Psych exam 2

Transducer

A device that converts variations in a physical quantity in an electrical signal

Touch

Mechanical and thermal, skin detects contact and temperature

Hearing

Mechanical, Ears detect vibrations in air or water

Vision

Photic, Eyes detect photons from light source or reflection

Taste

Chemical, Receptors on tongue detect chemicals

Smell

Chemical, Receptors in nasal passage detect chemical Vestibular, proprioceptive, interoceptive (Varied)

Animals

Different organisms sample different parts of the sensory world

Sensation

The detection of physical stimuli by receptor cells

Perception

Conscious awareness of the stimuli detected by our receptors, influenced by your expectations, current mental state, your actions, and past experiences, a personal interpretation of the sensations your body detects.

Bistable Perception

when a stimulus can be perceived in two (or more) ways, but not simultaneously.

Illusion

something that is wrongly perceived by the senses, highlight some of the shortcuts our brains take when translating sensation into
perception

labeled lines

refer to neurons that carry information about one sensory modality, but not others, iformation about each sensory modality is segregated until the brain uses these

Binding

In the brain, information gets combined together in a process, can help us get a more complete idea of a stimulus, helps us create accurate models of our environment and the associations between objects in it

Receptor cells

Specialized neurons that detect physical attributes about the world and convert them into electrical signals – action potentials, transducers of the nervous system

Stimulus

A physical event that triggers a sensory response

Action potential indentify a stimulus

What- determined by which sensory receptors and pathways are activated, he brain interprets signals based on the pathway they travel

Where-Encoded by which neurons are activated and their receptive fields. Each sensory neuron responds to a specific area,the brain maps these inputs

How strong- Encoded by frequency and number of action potentials.Stronger stimulus → higher firing rate, Stronger stimulus → more neurons recruited

How long- Encoded by the timing and pattern of firing over time, As long as the stimulus is present, action potentials continue.

• Some receptors adapt:

  • Rapidly adapting (phasic) → respond at onset/offset

  • Slowly adapting (tonic) → continue firing during the stimulus

Sensory Transduction

the process by which a physical or chemical stimulus is converted into an electrical signal that the nervous system can understand.

Touch and Thermal receptors

• Some mechanosensory neurons have a specialized ion
  channel called PIEZO

• PIEZO is normally closed, but movement of the cell
  membrane causes it to open and lets Na + ions flow in.

• When enough Na+ flows in, an action potential is triggered

• Neurons expressing PIEZO are sensitive to touch.

• Other receptors have ion channels that are opened by
  changes in temperature

• TRPV1 responds to painfully hot temperatures

• TRPV1 is also activated by Capsaicin, the chemical that
  makes food taste spicy!

Hair cells

Detecting sounds requires both receptors and the ear – a
highly specialized sensory organ
The cochlea is a snail-shaped organ in the inner ear
The eardrum is vibrated by sounds, and different frequencies
of sounds vibrate different parts of the cochlea
Hair cells live along the cochlea and are the transducers of
hearing.
Different frequencies (similar to pitch) are measured by hair
cells that live in different parts of the cochlea

Each hair on a hair cell has spring-loaded ion channels
called tip links that are physically connected to eachother
Sound waves bend hairs, pull on the tip links, and open ion
channels
Hair cells release neurotransmitters at their base which is
measured by the dendrites of other neurons.

Hair cells do not fire action potentials and instead use
graded release, meaning they release more neurotransmitter
as there is more depolarization
This allow for more detailed information from each receptor
Neurons that receive input from hair cells then convert
information to binary signals as action potentials

Rods and cones

• The retina contains several layers of neurons at the back of
  the eye, including photoreceptors like rods and cones.

• Rods and cones are the transducers of the visual system

• Yes, light travels through other cells before getting to the
  rods and cones!
  

• Rods: Active at low levels of light,
  most responsible for peripheral
  vision

• Cones: Active at high light levels
  and responsible for color vision.

