Neurons and Neurotransmitters

n Neuron

• A specialized cell that conducts impulses through the nervous system and contains three major parts:

• Cell body

n Contains nucleus and carries out metabolic functions of the neuron

• Dendrites

n Branchlike extensions of the cell body

n Receive and send messages from other neurons

• Axon

n Slender, tail-like extension of the neuron

n Transmits signal to dendrites or cell body of other neurons, to muscles, glands, and other body parts

Neurons and Neurotransmitters

n Neuron

• Glial cells

n Specialized cells in the brain and spinal cord

n Hold neurons together

n Remove waste (dead neurons) and do clean-up tasks

n Perform manufacturing and nourishing activities

• Synapse

n Junction where axon terminal of a sending neuron communicates with a receiving neuron across the synaptic cleft

• Synaptic cleft

n Tiny, fluid-like gaps separating axon terminals from receiving neurons

Neurons and Neurotransmitters

Types of Neurons

n Afferent neurons (sensory)

• Relay information from the senses to the brain and spinal cord

n Eyes, ears, nose, mouth, and skin

n Efferent neurons (motor)

• Send information from the central nervous system to the glands and muscles

n Enables the body to move

n Interneurons

• Carry information between neurons

n In the brain

n In the spinal cord

Communication between Neurons

n Neurotransmitters

• Chemical substances released into the synaptic cleft from the axon terminal of a sending neuron

• Cross a synapse,

• Bind to appropriate receptor sites on dendrites or cell body of a receiving neuron

• Influence a cell to either fire or not fire

n Receptors

• Protein molecules on surface of dendrites and cell bodies

• Have distinctive shapes

• Only interact with specific neurotransmitters

n Reuptake

• Neurotransmitters taken from the synaptic cleft back into the axon terminal for later use

• Terminates the excitatory or inhibitory effect on the receiving neuron

Communication Between Neurons

The Human Nervous System

n Central Nervous System (CNS)

• Comprises the brain and spinal cord

n Peripheral Nervous System

• Connects the CNS to the rest of the body

n Spinal Cord

• An extension of the brain

• Transmits messages between the brain and the peripheral nervous system

n Hindbrain

• A link between the spinal cord and the brain

• Contains structures that regulate heart rate, respiration, and blood pressure

The Human Nervous System

Major Brain Structures

Major Brain Structures

Major Brain Structures

n Pons

• Relays messages between cerebellum and motor cortex

• Influences sleep and dreaming

n Medulla

• Control center for heartbeat, breathing, blood pressure, swallowing, and coughing

n Reticular Formation

• Arousal system and activates cerebral cortex

n Cerebellum

• Coordinates skilled movement

• Regulates muscle tone and posture

• Role in motor learning and probably cognition

The Forebrain

Neurotransmitters and Their Functions

Variety of Neurotransmitters

Peripheral Nervous System

n Somatic Nervous System

• All sensory nerves

• Transmits sense receptor information (eyes, ears, nose, tongue, and skin) to the central nervous system

• All motor nerves

• Relays CNS messages to the skeletal muscles of the body

The Brain’s Mysteries

Brain activities are revealed via:

n EEG – electroencephalogram

• Records electrical brain wave activity

n CT Scan – computerized axial tomography

• Cross-sectional x-ray images

n MRI – Magnetic resonance imagery

• High resolution images w/o x-rays

n Functional MRI

• Reveals precise brain structure and activity

Brain Waves

n Beta wave

• Associated with physical or mental activity

n Alpha wave

• Associated with deep relaxation

n Delta wave

• Associated with slow-wave deep sleep

n Microelectrode

• Small wire that monitors electrical activity or stimulates a single neuron

The Brain’s Mysteries

n PET Scan – positron emission tomography

• Reveals brain activity based on blood flow, oxygen use, and glucose consumption

n SQUID – superconducting quantum intereference device

• Measures magnetic changes in brain when neurons fire

n MEG – magnetoencephalography

• Measure magnetic changes showing neural activity within the brain as rapidly as it occurs

The Close Up Brain

n Cerebrum

• Largest structure of the brain

• Two cerebral hemispheres

• Connected by the corpus callosum

• Covered by the cerebral cortex

The Close Up Brain

n Cerebral hemispheres

The Close Up Brain

Cerebral hemispheres

n Corpus callosum

• Thick band of nerve fibers connecting the two cerebral hemispheres

• Enables transfer of information and synchronizes activity between hemispheres

n Association areas

• Areas of the cerebral cortex housing memories, involved in thought, perception, and language

n Lateralization

• Functional specialization of one of the cerebral hemispheres

Lateralized Brain Functions

n Left hemisphere

• Controls:

n Right side of body

n Most functions of speech and written language

• Coordinates complex movements

n Right hemisphere

• Controls left side of body

• Specialized for:

n Visual-spatial perception

n Interpreting nonverbal behavior

n Unilateral neglect

• Right hemisphere damage can cause:

n Attentional deficits

n Inability to view objects in the left visual field

The Close Up Brain

The Close Up Brain

The Split Brain

n The Split Brain Operation

• Rare surgical treatment for severe epilepsy

• Corpus callosum is cut, separating the two hemispheres

• Each half has separate sensations, thoughts, and perceptions

• When picture is shown to the right eye:

n Left hemisphere verbally reports what is seen

• When picture is shown to the left eye:

n Right hemisphere remembers what is seen but can not verbally report it

n Can pick out the shown item by touch with left hand

• Increased knowledge about lateralization

Testing A Split Brain Person

n When a visual image (an orange) is flashed on the right side of the screen, it is transmitted to the left hemisphere.

n When asked what he sees, the split-brain patient replies, “I see an orange.”

n When an image (an apple) is flashed on the left side of the screen, it is transmitted only to the right hemisphere.

n Because the split-brain patient’s left hemisphere did not receive the image he replies, “I see nothing.” But he can pick out the apple by touch if he uses his left hand, proving his right hemisphere “saw” the apple.

