brain and brain dunctions

Some methods for understanding brain structure and function

1. effects of brain damage (e.g., stroke, lesions, traumatic brain injury)

2. observing the brain in action (e.g., PET, fMRI

MRI vs fMRI

1. MRI - studies brain anatomy

2. fMRI - studies brain function

Major brain Components

1. spinal cord→part of CNS, but can function independently of brain

2. brainstem→basics for survival

3. cerebellum→movement

4. subcortical structures→basic drives and emotions

5. cerebral cortex→complex mental activity

Brainstem

1. medulla →vital involuntary functions (breathing, heart rate, blood pressure)

2. pons → connects cerebellum to rest of brain; sleep, arousal, facial expressions

3. midbrain → sensory reflexes, movement, pain, orientation in environment

4. reticular formation → sleep, arousal, attention

5. cerebellum → balance, motor coordination; motor control, but also other function damage = deficits to perception. language, cognition

Forebrain

1. highest level of brain

2. complex cognitive, emotional, sensory and motor functions

Cerebral cortex

1. Frontal Lobe →

   thought, planning movement

2. Parietal Lobe →

   touch, spacial relations

3. Temporal Lobe →

   hearing, memory

4. Occipital Lobe →

   vision

Specialization and Localization of Function in Cerebral Cortex

1. Motor Cortex - voluntary movement functions

2. Somatosensory cortex → processing sensory information from the body, including touch, temperature, and pain

3. Broca's area →

   language production

4. Wernicke's area →

   language comprehension

5. auditory cortex

6. visual cortex

aphasias

1. Broca's aphasia →

   non-fluent speech with difficulty in producing grammatically correct sentences

2. Wernicke's aphasia →

   fluent but nonsensical speech

Subcortical structures

(limbic system) →

motivation, emotion, memory

1. Thalamus →

   sensory relay station, consciousness

2. Basal ganglia →

   voluntary movement

3. Amygdala →

   fear, disgust, aggression

4. Hippocampus →

   memory formation

5. Hypothalamus →

   regulates temperature, hunger, hormone release, activity of ANS, "pleasure center"

6. Nucleus accumbens →

   reward, pleasure, social inclusion

Split-brain research

Hemispheric specialization ↓

1. right brain: facial recognition, spatial and perceptual tasks

2. left brain: language center

Contralateral processing

sensory or motor functions on one side of the body are controlled or processed by the opposite hemisphere of the brain

Neuroplasticity

interplay of genes and enironment during development wires the brain

recovery from injury

Peripheral Nervous System (PNS)

1. Somatic nervous system →controls skeletal muscles (arms, legs)

2. Autonomic nervous system →

   controls visceral muscles (eyes, heart, stomach)

Autonomic nervous system

1. Sympathetic nervous system →

activating functions ('flight or flight').

2. Parasympathetic nervous system →

deactivating functions ('rest and digest')

3. Enteric nervous system →

   nerve cells in gut; communicates with endocrine system

Nervous system vs Endocrine system ↓

1. Nervous system: communicates with nerve cells

2. Endocrine system: communicates with hormones; coordinates with nervous system via hypothalamus

Neuron

basic unit of nervous system

communicates with other cells through electrical impulses and chemical signals

receives and integrates information in nervous system

Components of Neuron

1. Dendrites: Collect information

2. Cell body: Integrates information

3. Axon: Transmits information

Axon terminal

Synapse

Types of Neurons

Sensory neurons→Incoming information to CNS (afferent)

Motor neurons→Outgoing information from CNS to muscles (efferent)

Interneurons→Connect sensory, motor, or other interneurons

More on interneurons

Vastly outnumber sensory and motor neurons

Facilitate transmission of information within CNS; integration and organization functions

Glial Cells

Support structure; formation of myelin

Physical and metabolic support for neurons

Formation of blood-brain barrier

Supply nutrients to neurons

Myelin Sheath

provides insulation for axons

increases neural transmission speed

action potentials can 'jump' across Nodes of Ranvier

not all axons are myelinated

How do neurons communicate?

