Chapter 2: Neuroscience and Behavior

Chapter 2: Neuroscience and Behavior

Neurons and Synapses Types of Neurons Sensory Motor Interneurons 3

Figure 2.1 Glial Cells: Not Just Glue
This fluorescence micrograph of human brain tissue shows star-shaped glial cells (red) and their nuclei (yellow). Outnumbering brain neurons by about 10 to 1, glial cells provide support and nutrition for neurons. The type of glial cells shown here, called astrocytes, provide connections between neurons and blood vessels in the brain. Other types of glial cells form the myelin sheath, a fatty insulating substance wrapped around some neuron axons. Beyond those functions, researchers now know that glial cells are much more actively involved in regulating neuronal communication and activity than previously believed (see Gibbs & others, 2008; Theodosis & others, 2008).

Sensory Neurons INPUT From sensory organs to the brain and spinal cord
Drawing shows a somatic neuron Sensory Neuron Spinal Cord 5

Motor Neurons OUTPUT From the brain and spinal cord, to the muscles and glands Spinal Cord Brain Sensory Neuron Motor 6

Interneurons Interneurons carry information between other neurons only found in the brain and spinal cord Spinal Cord Brain Sensory Neuron Motor 7

Simple Neuron Model Your hand represents the "cell body"
Your fingers represent "dendrites" bringing information to the cell body Your arm represents the "axon" taking information away from the cell body.

Parts of a Neuron 9

The Cell Body Contains the cell’s nucleus
round, centrally located structure contains DNA controls protein manufacturing directs metabolism no role in neural signaling 10

Dendrites Information collectors
Receive inputs from neighboring neurons Inputs may number in thousands If enough inputs, the cell’s AXON may generate an output 11

Dendritic Growth Mature neurons generally can’t divide
But new dendrites can grow Provides room for more connections to other neurons New connections are basis for learning 12

Axon The cell’s output structure One axon per cell, 2 distinct parts
tubelike structure branches at end that connect to dendrites of other cells 13

Myelin Sheath White fatty casing on axon
Acts as an electrical insulator Not present on all cells When present, increases the speed of neural signals down the axon 14

Neurons and How They Work

How Neurons Communicate demonstration
Neurons communicate by means of an electrical signal called the action potential Action potentials are based on the movements of ions between the outside and inside of the cell When an action potential occurs, a molecular message is sent to neighboring neurons Resting potential is the state when the neuron is prepared to activate if sufficient stimulation is received.

Action Potential Within a Neuron

Neuron to Neuron Axons branch out and end near dendrites of neighboring cells Axon terminals are the tips of the axon’s branches A gap separates the axon terminals from dendrites Gap is called the synapse . 18

Basic Brain Structures

Neurotransmitter Release
Action potential causes synaptic vesicle to open Synaptic vesicles hold chemical messengers called neurotransmitters Neurotransmitter released into synaptic gap

Transmission of Information
Communication occurs in 2 ways Electronically – instantaneous Chemically – 99% of synapses in brain Reuptake – neurotransmitter molecules are reabsorbed by presynaptic neuron to be used again.

Neurotransmitters Neurotransmitter sends either
Excitatory message – increases action potential Inhibitory message - decreases chance neuron will activate

Types of Neurotransmitters
Acetylcholine Dopamine Serotonin Norepinephrine GABA Endorphins 24

Acetylcholine (Ach) Found in neuromuscular junctions
Involved in muscle movements Involved in learning and memory 25

Disruptions of Acetylcholine Functioning
Curare—blocks ACh receptors paralysis results Nerve gases and black widow spider venom; too much ACh leads to severe muscle spasms and possible death 26

Disruptions of Acetylcholine Functioning
Cigarettes—nicotine works on ACh receptors can artificially stimulate skeletal muscles, leading to slight trembling movements 27

Alzheimer’s Disease Deterioration of memory, reasoning, and language skills Symptoms may be due a to loss of ACh neurons 28

Dopamine Involved in movement, attention, and learning
Dopamine imbalance also involved in schizophrenia Parkinson’s disease is caused by a loss of dopamine-producing neurons 29

Parkinson’s Disease Results from loss of dopamine-producing neurons in the substantia nigra Symptoms include difficulty starting and stopping voluntary movements tremors at rest stooped posture rigidity poor balance 30

Parkinson’s Disease Treatments L-dopa
transplants of fetal dopamine-producing substantia nigra cells adrenal gland transplants electrical stimulation of the thalamus has been used to stop tremors 31

Involved in depression
Serotonin Involved in sleep Involved in depression Prozac works by keeping serotonin in the synapse longer, giving it more time to exert an effect 32

“Fight or flight” response
Norepinephrine Arousal “Fight or flight” response 33

Endorphins Control pain and pleasure Released in response to pain
Morphine and codeine work on endorphin receptors; involved in healing effects of acupuncture Runner’s high— feeling of pleasure after a long run is due to heavy endorphin release 34

GABA Inhibition of brain activity
Huntington’s disease involves loss of neurons in striatum that use GABA Symptoms: jerky, involuntary movements mental deterioration 35

Identify Parts of a Neuron
Copyright © Allyn & Bacon 2008

Summary Neuron structure Action potentials Synapses Neurotransmitters
37

Parts of the Nervous System
Central nervous system (CNS) Brain and spinal cord Peripheral nervous system (PNS) Carries messages to and from CNS

Central nervous system
Peripheral nervous system 39

Peripheral Nervous System
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 Copyright © Allyn & Bacon 2008

