Lecture 18 Flashcards
Mechanosensitive ion channels convert….
mechanical force into change of ionic current
Mechanical stimuli may trigger release of….
second messengers
Two-point discrimination varies at least _____ across the body
twenty fold
Two-point discrimination:
Higher density of mechanoreceptors
Enriched in receptor types that have small receptive fields
More brain tissue
Maybe special neural mechanisms for high-resolution discriminations
Fingertip for braille reading
Primary afferent axons enter the spinal cord through the ___ _____; their cell bodies lie in the…..
dorsal root;
dorsal root ganglia
Types of primary afferent axons and their groups, ordered in size from largest to smallest and fastest to slowest
A(alpha); Group I
A(beta); Group II
A(delta); Group III
C; Group IV
C fibers (3)
Mediate pain, temperature, and itch.
Have no myelin and are about 1 μm in diameter.
The slowest axons, conducting at about 0.5–1 m/sec
A(beta) mediates….
touch sensations
Each spinal segment is named after the….
vertebra adjacent to where the nerves originate
How many spinal segments are there, divided into ___ divisions of spinal cord?
30, 4 divisions of spinal cord
Four spinal segments and their numbers (top to bottom)
Cervical (C)
Thoracic (T)
Lumbar (L)
Sacral (S)
Cervical (C) 1–8, thoracic (T) 1–12, lumbar (L) 1–5, and sacral (S) 1–5
Dermatomes:
the area of skin innervated by the right and left dorsal roots of a single spinal segment
Dermatomes-
___ to ___ correspondence with spinal segments
one to one
Shingles
A type of herpes virus commonly known as chickenpox
The virus remains in our primary sensory neurons and revives
Restricted to the skin innervated by the axons of the affected dorsal root.
Aβ axons have 2 branches: on _____-order sensory neurons, rapid _____ _____; ascending input is responsible for ______
second-order;
unconscious reflexes;
perception
Dorsal column–medial lemniscal pathway (copy down)
The ascending branch of the large sensory axons (Aβ) enters the ipsilateral dorsal column of the spinal cord,
The axons of the dorsal column terminate in the dorsal column nuclei, at the junction of the spinal cord and medulla. some of the longest axons
From this point onward, decussate to ventral posterior (VP) nucleus of the thalamus, and primary somatosensory cortex, or S1
Adjacent somatic sensory areas: (2)
Postcentral gyrus: 3a, 1, 2
Posterior parietal cortex: areas 5, 7
Primary somatosensory cortex (S1)= Brodmann’s area __ lies on the _____ ______
Brodmann’s area 3b;
postcentral gyrus
Area 3b is the primary somatic sensory cortex because: (4)
1) It receives dense inputs from the VP nucleus
2) Very responsive to somatosensory stimuli
3) Lesions here impair somatic sensation
4) Electrically stimulated, it evokes somatic sensory experiences
3b projection to area 1 sends _____ _____, 3b projection to area 2 emphasizes _____ and ______
texture information;
size and shape
Wilder Penfield:
Electrical stimulation of the S1 surface can map somatic sensations localized across the body
Somatotopy:
mapping of the body’s surface sensations onto the brain
Cortical somatotopy guy is named…
Homunculus
Somatotopic maps are ____, they can change with things like _____ and ______
dynamic;
amputation and overstimulation
