(9) somatosensory, vestibular and olfactory systems Flashcards
-Sensory projections ascend from the
spinal cord into the brain through the brainstem.
When sensory projections travel through the thalamus, they act as…
which acts as a relay processing station of signals to other brain regions
What is a pathway?
Pathway is the receptor to the brain
What are the skins three layers?
- Epidermis: thin outer layer
- Dermis (thick inner layer)
- Hypodermis
What is Glabrous Skin?
- Smooth, thick skin on palms and soles of our feet , e.g. finger tips
- Epidermis = 1.5 mm Dermis = 3 mm
What is Hairy Skin?
- Thin skin populated with hair follicles, widespread
- Epidermis = 0.1 mm Dermis = 1-2 mm
What are sweat glands?
- Eccrine – secrete saline (heat regulation)
- Sebaceous – secrete complex cell cytoplasm
- (Primary source of human body odour!)
What are Meissner Corpuscles?
Small receptive fields, fast adapting
What are Merkel Cells?
Small receptive fields, slow adapting
What are Ruffini Endings?
large receptive fields, slow adapting
What are Pacinian Corpuscle?
large receptor fields, fast adapting
What is the ‘Two point discrimination test’ for?
which skin region is more accurate
The receptive field of an individual sensory neuron is the
particular region of the sensory space in which a stimulus will modify the firing of that neuron
Bell-Megendie Law, in the dorsal the sensory afferents or efferents?
-dorsal= sensory afferents
Bell-Megendie Law, in the ventral the sensory afferents or efferents?
-ventral= motor efferents
Whats a Dermatome?
an area of skin in which sensory nerves derive from a single spinal nerve root
Somatosensory signals are sent through the spinal cord via the dorsal column pathway to the
primary somatosensory cortex (S1) in the brain.
What is somatotopy?
Each part of the skin surface is represented by a specific region of primary somatosensory cortex
What is “sensory homunculus”?
(little man) The area devoted to each body part reflects the receptor density in that part
What is Cortical magnification?
The receptive fields and cortical representations give more acuity to fingers, mouth, nose and tongue
Pain and touch are processed by
separate neural systems, Pain is detected by special receptors in the skin
What are Nociceptors (free nerve endings)?
Signal mechanical & chemical pain
What are Thermoceptors?
Signal hot and cold pain, Ending of unmyelinated C-fibers
What are the three types of nociceptors?
- Mechano-sensitive nociceptors (high threshold)
- Thermo-sensitive nociceptors (high threshold)
- Polymodal (chemo-sensitive) nociceptors
What two types of firing occur at?
Two Types: Cold receptors fire when T decreases from 34°C, maximal firing at 25°C
Warmth receptors fire when T increases from 34°C, maximal firing at 45°C
How are hot sensations detected?
noxious stimulus detected by nociceptors, not thermal receptors
What are thermoceptors resting state?
34 degrees
Pain perception has two components
fast and slow
What is fast pain?
- Fast (first) pain is sharp, instantaneous, and tends to fade
- Fast pain is signalled by myelinated (fast) Aδ(”A-delta”) nerve fibers
What is slow pain?
- Slow (second) pain is delayed, dull, diffuse, and long-lasting
- Slow pain is signalled by unmyelinated (slow) C fibers
Pain signals travel through the spino-thalamic tract to the brain – runs parallel to…
somatosensory (dorsal column) pathways
Pain signals travel through the spino-thalamic tract are…
- Afferent to spinal cord laminae I & II
- Cross midline to contralateral anterolateral column
- Ascend via direct (spinothalamic) and indirect pathways to thalamus
- To somatosensory cortex
What are the two central pain systems?
EMOTIONAL AVERSIVE and SENSORY DISCRIMINATIVE
What is the emotional aversive?
- Amygdala, anterior cingulate cortex, insular cortex
- Mediate perception of fear, anxiety, and
What is the sensory discriminative?
- Somatosensory cortex (S1 & S2)
- Mediate perception of location, intensity, and “quality” of painful stimuli
The vestibular labyrinth answers two questions basic to the human condition:
where I am? which way is up?
What are Semicircular Canals?
head angular acceleration
What is a Otholiths head?
linear acceleration gravity
-Can’t stop from firing
Semi-circular canals filled with
liquid (endolymph)
Rotation of head cause liquid to move
opposite to rotation
Rotation of head cause liquid to move opposite to rotation which causes…
-This bends the jelly-like cupula, causing embedded vestibular hair cells to bend and fire action potentials
What does the otoliths consist of~?
The otoliths consist of hair cells embedded in a gelatinous (jelly-like) substance, covered with heavy calcium carbonate crystals
What does linear acceleration cause?
Linear acceleration (e.g. tilting the head) cause the crystals to pull the gelatinous substance downward, bending hair cell stereocilia and causing depolarisation
What is the Vestibulo-ocular reflex?
keep the eyes still in space when the head moves, stops feelings of sickness and gives stability
What is the Vestibulo-collic reflex?
keeps the head still in space –or on a level plane when you walk
What is the Vestibulo-spinal reflex?
adjusts posture for rapid changes in position, posture and balance
Information about rotation and tilt travels through the brainstem and cerebellum and helps maintain
posture
Vestibulo-ocular reflex allows maintaining
gaze while rotating or moving head
Smells are detected by specialised
Smells are detected by specialised olfactory receptors (6) in the nasal cavity (olfactory epithelium [4])
Olfactory receptors send axons to the
Olfactory receptors send axons to the olfactory bulb(1) where they contact mitral cells (2) that send signals to the brain through the olfactory nerve
Olfactory receptors and mitral cells contact each other in structures called
Olfactory receptors and mitral cells contact each other in structures called glomeruli. Each glomerulus responds to one type of odorant, corresponding to one type of olfactory receptor neuron
Olfactory receptors have special receptor proteins in their…
Each olfactory receptor has only…
- Olfactory receptors have special receptor proteins in their cell membrane
- Each olfactory receptor has only one type of receptor protein which bind specific odorant molecules
- This sets of a G-protein chain reaction that causes the receptor to depolarise and fire action potentials
Signals from the olfactory nerve travel to the
pyriform cortex
Neurons in pyriform cortex respond to
odours
-Olfactory signals are also sent to the
amygdala (emotional responses)
What are the 5 basic tastes?
- Sweet
- Sour
- Salty
- Bitter
- Savoury/umami
Taste (gustatory) receptors are located in
taste buds on surface of taste papillae
Information about taste is transmitted from taste receptors through the
thalamus to the gustatory cortex in the insula
