Chapter 4: The Brain and Behaviour Flashcards
Define NEURONS:
- Neurons: specialised cells which are the basic building blocks of the nervous system
- Link together in circuits
- Can vary greatly in size and shape
- Function to receive, process and send messages
- Neurons generate electricity that creates nerve impulses
- Release chemicals that communicate to other neurons, muscles and glands
What are the three main parts of the neurons?
- Cell Body
- Dendrites
- Axon
Explain the CELL BODY:
o Cell body
Also “soma” contains biochemical structures needed to keep the neuron alive, nucleus carries genetic information that determines how the cell develops and functions
Surface of cell body has receptor areas that can be directly stimulated by other neurons.
Explain the DENDRITES
o Dendrites
Emerge from the cell body in branch-‐like fibres. They are specialised receiving units that collect messages from neighbouring neurons and send them on to the cell body where information is combined and processed.
Explain the AXON:
Conducts electrical impulses away from the cell body to other neurons, muscles or glands
Branches out at its end to form axon terminals which may connect with dendrites from numerous neurons
What are GLIAL CELLS?
Glial cells of the peripheral nervous system include SHWANN CELLS, which form the MYELIN SHEATH, and SATELLITE CELLS, which provide nutrients and structural support to neurons.
GLIAL CELLS PURPOSE?
• Supported in function by glial cells (Greek roots for “glue”)
o Surround neurons and hold them in place
o Manufacture nutrient chemicals that neurons need
o Absorb toxins and waste that would damage/kill neurons
o Send out long fibres to guide newly developed neurons to targeted places during prenatal development, as new neurons are formed through cell division
How do nerve impulses occur in 3 steps?
• How nerve impulses occur: (3 steps)
o 1. At rest, neuron has electrical resting potential due to – and + ions distributed inside/outside the neuron
o 2. Action potential or nerve impulse produced when stimulated – i.e. ions flow in and out through cell membrane and reverse electrical charge of resting potential
o 3. Original ionic balance is restored, neuron is again at rest
What is the RESTING POTENTIAL?
• RESTING POTENTIAL:
o 1. Neurons surrounded by body fluids – separated by membrane
o 2. Membrane a sieve with ion channels which allow some substances in, limit others
o 3. Nerve impulse = flow of ions
- ***** Outside membrane Na+ and Cl-‐, inside K+ and negatively charged protein ions
- ***** High Na+ concentration outside and high protein ion concentration inside
- ***** This creates a difference of 70mV and is the neurons resting potential
What is ACTION POTENTIAL?
• ACTION POTENTIAL:
o 1. -‐70mV to +40mV when the neuron is stimulated – action potential/nerve impulse
o 2. When neuron is stimulated, sodium channels open up
o 3. Sodium ions flood through channels attracted by negatively charged protein ions: creates state of depolarisation
o 4. Restores to resting potential when positively charged potassium ions flow out through channels
What is ABSOLUTE REFRACTORY PERIOD?
o 1. Period once impulse has passed a point along the axon
o 2. When potassium ions are flowing out
o 3. Membrane not excitable, cannot discharge another impulse
What is GRADED POTENTIALS?
graded potentials are when changes in the negative resting potential do not reach the -‐50mV action potential threshold required, and thus do not create an action potential at all
What is the MYELIN SHEATH?
- Structure and Purpose
• Myelin sheath: a whitish, fatty insulation layer derived from glial cells during development.
