topic 3: nervous system and the eye
image from www.orlandohealthdocs.com
The human nervous system controls everything from breathing and standing upright, to memory and intelligence. It has three parts: detecting stimuli; coordinating; and effecting a response:
Stimuli are changes in the external or internal environment, such as light waves, pressure or blood sugar. Humans can detect at least nine external stimuli and dozens of internal stimuli, so the commonly-held believe that humans have just five senses is obviously very wide of the mark!
Receptor cells detect stimuli. Receptor cells are often part of sense organs, such as the ear, eye or skin. Receptor cells all have special receptor proteins on their cell membranes that actually do the sensing, so “receptor” can confusingly mean a protein, a cell or a group of cells.
The coordinator is the name given to the network of interneurones connecting the sensory and motor systems. It can be as simple as a single interneurone in a reflex arc, or as complicated as the human brain. Its job is to receive impulses from sensory neurones and transmit impulses to motor neurones.
Effectors are the cells that effect a response. In humans there are just two kinds: muscles and glands. Muscles include skeletal muscles, smooth muscles and cardiac muscle, and they cause all movements in humans, such as walking, talking, breathing, swallowing, peristalsis, vasodilation and giving birth. Glands can be exocrine – secreting liquids to the outside (such as tears, sweat, mucus, enzymes or milk); or endocrine – secreting hormones into the bloodstream.
Responses aid survival. They include movement of all kinds, secretions from glands and all behaviours such as stalking prey, communicating and reproducing.
Stimuli are changes in the external or internal environment, such as light waves, pressure or blood sugar. Humans can detect at least nine external stimuli and dozens of internal stimuli, so the commonly-held believe that humans have just five senses is obviously very wide of the mark!
Receptor cells detect stimuli. Receptor cells are often part of sense organs, such as the ear, eye or skin. Receptor cells all have special receptor proteins on their cell membranes that actually do the sensing, so “receptor” can confusingly mean a protein, a cell or a group of cells.
The coordinator is the name given to the network of interneurones connecting the sensory and motor systems. It can be as simple as a single interneurone in a reflex arc, or as complicated as the human brain. Its job is to receive impulses from sensory neurones and transmit impulses to motor neurones.
Effectors are the cells that effect a response. In humans there are just two kinds: muscles and glands. Muscles include skeletal muscles, smooth muscles and cardiac muscle, and they cause all movements in humans, such as walking, talking, breathing, swallowing, peristalsis, vasodilation and giving birth. Glands can be exocrine – secreting liquids to the outside (such as tears, sweat, mucus, enzymes or milk); or endocrine – secreting hormones into the bloodstream.
Responses aid survival. They include movement of all kinds, secretions from glands and all behaviours such as stalking prey, communicating and reproducing.
Recall that the central nervous system consists of the brain and spinal cord and is linked to sense organs by nerves
Recall: Remember or recognize from previous learning experiences
Recall: Remember or recognize from previous learning experiences
image from en.wikipedia.org
The nervous system consists of the brain, spinal cord, sensory organs, and all of the nerves that connect these organs with the rest of the body. Together, these organs are responsible for the control of the body and communication among its parts.
The brain and spinal cord form the control center known as the central nervous system (CNS), where information is evaluated and decisions made. The sensory nerves and sense organs of the peripheral nervous system (PNS) monitor conditions inside and outside of the body and send this information to the CNS. Efferent nerves in the PNS carry signals from the control center to the muscles, glands, and organs to regulate their functions.
The brain and spinal cord form the control center known as the central nervous system (CNS), where information is evaluated and decisions made. The sensory nerves and sense organs of the peripheral nervous system (PNS) monitor conditions inside and outside of the body and send this information to the CNS. Efferent nerves in the PNS carry signals from the control center to the muscles, glands, and organs to regulate their functions.
Explain that stimulation of receptors in the sense organs sends electrical impulses along nerves into and out of the central nervous system, resulting in rapid responses
Explain: Give a detailed account.
