Nerve, Neuron & Nervous System Structures

Structure of a Nerve

• A nerve is a bundle of neurons
• The structure includes the epineurium, perineurium, and endoneurium
• Nerves consists of blood vessels, supplying nerve(vasa nervorum)
• Fascicles are also present
• Peripheral nerves can be myelinated and non-myelinated

Structure of a Neuron

• Neurons contain dendrites and a soma (cell body)
• Neurons contain an axon, myelin sheath, and a nucleus
• At the end of the neuron is a nerve ending
• Some neurons contain Schwann cells

Types of Neurons

• Sensory neurons contain a receptor cell, cell body, axon, and myelin sheath
• Relay neurons contain dendrites, cell body, and an axon
• Motor neurons contain a cell body, Nodes of Ranvier, Schwann cells, and axon

Nervous System

• Electrical impulses act as messengers in the nervous system
• Key structures include the brain, spinal cord, peripheral nervous system, ganglion, and nerves

Endocrine System

• Hormones are the chemical messengers
• Hormones target cells in the endocrine system through the bloodstream
• Key examples of Endocrine glands are the pineal gland, pituitary gland, thyroid gland, thymus, adrenal gland, pancreas, ovaries (female), and testes (male)

Sensory Mechanism

• Sensory neurons, relay neurons, and motor neurons are all involved in the sensory mechanism
• The spinal cord contains grey and white matter
• The central nervous system coordinates a response

The Eye and Focus

• Key structures of the eye include the suspensory ligament, sclera, cornea, iris, pupil, lens, ciliary muscle, retina, fovea, and optic nerve
• To focus on near objects the ciliary muscle contracts, suspensory ligaments slacken, and the lens becomes fatter.
• To focus on distant objects the ciliary muscle relaxes, suspensory ligaments contract/stretch, and the lens becomes thinner

Hormone Production

• The pituitary gland is the 'master gland', situated at the base of the brain
• The thyroid gland produces thyroxine
• The pancreas produces insulin and regulates blood glucose levels, as well as digestive enzymes such as pancreatic amylase and lipase
• The adrenal glands produce adrenaline
• The testes produce testosterone (male sex hormone)
• The ovaries produce oestrogen (female sex hormone)

Hormones and Target Cells

• Hormones bind to specific receptors on target cells
• Non-target cells do not have a receptor for that particular hormone
• Some of these cells make and secrete the hormone

Homeostasis

• Homeostasis is the maintenance of a stable internal environment
• This involves several components input sent, control centre, receptor, output sent, effector, change detected, imbalance (stimulus), response to change and imbalance corrected
• The normal body temperature is around 37° C, and the body is composed around 70% water

Negative Feedback Loop

• Kidneys regulate water & mineral salts concentration
• Skin regulates body temperature
• The liver & pancreas regulate blood glucose level

Insulin and Glucose Regulation

• Beta cells of the pancreas release insulin at high blood glucose levels
• Insulin triggers body cells to take up glucose from the blood promoting cellular respiration
• Glucose is removed from the blood and stored as glycogen in the liver
• Alpha cells of the pancreas release glucagon at low blood glucose levels
• Glycogen in the liver is broken down into glucose and released into the blood

Type 1 Diabetes

• Symptoms include weight loss, frequent urination, irritability, blurry vision, and fruity breath

Type 2 Diabetes

• The body cannot use insulin properly
• Can develop at any age
• Most cases can be prevented
• Risk factors include: being overweight, having a family history and having diabetes while pregnant (gestational diabetes)
• Can be prevented or delayed via weight loss, eating healthier, and being more active
• Can be managed by working with a health professional, eating healthy and staying active

Skin

• Structure of Mammalian Skin consists of the epidermis, dermis, hair follicle, sebaceous gland, arrector muscle receptors, subcutaneous fat, nerve fibres, and blood capillaries
• The skin also contains sweat glands

Waste Substances

• Excess hormones, water and Salt/lons (Na+, Cl-, Mg+, Ca2+, HCO3-) are considered waste substances
• Urea, creatinine, and ammonia are also considered waste products

The Kidney Structure

• Internal structures include cortex, medulla, renal pelvis, fibrous capsule, branch of renal vein and branch of renal artery and the ureter

Nephron

• The nephron contains; a glomerulus, Bowman's capsule, proximal tubule, distal tubule, and collecting duct
• It also contains he ascending/descending Loop of Henle, afferent & efferent arteriole

Kidney Function

• Glomerulus filters small solutes from the blood
• 1st coiled tubule reabsorbs ions, water, removes toxins and nutrients
• The descending loop of Henle is where water is allowed to pass from the filtrate into 2nd tubule
• The ascending loop of Henle reabsorbs Na+ and Cl- from the filtrate
• 2nd tubule selectively secretes & absorbs different ions to maintain pH/ electrolyte
• Collecting duct reabsorbs solutes and water from the filtrate

Dialysis

• A dialyser is used to filter blood
• Clean blood is returned to the patient
• Used dialysis fluid contains the removed waste