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Biology and Behavior

Chapter 3

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Neural Communication

The body’s information system is built from billions of interconnected cells called neurons.

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Neuron

A nerve cell, or a neuron, consists of many different parts.

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Parts of a Neuron Cell Body: Life support center of the neuron.

Dendrites: Branching extensions at the cell body. Receive messages from other neurons.

Axon: Long single extension of a neuron, covered with myelin sheath to insulate and speed up messages through neurons.

Axon: Terminals: Branched endings of an axon that transmit messages to other neurons.

Synapse: Space between the neurons

How does a Neuron fire?

• Resting Potential: slightly negative charge.

• Reach the threshold when enough neurotransmitters reach dendrites.

• Go into Action Potential.• All-or-none response.• Transfer of ions across

axon’s membrane causes electrical charge.

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It is an electrochemical process•Electrical inside the neuron•Chemical outside the neuron

(in the synapse in the form of a neurotransmitter).

•The firing is call Action Potential.

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The All-or None Response

• The idea that either the neuron fires or it does not- no part way firing.

• Like a gun

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Steps of Action Potential• Dendrites receive neurotransmitter from

another neuron across the synapse.• Reached its threshold- then fires based on the

all-or-none response.• Opens up a portal in axon, and lets in positive

ions (Sodium) which mix with negative ions (Potassium) that is already inside the axon (thus Neurons at rest have a slightly negative charge).

• The mixing of + and – ions causes an electrical charge that opens up the next portal (letting in more K) while closing the original portal.

• Process continues down axon to the axon terminal.

• Terminal buttons turns electrical charge into chemical (neurotransmitter) and shoots message to next neuron across the synapse.

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Refractory Period & Pumps

Refractory Period: After a neuron fires an action potential it pauses for a short

period to recharge itself to fire again.

Sodium-Potassium Pumps: Sodium-potassium pumps pump positive ions out

from the inside of the neuron, making them ready for another action potential.

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Action Potential Properties

All-or-None Response: When the depolarizing current exceeds the

threshold, a neuron will fire. If the depolarizing current fails to exceed the

threshold, a neuron will not fire.

Intensity of an action potential remains the same throughout the length of the

axon.

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Synapse

Synapse [SIN-aps] a junction between the axon tip of the sending neuron and the

dendrite or cell body of the receiving neuron. This tiny gap is called the synaptic gap or

cleft.

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How Neurons Communicate

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Neurotransmitters

Neurotransmitters (chemicals) released

from the sending neuron travel across the synapse and bind to receptor sites on

the receiving neuron, thereby influencing it to generate an action

potential.

TYPES OF NEUROTRANSMITTERS

Acetylcholine (ACH)

• Deals with motor movement and memory.

• Lack of ACH has been linked to Alzheimer’s disease and muscle paralysis

Dopamine

• Deals with attention, motor movement and alertness.

• Lack of dopamine has been linked to Parkinson’s disease.

• Too much has been linked to schizophrenia.

Serotonin

• Involved in mood control.

• Lack of serotonin has been linked to clinical depression.

Endorphins

• Involved in pain control.

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Divisions of the Nervous System

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The Nervous System

Nervous System: Consists of all the nerve cells. It is the body’s speedy, electrochemical communication system.

Central Nervous System (CNS): the brain and spinal cord.

Peripheral Nervous System (PNS): the sensory and motor neurons that connect the central nervous system (CNS) to the rest of the body.

Peripheral Nervous System

• All nerves that are not encased in bone.

• Everything but the brain and spinal cord.

• Is divided into two categories….somatic and autonomic.

Somatic Nervous System

• Controls voluntary muscle movement.

Autonomic Nervous System

• Controls the automatic functions of the body.

• Divided into two categories…the sympathetic and the parasympathetic

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Autonomic Nervous System (ANS)

Sympathetic Nervous System: Division of the ANS that arouses the body, mobilizing its energy in stressful situations.

Parasympathetic Nervous System: Division of the ANS that calms the body, conserving its energy.

Sympathetic Nervous System

• Fight or Flight Response.

• Automatically accelerates heart rate, breathing, dilates pupils, slows down digestion.

Parasympathetic Nervous System

• Automatically slows the body down after a stressful event.

• Heart rate and breathing slow down, pupils constrict and digestion speeds up.

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The Brain

Brain Structures

• Some scientists divide the brain up into three parts.

• Hindbrain• Midbrain• Forebrain

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Hindbrain

• Structures on top of our spinal cord.• Controls basic biological structures.

The brain in purple makes up the hindbrain.

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Medulla Oblongata• Located just

above the spinal cord.

Involved in control of

•blood pressure•heart rate•breathing.

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Pons • Located just above the medulla.

• Connects hindbrain with midbrain and forebrain.

• Involved in facial expressions, sleep, and attention

Cerebellum• Located in the back

of our head- means little brain.

• Coordinates muscle movements.

Midbrain

• Coordinates simple movements with sensory information.

• Contains the reticular activating system: arousal and ability to focus attention.

• If damaged…Coma

Forebrain

• Thalamus• Receives sensory

information and sends them to appropriate areas of forebrain.

• Like a switchboard.• Everything but

smell.

