14. Coordination and Response Flashcards
Stimulus
A change in the environment that can be detected by an organism.
Nervous system
An organ system consisting of the brain, spinal cord and neurones. It responds quickly to changes inside and outside of the body.
(Allows humans / organisms to detect and respond to stimuli)
Neurones
A neurone is a specialised cell that transmits electrical nerve impulses.§
What are the nervous systems in the human body
- Central nervous system (CNS)
- Peripheral nervous system (PNS)
Central nervous system
- Contains the brain and the spinal cord.
- Responsible for coordinating all reactions + nervous communication around the body.
→ Every reflex you have needs to go to the spine or the brain.
Always travels the fastest route. Eg. mouth –> brain, leg –> spine
Peripheral nervous system
- Nerves in other body parts.
- Responsible for transmitting the impulses from the CNS to all parts of the body.
Three main neurons
- Sensory neurons
- Relay neurons
- Motor neurons
Sensory neuron
Nerve cell that carries nerve impulses from a receptor to the spinal cord.
Sensory neuron - Features
- Can be long (Impulse travels large distance to CNS)
- Carry nerve impulses away from the receptor cells when a stimulus is detected.
- Transmitted towards the CNS
- Cell body found in the middle of the axon.
- Insulated myelinated sheath helps the electrical impulse travel fast over long distance
Dendrite
Further branches at the end of dendrons in a neurone that receive signals from other neurones via the synapse.
Dendron
Branched structure of a neurone that receives signals from other neurones via the synapse.
Relay neurones
Nerve cell in the spinal cord that carries nerve impulses from a sensory neurone to motor neurones, coordinating a response to a stimulus.
(Found in the CNS and decide where the impulse goes - Like a telephone operator)
Relay neurons - Features
- Decides what the message is and redirects it along the correct neuron pathway
- Has no myelinated sheath because it is found in the central nervous system (already insulated) + doesn’t have to travel a long distance.
Motor neuron
Nerve cell that carries nerve impulses from the spinal cord to an effector.
Effector
In the nervous system, a muscle or gland that produces a response to a stimulus.
Motor neuron - Features
- Can be long because transmit impulses long distances (CNS –> body)
- Dendrite attached to the central nervous system + neuron also attached to effector.
- Cell body found in the dendrite.
- Insulated myelinated sheath helps the electrical impulse go at a fast speed (over a long distance)
Synapses
Junction between two neurones.
Allows an impulse to travel from an axon terminal of one neurone to a dendrite in another neurone.
How synpases work
1) Vesicles release neurotransmitters into the synaptic cleft (also called the synaptic gap).
2) The neurotransmitters travel across the gap by diffusion.
3) The neurotransmitters bind with receptor molecules on the dendrite of the right-hand neurone.
4) A nerve impulse is triggered in this neurone.
Axon terminals
The end of an axon in a neurone that releases neurotransmitters from vesicles into the synaptic gap.
Neurotransmitters
A substance that allows the transmission of information across a synaptic gap.
Presynaptic neuron
Transmits the signal toward a synapse
Postsynaptic neuron
Transmits the signal away from the synapse
Reflex action
Involuntary reaction in response to a stimulus resulting in the use of an effector (muscle or gland)
What are reflex actions?
- Automatic (you do not have to think about what to do)
- Rapid (they happen very quickly)
- Innate (you do not need to learn how to do them).
Reflex arc
Pathway through the body that brings about a reflex action.
Reflex arc - Pathway
Receptor → Sensory neurone → Relay neurone → Motor neurone → Effector
Receptors - Nervous system
A cell that detects a stimulus.
Examples of receptors
- Touch receptors in the skin
- Sound receptors in the ear
- Light receptors in the eye (rods and cones)
- Chemical (taste) receptors in the nose, tongue and mouth
- Temperature receptors in the skin and brain.
Effector
In the nervous system, a muscle or gland that produces a response to a stimulus.
Sense organs
A group of receptor cells that respond to a specific stimulus.
Light - Sense organ
Eye
Sound - Sense organ
Ear
Touch - Sense organ
Skin
Temperature - Sense organ
Skin
Chemicals - Sense organ
Nose, tongue
Eye
Sense organ that is sensitive to light.
Pupil
The hole in the iris at the front of the eye that allows light to enter.
Iris
A coloured ring of muscles that controls the size of the pupil in the eye. (controls how much light enters)
Cornea
A tough, colourless and transparent outer layer covering the iris and pupil of the eye.
Most refraction of light happens through the cornea.
Components of the eye
Lens
Pupil
Iris
Cornea
Retina
Blind spot
Optic nerve
Direction of light entering the eye
cornea → pupil → lens → optic nerve
(Cornea + lens focuses the light)
Optic nerve
The nerve connecting the retina of the eye to the optical centre in the brain.
