The Nervous System Flashcards
What is meant by the term myogenic?
Muscle that contracts spontaneously without input from the nervous system
Name the three types of muscle
Skeletal muscle, smooth muscle and cardiac muscle
Striated muscle is made up of muscle________, each of which is made up of myofibrils.
Each myofibril is made up of myofilaments. The pattern of ________ myofilaments (made up of protein _______) and ________ myofilaments (made up of protein _______) gives the striation in the muscle
Fibres, thin, actin, thick, myosin
What is a neurotransmitter?
A chemical messenger that diffuses across a synapse
What is the cardiovascular centre?
A specific region of the medulla oblongata that receives sensory inputs about the levels of physical activity, blood CO2 concentration, and blood pressure.
It sends nerve impulses to the SAN in the heart to alter the frequency of excitation waves
What is the medulla oblongata?
A region found at the base of the brain, that coordinates the unconscious function of the body, such as breathing rate and heart rate
The accelerator nerve and the vagus nerve run from the medulla oblongata to the heart
What does myogenic mean?
Contraction if the muscle is generated from within the muscle itself
The term is used to describe the contraction of the heart, which is controlled by the action of SAN
What is resting potential?
The potential difference or voltage across the neurone cell membrane while the neurone is at rest
It is about -60mV inside the cell compared with the outside
Other cells may also maintain a resting potential that might change under certain circumstances
What are voltage gated channels?
Channels in the cell membrane that allow the passage of charged particles or ions
They have a mechanism called a gate which can open and close the channel
In these channels the gates respond to changes in the potential difference across the membrane
What is the threshold potential?
A potential difference across the membrane of about -50mV
If the depolarisation of the membrane does not reach the threshold potential then no action potential is created
If the depolarisation reaches the threshold potential then an action potential is created
What is an action potential?
A depolarisation of the cell membrane so that the inside of the cell membrane so that the inside is more positive than the outside, with a potential difference across the membrane of +40mV
This can be transmitted along the axon or dendron plasma membrane
What are local currents?
The movements of ions along the neurone
The flow of ions is caused by an increase in concentration at one point, which causes diffusion away for, the region of higher concentration
What are the first 4 stages of an action potential?
1 – The membrane starts in its resting state - polarised with the inside of the cell being -60mV compared to the outside
2 – Sodium ion channels open and some sodium ions diffuse into the cell
3 – The membrane depolarises - it becomes less negative with respect to the outside and reaches the threshold value of -50mV
4 – Voltage gated sodium ion channels open and many sodium ions flood in. As more sodium ions enter, the cell becomes positively charged inside compared with outside
What are the last 4 stages of an action potential?
5 – The potential difference across the plasma membrane reaches +40mV. The inside of the cell is positive compared with the outside
6 – The sodium ion channels close and potassium channels open
7 – Potassium ions diffuse out of the cell, bringing the potential difference back to negative inside compared with the outside - repolarisation
8 – The potential difference overshoots slightly, making the cell hyper polarised. The original potential difference is restored so that the cell returns to its resting state
Following stimulation, calcium ions binds to __________ on the actin filaments.
This cause another protein called __________ to change position and unblocked the binding sites on the actin filaments
Troponin
Tropomyosin
The myosin heads attach to the binding sites, forming _________
bridges between the two filaments
Actomyosin
_________ provides the energy for the cross-bridges to detach and reattach further along the actin filament
ATP
Explain what is meant by a spinal reflex
A rapid and automatic response to a stimulus that does not involve though processes in the brain
Name the three types of neurone involved in a spinal reflex, in order of their stimulation
Sensory neurone, relay neurone, motor neurone
A hand is placed on a hot object and immediately withdrawn
For this reflex action, name:
a) the stimulus
b) the receptor
c) the coordinator
d) the effector
a) Touching the hot object
b) Heat receptors in the hand
c) Reflex arc in the spinal cord
d) Muscles involved in the withdrawal of the hand
What is the autonomic nervous system?
The part of the nervous system that controls unconscious or involuntary activities, such as action of the heart or digestive system
Describe the features of the sympathetic nervous system according to the following criteria:
a) neurotransmitter at synapses
b) effect on heart rate
c) effect on ventilation rate
a) Noradrenaline
b) Increased
c) Increased
Describe the features of the parasympathetic nervous system according to the following criteria:
a) neurotransmitter at the synapses
b) effect on heart rate
c) effect on ventilation rate
a) Acetylcholine
b) Decreased
c) Decreased
Name the two components of the central nervous system
The brain and spinal cord
State one function for:
a) hypothalamus
b) medulla oblongata
a) Homeostasis
b) Controlling heart and ventilation rates
Identify the parts of the brain that carry out the following functions:
a) balance and posture
b) voluntary activities, learning and memory
a) Cerebellum
b) Cerebrum
Distinguish between innate and learned behaviour
Innate behaviour is programmed at birth and is genetic in nature
Learned behaviour is acquired during the lifetime of the organism through interaction with the environment
Distinguish between a taxis and a kinesis
A taxis is a directional movement in response to a stimulus — for example woodlice show negative phototaxis i.e. they move away from light
A kinesis is a change in the rate of movement in response to a stimulus — for example sea anemones move their tentacles more when stimulated by chemicals emitted by potential prey
What is the term given to sequences of behaviour that control stereotyped responses such as courtship rituals?
