The human nervous system consists of the...
- Central nervous system (brain and the spinal cord)
- The peripheral nervous system
- The nervous system allows us to coordinate and regulate body functions
- Nerve impulses are electrical signals that passes along nerve cells called neurones. They transmit information and allow communication between cells
Involuntary and voluntary actions
- The actions we do are grouped into involuntary and voluntary actions
- Voluntary actions are actions where you consciously think and decide to carry out an action. The decision starts with your brain
- Involuntary actions are basically your reflexes, where you do not consciously think before an action (eg. breathing, heart pumping, blinking)
- They are automatic and happen very quickly, and is used to prevent your body from being damaged. Examples of reflex actions include withdrawing your arm when touching a hot or sharp object
Motor, Relay, and Sensory Neurons
These are the neurons that work together to carry out reflex actions
- Motor Neurons: Sends signals to the effector (the muscles that carry out the reflex action)
- Relay Neurons: Connects motor and sensory neurons
- Sensory Neurons: Sends impulses to relay neurones after detecting stimulus
Diagram of different neurones
Reflex Arc
The reflex arc is the pathway of the signals through the nerves in a reflex action. This is the general pathway of a simple reflex action
- A stimulus is detected by a receptor on the skin
- This causes sensory neurones to send impulses to the spinal cord
- The spinal cord passes the signal on to the relay neurone
- The relay neurone passes the signal to the motor neurone
- The motor neurone sends the impulse to the effector, or the muscle(s) involved
- The muscles then perform the reflex action
B9.2: Sense Organs
Structure of the Eye
- Cornea: A transparent layer of the eye that refracts light rays entering the eye
- Iris: The tissue at the front of the eye that controls the amount of light rays that enter
- Pupil: The hole in the iris that allows light to enter the eye
- Lens: Transparent structure that focuses light rays onto the retina by changing shape
- Retina: A layer positioned at the back of the eyeball containing light receptor cells (grouped into rods (that detect the intensity of light) and cones (detect the colour of the waves)
- Optic nerve: The nerve that transmits impulses (signals) from the retina to the brain
- Ciliary muscles: A muscle that focuses the vision by tightening or relaxing, changing the shape of the lens
- Suspensory ligaments: Fibres that connect ciliary muscles and the lens muscles, holding them in place
- Blind spot: The blind spot is the area within the retina that cannot detect images. This is because light is detected by the rods and cones. However, there are no rods and cones at the spot where the optical nerve attaches to the retina
Pupil Reflex
The pupil reflex is a reflex action to prevent damaging the pupils when the eye is exposed to different light intensities
Accommodation of close and far objects
- The lens focuses on objects of different distances by accommodation
- Accommodation is the change of shape of the lens through the tension of the suspensory ligaments and ciliary muscles
- When the eye is focusing on a close object...
- The ciliary muscles contracts
- The suspensory ligaments relax
- The lens becomes bigger
- More lights are refracted
- When the eye is focusing on a far object...
- The ciliary muscles contracts
- The suspensory ligaments relax
- The lens becomes smaller
- More lights are refracted
B9.3: Hormones
- A hormone is a chemical substance produced by a gland, carried by the blood, which alters the activity of one or more specific target organs
- Adrenaline is a hormone produced in ‘fight or flight’ (dangerous) situations, and prepares the body through different changes, including...
- Increase of concentration of blood glucose in the blood (to increase the rate of respiration)
- Increase of breathing and pulse rate to deliver oxygen and glucose, and remove carbon dioxide from the blood quicker
- Directing blood more to the muscles and less to the non-essential parts of the body to make sure respiration occurs faster
- Widening pupils to allow more light and information to enter the brain
Nervous and endocrine (hormonal control) systems
The nervous system
- The nervous system is made up the brain, nerves, and spinal cords
- It sends messages with electrical impulses
- The speed of transmission is very fast
- The length of the transmission is short
The endocrine system
- Glands that secrete hormones
- It sends messages with chemical hormones
- The speed of transmission is smaller
- The length of the transmission is long
B9.4 Homeostasis Definitions and Negative feedback
- Homeostasis is defined as the maintenance of the control of internal conditions within set limits
- Homeostasis is necessary for the survival of an organism and when internal conditions are not within these limits, your body malfunctions and may lead to death
- Homeostasis is controlled through negative feedback
- Negative feedback is a continuous cycle to regulate levels within the body
- If levels rise, the negative feedback would be to reduce the levels back to the ideal point
- If levels fall, the negative feedback would be to increase the levels to the ideal point
Control of glucose in the blood
- Blood glucose levels are controlled by hormones insulin and glucagon (from the pancreas)
- They do this through negative feedback
- When blood glucose levels rise, insulin is produced and released by the pancreas to cause the liver to convert and store some of the glucose as glycogen
- This causes the levels of glucose in the blood to decrease towards a normal blood glucose level
- When blood glucose levels fall, glucagon is produced, causing the liver and muscles cells to convert the stored glycogen into glucose, which later goes to the blood
- This causes blood glucose levels to increase
Maintenance of Body Temperature
- Temperature is regulated so that the temperature levels within the body provide a good environment for enzymes to work in (about 37°C)
- If temperature increases beyond the optimal temperature for enzymes, the will change the shape of the enzymes and make them less effective (causing slower chemical reactions)
- The brain and receptors that sense the temperature of hte blood
- The skin has temperature receptors with sensory neurons that transmit signals to the brain
- Effectors maintain the temperature by sending nerve impulses to the effectors in the skin to keep the internal temperature within 37°C
- Fatty tissue in the skin prevent body heat from escaping the body from the skin
- When there is an increase in body temperature...
- The body starts to sweat more (sweat carries excess heat outside your body and evaporates)
- The hairs on the skin lie flat and relax (allowing air to move freely and transfer heat more)
- The arterioles (blood vessels) near the skin widen, increasing heat loss through the skin (this is called vasodilation). This is because more blood flows to the surface of the skin, causing more heat to be lost
- When there is a decrease in body temperature...
- The body begins to shiver (causing skeletal contractions that use energy from respiration, with some energy in the form of heat)
- The hairs on the skin stand (trapping a thick layer of air around the skin to prevent heat loss)
- The arterioles (blood vessels) near the skin thin, decreasing heat loss through the skin (this is called vasoconstriction). This is because less blood flows to the surface of the skin, causing less heat to be lost
B9.5 Tropic Responsees
- Plants response to changes in the environment
- Gravitropism is a response in which parts of a plant grow towards or away from gravity
- Phototropism is a response in which parts of a plant grow towards or away from the direction from which light is coming
- Shoots grow upwards towards light, and the opposite direction of gravity (as they grow upwards)
- Roots grow away from light and in the same direction as gravity (as they grow downwards)
- Phototropism and Gravitropism is caused by the growth homrone
- Auxin is mainly produced at the tips of the stems and roots, and move through diffusion
- Auxin elongates the cells, and the plant grows in a certain direction according to the distribution of auxin
- When light shines on the plant, the auxin moves to the darker side
- In the stem, auxin causes the cells to grow more. As they move to the darker side are longer, the stem will bend towards the light
- In the root, auxin causes the cells to grow less, causing the root to grow away from light
- Gravity causes the auxin to move to the bottom of the plant and causes the bottom of the plant to grow more against the force of gravity
- Auxin causes cells to grow less in the root, and more in the stem. This means that the root grows along with the direction of gravity in the root and the stem grows against it
Diagram of the skin
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