Chapter 3 Flashcards
1
Q
What are nerve cells or neurons
A
The basic structural and functional unit of life
2
Q
What is the cell body
A
Contains the nucleus and is responsible for the controlling and functioning of the cell
3
Q
Dendrites and function
A
Are the short extension of the cytoplasm of the cell body and carry message or nerve impulses into the cell body
4
Q
Nodes of ranvier
A
The gaps at the intervals along the axons
5
Q
What is the axon covered with
A
My lien sheath and nurilemma
6
Q
What is the Schwann cell (glial cells)
A
Special cell that forms the myelin sheath in the peripheral nerve fibers.
They also form nurmellia which is a thin layer surrounding the myelin and help repair injured fiber
On the brain and spinal cord oligodendrocyte produce them
7
Q
Axon and function
A
Single long extension of the cytoplasms.
Carries nerve impulses away from the cell body
8
Q
Neurilemma
A
Outermost coil of Schwann cell.
Helps in repair of injured fiber
9
Q
Myelin sheath
A
Fatty material that covers the axon
10
Q
Functions of the myelin sheath
A
Acts as an insulator
Protects axon from damage
Speeds up the movement of nerve impulses among the axon
11
Q
What is the mylein sheath produced by in the brain and spinal cord
A
Oligdendrocyte
12
Q
What is a synapse
A
A junction where nerve impulses are passed from neuron to neuron, where the axon terminal of one neuron joins with a dendrite or the cell body of another
13
Q
Do neurons touch?
What carries the message
A
No
Neurotransmitter are chemical messengers that transmit singnal between nerve cells or between neurons and other cells like muscles or gland
14
Q
Neuromuscular junction
A
A similar synapse exist where an axon meets a skeletal muscle
15
Q
Types of functional neurons
A
Sensory neurons/ afferent /receptor
Motor/ efferent/ effector
Inter neuron/ association/ connector/ relay
16
Q
What are sensory neuron
A
Neurons that nerve impulses from the receptor in the sensory organs or in the skin to the central nervous system( brain and spinal cord)
17
Q
What are motor neurons
A
Neurons that carry nerve impulses from the cns to the effector, the muscles and the gland
18
Q
What are interneuron
A
Located in the cns and are the link between the sensory and motor neuron
19
Q
What are the structural type of neuron
A
- Multipolar
- Bipolar
3.unipolar
4.psenudounipolar
20
Q
What is multipolar neuron
A
1 axon and multiple dendrites.
Interneurons and motor neuron
21
Q
What is bipolar neuron
A
1 axon and 1 dendrite.
Occurs in the neurons of the eyes ears and nose where they take impulses from the receptor cell to other neurons
22
Q
Unipolar neuron
A
1 extension and 1 axon.
Only found in insects.
23
Q
Pseudounipolar neuron
A
Both properties of unipolar and bipolar neuron.
1 axon from cell body which separates into 2 extension.
1 extension connects to dendrites and the other to axon terminal.
Most sensory neuron that carry message to spinal cord are this type of neuron
24
Q
What is the role of never fibres in forming a nerve
A
A group of never fiber held together by connective tissues with multiple bundles joining together forms a never
25
What are nerve impulses
The electrochemical change that travels along the membrane of a neuron.
26
Why is nerve impulse describe as a electrochemical change
A change in electrical voltage
Bought about by change in chemicals
27
What is a receptor
Receptor is a structure that is able to detect a change in the bodies external or internal environment
28
What are some internal changes?
Core body temperature, hormone and water content in the body
29
What are some external changes?
Sight sound touch and pressure
30
What is thermo receptor?
Inform the brain, the hypothalamus and cerebrum,of changes in temperature outside the body.
consciously aware of surrounding temperature .
Using information from the peripheral and central thermo receptor,the hypothalamus can regulate body temperature .
There are generally more warm central thermo receptor than cold
31
What are peripheral thermo receptor?
Nerve endings that are sensitive to heat and cold but generally more cold
32
What is central thermo receptor?
They are located in the hypothalamus and monitor core body temperature
33
What is Osmo receptor?
Osmoreceptor are sensitive to osmotic pressure.
Osmotic pressure is determined by the concentration of substance dissolved in water of the blood plasma.
Higher the concentration, the greater the osmotic pressure .
Osmo receptors are located in the hypothalamus
34
What is hyperosmolar?
