Biology and Behavior Chapter 3

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

A nerve cell, or a neuron, consists of many different parts. OBJECTIVE 3| Describe parts of a neuron and explain how its impulses are generated.

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.

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.

The All-or None Response The idea that either the neuron fires or it does not- no part way firing. Like a gun

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.

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.

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.

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. OBJECTIVE 4| Describe how nerve cells communicate. Synapse was coined by Lord Sherrington (1857-1952) who inferred it through behavioral experiments. Cajal (1852-1934) described the synapse based on his anatomical studies of the brain.

How Neurons Communicate

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.

Divisions of the Nervous System

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

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.

The Brain

Brain Structures Some scientists divide the brain up into three parts. Hindbrain Midbrain Forebrain

Hindbrain Structures on top of our spinal cord. Controls basic biological structures. The brain in purple makes up the hindbrain.

Medulla Oblongata Located just above the spinal cord. Involved in control of blood pressure heart rate breathing.

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.

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.

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.

The Limbic System 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. OBJECTIVE 13| Describe the structures and functions of the limbic system, and explain how one of these structures controls the pituitary gland.