Handedness

Brain differences suggest hemispheric specialization and development of handedness is related.

• 83% of population is right-handed

• 14% of population is left-handed

• 3% is ambidextrous

• LEFT-HANDERS

n Corpus callosum is 11% larger

n 2.5 million more nerve fibers

n Two sides of brain are less specialized

n New learning is more easily transferred from one side to the other

n Higher rates of learning disabilities and mental disorders

n Less language loss when injured and more likely to recover

n Artists, musicians, and political leaders more likely left-handed

Lobes of the Brain

n Frontal Lobe

• Motor cortex

n Special Language Centers

n Parietal Lobe

• Somatosensory cortex

n Occipital Lobes

• Primary visual cortex

n Temporal Lobes

• Primary auditory cortex

Special Centers of the Brain

n Language

• Broca’s Area

• Wernicke’s Area

n Visual

• Occipital lobe

The Frontal Lobes

n Extend from front of brain to skull’s top center

n Largest of brain lobes

n Contain motor cortex, Broca’s area, & frontal association areas

n Motor cortex

• Rear of frontal lobes

• Controls voluntary body movement

• Participates in learning and cognitive events

n Broca’s area

• Control’s production of speech sounds

n Broca’s asphasia

• Physical inability to create speech or speech sounds

• Caused by damage to Broca’s area

n Frontal association areas

• Thinking, motivation, planning, impulse control, emotional responses

Left Hemisphere Cerebral Cortex

The Frontal Lobes

n Parietal Lobes

• Somatosensory cortex

• Body awareness and spatial orientation

• Somatosensory cortex

n Touch, pressure, temperature, and pain register

n Somatosensory cortex

• Front of parietal lobes

• Touch, pressure, temperature, and pain register

• “Wired” to opposite sides of body

• Affected by experience

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Brain Across Life Span

n When does the brain reach full maturity?

• Growth occurs in spurts from conception into adulthood

• Childhood and adolescent growth associated with physical and intellectual advances

• Each growth spurt involves different brain area

• Age 17-20 frontal lobe growth achieves ability to plan and control emotions

• Gains and loses synapses through out life

• Positive influence ongoing intellectual and motor skill training

n Synaptogenesis

• Dendrites and axons grow as synapses develop

n Myelination

• Development of myelin sheaths around axons

n Plasticity

• Brain’s ability to reorganize or reshape in response to internal and external sources

Gender Differences in the Brain

n Women have equal amounts of gray and white matter

• May explain superior ability to perceive emotions

n Men have more white matter than gray, yet less white matter in left hemisphere

• May explain superior ability in spatial tasks

n Navigational information processed in different parts of brain

• Women use right parietal cortex and right frontal cortex

• Men use left hippocampus

• Both use different areas to process location of sound

n Synapses decrease throughout life

• When older, new synapse growth is slower than decay

n Brain weight decreases begin around 30 years old

n Stroke

• Artery blockage/blood vessel bursting cuts blood supply to brain

• Most common cause of brain damage

• Physical therapy can help recover some brain functioning

Endocrine System

n A system of ductless glands that manufacture hormones and secrete them into the blood stream to affect other parts of the body.

n Hormone

• Chemical made and secreted in one part and affects another part of the body.

n Pituitary gland – “the master gland”

• Controls growth hormone and activates other endocrine glands

n Pineal gland

• Secretes hormone that controls sleep/wakefulness cycle

Endocrine System

n Parathyroid glands

• produce PTH, helps body absorb minerals from diet

n Thymus gland

• Produces essential immune system functioning hormones

n Adrenal glands

• Hormones that prepare body for emergencies and stress also releases corticoids and some sex hormones

n Gonads

• Ovaries in females and testes in males

Genes and Behavioral Genetics

n Genes – segments of DNA on chromosomes transmit heredity traits

n Genotype – an individual’s genetic make up

n Chromosomes – rod shaped; contain all genes that carry genetic information to make a human being

n Dominant-recessive pattern – one dominant gene or two recessive genes required for a trait to be expressed

n Multifactorial inheritance –inheritance pattern in which a trait is influenced by both genes and environmental factors

n Polygenic inheritance – many genes influence a particular characteristic like skin color

n Sex linked inheritance – involves genes on the X and Y chromosomes

• e.g., male or female body type or red-green color blindness

n Behavioral genetics – field of research that uses twin and adoption studies to investigate the relative effects of heredity and environment on behavior

Summary and Review

n What are the functions of the various parts of the neuron?

n How are messages transmitted via the nervous system?

n What are neurotransmitters?

n What do they contribute to nervous system functioning?

n What are the functions of some major neurotransmitters?

n Why is an intact spinal cord important to normal functioning?

n Which brain structures and functions are in the hindbrain?

n What important structure is located in the midbrain?

n Which brain structures and functions are in the forebrain?

n How do the sympathetic and parasympathetic nervous system differ?

n What does an EEG reveal about the brain?

n How are a CT scan and an MRI helpful to study the brain?

n How are a PET scan and new devices used to study the brain?

Summary and Review

n What are the components of the cerebrum?

n What are the specialized functions of the left and right cerebral hemispheres?

n Which psychological functions are associated with the frontal lobes?

n What important structure is found in the parietal lobes?

n Why are the occipital lobes critical to vision?

n What major areas are within the temporal lobes? What are their functions?

n How does the brain change across the life span?

n How do male and female brains differ?

n What functions do the glands of the endocrine system perform?

n What patterns of inheritance are evident in the transmission of genetic traits?

n What kinds of studies are done by behavioral geneticists?