More solute outside or more concentrated outside
35
Hyposmolar
More solute inside or more concentrated inside
36
What are chemo receptors?
Chemo receptors are sensitive to particular chemicals.
In the nose they’re sensitive to odour
In the mouse there sensitive to taste
In the blood vessels there are sensitive to pH of the blood and concentration of oxygen and carbon dioxide
Central chemo receptors are located in the medulla oblongata
They are responsible for the regulation of heartbeat and breathing
37
What are touch receptors or mechanoreceptors?
They are pressure receptors that are mainly found in the skin.
There are many types of mechanoreceptors.
- close to the surface of the skin and are sensitive to light touch.
-base if hair follicles are sensitive to the movement of hair.
- Touch receptor close to surface rapidly adapts and become unaware of touch
38
What are the types of mechanoreceptor?
1- close to the surface on skin. they are sensitive to light touch.
2-base of hair follicle -sensitive to movement of hair
3-deep within skin- they’re sensitive to pressure and vibration
39
What are pain receptors?
Pain receptors also known as nociceptors.
Stimulated by damage to tissues .
Eg- cut to the skin or surface tissue
Heavy bump
Poor Blood flow to a tissue
Excessive stimulation from stimuli like heat or chemicals
They are located in skin and mucus membranes,
present in all organs except the brain
Prolong stimulation of pain receptors make pain worse indicating the damage to tissue is still occurring
40
Why is the outside of the cell membrane more positive than the inside?
Side of the cell membrane is more positive than the inside of the cell membrane due to;
1-The concentration of sodium ion is 10 times higher outside the neuron.
- the concentration of potassium ion is 30 times higher inside the neuron.
However cell membrane is only slightly permeable to sodium ion due to limited number of sodium leaked channels limiting the facilitated diffusion of sodium ion,whereas the cell membrane is highly permeable to potassium ion due to larger number of potassium leakage channel. This leads to more potassium ions leaving the cell membrane from inside the cell to the outside .
Furthermore, there are more chloride irons outside the neuron that are highly permeable to chloride ions allowing diffusion through protein channel to inside the cell
-whereas there is concentration of large negatively charged organic iron inside the cell that are impermeable to the cell membrane resulting in the inability to leave the cell. Therefore, the inside of the cell is more negative than the outside of the cell.
Furthermore, sodium potassium pumps, pump two potassium ions inside the cell for every three sodium ions removed therefore there is a net reduction of positive ion inside the cell.
41
What is an action potential?
Action potential is an electrical signal that travels along the membranes of a nerve or a muscle cell enabling communication between cells. It occurs when a cells membrane potentially rapidly changes primarily due to the movement of irons, sodium and potassium,in and out of the cell through ion channels
42
What is resting membrane potential?
Membrane potential of unstimulated nerve cell.
It is -70 mili volts
43
What causes an action potential?
If the stimulus to neuron, particularly the dendrite, is sufficient, the signal will be passed along the neuron causing action potential to occur
44
What is the depolarisation
- when neuron is stimulated by a neurotransmitter or sensory receptor, it triggers the mechanical/ ligant gated sodium channel to open causing the sodium ions to move into the cell increasing the membrane potential .depolarisation occurs if the stimulation exceeds 15 mvor the threshold.
- if the stimulus is strong enough to increase membrane potential to -55 mv, the voltage gated sodium channels are opened.
This is an all or none response.
- the inward movement of sodium is too great to be balanced by the outward movement of k+, making the inside more positive. The polarity of membrane always reached +40 mv where the membrane is then polarised.
45
What is repolarisation?
During repolarisation the sodium channel closes , therefore the influx of sodium ions stop at +40millivolts.
-at 40 mil bolts, voltage gated potassium channel opens increasing potassium flow out of the cell.
-Extra cellular fluid then becomes more positive than the intercellular.
Therefore membrane potential decreases.
Potassium channel remain open longer than what is needed resulting in membrane potential dropping lower than the resting membrane potential and therefore the membrane is said to be hyper polarised.
46
What is the refractory Period?
Once sodium channels have opened, they quickly become inactivated and unresponsive to stimulus.
Therefore, membrane will not undergo another action potential, this is known as a refractory period
-It cannot stimulate axon once it has undergone action potential and therefore is known to be uni directional
-The part of the axon that has undergone action potential goes back to resting potential through sodium potassium pump where,for every two potassium ions that are bought inside the cell, three sodium ions are removed.
