Unit 2: Biological Basis

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Neuron

Neuron

a nerve cell; the basic building block of the nervous system.

Afferent (sensory) neurons

neurons that carry incoming information from the sensory receptors to the brain and spinal cord.

Efferent (motor) neurons

neurons that carry outgoing information from the brain and spinal cord to the muscles and glands.

Interneurons

neurons within the brain and spinal cord that communicate internally and intervene between the sensory inputs and motor outputs.

Dendrite

the bushy, branching extensions of a neuron that receive messages and conduct impulses toward toward the cell body.

Soma

cell body where the nucleus of the neuron is located.

Axon

the extension of a neuron, ending in branching terminal fibers, through which messages pass to other neurons or to muscles or glands.

Mylein sheath

a layer of fatty tissue segmentally encasing the fibers of many neurons; enables vastly greater transmission speed of neural impulses as the impulse hops from one node to the next.

Glial cells

cells in the nervous system that support, nourish, and protect neurons.

Synapse

the junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. The tiny gap at this junction is called the synaptic gap or synaptic cleft.

Synaptic vesicle

the vesicle that holds neurotransmitters at the synapse, then releases them into the synaptic gap.

Neurotransmitters

chemical messengers that cross the synaptic gaps between neurons. When released by the sending neuron, neurotransmitters travel across the synapse and bind to receptor sites on the receiving neuron, thereby influencing whether that neuron will generate a neural impulse.

Reuptake

a neurotransmitter's reabsorption by the sending neuron.

Resting potential

when a neuron is completely polarized and not active.

Action potential

a neural impulse; a brief electrical charge that travels down the axon (depolarizes the neuron as it travels through).

Threshold

the level of stimulation required to trigger a neural impulse.

All-or-none principle

neurons will only fire at full power, either all the way or not at all.

Polarization

at resting potential a neuron is polarized. All sodium ions are on the outside of the neuron and all potassium ions are on the inside.

Depolarization

occurs when action potential travels down the axon, causing the sodium ions to rush in (a mixing of different ions) causing depolarization and the energy to fire.

Refractory period

a neuron's resting period after firing, when it recharges and can not fire again until recharged.

Endorphins

"morphine within," natural, opiatelike neurotransmitter linked to pain control and to pleasure. Gives a "runner's high" feeling, released when injured or in pain.

Dopamine

a neurotransmitter that influences movement, learning, attention, and emotion. Some stimulant substances mimic its effects. Too much is linked to schizophrenia, too little is linked to Parkinson's disease.

Serotonin

a neurotransmitter that affects mood, hunger, sleep, and arousal. An undersupply is linked to depression.

Acetylcholine

a neurotransmitter that enables muscle action, learning and memory. With Alzherimer's disease, Ach-producing neurons deteriorate. Blocking of it causes paralyses.

Norepinephrine

a neurotransmitter that helps control alertness and arousal. An undersupply can cause a depressed mood.

GABA

a major inhibitory neurotransmitter. Undersupply is linked to seizures, tremors, and insomnia.

Glutamate

a major excitatory neurotransmitter, involved in memory.

Blood-brain barrier

prevents materials (foreign substances, neurotransmitters and hormones in the body) in the blood from entering the brain or spinal cord

Agonist

foreign substance that mimics certain neurotransmitters, having similar effects.

Antagonist

foreign substance that blocks certain neurotransmitters, not allowing them to do their job.

Nervous System

the body's speedy, electrochemical communication network, consisting of all the nerve cells of the peripheral and central nervous systems.

Central Nervous System

the brain and the spinal cord.

Peripheral Nervous System

the sensory and motor neurons that connect the central nervous system to the rest of the body.

Somatic Nervous System

the division of the peripheral nervous system that controls the body's skeletal muscles.

Autonomic Nervous System

the part of the peripheral nervous system that controls the glands and the muscles of the internal organs (such as the heart). Its sympathetic division arouses; its parasympathetic division calms.

Sympathetic Nervous System

the division of the autonomic nervous system that arouses the body, mobilizing its energy in stressful situations; prepares the body for fight or flight response.

Parasympathetic Nervous System

the division of the autonomic nervous system that calms the body, conserving its energy.

Reflex

a simple, automatic response to a sensory stimulus, such as the knee-jerk response.

