A.1 Communication

Nervous System

A complex, highly organised network of billions of neurons. Divided into two main divisions (central and peripheral nervous systems).

Three Functions of the Nervous System

• Sensory function: Detecting internal stimuli, such as an increase in blood acidity

• Integrative function: Analysing (and storing some) sensory information and making decisions for responses

• Motor function: Responding to integration decisions; motor (efferent) neurons carry information from the brain towards the spinal cord

Hormone

1. A molecule that is released in one part of the body but regulates the activity of cells in other parts of the body

2. Chemicals released by glands or tissues to control and regulate the activity of other cells around the body

3. Can be grouped into two categories: Steroid (not included in the test) and non-steroid

Central Nervous System (CNS)

Consists of the brain and the spinal cord:

• The brain acts as a computer for both conscious and unconscious nervous activity

• The spinal cord allows information to travel between the brain and the rest of the body

Peripheral Nervous System (PNS)

Consists of all the nerves outside the CNS. It is divided into:

• Sensory (afferent) nerves

• Motor (efferent) nerves (are divided into the somatic and autonomic nervous systems)

Sensory (Afferent) Nerves

Inform the CNS about what is going on within the body and outside the body

Motor (Efferent) Nerves

In response to signals coming in from the sensory division, motor nerves send information from the CNS to tissues, organs and systems of the body.

Somatic Nervous System

Controls voluntary movements of the skeletal muscles.

Autonomic Nervous System

Regulates involuntary bodily functions, such as heart rate, digestion and breathing. This system is further divided into the sympathetic and parasympathetic nervous systems.

Sympathetic Nervous System

Activates the “flight-or-flight” response.

Parasympathetic Nervous System

Has a major role in carrying out involuntary processes such as digestion, urination, glandular secretion and conservation of energy (is the body’s “housekeeping system”).

Vasodilation

An effect of sympathetic stimulation. Refers to the widening of blood vessels to increase blood flow to active skeletal muscles during exercise.

Vasoconstriction

Another effect of sympathetic stimulation. Refers to the narrowing of blood vessels to divert blood to the active muscles, where it is needed most.

Organization of the Nervous System

Four Major Parts of the Brain

• Brainstem: Connects the brain and the spinal cord; nerve messages pass through it

• Cerebellum: Governs balance and coordinates skilled movements

• Cerebrum: Composed of 2 connected hemispheres that communicate with each other

• Diencephalon: Contains the thalamus and hypothalamus

2 Connected Hemispheres in the Cerebrum

The cerebral cortex is the outermost layer of the cerebrum (about 2-4 mm thick). The cerebral cortex is the conscious brain allowing athletes to think, be aware of sensory stimuli and voluntarily control their movements.

Thalamus

Very important for motor control.

Hypothalamus

Responsible for maintaining homeostasis. This is done by regulating processes that affect the body’s internal environment, such as blood pressure, heart rate and stroke volume, etc.

Heart

Main pump for circulating blood through the cardiovascular system. It has two atria that act as receiving chambers and two pumping chambers (the right and left ventricles).

Intrinsic Excitation

Refers to the cardiac muscle having the unique ability to generate its own electrical signal, which allows it to contract without any external stimulation. It is controlled by the SA node.

Sinoatrial (SA) Node

1. The impulse for heart contraction is initiated in the SA node located in the wall of the right atrium

2. Is sometimes referred to as the heart’s natural pacemaker

Atrioventricular (AV) Node

The electrical impulse generated by the SA node spreads through both atria and reaches the AV node located in the right atrial wall near the centre of the heart. AV node conducts the electrical impulse from the atria into the ventricles.

Bundle of His (Atrioventricular Bundle)

From the AV node, the electrical impulse enters the bundle of His, which is the only site where electrical impulses can conduct from the atria to the ventricles.

Purkinje Fibres

After moving along the bundle of His, the electrical impulse is conducted by Purkinje fibres from the apex of the heart upwards to the ventricles.

Extrinsic factors

Both the heart rate and the force of contraction can be altered by three extrinsic factors

• Parasympathetic nervous system

• Sympathetic nervous system

• Endocrine system (hormones)

Proprioreceptors

Specialized cells located in muscles, tendons, joints, and the inner ear that provide information about body position, muscle length and tension, position and movement of joints, and help maintain balance (and equilibrium).

Chemoreceptors

Monitor chemical changes (O2/CO2/H+) in the blood and detect chemicals in the mouth (taste), nose (smell) and body fluids. They are located in different parts of the body, including the neck and the aorta.