Fixed action patterns
Describe what is meant by the term habituation
Learning not to respond to a neutral stimulus
What is meant by the term all-or-nothing?
All-or-nothing is a term used to describe the fact that action potentials in nerve cells are always identical in size
What is the refractory period of a neurone?
The time interval during which a nerve cell is incapable of responding to a stimulus
Name three factors that speed up the transmission if nerve impulses along axons
Diameter of the axon – impulses travel faster in larger axons because there is less electrical resistance
Temperature – impulses go faster as temperature increases, up to 40C (above this, proteins begin to denature)
Presence of a myelin sheath
What is a synapse?
The junction between two nerve cells
Name the two most common neurotransmitters found in synapses
Acetylcholine and noradrenaline
Vesicles containing neurotransmitter fuse with the ___________ and release their contents into the synaptic cleft
Neurotransmitter diffuses across the cleft and attaches to _____________ on the post-synaptic membrane
Pre-synaptic membrane
Receptor molecules
How does an inhibitory neurotransmitter work?
It makes the post-synaptic membrane hyperpolarised and therefore harder to excite
What is a neuromuscular junction!
The point at which a motor neurone connects with a muscle
Distinguish between temporal and spatial summation
Summation is the process that occurs in synapses due to the additive effect if a number of stimuli.
A single stimulus may not be sufficient to trigger an action potential, usually because there is not enough neurotransmitter produced.
In temporal summation, two or more impulses arriving at the synapse in a short period of time may generate an action potential – the effects of the impulse add up over time
In spatial summation, an action potential may be triggered if several synapses act at the same time on the post-synaptic cell
What is neurone?
A cell specialised for the conduction of nerve impulses
What are the functions of the myelin sheath?
- To insulate and protect the neurone
- To speed up the conduction of nerve impulses
What are receptors?
Cells that are specialised to detect a particular stimulus
Outline how a stimulus might trigger a response in a sensory neurone
If the stimulus exceeds a minimum threshold value, the receptor is depolarised and an action is set up in a sensory neurone
Name four types of receptor found in humans
Baroreceptors (blood pressure)
Chemoreceptors (blood pH)
Photoreceptors (light)
Mechanoreceptors (sound/pressure)
What are effectors?
Cells or organs that respond to a stimulus
State two types of effector found in animals
Muscles or gland
Distinguish between gluconeogenesis and glycogenolysis
Gluconeogenesis is the synthesis of glucose from non-carbohydrate sources, such as lipid and protein.
Glycogenolysis is the conversion of glycogen to glucose
Explain why insulin and glucagon affect mainly skeletal muscle cells and liver cells
Insulin and glucagon bind to protein receptors in the plasma membranes of skeletal muscle and liver cells.
The protein receptors have a specific shape so that only these hormones will fit.
Other body cells do not have these specific receptors
Name one hormone, other than insulin and glucagon, that can influence the concentration of plasma glucose
Adrenaline
Explain why the blood concentration of glucose rises during exercise, while that of insulin falls
During exercise, the skeletal muscles rapidly respire and therefore use a lot of glucose.
Homeostatic mechanisms are required to increase the level of glucose in the blood
Since glucagon stimulates a rise in blood glucose concentration, this hormone is secreted by the pancreas
Insulin (which stimulates the concentration of blood glucose to fall) is not secreted
Explain how one molecule of glucagon can bring about the conversion of many molecules of glycogen to glucose
Many hormones operate on a cascade principle.
When one molecule of glucagon binds to its receptor, it activates an enzyme which catalyses the breakdown of glycogen to glucose
One enzyme molecule can catalyse the breakdown of many glycogen molecules
The enzyme is said to have a high turnover rate
What is meant by the term resting potential?
In an unstimulated neurone, there is a high concentration of sodium ions outside the cell
The inside is negative relative to the outside
Describe the changes that occur to the restoration of the resting potential when a neurone is stimulated
Depolarisation – Stimulation of the neurone causes sodium ions to enter the cell, making it positive relative to the outside.
Repolarisation – Potassium ions then leave the cell, restoring the negative potential difference
The true resting potential is then restored by sodium-potassium pumps, which actively transport potassium into the cell and sodium out of the cell