• Abundant at the fovea, the central
  portion of the retina.

• Rods and cones have special ion
  channels that open when light
  photons hit them.

• Rods and cones release
  neurotransmitters onto bipolar cells

• Rods and cones use graded release
  

Odorants

Smell starts in the nose, where receptor cells detect
chemicals in the air

Odor

complex smells made up of many different odorants

Olfactory receptors

• Olfactory receptors cells are the
  transducers of the olfactory
  system

• Receptor cells have fine branches
  that extend into the inner surface
  of the nose

• These branches express olfactory
  receptors, which are G-protein
  coupled receptors (like the
  neurotransmitter receptors in the
  brain!)

An olfactory receptor cell
expresses one type of receptor,
and all cells expressing one
receptor send their axons to one
location called a glomerulus

Taste buds and receptors

we only have 5 taste receptors:
• Salty
• Sweet
• Sour
• Bitter
• Umami
Taste buds are clusters of 50-100 receptor cells on the
tongue
Each receptor cell detects one of the 5 basic tastes, and are
intermixed in a taste bud
Taste receptor cells transduce their tastes using a
combination of ionotropic and metabotropic receptors

Sensory Processing

• Sensory information is processed and
  transformed by neural circuits

• Perception is built up from sensation over
  the course of many stages of processing
  in the spinal cord and brain

• There are many similarities in the way
  sensory information is processed across
  senses

• The actual way that information is
  processed is customized to suit the
  needs of the sensory system in question

• Sensory processing is complex, and is an
  activate area of neuroscience research

Receptive field

• Describe which specific stimulus features or
  locations cause a neuron to produce action potentials.

• One of our biggest clues about what a given neuron or brain area ‘does’

• For touch-sensitive neurons, are
  regions of space (on the body) where a stimulus will
  alter a neuron’s firing rate.

• Different neurons are active when we poke at different places

• Reveal brain maps-This spatial organization is present at every level of somatosensory (touch) processing

Center-surround receptive field

It responds strongly to stimuli at the center of its receptive field, but is inhibited as you move away from the center

The area of the cortex that contains touch-
sensitive neurons is called the somatosensory
cortex
• Neurons are organized by their receptive field
• Different parts of the body get different numbers
of neurons

Hierarchy of sensory areas

Periphery-early CNS-Thalamus, Cortex

hierarchical areas help us extract bigger and more abstract information about sensory input

Retinal ganglion cells

output of the retina and transmit information from rods and cones

have center-surround receptive fields

If light is outside of the receptive field there is no change in firing

Respond when there is light at the center of their ‘area’

Inhibited by light in an outer area

If light covers bothm the activity of the neuron is unchanged

has receptive field that is for a small point in space- together they can detect dots anywhere, like pixels on a camera

Neurons in LGN have similar receptive fields

Primary visual cortex

(V1) respond to edges and gratings

Cortical cells respond even better to these repeating patterns of light than to single bars of light

Each cortical cell fires best to such patterns in a particular orientation- vertical- horizontal or somewhere in between with a particular frequency and in a particular part of the visual field

build receptive fields

receptive field of many center-surround neurons in thalamus

a subset of neurons will have receptive fields that line up with one another

If these thalamic neurons all synapse onto and excite the same V1 neuron, we can build a V1 neuron that is responsive to bars instead of dots

The correct orientation bar will activate all of the presynaptic neurons at the same time and provide strong activation, driving an action potential in the cortical neuron

An incorrect orientation bar will excite a small number of presynaptic neurons, which will not provide enough excitation to drive an action potential in the cortex neuron

Simple cells

Visual cortex neurons that respond to bars

Simple cell receptive field

Simple cells receive input from LGN neurons and respond to a certain direction bar of light

Simple cells have preferences for different bar sizes and directions depending on what neurons it gets input from

These specific connection patterns are established during the synaptic rearrangement phase during development and require visual activity

