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neuroscience > Sensory & Effector Systems > Flashcards

Sensory & Effector Systems Flashcards

1
Q

Where do retinal ganglion cells output to

A

Project to the thalamus (lateral geniculate nucleus), then LGN neurons project to layer IV of the visual cortex in the occipital lobe

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2
Q

Occular dominance columns

A

LGN (lateral geniculate nucleus) neurons from both eyes project to layer IV of the visual cortex, forming a zebra stripe pattern (visible using 3H-proline labelling) postnatally.

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3
Q

types of mechanoreceptors in glabrous (hairless) skin

A

Close to the skin:
Meissner corpuscles (rapid)
Merkel complexes (slow)

Deeper:
Ruffini organs (slow)
Pacinian corpuscles (fast)

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4
Q

what are mechanoreceptors innervated by

A

Large myelinated axons with cell bodies in dorsal root ganglia

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5
Q

Slowly adapting mechanoreceptors

A

Merkel complexes (surface -> respond to indentation)
Ruffini endings (respond to skin movement)

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6
Q

Rapidly adapting mechanoreceptors

A

Meissner receptors (near surface)
Pacinian (respond to vibration)

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7
Q

mechanosensory pathway

A

Mechanosensory receptors -> dorsal root of lumbar (lower body) or cervical (upper body) spinal cord

Crosses side in dorsal column nuclei

Inputs to cerebrum and primary somatic sensory cortex

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8
Q

what inputs to the secondary somatosensory cortex

A

throat, tongue, teeth, jaw, gums

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9
Q

which cranial nerve is olfactory

A

1

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10
Q

how does signal transduction occur in olfactory receptors

A

Odorants active GPCRs which produces cyclic AMP, which opens cyclic nucleotide gated ion channel to allow Na and Ca influx for depolarisation

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11
Q

how do GPCRs bind to odorants

A

Odor binding proteins on membrane allow odorant to dissolve in mucus layer (we smell lipophilic molecules)
Once in mucus layer they can make contact with receptor

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12
Q

How does odor habituation occur

A

UGT (uridyl glucyronic transferase) and Cytochrome p450 enzymes

Make lipophilic molecules hydrophilic so that is is metabolised by cell
Then influx of Ca when cell is depolarised activates an enzyme cascade resulting in inhibition of cAMP production and therefore no further depolarisation can occur

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13
Q

Cells in the olfactory bulb

A
  1. mitral cells
  2. tufted cells
  3. granule cells
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14
Q

where are olfactory receptors located

A

on cilia in olfactory epithelium

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15
Q

layers of the olfactory bulb

A
  1. glomerular layer (where olfactory receptor axon terminals are)
  2. External plexiform layer
  3. mitral cell layer
  4. internal plexiform layer
  5. granule cell layer
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16
Q

olfactory bulb neural circuit

A

Receptor cells synapse with mitral cells

There are two lateral connections between mitral cells:
perimglomerular cells at synapse with receptor cells
granule cells between mitral cells

Allows for sharpening of response to stimulus

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17
Q

olfactory central pathway (CNS)

A

Olfactory receptors -> olfactory bulb via olfactory nerve (cranial nerve 1)

Initial targets in the CNS include:
Amygdala
Olfactory tubercle
Pyriform and entorhinal cortex

Then to:
Thalamus, hypothalamus, hippocampus and orbitofrontal cortex

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18
Q

Location of taste receptor cells

A

Within tastebuds that line crevices of papillae
One tastebud has 10-150 TRCs

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19
Q

Shapes of papillae

A

Circumvalate: back of tongue, molecule must be dissolved in water to reach these tastebuds

Foliate: Back sides of tongue

Fungiform: Front of tongue

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20
Q

How is taste encoded

A

Two theories:
1. Labelled-line model (one receptor/neuron: one flavour)
Each TRC detects one flavour sensation

  1. Across-fibre model (one receptor/neuron: many flavours)
    Either: each TRC detects one flavour but neurons connect to more than one TRC
    Or: each TRC can discriminate multiple flavours and are tuned for different combinations/preferences
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21
Q

Signal transduction in taste receptor cells

A
  1. Salt / sour (acids): activate ligand gated ion channel (Na+ and H+ respectively)
  2. Sweet, bitter, umami: second messenger system
22
Q

central pathways for gustation

A

Involves cranial nerves 7, 9 and 10 which input to solitary nucleus of brainstem
Then to either hypothalamus, amygdala or VPM (ventral posterior medial nucleus) of thalamus

Then VPM to frontal cortex

23
Q

How does flavour sensation combine olfaction and gustation (and where)

A

Both input to the amygdala and the orbitofrontal cortex

24
Q

where are neurons in the GIT tract

A

the myenteric plexus

25
Q

Definition & role of the ENS

A

Neurons intrinsic to the walls of ENS (entirely within); includes sensory, motor and interneurons

Role: short reflexes for localised response to stimuli

26
Q

Role of ANS in digestion

A

PSNS: increase muscle tone and gland secretion

SNS: muscle relaxtion & decreased gastric blood flow

27
Q

phases of digestion

A

Cephalic phase: anticipation of food (sensory nerves), results in secretion of gastric juice

Gastric phase: bolus in stomach, gastric juice secretion (via nerves and hormones)

Intestinal phase: Chyme in intestine, control rate of gastric emptying via stimulation or inhibition of secretion of gastric juice (hormonal control)

