The Nervous System

Characteristics of lifeAll organisms carry out the same functions

of life:1) All life is made of cells.

2) Homeostasis: maintain constant conditions.

3) Reproduction: life comes from life (biogenesis).

4) Heredity directed by DNA for growth & development.

5) Metabolism: energy utilization and transformation.

6) Response to stimuli: organisms sense and react to their environment.

7) Evolutionary adaptation: life changes in response to interactions between organ- isms and the environment.

Maintain constant internal body conditionsExamples of homeostasis:

Osmosis & diffusion remove wastes from single cells.Birds and mammals regulate body temperature.Guard cells control water loss in leaves.

Maintain constant internal body conditionsRequirements for homeostasis:

Ability to sense when changes have occurred in the internal and external

environment.Ability to respond with appropriate

adjustments.

Phototrophism – a plantsenses and grows toward the sun

The mammalian nervous systemThe nervous system consists

of the central nervous sys- tem (CNS)

and peripheral nervous system (PNS).

CNS = brain & spinal cord

Organization of the nervous systemThe brain’s anatomy

Conscious thought resides in the forebrain.Reflexes & voluntary movement are controlled by the midbrain.Vital body functions & co-

ordination are controlled by the hindbrain.

Front Back

Organization of the nervous systemThe brain’s anatomy: the forebrain

The cerebrum is for conscious thought.Two hemispheres manage different tasks.The corpus callosum connects the two halves of the brain.

Crossover in the corpus callosum causes the left hemisphere to manage the right side of the body.

Organization of the nervous systemThe brain’s anatomy: the forebrain

In the cerebrum, nerve connections create memories.

Cerebral cortex: the outer surface (gray matter) where infor-mation processing occurs is composed of nerve cell bodies. White matter consists of the connecting cables of nerve cells (the axons).

The many folds increase surface area = more nerve cells.

Organization of the nervous systemThe brain’s anatomy: the forebrain

The cerebral cortex is divided into 4 sections called lobes.

Frontal Lobe - reasoning, planning, parts of speech, move- ment, emotions, and problem solving.Parietal Lobe - movement, orientation, recognition, and perception of stimuli.

Occipital Lobe - visual processing.Temporal Lobe – per-

ception and recog-nition of sounds,

memory, speech.

Organization of the nervous systemThe brain’s anatomy: the forebrain

The hypothalamus controls the autonomic nervous system. It synthesizes and secretes hormones that stimulate or inhibit the secretion of pituitary hormones, which then control body tem- perature, hunger, thirst, fatigue, sleep, and circadian cycles (like menstruation).

Above the hypothalamus lies the thalamus, a major clearinghouse for infor-mation going to and from the spinal cord and the cerebrum.

Organization of the nervous systemThe brain’s anatomy: the midbrain

The uppermost part of the brain stem; relays information associated with vision, hearing, motor control, sleeping & waking, arousal (alertness), and temperature regulation.

Organization of the nervous systemThe brain’s anatomy: the hindbrain

Composed of the pons, medulla oblongata, and cerebellum.

The oldest part of the human brain.

The cerebellum is for balance. (Remember: humans are bipedal.)

Organization of the nervous systemThe brain’s evolution

The human brain has a largecerebrum with many folds

to increase surface area.

Brains of primates(also note the cerebellum)

Organization of the nervous systemThe PNS transmits information to and from

the CNS and regulates movement and internal environment

The somatic nervous system carries signals to skeletal muscles. *The autonomic nervous system regulates the internal environment, in an involuntary manner (homeostasis).

*soma = body: chromosome liposome

Conduction of nerve impulsesNerve impulses are conducted from receptors

to the CNS by sensory neurons, within the CNS by relay neurons, and from the CNS to effectors by motor neurons.

Conduction of nerve impulses

Organization of the nervous systemThe nervous system is composed of cells

called neurons that carry rapid electrical impulses.

Draw and label:

Conduction of nerve impulsesNerve impulse passing along a non-

myelinated neuron.

Myelin sheath speeds depolarizations, which can only occur at the nodes of Ranvier.

In multiple sclerosis the sheath degenerates, andmuscles don’t respond to desires.

Conduction of nerve impulsesNerve impulse passing along a non-myelinated neuron.

