Exam 2: Sensory and Motor Systems Flashcards
What 2 ways can light be thought of?
- Particles of energy (photons)
2. Waves
Visible light for humans
380-760nm
Wavelength=
Color
Intensity=
Brightness
Sensitivity
Ability to detect the presence of dimly lit objects
Acuity
Ability to see details of objects
What does the lens do?
Focuses light on retina
What do ciliary muscles do?
Alter the shape of the lens as needed
Accommodation
Process of adjusting the lens
What 2 things allow for depth perception?
- Convergence
2. Binocular disparity
Convergence
Eyes must turn slightly inward when viewing objects
Binocular disparity
Difference in position of same image on two retinas
What does the retina do?
Converts light to neural signals
5 layers of retina
- Retinal ganglion cells
- Amacrine cells
- Bipolar cells
- Horizontal cells
- Receptors (deepest)
“Inside out”
Far objects: round or flat?
Flat
Near objects: round or flat?
Round
Fovea
High-acuity area at center of retina
What reduces distortion due to cells between the pupil and the retina?
Thinning of the ganglion cell layer
Blind spot
No receptors where retinal ganglion cell axons exit the eye (optic nerve)
Completion
Visual system interpolates the blind spot based on surrounding detail and info from other eye
What is more sensitive to shorter wavelengths of light?
Rods
What is more sensitive to longer wavelengths of light?
Cones
3 types of cones
- Red (L)
- Green (M)
- Blue (S)
Component (trichromatic) theory
Color is encoded by ratio of activity in 3 kinds of receptors
Opponent-process theory
Color processed in an antagonistic manner (red/green, blue/yellow, white/black)
Temporal integration
Saccades allow for bits of info to be summated over time
Receptive field
Area of visual field within which it is possible for a visual stimulus to influence the firing of a neuron
What type of receptors do off-center bipolar cells have?
Ionotropic glutamate receptors
What type of receptors do on-center bipolar cells have?
Metabotropic glutamate receptors
Lateral inhibition
Inhibition that neighboring neurons in brain pathways have on each other, increases visual system’s ability to respond to edges of a surface b/c edge neurons receive less or more inhibition from neighbors
What type of input does the optic nerve receive?
Input from one eye
What type of input does the optic tract receive?
Input from both eyes, but not depth perception
2 channels in LGN
- P
2. M
What layer does the LGN project to?
Layer IV
P cells
Small, top 4 layers, color, still, cones
M cells
Large, bottom 2 layers, no color, motion, rods
What do cells in lower (input) layer IV tend to have?
Receptive fields with a center-surround organization
What do cells in upper layer IV tend to be?
“Simple” cells
Simple cell characteristics
- Rectangular receptive field
- “On” and “Off” regions
- Orientation and location sensitive
- All are monocular (in one eye)
How are simple cells constructed?
Convergence of center surround inputs
Ocular dominance columns
Stripes of neurons in visual cortex that respond preferentially to input from one eye or the other
What do hypercolumns consist of? (3)
- Pairs of ocular dominance columns
- Blobs
- Many orientation columns
Color constancy
Color perception is not altered by varying reflected wavelengths
Retinex theory (Land)
Color is determined by comparing the light reflected from adjacent surfaces (contrast)
What are dual-opponent color cells sensitive to?
Color contrast, found in cortical “blobs”, receive P inputs
Blobs
Color
Interblobs
Shape
Where in the visual system is depth perception?
Interblobs
Pitch
Difference in frequency harmonics
Sound propagation steps (6)
- Wave enters auditory canal
- Strikes eardrum (or tympanic membrane)
- Ossicles (hammer, anvil, and stirrup) vibrate
- Oval window vibrates
- Fluid in cochlea set in motion
- Vibrations of fluid dissipated at round window
What divides the cochlea into 3 chambers?
Reissner’s membrane and basilar membrane
What is the auditory receptor organ called?
Organ of Corti
Motion of basilar membrane at base
Like a guitar string, plucked and vibrated quickly, high frequencies, light
Motion of basilar membrane at apex
Like a jump rope, heavy and slow, vibrates at low frequencies
2 types of hair cells in Organ of Corti
- Inner hair cells: 3,500
2. Outer hair cells: 14,000
What do all hair cells have?
Stereocilia on upper surfaces, in or near tectorial membrane
Mechanotranduction
Conversion of mechanical stimulus to an electrical or chemical signal
What is the job of the outer hair cells in transduction?
Change length and augment basilar membrane motion
What is the job of the inner hair cells in transduction?
Release transmitter onto axons of auditory nerve
What type of organization is the auditory system?
Tonotopic, arrayed according to frequency
What does the auditory cortex include? (2)
- A core (primary; A1)
- Up to 10 belt (secondary) regions
- Each area organized tonotopically
What 2 areas of association cortex are auditory signals conducted to?
