Regulatory Mechanisms in Animals

Chapter 15

Hormones Are:• Produced in one part of the organism and

pass through a transport system to target tissue

• Specific– stimulus only affects certain hormone

secreting cells– only certain cells can respond

• Relatively slow

Endocrine Glands• Organs that produce and release

hormones directly into the circulatory system

• Fig 15.2 page 280

For a list of the glands and what they do see Table 15.1 page 281 of your text

Note:

Endocrine glands release hormones directly into the _____________ system

see figure 15.3 in your textbook

pituitary

hypothalamus

Pituitary Gland• Central role in overall endocrine regulation• Growth, lactation, reproductive state, skin

pigmentation, fat tissue, kidney function & activity of thyroid and adrenal glands

• Connected to the hypothalamus– Hypothalamus -collects info about the body’s state

(water, food, pain, emotions) and releases releasing hormones to the pituitary

– Pituitary- receives this info and releases hormones to regulate the body’s response

• Fig 15.4 page 283

Thyroxin Hormone

• Stimulates metabolic rate of cells

• Involved in physical development

Anterior Pituitary Gland

Thyroid Stimulating Hormone

Thyroid Gland

Thyroxine

Target Cells (most cells in the body)

via blood vessels

Stimulates an increase in metabolic rate in cell

Thyroid stimulating hormone releasing hormone

Hypothalamusvia blood vessels

releases

releases

via blood vessels

Nervous Systems• More direct pathway of communication• Extremely rapid responses are possible• Functional unit is the neuron• Neurons communicate between

– Sensory cells that detect a disturbance– Effector cells that produce the response

• Specific receptors bring about highly precise responses

• Expensive, require a lot of energy to run

Nervous Systems – EvolutionNote development of a bundle of nerves at the front of the animal

Knee-Jerk Response – Simplest of all

Stretch Receptor

Effector Muscle

Count the nerves!

Sensory Neuron?

Receptors in Skin Effector Muscle

Interneuron?Motor Neuron?

Withdrawal Reflex

Spinal cord

Nervous Response

Environmental Disturbance

(eg. hot plate)

Sensory Cells (skin)

Effector Cells

(muscles)

Neurons sensory,

interneurone & motor

Response

(pull hand away)

Interneurons• Neurons that transmit information from

one neuron to another

• Allow more co-ordinated responses– Withdrawal reflex in hand

• Triceps stay relaxed– Withdrawal reflex in foot

• Opposing foot braces itself

• Task try balancing on one foot.

The Reflex Response• A reflex is a rapid, unconscious response

– hand on a stove– Stand on a pin

• Brain registers the ‘pain’ but doesn’t facilitate the response (spinal cord does)

• Knee-jerk response involves only 2 neurons!

Reflexes in Homeostasis• Baroreceptor-heart rate reflex maintains

blood pressure

• Also see Fig 15.10 page 287

Task

• Draw a stimulus response model to represent the control of blood pressure

Cell Body

Myelin sheath

Axon

Nerve endings

Nucleus

Dendrites

THE STRUCTURE OF NEURONS

Nerve Endings

Nerve endings

Mammalian Nervous Systems• Central nervous system (CNS) – ‘co-

ordinating centre’ – Brain– Spinal cord

• Peripheral Nervous System – ‘sensing and responding’– Motor (muscular) neurons– Sensory neurons

Human Nervous System

• See Fig 15.3 page 282• Note location and function of:

– Cerebral cortex– Hypothalamus– Cerebellum– Brainstem

Human Nervous System

Central Nervous System (brain & spinal cord)

Peripheral Nervous System

Voluntary (somatic) -skeletal muscles

Involuntary (autonomic) -unconscious responses

See Table 15.2 page 288

Sensory (info to the CNS)

Motor (signals to effector-organs)

Autonomic Nervous System(unconscious responses)

• Sympathetic division– Increases energy use– Prepares body for action

• Parasympathetic division– Conserves energy– Slows heart rate

• Enteric division– Nerves specific to gut

Major Sense OrgansTypes of Receptors

• Photoreceptors– Visible light, infrared radiation

• Chemoreceptors– Taste, smell, communication– Oxygen, CO2, pH, water, salts etc

• Mechanoreceptors– Hearing, balance, pressure, touch

• Thermoreceptors – Heat and cold

Vision• Photoreceptor cells contain light-sensitive

pigments that • The interaction of light with the pigment

creates an electrical signal in a sensory nerve

• Types of eyes– Simple– Compound (see fig 15.11 p 289)

Neurons• Cell body

– Nucleus– Usual cell functions

• Dentrites– Carry impulses towards cell body

• Axons– Carry impulses away from cell body to next neuron

• Synapse– Space across which one neuron makes contact with another

• Myelin – Like insulation tape around a neuron (fatty)

Cell Body

Nerve Endings

Nerve endings

Neurons• Signals travel quickly along neurons an

electrical impulses

• The signals that travel between neurons, across the synapse are chemical

Nerve Bundles• See fig 15.12 p 291

• Many neurons group together forming a single nerve

Action Potentials“When a nerve is stimulated its cell membrane is

depolarised so that the inside of the cell becomes less negative. The potential is conducted along the axon to the axon terminal. At the dendrite it stimulates the realease of a chemical transmitter, which diffuses across a synapse. The transmitter binds to receptor sites on the postsynaptic cell membrane to stimulate the generation of another impulse.”

• My advice– carefully read and re-read page 291-293 when you have a quite

period at home