Explain: Give a detailed account.
image from brainu.org
A neuron is a nerve cell that is the basic building block of the nervous system. Neurons are similar to other cells in the human body in a number of ways, but there is one key difference between neurons and other cells. Neurons are specialized to transmit information throughout the body.
These highly specialized nerve cells are responsible for communicating information in both chemical and electrical forms. There are also several different types of neurons responsible for different tasks in the human body.
Sensory neurons carry information from the sensory receptor cells throughout the body to the brain. Motor neurons transmit information from the brain to the muscles of the body. Interneurons are responsible for communicating information between different neurons in the body.
These highly specialized nerve cells are responsible for communicating information in both chemical and electrical forms. There are also several different types of neurons responsible for different tasks in the human body.
Sensory neurons carry information from the sensory receptor cells throughout the body to the brain. Motor neurons transmit information from the brain to the muscles of the body. Interneurons are responsible for communicating information between different neurons in the body.
Describe the structure and functioning of a simple reflex arc illustrated by the withdrawal of a finger from a hot object
Describe: Give a detailed account or picture of a situation, event, pattern or process.
Describe: Give a detailed account or picture of a situation, event, pattern or process.
A reflex is a response to a perturbing stimulus that acts to return the body to homeostasis. This may be subconscious as in the regulation of blood sugar by the pancreatic hormones, may be somewhat noticeable as in shivering in response to a drop in body temperature; or may be quite obvious as in stepping on a nail and immediately withdrawing your foot.
A reflex arc refers to the neural pathway that a nerve impulse follows. The reflex arc typically consists of five components:
A reflex arc refers to the neural pathway that a nerve impulse follows. The reflex arc typically consists of five components:
- The receptor at the end of a sensory neuron reacts to a stimulus.
- The sensory (afferent) neuron conducts nerve impulses along an afferent pathway towards the central nervous system (CNS).
- The integration center consists of one or more synapses in the CNS.
- A motor (efferent) neuron conducts a nerve impulse along an efferent pathway from the integration center to an effector.
- An effector responds to the efferent impulses by contracting (if the effector is a muscle fiber) or secreting a product (if the effector is a gland).
image from danielscienceblogg.blogspot.com
Describe how the nerve impulse travels from one neuron to another
Describe: Give a detailed account or picture of a situation, event, pattern or process.
Describe: Give a detailed account or picture of a situation, event, pattern or process.
image from science.education.nih.gov
Individual nerve cells connect with one another through gaps, called synapses. When a nerve impulse reaches the synapse, it releases a chemical messenger called a neurotransmitter. The neurotransmitter diffuses across the synapse and triggers a new impulse in the dendrite of one or more connecting neurons.
As the impulse reaches the end of the first neurone which causes several hundred vesicles containing the neurotransmitter to fuse with the cellmembrane. The neurotransmitter is released into the synaptic cleft.
The molecules of neurotransmitter bind with complementary receptors (similar to an enzyme and substrate fitting together) in the cell membrane. The impulse continuous down the next neuron
As the impulse reaches the end of the first neurone which causes several hundred vesicles containing the neurotransmitter to fuse with the cellmembrane. The neurotransmitter is released into the synaptic cleft.
The molecules of neurotransmitter bind with complementary receptors (similar to an enzyme and substrate fitting together) in the cell membrane. The impulse continuous down the next neuron
Explain how substances such as pesticides, drugs and alcohol can inhibit the nerve impulse travelling across the synapse
Explain: Give a detailed account
Explain: Give a detailed account
image from neuroscience.mssm.edu
Almost all drugs taken by humans (medicinal and recreational) affect the nervous system, especially synapses. Drugs that stimulate a synapse are called agonists, and those that inhibit a synapse are called antagonists. By
designing drugs to affect specific synapses, drugs can be targeted at different parts of the nervous system.
The following examples show how some common drugs work. You do not need to learn any of this, but you should be able to understand how they work.
designing drugs to affect specific synapses, drugs can be targeted at different parts of the nervous system.