Sympathetic and parasympathetic divisions of the nervous system
44

Endocrine System Pituitary gland—attached to the base of the brain, hormones affect the function of other glands Adrenal glands—hormones involved in human stress response Gonads—hormones regulate sexual characteristics and reproductive processes; testes in males, ovaries in females

Brain Plasticity – capacity to change in response to experience
Functional plasticity - Brain has the ability to shift functions from damaged to undamaged brain areas Structural plasticity – Brain can physically change its structure in response to learning, practice or stimulation

Major Brain Structures
Copyright © Allyn & Bacon 2008

Brain Brainstem Hindbrain Midbrain Forebrain Limbic system Cortex 49

Forebrain Structures Thalamus Limbic System Cortex 50

Thalamus Relay station in brain
Processes most information to and from higher brain centers 51

The Limbic System Hypothalamus Amygdala Hippocampus
Group of structures involved in emotional expression, memory, and motivation Hypothalamus Amygdala Hippocampus 52

The Forebrain Thalamus Acts as relay station for information in and out of forebrain Hypothalamus Controls hunger, thirst, and body temperature; involved in emotions; helps control the endocrine system Amygdala A role in emotional responses to unpleasant or punishing stimuli Hippocampus Memory storage, navigation, and response to new or unexpected stimuli Copyright © Allyn & Bacon 2008

Hypothalamus Contains nuclei involved in a variety of behaviors
sexual behavior hunger and thirst sleep water and salt balance body temperature regulation circadian rhythms role in hormone secretion 54

Hypothalamus and Hormones
Hypothalamus releases hormones or releasing factors, which in turn cause pituitary gland to release its hormones 55

Brain Development Emotions and the Brain

Amygdala and Emotion Identify emotion from facial expressions
Amygdala damage makes this task difficult. (click on picture to advance photos) 57

Hippocampus In the limbic system Stores new memories Responds to new/unexpected stimuli Aids in navigational abilities saf&template=template.html&query=hippocampus&category=0& viKeyword=hippocampus&submit=Search Copyright © Allyn & Bacon 2008

The Human Nervous System
Hindbrain A link between the spinal cord and the brain Contains structures that regulate heart rate, respiration, and blood pressure Spinal Cord An extension of the brain Transmits messages between the brain and the peripheral nervous system Copyright © Allyn & Bacon 2008

Hindbrain Structures Cerebellum Brainstem medulla reticular formation
pons 61

Cerebellum Coordinates skilled movement Regulates muscle tone and posture Role in motor learning and probably cognition Pons Relays messages between cerebellum and motor cortex Influences sleep and dreaming Medulla Control center for heartbeat, breathing, blood pressure, swallowing, and coughing Reticular Formation Arousal system and activates cerebral cortex Copyright © Allyn & Bacon 2008

Cerebellum Coordinated, rapid voluntary movements Lesions to
playing the piano, kicking, throwing, etc. Lesions to cerebellum jerky, exaggerated movements difficulty walking loss of balance shaky hands 63

Medulla Breathing Heart rate Digestion Other vital reflexes swallowing
coughing vomiting sneezing 64

Reticular Formation Network of neurons in the brainstem (and thalamus)
Sleep and arousal Attention 65

Pons Helps coordinate movements on left and right sides of the body
eg, postural reflexes that help you maintain balance while standing or moving 66

Lobes of the Cortex Frontal lobe—largest lobe, produces voluntary muscle movements; involved in thinking, planning, and emotional control Temporal lobe—primary receiving area for auditory information Occipital lobe—primary receiving area for visual information Parietal lobe—processes somatic information

Phineas Gage tchonline.htm?user5=pbs- saf&template5=publishmain.html&qu ery5=scientific+american&squery5=s query%3D%252BClipID%3A2%2B% 252BVideoAsset%3Apbssaf1302&sel ect4=77000&submit5=GO M-nDYzX0

The Close Up Brain Cerebral hemispheres Corpus callosum Thick band of nerve fibers connecting the two cerebral hemispheres Enables transfer of information and synchronizes activity between hemispheres Association areas Areas of the cerebral cortex housing memories, involved in thought, perception, and language Lateralization Functional specialization of one of the cerebral hemispheres Copyright © Allyn & Bacon 2008

Testing Hemispheric Lateralization
With both eyes open, hold up your right thumb at arm’s length under an object across the room directly ahead of you. Now alternately close your left and right eyes and see if your thumb appears to “jump” to the right or left This shows brain specialization. Copyright © Allyn & Bacon 2008

Split-brain operation—procedure used to reduce recurrent seizures in severe cases of epilepsy
Corpus callosum—thick band of axons that connects the two cerebral hemispheres

The Electrical Synapse
Most mammalian synapses are chemical, but there is a simple form of electrical synapse that allows the direct transfer of ionic current from one cell to the next. Electrical synapses occur at specialized sites called gap junctions. They form channels that allow ions to pass directly from the cytoplasm of one cell to the cytoplasm of the other. Transmission at electrical synapses is very fast, thus, an action potential in the presynaptic neuron can produce almost instantaneously, an action potential in the postsynaptic neuron. Electrical synapses in mammalian CNS, are mainly found in specialized locations where normal functions requires that the activity of neighboing neurons be highly synchronized. Although gap junctions are relatively rare between adult mammalian neurons, they are very common in a large variety of non-neural cells, including smooth cardiac muscle cells, epithelial cells, some glandular cells, glia, etc. They are also common in many invertebrates.

The Electrical Synapse

Chapter 2: Neuroscience and Behavior

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