Chapter 2

reflex

automatic, stereotyped movement produced as the direct result of a stimulus

reflex pathway example with a kneetap

sensory neuron from muscle → spinal cord (back part) → either to brain, to other leg, or to single synapse in reflex

single synapse in reflex → reflex motor output in front part of spine, causing thigh muscle to contract

the electrical signal is sent across…

the synapse, the gap between 2 neurons (presynaptic & postsynaptic)

nerve fiber

bundle of nerve cells

there are between ____ & ____ neurons in the body with ____ connections each

there are between 10 billion and 1 trillion (estimated 86 billion) with 10,000 connections each

parts of neuron

dendrites, cell body or soma, axon, terminal endings/buttons

dendrites

branches off cell body

axon

inside the myelin sheath

terminal endings/buttons

ending of neuron

in what direction do messages travel in the neuron?

from the dendrites/soma downward toward the terminal endings

do neurons take different shapes in different areas of the body?

yes

axodendritic

axon terminal of one neuron synapses on dendritic spine of another

are there other ways neurons can connect besides axodendritic?

yes

myelin sheath

fatty tissue produced by other cells (glia) in the brain/nervous system that protects the length of the axon

what does the myelin sheath allow to occur?

it allows electricity to travel smoothly down the axon

in the _______ the _______ is not protected by the myelin sheath

in the gaps at the Nodes of Ranvier, the electrical signal is not protected

What happens when the electrical signal is not protected?

ion exchange

How does a neuron fire? What is the nerve impulse?

action potential

How does a firing neuron cause the next neuron to fire? How do they communicate?

neurotransmitters

action potential is…

voltage

action potential steps

1. Starts with electrical resting potential: inside of the cell is 70 mV more negative than outside due to Cl- ions inside & Na+ ions outside (resting potential = -70 mV)

2. Stimulation of the neuron causes the opening of ion gates that let in Na+ ions, which makes the inside more positive: -70, -69, -68, -67…

3. When enough Na+ ions get in for the potential to be reduced to -55 mV, suddenly the ion gates to the cell membrane are flung open, allowing Na+ to rush in.

4. So much Na+ enters that the potential shoots all the way up to +40 mV, so the inside is now positive relative to the outside (the action potential)

5. The ion pumps work to reduce the potential back to -70 mV by pushing positive ions out (K+ because Na+ goes out slower) then another pump takes Na+ back out and puts K+ back in

Na+ goes ____ & K+ goes ____, until it switches

Na+ goes in and K+ goes out

-55 mV is a ________

threshold; below that voltage there is no action potential

firing is ____ or ____

all or none, it won’t happen if it doesn’t meet the threshold

does more intense stimulation cause a more intense action potential?

no, it just causes more frequent ones (up to 1000/sec) and in more neurons

action potential travels down _______________ by _____________

action potential travels down the length of the axon from the cell body by depolarizing neighboring areas

how fast does action potential travel?

50 to 100 m/sec

the myelin sheath _______________ the speed of action potential and ion exchange

the myelin sheath speeds these processes up

Herman Van Helmholtz

measured the speed of a nerve

Where does action potential happen?

at the Nodes of Ranvier

How does communication across the synapse happen?

neurotransmitters

Communication across the synapse (neurotransmitters) steps

1. synapse; terminal endings of presynaptic neuron: may relay impulse to dendrites of postsynaptic neuron

2. terminal buttons contain little sacs (vesicles_ of chemicals (neurotransmitters) and at action potential, vesicles burst and release neurotransmitters into synapse

3. receptor molecules on membrane of dendrite are like little locks to be opened: neurotransmitters are the keys, and this is what opens ion gates to allow Na+ inside in the first place

   • These are based on shape (lock & key model)

neurotransmitter life cycle stages

1. Synthesis

2. Storage

3. Release

4. Receptor Interaction

5. Inactivation

6. Reuptake

   1. Degradation

serotonin

• neurotransmitter responsible for long term good feelings

• SSRI (selective serotonin reuptake inhibitors) block reuptake of serotonin; anti-depressants

dopamine

neurotransmitter responsible for short term good feelings

Neurotransmitters may open a gate to to let _____ inside. Is this excitatory or inhibitory?

Neurotransmitters may open a gate to let Na+ inside. This is excitatory (more likely to fire) because the potential is getting smaller, toward -55 mV.

Neurotransmitters may open a gate that pushes ________ out. Is this excitatory or inhibitory?

