Human Anatomy: Organ Systems Overview

• The nervous system controls all organs, physiological reactions, and psychological reactions.
• The nervous and endocrine systems are the body's main regulatory and coordinating systems.
• The nervous system coordinates the body's actions and sensory information by transmitting electrical signals/impulses.
• The endocrine system consists of hormone-producing glands.
• The digestive system converts food into nutrients and produces glucose, amino acids, and fatty acids that are absorbed through the small intestine.
• The respiratory system expels unwanted gases like carbon dioxide, warms air, protects from particles, and allows speech.
• The circulatory system transports nutrients, wastes, and gases.
• The excretory system removes waste products from the body (two kidneys, two ureters, bladder, and urethra).
• The levels of organization include cells, tissues, organs, and body systems.
• All animals, except simple ones like sponges, have a nervous system.
• Human nervous systems are the most distinctive feature of the species.

Functions of the Nervous System

• The nervous system's activities can be reduced to three main functions: sensory input, integration, and motor output.
• Sensory input is information that sensory receptors detect from a stimulus.
• Sensory receptors are specialized cells in specialized organs (skin, eyes, tongue, ears, nose) that detect changes in the environment.
• Sensory receptors convert changes into electrical signals for the nervous system to process and relay information to the CNS.
• Integration is the process by which the nervous system processes sensory input and decides what to do about it.
• Motor output is a response that occurs when the nervous system activates certain body parts to reply to a stimulus.
• The vertebrae nervous system sends messages along neurons and consists of the central nervous system (CNS) and peripheral nervous system (PNS).
• The central nervous system consists of the brain and spinal cord.
• It is the main control center of the nervous system, decides to activate responses to different stimuli, and gives orders to certain body parts.
• The peripheral nervous system is composed of all the nerves (sensory & motor neurons) that connect to the CNS, enabling communication with the rest of the body.
• Peripheral nervous system is responsible for communication.
• Plays an integral role in communication, it is set up to work in both directions

Sensory and Motor Divisions

• The sensory/afferent division picks up sensory stimuli and sends information to the brain (CNS).
• The motor/efferent division sends directions from the brain to muscles & glands.
• The motor/efferent division includes the somatic/voluntary and autonomic/involuntary nervous systems.
• The somatic/voluntary nervous system controls voluntary functions and skeletal muscle movement.
• The autonomic/involuntary nervous system controls involuntary functions like heart beating, lung breathing, and stomach churning.

Cells of the Nervous System

• The nervous system is made up of mostly nervous tissue, which is densely packed with cells with less than 20% extracellular space.
• These cells include neurons/nerve cells and neuroglia/glial cells.
• Neurons respond to stimuli and transmit signals.
• Neurons account for a small part of the nervous tissue and are protected and surrounded by neuroglial cells.
• Neuroglia were once considered just scaffolding, glue thet holds neurons but serve important functions.
• Neuroglia makes up about half the mass of the brain and outnumbers neurons by about 10:1.

Neuroglia Types in the CNS

• Astrocytes are star-shaped, abundant, and versatile glial cells.
• Astrocytes anchor neurons to their blood supply and govern the exchange of materials between neurons and capillaries.
• Capillaries deliver nutrients and oxygen cells and connect arteries and veins help organs function by removing carbon dioxide and other wastes.
• Arteries are blood vessels that distribute oxygen-rich blood
• Veins are blood vessels that collect oxygen-poor blood and return it to the heart.
• Microglial cells are smaller than astrocytes and act as the main source of immune defense against microorganisms in the CNS.
• Ependymal cells line cavities in the brain and spinal cord and create, secrete, and circulate cerebrospinal fluid.
• Oligodendrocytes wrap around neurons and produce the myelin sheath around axons.

Neuroglia Types in the PNS

• Satellite cells surround and support neuron cell bodies.
• Schwann cells wrap around axons to make insulating myelin sheath.

Neurons

• Neurons carry messages/nervous impulses around the body.
• Messengers and the nervous impulse is the message.
• A ganglion is a cluster of nerve cell bodies.
• Neurons link together to form circuits that carry out specific jobs.
• The vertebrate brain is divided into 3 sections, the cerebellum, medulla oblongata and cerebrum.
• The cerebellum controls balance and movement.
• The medulla oblongata regulates heartbeat, body temperature, and breathing rate.
• The cerebrum controls thinking, intelligence, memory, language, reasoning, feeling, and learned skills.

Neuron Shared Characteristics

• Neurons are some of the longest-lived cells in the body.
• Neurons are irreplaceable-amitotic cells that lose their ability to divide once they take on their roles in the nervous system.
• Neurons have high metabolic rate and need a steady supply of glucose and oxygen, consuming about 25% of the calories consumed in a day.

Neuron Structure

• Soma/cell body: life support that contains cell parts necessary for the neuron's survival, i.e. nucleus, DNA, mitochondria, ribosomes & cytoplasm.
• Dendrites: bushy, branch-like things projecting out from the soma that pick up messages from other cells and convey the information to the cell body
• Axon: a long extension/fibre that varies in length by is small in diameter.
• Axons transmit electrical impulses from of most abundant neuron type, away from the cell body to other neurons.
• Axon terminals connect to dendrites of other neurons. Processes extending from the cell body are used to classify nerve cells.

