neuroscience block #2

all lecture slides from block #

Sensory systems ____

• reflect the environmental properties of importance (for survival) to a species

What is the stimulus for sensory systems?

• an environmental event that transmits energy

What is the role of receptors in sensory systems?

• they detect some of the energy from the stimulus

How do we NOT view the world as it truly is?

• receptors act as filters that signal to the brain the existence of certain types of energy → then ignoring others

• we view the world as it appears to our sensory and perceptual systems

Sensory information is ____

• selective

• analytical

What is Environmental energy?

• photons

• air pressure waves

• direct contact with objects

• temperature

• chemicals

How is environmental energy transformed?

• sensory receptors and systems detect physical energy and convert it to information coded as action potentials

Sense organs ____

• transmit action potentials to the brain

• modality specific

What are some Modality specific receptors?

• sense organs (receptors)

• photo receptors (vision)

• eardrum, inner ear structures (hearing)

• labeled lines

• sensory transduction

• receptor potential

what are labeled lines?

• the brain recognizes the sense as distinct because their action potentials travel along separate nerve tracts

what is sensory transduction?

• the conversion of physical energy from a stimulus into a change in membrane potential in a receptor cell

what is receptor potential?

• a local change in membrane potential in response to stimulus that may result in an action potential

what is the pacinian corpuscle?

• a skin receptor that responds to vibration and pressure

• they sense textures

how does a pacinian corpuscle work?

• when stimuli stretch its membrane → sodium channels open → creates a graded receptor potential

• if this potential exceeds the firing threshold → action potential is generate

what are Mesisner’s corpuscles?

• touch receptors that respond to changes in stimuli

what are Merkel’s discs?

• touch receptors that respond to edges and isolated points

what are Ruffini corpuscles?

• touch receptors that detect the stretching of the skin when we move fingers or limbs

what are free nerve endings?

• nerve endings in the skin that respond to pain, heat, and cold

what is the upper limit for the rate of an action potential firing?

• ~1,000 action potential PER second

• stimuli may change/oscillate faster

how can the intensity of a stimulus be shown?

• number

• thresholds of activated cells what

what is the somatosensory system?

• determines if body sensations are coming from outside or inside the body, along where they originate

how does the somatosensory system determine origins of body sensations?

• labeled lines

• stimulus location is found based on a map-like representation of the position of the activated receptors

what is the receptive field?

• the area within where the presence of a tumulus will alter a sensory neuron’s firing rate

what is sensory adaptation?

• a progressive decrease in a receptor’s response to a sustained stimulation

which receptors are involved in sensory adaptation?

• phasic receptors: display adaptation

• tonic receptors: shows little or no adaptation

how can information be suppressed?

• removing the stimulus

• central modulation of sensory modulation

what is central modulation of sensory modulation?

• the brain actively suppresses some sensory inputs and amplifies others

what does the dorsal column system do?

• deceivers touch information

how does the dorsal column system deliver information?

1. receptors sense axons through the dorsal spinal cord to synapses on neurons in the brainstem

2. axons from those neurons cross the midline and go to the thalamus

3. information about each sensory modality is sent to a different region of the thalamus where it may be emphasize or suppressed

what are dermatomes?

• 5 segmented areas in the brainstem that correlate to different areas of our body

what are the areas in the brain and body that correlate, dermatomes?

• cervical : cervical

• Thoracic : thoracic

• lumbar : lumbar

• sacral : sacral

• coccygeal

how is the sensory cortex organized?

• primary sensory cortex

• nonprimary sensory cortex

what is the nonprimary sensory cortex?

• a secondary sensory cortex, that receives direct projections from the primary sensory cortex area for the modality

what is the primary sensory cortex (S1)?

• recieves touch information from the opposite side of the body

• located in the post central gyrus

how are S1 cells arranged?

• a map of the body → a sensory homunculus

what is a reflex?

• a simple, stereotyped, and unlearned response to a certain stimulus

what are acts in the motor system?

• complex, sequential behaviors

what is a motor plan?

• set of muscle commands that is established before the action happens

what are the different levels of the motor system?

• primary motor cortex

• nonprimary motor cortex

• basal ganglia

• cerebellum

• thalamus

• brainstem

• spinal cord

what do muscles and the skeleton do?

• work together to move the body

what do tendons do?

• connect muscles to bone in a reciprocal way

what happens when a muscle group contracts?

• it stretches the other group - antagonists

what are synergists?

• muscles that act together to move a limb

what are skeletal muscles?

• muscles used for movement of the skeleton

what do motor neurons in the spinal cord and brainstem do?

• send action potentials down their axons to inner age muscles

what happens at the neuromuscular junction?

• acetylcholine (ACh) is released

what is the final common pathway?

• motor neurons through the brain and spinal cords controlling muscles

what is proprioception?

• the collection of information about body movements and positions

what are the two kinds of proprioceptors?

• muscle spindle

• Golgi tendon organ

what is a muscle spindle?