Neurotransmitters may open a gate that pushes positive K+ ions out. This is inhibitory (less likely to fire) because the potential inside the cell is getting larger (-70, -71, -72).

inhibition of a reflex example

swearing ups pain tolerance

spatial summation

simultaneous signals coming from multiple presynaptic neurons being received by a single postsynaptic neuron; several weak signals from different locations → 1 large signal

temporal summation

single presynaptic neuron rapid-firing signals to a post-synaptic neuron; several weak signals at different times from one location → 1 large signal

EPSP

Excitatory Post-Synaptic Potential; increases chance of action potential

IPSP

Inhibitory Post-Synaptic Potential; decreases chance of action potential

reciprocal inhibition example

when extensor muscle is excitated, flexor muscle is inhibited & vice versa

disinhibition examples

• alcohol: temporarily damages higher brain areas, resulting in loss of inhibition of impulsive behaviors

• disconnecting spine from dog’s brain

• withdrawal reflex might be inhibited by the higher-level knowledge that although a heated dish of food hurts, avoid letting go until you reach the table

Nervous System Parts

• Central vs. Peripheral

• Peripheral: Somatic vs. Autonomic

  • Autonomic: Sympathetic vs. Parasympathetic

Central NS (CNS)

• brain, spinal cord

• contains the hindbrain, midbrain, and forebrain

Peripheral NS

• away from center

• everything besides the brain and spinal cord

• includes somatic division and autonomic division

Somatic NS

• body

• nerve fibers connecting to muscles and senses

Autonomic NS

• self rule

• vital functions: heart rate, breathing, digestion, reproduction

• contains sympathetic and parasympathetic branch

Sympathetic NS

• “with feeling”

• excited states

• energy-consuming

• fight or flight

• arousal: mobilizes for emergency (speeds heart and lungs, inhibits digestion & sexual function)

Parasympathetic NS

• “goes with the sympathetic”

• vegetative, calm states

• energy conserving or storing

• rest & digest or feed & breed

• calm: maintains normal functioning (slows heartrate and lungs, etc.)

Sympathetic NS functions

• dilates pupil

• relaxes bronchi

• accelerated heart beat

• inhibits activity

• contracts vessels

Parasympathetic NS functions

• contracts pupil

• constricts bronchi

• slows heart beat

• stimulates activity

• dilates vessels

brain parts bottom to top/inside to outside/old to new

hindbrain, midbrain, forebrain

hindbrain parts

• medulla oblongata ("oblong marrow”)

• pons (“bridge”)

• cerebellum (“little brain”)

medulla

• part of hindbrain

• breathing

• heartbeat

• blood circulation

pons

• part of hindbrain

• arousal and attention

• facial expressions

cerebellum

• part of hindbrain

• integration of muscles to perform fine movements

• no coordination or direction of these movements

• balance

cat transected above the hindbrain

• low-decerebrate cat

• can move but not act

midbrain

• forms movements into acts

• controls whole body responses to visual and auditory stimuli

• contains the tectum and tegmentum

  • tectum (“roof”)

    • superior colliculus (“upper hills”)

    • inferior colliculus (“lower hills”)

  • tegmentum (“floor”)

    • substantia nigra (“black substance”)

    • red nucleus

responsible for responses to visual stimuli

superior coliculous

responsible for responses to auditory stimuli

inferior coliculous

forebrain parts

• thalamus (“inner chamber”)

• hypothalamus (“below the inner chamber”)

• basal ganglia

• limbic (“border”) system

• cerebral cortex/neocortex

thalamus

sensory & motor relay center (to various cerebral lobes)

hypothalamus

• controls responses to basic needs (food, temperature, sex)

• responsible for the 4 F’s

4 F’s of Motivation

fighting & flighting (sympathetic), feeding & mating (parasympathetic)

basal ganglia

• regulates muscle contractions for smooth movements

• exerts inhibition for movement and relaxes that body part when the signal is sent

• translates signal in brain into movement

limbic system

• hippocampus (memory)

  • amygdala (emotion)

The amygdala is responsible for what emotions?

fear, rage, fight-or-flight

cerebral cortex/neocortex & four lobes

• four lobes:

  • frontal: front; decision making, personality

  • parietal: near top & back of brain; sensory perception, spatial awareness

  • occipital: back of brain; visual processing

  • temporal: sides of brain near temples; auditory processing, memory

• seat of “higher” intellectual functions

cat transected above the limbic system

acts normal, with purpose, just is clumsy

Dopamine is sent to the forebrain to… & from…

Dopamine is sent to the forebrain to allow basal ganglia to work. It is sent from the substantia nigra.