Barorecpetors

Are pressure-sensitive nerve cells that can detect higher or lower pressure. They are located in the aorta and carotid arteries. When arterial pressure changes, they send messages to the cardiovascular centre to regulate blood pressure.

Endocrine System

1. Consists of all tissues or glands that secrete hormones

2. Partners the nervous system in regulating the human body and controlling responses to physiological challenges

3. Its responses tend to be a little slower than the nervous system, but effects last longer

Major Endocrine Glands

Hormones Important for Sports (Excluding Reproductive Hormones)

Non-Steroid Hormones

1. Not fat-soluble

2. Must interact with receptors on the cell surface to trigger messenger chemicals inside the cell that then elicit the response

3. Examples include epinephrine (adrenaline) or glucagon

Prostaglandins

1. Fall into the non-steroid group

2. Produced in membranes of most cells

3. Are secreted very near the site of actions (or some can be transported short distances)

Three Main Sources of Information That Decrease Hormone Secretion

• Neural

• Humoral

• Hormonal

Neural

Are signals from the nervous system.

Humoral

Are due to changes in the chemistry of blood.

Hormonal

Hormones relay information by responding to changes in other hormone levels.

Pituitary Gland (“Master Gland”)

1. The pituitary gland in the brain is the most important endocrine gland involved in maintaining homeostasis

2. Secretes many different hormones to stimulate or inhibit organs in a highly coordinated way

3. Often considered the “master gland” governing homeostasis (even though it is primarily controlled by the hypothalamus)

Homeostasis

1. The condition in which the body’s internal environment remains relatively constant, within psychological limits

2. Occurs due to the body’s continuous balancing act of various regulatory processes (it is a dynamic state)

Three Basic Components of a Feedback Mechanism

• A receptor (such as nerve endings in the skin that sense temperature)

• A control centre (such as the hypothalamus)

• An effector (such as shivering if your body temperature drops sharply)

Blood pH

1. The normal pH range of arterial blood is 7.35-7.45 (slightly alkaline)

2. An increase in CO2 concentration in the blood can increase hydrogen ion concentration, decreasing blood pH and making it more acidic (which can have harmful effects on the body’s tissues and organs)

Regulation of the Heart

1. The cardiac cycle does not require a nerve stimulation to make the heart muscle contraction

2. Involves both intrinsic and extrinsic excitation

Extrinsic Excitation

1. Refers to the signals that come from outside the heart, such as from the nervous and hormonal systems

2. Is controlled by the autonomic nervous system

Acetylcholine

a hormone which slows down the firing rate of the SA node, reducing the force of contraction, and results in a decrease in both heart rate and cardiac output.

Stroke Volume

The volume of blood pumped out of the heart’s ventricle with each heartbeat.

Glycogenolysis

Breakdown of liver glycogen to glucose.

Gluconeogenesis

Conversion of protein or fat into glucose.

Thermoregulation (Regulation of Body Temperature)

Relies on the cardiovascular, muscular, nervous, and integumentary systems working together to maintain a core body temperature of 37±1°C.

ATP (Adenosine Triphosphate)

A high-energy compound for storing and conserving energy for muscles to contract and provide movement.

Metabolic Rate

The speed at which your body converts food and oxygen into energy needed to sustain basic life functions.

Ways Heat Can Be Transferred Away From the Body

• Conduction: Heat generated deep in your body can be conducted to the body’s surface

• Convection: Involves moving heat from one place to another by the motion of air (or water)

• Radiation: The transfer of energy waves that are sent out from one object and absorbed by another

• Evaporation: Evaporative cooling (conversion of sweat from liquid to water vapour) is the main way for the body to lose heat during higher-temperature exercise

Hyperthermia

Refers to an elevated body temperature, usually above 39°C.

Non-Shivering Thermogenesis

1. A process by which the body generates heat in response to cold temperature exposure without shivering

2. During this, the sympathetic nervous system stimulates increased metabolism to increase heat production

Shivering

1. Involuntary contractions of skeletal muscle that happen in cold environments

2. Can greatly increase the rate of heat production

Insensible Water Loss

1. Refers to water vaporizing from the respiratory passages and skin surface

2. Continually transfers heat from the body to the environment

3. Accounts for about 80% of heat loss when physically active, but 20% at rest.

Visual of Wasserman’s Three Cogs

Gas Exchange

The transfer of oxygen and carbon dioxide between the cardiovascular and respiratory systems, and body tissues.

Respiratory System

Enables the transport and exchange of oxygen for use in cellular respiration.

