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
What are the main consequences of cephalisation in invertebrates?
A
- More nerve cells
- Neurons > ganglia > brains
- Nerves > nerve cords
- Allow more complex movements
- Development of interneurons
- Ventral nerve cord with afferent and efferent neurons.
10
Q
What is segmentation?
A
The development of repeating body units along the length of the animal.
11
Q
What are the consequences of segmentation in invertebrates?
A
- Coordinated movement between adjacent segments
- Development of segmental ganglia to coordinate movement.
12
Q
Describe the nervous systems of arthropods.
A
Ganglia joined by connecting nerves, coordinated by brains, and use of central pattern generators for rhythmic motor output.
13
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.
14
Q
A
15
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
16
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
17
Q
What is white matter?
A
Myelinated axons in the CNS
18
Q
What is grey matter?
A
Collections of cell bodies, dendrites and synapses in the CNS
19
Q
What is a cortical layer (laminae)?
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)
20
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
21
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)
22
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
23
Q
What is the CNS?
A
The brain and spinal cord
They receieve and project nerve signals across the body
24
Q
What is the PNS?
A
The nervous system outside of the brain and spinal cord
Contains sensory (afferent), and motor (efferent) nerves
25
What are the subdivisions of the PNS? What do they do?
- 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
26
What are the subdivisions of the ANS?
- Sympathetic nervous system: controls the fight or flight response
- Parasympathetic nervous system: controls the 'rest and digest' action of the nervous system, maintains homeostasis
27
Describe the structural organisation of the spinal cord (dorsally to ventrally)
- Segmented into repeating units
- Dorsal root ganglia > white matter > grey matter > ventral root ganglia (dorsally to ventrally)
- Dorsal horn is sensory, and the ventral horn is motor
28
What are the ascending pathways we need to know?
dorsal pathway and the spinothalamic pathway
29
Describe the dorsal pathway
1st order neuron: cell body in the dorsal root ganglia (ipsilateral)
2nd order neuron: neuron decussated at the medulla oblongata (now contralateral), passes through to the thalamus
3rd order neuron: passes through to the somatosensory cortex
30
Describe the spinothalamic pathway
1st order neuron: cell body in the dorsal root ganglia
2nd order neuron: neuron immediately decussates (contralateral)
3rd order neuron: travels up to the thalamus
31
What is a LMN?
- 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
32
What is the descending pathway we need to know? Describe it
- The pyramidal / corticospinal tract (2 names sorry)
- Tract passes through the pyramidal structures of the medulla and decussates there
- Controls the LMNs
- Controls non-stereotyped (purposeful) movements
33
What are the consequences of interruptions to the ascending and descending pathways?
- Dorsal tract: affects fine touch and proprioception
- Spinothalamic: affects pain and temperature perception
- Pyramidal/corticospinal: affects movement, can cause paralysis
34
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
35
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
- Neurongenesis is confined to specific areas
36
What does the cerebellum control?
- Extrapyramidal system for stereotyped (repetitive) movements
- Coordinates motor output
- Involved in initiating, timing, and terminating movements
37
What does the basal ganglia control?
- A collection of nuclei that produce regulated movements
- Extrapyramidal motor control, recieving inputs and outputs from the cerebral cortex, thalamus, and brainstem
38
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
39
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
40
What does the brainstem do?
- Connects the brain top the spinal cord
- Composed of the midbrain, the pons, and the medulla oblongata
- Involved in:
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
41
What are the main areas of the brain involved in movement?
Basal ganglia - enhances desired movement, inhibits unwated
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
42
What are the main ascending pathways? What information do they carry?
Dorsal: vibration, proprioception, fine touch
Spinothalamic: pain, temp, pressure
43
What are the main descending pathways? What information do they carry?
Pyramidal / corticospinal: non-stereotyped movement of muscles
Extrapyramidal pathway: stereotyped movement of muscles
44
How does a reflex arc work?
- Sense organ / receptors send APs in afferent neuron
- Interneuron releases inhibitory mediator
- AP passes onto the efferent motor neuron (EPSPs and IPSP)
- This travels out of the ventral root
- Neurotransmitter is released at the neuromuscular junction, causing muscular contraction
- Responses are not dependent on conscious perception
45
What is the knee jerk somatic reflex used to test?
