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