Biological Bases of Behavior
Neural Processing and the Endocrine System
Phrenology
Early 1800s (pre-scientific psychology) Bumps on skull revealed mental
abilities and personality traits Used by academics to justify racism False. First to suggest that different areas of
the brain control different behaviors
Figure 3A.2 A motor neuron
© 2010 by Worth Publishers
Dendrites (close to cell body) receive messages
Axons pass messages on to other cells (may be very long)› End in terminal branches or terminal buttons
The myelin sheath insulates axons and allows messages to travel faster› Lack of myelin causes multiple sclerosis
Nodes of Ranvier - spaces between myelin cells
Demonstration!
Types of Neurons
Sensory neurons relay signals from sensory organs to brain/spinal cord (millions)
Motor neurons relay signals from brain/spinal cord to tissues (millions)
Interneurons process and respond to information (billions)
Neuroglia - Neural Support Cells
Oligodendroglia - produce myelin in the central nervous system
Schwann cells produce myelin in the peripheral nervous system AND can help axons regenerate
Astocytes - form the matrix that holds the other neural cells and blood vessels
Resting Potential
Ions are electrically charged atoms (+ or -)
Potassium (K) and sodium (Na) both form positive ions
Resting potential for a neuron is to have more Na+ outside the axon than there are K+ inside the axon, creating an imbalance
Figure 3A.3Action potential
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Action Potential
A stimulus can cause the axon membrane to allow some Na+ in, depolarizing that segment of the axon
This starts a chain reaction that travels the length of the axon
In the refractory period, sodium-potassium pumps push the Na+ back out of the axon to reset it
A neuron must receive enough signals to reach the threshold for starting the action potential
“all-or-nothing response” means the neuron either reacts or does not react, with the same intensity every time (no partial reactions)› Ex: gun firing, toilet flushing
Neurotransmission
Neurons are separated by the synaptic gap or cleft
Neurotransmitters (NTs) are chemicals that are released into that gap by axons and picked up by dendrites
1. An action potential reaches the terminal buttons of an axon
2. NTs are released into the synapse 3. NTs bind to specific receptors on the
dendrites of second neuron and cause (or stop) an action potential
4. The first neuron reabsorbs extra NTs (reuptake)
5 Nts to Know (see pg 57)
Acetylcholine (ACh)muscle action, learning, memory
Dopaminemovement, learning, attention, emotion
Serotoninmood, hunger, arousal
Norepinephrinealertness, arousal
Endorphins› Natural painkillers, elevate mood
Drugs and NTs
Agonists› Imitate NTs and
create similar reaction
› Bind to receptors and stimulate them
› Ex: cocaine and dopamine
Antagonists› Block functioning of
NT› May prevent NT
release› May bind to
receptor without stimulating it
› Ex: Botox and ACh
The Nervous System
Central› Brain › Spinal cord
Peripheral› Communicates with
sensory receptors, muscles, and glands
› Nerves = bundles of axons
› “edges” of body
Peripheral Nervous System (PNS) Autonomic
› “Automatic” actions, internal organs, glands
› Heartbeat, digestion, breathing
› Can be consciously controlled but usually isn’t
Somatic› Voluntary movement› Actions you are
conscious of and do on purpose
Autonomic Nervous System
Sympathetic› Arousal, deals with
stress› Fight or flight› Dilates pupil,
increases heart rate,, slows digestion, raises blood sugar (increases energy), causes perspiration, relaxes bladder
Parasympathetic› Calming, conserves
energy› Contracts pupil,
slows heart rate, stimulates digestion and gallbladder, contracts bladder
Central Nervous System
In the brain, neurons form “neural networks” where many neurons connect
Networks are created with learning and strengthened with practice
Neurons grow more dendrites to form more connections
Central Nervous System cont.
The spinal cord controls reflexes › Sensory neuron, interneuron, motor neuron
form a simple pathway› Signal does not go through brain at all› Knee-jerk response, pain
Spinal cord also passes signals from brain to PNS
Endocrine System
Endo = internal Create and release hormones
(chemical signals) Hormones travel in the bloodstream
(slower than NTs in brain) Effects of hormones last longer than
NTs
Major Endocrine Glands
Pituitary gland - controlled by hypothalamus, influences growth and the function of other glands
Adrenal glands release adrenaline and noradrenaline, › Increased heart rate, blood pressure, blood
sugar, and energy
Other endocrine glands
Anterior pituitary - growth hormone Posterior pituitary - vasopressin (raises
blood pressure) and oxytocin (causes pregnant women to go into labor)
Thyroid - influences metabolism, growth, and physical maturation
Pancreas - insulin (regulates blood sugar)
Overies - estrogen Testes - androgens
Brain (hypothalamus) > pituitary> other glands> hormones> physical response> brain’s reaction
Brain Structures
Brainstem (hindbrain)
Brainstem functions happen without conscious effort
Medulla - heartbeat, breathing Reticular formation - bundle of nerves that
passes information from spinal cord to brain, involved in arousal› Nerves from left body go to right brain and vice
versa Pons - connects cerebellum to other
structures, contains nerves going from face to brain
Midbrain
Hormones, memory, sensory input Thalamus - traffic control for sensory
input (except smell) Cerebellum: “little brain”
› Coordinates voluntary movement - tells your b rain what to expect from movement
› Tracks time, modulates emotions, discriminates sounds and textures, nonverbal learning/memory, balance
Limbic System (still midbrain)
Amygdala - agression and fear (two parts
Hippocampus – processes memories Hypothalamus (below thalamus) -
controls pituitary gland to regulate functions such as hunger and thirst› Many animals (including humans) have
reward centers in their hypothalamus
Forebrain (Cerebral Cortex)
Contains neurons and glial cells› Glial cells feed neurons, provide myelin,
clean up extra ions and NTs, and guide neural connections
› Higher ratios of glial cells to neurons is associated with greater brain function
Wrinkles on the surface of cortex are made up of gyri (grooves) and sulci (bumps)
Cortex is divided into 2 hemispheres (right and left)
Each hemisphere has 4 lobes Frontal lobes (forehead) – higher level
thinking, personality, motor cortex Parietal lobes (top of head)- sensory Occipital lobes (back of head) - vision Temporal lobes (sides, by ears) -
auditory
Figure 3B.13 Left hemisphere tissue devoted to each body part in the motor cortex and the sensory cortex As you can see from this classic though inexact representation, the amount of cortex devoted to a body part is not proportional to that part’s size. Rather, the brain devotes more tissue to sensitive areas and to areas requiring precise control. Thus, the fingers have a greater representation in the cortex than does the upper arm.
© 2010 by Worth Publishers
Association Areas
Cortex that is not used for motor or sensory purposes
Integrate, interpret and act on information
Frontal: judgment, planning, new memories
Parietal: mathematical and spatial reasoning
Language Processing
Brain subdivides this task into many simpler functions
Reading Out Loud:1. Visual cortex2. Angular gyrus (converts visual to
auditory)3. Wernicke’s area (interprets auditory
code – needed for understanding)
4. Broca’s area (controls speech muscles via motor cortex)
5. Motor Cortex (moves muscles in jaw and throat area)
Plasticity
Brain tissue usually doesn’t regenerate, but it can reorganize itself
Adjusts to losses by using more neurons for other senses/body areas