• capsule buried in other muscle fibers, that has intramural fibers

• responds to stretch

what are Golgi tendon organs?

• proprioceptor that is sensitive to muscle tension

what does the stretch reflex provide?

• a mechanism for automatically adjusting muscle activity

what causes the stretch of the biceps?

• increasing the load

what happens if there s increased in the load?

• muscle spindle will activate bicep and inhibit triceps

what happened after increasing the load?

• a compensation for change in the wright of the object being held

the stretch reflex does NOT ___

• doesn’t not require any cortical mechanisms

what are Central Pattern Generators (CPG)?

• rhythmic behaviors generated by spinal circuits

what is Sherrington?

• complex coordinated actions in the absence of cortical control

where does CPG reside?

• existence is in the spinal cord

what are spinal circuits able to do?

• capable of controlling coordination and timing of muscles

what happens when an animal has a transected spinal cord?

• can no longer adjust to avoid obstacles

what is the pyramidal system?

• axons of neuronal cell bodies in the cerebral cortex → pass through the brain stem → formation of the pyramidal tract

• in the spinal cord and cross to the contralateral side

where do axons in the pyramidal tract originate?

• primary motor cortex (M1)

• precentral gyrus

what does the extrapyramidal system also consist of?

other axon pathways with tracts that lie outside of the pyramids in the medulla

what happened in the M1 recordings from monkeys making arm movements?

• M1 cells change firing rate according to direction of movement

• each cell has one direction that produces the highest discharge rates

• average of neuronal activity allows scientists to predict the direction of arm movements

what is the premotor cortext?

• extension of dorsal stream

• involved in externally guided action

• translate perception into action

What is the premotor cortex connected to?

• the parietal cortex

what is the SMA connected to?

• the frontal lobe

what does the SMA do?

• more involved in internally guided action

• selection of action based, based on internal goals, experience

• potential inhibition of undesired actions

what are the key parts of the visual system?

• cornea

• lens

• fovea

• retina

• optic nerve

what is the blind spot?

• where axons of the optic nerve exit

what causes the blind spot?

• there are no photoreceptors in the optic disc

  • leaving a hole in our visions

what is the inside out cellular organization?

• where light must pass through all layers of the retina to reach the photoreceptors

what are the retinal cell types?

• rods

• cones

• horizontal cells

• bipolar cells

• amacrine cells

• ganglion cells

what do rods do?

• respond to light

what do cones do?

• respond to specific wavelengths

• color processing

what do cones have?

• three different photopigments that respond to different colors of light

what photopigment do photoreceptors have?

• opsins

what is the meaning of trichromatic?

• having 3 cones with opsins that are sensitive to

  • short wavelengths (blue)

  • medium wavelengths (green)

  • long wavelengths (red)

how much can the fovea really see in the visual field?

• about 2 degrees

what is the fovea?

a small region specialized for detailed vision

what makes the fovea good for detailed vision?

• high density of cones

• fewer blood vessels

• large amount of cortical representation

• small receptive fields

what negatively affects acuity?

• more coverage with rods than cones onto bipolar cells

what allows the eyes to work in different light intensities?

• pupil, iris

• range fractionation

• photoreceptor adaptation

how does the pupil allow eyes to work in different light intensities?

• adjusting the size of pupil (opening of the iris)

how does range fractionation allow the to eye to work in different light intensities?

• uses different photoreceptors to handle different intensities

  • cones need more light

  • rods need less

how does photoreceptor adaptation allow the eye to work in different light intensities?

• each photo receptor adjusts it level of sensitivity to match the average level of light

what do opsin and retinal do?

• together, they form “rhodopsin”

what is rhodopsin?

• the photopigment found in rods → altered by light

what happens during darkness in the dark current?

• sodium channels are open → depolarizing the cell (graded)

• glutamate is released

what happens in the light during the dark current?

• sodium channels close → hyperpolarizing the cell

• decreased glutamate released

how does our brain begin to process light levels?

• more light → less glutamate

• glutamate is released in a graded matter

how is our visual system good at detetecting edges and color?

• through receptive fields that center surround organization

how is visual processing accomplished by receptive fields?

• receptive fields of many ganglion cells combine

  • forming the receptive field of a single LGN cell

• recent e fields of many LGN cells combine to form the receptive field of one V1 cell

what do bipolar cells’ receptive field do?

• they help identify contrast

• antagonistic center-surround organization

what does glutamate do to bipolar cells?

• glutamate hyperpolarizes one group of bipolar cells and depolarizes another

what are on center bipolar cells?

• turning on light in the center of its receptive field excites the cell because it gets LESS glutamate

  • inhibits this type of bipolar cell

what is an off center bipolar cell?

• turning off light in the center of the field excites the cells because they get MORE glutamate

  • depolarized

what does less glutamate do to bipolar cells?

• less glutamate = less inhibition of bipolar cell

• leads to greater excitation of ganglion cell

what do bipolar cells release?

• glutamate

  • which always depolarized ganglion cells