Complex cells receptive field

Complex cells in the primary visual cortex respond to gratings by receiving input from multiple simple cells with similar preferred orientations

Complex cells in the primary visual cortex have preferred orientations as well as spatial frequency

These neurons are intermingled spatially so it’s very impressive and important that they can form the correct connection patterns

When a neuron with a specific receptive field is active, it tells the rest of the brain what pattern or feature is present

this pattern of neural activity in sensory areas is called a neural representation

The representation of these gratings alone contain a lot of information about the world you are seeing

Complex receptive fields

The brain combines receptive fields in many ways to build different and more complex receptive fields

Neurons with complex receptive fields can represent detailed features and objets that are very informative to us

More complex features are typically represented as we move up the sensory hierarchy

Neurons in V2 respond to textures

Neurons in V4 respond to spirals and colors

Neurons in V5 respond to movement and movement coherence

Neurons in area IT in the temporal lobe takes complex visual patterns and build receptive fields to specific objects

Sensory processing

This hierachical process we described in the visual system is happening for all our sensory modalities in similarly structured circuits

The neural connection patterns and receptive fields differ across modalities to suit the needs of the specific sense

Bottom up processing

Building complex features from sensory information

Continues in multi-sensory cortical areas that bind features across modalities

The ‘final’ information is sent to frontal cortex areas involved in working memory, decision making and voluntary movement

Sensory processing is also shaped by top-down influences that help sensory signals be maximally efficient and informative

bottom up and top-down process help us turn sensation into perception

Movement

A single relocation of a body part. Some are intentional, others are reflexive

Action

a complex behavior made up of multiple movements

Motor plan

a plan for a series of muscle contractions with a single goal in mind

often optimized for the following goals

Accuracy: to prevent or minimize errors

Speed: to complete a task quickly and efficiently

The speed accuracy tradeoff

the concept that improvement in one of these goals usually comes at some cost to the other goal

Neuromuscular junction

the interface between the nervous system and the muscular system

motor neurons in the spinal cords send axons to the muscles

Action potentials produced by motor neurons release the neurotransmitter acetylcholine at all the motor neuron’s terminals

all transmission from motor neurons to muscles is excitatory

Innervation ratio

the number of muscle fibers innervated by one motor neuron

high innervation ratios lead to less complex but forceful movements like in biceps or hamstring

Low innervation ratios lead to more complex and finely controlled movements like in vocal cords, fingers, eyes

Motor unit

a motor neuron and muscle fibers connect to form

Muscle contraction

the basis of almost all movement and nervous system output

a muscle fiber is made up of two types of filaments, actin and myosin, arranged in a repeating pattern

the muscle begins relaxed, with only a small amount of overlap between actin and myosin

when a motor neuron fires an action potential, acetylcholine binds to muscle receptors, causing them to contract

each unit of the pattern contracts, decreasing the entire muscle length by up tp 25%

Muscle contraction 2

Acetylcholine binds to ionotropic receptors that open Na+ ion channels, generating an action potential that travels throughout muscle fibers

Depolarization during the action potential opens voltage-gated Ca2+ channels

Ca2+ causes myosin heads to undergo a conformational change

Muscle contraction occurs because the ‘heads’ of myosin change shape and pull the muscle together

A single conformational change pulls the actin a tiny amount of(5-10nm)

Similarities between excitatory transmission at the neuronmuscular junction compared to in the brain

Action potentials involving voltage-gated Na+ and K+ channels

Initiated by neurotransmitters opening ionotropic Na+ channels

Voltage gated Ca++ channels cause a conformational change

Differences between excitatory transmission at the nmj and the brain

Brain:

Nt: Glutamate

Action potential flows down axon

Ca++ entry causes vesicle fusion

Achieves neurotransmitter release

NMJ:

Nt: Acetylcholine

Action potential fills muscle fiber

Ca++ entry causes myosin head ‘pivot’

Achieves muscle contraction