Basis of Air Movement

1. Breathing during rest and exercise will flow from an area of higher pressure to an area of lower pressure

2. During inhalation, the air pressure in the lungs needs to be lower than in the atmosphere

3. At rest, inhalation is mainly caused by contraction of the muscular diaphragm at the base of the chest cavity

4. At rest, the exhalation process doesn’t require energy as the diaphragm relaxes

Alveoli (Plural for Alveolus)

Small air sacs created from smaller bronchioles (initially branched from airways) where gas exchange takes place.

FEV₁ (Forced Expiratory Volume in One Second)

Refers to the maximum volume that can be breathed out in one second.

Diffusion

Gas exchange takes place according to diffusion, a process that is passive (doesn’t require energy).

Partial Pressure

Represents the pressure exerted by a single gas (such as oxygen) within a mixture (such as air, blood, or tissue fluid)

Pulmonary Gas Exchange

The movement of oxygen from air in the alveoli of the lungs to blood, and the movement of carbon dioxide in the opposite direction.

Minute Ventilation (Vₑ)

1. Describes the volume of air being exhaled per minute (and inhaled as we do not store air).

2. Formula - Vₑ = Vₜ (tidal volume) × Bf (breathing frequency or respiration rate)

3. Vₜ: The size of each breath / Bf: The number of breaths per minute

Hyperventilation

Refers to an increase in ventilation above what is actually required to meet the oxygen demand of the exercise.

Blood

During exercise, its primary function is to transport gases, nutrients, waste products, hormones, and heat to and from various tissues. Its total volume in the body is around 5 litres for a person of mass 70 kg.

Major Components of Blood

• Plasma (~55% of blood volume): A fluid that is a mixture of water and dissolved substances

• Platelets (<1% of blood volume): Assist in the process of repair following injury; play a vital role in blood clotting

• White blood cells (leucocytes) (<1% of blood volume): primarily involved in immune function; protect the body from infection

• Red blood cells (erythrocytes) (~40%-45% of blood volume): They carry O2 from the lungs to tissues, and carry CO2 back to the lungs for exhalation

Haematocrit

Percentage of red blood cells.

Haemoglobin

Iron-rich pigment in the blood which oxygen binds to.

Erythropoietin

Hormone responsible for stimulating red blood cell production.

Circulation

Blood is transported around the body through an extensive network of blood vessels, which include the following:

• Arteries: Are responsible for transport away from the heart to tissues

• Capillaries: Are the sites of exchange between blood and tissues

• Veins: The larger veins are the vessels that deliver mostly deoxygenated blood back towards the heart

Cardiac Muscle Fibres

Walls of specialist muscle fibres.

Pulmonary Circulation

Delivers deoxygenated blood from the right side of the heart to the lungs for oxygenation and then back to the left side of the heart.

Systemic Circulation

Delivers oxygenated blood from the left side of the heart to the other tissues of the body where oxygen is used up, and then delivers deoxygenated blood back to the right side of the heart for the cycle to continue.

Coronary Arteries

The blood vessels that wrap around the outside of the heart to supply oxygen-rich blood to the heart muscle itself.

Two Sides of the Heart

Each have an atrium (receives blood) and a larger ventricle (ejects blood from the heart).

Hepatic Veins

Drain the liver.

Mesenteric Vein

Carries nutrient-rich blood away from the intestines.

Hepatic Artery

Carries blood to the liver.

Gastric Artery

Carries blood to the stomach.

Mesenteric Artery

Delivers blood to our intestines.

Superior Vena Cava

Large vein that collects blood from parts of the body superior to the heart and returns it to the right atrium.

Inferior Vena Cava

Large vein that collects blood from parts of the body inferior to heart and returns it to the right atrium.

Mitral Valve

Located between the left atrium and the left ventricle and acts as a barrier that opens and closes to regulate the flow of blood.

Aortic Valve

1. Blood passes from the left ventricle through the aortic valve

2. Is like a door in the heart that controls the flow of blood as it leaves the heart to go to the rest of the body

Tricuspid Valve

1. Located between the right atrium and right ventricle

2. When the heart beats, it opens up, allowing blood from the right atrium to flow into the right ventricle

3. Then, when the right ventricle contracts to pump the blood to the lungs, it closes, preventing blood from flowing backwards into the right atrium

Pulmonary Valve

1. Blood passes from the right ventricle through the pulmonary valve

2. It opens and closes to control the flow of blood, allowing blood to leave the heart and enter the pulmonary artery

3. It then closes to prevent any backwards blow, making sure the blood goes in the right direction to reach the lungs for oxygenation