Introduction to Psychology Chapter 3 The Biological Basis

Introduction to Psychology Chapter 3: The Biological Basis of Behavior 1

Nervous Tissue l 2 kinds: neurons & glia l Neurons: l - nerve cells – l- most communicate w/ l - some communicate w/ 2

Nervous Tissue l Parts of neuron – soma, dendrites & axon l Soma (body) – nucleus, cellular material l Dendrites (trees) – receive information, usually from the axons of other neurons – communicate w/ multiple cells l Axon (axle) – most neurons have one – like a fiber – sends info to another neuron (dendrite), muscle or gland 3

Nervous Tissue l Axons l may be branched l Healthy axons covered w/ myelin sheaths – fatty covering – holds in signal ~ plastic on electric cord – loss of myelin causes 4

Nervous Tissue l Axon l Ends in a terminal button – bump that secretes neurotransmitters (chemicals) l Synapse (junction) – space between axon and dendrite l Exceptions – multiple axons, axon to soma 5

Nervous Tissue l Glia (glue) l Matrix for neurons l More glia cells than neurons, more than half the brain l Help feed and metabolize waste for neurons l Insulate neurons 6

Nervous Tissue l Glia l Workhorse of nerve tissue l May have some role in 7

Nerve Impulse l Electrochemical l Neurons surrounded by ions l Ions = charged particles (sodium & potassium are +/chloride are – l Ions cross cell membranes – l Resting potential – neuron negatively charged – 8

Nerve Impulses l Action potential – neuron is stimulated > positive ions go into cell’s axon > cell becomes positive and “fires” its impulse l A brief change in charge along the axon l Changing back ? ? l Absolute refractory period – minimum time before neuron can have its next action potential – much less than 1 sec 9

Nerve Impulse l All or none law – action potential is an action potential – no light/heavy 10

Synapse l Space between neurons l Synaptic cleft – actual gap between l Presynaptic neuron – sends a signal l Postsynaptic neuron – receives a signal l Signals are 11

Synapse l Presynaptic neurons l Have neurotransmitters stored in synaptic vesicles in the l Vesicles ~ bubbles – when neuron active, vesicles move to membrane of button l Vesicles attach to 12

Synapse l Neurotransmitters cross membrane > pass through cleft (liquid through liquid) l Postsynaptic neuron has receptors in dendrites l Receptors/receptor sites are places where neurotransmitter can be read l Receptors very specific – usually sensitive to 1 (lock-and-key) 13

The Signal & the Synapse l Postsynaptic potential (PSP) – ability of receptor to change voltage when it receives neurotransmitter l No all-or-none rule l PSPs are strong/weak depending on strength of signal l 2 types of PSP = excitatory or inhibatory 14

The Signal & the Synapse l Excitatory PSP = + ionic shift that makes it likely that neuron will fire (action potential) l Inhibatory PSP = - ionic shift that makes it less likely that neuron will fire its action potential l Reuptake – after the PSP, neurotransmitter taken in by postsynaptic neuron - metabolized 15

Pruning l Synapses Δ over time – neural tissue becomes more efficient – babies/children form many synapses > cut back l Pruning – elimination of 16

Neurotransmitters l Natural chemicals l Some drugs interfere with them l Agonist – a chemical that imitates a certain neurotransmitter l Antagonist – a chemical that blocks a certain neurotransmitter l Agonists & antagonists act on receptor sites 17

Neurotransmitters l Acetylcholine (ACh) l 1 st one discovered l Voluntary muscle action, attention, arousal, memory l Increased ACh therapy helps Alzheimer’s dz l Nicotine is agonist > stimulant l Curare is antagonist > dart poison 18

Neurotransmitters l Monoamines l 3 main types = dopamine, norepinephrine & serotonin l Dopamine (DA) – movement –when neurons break down (usually age) > may cause loss of DA > Parkinson’s dz – impaired movement, tremors, rigidity 19

Neurotransmitters l Monoamines l Serotonin – sleep cycles, l Monoamines involved in mental illness l Depression > not enough serotonin & norepinephrine (NE) l Schizophrenia > too much DA activity, meds are DA antagonists 20

Neurotransmitters l l l Monoamines Abused drugs, especially cocaine/crack, amphetamines (speed) inc DA & NE ********************** Endorphins Behave like opiates Scientists curious why opiates work when not native to our bodies > morphine an opiate agonist > eating, stress, pleasure 21

Neurotransmitters l GABA & Glutamate l Amino acids l Gamma-aminobutyric acid (GABA) l Common in l Only for inhibitory PSP (others do both) l Regulates sleep l Imbalance can cause epilepsy 22

Neurotransmitters l Glutamate l Commonly found l Only involved in excitatory PSP l Linked to learning, memory l Linked to long-term potentiation – when a specific neural path has synapses that stay excited > may be part of memory creation; schizophrenia 23

Nervous System l Much still unknown l 100 billion neurons in human brain l Divided – central nervous system (CNS) & peripheral nervous system (PNS) l CNS = brain & spinal cord l PNS = all nerves outside CNS, throughout the body l Nerves = bundles of axons 24

Peripheral Nervous System l System outside CNS l 2 parts = somatic nervous system (SNS) & autonomic nervous system (ANS) l Somatic nervous system l - linked to sensory systems l - linked to voluntary skeletal muscles l - has 2 kinds of nerves = afferents & efferents 25

Peripheral Nervous System l Somatic nervous system l Afferent nerve fibers – carry info toward CNS l Efferent nerve fibers – carry info from CNS toward body l Nerves have both fibers 26

Peripheral Nervous System l Autonomic nervous system l Nerves connected with smooth muscle tissue (organs, like the heart, stomach), blood vessels & glands l Involuntary, visceral (guts) functions l Salivation, heartbeat, sweating l Active w emotions – 27

Peripheral Nervous System l ANS divided = sympathetic & parasympathetic systems l Sympathetic branch handles emergencies > regulates breathing, digestion, bleeding l Parasympathetic branch handles normal life > conserves resources 28

Central Nervous System l CNS = brain & spinal cord l Protected by bone & cerebrospinal fluid (CSF) l CSF give nutrients l Blood-brain barrier – semipermeable membrane around brain & spinal cord that blocks most chemicals & blood from touching neural tissue 29

Central Nervous System l l l l Spinal cord links brain to PNS Runs from base of head to waist Most kinds of paralysis involve spinal cord Brain 3 lbs Command center Much unknown 30