Neuron Classification

• Bipolar neurons have 2 processes (1 axon + 1 dendrite), rare, and mostly found in special sensory places, i.e. retina of the eye.
• Unipolar neurons have 1 process (usually 1 axon) and are mostly found in sensory receptors.
• Multipolar neurons have 3+ processes (1 axon + lots of dendrites).
• About 99% of neurons are multipolar.

Neuron Function

• Neurons can be classified by physiology, how an impulse travels relative to the brain and spine.
• Neurons typically consist of a cell body, dendrites, and a long axon.
• Sensory/afferent neurons are only found in the PNS and are mostly unipolar.
• They connect to sensory receptors to detect environmental changes.
• Transmit impulses via a dendron to connector neurons via an axon.
• They have a myelin sheath that protects/insulates the axon and produce neurotransmitters
• Interneurons/association/connector/relay neurons are only found in the CNS.
• Interneurons join sensory & motor neurons and transmit impulses between them.
• Interneurons are mostly multipolar without a myelin sheath and can be part of a reflex arc.
• Motor/efferent/effector neurons are only found in the PNS and are mostly multipolar.
• Motor neurons transmit impulses out to the body's muscles and glands for a response.

Stimulus Response

• A stimulus initiates a message that travels nerves to the responding organ (effector)
• Cells outside the CNS are supported by Schwann cells that form a wrapped myelin sheath around axons.
• Myelin is an electrically insulating layer around the axon, increasing the speed of impulse conduction.
• Larger diameter axon = faster impulse conduction.
• At intervals along the axon, there are gaps between the sheath called nodes of Ranvier
• Sheath prevents ion flow, impulses 'jump' along at the axon.

Neurotransmission Process

• Messages travel along a single neuron as electrical impulses, but between neurons travel differently through 'synapses'
• Carried across to a special compounds called neurotransmitters
• Communication between results in a releases Neurotransmitters from axon to the synapse cross over.
• The Neutransmitters bind onto the receptors of receiving dendrites
• Neurotransmission travel speed depends on diamater, the thickest are fastest (0.4m - 180m/s)
• Neurotransmitters have specific receptrors
• After its release either broken down or returned for later use

Reflexes

• Reflex: immediate automatic motor response to specific stimulus, and involves a small number of CNS processing point
• A refex will send same data conscious brain
• A reflex action includes receptor detecting stimulus, the travels to motor/efferent/effector neuron for response via CNS information
• Allows classifies synapse count according to the CNS
• Monosynaptic only involves 1 synapse: Knee Jerk
• Polysynaptic needs involved 2 or more synapse: pain withdrawal

Neurotoxins

• Neurotoxins: targets Neurons, synapses and glial cells and neurotransmitters
• Common effects incldue muscle weakness, autonomic issues, respritory,paralysis
• Two Types:
  • Exogenous from animals, bacteria, plants and animals
  • Endogenous produced inside metabolize by products

Homeostasis

• Enzymes: proteins that regulate chemical reactions in the body
• Enzymes: work best within a narrow range of conditions
• Blood, Body, PH and Salt needs to be within range

Terminology

• Homeostasis the process to maintain a stable internal environment whilst adjusting
• Ability based on the nervous system to interpret and correct.
• Internal body conditions are fairly constant despite changes in the external environment

Negative Feedback

• A control mechanism in homeostasis can balance out states
• 3 Step loop of detection-transmission-response, to return to body to normal steady state.
• Insulin signals the body to reduce glucose when high.
• Glucagon signals the body to increase when glucose is low

Regulating Body Temperature via NF

• Hot: receptors signals brain, brain sends instructions capillaries and sweat glands, cooling through dilated capillaries and sweat
• Heat goes back to steady state when colling responses shut off
• Cold: receptors signal brain, brain sends instructions to contract capillaries and muscles, create heat and less loss
• Goes back to steady state when warming responses turn off

Regulating Salt and Water Balance via NF

• Kidneys use feedback loop to regulate the negative feedback.
• Inside Kidneys, there are structures called nephrons the contain renal corpuscles.
• Renal copruscles do filtration with glomeulus capsule fluid
• Fluids end up getting excreted but balanced with constant composition change

Loop

• Absorbed and level adjusted
• The excretion outcome is tightly maintained and regulated

Regulation

• Regulaiton Excretion relies on Anti diuretic hormone (ADH)
• If you drink less signals sent by hypothalamus to release little ADH: dilute
• If you drink more signals sent to release ADH: less dilute
• Blood flow is regulated vasodilation: widened muscles which relax
• Vasoactive hormones include: serotonin, norepinephrine, insulin & endothelin

Blood Flow Via NF

• Signals indicate Svs resistnace to lower pressure.

Positive Feedback

• Opposite to regulation, changes trigger reactions that change other reactions.
• EX: ChildBirth: baby puts pressure on cervix, cervix signals more oxytocin production until done
• Once over signals turn off.