- Covers many axons that transmit through brain and spinal cord
- Interrupted at regular intervals by Nodes of Ranvier
- Axons lacking myelin sheath – “fuse-‐like” transfer of action potential
- Myelinated axons – Nodes of Ranvier allow more frequent depolarisation and thus higher electrical conduction speeds
How do neurons talk: STEP 1
Step 1
• Regulating ion flow in and out of the cell body and creates a resting membrane potential
- Meaning a voltage difference between the inside and outside of the neuron ****(-‐75 millivolts)
- Meaning a teeny-‐tiny battery
How do neurons talk: STEP 2
Step 2:
• Excitatory and inhibitory messages from other neurons (via dendrites) change resting potential
• If enough excitatory messages are received, resting potential will excess a threshold ****(~-‐55mv)
How do neurons talk: STEP 3
Step 3:
• This initiates a rapid depolarization at the axon hillock which creates a current that moves down the axon
• This current is called an action potential
Action Potentials:
• Depolarization and repolarization occurs in less than ***0.02 seconds
- Depolarization “overshoots” and repolarization “undershoots”
- This slows down the action potential and leads to a refractory period of about **0.0015 seconds
How do neurons talk: STEP 4 - The problem and Solution(s)
Step 4: the Problem
• For a number of reasons, the charge sent down the axon wouldn’t travel far enough or fast enough if not for some help
Step 4: The solution (PART I):
• One form of help comes form the oligodendrocytes (a type of glial cell) that form the myelin sheath
• The myelin sheath prevents the ions from escaping
Step 4: The solution (PART II):
• The Nodes of Ranvier act like the amplifiers that re-‐generate the action potential
How do neurons talk: STEP 5
Step 5:
• Ultimately, the current reaches the end of the axon
- While communication within the neuron is purely electrical this is not how it goes between neurons
- Arrival of action potential at ***presynaptic axon terminal triggers release of chemicals (neurotransmitters)
How do neurons talk: STEP 6
Step 6:
• Neurotransmitters enter the synaptic cleft and float through cerebrospinal fluid
• Some then bind with receptors on dendrites of adjacent neurons
How do neurons talk: STEP 7
Step 7:
• Depending on the neurotransmitter and the dendrite, two things can happen…
***** Excitatory post synaptic potential (ESSP): depolarizes postsynaptic neuron
**** Inhibitory post-‐synaptic potential (ISSP): hyperpolarizes postsynaptic neuron
What is the Synaptic Space
• Synaptic space: a tiny gap between the axon terminal and the next neuron
What are NEUROTRANSMITTERS?
• Neurotransmitters: chemical substances that carry messages across the synaptic space to other neurons, muscles or glands
5 STEPS in the PROCESS of CHEMICAL COMMUNICATION:
LIST
• 5 steps in this process of chemical communication:
- Synthesis
- Storage
- Release
- Binding
- Deactivation
Explain the 5 steps of CHEMICAL COMMUNICATIONS:
- Synthesis: transmitter molecules formed inside neuron
- Storage: molecules stored in synaptic vesicles, or chambers within axon terminals
- Release: when action potential comes down axon, vesicles move to surface of axon terminal and molecules are released into fluid-‐filled space between axon of presynaptic (sending) neuron and membrane of postsynaptic (receiving) neuron
• 4. Binding: molecules cross synaptic space and bind to receptor sites, large protein molecules embedded in the receiving neuron’s cell membrane. Transmitters will match only a particular receptor molecule in the postsynaptic membrane.
o Chemical reaction occurs during binding: two effects on receiving neuron
o Excitation or inhibition
**Excitation: sodium channels open and depolarisation, creating a graded potential or action potential
. ***Inhibition: potassium ions or negative chloride ions flow, increasing neuron’s negative potential and making it harder to fire the neuron.
• 5. Deactivation: once a neurotransmitter molecule binds to its receptor, it continues to excite or inhibit the neuron until it is deactivated or shut off.
o **some are broke ndown by other chemicals
o **some are deactivated by reuptake, where transmitter molecules are taken back into the presynaptic axon terminals
What are NEUROMODULATORS?
• Specialised neurotransmitters: neuromodulators
o circulate through the brain and increase or decrease sensitivity of neurons to their specific transmitters
e.g. endorphins
What re the 3 major neuron types:
• 3 major neuron types:
o Sensory neurons – carry input messages from sense organs to spinal cord and brain
o Motor neurons – transmit output impulses from the brain and spinal cord to body’s muscles and organs
o Interneurons – perform connective or associative functions within the nervous system
Define Peripheral Nervous System:
• Peripheral nervous system:
contains all neural structures that lie outside of the brain and spinal cord. Neurons are interneurons.
How can the Peripheral Nervous System be broken down?
PERIPHERAL NERVOUS SYSTEM
- Somatic Nervous System
- Autonomic Nervous System
- — Sympathetic Nervous System
- — Parasympathetic Nervous System
Explain the Somatic Nervous System:
Somatic nervous system:
sensory neurons specialised to transmit messages from sensory receptors, and motor neurons. The axons of these nerves group together to form sensory nerves and motor nerves.
Specialises in voluntary muscle action
Explain the Autonomic Nervous System:
Autonomic nervous system: regulates body’s internal environment; controls involuntary functioning i.e. muscles forming the heart, blood vessels, lining of stomach and intestines, and glands. Thus it regulates respiration, circulation and digestion
***** CAN BE SEPARATED INTO 2 PARTS
- Sympathetic nervous system
- Parasympathetic nervous system
Sympathetic vs Parasympathetic nervous system
Sympathetic nervous system (generally activates; speeds up)
Parasympathetic nervous system (generally inhibits; slows down)
(part of the autonomic nervous system)
What is the CNS?
PARTS?
