Neuron and Its Parts

Neuron: Individual nerve cell; 100 billion in brain

Soma: Cell body; body of the neuron.  Receives messages and sends messages down axon

Axon: Fiber that carries information away from the cell body of a neuron

Axon terminals: Branches that link the dendrites and somas of other neurons

Dendrites: Receive messages from other neurons

The Nerve Impulse

Resting potential: Electrical charge of an inactive neuron

Threshold: Trigger point for a neuron’s firing

Action Potential: Nerve impulse

More on Nerves

Ion channels: Tiny openings through the axon membrane

Negative after-potential: A drop in electrical charge below the resting potential

Synapse: Microscopic space between two neurons over which messages pass

Saltatory Conduction

Process by which nerve impulses conducted down the axons of neurons coated with myelin jump from gap to gap in the myelin layer

Myelin: A fatty layer coating some axons

Neurotransmitters

Chemicals that alter activity in neurons; brain chemicals

Receptor site:  Area on the surface of neurons and other cells that is sensitive to neurotransmitters or hormones

Types of Neurotransmitters

Acetylcholine: Activates muscles

Dopamine: Muscle control

Serotonin: Mood and appetite control

Neural Regulators

Neuropeptides: Regulate activity of other neurons

Enkephalins: Relieve pain and stress; similar to endorphins

Endorphins:  Released by pituitary gland; also help to relieve pain

Placebos raise endorphin levels

Neuroplasticity

Capacity of our brains to change in response to experience

Neural Networks

Central nervous system (CNS): Brain and spinal cord

Peripheral nervous system: All parts of the nervous system outside of the brain and spinal cord

Nerves and Neurons (cont)

Neurilemma: Thin layer of cells wrapped around axons outside brain and spinal cord; forms a tunnel that damaged fibers follow as they repair themselves

Two Divisions of the Peripheral Nervous System

Somatic System: Carries messages to and from skeletal muscles and sense organs; controls voluntary behavior

Autonomic System: Serves internal organs and glands; controls automatic functions such as heart rate and digestion pressure

Two Divisions of the Autonomic Nervous System

Sympathetic: Arouses body; emergency system

Parasympathetic: Quiets body; most active after an emotional event

The Spinal Cord

Spinal Nerves: 31 of them; carry sensory and motor messages to and from the spinal cord

Cranial Nerves: 12 pairs that leave the brain directly; also work to communicate messages

The Spinal Cord and Behavior

Reflex Arc: Simplest behavior; occurs when a stimulus provokes an automatic response

Sensory Neuron: Nerve cell that carries messages from the senses toward the CNS

Connector Neuron: Nerve cell that links two others

Motor Neuron: Cell that carries commands from the CNS to muscles and glands

Effector Cells

Cells capable of producing a response - out of the brain

                                     Affector Cells

Cells capable of bringing information into the brain

Neurogenesis

The production of new brain cells

Brain Imaging Techniques

Computed Tomographic Scanning (CT): Computer-enhanced X-ray of the brain or body

Magnetic Resonance Imaging (MRI): Uses a strong magnetic field, not an X-ray, to produce an image of the body’s interior

Localization of Function

Research strategy of linking specific structures in the brain with specific psychological or behavioral functions

Researching the Brain

Ablation: Surgical removal of parts of the brain

Deep lesioning: A thin wire electrode is lowered into a specific area inside the brain;  electrical current is then used to destroy a small amount of brain tissue

Electrical stimulation of the brain (ESB): When an electrode is used to activate target areas in the brain

Electroencephalograph (EEG)

A device that detects, amplifies, and records electrical activity in the brain

More Brain Imaging Techniques

Functional MRI: MRI that makes brain activity visible

Positron emission tomography (PET): Computer-generated color image of brain activity, based on glucose consumption in the brain

Cerebral Cortex

Definition: Outer layer of the brain; contains 70% of neurons in CNS

Cerebrum: Two large hemispheres that cover upper part of the brain

Corticalization: Increase in size and wrinkling of the cortex

Cerebral hemispheres: Right and left halves of the cortex

Corpus Callosum

Bundle of fibers connecting cerebral hemispheres

Neurological Soft Signs

Subtle behavioral signs of brain dysfunction

Clumsiness

Awkward gait

Poor hand-eye coordination

Other perceptual and motor problems

Split Brains

Corpus callosum is cut; done to control severe epilepsy (seizure disorder)

Result: The person now has two brains in one body

This operation is rare and is often used as a last resort

Right Brain/Left Brain

Humans use 95 percent of our left brain for language

Speaking, writing, understanding

The Left Hemisphere

Left hemisphere better at math, judging time and rhythm, and coordinating order of complex movements