28
Q

Optical factors affecting visual acuity (VA)

A

Pupil size
Clarity of optical media (eg cataracts or opacity)
Refractive errors (lead to blur, incl astigmatism)

29
Q

Cone and rod density

A

Cones are concentrated on the macula/fovea

Rods are absent in the fovea and present in the periphery

Neither are present in the optic disc

30
Q

Photoreceptor types

A

All contain photopigments activated by light (opsins = bind to vitamin A)
Rods = rhodopsin
Cones = three different cone-opsins

31
Q

phototransduction

A

Photoreceptors release glutamate in response to light in graded potentials (they are NOT neurons, constantly releasing glutamate just amount changes)

In the presence of LIGHT 11-cis retinal in opsins changes to trans-retinal

This activates transducin, then phosphodiesterase (PDE) which breaks down cGMP, therefore CLOSING cyclic gated sodium channels and leading to HYPERPOLARISATION

In the DARK, cGMP is present so Na+ channel is open & cell is DEPOLARISED

32
Q

Neuronal pathway through retina

A

Photoreceptors -> bipolar cells -> ganglion cells

Lateral interactions (inhibitory):
1. horizontal cells between PRs and bipolar cells
2. Amacrine cells between bipolar and ganglion cells

33
Q

Bipolar cells

A

Second order neurons that receive input from photoreceptors and output to ganglion cells

10 types (one for rods, 9 for cones)

34
Q

Ganglion cells in the eye

A

Output neurons of the retina, respond to light by changing action potential firing rate, response can be transient or sustained

~40 different types for different types of info (ON, oFF, M and P)

Release glutamate and fire action potentials

Tuned to see EDGES: center of receptive field acts differently to peripheral

35
Q

M and P ganglion cells

A

M: magnocellular (large), motion detection, large receptive field

P: parvocellular (small) , visual acuity and colour vision, more numerous

35
Q

M and P ganglion cells

A

M: magnocellular (large), motion detection, large receptive field

P: parvocellular (small) , visual acuity and colour vision, more numerous

36
Q

Visual pathway

A

Retina -> optic nerve (axons of all ganglion cells) -> LGN (lateral geniculate nucleus)

From LGN there are optic radiations to the striate cortex (visual cortex V1)

37
Q

Lateral geniculate nucleus (LGN)

A

Part of the thalamus, receives input from ganglion cells

Six layers:
1 & 2: magnocellular, input from M ganglion cells
3-6: parvocellular, input from P ganglion cells

38
Q

Primary visual cortex (V1)

A

LGNs input into layer 4C
Occular dominance columns: arrangement of two eyes (one layer each in LGN) into one layer

39
Q

Dorsal stream of visual processing

A

“where” pathway
Area MT: Medial temporal lobe, receives info from V2 and V3 and layer 4B of V1

Specialised in processing object motion

40
Q

Ventral stream of visual processing

A

“what” pathway
V1, V2, V4

Area V4: perception of shape and colour

V4 outputs to area IT (inferior temporal), important for visual memory and perception (incl perception of faces)

41
Q

Hair cells

A

Have their cilia embedded in tectorial membrane

Inner: do the hearing
Outer: modulators (efferent nerves, receive signals to control sensitivity)

42
Q

Basilar membrane

A

Performs spectral decomposition as sound waves travel all the way down and back up

At cochlear base (near round window), membrane is THICK with short fibers, so picks up high frequency sounds

At cochlear apex, membrane is THIN with longer fibers so picks up low frequency sounds

Movement of membrane vibrates hair cells by “shearing” them across tectorial membrane

43
Q

Sound transduction by hair cells

A

Mechanically gated potassium channels allows potassium influx into cell and depolarisation

Why potassium?
There is a high conc. of potassium outside the hair cells in the scala media due to capillaries in stria vascularis pumping potassium out into scala media
*loss of potassium gradient can cause deafness

44
Q

Sound pathway in CNS

A

Cochlea -> cochlear nuclei in brainstem -> other brainstem nuclei -> medial geniculate nucleus (MGN) in thalamus -> primary auditory cortex

45
Q

SNS vs PSNS

A

Sympathetic: thoraco-lumbar, ganglia closer to CNS, ACh and NA
Preganglionic neurons can also innervate adrenal medulla to secrete hormones for mass activation

Parasympathetic: Cranio-sacral, ganglia closer to organs, ACh

46
Q

Types of sympathetic ganglia

A

Paravertebral: sympathetic chain

Prevertebral: mesenteric ganglia

Axons project via spinal nerves

47
Q

Parasympathetic structure

A

Preganglionic neurons in two sites:
1. Brainstem nuclei: project via cranial nerves
2. Sacral spinal cord: project via spinal nerves

Sacral postganglionic cells (and some sympathetic neurons) lie in the pelvic plexus

48
Q

what brain center coordinates autonomic output

A

the hypothalamus
receives sensory input and contextual information from amygdala, hippocampus and cerebral cortex

49
Q

what does the NTS do (nucleus of the solitary tract) & where is it

A

In the medulla (brainstem)
Receives cardiovascular, visceral, respiratory, gustatory, and orotactile information.
Major integrative center for autonomic function, out puts to: preganglionic neurons controlling reflexes in organs/tissue
Other brain centers (hypothalamus, medial & ventral forebrain) for more complex functions

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