Biology Flashcards
Distinguish btwn endocrine and exocrine glands
Exocrine – secreting liquids to the outside (such as tears, sweat, mucus, enzymes or milk); while endocrine – secreting hormones into the bloodstream.
Difference between dendrons and axons
Dendrons carry nerve impulses towards the cell body, while a single long axon carries the nerve impulse away from the cell body
Types of neurons
- Sensory neurones
have long dendrons and transmit nerve impulses from sensory receptors all over the body to the central nervous system. - Motor neurones (also called effector neurones)
have long axons and transmit nerve impulses from the central nervous system to effectors (muscles and glands) all over the body. - Interneurones (also called connector neurones or relay neurones)
are much smaller cells, with many interconnections. They comprise the central nervous system. 99.9% of all neurones are interneurones.
The Membrane Potential
- All animal cell membranes contain a protein pump called the Na+K+ATPase. This uses the energy from ATP splitting to simultaneously pump 3 sodium ions out of the cell and 2 potassium ions in.
- These channels are normally closed, but even when closed, they “leak”, allowing sodium ions to leak in and potassium ions to leak out, down their respective concentration gradients.
- The combination of the Na+K+ATPase pump and the leak channels cause a stable imbalance of Na+ and K+ ions across the membrane.
Depolarisation and repolarisations
- Depolarisation. The sodium channels open, causing sodium ions to diffuse in down their gradient, and making the inside of the cell more positive.
- Repolarisation. The potassium channels open for, causing potassium ions to diffuse out down their concentration gradient, making the inside more negative again.
Depolarisation and repolarisations
- Depolarisation. The sodium channels open, causing sodium ions to diffuse in down their gradient, and making the inside of the cell more positive.
- Repolarisation. The potassium channels open for, causing potassium ions to diffuse out down their concentration gradient, making the inside more negative again.
Action potential
Is the change in the polarity of the memberane where the inside of the membrane is more positive than the outside of the cell
How do Nerve Impulses Start?
In living cells they are started by receptor cells. The receptor proteins are sodium channels gated by the appropriate stimulus (directly or indirectly).
How are Nerve Impulses Propagated
Once an action potential has started it is propagated (moved) along an axon automatically.
How can Nerve Impulses convey strength?
The strength of stimulus is indicated by the frequency of nerve impulses.
a. A weak stimulus (such as dim light, a quiet sound or gentle pressure) will cause a low frequency of nerve impulses along a sensory neurone.
b. A strong stimulus (such as a bright light, a loud sound or strong pressure) will cause a high frequency of nerve impulses along a sensory neurone (up to 100Hz).
The speed is affected by 3 factors namely
- Temperature.
The higher the temperature, the faster the speed. - Axon diameter.
The larger the diameter, the faster the speed. - Myelin sheath. Only vertebrates have a myelin sheath surrounding their neurones. The action potential can therefore jump large distances from node to node, a process that is called saltatory propagation. This increases the speed of propagation dramatically
The speed is affected by 3 factors namely
What is a refactory period
After an ion channel has opened, it needs a “rest period” before it can open again.
Different Types of Synapse
- Excitatory Ion-channel Synapses.
-These synapses have neuroreceptors that are sodium (Na+) channels.
-When the channels open, positive ions diffuse in, causing a local depolarisation called an excitatory postsynaptic potential (EPSP) and creating an action potential. - Inhibitory Ion-channel Synapses.
-These synapses have neuroreceptors that are chloride (Cl-) channels.
-When the channels open, negative ions diffuse in causing a local hyperpolarisation called an inhibitory postsynaptic potential (IPSP) and inhibiting an action potential. - Non-channel Synapses.
-These synapses have neuroreceptors that are not channels at all, but instead are membrane-bound enzymes.
-When activated by the neurotransmitter, they catalyse the production of a “messenger chemical” (e.g. Ca2+) inside the cell, which in turn can affect many aspects of the cell’s metabolism.
-These synapses are involved in slow and long-lasting responses like learning and memory. Typical neurotransmitters are adrenaline, noradrenaline - Neuromuscular Junctions.
-These are the synapses formed between effector neurones and muscle cells.
-They always use the neurotransmitter acetylcholine, and are always excitatory. - Electrical Synapses.
-In these synapses the membranes of the two cells actually touch, and they share proteins allowing the action potential to pass directly from one membrane to the next without using a neurotransmitter.
Define the following terms Spatial and temporal summation
Spatial summation
-Is the summing of postsynaptic potential PSPs from different synapses over the cell body and dendrite tree
Temporal summation
-Is the summing of a sequence of postsynaptic potential PSPs at one synapse over a brief period of time.
Differentiate between agonists and antagonists
Drugs that stimulate a synapse are called agonists, and those that inhibit a synapse are called antagonists.
Why are Fertilisation and development internal
To limit wastage of gametes and provide protection to the young respectively.
Why does breeding coincide with the season cycle
so that birth occurs at a time when environmental conditions are most favourable for growth of young.
Use of developing a placenta
enables gaseous exchange and the young to excrete wastes
Main features of sexual reproduction
-Fertilisation is internal
-Females go through a sexual cycle known as menstrual cycle
-Sexual cycle is restricted to the breeding season, except in humans and other primates, which are sexually receptive throughout the year
-Young ones are born at an advanced stage.
-There is display of courtship behaviour that leads to mating.
- Development of embryo is internal and completely dependent on the mother for food and protection.
-The young are fed on milk
-Parental care to the young is prolonged
Differenciate btw primary and secondary sex organs
-Primary sex organs produce gametes while secondary sex organs do not produce gametes
-Primary sex organs are organs secrete sex hormones while secondary sex organs do not secrete sex hormones
-Primary sex organs are organs development is under the control of FSH and LH while secondary sex organs development is under the control of Oestrogen and progesterone in females and testosterone in males
Functions of the penis
-Delivers sperm to the neck of
the cervix, as close to the site of ovulation as possible.
Fucntions of the scrotum
-Regulates teste’s temperature at 30C lower than body temperature for proper sperm formation. When cold, the cremaster musclebelevates the testes to absorb heat from the body, this’s reversed at high temperature.
Functions of the testes
-Contain seminiferous tubules that produce sperm.
-Produce the male sex hormone
testosterone.
