibrations?
Johnston’s organ at the base of the antenna
88
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
89
Where is sound detected in insects compared to vertebrates?
Insect: leg/antenna; Vertebrate: tympanic membrane
90
How is sound **amplified** in insects versus vertebrates?
Insect: minimal amplification by sensory dendrites; Vertebrate: external ear, ossicles, cochlear amplifier
91
Where does tonotopy occur in insects and vertebrates?
Insect: normally in the ganglion; Vertebrate: in the CNS
92
What are the five types of human taste?
* Sweet
* Salt
* Bitter
* Sour
* Umami
93
What channels do taste cells for salt and acid have?
Channels for Na+ and H+ ions
94
What do taste cells for bitter, sweet, and umami have?
G-protein coupled receptors that bind to food molecules
95
Why do we need olfaction?
* To smell if food is rancid/rotten
* Social signaling (pheromones)
* Environmental information (presence of predators, sources of food)
96
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
97
Where do invertebrates have taste receptors?
All over the body, e.g. flies have them on their feet
98
What is the pathway for olfaction in mammals?
Olfactory epithelium > olfactory bulb (glomeruli) > olfactory cortex
99
What is the pathway for olfaction in insects?
Antenna maxillary palp > antennal lobe (glomeruli) > mushroom body
100
What are the 3 brain divisions of a 3-4 week old embryo?
Prosencephalon
Mesencephalon
Rhombencephalon
101
What are the 5 brain divisions of a 5 week old embryo?
Telencephalon
Diencephalon
Mesencephalon
Mesencephalon
Myelencephalon
Ten dicks might melt me
102
What does the telencephalon become?
Cerebrum
103
What does the diencephalon become?
Thalamus
Hypothalamus
Epithalamus
104
What does the mesencephalon become?
Midbrain
105
What does the metencephalon become?
Pons
Cerebellum
106
What does the myelencephalon become?
Medulla oblongata
107
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
108
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)
109
What are layers in the brain called?
Laminae
110
What are CPGs?
Central pattern generators - networks of
neurons which produce rhythmic behaviours
111
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
112
What are CPGs controlled by in lampreys?
Locomotor command centres in the brainstem
113
What are locomotor command centres controlled by?
The basal ganglia in the cerebral hemisphere
114
What is the fast escape/startle response mediated by in fish?
Mauthner neurones (M-neurones)
115
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
116
In the evolution of walking on land, what part of the cerebellum evolved for balance?
Vestibulocerebellum
117
In the evolution of walking on land, what part of the cerebellum evolved for raising the body off the ground?
Spinocerebellum
118
In the evolution of walking on land, what part of the cerebellum evolved and connected to the cerebral cortex for motor coordination?
Neocerebellum
119
What are the 4 phases of the walking cycle?
Flexion (F)
First Extension (E1)
Second extension (E2)
Third extension (E3)
120
What is the basic pattern of walking on land?
Flexors and extensors inhibit each other reciprocally, giving rise to alternating stepping movements.
121
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
122
Name the 3 types of interneurones
Relay neurones, association neurones, and connector neurones
123
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
124
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
125
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
126
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
127
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
128
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
129
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
130
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
131
Define ipsilateral
The same side
132
Define contralateral
The other side
133
Which part of the nervous system is divided into sympathetic and parasympathetic?
Peripheral autonomic
134
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
135
What is the gap in the middle of the spinal cord called?
Ventral median fissure
136
Which end of the spinal cord has the ventral median fissure?
Ventral - motor
137
What kind of matter are the horns of the spinal cord?
Grey matter
138
What are the 4 kinds of spinal nerve fibres?
General sensory afferent
General visceral afferent
General visceral efferent
General somatic efferent
139
Define somatotopy
The orderly arrangement of the nervous system in relation to the parts of the body
140
What is the association cortex involved in?
Communication, memory, planning future behaviour, and thought. i.e. complex
processes
141
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
142
What are 3 areas of grey matter deep within the brain hemisphere?
Basal ganglia (nuclei)
Thalamus
Hypothalamus
143
What neurotransmitter excites muscles?
Acetylcholine
144
What is the knee-jerk reflex also called?
Stretch reflex / mono-synaptic reflex
145
What is the parasympathetic outflow in the ANS?
Craniosacral
4 cranial nerves - head secretory glands and eyes
Sacral spinal cord 2, 3, 4 - emptying
146
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)
147
What set of ganglia is the sympathetic chain?
paravertebral ganglia
148
What are photoreceptors?