Endocrine System

the body's "slow"chemical communication system; a set of glands that secrete hormones in the bloodstream.

Hormones

chemical messengers that are manufactured by the endocrine glands, travel through the bloodstream, and affect other tissues.

Pituitary gland

the endocrine system's most influential gland. Under the influence of the hypothalamus, the pituitary regulates growth and controls other endocrine glands.

Lesion

tissue destruction. A brain lesion is a naturally or experimentally caused destruction of brain tissue.

Electroencephalograph (EEG)

an amplified recording of the waves of electrical activity that sweep across the brain's surface. These waves are measured by electrodes placed on the scalp.

CT Scan

a series of X-ray photographs taken from different angles and combined by computer into a composite representation of a slice through the body.

PET

a visual display of brain activity that detects where a radioactive form of glucose goes while the brain performs a given task.

MRI

a technique that uses magnetic fields and radio waves to produce computer-generated images of soft tissue. MRI scans show brain anatomy.

FMRI (functional MRI)

a technique for revealing bloodflow and, therefore, brain activity by comparing successive MRI scans. FMRI scans show brain function.

Brainstem

the oldest part and central core of the brain, beginning where the spinal cord swells as it enters the skull; the brainstem is responsible for automatic survival functions.

Medulla

the base of the brainstem; controls heartbeat and breathing.

Reticular formation

a nerve network in the brainstem that plays an important role in controlling arousal.

Pons

part of the brainstem that influences sleep, dreaming, and respiration.

Thalamus

the brain's sensory switchboard, located on top of the brainstem; it directs messages to the sensory receiving areas in the cortex and transmits replies to the cerebellum and medulla.

Cerebellum

the"little brain" at the rear of the brainstem; functions include processing sensory input and coordinating movement output and balance.

Limbic system

doughnut-shaped neural system (including the hippocampus, amygdala, and hypothalamus) located below the cerebral hemispheres; associated with emotions and drives.

Amygdala

two lima bean-sized neural clusters in the limbic system; linked to emotion (specifically levels of aggression and fear).

Hippocampus

a neural center that is located in the limbic system; helps process explicit memories for storage.

Hypothalamus

a neural structure lying below (hypo) the thalamus; it directs several maintenance activities (eating, drinking, body temperature, sex drive), helps govern the endocrine system via the pituitary gland, and is linked to emotion and reward.

Cerebral cortex

the intricate fabric of interconnected neural cells covering the cerebral hemispheres; the body's ultimate control and information-processing center.

Corpus callosum

the large band of neural fibers connecting the two brain hemispheres and carrying messages between them.

Frontal lobes

portion of the cerebral cortex lying just behind the forehead; involved in speaking and muscle movements and in making plans and judgments. Also involved in personality.

Motor cortex

an area at the rear of the frontal lobes that controls voluntary movements.

Parietal lobes

portion of the cerebral cortex lying at the top of the head and toward the rear; receives sensory input for touch and body position.

Somatosensory cortex

area at the front of the parietal lobes that registers and processes body touch and movement sensations.

Occipital lobes

portion of the cerebral cortex lying at the back of the head; includes areas that receive information from the visual fields.

Primary Visual cortex

area at the back of the occipital lobes that process visual information.

Temporal lobes

portion of the cerebral cortex lying roughly above the ears; includes the auditory ares, each receiving information primarily from the opposite ear.

Primary Auditory cortex

area in the temporal lobes responsible for receiving auditory information.

Association areas

areas of the cerebral cortex that are not involved in primary motor or sensory functions; rather, they are involved in higher mental functions such as learning, remembering, thinking, and speaking.

Aphasia

impairment of language, usually caused by left hemisphere damage either to Broca's area (impairing speaking) or to Wernicke's area (impairing understanding).

Broca's Area

controls language expression - an area, usually in the left frontal lobe, that directs the muscle movements involved in speech.

Wernicke's area

controls language reception - a brain area involved in language comprehension and expression; usually in the left temporal lobe.

Plasticity

the brain's ability to change, especially during childhood, by reorganizing after damage or by building new pathways based on experience.

Long-term potentiation (LTP)

an increase in a synapse's firing potential after brief, rapid stimulation. Believed to be a neural basis for learning and memory.