Sports Science Test 9/25

Nervous System

A complex, highly organised network of billions of neurons.

Three Basic Functions of the Nervous System

• Sensory function

• Integrative function

• Motor function

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. In other words, motor (or efferent) neurons carry information from the brain towards the spinal cord (or from the brain and spinal cord to, for example, muscle fibres).

2 Main Divisions of the Nervous System

• Central nervous system (CNS)

• Peripheral nervous system (PNS)

Central Nervous System (CNS)

Consists of the brain and the spinal cord.

Peripheral Nervous System (PNS)

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

• Sensory (afferent) nerves

• Motor (efferent) nerves

Sensory (Afferent) Nerves

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

Motor (Efferent) Nerves

Send information from the CNS to tissues, organs and systems of the body. These nerves are further divided into:

• Somatic nervous system

• Autonomic nervous system

Somatic Nervous System

Controls voluntary movements of the skeletal muscles.

Autonomic Nervous System

Regulates involuntary bodily functions. Consists of the:

• Sympathetic nervous system

• Parasympathetic nervous system

Sympathetic Nervous System

Activates the “flight-or-flight” response.

Parasympathetic Nervous System

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

Vasodilation

The widening of blood vessels (caused by relaxation of the smooth muscle in the wall of the blood vessel).

Vasoconstriction

The narrowing of blood vessels (caused by contraction of the smooth muscle in the wall of the blood vessel).

Cerebrum

Is composed of two connected hemispheres that communicate with each other.

Cerebral Cortex

The centre of conscious motor control.

Diencephalon

A major control centre for maintaining the body’s internal environment. Contains the:

• Thalamus

• Hypothalamus

Thalamus

Acts as the body’s primary information relay station; it is very important for motor control.

Hypothalamus

Is responsible for maintaining homeostasis.

Cerebellum

Critical for coordinating movement.

Brain Stem

Connects the brain and the spinal cord.

Intrinsic Excitation

Cardiac muscle has the unique ability to generate its own electrical signal, which allows it to to contract without any external stimulation.

Sinoatrial (SA) Node

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

Atrioventricular (AV) Node

The electrical impulse generated by the SA node spreads through both atria and reaches the AV node, which is located in the right atrial wall near the centre of the heart.

Bundle of His

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.

Heart Rate and Force of Contraction

They can be altered by three extrinsic factors:

• The parasympathetic nervous system

• The sympathetic nervous system

• The endocrine system (hormones)

Extrinsic Factors

External influences, conditions, or forces that originate outside of a person, object, or system rather than from within.

Proprioceptors

Provide information about body position and movements.

Baroreceptors

Sense changes in blood pressure.

Chemoreceptors

Detect the presence of an react to a chemical stimulus.

Endocrine System

Includes all tissues or glands that secrete hormones.

Hormones

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

Hormone Actions vs. Neural Actions

Hormone actions take longer than neural actions but effects often last longer.

Tissues (In Relation to Receptors and Hormones)

Only tissues with very specific receptors can be controlled by a specific hormone.

Main Endocrine Organs

• Hypothalamus

• Pineal gland

• Pituitary gland

• Thyroid gland

• Adrenal gland

• Pancreas

• Ovaries

• Testes

Hormone Classification

Hormones are classed as steroid (not in this test) or non-steroid (epinephrine, glucagon, etc.), with a third category of hormone-like prostaglandins.

Epinephrine and Nonrepinephrine

Increase heart rate, force of contraction and the pumping output of the heart.

Insulin and Glucagon

Help regulate blood sugar concentration. Insulin decreases blood sugar concentration, while glucagon increases it.

Antidiuretic Hormone (ADH)

Secreted by the pituitary gland, it regulates the fluid and electrolyte balance in the blood by reducing urine production.

Hormone Secretion

Hormones can be secreted into the blood or produced locally to the target action.

Endocrine glands (In Relation to Feedback Loops)

Endocrine glands use negative feedback loops.

Main Sources of Information That Influence Hormone Secretion

Three main sources of information that increase or decrease hormone secretion:

• Neural

• Humoral

• Hormonal

Neural

Neural sources of information are signals from the nervous system.

Humoral

Humoral sources of information are due to changes in the chemistry of the blood.

Hormonal

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

Hypothalamus and Pituitary Gland

Are the main endocrine glands maintaining homeostasis in the body.

Hypothalamus (In Relation to Pituitary Action)

The hypothalamus regulates pituitary action using hormones and nervous system signals.

Stroke Volume

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

Muscle Contraction

Is only about 20% efficient, with about 80% of energy released as heat. This heat must be lost from the body to avoid overheating.