The following examples show how some common drugs work. You do not need to learn any of this, but you should be able to understand how they work.
- Caffeine, theophylline, amphetamines, ecstasy (MDMA) and cocaine all promote the release of neurotransmitter in excitatory synapses in the part of the brain concerned with wakefulness, so are stimulants.
- Alcohol, benzodiazepines (e.g. mogadon, valium, librium), barbiturates, and marijuana all activate the inhibitory neuroreceptors in the same part of the brain, so are tranquilizers.
- The narcotics or opioid group of drugs, which include morphine, codeine, opium, methadone and diamorphine (heroin), all block opiate receptors, blocking transmission of pain signals in the brain and spinal chord. The brain’s natural endorphins appear to have a similar action.
- Parkinson’s disease (shaking of head and limbs) is caused by lack of the neurotransmitter dopamine in the midbrain. The balance can be restored with levodopa, which mimics dopamine.
- Curare and α-bungarotoxin (both snake venoms) block the acetylcholine receptors in neuromuscular junctions and so relax skeletal muscle.
- Nerve gas and organophosphate insecticides (DDT) inhibit acetylcholinesterase, so acetylcholine receptors in neuromuscular junctions are always active, causing muscle spasms and death.
- Tetrodotoxin (from the Japanese puffer fish) blocks voltage-gated sodium channels, while
- tetraethylamonium blocks the voltage-gated potassium channel. Both are powerful nerve poisons.
image from www.drugabuse.gov
Compare the nervous system with the endocrine system
Compare:Give an account of similarities and differences between two (or more) items, referring to both (all) of them throughout.
Compare:Give an account of similarities and differences between two (or more) items, referring to both (all) of them throughout.
Describe the structure and function of the eye as a receptor
Describe: Give a detailed account or picture of a situation, event, pattern or process.
Describe: Give a detailed account or picture of a situation, event, pattern or process.
When you look at an object, light rays reflected from the object hit the transparent cornea at the front of your eye. The rays are partly focused and pass through the pupil, which enlarges or constricts depending on light conditions. The lens varies its focusing power for near and distant objects and fine-focuses the rays to create a sharp image on the fovea, the most responsive area of the light-sensitive retina at the back of the eye.
The mechanism of visionLight rays focused by the cornea and lens produce an image on the retina that is upside down. Electrical signals from stimulated cells in the retina travel along the optic nerve to the brain, where the image is interpreted as being upright.
The mechanism of visionLight rays focused by the cornea and lens produce an image on the retina that is upside down. Electrical signals from stimulated cells in the retina travel along the optic nerve to the brain, where the image is interpreted as being upright.
image from www.glaucoma.org
Describe the function of the eye in responding to changes in light intensity
Describe: Give a detailed account or picture of a situation, event, pattern or process.
Describe: Give a detailed account or picture of a situation, event, pattern or process.
image from encyclopedia.lubopitko-bg.com
The iris consists of radial muscles arranged like the ciliary muscles, when they contract the radius decreases, the surface area of the iris increases (the contracted muscles take up more space when arranged in a circle) and less light is let into the eye.
- Bright light: Radial muscles contract (these run through the diameter of the iris)
- Dim light: Circular muscles contract (these run along the circumference of the iris)
Describe the function of the eye in focusing near and distant objects
Describe: Give a detailed account or picture of a situation, event, pattern or process.
Describe: Give a detailed account or picture of a situation, event, pattern or process.
image from atlasofophthalmology.org
The eye adjusts for near and distant vision by changing the shape of its lens. This varies the extent to which incoming light is refracted (bent). To create a sharp image on the retina, light rays from near objects must be bent more than those from distant objects. This process is called accommodation.
When you look at an object in the distance, muscles in the ciliary body relax and the lens assumes a flatter shape.
When you look at a close object, muscles in the ciliary body contract, allowing the elastic lens to assume a more spherical shape.
When you look at an object in the distance, muscles in the ciliary body relax and the lens assumes a flatter shape.