Parkinson’s Disease attacks…

things that make dopamine, which doesn’t allow basal ganglia to work and prevents smooth movements

CS

conditioned stimulus

CR

conditioned response

US

unconditioned stimulus

UR

unconditioned response

determine the US, UR, CS, & CR for Pavlov’s dogs

• unconditioned stimulus: food

• unconditioned response: salivate

• conditioned stimulus: bell

  • conditioned response: salivate

cerebral hemispheres (cerebrum)

• corpus callosum

• cerebral cortex

corpus callosum

• large band of neural fibers that connects hemispheres

• each hemisphere controls opposite side of body

• largest “commissure” or pathway between brain hemispheres, but not the only one

cerebral cortex (= skin or bark)

• 1 to 3 mm thick, 3ft² if flattened out

• higher motor, sensory, and intellectual functions

Phineas Gage

• pole through frontal lobe (likely pre-frontal area)

• personality change: responsible and gentle → more argumentative

• loss of inhibition of impulsive behaviors due to the lack of social constraints normally imposed through the action of his missing pre-frontal brain areas

Paul Broca

Broca’s area: region in brain responsible for speech

Carl Wernicke

Wernicke’s area: region responsible for comprehension

high-decerebrate cat

• transected just above the midbrain

• can act, but without regard to environment, without purpose

The patient with the damaged amygdala knew the blue slide had been followed by the loud noise, but did not show a fear response (Galvanic skin response) to it. On the other hand, the patient with the damaged hippocampus did show the fear response to the blue slide, but did not remember that the blue slide had been followed by the loud noise during the experiment.

• This is because the amygdala is responsible for a fear response and the hippocampus is responsible for memory.

• A "double dissociation" is strong evidence that these two brain regions are involved in separate independent functions -- and indeed, that the the two functions ARE independent

• US: loud noise, UR: Galvanic skin response (fear)

• CS: blue slide, CR: fear

• US: unconditioned stimulus

  • food in mouth

  • input to a reflex

• UR: unconditioned response

  • salivation to food

  • output of reflex

• CS: conditioned stimulus

  • bell

  • initially results in investigatory response, then habituation

  • after conditioning, results in CR

• CR: conditioned response

  • salivation to bell

  • response to CS

  • measure amplitude, probability, latency

Franz Joseph Gall (1758-1828) 4 discoveries

1. Cortex is a functioning tissue, not just protective covering (bark/skin)

2. Commissures (connecting pathways) exist between brain hemispheres, other than the corpus callosum

3. There is a crossing of ascending nerve pathways from the spinal cord to contralateral hemispheres of the brain

4. Distribution of and distinction between grey matter and white matter tracts

   a. grey matter: neuron cell bodies doing information processing

   b. white matter: mostly myelinated axons sending signals over longer distances

Franz Joseph Gall Phrenology - 4 Items

1. The brain is the material instrument (organ) through which the mind holds intercourse with the outer world

2. The mind has a mix of separate mental abilities, all in its own specific place

3. The size of each center/organ corresponds with the functional efficiency of each faculty

4. The development of the organ is reflected in the shape, size, and irregularities of the cranium

• Believed could measure bumps on the skull to predict mental traits

Why wasn’t Franz Joseph Gall honored in textbooks?

• He believed the degree of development of a mental organ could be measured by the relative size of the corresponding brain area

• He believed the skull fits the brain as a glove fits a hand

blindsight

• brain damage to the visual cortex that leads to blindness

• patients could not hold a card so that its orientation matched a slot, but they could put the card perfectly into a slot

• they can in a sense, see, but they are not aware of seeing

dual-center theory: hypothalamic control centers

one part of the hypothalamus (lateral region) served as the “go” center for eating, while the ventromedial region served as the “stop” center.

rat with ventromedial hypothalamus lesion will…

be a fat rat because it can’t stop eating 💔 #vomit

motor cortex

• region in brain that controls voluntary muscle movements, coordinating and executing motor functions throughout the body

• cerebral cortex in the frontal lobe

somatosensory cortex

• part of the brain that processes sensory information from the body, such as touch, temperature, and pain, providing humans with a sense of physical self

• located in the parietal lobe

visual cortex

• region in brain responsible for processing visual information received from the eyes, allowing humans to perceive and interpret visual stimuli

• located in occipital lobe

auditory cortex

• part of brain that processes auditory information, allows perceiving and interpreting of sounds, including speech and music

• located in the temporal lobe

prefrontal cortex

• part of brain involved in higher cognitive functions, decision making, personality expression, and social behavior regulation

pre-frontal lesion

• damage to prefrontal cortex

• deficits in social behavior regulation, loss of planning, moral reasoning, unable to take action

apraxia

• failure in sequencing components of actions, inability to organize movements

• caused by frontal lesions just forward of the motor cortex

• not paralysis, caused by motor cortex lesion

• can’t tie shoes, brush teeth

• “no doing”