Processes information sequentially

The Right Hemisphere

Right hemisphere good at perceptual skills, and at expressing and detecting other’s emotions

Good at recognizing patterns, faces, and melodies

Processes information simultaneously and holistically

Frontal Lobe

Movement, sense of smell, higher mental functions

Contains primary motor cortex; controls motor movement

Mirror neurons: Contained in motor cortex; become active when motor action is carried out and when another organism is observed carrying out the same action

Association Cortex

All areas of cerebral cortex that are not primarily sensory or motor in function

Aphasia

Language disturbance resulting from brain damage (think of the word “phrase”)

Broca’s Area

Related to grammar and pronunciation

If damaged, person knows what s/he wants to say but can’t say the words

Prefrontal Cortex

Front of frontal lobes; involved in sense of self, reasoning, and planning

Parietal Lobe

Just above occipital; bodily sensations such as touch, pain, and temperature (somatosensory area)

Primary somatosensory cortex: Receiving area for bodily sensations

Temporal Lobe

Each side of the brain; auditory center and, for 95 percent of humans, language centers

Primary auditory area: Auditory information is first registered here

Wernicke’s Area

Related to language comprehension; in left temporal lobe

If damaged, person has problems with meanings of words, NOT pronunciation

Occipital Lobe

Back of brain; vision center

Primary visual area: Part of occipital lobe that first receives input from the eyes

Agnosias

Visual Agnosia: Inability to identify seen objects

Facial Agnosia: Inability to perceive familiar faces

Subcortex

All brain structures immediately below cerebral cortex

Hindbrain (Brainstem)

Consists mainly of medulla and cerebellum

Also includes pons and reticular formation

Medulla

Controls vital life functions such as heart rate, swallowing, and breathing

Pons (Bridge)

Pons (Bridge): Acts as a bridge between medulla and other structures

Influences sleep and arousal

Cerebellum

Cerebellum: Located at base of brain

Regulates posture, muscle tone, and muscular coordination

Reticular Formation (RF)

Inside medulla and brainstem

Associated with alertness, attention, and some reflexes (breathing, coughing, sneezing, vomiting)

Reticular Activating System (RAS)

Part of RF that keeps it active and alert

RAS acts like the brain’s alarm clock

Activates and arouses cerebral cortex

Forebrain

Structures are part of the limbic system, the system within the forebrain closely linked to emotional response and motivating behavior

Thalamus

Relays sensory information on the way to the cortex; switchboard

Hypothalamus

Regulates emotional behaviors and motives (e.g., sex, hunger, rage, hormone release)

Amygdala

Associated with fear responses

Hippocampus

Associated with storing permanent memories; helps us navigate through space

Endocrine System

Glands that pour chemicals (hormones) directly into the bloodstream or lymph system

Pituitary Gland

Regulates growth via growth hormone

Its hormones influence other endocrine glands

Pituitary Problems

Too little growth hormone means person will be smaller than average

Hypopituitary dwarfism: As adults, perfectly proportioned but tiny

Treatable by using human or synthetic growth hormone; will add a few inches

Pituitary Problems (cont)

Too much growth hormone leads to gigantism (excessive body growth)

Acromegaly: Enlargement of arms, hands, feet, and facial bones; due to too much growth hormone secreted late in growth period

Andre the Giant

Pituitary also governs functioning of other glands, especially thyroid, adrenals, and gonads

The Pineal Gland

Regulates body rhythms and sleep cycles

Releases the hormone melatonin, which responds to daily variations in light

The Thyroid Gland

In neck; regulates metabolism

Hyperthyroidism: Overactive thyroid; person tends to be thin, tense, excitable, nervous

Hypothyroidism: Underactive thyroid; person tends to be inactive, sleepy, slow, obese, and depressed

The Adrenal Glands

Adrenals: Arouse body, regulate salt balance, adjust body to stress, regulate sexual functioning; located on top of kidneys

Releases epinephrine and norepinephrine (also known as adrenaline and noradrenaline)

Adrenal Hormones

Epinephrine arouses body; is associated with fear

Norepinephrine arouses body; is linked with anger

The Adrenal Glands (cont)

Adrenal medulla: Inner core of adrenals; source of epinephrine and norepinephrine

Adrenal cortex: Produces hormones known as corticoids

Regulate salt balance, among other functions

Adrenal Malfunctions

Oversecretion of adrenal sex hormones can cause virilism: exaggerated male characteristics (bearded woman)

May also cause premature puberty if oversecretion occurs early in life

Handedness

Preference for right or left hand in most activities

Dominant Hemisphere: Term usually applied to the side of the human brain that produces language

Lateralization: Specialization in abilities of brain hemispheres