Blind spot
Area at the back of the retina where the optic nerve enters the eye that contains no light-sensitive cells
(don’t notice it because the brain combines images from each eye + fills in the missing part of the image)
Retina
The layer in the eye that contains receptor cells that are sensitive to light.
Receptor cells are called rods and cones.
Lens - Eye
The part of the eye behind the pupil that allows fine focusing of light.
(refracts less light than cornea)
Cornea vs lens
Cornea - Focuses light towards the retina
Lens - Focuses light on the retina
(after one another)
Pupil reflex
Reflex action in the eye that controls the amount of light entering the pupil, controlled by the radial and circular muscles of the iris working antagonistically.
(stimulated by changes in light intensity)
Prevents damage to the eye!!!
What happens to pupil size as light intensity increases.
In bright light, the pupil becomes smaller, letting less light into the eye.
What happens to pupil size as light intensity decreases.
In dim light, the pupil becomes larger, letting more light into the eye
Circular muscles
Found in the iris
Surround the circumference of the iris.
Radial muslces
Found in the iris.
Connect the edge of the pupil to the edge of the iris.
Low light intensity - Muscle reaction
Radial muscles - Contracts
Circular muscles - Relax
Pupil diameter - Increases
High light intensity - Muscle reaction
Radial muscles - Relax
Circular muscles - Contract
Pupil diameter - Decreases
Why does the pupil reflex exist=
It prevents damage to the eye.
The retina can be damaged if too much light enters the eye.
Ciliary muscles
Muscles connected to the lens of the eye by suspensory ligaments.
(Contract or relax to change the shape of the lens)
Accomodation
Changes in the ciliary muscles, suspensory ligaments and lens that allow the eye to focus on distant and near objects.
Suspensory ligaments
Structures in the eye that connect the ciliary muscles to the lens.
Focusing light from distant objets
(Light enters in nearly parallel lines)
- Ciliary muscles contract
- Tensions in the suspensory ligaments increases
–> Lens becomes thinner
–> Light is refracted less strongly
Focusing light from near objets
(Light from nearby objects is diverging (spreading) as it enters the eye)
- Ciliary muscles relax
- Tensions in the suspensory ligaments decreases
–> Lens becomes thicker
–> Light is refracted more strongly
Two types of receptor cells in the retina
Rods + Cones
Rods
Receptor cells in the retina responsible for vision in dim light bc more sensitive to light.
Don’t provide colour vision.
Located at the sides of the retina –> away from the fovea.
Cones
Light-sensitive cells in the retina responsible for colour vision.
Located on the fovea creating the clearest + sharpest image there.
3 types of cones - Detect red/green/blue light (combination for other colours)
Where is light refracted to in the eye
The fovea (bc it contains the cones)
Why don’t you see in colour when there is little to no light.
Only the rods work in dim light –> they do not provie colour vision.
Fovea
Central part of the retina where the cones are concentrated. (found above the optic nerve in diagrams?)
Hormone
A substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs.
Gland
An organ that creates and secretes hormones.
Endocrine system
A system of glands that secrete hormones that help to regulate body functions.
Target organ
An organ that is affected by a particular hormone.
Adrenal glands
- Located on top of your kidneys.
- Adrenaline secreted from these glands
Testes - Hormones
- Only found in males
- Responsible for production + release of testosterone
- Located in scrotum
Pancreas - Hormones
- Secretes both insulin + glucagon
- Located behind the stomach
Ovaries - Hormones
- Found in females only
- Responsible for the production + release of oestrogen
Located on each side of the uterus near the end of the fallopian tubes.
Nervous vs Hormonal controls
Nervous control systems involve the nervous system.
Hormonal control systems involve the endocrine system.
Hormonal control is slower + longer lasting + carried in blood (not impulses).
Adrenaline
A hormone secreted by the adrenal gland that causes the ‘fight or flight’ response.
Effects of adrenaline
Lungs - Increased breathing rate to remove CO^2 and increas oxygen uptake
Heart - Increased pulse rate to increase delivery of glucose + oxygen to muscles.
Eye - Pupils dilate to allow more light to the retinas
Liver - Increase in blood glucose levels due to breakdown of glycogen stored in liver + muscles. –> More glucose available for respiration in muscle cells.
Adrenaline - Facial changes during fear
- Eyebrows raised + pulled together
- Raised upper eyelids
- Tensed lower eyelids
- Lips slightly stretched horizontally back to ears
Adrenaline - Facial expression during anger
- Eyebrows down + together
- Eyes glare
- Narrowing of the lips
Insulin
The hormone that stimulates the liver to turn glucose into glycogen.
Secreted + produced by the pancreas.
Glycogen
A complex carbohydrate used to store glucose in liver and muscle cells.
Glucagon
The hormone that stimulates the breakdown of glycogen into glucose.
Secreted + produced by the pancreas
Oestrogen
The main female sex hormone. It plays a major role in the control of the menstrual cycle.