Action potential: occurs at Nodes of Ranvier

Electrical signaling through depolarization and hyperpolarization

Membrane potentials

1. Resting membrane potential ↓

electrical difference between inside and outside of neuron

in resting state, charge inside neuron is slightly more negative than outside

2. Depolarization ↓

Excitatory signal: Neuron more likely to fire

Channel opens in cell membrane to allow sodium ions in; charge inside neuron becomes more positive

3. Hyperpolarization
   Inhibitory signal: Neuron less likely to fire

   Sodium channels less likely to allow sodium into neuron

   Charge inside neuron becomes more negative than at resting potential

What Occurs at the Synapse? ↓

Action potential results in release of neurotransmitters at synapse

Neurotransmitter: Chemical communication across neurons

Termination of Neurotransmission

→

reuptake, autoreceptors, enzyme deactivation

General Categories of Neurotransmitters

1. Acetylcholine ↓’ motor control; learning, memory, sleeping, dreaming

2. Monoamines → arousal, motivation

3. Amino acids → general excitatory and inhibitory processes

4. Peptides → modulate neurotransmission

Monoamines

1. Epinephrine (adrenaline) ↓

sympathetic nervous system responses ('fight or flight')

pupil dilation

increase in blood flow and blood sugar

2. Norepinephrine ↓

   arousal and vigilance

   shortage: depression | excess: mania

3. Dopamine ↓

   reward and motivation

   motor control over voluntary movement

   shortage: depression | excess: schizophrenia

4. Serotonin ↓

   physiological arousal, sleep-wakefulness

   aggression (if low)

   shortage: depression | excess: mania

Amino acids

1. GABA (gamma-aminobutyric acid) ↓

inhibition of action potentials

shortage: anxiety, epilepsy, hungtington's

excess: unmotivated

2. Glutamate ↓

   enhances action potentials

   learning and memory

   increased speed of synaptic connections

Peptides

1. CCK (cholecystokinin) → digestion, satiety (administer before meal and feel fuller sooner)

2. Endorphins → pain reduction, reward

3. Substance P → pain perception

Agonists and antagonists

1. Agonist → increases/amplifies effect of neurotransmitter

2. Antagonist → decreases/dampens/blocks effect of neurotransmitter

Psychoactive drugs

1. Tricyclic antidepressants ↓

2. SSRIs ↓

   
   

3. Antipsychotics ↓

   
   

4. Alcohol, Sedatives ↓

   
   

5. Amphetamines, Cocaine ↓

   
   

6. Nicotine ↓

   
   

7. Benzodiazepines ↓

   
   

8. Opioids ↓

   
   

9. Hallucinogenics ↓

   
   

10. Marijuana ↓

    
    

1. Tricyclic antidepressants ↓

agonist

inhibit reuptake of norepinephrine

treatment for depression, ADHD, chronic pain

SSRIs ↓

agonist

selective serotonin reuptake inhibitors

treatment for depression, anxiety, OCD, eating disorders

Antipsychotics ↓

antagonists

dopamine (typical) & serotonin (atypical)

treatment of schizophrenia, bipolar disorder

Alcohol, Sedatives ↓

glutamate inhibitors

mimic effects of GABA

Amphetamines, Cocaine ↓

agonists

increase norepinephrine and dopamine by blocking reuptake

activate SNS (increase heart rate and blood pressure)

Nicotine ↓

agonist

acts on same sites as acetylcholine (Ach)

excess of Ach b/c receptors activated by both Ach and nicotine

brain then decreases production of Ach; more nicotine is required (pos feedback loop)

Benzodiazepines ↓

increase response to GABA (relaxes)

Opioids ↓

activate receptors that usually respond to endorphins

increased activation in nucleus accumbens, binding with opiate receptors

highly addictive due to dual activation of dopamine and opiate receptors

Hallucinogenics ↓

ex: LSD

LSD has similar structure to serotonin

Marijuana ↓

THC stimulates release of dopamine

produces relaxed mental state, perceptual distortions