Nervous Communication Flashcards
What are the 2 main divisions in the nervous system?
- central nervous system.
- peripheral nervous system.
The CNS is a major division of the nervous system. What does it include?
The brain and spinal cord.
The PNS is a major division in the nervous system. What does it include?
It is made up of pairs of nerves that originate from either the brain or spinal cord.
The PNS is a division of the nervous system. What can this further be divided into?
- sensory neurones. These carry nerve impulses from receptors to the CNS.
- motor neurones. These carry nerve signals away from the CNS to effectors.
The motor nervous system (from the PNS) can be further subdivided into what?
- the voluntary nervous system. This carries nerve impulses to body muscles under voluntary (conscious) control.
- the autonomic nervous system. This carries nerve impulses to glands, smooth muscles and cardiac muscles and isn’t under conscious control; so is involuntary.
What is a spinal cord?
A column of nervous tissue that runs along the back and lies inside the vertebral column for protection.
Emerging at intervals along the spinal cord are pairs of nerves.
Define ‘reflex’.
An involuntary response to a sensory stimulus.
Define reflex arc.
The pathway of neurones involved in a reflex.
Involves 3 neurones.
Outline the reflex arc.
- The stimulus - heat from a candle.
- Receptor - temperature receptors generate nerve impulse in the sensory neurone.
- Sensory neurone - passes nerve impulses to spinal cord.
- Coordinator - passes impulses along spinal cord.
- Motor neurone - carries nerve impulses from spinal cord to muscle.
- Effector - muscle, which is stimulated to contract.
- Response - pull hand away from candle.
What is the importance of reflex arcs?
- the absence of any decision making processes means the action is rapid.
- protect the body from harm. They are effective from birth and don’t need to be learnt.
- fast, because the neurones pathway is short with very few synapses where neurones communicate with each other (synapses are the slowest link in a neurone pathway). This is important in withdrawal reflexes.
- involuntary, so not need the decision making powers of the brain, thus leaving it to carry out more complex resources. In this way, the brain is not overloaded with situations in which the response is always the same.
Outline the features of sensory receptors (including the pacinian corpuscle).
- it’s specific to a single type of stimulus.
- produces a generator potential by acting as a transducer.
Receptors in the nervous system convert (transduce) the energy of the stimulus into a generator potential (aka a nerve impulse).
What is a transducer.
A transducer converts the change in the form of energy by the stimulus into a nerve impulse that can be understood by the body.
What are pacinian corpuscles?
Sensory receptors that respond to mechanical stimuli eg pressure. They occur deep in the skin.
How does the Pacinian Corpuscle work?
- In its resting state, the stretch mediated sodium channels of the membrane around the corpuscle are too narrow to allow sodium ions to pass along them.
- When pressure is applied to the corpuscle, it becomes deformed and the membrane around its neurone become stretched.
- This stretching widens the sodium channels and sodium ions can diffuse into the membrane.
- This influx of sodium ions causes depolarisation, thereby creating a generator potential.
- This generator potential creates an action potential (nerve impulse) that passes along the neurone and then the CNS.
Where are the light receptors in mammals found?
In the retina.
What are the 2 main types of light receptor?
Rod cells and cone cells.
Both rod and cone cells act as ______________?
How do they act as this?
Transducers by conserving light energy into the electrical energy of a nerve impulse.
Outline the features of rod cells.
- rod shaped
- sensitive to low level light
- give poor visual acuity
- more found at the periphery of the retina. Absent at the fovea.
- greater number of them than cone cells.
Why are images only seen in black and white in rod cells?
Because rod cells cannot distinguish between different wavelengths of light.
Why are rod cells sensitive to dim light?
Because many rods join one neurone (retinal convergence), so many weak generator potentials combine to reach the threshold and trigger an action potential.
There is enough energy in this dim light to trigger a generator potential which breaks down rhodopsin.
Why do rod cells have a low visual acuity?
Because many rods join the same neurone (retinal convergence). Therefore, only a single impulse is generated, regardless of how many neurones are stimulated (as they all link to a single bipolar cell).
This means that the brain cannot distinguish between the separate sources of light that stimulated them.
What is needed to create a generator potential in rod cells?
The break down of rhodopsin. There is enough energy in low intensity light do this - explaining why rod cells are sensitive to low intensity light.
Outline the features of cone cells.
- cone shaped
- concentrated at the fovea. fewer at the periphery of the retina
- give good visual acuity
- insensitive to low intensity light
- three types (each responding to a different wavelength of light)
- less of them than rod cells
Why are cone cells sensitive to high intensity light, but not low intensity light?
Because one cone cell joins one neurone, so it takes more light to reach the threshold and trigger an action potential.
How are cone cells and rod cells different in the intensity of light?
Unlike rod cells, individual cone cells are connected to an individual neurone.
Therefore, the stimulation of a number of rod cells cannot be combined to help exceed the threshold value and is create a generator potential.
As a result, cone cells only respond to high intensity light an rod cells respond to low intensity light.
Cone cells are found on the fovea. Explain why.
Because light is focused by the lens onto the fovea - therefore receiving the highest intensity of light.
As a result, rod cells are not found here, but cone cells are.
Why are rod cells found at the edge of the retina?
Because light intensity is at its lowest here.
How does light create an electrical impulse?
- Light enters the eye, hits the photoreceptors and is absorbed by light-sensitive optical pigments.
- Light bleaches the pigments, causing a chemical change and altering the membrane permeability to sodium ions.
- A generator potential is created. If it reaches threshold, a nerve impulse is sent along a bipolar neurone.