• Central nervous system (CNS):
connects most parts of the peripheral nervous system (PNS) with brain
SPINAL CORD AND BRAIN
What is the Spinal Cord?
Spinal cord: where most nerves enter and leave central nervous system. Vertebrae (bones of the spine) protect the spinal cord’s neurons.
Spinal reflexes, or simple stimulus-‐response sequences, can be triggered at the level of the spinal cord without any involvement of the brain.
This significantly reduces reaction time in quick situations, e.g. touching something hot.
What is the Brain?
Brain: protein, fat and fluid. The primary control of the nervous system. It can be studied using neuropsychological testing, destruction and stimulation techniques (removal of brain portions or chemical stimulation of an area), electrical recording which stimulates and records brain activity (e.g. the electroencephalograph), and brain imaging (CT scans and MRIs for visualising brain structure, PET scans and fMRIs to view brain activity).
What is the BRAIN PARTS?
- HINDBRAIN
- MINDBRAIN
- FOREBRAIN
What is the HINDBRAIN? PARTS?
Hindbrain: supports vital life functions -‐ most primitive level.
• See: cerebellum, spinal cord, brain stem, medulla, pons (diagram)
What is the MIDBRAIN? Parts?
Midbrain: contains clusters of sensory and motor neurons. Contains relay centres for visual and auditory systems.
• Constituted by reticular formation
Whta is the Forebrain? Parts?
Forebrain: brains most advanced portion. Structures include:
- thalamus
- hypothalamus (connected with the endocrine system)
- the limbic system (involved in memory, and coordinates behaviours to satisfy urges that arise in the hypothalamus – hippocampus, amygdala),
- Cerebral cortex (outer layer of brain, cerebrum) which is divided into the frontal, parietal, occipital and temporal lobes; primary motor cortex, somatic sensory cortex, wernicke’s area, broca’s area, association cortex, frontal lobes, and the prefrontal cortex (see figures 4.14 and 4.15 on page 115)
• *****Primary motor cortex: controls muscles involved in voluntary body movements. Each hemisphere governs movement on the opposite side of the body (nerve tracts from the motor cortex cross over at the level of the medulla)
• **Somatic sensory cortex: receives sensory input that gives rise to sensations of heat, touch and cold, and sense of balance and body movement.
• **Wernicke’s area: temporal lobe. Primarily involved in speech comprehension.
• **Broca’s area: in the frontal lobe. Involved in production of speech through connections with the motor cortex region that controls the muscles used in speech.
• **Association cortex: perception, language and thought – important mental functions. 75% human cerebral cortex. Agnosia, the inability to identify familiar objects, occurs with damage to his area.
• **Frontal lobes: 29% of cortex. Involved in emotional experience
Prefrontal cortex: region of the frontal cortex. Seat of executive functions such as goal setting, judgement, strategic planning and impulse control (Phineas gage primary example of effects of damage to this area)
Whta is CORPUS CALLOSUM?
• Corpus callosum: neural bridge consisting of white myelinated fibres that acts as a major communication link between the two hemispheres and allows them to function as a single unit.
What is LATERALISATION?
• Lateralisation: relatively greater localisation of a function in one hemisphere or the other.
Right hemisphere accounts for mental imagery, musical and artistic abilities and the ability to perceive and understand spatial relations
Left… ?
• We have an optic chiasma over which the fibres of the optic nerve for each eye cross over and travel to the opposite brain hemisphere. This produces a unified image.
What is NEURAL PLASTICITY?
• Neural plasticity: the ability of neurons to change in structure and function
• Brain loses some plasticity over time
*****greatest amount of brain synapses at birth
- Production of new neurons in nervous system is called neurogenesis.
- Stem cells may hold the key to countering the effects of aging on brain functioning – but further research is required.
How experience influences brain development: examples - NEURAL PLASTICITY
- Chronic alcoholism inhibits the production of new neural connections in the hippocampus – this impairs learning, memory and other cognitive functions
- Life stress has a similar negative effect on neuron formation in the brain, thereby causing or maintaining clinical depression
- Cultural factors – e.g. Chinese language based on pictures means less left-‐hemisphere lateralisation of language amongst native Chinese speakers.
What is Endocrine System?
• Endocrine system: consists of numerous hormone-‐secreting glands distributed throughout the body
*****conveys messages using hormones, chemical messengers that are secreted from its glands into the bloodstream, rather than neurons
• hormones influence our development, capacities and behaviour before we’re born
What is the ADRENAL GLANDS?
• Adrenal glands:
twin structures perched atop the kidneys that serve as hormone factories producing and secreting about 50 different hormones that regulate many metabolic processes within the brain and other parts of the body
****produce dopamine as well as several stress hormones
SIZE OF THE BRAIN MATTER?
