nervous control in humans
1) Describe a Nerve Impulse
- A nerve impulse is an electrical signal that passes along nerve cells called neurones.
2) Describe the Human Nervous System:
The nervous system consists of two parts:
The nervous system consists of two parts:
- Central Nervous System (CNS): made up of the brain and spinal cord, which are the areas of coordination.
- Peripheral Nervous System (PNS): made up of motor and sensory neurones, which carry impulses to and from the CNS.
3) Distinguish between Voluntary and Involuntary Actions
Voluntary actions:
Involuntary actions:
- Impulses are controlled by the brain.
Involuntary actions:
- The nerve impulse does not travel to the brain.
- Organisms have adapted to carry out automatic reflexes in order to quickly remove themselves from a hazard or danger. As these reactions must occur almost instantly to protect the organism, the nerve impulse does not travel to the brain.
4) Identify Motor (effector), Relay (connector) and Sensory Neurones
source: tutor2u
5) Describe a reflex action
- Are means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors (muscles and glands).
6) Describe a Simple Reflex Arc
- A reflex action is an involuntary, quick action to respond to a stimulus, in order to protect the body from danger e.g. quickly removing your hand from hot metal surface.
- They involve three neurones: a sensory neurone, relay neurone and motor neurone.
- The gap between neurones is called a synapse.
source: toppr
How the reflex arc works:
- A stimulus detected by a receptor.
- Receptor sends an impulse down the sensory neurone to the spinal cord.
- Connector/relay neurone in the CNS passes the impulse to the motor neurone.
- The impulse travels along the motor neurone to an effector, which reacts to remove the organism from the danger.
* 7) Describe the Structure of a Synapse
- Synapse is a junction between two neurones.
- Once an impulse arrives at the synapse, the impulse triggers the release of a neurotransmitter from the vesicles in the cytoplasm into the synaptic gap/cleft. The neurotransmitter rapidly diffuses across the synaptic gap and binds with neurotransmitter receptor molecules in the membrane of the neuron on the other side of the synapse. This triggers a nervous impulse in the other neurone, thus the impulse can continue.
- Synapses ensure that impulse travel in one direction only, as the vesicles containing the neurotransmitter are only present in the presynaptic neurone, whilst the receptors are only present in the postsynaptic neurone, thus the impulse cannot travel backwards.
- Many drugs act upon synapses. Stimulants, such as caffeine, can cause the release of neurotransmitters like dopamine and serotonin into the synapse, whereas depressants, such as heroin and alcohol, inhibit synapses by blocking the receptors on the postsynaptic neurone so that impulses cannot be sent.
sense organ
8) Identify the Structures of the Eye
source: beverlyhigh
- Cornea: refracts light into the eye.
- Iris: controls how much light enters the eye by contracting and dilating the pupil.
- Pupil: allows light into the eye.
- Lens: changes shape to focus image on the retina.
- Retina: contains light receptors (photoreceptors), some sensitive to light of different colours.
- Optic nerve: carries impulses to the brain.
9) Explain Pupil Reflex
- The pupil of the eye can expand and contract to control the amount of light that enters the eye.
- This action is carried out by two sets of muscles, circular muscles and radial muscles, which work antagonistically.
- At low light intensities, the pupil dilates to allow more light to enter the eye by relaxing the circular muscles and contracting the radial muscles.
- At high light intensities, the pupil constricts to limit the amount of light entering the eye by relaxation of the radial muscles and contraction of the circular muscles.
- This is to prevent the eye being damaged by the bright light.
10) Explain Accommodation
- The eye can focus on both near and far objects.
- This is achieved by changing the shape of the lens, which is controlled by ciliary muscles and suspensory ligaments. These work antagonistically.
- The shape of the lens, as well as its curvature, is altered to change the way light is refracted onto the retina, focusing the image.
- To focus on near objects, the ciliary muscles contract whilst the suspensory ligaments relax, making the lens fatter and curved.
- To focus on distant objects, the ciliary muscles relax whilst the suspensory ligaments contract, making the lens thinner and less curved.
* 11) Outline the function of Rods and Cones
- Rods and cones are two types of photoreceptor cells in the eye.
Rods:
- Rod-shaped.
- Used for night vision as they are more sensitive to low levels of light.
- Evenly distributed at the periphery of the retina; absent at the fovea.
Cones:
- Cone-shaped.
- Used for colour vision in bright light. There are three types of cone cells, each sensitive to a different colour (red, green and blue).
- Concentrated at the fovea.
hormones
* 12) Identify specific Endocrine Glands and their Secretions
- 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.
Adrenal gland:
- Secrete adrenaline.
- Secreted during the ‘fight or flight’ situations, and when stressed or excited. It leads to an increase in pulse rate and widened pupils. It also causes glycogen to be converted to glucose in cells so that it can be used in respiration for energy. Heart rate increases to provide more oxygen for this.
Pancreas:
- Secrete Insulin.
- Maintains blood-glucose concentration.
Testes
- Secrete Testosterone.
- Maintains muscle and bone strength and plays a role in reproduction.
Ovaries:
- Secrete Oestrogen.
- Regulates female reproductive system.
13) Describe the hormone Adrenaline
- A hormone secreted by the adrenal gland (located at the top of the kidneys) in ‘fight or flight’ situations, and when stressed or excited.