When you look at a close object, muscles in the ciliary body contract, allowing the elastic lens to assume a more spherical shape.
image from healthy-ojas.com
Key Terms
|
stimulus
response coordination receptor effector impulse transducers sensory neurone sclera cornea pupi iris |
spinal cord
cranium cranial motor neurons cell body axon dendrites fovea refracted suspensory ligaments ciliary muscles conjunctiva |
myelin sheath
synapse cell fibre reflex action dorsal root relay neurones ventral root reflex action blind spot accommodation inverted choroid |
sensory neurone
neurotransmitter PNS cerebellum medulla cerebrum cerebral cortex constricted radial muscles dilating lens |
transduction
neuron CNS ganglion grey matter white matter voluntary action retina rods cone optic nerve |
Classroom Material:
Nervous System
Nervous System Lab
Big Picture Inside the Brain
Nervous System (study guide)
Neuron Diagram
Nerves and Synapses Internet Research
Nerves Revision
Mouse Party - Drugs and the Nervous System activity
Investigate one neurological disease and its effect on the body
Sensitivity to Temperature Practical
Design an experiment to test the sensitivity of skin (in class assignment)
Reflex Arc review
Reaction Time practical
Nervous System Lab
Big Picture Inside the Brain
Nervous System (study guide)
Neuron Diagram
Nerves and Synapses Internet Research
Nerves Revision
Mouse Party - Drugs and the Nervous System activity
Investigate one neurological disease and its effect on the body
Sensitivity to Temperature Practical
Design an experiment to test the sensitivity of skin (in class assignment)
Reflex Arc review
Reaction Time practical
Part 1 The Brain
Part 2 Nervous System
Part 3 Reflex Arc
Part 4 Jumping The Gap
Human Eye
Structure of the Human Eye (ppt)
Structure of the Human Eye (study guide)
Sheep Eye Dissection practical
Binocular Vision practical
Part 5 Structure of the Eye
Part 6 How We See
Useful Links:
BBC Bitesize Nervous System activity
Fight or Flight and Negative Feedback from How Stuff Works. A good read
Impact of Drugs on Neurotransmitters
Impact of Alcohol on Neurotransmitters
Laser Corrective Surgery
Check out this video on Eye Corrections
Click here for an animation on the eye and accommodation
BBC Bitesize Eye revision
BBC Bitesize Nervous System activity
Fight or Flight and Negative Feedback from How Stuff Works. A good read
Impact of Drugs on Neurotransmitters
Impact of Alcohol on Neurotransmitters
Laser Corrective Surgery
Check out this video on Eye Corrections
Click here for an animation on the eye and accommodation
BBC Bitesize Eye revision
Video Clips:
Hank look at the nervous system and all of the things that it is responsible for in the body.
Breath taking HD video with powerful music to introduce students - Human Nervous System
Everyone experiences pain -- but why do some people react to the same painful stimulus in different ways? And what exactly is pain, anyway? Karen D. Davis walks you through your brain on pain, illuminating why the "pain experience" differs from person to person.
Some people take aspirin or ibuprofen to treat everyday aches and pains, but how exactly do the different classes of pain relievers work? Learn about the basic physiology of how humans experience pain, and the mechanics of the medicines we've invented to block or circumvent that discomfort.
Paul Andersen explains how epinephrine is responsible for changes in chemistry of our body associated with the fight or flight response. Epinephrine released by the adrenal medulla are received by a number of organs associated with the sympathetic nervous system.
The brain is what makes us function, yet we understand so little about how it works. We are learning more about the brain by using new technology to monitor epilepsy patients during surgery. Moran Cerf explains the process doctors use to explore the brain further.
Human Brain - How does it work
Great video clip on strokes.
When under anesthesia, you can’t move, form memories, or — hopefully — feel pain. And while it might just seem like you are asleep for that time, you actually aren’t. What’s going on? Steven Zheng explains what we know about the science behind anesthesia.
Information on the Human Eye
This CGI animated sequence demonstrates how cocaine effects the user's brain.
