Introduction to Psychology Chapter 3: The Biological Basis of Behavior

Nervous Tissue 2 kinds: neurons & glia Neurons: - nerve cells – carry, process & pass electrochemical info - most communicate w/ other neurons - some communicate w/ muscles, organs

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

Nervous Tissue Axons may be branched Healthy axons covered w/ myelin sheaths – fatty covering – holds in signal ~ plastic on electric cord – loss of myelin causes impairment, especially motor – multiple sclerosis (MS) – is loss of myelin

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

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

Nervous Tissue Glia Workhorse of nerve tissue May have some role in memory, learning

Nerve Impulse Electrochemical Neurons surrounded by ions Ions = charged particles (sodium & potassium are +/chloride are – Ions cross cell membranes – imbalance – more neg ions inside Resting potential – neuron negatively charged – neuron at rest

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

Nerve Impulse All or none law – action potential is an action potential – no light/heavy Weak or strong stimulus will influence rate of firing

Synapse Space between neurons Synaptic cleft – actual gap between button & dendrite Presynaptic neuron – sends a signal Postsynaptic neuron – receives a signal Signals are neurotransmitters (chemicals)

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

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

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

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

Pruning Synapses Δ over time – neural tissue becomes more efficient – babies/children form many synapses > cut back Pruning – elimination of synapses to improve system > new synapses may form

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

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

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

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

Neurotransmitters 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

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

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

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

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

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

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

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

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

Central Nervous System 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