Core Body Temperature

Increases during exercise, and the intensity of the exercise determines the size of the increase.

Control Centre for Temperature Regulation

The control centre for temperature regulation is the hypothalamus, located in the brain.

ATP

A high-energy molecule that stores ‍and supplies energy for biological functions.

Four Factors That Contribute to Heat Loss

• Radiation

• Conduction

• Convection

• Evaporation

Radiation

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

Conduction

The process where heat energy moves through direct physical contact between materials or within an object from a warmer area to a cooler one, causing heat loss.

Convection

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

Evaporation

Cools the human body by converting liquid sweat into water vapour, which removes thermal energy from the skin. Accounts for almost all heat loss during exercise and at high ambient temperatures.

Hyperthermia

An elevated body temperature, usually above 39°C.

Effectiveness of Evaporative Heat Loss

The effectiveness of evaporative heat loss is reduced significantly in warm, humid environments.

Non-Shivering Thermogenesis

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

Shivering

Involuntary contractions of skeletal muscle in cold environments.

Three Factors That Influence Sweat Vaporization From the Skin

The three factors that influence sweat vaporization from the skin are:

• The amount of body surface exposed to the air

• The ambient air temperature

• The relative humidity

Dehydration

Too much sweating without fluid replacement can lead to dehydration.

Homeostasis

A tendency towards a relatively stable, constant internal environment.

Homeostasis (In Relation to Feedback Mechanisms)

Homeostasis is generally obtained by negative feedback mechanisms.

Homeostasis (In Relation to CO2)

Homeostasis is influenced by carbon dioxide concentration.

pH

Is monitored via the respiratory control centre of the brain and chemoreceptors throughout the body.

Regulation of the Heart

Depends on intrinsic and extrinsic excitation.

Thermoregulation (Regulation of Body Temperature)

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

Regulation of Blood Glucose

Relies on insulin and glucagon.

HL: Adaptations

The body’s attempts to counteract stressors, such as heat, humidity, and cold, and maintain homeostasis.

HL: Acclimatization

A natural adaptation, for example, to improve exercise performance and heat tolerance in a hot climate.

HL: Acclimation

Is acclimatization in an artificial environment, such as an environmental chamber.

HL: Heat Acclimization

Produces a lower resting core temperature, greater plasma volume and an increased sweating rate, which improve exercise capacity and reduce discomfort during heat exposure.

HL: Main Heat Illness Risks During Exercise in Hot (and Humid) Environments

• Heat cramps

• Heat exhaustion

• Heat stroke

HL: Hypothermia

Low body temperature that has different clinical categories depending on the severity.

HL: The Body During Cold Stress

• Initially constricts blood vessels in the outer part of the body to prevent heat loss

• Begins the shivering response to produce heat, if there has been too much heat loss

HL: Frostnip

The initial freezing of the superficial skin tissue.

HL: Frostbite

The continued cooling and freezing of cells.

HL: Intense Exercise in Cold-Air Environments

Can produce enough heat to maintain core body temperature.

HL: Fat (In Relation to Cold Stress)

Provides an extremely good insulation against cold stress.

HL: Ambient Temperature and Wind

Both influence the coldness of an environment.

HL: Water vs. Air (Conduction)

Water conducts heat faster than air and this has serious effects if clothing is wet during exercise in cold air or if immersed in cold water.

HL: Barometric Pressure (Pb)

The force or weight exerted by air molecules pressing down on the Earth’s surface.

HL: Partial Pressure of Oxygen (PO2)

The part of Pb exerted only by the oxygen molecules in the air.

HL: Altitude

Height above sea level.

HL: Altitude (In Relation to PO2)

When you ascend to altitude reduced PO2 (partial pressure of oxygen) limits and/or impairs performance.

HL: Hypoxia (Low Oxygen)

Low PO2 in the air.

HL: Hypoxemia

Low PO2 in the blood.

HL: Acute Exposure to High/Extreme Altitude

Can be life-threatening.

Respiratory and Cardiovascular Systems

Function together to maintain homeostasis during exercise.

Gas Exchange

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

Ventilation

Functions to ensure that blood leaving the lungs is oxygenated and low in carbon dioxide.

Breathing

Occurs by repeated contraction and relaxation of muscles around the chest cavity.

Ventilation Response

No single factor controls the ventilation response, although carbon dioxide plays an important role.

Static Lung Volumes vs. Dynamic

Static lung volumes are more related to size than to health or fitness, although dynamic volumes are more functional and sensitive to illness.

Gas Exchange in the Lungs and Tissues

Occurs by diffusion from higher partial pressure to lower partial pressure, through thin capillary, alveoli and cell walls.