- Bipolar neurones connect photoreceptors to the optic nerve, which takes impulses to the brain.
What does the Autonomic Nervous System do?
The ANS controls the involuntary (subconscious) activities of internal muscles and glands. It has two divisions:
- sympathetic nervous system
- parasympathetic nervous system
In the autonomic nervous system, there is a division called the sympathetic nervous system. What is this?
This stimulates effectors, so speeds up any activity.
It helps us to cope with stressful situations and prepares us for activity (fight or flight response).
In the autonomic nervous system, there is a division called the parasympathetic nervous system. What is this?
In general, this inhibits effectors, so slows down any activity.
It controls activities under normal resting conditions.
It is concerned with conserving energy and replenishing the body’s reserves.
How is the autonomic nervous system antagonistic?
Because the sympathetic and the parasympathetic nervous systems normally oppose one another.
Eg if one system contracts a muscle, the other relaxes it.
The muscle of the heart is __________.
Myogenic.
This means it’s contraction is initiated from within the muscle itself, rather than by nervous impulses from outside.
Where is the SAN found?
Within the wall of the right atrium of the heart.
Why is the SAN often called a pacemaker?
Because the SAN has a basic rhythm of stimulation that determines the beat of a heart.
Outline the the stages of the basic heart rate.
- A wave of electrical excitation spreads out from the SAN across the right and left atria, causing them to contract.
- A layer of non-conductive collagen tissue prevents the wave from crossing into the ventricle.
- Instead, these waves are transferred to the atrioventricular node (AVN).
- After a short delay, the AVN conveys a wave of electrical excitation onto the bundle of His.
- This bundle of His conducts the wave through the atrioventricular septum to the apex, where the bundle branches into smaller fibres of Purkyne tissue.
- The wave of excitation is released from the Purkyne tissue, causing the ventricles to contract quickly at the same time, from the bottom of the heart upwards.
What is ‘Purkyne tissue’?
A series of specialised muscle fibres which collectively makes up the bundle of His.
What does the ‘medulla oblongata’ do?
Controls the changes of heart rate.
This has two centres:
- a centre that increases HR (linked to the SAN by the SNS)
- a centre that decreases HR (linked to SAN by the PNS)
In the context of the heart, describe chemoreceptors.
Found in the wall of the carotid arteries. They are sensitive to changes in the pH of the blood that result in changes in CO2 concentration. (In solution, CO2 forms an acid, thus lowering the pH).
Outline the stages of the heart when there is a higher concentration of CO2 in the blood (eg by exercise).
- Blood = higher conc. of CO2, so pH is lowered.
- The chemoreceptors in the wall of the aorta detect this, so more impulses are sent to the medulla oblongata.
- This sends the impulses via the SNS. The sympathetic neurones secrete noradrenaline, which binds to receptors on the SAN.
- HR increases. CO2 levels back to normal.
- This centre increases the frequency of impulses via the SNS to the SAN. This, in turn, increases the rate of production of electrical waves by the SAN - thus increasing HR.
Outline the stages in the heart when there are low CO2 levels.
- Chemoreceptors detect higher pH levels.
- Nervous impulses are sent to the medulla oblongata.
- This sends impulses along parasympathetic neurones.
- These secrete acetylcholine, which binds to records on the SAN.
- This causes the HR to decrease. CO2 concentration levels return.
How is pressure controlled in the heart?
- when blood pressure is higher than usual.
Then pressure receptors transmit more nervous impulses to the centre in the medulla oblongata.
This centre sends impulses via the PARASYMPATHETIC system the the SAN - leading to a decrease in HR. - when blood pressure is lower than normal.
Then pressure receptors transmit more nervous impulses to the centre in the medulla oblongata.
This centre sends impulses via the SYMPATHETIC nervous system to the SAN - leading to an increase in HR.
What are the 2 main forms of coordinations in animals?
- the nervous system
- the hormonal system
What does the nervous system do?
Uses nerve cells to pass electrical impulses along their length. They stimulate their target cells by secreting neurotransmitters directly onto them. This results in rapid communication between specific parts of an organism.
The responses are short lived and localised.
What does the hormonal system do?
Produces hormones that are transported in the blood plasma to their target cells.
The target cells have specific receptors on their cell surface membranes and the change in the concentration of hormones that stimulate them.
Thus results in slower, less specific forms between parts of an organism.
What is the main difference between the nervous system and the hormonal system?
The responses in the nervous system are often short lived, and restricted to localised region of the body.
The effect is usually temporary.
Transmission is by the neurones.
The responses in the hormonal system are slow, long-lasting and wide spread.
The effect may be permanent.
Transmission is in the blood system.
What is a neurone (nerve cell)?
Specialised cells which are adapted to rapidly carry out nerve impulses (electrochemical changes) from one area of the body to another.
What is in a mammalian motor neurone?
- cell body
- dendron
- axon
- Schwann cells
- myelin sheath
- nodes of Ranvier
What do Schwann cells do?
Makes up a mammalian neurone, Schwann cells surround the axon, protecting it and providing electrical insulation.
They also carry out phagocytosis.
What is an axon?
A single, long fibre that carries nerve impulses away from the cell body.
What are dendrons?
Extensions of the cell body, which subdivide into dendrites, that carry nerve impulses towards the cell body.
What is a myelin sheath?
This forms a covering to the axon and is made of the membranes of the Schwann cells.
These membranes are rich in a lipid called myelin.
What are nodes of Ranvier?
Constrictions between adjacent Schwann cells where there’s no myelin sheath.
What do sensory neurones do?
Transmit nerve impulses from the receptor to a motor neurone
