Types of Neurons

In the study of coordination and control in biology, understanding the types of neurons in nervous system is essential. There are three main types of neurons, each with distinct characteristics and functions:

1. Sensory Neurons

   • Convert stimuli into electrical impulses
   • Have long dendrites and short axons
   • Cell body is bulging out of the neuron

2. Motor Neurons

   • Transfer messages from the central nervous system to effector organs
   • Have short dendrites and long axons
   • Neurotransmitters are released at the end of the axon

3. Relay Neurons

   • Link sensory and motor neurons, allowing uninterrupted impulse movement
   • Present in the brain and spinal cord
   • Do not have a myelin sheath

Vocabulary: Myelin sheath - A fatty layer that covers and insulates the axon of some neurons, increasing the speed of electrical impulse transmission.

Highlight: The structure of neurons is specialized to their function, with variations in the length of dendrites and axons, as well as the presence or absence of myelin sheaths.

Mechanism of Synapses

Synapses play a crucial role in the coordination and control in biology, particularly in the nervous system. They are junctions between two nerve cells where impulses pass by diffusion of a neurotransmitter.

Key components of a synapse include:

1. Pre-synaptic neuron
2. Post-synaptic neuron
3. Synaptic cleft (the gap between neurons)
4. Vesicles containing neurotransmitters
5. Neurotransmitter receptors on the post-synaptic membrane

Definition: A synapse is a junction between two nerve cells consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter.

The process of synaptic transmission involves:

1. Arrival of an electrical impulse at the pre-synaptic neuron
2. Release of neurotransmitters into the synaptic cleft
3. Binding of neurotransmitters to receptors on the post-synaptic neuron
4. Generation of a new electrical impulse in the post-synaptic neuron

Highlight: Synapses allow for the conversion of electrical signals to chemical signals and back to electrical signals, enabling complex information processing in the nervous system.

The Endocrine System and Hormones

The endocrine system is a crucial component of coordination and control in biology, working alongside the nervous system to regulate bodily functions. It consists of glands that produce and secrete hormones directly into the bloodstream.

Definition: A hormone is a chemical substance produced by a gland and secreted into the bloodstream, which alters the activity of specific target organs.

Key characteristics of hormones:

• Produced by endocrine glands
• Secreted directly into the bloodstream
• Act on specific target organs
• Once used, they are destroyed by the liver

Example: Adrenaline, often called the "fight or flight hormone," is produced by the adrenal glands and prepares the body for action in stressful situations.

Important endocrine glands and their hormones:

1. Thyroid gland: Produces thyroxine, which controls metabolism
2. Hypothalamus: Produces various hormones that regulate other glands
3. Pituitary gland: Produces growth hormone and ADH (Anti-Diuretic Hormone)
4. Pancreas: Produces insulin and glucagon to regulate blood sugar levels
5. Ovaries: Produce estrogen, which controls female reproductive functions
6. Testes: Produce testosterone, which controls male reproductive functions

Highlight: Unlike exocrine glands, which have ducts to secrete their products, endocrine glands secrete hormones directly into the bloodstream.