-Refractory period last from when the membrane reaches a threshold of -55 Milli Voltz to -70 Milli Voltz
47
What is the difference between a neuron nerve fiber and nerve
Neuron- a nerve cell
Nerve fiber- any long extension of cytoplasm of a nerve cell body. Usually an axon .
Nerve-bundle of Nerve fiber held together by connective tissue
48
What is a resting membrane potential?
Membrane potential of an unstimulated nerve cell. It is -70 mil volts.
49
What is a nerve impulse?
An action potential in one section of membrane that triggers action potential in the adjacent membrane is called a nerve impulse
50
Outline the conduction of nerve impulse along unmyelinated fiber
1)One area of neuron goes through depolarisation, causing the movement of sodium ion into the adjacent area.
2) presence of sodium ion causes voltage gated channel in the next section to open, causing influx of sodium ion and an action potential to occur.
3) this process repeats itself along the whole length of the membrane.
4) nerve impulses are prevented from going in wrong direction because of refractory period.
- unmyelinated fibre can conduct an impulse up to 2 meter per second
51
Transmission along myelinated fibre
In myelinated fibre, the myelin sheath insulates the nerve fibre/axon from extracellular fluid, therefore ions cannot flow in an out of the membrane, and an action potential cannot form.
-The nodes of ranvier are exposed area of axon, action potential jumps from one node to the next known as saltatory conduction.
-A large myelinated fibre can conduct an impulse of up to 140 meter per second.
52
Is the size of the nerve impulse always the same?
The size of the nerve impulse is always the same regardless of the size of stimulus.
Is strong stimulus causes of more nerve cells and produces more nerves impulse in a given time. This is because of the all or nothing nature of action potential which states that stimulus is either strong enough to trigger or it is not.
53
What is a reflex?
Rapid, automatic response to change in the external or internal environment
54
What are the four important properties of a reflex?
1) stimulus-required trigger reflex
2) a reflex is involuntary which occurs without any conscious thought.
3) reflex is rapid which involves only small number of neuron
4) reflex stereotyped-it occurs the same way every time it happens
Reflex are involved in the unconscious part of the brain . But most of them are involved in the spinal court.
55
What is the spinal reflex?
Sensory message that is automatically carried to the appropriate motor neuron in the spinal cord is called as the spinal reflex
56
What is a reflex arc?
Nerf pathway taken by a reflex
57
What are the confidence of a reflex arc?
1-receptor: detect changes in the internal and external environment. It initiates nerve impulse.
2-sensory neuron - carry impulse from receptor to the spinal cord or brain
3- synapse- nerve impulse will be directed to motor neuron or an inter neuron which carries it to the correct motor neuron .
4-Motor neuron-impulses from spinal cord to an effector
5-effector-effector receives the nerve impulse and act appropriately . They are usually the muscle or the secretory cells
58
What are innate reflex?
Complex reflexes such as chewing cycling and following movement with eyes when a child develops and called innate reflexes.
59
What are required reflexes?
Some complex motor patterns are learned through constant repetitions and are called acquired reflexes.
60
61
What does threshold mean
The membrane potential in a neuron that must be reached during deplorisation to trigger an action potential
62
Transmission across a synapse
1. Nerve impulses arrives at axon terminal and activates voltage gated calcium ion channels to open.
2. Due to high concentration gradient, calcium ions flow into the pre synaptic axon terminal.
3. This causes synaptic vesicles to fuse with membrane, releasing neurotransmitter by exocytosis.
4. Neurotransmitters diffuse across synaptic cleft and attach to receptors on membranes of next neuron.
5. Lignat gated protein channels open causing the influx of sodium ions and indicates an action potential at the post synaptic membrane.
6. The neurotransmitter is broken down by specific enzymes in the synaptic cleft.
63
Which enzyme breaks down the neurotransmitter acetylcholine
The enzyme acetylcholinesterase
64
What happens to the broken down products
They are absorbed by the pre synaptic neuron by endocytosis and used to resynthesis more neurotransmitters using energy from the mitochondria. Which stops the synapse from being permanently on.
65
What are organophosphate and what do they do
Nerve agents contain organophosphate which causes the build up of acetylcholine at the neuromuscular junction. All muscles in the body then try to contract and the loss of muscle control prevents breathing. They are used in insecticides