Cells that contain opsins (light-sensitive molecules) in their external membranes, allowing them to absorb photons.
149
Why are photoreceptors expanded into discs or finger-like rods?
To increase the efficiency of light trapping by increasing membrane surface area.
150
What are the two evolutionary origins of photoreceptive membranes?
1) Modified cilium (ciliary system – vertebrates); 2) Cell body-derived membranes (rhabdomere – invertebrates).
151
What are the two main types of photoreceptors in the vertebrate eye?
Rods (low light, more opsin) and cones (bright light, color vision).
152
How does vertebrate phototransduction work in the dark?
High cGMP keeps Na+ and Ca2+ channels open, depolarising the cell and increasing neurotransmitter release.
153
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.
154
What role does cGMP play in vertebrate photoreceptors?
It keeps ion channels open in the dark; breakdown leads to hyperpolarisation in light.
155
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.
156
What is the main site of visual processing in reptiles, amphibians, and fish?
The optic tectum in the midbrain.
157
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.
158
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.
159
What are compound eyes?
Eyes made up of multiple photoreceptor units (ommatidia), each with its own lens, allowing nearly 360° vision.
160
What visual features are insects sensitive to?
Color, polarized light, motion, looming objects, and field slippage.
161
Why are central rhabdomeres important in insect eyes?
Their microvilli detect polarized light in specific directions, aiding navigation.
162
What is UV sensitivity used for in bees?
To detect flower patterns that guide them to nectar, supporting pollination.
163
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.
164
What is the visual capability of the mantis shrimp?
It can detect at least 12 different spectral bands, including polarized light.
165
What are simple eyes (ocelli)?
Small eyes with many receptors under a single lens, used by spiders and insects for wide fields of view.
166
What are the visual adaptations of cephalopods?
They have complex eyes and brains, with the ability to change color/texture and perform visual signaling.
167
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.
168
What are simple eyes called?
Ocelli
169
What are the three parts of the vertebrate ear?
External ear, middle ear, and inner ear.
170
What structure detects sound in vertebrates?
The cochlea, specifically the Organ of Corti.
171
How is frequency information encoded in the cochlea?
Tonotopy: different frequencies stimulate different locations along the cochlea.
172
Where is the 'ear' located in insects?
In the legs, with tympanum-like structures and the crista acoustica.
173
What is Johnston’s organ in mosquitoes used for?
Detecting wingbeat frequencies of mates via antennal vibrations.
174
What are the five modalities of human taste?
Sweet, salty, bitter, sour, and umami.
175
How do salt and sour taste receptors work?
Via Na+ and H+ channels causing depolarization and neurotransmitter release.
176
What is the mechanism of olfactory transduction in vertebrates?
Odorants increase cAMP, opening ion channels and generating an action potential.
177
How many odor receptor genes do mammals typically have?
Up to 1000, enabling discrimination of around 10,000 odours.
178
Where do olfactory axons converge in the brain?
Olfactory glomeruli.
179
What structure in insect olfaction is similar to the mammalian olfactory bulb?
The antennal lobes.
180
What is an example of convergent evolution in sensory systems?
Similar olfactory processing in mammals and insects.
181
What is the difference between exteroception and proprioception?
Exteroception senses the external environment; proprioception senses body position and movement.
182
What are receptive fields?
Regions of skin where sensory neurons respond to stimuli; smaller fields mean greater acuity.
183
What are the main proprioceptors in vertebrate muscles?
Muscle spindles and Golgi tendon organs.
184
How do muscle spindles work?
They detect stretch; alpha motor neurons contract muscle; gamma motor neurons restore spindle sensitivity.
185
What do Golgi tendon organs monitor?
Stretch and tension in tendons.
186
What structures mediate exteroception in invertebrates?
Mechanosensory hairs such as trichoid sensilla.
187
What is the chordotonal organ?
A stretch receptor in insects with its own tendon, detecting joint position and movement.
188
What are campaniform sensillae?
Sensory structures at the base of halteres that detect strain during flight.
189
What is the muscle receptor organ (MRO) in crustaceans?
Accessory muscles used to sense stretch, similar to muscle spindles.
190
What are ampullae of Lorenzini?
Electroreceptors in aquatic animals detecting electric fields via conductive gel.
191
What are the two types of electric fish?
High-voltage predators (e.g. electric eels) and weakly electric communicators (e.g. mormyrids).
192
What is the most supported theory of magnetic sense in birds?
A light-dependent mechanism altering electron spin states in photopigments.