- It leads to an increase in pulse rate and widened pupils.
- It also causes glycogen to be converted to glucose in cells so that it can be used in respiration for energy. Heart rate increases to provide more oxygen for this.
14) Compare Nervous and Hormonal Control System
- Nervous impulses travel along neurones whereas hormones travel in the blood.
- Nervous impulses are much quicker than hormones, as hormones must be transported in the blood whereas nervous impulses can travel along specialised nerve cells.
- Nervous impulses are instantaneous and short-lived, whereas a hormonal response can be long-lasting.
- The endocrine system uses chemicals (hormones) whereas the nervous system uses electrical signals.
homeostasis
15) Define Homeostasis
- The maintenance of a constant internal environment. Homeostasis is the control of internal conditions within set limits.
16) Explain the concept of Control by Negative Feedback
- Homeostasis allows the environment to be at an optimum for cells to function.
- Internal conditions must be maintained between set limits and if these limits are exceeded, negative feedback mechanisms work to correct the change and restore the internal environment to the optimum.
17) Describe the Control of Glucose Content in Blood
- The level of glucose in the blood must be maintained as part of homeostasis.
- If the level of glucose in the blood is too high, the water potential of the blood becomes very low, water will moves out of cells into the blood by osmosis. This leads to cells shrinking and eventually dying.
- If the level is too low, water potential is high and water will moves from the blood into the cells, causing them to burst.
- Maintaining a constant blood-glucose level therefore maintains a constant water potential so no unwanted osmosis occurs.
- There are two hormones that are used to regulate blood-sugar levels: glucagon and insulin. Both of these are synthesised in cells in the pancreas and are released into the blood from here when the levels of blood-glucose are too high or too low
- Insulin is released when blood-glucose concentration is too high. This is detected in the pancreas. Insulin causes glucose to be converted to glycogen in the liver. This lowers the concentration of glucose in cells, thus glucose diffuses into cells from the blood, lowering the amount of glucose in the blood.
- Glucagon is released when blood-glucose concentration is too low. Glucagon inhibits glucose being converted to glycogen in the liver and activates an enzyme that converts glycogen to glucose, making more glucose available to cells. It also decreases the respiratory rate in cells so that less glucose is used in respiration.
18) Identify Parts of the Skin
19) Describe the Maintenance of Constant Internal Body Temperature
- It is important to maintain a constant temperature of 37°C in humans as this is the optimum temperature for enzyme reactions.
- If the temperature was lower, the rate of reaction would decrease so reactions would take too long to occur.
- If it was too high, the enzymes may denature and prevent reactions from occurring.
- The temperature is regulated by the hypothalamus in the brain, which contains thermoreceptors.
- If the temperature moves away from the optimum, a response is triggered to return the temperature to the optimum.
Reactions to a low internal temperature:
- Shivering: muscles contract to produce heat.
- Vasoconstriction: blood vessels constrict to reduce surface area and move away from the surface of the skin to reduce heat loss.
Reactions to a high internal temperature:
- Sweating: sweat evaporates from the skin, reducing the surface temperature.
- Vasodilation: blood vessels dilate, causing more heat loss to the environment.
* 20) Outline Symptoms and Treatment of Type 1 Diabetes
- People with diabetes cannot produce insulin.
- Type 1 diabetes is caused by an autoimmune response in which antibodies attack cells in the pancreas which usually make insulin. This means that no insulin can be produced.
- Type 1 diabetes is usually treated by patients injecting insulin themselves. There are several new treatments being developed, including the use of stem cells and artificial pancreases, although these treatments will be very expensive.
tropic responses
- Tropisms are growth movements in plants that occur in reaction to external stimuli.
- Plants can show a positive or negative response, and different parts of the plants can show different responses. These responses are controlled by plant hormones called auxins which cause cell elongation.
- Auxins are made in shoot tips and move through the plant by diffusion and active transport (short distances), or via the phloem (longer distances).
- Gravitropism: Gravitropism (also known as geotropism) is a response to gravity.
21) Define Gravitropism
- A response in which a plant grows towards (positive) or away (negative) from gravity.
- Plant shoots are negatively gravitropic. Build up of auxin on the lower side stimulates the growth on the lower side, and the shoot bends upwards.
- Plant root are positively gravitropic. Build up of auxin on the lower side of the root slows down the growth of the lower side, and the root bends downwards.
22) Define Phototropism
- A response in which parts of a plant grow towards or away from the direction from which light is coming.
- Plant shoots are positively phototropic, as they move towards light in order to allow the plant to absorb more light to photosynthesise.
- Plant roots are negatively phototropic as they move away from light.
23) Explain role of Auxin in Controlling Shoot Growth
- Auxins are produced in the shoot tips only, and spreads through the plant from the shoot tip.
- Light causes the auxin to move to the shady side of the shoot.
- Build up of auxin stimulates cell elongation on the shady side.
- The cells grow faster on the shaded side, thus the shoot bends towards the light.
* 24) Describe the use of Weed Killers
- Weed killers are used to selectively kill plants.
- One of the main herbicides contains an organic compound known as 2,4-D, which is a synthetic plant hormone.
- When a plant is exposed to 2,4-D, it results in uncontrolled growth, leading to the plant’s death.