- There has been steady growth in the brain capacity and size of the brain cavity over the past 3 million years
- Ratio of the size of the brain relative to the size of the body; the smaller the ratio the more complex the organism
What is GROSS STRUCTURE?
- Two asymmetric hemispheres connected by “corpus callosum”
- Sulcus are like guidelines, prominent valley that acts like a landmark in the same way that rivers separate countries
- The pre-‐occipital notch works in the same way as a dent
WHAT IS THE DETAILED STRUCTURE(S)
- Cytoarchitectonics: division of the brain based on differences in structure of stained tissue
- Korbinian Brodmann (1868-‐1918)
- He we would stain the difference sections of the brain
- Making a map of the brain by dividing it up based upon how the cells look.
- The structure is different as the function is different
Explain the BRAIN at CELLULAR STRUCTURE?
• The Brain: consists of glial cells and neurons
• Neurons: process information
100 billion in adult brain
100 trillion neuronal connections
- Neurons: Performs to process information quickly; have a lot of raw computational power
- Glial Cells: provide structure to the brain, carries off waste, protect the brain from foreign objects, the support crew
Parts of the Brain and What does it do?
FRONTAL CORTEX
Frontal Cortex ‘Executive Function’ such as planning, inhibition, working memory
Parts of the Brain and What does it do?
CORTEX: MOTOR
Cortex: Motor Contains 3 areas:
- PRIMARY: planning
- PRE-‐MOTOR: selection of movements
- SUPPLEMENTARY: bimanual coordination
Parts of the Brain and What does it do?
CORTEX: SOMATOSENSORY
Cortex:
Somatosensory
Responsible for processing pressure, pain, temperature
Feedback about things happening to your body
Parts of the Brain and What does it do?
CORTEX VISUAL
Cortex: Visual
Processes form, motion, orientation, color, object identification; Area 17
Lowest areas contain accurate spatial “map” of visual world
Parts of the Brain and What does it do?
CORTEX AUDITORY
Cortex: Auditory
Processes sound frequency, location, music, prosody (the tone of language, the way we say
words), oral language helps decipher intent and meaning
Parts of the Brain and What does it do?
lLIMBIC SYSTEM
Limbic System
“Older mammalian brain”
Involved in key aspects of memory, reward and emotional processing
Parts of the Brain and What does it do?
BASAL NUCLEI
INVOLVED IN
Motor suppression
Motor learning
Motor response selection
Enacts the functions of the motor cortex and desire to move
Parts of the Brain and What does it do?
CEREBELLUM
- Coordinates complex movement
- Stores procedural memories (motor learning)
- Balance and posture; learned reflexes
Parts of the Brain and What does it do?
BRAIN/HINDBRAIN
Regulates breathing, basic autonomic functioning; sleep/wakefulness
What are traditional methods?
- Lesions: brain tissue can be damaged by injury, stroke, disease or surgery
- The Logic: “if area X does function Y, a lesion to X should impair function Y”
- Problems:
a) Injury often extensive; i.e. it isn’t discrete
b) Impairment often extensive
c) “Compensatory” changes in other brain areas; the brain requires itself in response to injury, the brain becomes more adaptive to the lesion. The behaviour may be more a response to this rather than the lesion itself
d) Convenience sample
What are modern methods?
Modern Methods:
- The logic: “to figure out what part of the brain does what, figure out where it’s active during a task”
- How to map activity:
a) Electrical activity (neurons)
b) Blood flow
Define ELECTROENCEPHALOGRAM?
• Electroencephalogram: records electrical fields generated by groups of neurons firing action potentials
Provides gross estimate of overall brain activity
What is EVENT-RELATED POTENTIALS (ERPSs)
• Event-‐related potentials (ERPs): Isolates activity due to a particular event from overall EEG
FUNCTIONAL MAGENTIC RESONANCE IMAGING (fMRI):
Blood flow
• Functional Magnetic Resonance Imaging (fMRI): Imaging protons in hydrogen that are part of water molecules in the bloodstream; Resolution: ~ 1mm3
How to isolate Activity?
How to isolate activity?
• FMRI measures whole-‐brain activity. Which area is activated in response only to what I’m interested in?
Do activity of interest –> Measure blood flow Measure blood flow
Explain Beyond Correlation:
Beyond Correlation:
- ERPs and FMRI are all correlative. How do we know activity causes behaviour
- Transcranial magnetic stimulation (TMS)
How does TMS work?
How does TMS work? Electric current disrupts brain activity creating “virtual lesion”