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Hypothalamus

The Hypothalamus lies below (hypo) the thalamus. It directs several maintenance activities like eating,

drinking, body temperature, and

control of emotions. It helps govern the

endocrine system via the pituitary gland.

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Hypothalamus• Maybe most

important structure in the brain.

Controls and regulates• Body temperature• Sexual Arousal• Hunger• Thirst• Endocrine System

The most powerful structure in the brain.

Limbic System

• EMOTIONAL CONTROL CENTER of the brain.

• Made up of Hypothalamus, Amygdala and Hippocampus.

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The Limbic System is a doughnut-shaped system of neural

structures at the border of the brainstem and cerebrum, associated with emotions such as fear, aggression and

drives for food and sex. It includes the hippocampus, amygdala, and hypothalamus.

The Limbic System

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The Limbic System

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Amygdala

• Involved in how we process memory.

• More involved in volatile emotions like fear & anger.

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Hippocampus

• Involved in the processing and storage of memories.

Cerebrum

• Largest part of the brain

• Surface of brain called the: cerebral cortex

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Areas of the Cerebral Cortex

• Divided into 4 lobes – Frontal– Temporal– Parietal– Occipital

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Frontal Lobes• Deals with planning,

maintaining emotional control and abstract thought.

• Contains Motor Cortex: sends signals to our body controlling muscle movements.

• Contains Broca’s Area: responsible for controlling muscles that produce speech.

• Damage to Broca’s Area is called Broca’s Aphasia: unable to make movements to talk. Contains Broca’s Area.

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Motor and Sensory Cortexes

Parietal Lobes

• Located at the top of our head.

• Contains the somato-sensory cortex.

• Rest are association areas.

Temporal Lobes• Process sound

sensed by ears.• Not lateralized.• Contains Wernicke’s

area which interprets written and spoken speech.

• Wernike's Aphasia: unable to understand language: the syntax and grammar

Occipital Lobes

• In the back of our head.

• Handles visual input from eyes.

• Right half of each retina goes to left occipital lobe and vice versa.

• Contains Visual Cortex: interprets messages from our eyes into images we can understand.

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The Corpus CallosumDivides the 2 hemispheres.

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Hemispheres

Divided into to hemispheres.

• Contralateral control: right controls left and vice versa.

In general,Left Hemisphere: logic

and sequential tasks.Right Hemisphere:

spatial and creative tasks.

Hemispheres• Divided into a left and

right hemisphere.• Contralateral

controlled- left controls right side of body and vice versa.

• Brain Lateralization.• Lefties are better at

spatial and creative tasks.

• Righties are better at logic.

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Accidents

Phineas Gage Story• Personality changed

after the accident.

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Brain Plasticity• The idea that the

brain, when damaged, will attempt to find news ways to reroute messages.

• Children’s brains are more plastic than adults.

Lesions

Brain tumors also lesion brain tissue.

Ways to study the Brain

• Electroencephalogram (EEG)

• Computerized Axial Tomography (CAT)

• Magnetic Resonance Imaging (MRI)

• Positron Emission Tomography (PET)

• Functional MRI (fMRI)

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Electroencephalogram

• Detects brain waves through their electrical output.

• Used mainly in sleep research.

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PET Scan

PET (positron emission tomography)

Scan is a visual display of brain

activity that detects a radioactive form of glucose while the

brain performs a given task.

Courtesy of N

ational Brookhaven N

ational Laboratories

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Positron Emission Tomography

• Measures how much glucose the brain uses.

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MRI ScanMRI (magnetic

resonance imaging) uses magnetic fields and radio waves to produce computer-

generated images that distinguish among

different types of brain tissue.

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Magnetic Resonance Imaging

• More detailed picture of brain using magnetic field to knock electrons off axis.

• Takes many still pictures and turns images into a movie like production.

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Computerized Axial Tomography

• function3D X-Ray of the brain.

• Good for tumor locating

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Functional MRI

Shows the tissue and the function of the brain

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The Endocrine SystemA system of glands that secrete hormones.Similar to nervous system, except hormones work a lot slower than neurotransmitters.

Neurotransmitters

Hormones

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The Endocrine System

The Endocrine System is the body’s “slow”

chemical communication

system. Communication is

carried out by hormones

synthesized by a set of glands.

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Hormones

Hormones are chemicals synthesized by the endocrine glands that are secreted in the

bloodstream. Hormones affect the brain and many other tissues of the body.

For example, epinephrine (adrenaline) increases heart rate, blood pressure, blood

sugar and feelings of excitement during emergency situations.

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The Major Endocrine Glands

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Pituitary Gland

Is called the “master gland.” The anterior pituitary lobe releases hormones that

regulate other glands. The posterior lobe regulates water and salt balance.

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Thyroid & Parathyroid Glands

Regulate metabolic and calcium rate.

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Adrenal GlandsAdrenal glands consist of the adrenal medulla and the cortex. The medulla secretes hormones (epinephrine and norepinephrine) during stressful and

emotional situations, while the adrenal cortex regulates salt and carbohydrate

metabolism.

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Gonads

Sex glands are located in different places in men and women. They regulate bodily

development and maintain reproductive organs in adults.