- Produced + secreted bby ovaries
Testosterone
The main male sex hormone. It plays a key role in the primary and secondary sexual systems in males
- Secreted + produced by testis
Homeostasis
The maintenance of a constant internal environment in the body.
Controls these factors…
- Body temperature
- Concentration of glucose in the blood
- Water levels
Negative feedback
A response which is the reverse of the change detected. For example, when you are cold you start to shiver, which leads to an increase in body temperature.
- Mechanism that controls homeostasis
Why homeostasis is important (temperature)
- Enzymes denature if temp is too high.
Mechanism of homeostasis –> steps
- Receptor cells detect stimulus (change in the environment)
- Coordination centre (eg. brain or pancreas) process info and then determine action.
- Effectors –> glands/ muscles –> bring about a suitable response to restore levels within set limits.
Thermoregulation
Process that allows the body to maintain a stable core temperature
(Homeostasis)
Normal body temperature
37C
Lower than 35C = life-threatening
Higher than 40C = life-threatening
Structure of the skin
- Hair
- Sweat gland
- Hair erector muscle
- Receptor
- Blood vessels
- Sensory nerve
Cooling mechanisms of the body
- Sweating
- Vasodilation
- Hair lays flat
How thermoregulation is activated
The hypothalamus contains receptors that constantly measure the temperature of the blood.
Coordiates the changes needed to control body temperature.
Heating mechanisms of the body
- Shivering
- Vasoconstriction
- Hair stands up erect
Arterioles
Small arteries leading to capillaries
Vasodilation + Vasoconstriction - How it works
Muscles around arterioles in the skin control the flow of blood.
–> Can be controlled by nerve impulses from the hypothalamus.
Vasodilation
When temperature is too high, arterioles widen.
Lets more blood flow through capillaries near the surface of the skin
–> More heat is lost from the body.
–> This is why someone’s face flushes in hot weather / during exercise.
Vasoconstriction
When temperature is too low, arterioles constrict.
Reduces blood flow through capillaries near the surface of the skin
–> Less heat is lost from the body.
–> This is why someone’s face looks paler in cold weather.
Where is glucose found in blood?
Glucose is dissolved in the plasma of the blood.
How is the concentration of glucose in the blood monitored?
The pancreas monitors the concentration of glucose in the blood.
Receptors in the pancreas detect changes in the blood glucose levels
Responses to high blood glucose levels
Insulin is released.
This stimulates the cells in the liver + tissues such as muscles, to take in glucose from the blood.
The glucose is used for respiration or converted into glycogen for storage.
–> Thus blood glucose concentration falls.
Responses to low blood glucose levels.
Glucagon is secreted by the pancreas.
This stimulates liver cells to convert stored glycogen into glucose.
–> Thus blood glucose concentration increases.
Type 1 diabetes
Autoimmune disease in which the insulin-producing cells in the pancreas are attacked, leading to the inability to control blood glucose levels.
The pancreas doesn’t make enough insulin.
–> Glucose in the bloodstream (from food) can’t enter cells + isn’t converted into glycogen.
–> Thus glucose concentration can reach over 2 g/dm³
Symptoms of type 1 diabetes
- Frequent urination (because the body is trying to excrete excess glucose)
- Increased thirst (resulting from the frequent urination, and also because the body is trying to dilute the blood to reduce the blood glucose concentration).
Long-term results of type 1 diabetes
Can cause damage to organs such as the eyes, kidneys, nerves and heart.
Can lead to serious complications, including blindness, amputation, kidney failure, heart attack and stroke.
Treatments for type 1 diabetes
- Careful monitoring of diet + insulin levels + insulin injections.
Tropism
A response by a plant to a stimulus.
Can detect the directions of gravity + light.
Can be negative or positive.
Positive (plant grows towards stimulus)
Negative (plant grows away from stimulus)
Gravitropism
A response in which parts of a plant grow towards or away from gravity.
(Depends on the part of the plant)
Phototropism
A response in which parts of a plant grow towards or away from the direction of light.
Shoot (tropisms)
Gravitropism - Negative (grow upwards)
Phototropism - Positive (grows towards sunlight)
Root (tropisms)
Gravitropism - Positive
(grows downwards)
Phototropism - Negative
(grows away from sunlight)
Auxin
Plant hormone that affects the rate of elongation in shoots and roots, causing tropisms in response to stimuli.
How auxin is produced / distributed when sun is overhead
Auxin is only produced in the tip of a growing shoot (or root).
It diffuses from the tip into the rest of the shoot.
When the source of light is directly overhead, auxin is distributed equally on all sides of the shoot.
How auxin affects the growth of a shoot
- Auxin produced in tip + diffuses down throguh plant
- Auxin hormone moves to darker side (away from sunlight)
- Auxin stimulates cells on the dark side to grow more.
- The more elongated side of the shoot therefore bends towards (grows towards) the sunlight.
