What is behavior

• Hormonal and neural responses to a stimuli

How Do We Build a World of Experience

• Sensations are the fundamental, elementary components of an experience

• Perception refers to the processes used to arrive at a meaningful interpretation of sensations

Sensory Processes

• Reception

  • Environmental stimulus

    • e.g. tree

  • Transformation

    • Light is reflected off the tree and enters the eye (vision)

    • Sound waves (audition)

    • Chemicals (olfactory)

    • Tastebuds (taste)

    • Pressure, temperature, pain, stretch (touch)

      • all these things activate the sensory receptors

  • Sensory receptors

• Transduction

  • Sensory receptors

  • Change the stimulus energy into an electrochemical neuronal change

    • action potential

• Coding

  • Neural processing

    • Correspondence between stimulus features and neuronal activity

    • ex: occipital lobe (for vision), temporal lobe (audition and smell), parietal lobe (touch), insula (taste), not part of the brain (smell)

Behavioral Response

• Perception

  • How to study perception?

    • psychological approach

    • physiological approach

• Recognition

• Action = Behavior

Psychophysics

• Measure the relationship between the stimuli and the behavioral response

• ex. easier to perceive the vertical lines box in between two diagonal boxes

Physiological

• Measure two relationships

  • Relationship between stimuli and physiological responses

  • Relationship between physiological response and behavioral response

• Eye-tracking

• Functional MRI

• We’re surrounded by vertical and horizontal lines every day

Anatomy of a Neuron

• cerebellum = little brain

  • contains 50% of our neurons

  • contains lobules

  • Biggest neuron = meninge

Are Neurons Individual Cells?

• Neural net hypothesis

  • The reticular theory

  • Nervous system is a continuous mass of tissue

  • Camilo Golgi

• Cell hypothesis

  • Neurons are individual cells

  • Santiago Ramon y Cajal

    • Neuron Doctrine

      • neurons are cells that form the basic unit of the nervous system

• Behavior is undivided

  • it is a sum of parts

The Brain

• Two main types of cells within the brain

  • neurons

  • glia (non-neuronal cells)

Neural Tissue

• Two types of neural cells in the nervous system:

  • Neurons: for processing, transfer, and storage of info

  • Neuroglia: for support, regulation, and protection of neurons

How do you identify a neuron?

• Dendrites

  • Receives information from other neurons

• Soma

• Axon

  • Carries information away from the neuron

• Afferent axon

  • admission

• Efferent axon

  • exit

• Interneuron

• Synaptic (axon) terminals

• Receptors are in the dendrites and take it to the soma, which then goes to the axon terminal and the dendrites of the interneuron

• Sensory (afferent axons) —> interneuron —> motor (efferent axons)

Classification Of Neurons

• Based on form

• Anaxonic neurons

  • no anatomical clues to determine axons from dendrites

  • functions not well known; likely interneurons

• Multipolar neuron

  • multiple dendrites and single axon

  • most common type

• Bipolar neuron

  • two processes coming off cell body - one dendrite and one axon

  • the soma is small

  • only found in eye, ear, and nose

• Unipolar (pseudo unipolar) neuron

  • single process coming off cell body, giving rise to dendrites ( at one end) and axon (making up rest of process)

• Functional classification based on type of information and direction of information transmission:

  • Sensory (afferent) neurons

    • transmit sensory info from receptors of PNS toward the CNS

    • most sensory neurons are unipolar, a few are bipolar

  • Motor (efferent) neurons

    • transmit motor info from the CNS to effectors (muscles, glands, adipose tissue) in the periphery of the body

    • all are multipolar

  • Association (interneurons)

    • transmit info between neurons within the CNS; analyze inputs, coordinate outputs

    • are the most common type of neuron (20 billion)

    • are all multipolar

• If just your sensory neuorn were impaired, you’d be able to act and move but not the appropriate responses

• If just motor neurons were impaired, you won’t be able to move but you can feel and think