- Posterior parietal cortex
2. Prefrontal cortex
Damage: lesions of auditory cortex (2)
- Unilateral
2. Bilateral
Damage: deafness (2)
- Conductive
2. Nerve
3 divisions of somatosensory system
- Exteroceptive external stimuli
- Proprioceptive body position
- Interoceptive body conditions
Cutaneous receptors (4)
- Meissner’s corpuscles
- Merkel’s disks
- Ruffini endings
- Pacinian corpuscles
Stereognosis
Identification of objects by touch
What type of transduction occurs at free nerve endings?
Painful and thermal stimuli
What do nociceptors respond to?
Strong mechanical, thermal, or chemical stimuli (or all 3)
Dermatome
Area of the body that is innervated by the left and right dorsal roots of a given segment of the spinal cord, unipolar and sensory
Dorsal-Column Medial Lemniscus
Mainly touch and muscles/joints, first synapse in dorsal column nuclei of medulla
Anterolateral System
Mainly pain and temperature, first synapse in spinal cord, 3 tracts
Muscle spindles
Signal muscle length, in parallel with muscle fibers
Muscle fibers
Signal muscle tension, in series with Golgi tendon organs
What do mechanosensitive proprioceptors in joints respond to?
Angle, direction, and velocity of joint
What 2 structures are in the vestibular system?
- Semicircular canals
2. Otolith organs
What do the semicircular canals detect?
Turning movements of head, angular accelerations, push-pull
What do the otolith organs sense?
Changes of head angle (position of head) and linear accelerations, push-pull “rocks”)
Olfaction neurogenesis
Receptors are regularly replaced (10-20 million in humans)
How is odor encoded?
By component processing: by pattern of activity across receptor types
Where do axons of olfactory receptors terminate?
Olfactory glomeruli (clusters of neurons near surface of olfactory bulb)
Where does the olfactory tract project?
Bilaterally to medial temporal lobe structures including piriform cortex and amygdala
2 pathways from medial lobe in olfactory system
- Limbic system
2. Thalamus-orbitofrontal cortex
Taste
Sensations relayed by taste receptor cells, 5 tastes
5 tastes
- Sweet
- Sour
- Salty
- Bitter
- Umami
Flavor
Multi-sensory percept depending on taste, smell, texture, temperature, and pain
What 3 accessory structures (papillae) are taste buds grouped into?
- Vallate
- Foliate
- Fungiform
How many taste buds do each papilla have?
~1-200
How many taste buds does a person have?
~2,000-5,000
How many taste receptor cells do buds have?
~50-150
Direct transduction in gustatory
Salty and sour
Indirect transduction in gustatory
Bitter, sweet, and umami
At what cranial nerves do gustatory afferent neurons leave?
7th, 9th, and 10th and goes to solitary nucleus of medulla
Where do chemical senses first merge?
Orbitofrontal cortex
Anosmia
Inability to smell
Ageusia
Inability to taste
Dorsolateral Tracts (2)
- Corticospinal tract
2. Corticorubrospinal tract
Ventromedial Tracts (2)
- Corticospinal tract
2. Cortico-brainstem-spinal tract
What is at the top of the sensorimotor hierarchy?
Association cortex
2 major areas of sensorimotor association cortex
- Posterior parietal
2. Dorsolateral prefrontal
What input does the PPAC receive?
Dorsal streams of somatosensory, auditory, and visual systems
What does electrical stimulation of PPAC cause?
INTENT to perform action
Apraxia
Inability to make a requested movement (cannot form intent)
Contralateral neglect
Inability to respond to stimuli contralateral to lesion
What does the DLPFAC do?
Anticipates consequences of various movements and forms a plan of action
3 major areas of secondary motor cortex
- Premotor
- Supplementary
- Cingulate
What does the secondary motor cortex do?
Converts general plans of action into specific sets of instructions
What does the primary motor cortex do?
Controls execution of movement
How many neurons in sensorimotor cortex are active for mirror neurons?
Up to 50%- not enough to perform action
What layer does primary motor cortex send input to?
Layer V
What is the cerebellum involved in?
Coordination, precision, and timing of execution + motor learning
Basal ganglia: direct-excitation
(D1-yes voter) Facilitates motor (or cognitive) programs in secondary motor cortex that are adaptive for present task
Basal ganglia: indirect/hyper-direct-inhibition
(D2-no voter) Inhibits execution of competing motor programs
What is the cause of Parkinson’s?
Loss of dopaminergic neurons in substantia nigra
What is a motor unit?
Motor neuron + all muscle fibers it contacts, smallest unit of motor activity
What happens at the neuromuscular junctions?
Ach is released by motor neurons, which activates the motor end-plate on each muscle fiber and causes the fiber to contract
What do extrafusal fibers cause?
Muscle contraction
What do intrafusal fibers do?
Detect the amount and rate of change in length of a muscle
Recurrent Collateral Inhibition
Allows Renshaw cells to inhibit a neuron. This system hinders repetitive firing of a single motor neuron
What do stretch reflexes do?
Produce immediate compensatory contraction to prevent external forces from altering the intended position of the body
Motor equivalence
Given movement can be accomplished various ways, using different muscles