Conduction of nerve impulsesIn an electrical synapse, current flows

directly from one cell to another via a gap junction.

Conduction of nerve impulsesThe vast majority of synapses are

chemical synapses.

1) The action potential causes Ca++ ions to enter the pre-synaptic cell.2) Vesicles of neurotransmitter leave the cell by exocytosis.3) Neurotransmitter diffuses to post-synaptic cell.4) Neurotransmitter opens Na+ channels to propagate a new action potential.5) Neurotransmitter is reabsorbed by pre-synaptic cell.

Pre-synapticcell

Post-synapticcell

The Endocrine System

Response to stimuliInternal sensory nerves send signals to the

hypothalamus.The hypothalamus monitors body chemistry. It reacts to changes and responds by sending chemical signals to endocrine glands.

Hormones are the chemical mes-

sengers.

The endocrine systemHomeostasis in humans involves maintaining

blood & tissue fluid (pH, CO2 concentration, sugar levels, body temper-ature, and water balance) between certain limits:

Levels of variables are corrected by negative feedback (hormones are released until the stimulation is removed).

The endocrine systemThe endocrine system con-

sists of glands that release hormones that are trans- ported in the blood.

The endocrine systemAnimal hormones are chemical signals that

are secreted into the circulatory system and communicate regulatory messages within the body.

Hormones reach all parts of the body, but only

target cells are equipped

to respond.

Receptor in: cell membrane nucleus

ThermoregulationThe hypothalamus monitors

body heat.

ThermoregulationThe control of body temperature involves

physiological and behavioral adjustments that balance heat gain and loss.

Most biochemical and physiological processes are very sensitive to changes in body temperature;

enzymes are damaged.

ThermoregulationHumans are endotherms; blood transfers

metabolic heat throughout the body.The hypothalamus monitors body heat and sends out hormones that make skin arterioles constrict, cause us to shiver or perspire, increase metabolism, or produce discomfort so we change clothes, etc.

As a result mammals need more food thanreptiles.

ThermoregulationThe human body is adapted to avoid over-

heating (or getting chilled):Upright postureSweat glandsLack of hair

Skin arterioles

DehydrationDehydration – a lack of water (our skin is not

water-tight like that of a reptile; cells lose water AND we perspire).

Water serves many purposes within the body.

DehydrationDehydration – a lack of water (our skin is not

water-tight like that of a reptile; cells lose water AND we perspire).

Typically we need 2 ½ liters of water per day; more in hot, dry weather or with heavy exertion.

DehydrationDehydration

Severe dehydration causes heat stroke, which can be

deadly in a short time.

Control of blood glucoseNot only does the pancreas produce digestive

enzymes, it secretes hormones that maintain glucose homeostasis.

Acinar cells (exocrine system) secrete digestive enzymes.Islets of Langerhans secrete the hormones insulin and glucagon.

Control of blood glucoseInsulin and glucagon are antagonistic

hormones that help maintain glucose homeostasis.

Glucagon (produced by alpha cells) increases blood glucose levels:

Stimulates conversion of glycogen to glucose in the liverStimulates breakdown of fat and protein into glucose.

Control of blood glucoseInsulin and glucagon are antagonistic

hormones that help maintain glucose homeostasis.

Insulin (produced by beta cells) reduces blood glucose levels:

Promotes the cellular uptake of glucoseSlows glycogen breakdown in the liver and promotes fat storage

Control of blood glucoseKnow how insulin

and glucagon bal- ance each other.

DiabetesDiabetes mellitus is caused by a deficiency of

insulin or a decreased response to insulin in target tissues.

It is marked by elevated blood glucose levels.

Type I diabetes is an autoimmune disorder in which the immune system destroys pancreatic beta cells .Type II diabetes involves insulin deficiency or reduced response of target cells due to change in insulin receptors.

DiabetesType 1 diabetes

Usually starts in childhood and accounts for5 - 10% of all diagnosed cases of

diabetes. People with type 1 diabetes produce little or no insulin and must use insulin daily to control their condition.

Injection sites

DiabetesType 2 diabetes

Usually starts in adulthood, but it is being diagnosed more often in children because of greater childhood obesity. It accounts for 90 - 95% of cases. People with type 2 diabetes are resistant to the insulin the body makes. It is controlled with diet and exercise, and sometimes oral drugs or

insulin.