Whether the LMNs of the legs are functional
46
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
47
What is reciprocal inhibition of a reflex action?
muscle opposed to the one being activated is inhibited, or relaxed (occurs in the spinal cord)
48
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)
49
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
50
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
51
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
52
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*
53
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
54
What does the ACh produced by preganglionic neurons act on?
Nicotinic ACh receptors
55
What is the other thing that SOME postganglionic neurons release?
some release a peptide
56
What controls ALL preganglionic neurons?
ALL preganglionic neurons are under the direct control of the descending pathways
57
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
58
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
59
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
60
What is the enteric nervous system?
- The enteric nervous systems is the innervation of the GI tract, and its intrinstic control by the parasympathetic nervous system
61
What is exteroception?
- Sensory endings that monitor interactions with the external environment
- If there is a higher receptor density, each receptor has a smaller receptive field the have to gather info from, leading to greater acuity
- Sends info through ascending sensory tracts
62
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
In muscle spindles:
In golgi tendon organs: they monitor stretch in tendons
In joint receptors: endings provide sensations of pain when the joins is moved beyond its normal range of movement
63
How does proprioception work in muscle spindles?
Detects muscle stretch and length changes
64
What do proprioception receptors monitor is golgi tendon organs?
Monitor tension in tendons
65
What do proprioception receptors monitor in joints?
Detect joint angle and position
66
what are the different nerve endings in exteroception detect?
- 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
67
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
68
what organs do insect have for proprioception? What do they do?
- Hair plates: as the hair plate is hit, it indilcates 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
69
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
70
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
71
What is the primary function of photoreceptors in invertebrates?
Light depolarises the photoreceptors
## Footnote
Invertebrate photoreceptors include rhabdomeres formed by microvilli and retinula cells.
72
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.
73
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.
74
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.
75
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.
76
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.
77
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.
78
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.
79
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.
80
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.
81
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.
82
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
83
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
84
What are hair cells in the ear?
Sound sensitive cells with tufts called stereocilia that send signals to the auditory nerves
85
Where are hair cells embedded?
In supporting cells, sandwiched between the tectorial membrane and the basilar membrane
86
What triggers an electrical signal in hair cells?
The movement of stereocilia against the tectorial membrane
87
What is tonotopy?
The brain can tell what frequency the noise is by which part of the brain the signal travels to
88
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
89
What is the role of the prothoracic ganglion in invertebrate hearing?
Processes the electrical signal with tonotopy for different frequency sounds
90
What is the primary use of auditory information in insects?
To attract mates at a certain frequency
91
How do bats use sound?
For echolocating calls for navigation and catching prey
92
What role do moths' auditory systems serve?
To detect predators and take evasive action
93
How do male mosquitos use hearing?
To detect the humming of female wingbeats
94
What structure in male mosquitos detects vibrations?
Johnston’s organ at the base of the antenna
95
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
96
Where is sound detected in insects compared to vertebrates?
Insect: leg/antenna; Vertebrate: tympanic membrane
97
How is sound **amplified** in insects versus vertebrates?
Insect: minimal amplification by sensory dendrites; Vertebrate: external ear, ossicles, cochlear amplifier
98
Where does tonotopy occur in insects and vertebrates?
Insect: normally in the ganglion; Vertebrate: in the CNS
99
What are the five types of human taste?
* Sweet
* Salt
* Bitter
* Sour
* Umami
100
What channels do taste cells for salt and acid have?
Channels for Na+ and H+ ions
101
What do taste cells for bitter, sweet, and umami have?
G-protein coupled receptors that bind to food molecules
102
Why do we need olfaction?
* To smell if food is rancid/rotten
* Social signaling (pheromones)
* Environmental information (presence of predators, sources of food)
103
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
104
Where do invertebrates have taste receptors?
All over the body, e.g. flies have them on their feet
105
What is the pathway for olfaction in mammals?
Olfactory epithelium > olfactory bulb (glomeruli) > olfactory cortex
106
What is the pathway for olfaction in insects?
Antenna maxillary palp > antennal lobe (glomeruli) > mushroom body
