Unit 2: The Brain

UNIT 2

THE BRAIN

Neural and Hormonal Systems

Neuron

• Terminal branches of axon (from junctions with other cells)
• Axon (passes messages away from the cell body to other neurons, muscles, or glands)
• Meylin Sheath (covers the axon of some neurons and helps speed neural impulses)
• Neural Impulses (electrical signals traveling down the axon)
• Dendrites (receive messages from other cells)
• Cell Body (the cell's life support; support center)
• Neurons do NOT touch each other - the space in between

How does a Neuron fire?

It is an electrochemical process

• electrical inside the neuron
• chemical outside the neuron (in the synapse in the form of a neurotransmitter)
• the firing is called Action Potential

The All-or-None Response

• The idea that either the neural fires or it does not- no part way firing
• like a gun

Steps of Action Potential 

• dendrites receive neurotransmitter from another neuron across the synapse
• reached its threshold- then fires based on the All-or-None response
• opens up a portal in axon, and lets in positive ions (sodium) which mix with negative ions (potassium) that's already inside the axon (thus neurons at rest have a slightly negative charge)
• the mixing of + and - ions causes an electrical charge that pens up the next portal (letting in more K) while closing the original portal
• process continues down the axon to the axon terminal 
• terminal buttons turns electrical charge into chemical (neurotransmitters) and shoots messages to the next neuron across the synapse

Neurotransmitters

• chemical messengers released by the terminal buttons through the synapse

Acetylcholine 

• Its function is motor movement and maybe memory
• If you have too much Ac H you get depression
• If you don't have enough Ac H it leads to Alzheimer's 

Dopamine

• Its function is motor movement and alertness
• Lack of Dopamine is associated with Parkinson's disease 
• Overabundance is associated with Schizophrenia 

Serotonin

• Function deals with mood control
• Does affect hunger, sleep, and arousal 
• Lack of Serotonin has been linked with depression

Endorphins 

• Function deals with pain control
• We become addicted to endorphin causing feelings

GABA

• It's a major inhibitory neurotransmitter 
• An under supply of GABA is linked to seizures, trimmers, and insomnia 

Norepinephrine

• It's associated with alertness and arousal 
• Under supply can depress the mood

Glutamate 

• It's a major excitatory neurotransmitter 
• It's involved in memory
• An oversupply can overstimulate the brain produce migraines or seizures 

Epinephrine 

• Involved in energy and glucose metabolism 
• Too much ca result in anxiety and restlessness 
• Too little has been associated with depression   

Nervous Systems

• Agonists - make neurons fire
• Antagonists - stop neural firing
• Reuptake Inhibitors - block neurotransmitters from entering the neuron

Divisions

Central Nervous System

• The brain and spinal cord 
• CNS

Peripheral Nervous System

• All nerves that are encased in bone
• Everything but the spinal cord and brain
• Divided into 2 categories... Somatic and Autonomic 

Somatic Nervous System

• controls voluntary muscle movement 
• uses motor (efferent) neurons

Autonomic Nervous System

• controls the automatic functions of the body
• divided into 2 categories... the Sympathetic and Parasympathetic 

Sympathetic Nervous System

• fight or flight response 
• automatically accelerates heart rate, breathing, dilates pupils, slows down digestion

Parasympathetic Nervous System

• automatically slows down body after a successful event
• Heart rate and breathing slows down, pupils constrict, and digestion speeds up

Endocrine System 

• a system of glands that secrete hormones 
• similar to nervous system, except hormones work a lot slower than neurotransmitters 

Ways to Study the Brain

Accidents 

 - Phineas Gage story

 - personality changed after the accident

Lesions 

 - Removal destructions of some part of the brain

Electroencephalogram (EEG)

 - detects brain waves through their electrical output

 - used mainly in sleep research

Computerized Axial Tomography (CAT Scan)

 - 3-D Xray of the brain

 - Good for locating tumors, but tells us nothing about function  

Magnetic Resonance Imaging (MRI)

 - More detailed picture of brain using magnetic field to knock electrons off axis

 - Takes many still pictures and turns images into a movie like production

Positron Emission Tomography  (PET Scan)

 - Measures how much of a chemical the brain is using (usually glucose consumption)

Functional MRI

 - Combination of PET and MRI  

Parts of the Brain

Hind-brain

• controls basic biological structures 

Medulla

• part of the hind 
• located just above the spinal cord
• involved in the control of breathing, heart rate, and blood pressure

Pons

• located just above the medulla
• it connects the hind-brain, mid-brain, and fore-brain
• involved with facial expressions and deals with emotions

Cerebellum

• bottom rear of the brain 
• known as the little brain
• coordinates fine muscle movement

Mid-Brain

• coordinates simple movement with sensory information
• the most important structure in the mid-brain is know as reticular formation
• Reticular Formation- controls arousal and ability to focus our attention

Fore-Brain

• what makes us human
• largest part of the brain
• made up of thalamus, lymbic system, and cerebral cortex

Thalamus

• switch board of brain 
• receives sensory signals from the spinal cord and sends them to other parts of the fore-brain
• every sense except smell

Lymbic System

   - Hypothalamus 

• may be the most important structure of the brain
• controls and regulates body temperature, sexual arousal, hunger, thirst, and the endocrine system

   - Hippocampus

• involved in the processing and storage of memories

   - Amygdala

• involved with how we process memory
• also deals with emotions

   - Pituitary Gland

• secretes hormones to your bloodstream

Cerebral Cortex

• made up of packed neurons we call "gray matter"
• Glial Cells- support brain cells
• wrinkles are called fissures

Corpus Callosum

• thick bundle of nerves 
• divides the two hemispheres

Hemispheres 

• brain divided into two hemispheres 
• contralateral control- right controls the left and vice versa
• Left Hemisphere: logic and sequential tasks
• Right Hemisphere: Spacial and creative tasks

Brain Plasticity 

• the idea that the brain, when damaged, will attempt to find new ways to reroute messages 
• Children's brains are more plastic than adults

Four Frontal Lobes

    Frontal Lobe

• Thought and emotional control
• Contains Motor Cortex: sends signals to the body to control muscle movemet
• Contains Borca's Area: responsible for controlling muscles and produce speech
• Damage to Borca's Area is called Borca's Aphasia: unable to make movement to talk

    Parietal Lobe 

• Contains the Sensory Cortex: receives incoming touch sensations from the rest of the body
• Association Areas: any area not associated with receiving sensory information or coordinating muscle movement 

    Occipital Lobe

• deals with vision
• Contains Visual Cortex: interprets messages from our eyes into images we understand 

    Temporal Lobe

• deals with hearing
• process sound sensed by our ears 
• interpreted in auditory cortex
• not laterized
• Contains Wernike's Area: interprets written and spoken speech
• Wernike's Aphasia: unable to understand language- the syntax and grammar jumbled