  • Motor neuron disease: amyotrophic lateral sclerosis

Glia

• Neuroglia

  • the other cellular component of the nervous system

• Astrocytes

  • wraps synaptic terminals

  • scaffolding: mechanical and metabolic support

  • increases in number after brain injury

• Microglia

  • most likely to be found

  • like pac man

  • good to get rid of dead cells/garbage

• Oligodendrocytes/Schwann cells

  • make myelin surrounding the axon so that it can help out the info flow to become much quicker

  • oligodendrocytes make it in the CNS, most likely helping the interneurons

  • Schwann cells make it in the PNS, most likely helping the motor neurons

    • Satellite cells

      • support groups of cell bodies of neurons within ganglia of the PNS

• Radial glia

  • literal ladder especially when you’re an embryo

Resting Potential and Action Potential

Neuronal Communication

• Cell membrane

  • semi-permeable: some things can go through

  • middle = hydrophobic

  • outside = hydrophilic

• How do neurons communicate with one another?

• Ions

  • Positive charge: cation

    • Na+

    • K+

    • Ca2+

  • Negative charge: anion

    • Cl-

• How can ions cross the membrane?

• Ion channels

  • ion selective

  • gated

    • open or closed

• What forces will push an ion across an open ion channel?

• Diffusion

  • concentration gradient

• Electrostatic

  • electrical gradient

Resting Membrane Potential

• What is potential?

  • difference in the charge between poles of the battery is referred to as the potential

• The resting membrane potential is -65 (-70) mV

  • the inside if the neuron is 65 mV more negative than the outside

• Why is there a resting membrane potential?

  • unequal distribution of ions

• Membrane potential

  • forces acting on the ions

• Why is there an unequal distribution of ions?

  • selective permeability of the cell membrane

    • membrane is moderately permeable to K+ and Cl-, but relatively impermeable to Na+

    • Na+/K+ pump

      • Pumps out 3 Na+ and pumps in 2 K+

Action Potential

• Changes in cell membrane potential

• Make the inside of the cell less negative: depolarization

  • line goes up

  • Na make it more positive since it can’t go in

  • If anions were to leave the neuron we would also have depolarization

• From depolarization it returns to resting membrane potential: repolarization

• Make the inside of the cell more negative from the resting membrane potential: hyperpolarization

  • line goes down

  • If anions were to come into the neuron, that would contribute to hyperpolarization

  • K+ channels slow to close

• What happens at the axon hillock?

  • Stimulus has to get to the threshold of excitation to create an action potential

  • Stimulus causes slight depolarization when it reaches the threshold, opening the gated voltage channels once Na enters making the inside of the cell positive, once it’s so positive it closes and Na can’t enter anymore

• What happens during action potential?

  • When cell membrane threshold is met, voltage-gated Na+ channels open up, Na+ enters the cell

  • Na+ channels close in 1 msec

  • In the mean time, voltage-gated K+ channels open, K+ leaves the cell, repolarizing it

• Similar to a light switch

• Off

  • inside is more negative

• On

  • inside is more positive

• How is info encoded by the nervous system?

  • Changes in pattern, frequency

  • Similar to morse code

• What would happen if I gave you a drug that blocked Na+ channels?

  • no depolarization

  • numbs you because no sensory neurons

• What would happen if I gave you a drug that blocked K+ channels?

  • no repolarization

  • Neurons would be constantly firing

  • Epileptic seizures

  • Need electrolytes, bananas

Absolute Refractory Period

• no action potentials at all during this period

• at peak of AP, Na+ channels close an another AP can’t be generated

• neurons need more time to recover

Relative Refractory Period

• You can’t open it right away (voltage-gated sodium channel) - this is the absolute refractory period

• You can open it until you give it a much bigger pool - this the relative refractory period

Propagation of the Action Potential

• As the action potential travels, it does not lose strength

• always the same size AP

• size matters

  • AP travels faster down fat axons (less resistance)

Myelin

• speeds up the propagation of the action potential

• saltatory conduction

  • action potential leaps from node of Ronvier (gaps between myelin/where ion channels are)

  • myelin blocks out distractions