Unit 5: Neural and Chemical Co-ordination

Co-ordination is the process by which different organs and systems in the body work together in a controlled and efficient way. This is achieved by two systems: the fast-acting Nervous System and the slower, long-lasting Endocrine (Hormonal) System.

Part 1: Neural Co-ordination

1. Types of Nervous System

The nervous system is the body's primary control and communication network.

[Image of a flowchart of the divisions of the nervous system]

1. Central Nervous System (CNS): The "command center."
   • Brain: The main processing unit.
   • Spinal Cord: A column of nerve tissue that connects the brain to the rest of the body and controls reflexes.
2. Peripheral Nervous System (PNS): All the nerves that branch out from the CNS.
   • Somatic Nervous System: Controls voluntary movements (e.g., skeletal muscles).
   • Autonomic Nervous System: Controls involuntary functions (e.g., heart rate, digestion, breathing).
     • Sympathetic Division: "Fight-or-flight" response (prepares body for action).
     • Parasympathetic Division: "Rest-and-digest" response (calms the body).

2. Structure of Human Brain

The brain is the complex organ that serves as the center of the nervous system.

[Image of the major parts of the human brain (Cerebrum, Cerebellum, Brainstem)]

a) Cerebrum

• Structure: The largest part of the brain, divided into two cerebral hemispheres (left and right). The outer layer is the highly folded cerebral cortex.
• Function: The center for all higher-order functions:
  • Conscious thought, memory, and learning.
  • Interpreting sensory information (vision, hearing, touch).
  • Initiating voluntary movements.
  • Language and problem-solving.

b) Cerebellum

• Structure: Located at the back of the brain, beneath the cerebrum.
• Function: The "little brain" is crucial for:
  • Co-ordination: Fine-tunes voluntary movements, making them smooth and precise.
  • Balance and Posture: Receives sensory input to maintain equilibrium.

3. Structure of a Neuron

The neuron (or nerve cell) is the basic structural and functional unit of the nervous system. It is specialized to transmit electrical and chemical signals.

[Image of the structure of a typical motor neuron]

Key Parts:

• Soma (Cell Body): Contains the nucleus and most organelles.
• Dendrites: Short, branched extensions that receive signals from other neurons and transmit them *towards* the cell body.
• Axon: A single, long extension that transmits signals (action potentials) *away* from the cell body to other neurons, muscles, or glands.
• Myelin Sheath: A fatty layer that insulates the axon (in many neurons), allowing the signal to travel much faster.
• Synaptic Terminals (Axon Terminals): The end of the axon, where the signal is passed to the next cell via a synapse (usually using chemical messengers called neurotransmitters).

4. Reflex Action

A reflex action is a rapid, involuntary, and automatic response to a specific stimulus, which does not require conscious thought from the brain.

The pathway of this response is called a reflex arc.

Example (Withdrawing hand from heat):

1. Stimulus: Hot object is touched.
2. Receptor: Sensory receptors in the skin detect the heat/pain.
3. Sensory Neuron: Transmits the signal *to* the spinal cord.
4. Relay Neuron (Interneuron): In the spinal cord, it passes the signal directly to a motor neuron. (It also sends a signal to the brain, but the reflex happens before the brain registers the pain).
5. Motor Neuron: Transmits the signal *away* from the spinal cord to the muscle.
6. Effector: The muscle (e.g., in the arm) contracts, pulling the hand away.

[Image of a reflex arc]

Part 2: Chemical Co-ordination

5. Definition and Functions of Hormones

Hormones are chemical messengers produced by endocrine glands. They are secreted directly into the bloodstream and travel throughout the body, but they only affect specific target cells that have the correct receptors for that hormone.

General Functions of Hormones:

• Regulating metabolism and energy balance.
• Controlling growth and development.
• Managing the body's response to stress and injury.
• Regulating reproduction and sexual characteristics.
• Maintaining homeostasis (e.g., blood sugar, calcium levels, water balance).

6. Endocrine Glands and their Hormones

Here are some of the major endocrine glands and their key hormones:

[Image of the major endocrine glands in the human body]

a) Pituitary Gland

The "master gland," located at the base of the brain. It controls many other endocrine glands.

• Anterior Pituitary:
  • Growth Hormone (GH): Stimulates growth, especially of bone and muscle.
  • Thyroid-Stimulating Hormone (TSH): Stimulates the thyroid gland.
  • FSH and LH: Regulate reproduction (see testis/ovary).
• Posterior Pituitary:
  • Antidiuretic Hormone (ADH): Tells kidneys to reabsorb more water.

b) Pineal Gland

Located in the brain.

• Hormone: Melatonin
• Function: Regulates sleep-wake cycles (circadian rhythms).

c) Thyroid Gland

Located in the neck.

• Hormones: Thyroxine (T4) and Triiodothyronine (T3)
• Function: Regulates the body's overall metabolic rate.

d) Thymus

Located in the chest, behind the sternum.

• Hormone: Thymosin
• Function: Essential for the development and maturation of T-lymphocytes (a type of white blood cell) for the immune system.

e) Pancreas (as an endocrine gland)

Has clusters of endocrine cells called Islets of Langerhans.

• Hormone: Insulin
• Function: Lowers blood glucose levels (tells cells to take up glucose from the blood).
• Hormone: Glucagon
• Function: Raises blood glucose levels (tells the liver to release stored glucose).

f) Testis (in males)

The male gonads.

• Hormone: Testosterone (an androgen)
• Function: Responsible for sperm production and the development of secondary male characteristics (e.g., deep voice, facial hair).

g) Ovary (in females)

The female gonads.

• Hormone: Estrogen
• Function: Responsible for egg maturation and the development of secondary female characteristics (e.g., breast development).
• Hormone: Progesterone
• Function: Prepares the uterus for pregnancy and maintains it.